:estimating impacts/Dale L. Keyes. Keyes, Dale L. Washington:Urban Institute,[1976] Land use Environmental aspects. Environmental impact analysis. Costal Zone Information Center DEC 2 1976 LAND DEVELOPMENT AND THE NATURAL ENVIRONMENT: ESTIMATING IMPACTS Dale L. Keyes COASTAL ZONE INFORMATION CENTER HD 111 .K47 THE URBAN INSTITUTE 1976 0 LAND DEVELOPMENT AND THE NATURAL ENVIRONMENT: ESTIMATING IMPACTS Dale L. Keyes u S DEPARTMENT OF COMMERCE NOAA COASTAL SERVICES CENTER 2234 SOUTH HOBSON AVENUE ChARLESTON SC 29405-2413 PR0PERTY OF THE UNITED STATES GOVERNMENT NATIONAL OCEANIC AND ATMOSPHERIC ADMINSTRATION For Retention When no longer needed, Please return to Technical Branch 0823 Property of CSC Library property of CSC Library The research for this report was made possible through a research grant from the, Office of Policy Development and Research of the U.S. Department of Housing and Urban Development under the provisions of .,Section 701(b) of the Housing Act of 1954, as amended, to The Urban Institute. The publication of this report was supported by the Ford Foundation. The findings and con- clusions presented in this report do not represent official policy of the Department of Housing and Urban Development, the Ford Foundation, or The Urban Institute. THE URBAN INSTITUTE Library of Congress Catalog Card Number 76-10104 U.I. 195-214-4 ISBN 87766-158-8 REFER TO URI 13500 WHEN ORDERING Available from: Publications Office The Urban Institute 2100 M Street, N.W. Washington, D.C. 20037 List Price $4.95 Printed in the United States of America First printing, April 1976 'UTZ12dia Dan 20 V*'M0q*'=tj" FOREWORD This is one of a series of reports by The Urban Institute's Land Use Center which discuss the evaluation of land developments and their economic, environmental, and social impacts. Increasingly, local governments are turning to formalized impact evaluation requirements in order to ascertain the likely effect of permitting land to be developed in various ways at specific locations. The degree to which this approach can improve land use decision making is largely dependent on the ability to ac- curately estimate a wide variety of potential impacts. The first report in this series, Measuring Impacts of Land Development: An Initial Approach, established an overall framework for evaluation and suggested a series of measures which could be used to estimate impacts for a wide range of.economic, social, and environmental concerns. Proce- dures for actually making impact estimates were also outlined, although in a general and preliminary fashion. The concluding report in the series, Using an Impact Measurement System for Evaluating Land Developments, reexamines the overall framework and describes potential problems and pros- pects for implementing an impact measurement system. This latter report thus provides a general per- spective on this as well as the other reports in this series. This report treats only those impacts related to the natural environment (primarily air quality, water quantity-including flooding-and water quality, wildlife and vegetation, and noise). In addi- tion, natural disasters and scarce resources are discussed briefly. The discussion of environmental im- pacts focuses on data collection and analysis procedures, with special attention given to assessing the costs and data requirements and reliability of specific analytical techniques appropriate for making es- timates in the various impact categories. It can be best described as a reference document for those who find themselves directly involved with the impact evaluation process. These would include planners, developers, and others actually making the estimates as well as decision makers and inter- ested Jay persons who wish to learn, more about the costs, assumptions, and general considerations which underlie the estimates. Companion reports in this series treat methodological issues in the following areas-fiscal bal- ance (local revenues and the cost of public services), the private economy (employment and property values), public services (the quality and level of service), and social effects (aesthetic considerations and the perceptions and behavior patterns of local residents). Taken together, these reports offer de- tailed guidance in the structuring and operation of a comprehensive impact evaluation system appro- priate for use by local governments. Even with improved information concerning the probable effects of proposed developments, arriving at decisions regarding specific projects will remain a difficult task. Rarely are the impacts so one-sided that no one is adversely affected or that no one is benefitted. Rather, decision makers must sort out and compare impact estimates which are often incommensurable and then balance the inter- ests of various affected parties, some of whom may be future generations. The task is an unenviable one and subject to much speculation. By using a well-documented and highly visible approach to im- pact analysis as is recommended here and in the companion reports, some of these difficulties may be mitigated. Land use conflicts will surely remain, but some of the obscurity and confusion which sur- rounds them may be reduced. WORTH BATEMAN, Executive Director Land Use Center The Urban Instiute CONTENTS Foreword .......................................................................... iii Acknowledgments .................................................................. ix Advisory Group .................................................................... x Summary ........................... I............................................... xi GENERAL INTRODUCTION ........................................................ I A. Comprehensive Impact Evaluations-An Approach ............................. 2 1. Impacts on Man ........................................................... 2 2. Comprehensiveness ... ........................ 113 3. Impacted Populations ("Clientele Groups") ................................. 3 4. Impact Categorization ..................................................... 3 B. Implementing Impact Evaluation Procedures-Major Issues ...................... 4 1. Comprehensive versus Incremental Review .................................. 4 2. The "Spillover" Problem ................................................... 4 3. Proposal Alternatives ...................................................... 5 4. Planning Department/Line Agency Interrelationships .......................... 5 5. Applicable Federal, State, and Local Laws .................................. 5 C. Needed Research ............................................................ 6 Part 1. AIR QUALITY ............................................................... 7 I. Introduction and Background .................................................... 9 A. Health and Welfare Effects .................................................... 9 1. Human Health Effects ..................................................... 9 2. Vegetation and Materials Effects ........................................... 11 B. Applicable State and Federal Laws ............................................ 11 C. Emissions and Atmospheric Dispersion: Fundamental Principles .................. 13 1. Emissions and Emission Sources ........................ ................... 13 2. Atmospheric Dispersion ......................................... I ......... 13 a. Principal Factors Affecting Dispersion ................................... 13 b. Removal and Transformation Processes .................................. 14 D. Air Quality Impacts of Land Development ..................................... 14 11. Methodological Approaches ........................ ..... 15 A. Measures, Standards, and Indices ............................................. 15 1. Measures and Standards ................................................... 15 2. Indices .................................................................. 16 B. Measurement/Estimation Procedures ........................................... 17 1. Measuring/Estimating CurTent Emissions .................................... 17 a. Point Sources .......................................................... 17 b. Stationary Area Sources ................................................ 18 c. Mobile Area or Line Sources ............................................ 18 d. Estimation Problems ................................................... 18 2. Estimating Future Emissions ............................................... 19 a. Aggregate or Large Area Analysis ....................................... 19 b. Small Area Analysis .................................................... 19 c. Individual Development Analysis ........................................ 20 d. Estimation Problems ............................... p ................... 21 3. Measuring/Estimating Current Ambient Concentrations ....................... 21 a. Quantitative Measurement .............................................. 21 b. Measurement Problems ................................................. 22 c. Vegetative Indicators ................................................... 22 4. Estimating Future Ambient Concentrations .................................. 22 a. Types of Models ............. 23 Theoretical versus Empirical ]4o*d'e*l*s*.* 23 Simple versus Complex Models ....................................... 25 Source versus Receptor Models ....................................... 25 iv Models Based on Type of Source ...................................... 25 Models Based on Type of Pollutant .................................... 25 Models Based on Scale of Application ................................. 25 b. Description of Individual Models ........................................ 26 Rollforward Models .................................................. 26 Miller/Holzworth Model .............................................. 28 Hanna/Gifford Model ................................................. 29 California Highway Model ............................................ 31 ERT/MARTIK Model (Modified AQDM) ............................... 31 TASSIM ............................................................ 33 Climatological Dispersion Model (CDM) ................................ 34 APRAC Model ...................................................... 35 Other Models ........................................................ 36 c. Summary and Comparison of Models ..................................... 36 5. Measuring/Estimating Odor and Smoke Problems ............................. 38 a. Odor Problems ......................................................... 38 b. Smoke Problems ....................................................... 40 6. Measuring/Estimating Exposure of People to Pollution ........................ 40 a. Intensity and Duration .................................................. 40 b. Number of People Exposed ............................................. 41 7. Measuring/Estimating Damage in Monetary Units ............................. 42 III. Conclusions and Recommendations ................................................ 45 A. Planning versus Project Review ............................................... 45 B. Specific Recommendations and Conclusions .................................... 46 Part 2. WATER QUALITY AND QUANTITY .......................................... 49 1. Introduction and Background .................................................... 51 A. Health, Safety and Welfare Effects ............................................ 51 1. Flooding .................................................................. 51 2. Water Pollution ........................................................... 51 3. Water Consumption ....................................................... 52 B. Applicable Federal and State Laws ............................................ 52 1. Flooding ................................................................. 52 2. Water Pollution ........................................................... 54 3. Water Consumption .... .................................................. 54 C. Fundamental Hydrologic Principles ............................................. 54 1. Physical Hydrology ....................................................... 54 2. Biological Hydrology ...................................................... 55 D. Water-Related Impacts of Land Development ................................... 55 1. Flooding ................................................................. 55 2. Water Pollution ........................................................... 57 3. Water Consumption ....................................................... 57 11. Methodological Approaches ...................................................... 59 A. Impacts on Flooding .......................................................... 59 1. Impact Measures ......................................................... 59 2. General Analytical Approaches ............................................. 60 3. Estimating Impacts on Stream Flow ........................................ 60 a. Analytical Techniques .................................................. 61 Rational Method ..................................................... 61 Flood Frequency Analysis ............................................ 6t Other Simple Techniques ............................................. 62 Complex Hydrologic Models .......................................... 63 b. Comparison and Summary .............................................. 65 4. Estimating Impacts on the Extent of Flooding ................................ 67 a. Analytical Techniques .................................................. 67 5. Estimating Impacts in Terms of Damages and Risks .......................... 67 B. Impacts on Water Pollution ................................................... 69 1. Measures, Standards, and Indices .......................................... 69 2. Measuring/Estimating Current Discharge Levels .............................. 70 3. Measuring Current Ambient Concentrations ................................. 71 v 4. Estimating Future Discharge Levels ........................................ 71 a. Point Sources .......................................................... 71 b. Nonpoint Sources ...................................................... 72 5. Estimating Future Ambient Concentrations .................................. 72 a. General Considerations ................................................. 72 b. Surface Water Models .................................................. 74 Streeter-Phelps 74 Simplified EPA @io*de*f 74 Auto-Qual ........................................................... 74 HSP, Water Quality Component ....................................... 75 Other Models ........................................................ 75 c. Groundwater Models ................................................... 75 d. Comparison and Summary .............................................. 76 6. Estimating the Number of People Affected .................................. 76 7. Estimating Monetary Benefits ......................................... I ...... 76 C. Impacts on Water Consumption ............................................... 78 1. Impact Measures ......................................................... 78 2. Measuring/Estimating Impacts on Storage and Yield .......................... 78 a. Surface Water ......................................................... 78 b. Groundwater ........................... .............................. 79 -3. Measuring/Estimating Salt Water Intrusion .................................. 79 III. Conclusions and Recommendations ............................................... 81 A. Planning versus Project Review ............................................... 81 B. Specific Recommendations and Conclusions .................................... 82 Part 3. WILDLIFE AND VEGETATION .............................................. 1. Introduction and Background .................................................... 87 A. Human Welfare ............................................................. 87 B. Fundamental Ecological Principles ............................................ 88 C. Definitions and Terms ........................................................ 89 11. Methodological Approaches ...................................................... 91 A. Measures and Indices ............................................. ........... 91 B. Measuring/Estimating Current Conditions ...................................... 92 1. Vegetation ............................................................... 92 a. Assessment of Areal Extent ................................... ..... 92 b. Assessment of Vegetation Quality and Quantity ........................ ... 92 c. Methods of Field Measurement ............. .............................. 94 2. Wildlife .................................................................. 95 a. Habitat Analysis .............. 6 ......................................... 95 b. Population Census ......................... ............................ 95 C. Estimating Future Conditions ................................................... 98 .1. Vegetation ............................................................... 98 2. Wildlife ......... ...... 98 a. Key Considerations ..... 6....................... 6 ...................... 98 b. Research Findings ...................................................... 99 Birds ................................................................ 99 Mammals ........................................................... 99 Amphibians and Reptiles ............................................. too c. Estimation Procedures .............................. 6 .................... 100 111. Conclusions and Recommendations ................................................ lot A. Planning versus Project Review ............................................... 101 B. Alternative Data Collection Approaches. . ................................ 6 ...... 101 C. Specific Recommendations and Conclusions ...................................... 102 Part 4. NOISE .............................. ............................. 103 1. Introduction and Background ...... ............................................. 105 A. Health and Welfare Considerations ............................................ 105 B. Fundamental Principles ....................................................... 106 vi II. Methodological Approaches ...................................................... 109 A. Measures, Standards, and Indices .............................................. 109 B. Analytical Techniques ........................................................ III 1. Construction-Related ...................................................... III 2. Transportation-Related .................................................... 113 a. Specific Examples ...................................................... 113 HUD Noise Assessment Guidelines, .................................... 113 TSC Methods 114 NCHRP Report 117 1@ie*t*ho*d' 114 Other Techniques .................................................... 114 b. Summary and Comparison ............................................... 115 III. Conclusions and Recommendations .......................................... ..... 117 A. Planning versus Project Review ..................................... .......... 117 B. Specific Recommendations and Conclusions .................................... 117 Part 5. OTHER TYPES OF IMPACT: NATURAL DISASTERS AND SCARCE RESOURCE PREEMPTION .................................................. 119 1. Introduction .................................................................... 121 11. Natural Disasters Other Than Floods ............................................. 123 A. Landslides and Subsidence ................................................... 123 B. Earthquakes ............................ 124 C. Other Types of Disasters ..................................................... 124 111. Scarce Resource Preemption ..................................................... 127 A. Agricultural Land ............................................................ 127 B. Mineral Deposits ........................................................... ! 128 C. Unique Natural Features ..................................................... 128 Tables 1. Suggested Direct Measures of Development Impact on the Environment .............. xii 1-1. A Summary of Human Health-Air Pollutant Relationships ........................... 10 1-2. National Ambient Air Quality Standards .......................................... 11 1-3. A Summary of Air Pollution Effects on Vegetation, Materials, and Man (Aesthetic and Nuisance Concerns) ............................................................ 12 1-4. Comparison of Atmospheric Dispersion Models .................................... 37 1-5. Results of Model Evaluation Using S02 Data ...................................... 39 1-6. Results of Model Evaluation Using Particulate Data ................................ 39 1-7. Planning and Project Review Considerations for Each of the-Major Air Pollutants ..... 46 2-1. Principal Water Pollutants and W 'ater Quality Indicators ............................ 53 2-2. An Illustrative For-mat for Presenting the Effect of a Development on Risks from Flooding 60 2-3. Results of a Flood Frequency Analysis ............................................ 62 2-4. Comparison of Techniques Used to Estimate Change in Stream Flow ................ 66 2-5. An Illustrative Format for Presenting the Effects of Development on Water Use ...... 70 2-6. Urban Runoff Quality Models (for Estimating Discharges from Nonpoint Sources) ..... 73 2-7. Assessment of Water Quality Models ............................................. 77 2-8. Levels of Analysis Applied to the Various Hydrologic Impact Areas ................. 82 4-1. A Summary of Human Health and Nuisance Relationships to Environmental Noise .... 106 4-2. Recommendations of Sound Levels in Various Spaces ...... -* 110 4-3. Tabular Presentation of Noise Impacts for a Hypothetical Development .............. 111 4-4. Approximate Noise Leve 'is for Construction Equipment ............................ Ill 4-5. Comparison of Predicted and Actual Noise Levels at Selected Sites .................. 115 4-6. Summary of Three Noise Estimation Techniques ................................... 115 Figures 1-1. Schematic Representation of the Gaussian Model .................................. 24 1-2. Summary of the Miller/Holzworth Model .......................................... 28 vii 1-3. Summary of the Hanna/Gifford Model ............................................ 29 1-4. Flow Diagram of the California Highway Model ................................... 32 1-5. The Use of Frequency Distributions to Estimate Exposure Intensity and Duration ..... 42 2-1. The Hydrologic Cycle ........................................................... 55 2-2. Material and Energy Flows in an Aquatic Ecosystem ............................... 56 2-3. An Example of Hydrograph for a Hypothetical Watershed .......................... 63 2-4. Flow Chart of Computations for a Complex Hydrologic Model ...................... 64 2-5. Representations of the Extent and Depth of Flooding ............................... 68 2-6. An Illustration of Saltwater Intrusion ............................................. 80 3-1. Example Formats for the Presentation of Estimated Impacts on Species Abundance and Diversity ...................................................................... 93 3-2. A Chart for Cataloging Baseline Data on Habitat Quantity .......................... 97 4-1. Loudness Range of Common Sounds ................. * ............................ 107 4-2. Map Presentation of Noise Impacts for a Hypothetical Development ................. 112 viii ACKNOWLEDGMENTS The research supporting the impact evaluation study of which this work is a part was sponsored by the Office of Policy Development and Research of the U.S. Department of Housing and Urban Development. The encouragement of Wyndham Clarke and Allen Siegel from this office and the specific suggestions of James Hoben, the HUD project manager, at various points in the overall study are greatly appreciated. The research was carried out under the general direction of Worth Bateman, Executive Director of The Urban Institute's Land Use Center. Philip Schaenman was the project manager. Their valuable insights, comments, and overall guidance are gratefully acknowledged. Kathleen Christensen of The Urban Institute and Harry Feldman of the Indianapolis Department of Parks and Recreation made substantive contributions to the report. Ms. Christensen provided valuable background material and text to the noise discussion, while Dr. Feldman wrote a paper on urbanization and wildlife/vegetation, parts of which were incorporated into the discussion of the same subject. The author is extremely appreciative of all who critiqued early drafts of this study and provided valuable suggestions: Roger Betson, Tennessee Valley Authority (Water Systems Development Branch); Eugene Darling, U.S. Department of Transportation (Transportation Systems Center); Aelred Geis, U.S. Fish and Wildlife Service; Donald Hey, Hydrocomp, Inc.; Michael McCarthy, University of Arizona (School of Renewable Natural Resources); Curt Miller, University of Michigan (Department of Landscape Architecture); J. A. Smedile, Northeast Illinois Planning Commission; Ethan Smith, U.S. Geological Survey (RALI Program); and Forest Steams, University of Wisconsin-Milwaukee (Department of Botany). Members of the Advisory Group also assisted in reviewing early drafts. Staff members from the Department of Community Development in Indianapolis and the Maryland National Capital Park and Planning Commission in Montgomery County, Maryland, are acknowledged for their cooperation and the insights they provided into impact evaluation procedures used by local governments. The participation of the following individuals in a survey of air dispersion model users is also acknowledged: Steven Albersheim, NUS Corporation; W. Brian Crews, Oregon Department of Environmental Quality; Richard Hawthorne, Oregon Department of Environmental Quality; and Richard Thuillier, San Francisco Bay Area Air Pollution Control District. ix ADVISORY GROUP TIMOTHY A. BARROW / Mayor, Phoenix, Arizona ROBERT H. PASLAY / Planning Director, Planning Commission, Nashville, Tennessee KURT W. BAUER / Executive Director, Southeast Wisconsin Regional Planning Commission, Waukesha, Wisconsi .n RICHARD A. PERSICO / Executive Director, Adirondack Park Agency, Ray Brook, New York FRANK H. BEAL / Director for Research, American Society of Planning Officials, Chicago, Illinois JAMES R. REID / Director, Office of Comprehensive Planning, Fairfax County, Virginia MELVIN L. BERGHEIM / Councilman, Alexandria, Virginia, and National League of Cities-U.S. Conference of Mayors E. JACK SCHOOP / Chief Planner, California Coastal Zone Con- servation Commission, San Francisco, California RICHARD F. COUNTS / Zoning Administrator, Planning De- partment, Phoenix, Arizona DUANE L. SEARLES / Special Counsel on Growth and Environ- ment, National Association of Home Builders, Washington, D.C. CARL D. GOSLINE / Director of General Planning, East Central PHILIP A. STEDFAST / Planning Director, Department of City Florida Regional Planning Council, Winter Park, Florida Planning, Norfolk, Virginia BERNARD D. GROSS /Planning Consultant, Washington, D.C. DAVID L. TALBOTT IDirector ofPlanning, Falls Church, Virginia HARRY P. HATRY / Director, State and Local Government Re- RICHARD E. TUSTIAN /Director ofPlanning, Maryland National search Program, The Urban Institute, Washington, D.C. Capital Parks and Planning Commission, Silver Spring, Maryland TED KOLDERIE / Executive Director, Citizens League, Minne- F. ROSS VOGELGESANG / Director, Division of Planning and apolis, Minnesota Zoning, Indianapolis, Indiana DENVER LINDLEY, JR. / Commissioner, Bucks County, Doyles- THORNTON K. WARE / Planning Director, Rensselaer County, town, Pennsylvania Troy, New York JACK LINVILLE, JR. / Deputy Executive Director, American JOSEPH S. WHOLEY / Member, Arlington County Board, Arling- Institute of Planners, Washington, D.C. ton, Virginiaj and Program Evaluation Studies Group, The Ur- ban Institute, Washington, D.C. ALAN H. MAGAZINE / Supervisor, Fairfax County Board, Fair- fax, Virginia, and Project Director, Contract Research Center, FRANKLIN C. WOOD / Executive Director, Bucks County Plan- International City Management Association, Washington, D.C. ning Commission, Doylestown, Pennsylvania X SUMMARY That land development may adversely affect the natural environment or, conversely, that the natural environment may pose problems for development is no longer in question. Attention has now turned to designing methods for mitigating these conflicts. The use of impact evaluation to detect ex- isting and potential problems is a valuable step in this process. This report discusses ways to estimate impacts associated with proposed development. Purpose and Scope The objective of this report is to provide information on (1) key issues and considerations in eval- uating the impacts associated with proposed development, and (2) the relative merits of alternative techniques for estimating impacts, in light of the costs, skills, and data required by each technique and the validity of the results, where information on these topics has been found. (Wherever a tech- nique was discovered to have been used by a local government or in a specific community, that fact is noted.) The report discusses development impacts on man associated with or operating through the nat- ural environment (air quality, water quality and quantity, noise, and scarce resource use preemption), impacts on the natural environment (wildlife and vegetation), and impactsfrom. the natural environ- ment (flooding and other natural disasters). Simple manual estimation procedures as well as complex, computerized assessment techniques are examined for each impact category (except for scarce resources and disasters other than flooding) and for three types of development-residential, com- mercial, and industrial. The treatment of scarce resource use preemption and natural disasters other than flooding is considerably reduced in scope and detail in comparison with the other impact areas. This is largely due to the relatively primitive nature of impact estimation techniques in these areas and to the exis- tence of an extensive body of literature documenting what is currently known. Throughout the discussion, the emphasis is on quantification and estimation of end impacts on man, rather than intermediate effects. For example, information on the number of people exposed to new ambient concentrations of pollutants is preferred to simply knowing what the new concentrations will be. For each impact category, measures incorporating these concepts are suggested for use in as- sessing the impacts of proposed development. For certain impacts, however, the preferred measures are impractical, at least for routine use. Either the requisite analytical techniques are lacking, or the costs of data collection and analysis seem prohibitively high. For these cases, alternative or fallback measures are specified. These measures typically incorporate expressions of intermediate effects such as development output (e.g., emission levels) or they reflect qualitative assessments. Even where the preferred measures seem practical, alternatives are offered for those governments which may prefer a less detailed, albeit less satisfactory, approach. Table I lists preferred and fallback measures. Rarely will a single development require detailed assessment in all areas. Evaluators must deter- mine the type of impacts which are likely to be significant at the initial screening stage, perhaps em- ploying the "target" planning approach suggested in the report and summarized below. Intended Audience The report is intended primarily for planners and other key local government staff members responsible for preparing impact evaluations. Elected officers and interested lay persons may also find selected sections 1of'value, especially the introduction and summary sections for each of the five impact categories. Findings and Recommendations The state of the art of impact evaluation regarding the natural environment.is very unevenly ad- vanced across the various impact categories. For some types of impact, fairly accurate and inexpen- sive techniques appear to be available for routine use. For others, the desired tools are only at the re- search and development stage or are still too expensive for most local governments. For still others, analytical methods necessary for quantified estimates of end impacts on man have not yet been developed. xi Table 1. SUGGESTED DIRECT MEASURES OF DEVELOPMENT IMPACT ON THE ENVIRONMENT IMPACT CATEGORY PREFERRED MEASURES FALLBACK MEASURES AIR QUALITY Health Change in the ambient concentration of each pol- Change in the ambient concentration of lutant, the frequency of exposure, and the number each pollutant (relative to standards) of people at risk Nuisance Change in the number and frequency of problems Change in the likelihood that aesthetic/ caused by smoke plumes, odors, and haze, and nuisance problems will occur or change number of people affected in severity WATER QUALITY AND QUANTITY Flooding Change in the number of people endangered by Change in flood frequency or severity flooding and the expected property damage (or value of the property endangered) Water pollution Change in the permissible or tolerable uses of the Change in the ambient concentration of water in question and the number of people affected each pollutant (relative to standards) Water consumption a. Change in the total duration and/or severity of Change in the likelihood of a water short- expected shortages and the number of people age and the number of people affected affected b. Change in the concentrations of those drinking water constituents important to health and the number of people affected WILDLIFE AND Change in the number of rare and endangered Change in the extent and quality of vege- VEGETATION species; change in the population size and diversity tation and wildlife habitat of common species NOISE Change in the level of noise, the frequency with which it occurs, and the number of people affected in the area surrounding the development OTHER NATURAL Change in the likelihood of the disaster and the DISASTERS number of people and the value of the property endangered SCARCE RESOURCE The type and value of the scarce resource and the USE PREEMPTION degree of preemption (such as farming, mining, and recreation) To some extent this unevenness reflects the importance that the federal government and, to a lesser extent, state governments have attached to the various types of impacts. Thus, flood prediction is much more advanced than the estimation of impacts on wildlife and vegetation. Recent air and water pollution legislation has spurred research in these areas, although affordable and accurate esti- mation techniques are available only for a limited number of situations. Noise legislation is likewise expected to improve the status of noise prediction models. Following are this report's specific findings and recommendations: 1. Quantitative estimates of end impacts on man appear to provide the most useful information to the decision maker. At the same time it is important to use recognized standards or other reference points in interpreting the quantified and often technically specified estimates in sev- eral of the impact categories. Local governments should consider using the measures suggested in this report (or similar ones) as part of their impact evaluation programs. 2. Comprehensive land use planning and the review of individual projects can and should be coordinated. Where a few large developments or many small ones have communitywide ef- fects, the impacts (ambient air and water quality, flooding) can be related to development out- xii put (emissions or effluents) or even to design characteristics (impervious ground cover) and targets or budgets established. Individual reviews in many cases may be reduced to com- paring the target with the output from or characteristic of the proposed development when added to the current levels. For example, the estimated emissions from a new development can be added to those from all existing developments in that part of the community for which an emission budget has been prepared. If the budget will not be exceeded even with the new development,. then no further analysis of air quality impacts will probably be needed. We rec- ommend that communities consider incorporating targets or budget values of air emissions, Water effluents, and impervious cover in their comprehensive plans. 3. Even though questions regarding the cost and validity of many techniques remain incom- pletely answered, several of the techniques reviewed seem superior to some of the currently popular rough approximation methods and are unquestionably better than purely qualitative or judgmental approaches. Following is a general appraisal of existing techniques for esti- mating impacts (using the suggested measures) in each of the major categories. a. Air Quality-Air dispersion models applicable to a limited number of pollutants and types of development are available for health assessments, although the reported accuracies are quite low. Generally, the accuracy of the estimates increases as the models become more complex. For communitywide estimates of long-term average pollutant concentrations due to overall growth, relatively simple and, in some cases, manual techniques are available. Accuracy for a few of the latter is good. Nuisance impact evaluations do not require highly accurate estimates and thus are not difficult to make. b. Water Quality and Quantity-The estimation of impacts in this category frequently re- quires the use of more than one technique or model. Simple techniques for estimating flood frequency and volumes are available but tend to be unreliable. Complex models are presumably more accurate but also more expensive. Translating flood volumes into water levels requires a complex model of uncertain cost and accuracy. Water pollution impacts can be estimated fairly accurately for a very few pollutants and under limited conditions. Estimates of values for the preferred measure require the use of a complex model, and judgments (based on limited evidence) of the implications for water use. Some produce relatively accurate results; all are presumably expensive. Assessments of the supply aspects of water consumption are analogous to flood frequency and volume assessments for sur- face water. Only qualitative assessments are normally possible for underground sources. Water quality assessments are made with water pollution techniques. It should be noted that certain complex models can be used for combined assessments of flooding, water pol- lution, and water consumption (water quality); thus some economies of scale can be achieved. c. Wildlife and Vegetation -Although accurate baseline documentation of existing condi- tions is possible (although often expensive), techniques for producing quantitative esti- mates of impacts are not available. Instead, informal judgments of experts familiar with the local environment are usually necessary. d. Noise-At least one simple and accurate model is currently available for estimating noise levels. However, it is not reliable under all conditions. Another simple technique is also available but produces estimates of unknown accuracy. e. Other Natural Disasters and Scarce Resource Use Preemption-Although specific esti- mation techniques were not reviewed in detail, existing estimation procedures appear to provide only general approximations of the degree of risk from disasters or the value of certain scarce resources. 4. Data on costs, skill level requirements, and accuracy of the various techniques examined Were extremely difficult to obtain in some cases and impossible in others. Few attempts at comparative testing and assessment of models have been made. Where the developers of individual techniques have undertaken validation studies the tests were often based on too few comparisons of estimated and observed values, and under conditions which were too similar, for validity to be established. In addition, different and frequently incomparable mea- sures of accuracy were sometimes used. We recommend that the federal government greatly xiii expand its limited testing program for impact estimation techniques. In the meantime, local governments should be cautious about accepting the results of unvalidated or poorly vali- dated models. 5. If some of the more complex computerized models are employed, the user should expect that initial start-up and calibration costs will be high, perhaps tens of thousands of dollars. Re- peated applications of the model for project reviews (or for planning purposes) should be much less expensive, typically hundreds of dollars for computing plus some additional data collection costs. Users will generally find three sources for computerized models: those of- fered by a consultant, those offered by the federal government together with some user as- sistance, and those available in the literature but without assistance and often poorly docu- mented. Regardless of the type selected, model users should seek to obtain data on costs of start-up, as well as continued use, from the model developer or others familiar with its appli- cation. Previous users are often the best sources for these data. 6. Where simpler techniques are used, costs may be reduced substantially. However, even though computerized techniques are not available for making estimates of impacts on wildlife and vegetation, estimates made by simple inferences will require relatively expensive field surveys (perhaps ten to twenty thousand dollars for a fifty-acre site) if the estimates are to be quantitative. More detailed findings and assessments of current analytical methods appear in the report itself. Tables comparing the various analytical techniques are found in the summary sections for each im- pact category. xiv GENERAL INTRODUCTION Impacts on, from, or operating through the nat- 3. Which techniques to employ, based on their ural environment have long been a primary concern identified strengths and weaknesses. in land use decision making but have attracted vastly We have discussed in detail those impact areas for increased attention and concern in recent years. This which several estimation techniques are currently report, one of a series on impact evaluation tech- available-air quality, water quality and quantity (in- niques published by The Urban Institute's Land Use cluding flood hazards), and noise. We have also des- Center, focuses on ways to estimate the impacts of cribed in some detail approaches to estimating im- residential, commercial, and industrial development. pacts on wildlife and vegetation, even though specific The intent is to provide urban planners and others analytical techniques for making estimates are not concemed with evaluating the impacts of land devel- currently available. The relative unfamiliarity of most opment with basic information on the state of the art. planners with wildlife and vegetation and the scarcity However, this report should not be considered a man- of relevant information justifies a more detailed dis- ual or "cookbook" for evaluating impacts. In almost cussion here. We have discussed to a much lesser ex- every case the referenced documents must be con- tent the estimation of impacts on certain scarce sulted for details of the data collection and analysis resources such as prime farmland and from natural procedures. Likewise, a complete discussion of the disasters in addition to floods. The more superficial relevant physicalibiological processes which charac- terize the complex natural systems being assessed is treatment of these last two impact areas should not be not included. Instead, a brief, simplified overview of interpreted to mean that they are unimportant. The basic scientific principles related to each specific im- existing analytical techniques in these areas are in a pact category is presented, followed by a discussion relatively primitive state of development and since of impact measures and alternative data analysis pro- what we do know about estimating these types of im- cedures. References to original sources and additional pacts is discussed quite well in the literature, the dis- readings are also given. The objective is to provide cussion here serves to highlight general approaches to information which can be used in designing and im- making impact estimates and to identify key refer- plementing an impact evaluation program and in as- ences. sessing the analytical products being promoted by pri- The detailed treatment of estimation procedures in- vate consulting firms for evaluating environmental cludes a discussion of general procedures as well as impacts. More specifically, the report should be of specific techniques. Where individual techniques or value in deciding: models are treated explicitly, those in the public do- main are emphasized. A few exceptions have been 1. Which impact categories to include in a planning made, but only where the technique is extremely and/or project evaluation program, innovative or the model readily available at an at- 2. Which measures to use within the constraints of tractive price. Although no attempt has been made time and available funds, and to review every existing technique or model, the ones included are broadly representative of the field in an innovative idea in decision making. A closer exam- each impact category. ination reveals that the term is fundamental to the In analyzing the comparative strengths and weak- very process of making decisions. Few would dis- nesses of the available techniques, the focus is on agree that most, if not all, decisions are based on inputs and outputs-what the techniques require their likely outcomes, or impact. No decision to ap- (dollars, skills, and data) and what they produce (de- prove a subdivision, grant a variance, or amend a tail and accuracy of results). The question of accu- zoning plan is made in a vacuum. Each is based on racy is extremely important. All too often numbers some analysis of the impact of making and imple- appear in impact evaluations with no indication of the menting that decision. What is suggested here is a range of error.' This is not to say that information on more comprehensive impact analysis procedure ap- the accuracy of the various techniques is readily plied systematically to land use decisions. Rather available. An extensive literature search, combined than introducing a new idea, we are suggesting the with a limited survey of both developers and users of expansion of an old one. identified techniques, has produced a base of infor- This is not to say that the suggestion is not some- mation, but a base which is far from complete. Exten- what disturbing. The usual constraints of time, sive validation of both simple' and complex. tech- money,. and knowledge, compounded by an intriguing niques is urgently needed. Data on the costs of using web of vested interests, hidden agendas, and political the various techniques were similarly difficult to find. pressures militate strongly against procedures which In addition to its support of this project, the U.S. may increase costs, tax knowledge and abilities, or Department of Housing and Urban Development has improve the visibility of public decision making. sponsored a related and complementary study of pro- However, a more comprehensive and systematic im- cedures for estimating impacts-Interim Guide For pact evaluation procedure, painful as it may be in cer- Environmental Assessment, HUD Field Office Edi- tain situations, holds the potential for improving the tion, prepared by Alan M. Voorhees Associates, Inc., allocation of a scarce resource-land. et al., for the HUD Office of Policy Development and Research, Washington, D.C., June, 1975. The In- 1. Impacts on Man terim Guide was prepared primarily for use by HUD Further discussion of "the land use pro blem" and personnel reviewing the impacts of HUD-assisted the rationale which underlies our suggested approach projects; however, much of the information is appro- can be found in the overview volumes of this series .2 priate for use by local planners as well. The preliminary concept presented in those volumes The Interim Guide lays out a system for the initial is that the utility of impact evaluations would be in- screening of development impacts to determine if spe- creased if the impacts were specified in terms of end cial in-depth evaluations of specific impacts are re- impact on man rather than in terms of intermediate quired. Procedures are outlined for making initial effects. The fact that addit Iional pollutants will appear judgments regarding the significance of potential ef- in the air or water or that wildlife habitats will be fects for each of 79 "environmental components." destroyed are merely descriptions of changes, not im- The use of national standards and rules of thumb in pacts. It is only as these change's affect man physi- the screening process are emphasized. cally or psychologically (e.g., air increase in emphy- This report, Land Development and the Natural sema, prohibition of swimming at a local beach, the Environment: Estimating Impacts, focuses on tech- presence of foul-smelling air), that impacts become niques which could be utilized in the detailed level interpretable. analyses-* The two reports thus tend to complement It also seems likely that the utility of the analysis is each other and the reader is encouraged to use both increased if impacts can be quantified. Knowledge'of in designing and implementing an impact evaluation changes in the number of people exposed to hazard- program. ous air or changes in the probability of flooding are preferable to knowing that conditions will "improve" A. COMPREHENSIVE IMPACT or "deteriorate." Even a rough approximation of EVALUATIONS-AN APPROACH magnitude is better than none. The emotionalism which 'has accompanied the use The suggested impact measures presented reflect of the term "impact evaluation" in environmental de- ba tes has led to the notion that the words represent 2. Philip S. SchaenmAn and Thomas Muller, Measuring Impacts of Land Development: An Initial Approach (Washington, D.C.: 1. In this connection, two questions are relevant: what is the The Urban Institute, 1974); Philip S. Schaenman, Using a Mea- probability that the impact will occur; and if it does, how confident surement System For Evaluating Land Development (Washington, are we that the estimated magnitude is correct? D.C., The Urban Institute: forthcoming, 1976). 2 Land Development and the Natural Environment this philosophy-they are designed to specify end im- most relevant to new residents or workers (e.g., pacts and are phrased in quantitative terms. Unfortu- building design, unit layout, site landscaping) are best nately, the state of the art is not yet advanced enough assessed by the private market. Of course, some im- intach of the impact areas to justify the use of every pacts affect the entire community by acting through "preferred" measure. Consequently, we have in- new residents, and these have been included in our cluded alternative (fallback) measures as well. These, discussion. For example, to the extent that a develop- typically, are expressions of intermediate effects ment endangers new residents' health or safety, the and/or are phrased in more qualitative terms. For ex- public-at-large may be required to provide specific ample, the suggested fallback measure for air quality types of relief. An example of such a danger is the lo- is "change in ambient concentration of each pollutant cation of a development in a flood plain. The public (relative to standards);" while that for wildlife and cost can be measured in terms of monetary and in- vegetation is "change in the amount and quality of kind subsidies to those persons in the development, if wildlife habitat altered (quality rating by animal and when a flood occurs .3 type)." Even where the preferred measure is techni- The "surrounding community" group can be fur- cally feasible, the time or resources available for data ther divided into localized (i.e., immediate vicinity) collection and analysis may necessitate use of the fall- and nonlocalized (the rest of the community) sub- back measure. groups. This is an important differentiation for those impacts which tend to have corresponding spatial 2. Comprehensiveness components. The impact of a regional shopping Let us turn for a moment to the issue of compre- center on access roads, for example, is typically far hensiveness. The comprehensive master plan ap- different from its impact on the entire highway net- proach has long been both a conceptual tenet and a work of a city. Alternative disaggregations of the source of consternation for professional planners. population can be made on the basis of special inter- Since the world is composed of a highly intercon- ests, socio-economic characteristics, jurisdiction of nected set of elements, the best way to measure the residence, type of employment, and other attributes. 4 impact of any perturbation is to embrace a holistic, Disaggregating impacts by clientele group is often systematic view-of the world. Unfortunately, as the necessary to detect important impacts that may be scope of analysis increases both the depth of treat- masked if only community-wide effects are consid- ment and the accuracy of the output tend to decrease, ered. at least when resources for data collection and analy- sis are limited. 4. Impact Categorization In view of the difficulties inherent in a comprehen- Impacts from land development can be grouped sive approach, we advocate comprehensiveness only into several somewhat arbitrary and overlapping at the initial project screening level. This translates categories: Local Economy, Natural Environment, into a comprehensive checklist, the use of which Aesthetics and Cultural Values, Public Services, and would help assure that no significant type of impact Social Conditions. Only the natural environment cat- would be ignored. A subset of important categories egory is discussed in this report .5 One danger in di- can then be investigated in greater-depth. The amount viding and compartmentalizing, however, is the tend- of time and funds available for analysis will probably ency to ignore interrelationships among the parts. play as much a role in selecting this. subset as the Some analysts, for example, may see a change in characteristics and setting of the development under fiscal balance as a consideration unrelated to impacts consideration. on water quality, transportation effects, or changes in neighborhood attractiveness. This results in a false 3. Impacted Populations ("Clientele Groups") picture of reality. Deterioration of water quality or It is often desirable to divide the population at risk overcrowding of public roads may necessitate addi- (or to benefit) into several distinct but not necessarily tional expenditures of public funds for new treatment mutually exclusive groups if the impacts will not be facilities or highways. The attractiveness of the neigh- shared equally by all community residents. One pos- sible division is between residents or workers in the 3. Consumer protection from unsafe construction is usually cov- development to be evaluated and their counterparts in ered by local health building and fire codes, although these are not the surrounding community. We are primarily con- universal nor always adequate. 4. See Schaenman and Muller, op. cit., Chap. IV, for further dis- cerned with the latter group, since the greatest cussion of clientele groups. number and most severe impacts usually occur to the 5. The others are dealt with in the companion reports in this surrounding community. We believe that the factors series. General Introduction 3 borhood will be reflected in property values, which in ditional levels of activity from older projects may be turn will affect public revenues. induced by new development. In a system where everything tends, either directly Although the focus here is on incrementally applied or indirectly , to affect everything else, analysis can evaluations, we recognize the complementary need proceed only if most variables can be controlled while for comprehensive planning. In discussing the con- a few are manipulated, or if only a few variables are cerns. associated with each impact category, we have clearly dominant. Thus, fiscal impact analysis often attempted to identify and differentiate between those assumes that a certain level of services will be main- aspects of the evaluation which are more appropri- tained and, tacitly, that a certain threshold of envi- ately addressed by the development of comprehen- ronmental damage will not be exceeded. The impacts sive land use and zoning plans and those which are of land development are then measured in terms of better treated through a project review process. For changes in public revenues and expenditures needed example, problems created by those air pollutants to maintain those threshold levels. Of course, as- which have slow decay rates and are thus dispersed sumed levels may be changed and another analysis throughout the community may be more amenable to performed. But the point is that expenditures and solution by setting limits on the number and location service/quality levels are not varied simultaneously. of pollution sources through large-scale analysis and Likewise, impact assessments in the other areas the adoption of zoning plans than by individual pro- usually assume constant expenditures and measure ject review. On the other hand, smoke and odor impact by changes in levels of services, environ- problems are typically localized in their impact and mental quality, and, in the case of social impacts, are best assessed and solved on an individual project changes in community activities and perceptions. basis. A second level of interrelatedness exists-that If generalizations can be made, perhaps the com- among impacts within the same category. For ex- prehensive planning/project review dichotomy can be ample, sulfur dioxide emitted into the atmosphere by clarified by considering the extent to which impacts a power plant may eventually become dissolved in have a community-wide versus a localized origin or nearby lakes and streams, producing dangerously effect. Sewage effluent which is collected community- acidic water conditions. These interrelations are dis- wide but treated and discharged at one geographical cussed within the individual impact categories. point, air pollutants with slow decay rates and uni- form dispersal patterns, and electricity generated at a B. IMPLEMENTING IMPACT EVALUATION single power plant for the entire community would af- PROCEDURES- MAJOR ISSUES fect community-wide pollution levels. These large- Beyond the technical questions of measurement scale, long-term problems are usually'best addressed procedures and analytical methods to which this by comprehensive planning. Impacts which are spe- reIport is addressed lie more fundamental issues con- cific to the spatial locations of development are more cerning the philosophy and strategy of implementa- appropriately treated on a case-by-case basis. Of tion: (a) How can incremental decisions be coordi- course, many developments generate impacts which nated with planning? (b) How can short-run outcomes are neither purely site-specific nor purely community- be balanced against long-run concerns? (c) Is the,only wide. Here, the interface between comprehensive alternative to a specific proposed development no planning and project review is much less clearly de- development? (d) Who should conduct the evalua- fined. And even where a comprehensive plan based tions-specialists or generalists? on environmental considerations has been imple- mented, a more detailed incremental evaluation of 1. Comprehensive versus Incremental Reviews proposed developments consonant with the plan may Urban planners will argue, rather persuasively, that occasionally be desirable, at least as a check on the evaluating the impact of individual projects is no sub- adequacy of the plan. stitute for comprehensive planning. At best, individ- 2. The "Spillover" Problem ual evaluations capture the incremental effects of one or possibly a few large developments. The combined Jurisdictional boundaries typically do not coincide effects of many developments over a period of sev- with other manmade or natural boundaries. This leads eral years are not easily seen when the incremental to "spillover" of pollution from one jurisdiction to approach is used. Even ff every project, large and another. Not only are air pollutants blown across small, were evaluated, individual developments tend boundaries, but mobile sources generated by a devel- to be mutually reinforcing and synergistic. Thus, ad- opment in one jurisdiction may be driven consider- 4 Land Development and the Natural Environment able distances in surrounding communities as well. predict with any degree of confidence where for Thus, "spillover" refers to sources as.well as to the example, ten-thousand new residents will choose to pollutants themselves. reside if the project being evaluated -is rejected? Where the -governmental unit in which the effects Still, the reality of rejection must be described, if of pollution are experienced does not also control pol- only in the most -general and qualitative way. lution sources, redress of grievances may not be sat- isfactorily achieved. In fact, it may clearly be to one 4. Planning Department/Line Agency jurisdiction's advantage to '.'export" its pollution Interrelationships while reaping the benefits of its pollution-generating Comprehensive planning departments are usually activities, usually measured in terms of additional charged with conducting evaluations of proposals for jobs and tax revenues. variances, rezonings, special zone adoptions, and Control of regional "spillover" problems depends other types of land use changes. Yet the technical ex- on both technical and institutional solutions. Large- pertise required for a competently conducted impact scale models which simulate the movement of pol- evaluation may well reside in line agencies; The qual- lutants and chemical reactions in atmospheric or ity of the evaluations produced is thus dependent on aquatic environments are needed to estimate the the extent to which this expertise.can be marshaled location and magnitude of regional-scale pollution and coordinated. The comprehensive planning staff problems. Once the problem has been identified and so- should make a special effort to find out- what tools lutions in terms of source and/or land use, controls exist (and their limitations) in the line agencies and to proposed, regional bodies must be organized and em- work with the agency staff in developing a checklist powered to act. The federal government is now either of measures and formats for expressing the results. assuming this role or mandating regional coopera- tion .6 5. Applicable Federal, State, and Local Laws For communities where the problems are defined The development of local impact evaluation pro- more in terms of individual shopping centers, planned grams occurs within the context of federal, state, and unit developments, or industrial plants than in terms local laws which relate to and, at times, overlap with of large industrialized areas, state or federal media- comprehensive evaluation requirements. tion is much less likely. For these situations we urge Federal legislation now exists in the areas of air, that project evaluations include the other affected water, and noise pollution. Although the thrust of this communities as "clientele groups." This certainly legislation is towards control at the source, the air does not insure resolution of the conflict, but it would and water laws also contain explicit language re- serve to heighten the level of the debate and may help garding land use planning and evaluation. Other rel- to reduce suspicion and mistrust. evant areas for which federal legislation exists in- 3. Proposal Alternatives clude flood hazards and transportation, the former One of the most difficult tasks in preparing specific through the flood insurance program and the latter as impact evaluations is to identify realistic alternatives a product of extensive federal support of highway to the project under review. Ideally, several propos- programs. State activities related to land development typi- als for a single tract of land would be submitted cally include granting permits for water and sewage simultaneously. Decision makers would then be able treatment facilities (both community-wide and on- to select on a comparative basis. Typically, however, site), for activities which affect the level or location the only alternative is no development. No develop- of surface waters, and for new sources of air emis- ment is not synonymous with no effect, however. sions or water effluents. Care must be exercised to gauge the effects in all At the local level, government review activities em- impact categories of diverting the demand for the phasize the application of building and subdivision proposed activity to other sites. The difficulties in codes. Some communities have broadened their ap- attempting this, however, are enormous. Who can proach by adopting ordinances such as those re- quiring "adequate public facilities." This represents a major step toward comprehensive evaluation. 6. An insightful, although sobering, examination of one area's Before any evaluation program is developed, a approach to regionalizing the analysis and solution of environ- thorough inventory should be made of relevant legis- mental problems caused by urbanization is documented in B. A. Ackerman et al., The Uncertain Search for Environmental Quality lation and activity at all levels of government. Simply (Riverside, N.J.: The Free Press, 1974). adding one more layer to the already bewildering General Introduction 5 array of overlapping requirements which guide the formed (and usually expensive) retrospective studies developers' application process does little to advance of individual developments (such as the power plant orderly and efficient land development. Coordination impact study in progress at the University of Wiscon- is an overworked but pertinent word. In many cases sin 7) , as well as less ambitious studies on the ability the successful application for federal, state, or local of a technique to estimate current conditions. Until development permits can substitute for the submis- such studies are made, progress toward developing sion 'of additional data. Where the scope of the improved techniques will be slow and the accuracy of permits is more limited, additional data will be neces- many impact estimates will remain suspect. This is sary at the time of impact evaluation. not to say that the use of any current impact esti- mation model is unjustified. Some produce results C. NEEDED RESEARCH clearly superior to purely qualitative approaches or The results of the methodological review reported "quick and dirty" quantitative methods. But without in this volume reveal that the state of the- art of im- better information on the accuracy of.many of the pact evaluation is unevenly advanced in the various more complex mathematical models, cost/benefit de- impact categories. Predictive techniques are not cisions on their use are most difficult to make. available for estimating impacts on wildlife and vege- tation, as they are under certain conditions for air and water pollution. But even for the latter, additional vali- 7. D. E. Willard, Preliminary Documentation of Environmental dation of available techniques is sorely needed. Ade- Change Related to the Columbia Electric Power Generating Site, Working Paper II (Madison: Institute for Environmental Studies, quate validation should be based on carefully per- University of Wisconsin, May, 1973). 6 Land Development and the Natural Environment PART I AIR QUALITY - 1. INTRODUCTION AND BACKGROUND The word "pollution" is tightly tied to the con- 3. Effects on materials ,(e.g., soiling and corro- cept of impacts on humans. Only to the extent that sion). emissions and resulting ambient concentrations of 4. Aesthetic and nuisance effects (e.g., odors and certain substances from either natural or manmade smoke plumes). sources negatively affect the health or welfare of man are substances considered pollutants. I Thus, carbon 1. Human Health Effects dioxide (COO is not considered a pollutant while sul- Data that bear on the health effects of air pollution phur dioxide (SO) is, even though the former is gen- are obtained from laboratory studies of animals, clin- erated by natural processes and human activities and ical obser-vation and limited human experimentation, subsequently emitted to the atmosphere in much studies in controlled, nonlaboratory settings (e.g., larger quantities than the latter .2 industrial plants), and epidemiological studies of large A. HEALTH AND WELFARE EFFECTS populations. The highly controlled environment of a laboratory is ideal for manipulating the level of a The effects of air pollution on human health and single pollutant while holding all other pollutants and welfare 3 can be categorized as follows: environmental conditions constant. However, ani- 1. Effects on health (morbidity and mortality). mals must usually substitute for human subjects and 2. Effect on other living organisms (which then im- only short-term (acute) effects can be measured. In pact upon man). addition, the possible exacerbation of existing disease conditions by air pollution is difficult to test in the 1. "Ambient" refers to the surrounding atmosphere to laboratory. which man, plants, and other receptors are exposed. The ambient Epidemiological studies (at the other extreme) concentration of any pollutant depends on the quantity emitted and focus on the "real world"-ambient pollutant con- the degree of dispersal. centrations and man in his normal setting. But even 2. Carbon dioxide may yet prove to be a pollutant if the long- when correlations between health and exposure levels term effect of increasing concentration on a global scale is an in- crease in climatic temperature. This is a subject of considerable de- are found, it is often difficult to prove a causal rela- bate among meteorologists. tionship. Urban activities may produce air pollution, 3. For further discussion of this subject, see Lester Lave and but they may also create stressful situations which, in Eugene Seskin, "Air Pollution and Human Health," Science 69 turn, cause an increase in morbidity and mortality. (1970): 723-33; The National Academies of Sciences and Engineer- ing, Air Quality and Automobile Emission Control, vols. 2 and 4, Thus, in spite of much effort, there remains consider- Senate Committee on Public Works (Washington, D.C.: Govern- able uncertainty about the hazard actually presented ment Printing Office, September, 1974); and George L. Waldbott, Health Effects of Environmental Pollutants (St. Louis: C. V. by various suspect pollutants. Mosby Co., 1973). Table 1-1 briefly summarizes curTent knowledge of 9 air pollutant health relationships, and the major rent knowledge of health/air pollution relationships development-related sources for each pollutant. are listed in Table 1-2. These relationships are only probabilistic. It is known The strongest case for unambiguous effects on that exposure to high levels of SO, will cause ill health can probably be made for SO, and particulates, health in some people. But for any individual the for which a statistical relationship between ambient probability of becoming ill is influenced by present concentration and mortality rate (aggregated on a na- health, genetic susceptibility, duration and frequency tional basis) has been ascertained.4 Evidence for the of exposure, presence of other pollutants, and a host of other factors. Air quality standards based on cur- 4. Lave and Seskin, op. cit. Table 1-1. A SUMMARY OF HUMAN HEALTH-AIR POLLUTANT RELATIONSHIPS@ -SUSCEPTIBLE POLLUTANT MAJOR SOURCES HEALTH EFFECTS POPULATIONS COMMENTS Carbon Transportation, industrial Reacts with hemoglobin re- Persons with cardiovascular Past knowledge was based on study monoxide processes ducing mental attentiveness, disease and others of high exposure for short periods (CO) physical exertion, and ex- with healthy, young individuals. acerbating cardiovascular New data show possible health disease symptoms effects for susceptible persons at CO levels in the blood found in urban populations. Nitrogen Transportation, space heat- Interfere with respiratory Persons with respiratory or Conclusions are based on limited oxides (NOx) ing/cooling, power functions producing long- cardiac disease, the young exposure of healthy adults to low generation term (chronic) disease and the elderly doses, extensive animal studies, symptoms and only limited data relevant to ambient conditions. Hydro- Transportation and indus- See photo-oxidants See photo-oxidants Indirectly polluting through the pro- carbons trial processes duction of photochemical oxidants (HQ upon reaction with NO and N02 in the presence of sunlight. Photo- See nitrogen oxides and Interfere with respiratory Persons with chronic respi- Ozone (0.,) is the most common oxidants hydrocarbons functions and cause eye ratory diseases, especially type and the key indicator for (01) irritations bronchial asthma photo-oxidants. Health effects are based on limited and inadequate data. ParticulateSb Power generation, space Interference with respiratory Persons with respiratory dis- The effects of particulates are diffi- heating/cooling, industrial functions, possible contribu- ease, the young and the cult to separate from those of processes, soil erosion tion to lung cancer elderly sulfur dioxide. Sulfur Power generation, space Little effect in the pure gas Persons with respiratory or Sulfur dioxide is readily converted oxides (SO,) heating/cooling, industrial form; similar effects as par- cardiovascular disease, the to S03 and then to sulfuric acid (a processes ticulates when combined young and the elderly particulate). Determining which with them effects are due solely to S02 is difficult. Heavy Power generation, industrial Specific to each pollutant Specific to each pollutant Pollution from these agents can be metals, processes intense at the source, but tends not radioactive to be widespread. agents, others' a. Information in this table is based primarily on the following references: National Academies of Sciences and Engineering, op. cit., vol. 2: Health Effects of Air Pollution; Waldbott, op. cit.; J. D. Williams, et aL, Interstate Air Pollution Study, Phase If Project Report, VI. Effects of Air Pollution (Cincinnati, Ohio: Public Health Service, U.S. Department of Health, Education, and Welfare, December, 1966). b. Particulates, also known as aerosols, are either solids or firie liquid droplets which vary by size, shape, and composition. Sulfuric acid formed from SO, is one of the most biologically significant particulates. Some particulates such as dust can be rather innocuous considered alone, but become lethal transport agents when toxic gases are adsorbed to their surfaces. c. For a more complete discussion of other pollutants see, for example, Waldbott, op. cit. @10 Land Development and the Natural Environment Table 1-2. NATIONAL AMBIENT AIR QUALITY STANDARDS PRIMARY SECONDARY STANDARD STANDARD PERIOD OF POLLUTANT MEASUREMENT Ag/-' PPM /Xg/m, PPM 1. Carbon monoxide (CO) 8 hours 10,000 9 Same Same I hour 40,000 35 Same Same 2. Hydrocarbons (HC) (nonmethane) 3 hours 160 0.24 Same Same 3. Nitrogen dioxides (NO2) Year 100 0.05 Same Same 4. Photochemical oxidants (0.) 1 hour 160 0.08 Same Same 5. Sulfur oxides (SO.) Year 80 0.03 None None 24 hours 365 0.14 None None 3 hours None None 1,300 0.5 6. Total suspended particulates (TSP) Year 75 60 24 hours 260 150 SOURCE: Federal Register, Vol. 36, No. 84 (April 30, 1971). NOTES: Concentrations are averaged over each period of measurement. The annual TSP concentration is a geometric mean of 24-hour samples; all other concentrations are arithmetic mean values. Standards for periods of 24 hours or less may not be exceeded more than once per year. Units of measurement are micrograms per cubic meter (jig/ml) and parts per million (ppm). Primary standards are designed to protect human health. Secondary standards are designed to protect human welfare (i.e., eliminate damage to vegetation and materials and aesthetic problems). other pollutants is highly suggestive. Extreme levels The primary ambient air standards were established are known to cause illness and even death, but these by identifying the lowest concentration for which levels are much higher than normal ambient concen- health effects have been observed (usually in clinical trations. The effects of long-term exposure to lower situations among patients with respiratory or cardio- concentrations are still highly speculative. vascular illnesses) and then reducing this level by a 41 safety factor." The secondary standards were estab- 2. Vegetation and Material Effects lished using data on damage to plants, animals, and Table 1-3 summarizes the known or suspected im- materials. pact of air pollution on vegetation, materials, and State governments are required to . designate geo- man in terms of aesthetic and nuisance concerns. graphic areas which fail to meet the standards (air Much of the data for vegetation and materials impact quality control regions) and to submit implementati 'on is based on laboratory or controlled field studies. As plans for stationary source emission and transpor- with health effects, sorting out causative agents and tation management controls adequate to solve the mechanisms of action is difficult. Vegetative damage problem by 1975-77.5 These requirements were de- can be mimicked, masked, or exacerbated by a vari- signed to satisfy the letter of the law, but two highly ety of factors, such as rainfall, plant disease, and sun- significant court decisions have greatly expanded light. Impact on materials is likewise a complex phe- EPA's role, thrusting the federal government fully nomenon. Aesthetic and nuisance effects are more into land use planning. easily identified, although the seriousness of effect is The first decision resulted from a challenge to EPA open to considerable question. by the Sierra Club (May 30, 1972) regarding EPA's practice of allowing the deterioration of air in rela- B. APPLICABLE STATE AND FEDERAL LAWS tively clean areas. As a result, no significant deteri- The federal government has assumed major respon- sibility for the maintenance of air quality in the United States. Pursuant to the 1970 amendments to 5. More specifically, the control plans may include emission lim- itation, relocation of sources, economic (dis)incentives, changes in the Clean Air Act, the Environmental Protection operating procedures and schedules of sources, motor vehicle Agency (EPA) has promulgated both primary and emission control and inspection, limitations in motor vehicle use, secondary ambient air standards (Table 1-2) together expansion of mass transportation, and other unspecified land use and transportation measures. In addition, EPA will establish new with an elaborate list of policies, guidelines, and re- source emission standards for all stationary source categories quirements for their implementation. deemed to endanger public health or welfare. Air Quality: Introduction and Background I I Table 1-3. A SUMMARY OF AIR POLLUTION EFFECTS ON VEGETATION, MATERIALS AND MANa (AESTHETIC AND NUISANCE CONCERNS) POLLUTANT VEGETATION MATERIALS AESTHETICS/NUISANCES Carbon monoxide None None None (CO) Nitrogen oxides Reduction in growth of plants with Accelerated deterioration of dyes and Creation of a brownish coloring in (NO,) broad leaves (e.g., beans, tomatoes) paints urban air Photo-oxidants Severe reduction in growth and even- Ozone causes the cracking of rubber Ozone has a distinct although not (01) tual death of leafy vegetables, field and and the accelerated deterioration of terribly offensive odor forage crops, shrubs, fruit and forest nylon, rayon, dyes, and paints trees caused by ozone and PANb Hydrocarbons None None None (HC) Particulates Reduction in plant growth by physical Soiling of fabrics and buildings and Creation of smoke plumes, scattering blockage of light when deposited on corrosion of metals when combined of sunlight to produce haze and color- leaf surface with SO@ ful sunsets,- and formation of hydro- scopic nuclei to produce fog Sulfur oxides Reduction in growth of plants with Corrosion of iron metals, accelerated Scattering of sunlight to produce haze, (501) broad leaves deterioration of building stone, cotton, production of unpleasant odors paper, leather, paints and other finishes Otherse Floride causes long-term damage to Tarnishing of metals by hydrogen Hydrogen sulfide produces extremely selected field crops (and animals) sulfide unpleasant odors a. The information in this table is taken primarily from Public Health Service, The Effects of Air Pollution (Washington, D.C.: U.S. Department of Health, Education, and Welfare, 1967). b. Peroxyacylnitrate, an oxidation product of hydrocarbons. c. Other pollutants, such as hydrochloric acid and ammonia, are present in small quantities on a national basis and are not discussed. oration in these areas will be allowed in the future.' At mentation plans addressed only the issue of remedial issue now is the definition of "significant deteriora- actions to be taken in areas presently violating na- tion. " Although final regulations had not been pro- tional standards. The pla ns, did not assure that air mulgated, EPA's expressed intention was to shift the quality would be maintained once the standards were definitional burden to the states. The draft regulations achieved. In response, the EPA is applying two new would allow the states to place planning areas (pre- approaches, Indirect Source RevieW7 and the devel- sumably analogous to air quality control regions) into opment of Air Quality Maintenance Plans (AQMPs).' one of three categories, which range from "no deteri- Under the first approach', states, or preferably local oration allowed" to "deterioration allowed up to a governments, must review all, new developments large fraction of the national standards." Regardless (above certain thresholds) which threaten to cause of how literally "significant" is interpreted, it is clear new or exacerbate existing violations of the national that new development in atmospherically clean as standards by inducing transportation-related emis- well as degraded areas must be controlled in order to sions.9 These developments include parking facilities, minimize air pollution. Thus, state and designated shopping centers, airports, and sports arenas. Where local governments will have to review land use plans such developments are estimated to cause the speci- as well as individual projects for their impact on air fied deterioration in air quality, they are to be pro- quality. hibited. The second court decision was a product of a chal- The second approach requires states to designate lenge to EPA-certified state implementation plans areas which, due to projected growth rates, present (January 1, 1973). The Natural Resources Defense threats to the continued maintenance of national stan- Council, Inc., successfully asserted that the imple- 7. See Federal Register, vol. 39, no. 38 pp. 7269-92 (February 25, 1974). 6. The Court of Appeals for the District of Columbia reaffirmed 8. See Federal Register, vol. 38, no. 116, pp. 15834-37 (June a lower court's order and the Supreme Court could not reach a de- 18, 1973). cision, thus allowing the original order to stand. 9. The thresholds are expressed in terms of number of cars. 12 Land Development and the Natural Environment dards. These areas are to be known as Air Quality area, and line. Point sources are those which are sta- Maintenance Areas (AQMAs). Once the nature and tionary, can be readily identified and located, and magnitude of the problems have been ascertained, air usually are substantial contributors to total pollutant quality maintenance plans are to be developed speci- loads in the atmosphere. Power plant smokestacks fying preventative measures. These are primarily land are an obvious example. Area sources are either use and transportation control measures, including sources of considerable areal extent (e.g., a burning emission-density zoning and a requirement for envi- landfill site) or combinations of small, difficult-to- ronmental impact evaluations antecedent to and identify stationary or mobile sources averaged over se rving as a basis for decisions on requests for land an area (e.g., residential structures). Line sources are use changes. 10 transportation corridors through which mobile Aside from implementing various aspects of the sources pass and, over time, can be represented as a Clean Air Act, states may, and in some cases have, continuous source in,the shape of a line. specified standards and implementation programs more stringent than the federal ones (e.g., California). 2. Atmospheric Dispersion14 In every state and in many local communities, public The escape of noxious materials from point, area, agencies have been designated to implement and en- and line sources is only the firist stage in the develop- force federal and state air pollution laws. Some ment of air pollution problems. In the path from states, such as Florida, have also added air quality source to receptor (who or what is exposed to or impact evaluation requirements to the review of cer- "receives" the pollution), atmospheric gases and tain large-scale developments." A few of the larger aerosols are driven by forces with disparate origins, cities, such as New York, have also established magnitudes, and directions. The actual path that the region-specific standards and regulations. 12 materials take will largely determine their strength at the receptor and thus their effect on man. C. EMISSIONS AND ATMOSPHERIC The forces which control atmospheric dispersion DISPERSION: FUNDAMENTAL PRINCIPLES are the product of differential heating of the earth's l..Emissions and Emission Sources13 surface by the sun and gravitational attraction between the earth and atmospheric constituents. Virtually every substance now identified as a pollu- These forces are most conveniently categorized by tant is produced to some extent by natural processes. the scale of effect. Synoptic or large-scale forces pro- These background levels are the product of oil and duce,major weather events and affect largeland and coal field leaks, volcanic eruptions, weathering of water. areas, meso or medium-scale forces produce rock, biological production and decay, sea spray, conditions which affect air quality for an entire com- forest fires, and a variety of other occurrences. In munity (or subarea thereof), and micro or small-scale some situations background levels may be high forces create localized conditions in the immediate vi- enough to be a cause of concern. Typically, however, cinity of a source. The most dramatic impacts from manmade emissions far exceed the natural ones. development. will normally be'localized and thus con- Man-related emission. sources are numerous and trolled to a large extent by micro factors. However, varied. The general categories in Table 1-1 refer to cumulative effects and extreme. conditions (i.e., those the type of development-related activity which pro- producing the hazards) are caused by factors at.all duces the emission. Concentrating on physical as- three scales. pects of emission sources, most air pollution mete- orologists recognize three types of sources: point, a. Principal Factors Affecting Dispersion Ambient concentration of pollution at any point in 10. For further information on the designation of AQMAs see, space is largely dependent on the extent to which pol- Environmental Protection Agency, Guidelines for Air Quality lutants have mixed with surrounding "clean" vol- Maintenance Planning and Analysis, vol. 1: Designation of Air Quality Maintenance Areas (Research Triangle Park, N.C.: EPA, umes of air. This in turn is a function of wind speed September, 1974). .(the greater the speed the faster the removal from the 11. The Environmental Land and Water Management Act, source and the greater the dilution) and mixing depth. Chapter 380, Florida Statutes, 1972. The latter is an expression of the vertical distance 12. See "Air Pollution Control News," The American City (August, 1972). from the ground to the inversion layer or area of 13. For additional information, see National Academies of Sci- ences and Engineering, op. cit., vol. 3 and The California State Air 14. For more information, see Brian J. L. Berry et al., Land Resources Board, Current Methodologies for Determining the Spa- Use, Urban Form, and Environmental Quality, Research Paper tial Distribution of Air Polluting Emissions (Sacramento: CSARB, No. 155 (Chicago: Department of Geography, University of Chi- July, 1974) (NTIS No. PB-237864). cago, 1974). Air Quality: Introduction and Background 13 warmer air aloft and represents the volume of air "decay" by adsorption to solid surfaces, absorption available for pollutant dispersal. When inversions are by vegetation, or dilution by increasingly larger vol- located close to the ground (i.e., the depth is small), umes of the atmosphere.19 The transformation pro- pollutants are trapped in relatively small volumes of cesses depend on pollutant concentrations, mete- air and ambient concentrations are consequently in- orological conditions, topography, and ground cover. creased. 15 The average mixing depth and the potential Tracing the fate of these pollutants is important not for low-level inversion formation (and thus the poten- only from an air pollution perspective-they also af- tial for dangerous pollutant build-ups) can be pre- fect water and "land" pollution. For example, pollu- dicted from historical records. Published data are tants such as S03 and N02 produce caustic acids available on mixing depths on a rather gross scale na- when dissolved in water. Heavy metals, if deposited tionally. 16 More disaggregated information is also in surface water from the atmosphere, may present available, at least for the state of California. 17 health hazards for many years. Radioactive materials Wind speed and direction are determined by forces present serious health problems regardless of their at all three scales (i.e., synoptic, meso, and micro). eventual place of deposition .20 More specifically, prevailing winds, storm systems, urban heat-island effects,18 topographic features, and D. AIR QUALITY IMPACTS OF manmade structures combine to create net move- LAND DEVELOPMENT ments of air at any point in space. The "concrete Air quality impacts resulting from land develop- canyons" created by rows of tall buildings produce ment differ by phase (site preparation, construction, special effects. Eddy currents concentrate internally occupancy) and type (residential, commercial, indus- generated pollutants, while the "canyon" walls retard trial). In addition, air quality impacts can be distin- flushing by crosswinds. guished on the basis of source location-on-site or b. Removal and Transformation Processes off-site. For all types of developments the most significant Once emitted and dispersed, the fate of atmo- impacts will normally be associated with the occu- spheric pollutants is an important but poorly under- pancy phase. Site preparation and construction tend stood story. Some pollutants, such as CO, SO3, to be relatively transitory activities and the resulting nitrogen oxides to some extent, and particulates are pollution (largely in the form of particulates) rather removed by precipitation. Some particulates are also localized .21 Consequently, attention will be focused on removed by gravitational settling, depending on their air quality impacts generated once the development size. Some, such as NO, NO,, and hydrocarbons are has been occupied. - either nonsoluble or participate in long-term chemical For residential and commercial developments the reactions, being transformed into nonsoluble gases in emission of pollutants will be caused by on-site space the process. These nonsoluble gases are presumed to heating, by off-site electrical power production, and by the generation of both on-site and off-site trans- 15. Inversions can occur when warmer air masses descend, portation. For industrial developments one additional when air near the ground cools more rapidly than that above, and, source will be the manufacturing processes them- in effect, creates an inversion (as typically happens in urban areas selves. The combustion of fuel, as well as the han- at night), or when cooler air underflows warmer air (as typically happens in valleys at night). dling of gaseous materials, can lead to significant 16. George C. Holzworth, Mixing Heights, wind Speeds, and emissions. Potential for Urban Air Pollution Throughout the Contiguous United States (Research Triangle Park, N.C.: EPA, January, 1972). 19. Existing evidence indicates that vegetation plays a relatively 17. California State Air Resources Board, Meterological Param- minor role in removing gaseous pollutants, although it may be ef- eters for Estimating the Potential for Air Pollution in California fective in removing particulates. See George Hagevik, Daniel R. (Sacramento: CSARB, July, 1974) (NTIS No. PB-237 869). Mandelker, and Richard K. Brail, Air Quality Management and 18. Urban areas are net producers of heat. This creates a "con- Land'Use Planning (Washington, D.C.: Praeger Publishers, 1974). vection cell" whereby warm air in the city rises, moves out over 20. Waldbott, op. cit. (see fn. 3). the cooler countryside, cools, descends and returns to the city at 21. However, for development occurring over extended periods ground level. This may produce a "recycling" of pollutants. of time in already developed areas, this may not be insignificant. 14 Land Development and the Natural Environment 11. METHODOLOGICAL APPROACHES Central to the problem of estimating the impact discussion of impact measures and related topics, the of land development on air quality is the relationship remaining portion of this chapter will discuss avail- between emissions and ambient concentrations. Most able techniques for each step. impact assessments, no matter how crude they may be, are based on the measurement or estimation of A. MEASURES, STANDARDS, AND INDICES emissions with and without the development in ques- 1. Measures and Standards tion and a translation of this difference into the change in ambient concentration. Since this transla- Measures of air quality impacts should preferably tion is dependent on highly variable meteorological reflect changes in (a) risk or damage to human health factors, the fidelity with which the translation tech- and possibly vegetation and materials, and (b) aes- nique represents local meteorological conditions will thetic and nuisance problems. Following is a list of al- largely determine the accuracy of the results. ternative measures, with the preferred one listed first The general steps in calculating the impact of pro- in each category: posed land developments on air - quality are as Health 2 follo ws. I 1. Change in the ambient concentration. of each I .Measure/estimate current emissions. pollutant, the frequency of exposure, and the 2. Estimate future emissions. number of people at risk. 3. Measure/estimate current ambient concentra- OR tions. 2. Change in the ambient concentrations of each 4. Estimate future ambient concentrations. pollutant (relative to standards). 5. Measure/estimate exposure of man, vegetation, and materials. AestheticlNuisance These steps are necessary in order to establish 3. 1Change in the number and frequency. of prob- baseline conditions for comparison purposes and, for 2. These measures could be expanded to include the exposure of some techniques, to make future estimates. After a vegetation (areal extent and vegetation type) and materials (amount and type) most likely to be severely affected. An alternative mea- sure is "new emissions as a percentage of the budgeted amount" 1. For retrospective analyses of existing developments, simply meaning that a budget has been prepared for the entire community compare the emission levels and ambient concentrations before or the area in question. See Part 1, 111, Section A for a more de- construction with those after it has been completed. tailed discussion. 15 lems caused by smoke plumes, odors, haze, and may also be used to infer the general impact of future the number of people affected. developments. The subject of measuring perceptions OR of air quality and other neighborhood attributes is dis- cussed in another report in this series .3 4. Change in the likelihood that aesthetic/nuisance Interpretation of values generated for the measures problems will occur or change in severity. is usually made by reference to historical values or Measures I and 3 are most directly related to the standards. In the case of the latter, federal standards end impact on man and thus are the preferred mea- are the most popular (and now mandated) reference sures. Each is a quantitative assessment of changes in point. Unfortunately, the relationships between pollu- ambient pollutant concentrations, including likely tant concentration and health typically do not display new levels and their frequency of occurrence. In ad- threshold characteristics with a single value sep- dition, these measures suggest that a detailed estima- arating completely safe levels from hazardous ones.' tion be made of who (or what) will be exposed to As mentioned earlier, hazard is best measured as a which levels and how often. Measures even more re- probability of deleterious effect which depends on flective of the end impact on man could be specified. current health, inherited susceptibility, length and fre- We could speak of changes in morbidity or mortality quency of exposure, the presence of other pollutants, rates or changes in the monetary value of property and other factors. Thus, single standards for each pol- damaged by air pollution. However, values for these lutant, convenient as they may be to apply, do not measures could not be obtained for individual com- adequately represent the physical and biological pro- munities due to the present lack of knowledge cesses involved. The point is not that the federal stan- regarding health and damage effects of air pollution. dards are invalid, but that they should be viewed as Measures 2 and 4 are much less desirable expres- merely the best available knowledge on a complex sions of impact but may be more practical in certain and imperfectly understood subject. Local govern- situations. They are more general indications of ments may well decide to specify more stringent stan- changes in area-wide pollutant levels, relying on long- dards as a protection against uncertainty. term concentration averages rather than the more de- Once a set of standards or targets has been speci- tailed data needed for measures I and 3. These fied, they can be used to interpret the results of the should thus be considered proxy measures. analysis. Since impact depends on both ambient con- One important consideration in choosing between centration and the frequency of occurrence, the stan- measures is the probable magnitude of the impact. If dards and the results could be expressed as the "total one or more new developments have the potential of number 'of days (or, less adequately, the number of significantly degrading air of currently acceptable times) a certain concentration is reached." Impact quality (based on a cursory qualitative assessment), can then be described as the "total number of days or then a detailed and comprehensive analyls:,is may be the number of times the standard is exceeded (or, justified, unless the initial assessment clearly shows closely approached)." an unambiguous violation of a standard. Small devel- opments, or those located in relatively noncritical 2. Indices areas, on the other hand, probably do not warrant the expense of an elaborate evaluation. For the purpose of comparing one development or plan with another it is sometimes desirable to express Data collection and analysis procedures appear to "air quality" by a single number. Several air quality be available for all of the measures listed, although indices have been developed to "sum up" or inte- the accuracy of values generated remains an impor- grate the changes in concentration of the various pol- tant and, in some cases, an unknown quantity. Issues lutants.5 These are typically root-sum-squares or related to the cost and accuracy of impact evaluations summations of ratios between observed concentra- are discussed in the next section. The four measures are intended to be objective statements of impacts on the affected population. 3. K. Christensen, Social Impacts of Land Developments However, citizen perceptions of annoying or unpleas- (Washington, D.C.: The Urban institute, forthcoming). ant air pollutants are needed to define reference stan- 4. For documentation of the nature of this relationship, see Na- tional Academies of Sciences and Engineering, op. cit., vols. 2 dards for interpreting the impacts, in addition to and 4. knowledge of pollutant concentration/aesthetic rela- 5. For a discussion of several indices, see James W. Curtin, Na- tionships based on controlled condition experiments. tional Environmental Policy Act of 1969: Environmental In- Where detailed impact evaluations are not feasible, dices-Status ofDevelopment, Pursuant to Section 102(2) (B) and 204 of the Act, Senate Committee on Interior and Insular Affairs data on current citizen satisfaction with air quality (Washington, D.C.: December, 1973) and. Berry et aL, op. cit. 16 Land Development and the Natural Environment tions and the standards .6 Indices can also be devel- The acquisition and assemblage of current data on oped to reflect the number of times the standard is point, area, and line source emissions are formidable exceeded within a specified period of time. and costly tasks. Even with a substantial investment However, indices have several inherent problems. of time and money, the results are often less than sat- The weighting schemes used are often arbitrary, and isfactory, or worse yet, are inaccurate to an unknown the numbers which result are difficult to interpret in degree. However, since an inventory of current emis- terms of the severity of the problem. Although higher sions is a prerequisite for air quality impact evalua- numbers for each of the various indices tend to indi- tions at any scale, the expenditure of the necessary cate greater pollution, differences in scores between funds to make estimates of emissions is probably jus- individual cities show wide variation, depending on tified! For most large metropolitan areas it is re- the index used .7 Also, those using an index may be quired under the Clean Air Act. unaware of the weighting. Both the EPA and, to a lesser extent, the U.S. De- Another problem is that indices tend to blur distinc- partment of Transportation (DOT) have been active tions among pollutants. The same numerical score in developing guidelines, analytical procedures, and can be obtained from a vast number of different com- mathematical models for use in preparing emission binations of pollutants. Thus, low concentrations for inventories.9 Rather than repeating what is covered in several pollutants could overshadow a high concen- these reports and others they reference, only the gen- tration for one. We believe that expressing the results eral approaches will be described. separately for each pollutant provides more usable in- formation for the decision maker. a. Point Sources The most accurate method of ascertaining the type B. MEASUREMENVESTIMATION PROCEDURES and quantity of emissions from a point source is to In order to obtain values for these measures, a place a monitoring device in the effluent stream. number of discrete data collection and analysis opera- However, the cost of applying this approach to every tions are necessary. These operations were sum- smokestack of every industrial firm and power plant marized in the introduction to this section and will in a metropolitan area is usually prohibitive. At a now be discussed in detail. minimum, instrumentation can provide an accurate test for other less direct approaches. 1. M easu ri ng/Esti mating Current Emissions A second, more practical approach is based on the All dispers Iion models used to estimate the air qual- quantity and type of fuel consumed or raw materi- ity impact of development need values for the total als used. When multiplied by emission factors (pollu- level of emission-current levels plus those added by tants per unit of activity)'O, these indicators will pro- the proposed development. Consequently, accurate vide estimates of aggregate emissions. If information estimates of current emissions will improve the accu- on the timing of emissions is desired, however, racy of the projected impact. schedules of operation must be obtained. Data on fuel and raw materials can be collected 6. The following are formulas for root-mean-square and linear from surveys of each point source (or a sample of summation indices, respectively: sources if many are similar). If this level of detail is not available, records of local fuel and raw material Ca j Z,/S0 2 distributions can be probed. Failing this, statewide 1=1 n b a (C,/Si)) 8. The EPA estimates that approximately three, man-years are required to inventory current emissions in a city the size of Wash- where I = index value, ington, D.C. (personal communication with a member of the Con- C = recorded concentration, trol Programs Development Division). S = standard, 9. See the EPA, Guide for Compiling a Comprehensive Emis- i = 1, 2, . . n time periods (e.g., 8 hours, 24 hours) sion Inventory (Research Triangle Park, N.C.: EPA, June, 1972); or, alternatively, pollutant,, pollutant2, - pollu- EPA, Compilation of Air Pollution Emission Factors (Research tant.. Triangle Park, N.C.: EPA, April, 1974); Federal Highway Adminis- a and b = scaling factors chosen so that the numerical val- tration, Urban Transportation Planning and Air Quality, Highway ues of the index fall within desired ranges (e.g., Planning Technical Report No. 33, and Federal Highway Adminis- I = I for the situation where no standards are ex- tration, Special Area Analysis (Washington, D.C.: Department of ceeded). Transportation, August, 1973). These can be used to weight the concentrations of one pollutant for 10. The emission factors relate the quantity of pollutants emitted different averaging times or the concentrations of different pollu- to levels of polluting activity (e.g., x pounds of S02 per y tons of tants for a single averaging time. coal) and are specific to the type of emission control device (if any) 7. See Berry et al., op. cit. in use at individual sources. Air Quality: Methodological Approaches 17 data on fuel and raw material consumption (collected building fires, and construction sites (dust) are ob- by such organizations as the U.S. Bureau of Mines or tained as detailed in the previously cited EPA reports state pollution control agencies) can be allocated to a (see page 17). local community, based on the community's state- wide share of the polluting activity. c. Mobile Area or Line Sources Likewise, community-wide data can be appor- A moving source of emissions is conveniently de- tioned to subareas using the same concept. It is clear, picted as a line source. However, most emission however, that these approaches are several times re- inventories and most dispersion models treat line moved from the physical measurement of emission sources as area sources by aggregating and then uni- levels; and with the loss in specificity comes a con- formly distributing the line sources throughout the comitant loss in accuracy." areal unit of analysis. The measurement of smoke plumes presents a The data base for estimating emissions from line slightly different problem. The most common param- sources is usually much richer than that for point or eter measured is opacity, and the most frequently area sources. Most medium to large size communities used measuring device is the Ringelmann Smoke have transportation departments which maintain de- Chart .12 tailed data on street capacities, traffic volumes, and sometimes vehicle mixes (both by type and age). This b. Stationary Area Sources allows calculation of vehicle miles of travel at various Most area sources are groups of point sources speeds at various times of day. Knowing in addition which are too small to investigate individually. Sec- the average mix (light duty and heavy duty) and the ondary sources of information are then typically age distribution of vehicles allows calculation of the used. For residential area sources, local fuel distribu- level of emissions. The analytical procedures are de- tors can be consulted to obtain information on the tailed in the EPA and DOT publications previously amount and mix of fuels used for space heating. A cited (see page 17). characteristic emission factor for each fuel is then ap- Again, if this level of detail is not available or plied to obtain total emissions. appropriate, indirect data can be used. These include Depending on the ultimate utilization of the inven- data on total gasoline sales for the community tory, spatial disaggregation may be desirable. Alloca- (obtainable from state tax departments) and on motor tion methods similar to those mentioned for point vehicle registrations (obtainable from state motor ve- sources are appropriate here as well. Alternatively, hicle departments). It must be remembered that small point sources (e.g., individual homes) in dif- increasing aggregate data usually means decreasing ferent areas of the community can be sampled and accuracy when these data are disaggregated and allo- heating bills used to obtain information on fuel con- cated to individual communities. sumption. Total consumption for each area is then calculated by multiplying the average unit consump- d, Estimation Problems tion by the number of units in that area. Potential sources of error in an emission inventory If changes over time (e.g., seasonal variations) are are obviously numerous. If every source could be to be considered, additional analysis by type of area physically monitored, then only instrumentation source is necessary. For example, the average errors would be present. Unfortunately, except for a number of degree-days 13 by season will provide an in- few large point sources, this is not practical for most dication of daily residential fuel consumption over the local governments today. Once secondary and ter- year. tiary sources of data are used, four possible error. Estimates for large area sources, such as fuel types multiply rapidly: depots (evaporative losses), landfills (trash burning), 1. Errors in collecting and recording the 11. If data on fuel and raw material consumption are to be used secondary/tertiary data. on a scale larger than individual sources, then the utilization -of 2. Inherent errors in using surrogate data (e.g., emission control devices must also be -aggregated and averaged-another possible source of error. how accurately do gasoline sales reflect vehicu- 112. R. Kudlich, (rev. by C. R. Burdick), Ringetmann Smoke lar emissions?). Chart, Information Circular 7718 (Washington, D.C.: Department 3. Inherent errors in using aggregate data (e.g., of the Interior, Bureau of Mines, August, 1955). how accurately can statewide data on fuel con- 13. "Degree-days" is an expression of heating load and is nu- merically equivalent to the outside temperature expressed as the sumption be allocated to local communities?). average number of degrees below a threshold temperature for a 4. Errors in ascertaining the effectiveness of pollu- given day. The threshold is that temperature which, when reached, will require some indoor heating (usually 65*F.). tion control equipment. 18 Land Development and the Natural Environment Information on the first type of error is typically types of data collection. If the inventory is to be used nonexistent. The second type of error relates to the for comparison with future emission levels, data of a use of emission factors and other coefficients which fairly aggregated nature can be used. On the other relate tertiary indicators (e.g., gasoline consumption) hand, estimating the effects of single developments to secondary data (e.g., vehicle miles). EPA has em- requires data on spatially differentiated emission ployed a combination of approaches in deriving its sources. emission factors for various pollutant-generating 2. Estimating Future Emissions activities, from detailed source testing to engineering appraisals." Consequently, individual factors vary in Much of what has already been said about current accuracy as reflected by qualitative rankings attached emission inventories applies equally well to estima- to each factor. These rankings are undoubtedly useful tions of future emissions. for judging the relative believability of the results but a. Aggregate or Large Area Analysis cannot be used to specify confidence intervals or other quantitative measures of accuracy. How believ- It is often useful to consider the effects of individ- able is "believable" remains an unanswered ques- ual developments along with those from growth in tion. The situation for coefficients other than emis- general (much of which may not require rezoning or sion factors is even worse. Typically, average values similar changes from the existing plan and thus could for relationships between tertiary and secondary vari- not normally be prevented). For large developments ables are used with no indication of how local condi- with long construction times, impacts can be esti- tions may. vary from the mean. mated only by adding the emissions to those from all Errors of the third type are likewise extremely diffi- other relevant developments at the point of ultimate cult to gauge. In selecting a method for allocating occupancy. shares of aggregated data, data availability and . Techniques for estimating overall increases in common sense become the yardsticks. emissions are detailed in at least two EPA publica- Determining the efficiency of pollution control tions and will be briefly summarized here. 15 First, equipment (the fourth type of error) is affected by emissions from existing sources are modified to re- many factors, including meteorological conditions, flect future mandated reductions, if appropriate." maintenance practices, age of the equipment, and the Second, growth factors for the various categories of mix of pollutants in the effluent stream. Errors which point and stationary area sources are derived from result from these factors are difficult at the present the land use plan being evaluated and/or current time to ascertain, due to a lack of data. Presumably, growth rates of suitable surrogates (i.e., population, as experience with pollution control equipment in- total earnings, and manufacturing earnings). These creases, knowledge about the relative magnitude of growth factors, modified by applicable new source these effects will improve. Presently, however, we emission standards promulgated by EPA, are then ap- can do little more than acknowledge the existence of plied to the current level of activity within each cate- these potential errors. gory to obtain emissions in the desired future year. In any one situation the aforementioned errors will Mobile area sources can be projected in a similar obviously not be of equal importance. Some a priori manner, except that the effects of EPA-mandated knowledge about local conditions should be brought source controls for new vehicles must also be taken to bear when the inventory procedure is designed. into account .17 Power plants, due to their importance Where the major problem is associated with point as emission sources, are projected separately, using sources, a greater investment of resources to inven- data obtained from individual companies. tory these sources would be appropriate. Where b. Small Area Analysis motor vehicles are the primary agents, additional Large area analysis may be adequate on a "first funds for obtaining transportation data would be justi- look" basis, but it does not allow the assessment of fied. If major problems occur during rush hours, accurate data on the time distribution of traffic vol- 15. EPA, Guidelines for Air Quality Maintenance Planning and umes would prove useful. In this way some of the Analysis, vol. 1: op. cit., and ibid., vol. 7: Projecting County Emis- problems associated with uncertainty in the data can sions. be reduced. 16. The state implementation plans for AQCRs specify planned In a similar vein the ultimate use of the data will reductions necessary to achieve the national ambient standards by 1975-77. influence the relative emphasis placed on different 17. The total effect is the combination of increasingly effective controls and the attrition of older vehicles over time. EPA- 14. EPA, Compilation of Air Pollution Emission Factors, 2d ed. mandated controls utilized after 1968 also affect the level of current (Research Triangle Park, N.C.: EPA, April, 1973). emissions. Air Quality: Methodological Approaches 19 air quality impacts caused by alternative spatial distri- sions. However, this is a question that must be ad- butions of future development within the community. dressed at the regional level. Increased power plant The projection of future emissions for each subarea capacities are planned to match regional growth rates, can be based on (a) distribution of aggregate growth, and the impact of expanding capacity is a product of or (b) estimation of growth for each individual sub- plant location, fuel type and composition, and the de- area. gree to which new capacities are created by bor- The basis for distributing growth (and also for sub- rowing from neighboring electric power grids. Indi- area delineation) can be as simple as reference to a vidual power companies should be consulted on their comprehensive plan. Aggregate growth is assumed to future plans and the impact of individual develop- be channeled to those areas which by designation can ments estimated in the context of projected regional receive it. This approach, together with variations on growth. the theme, was investigated by the Argonne National The inducement of transportation-generated emis- Laboratory as part of a general air pollution study of sions by new development is usually a much more im- Chicago." Since a comprehensive plan is but a rough portant consideration for individual projects. The ef- approximation of the future, analysts have relied on fects on air quality are frequently localized and thus simulation modeling techniques for more reasonable project-specific. The following component parts of approximations. 19 These are based on the theoretical the problem can be specified: behavior of firms and households, observed develop- (1) Number of trips generated (per day). ment patterns for the test community over a period of (2) Modal split (i.e., the choice of mode for each time or in analogous communities, or a combination of the two. 20 trip). (3) Time distribution of trips (hourly). c. Individual Development Analysis (4) Spatial distribution of trips. ' Project plans for major point sources (e.g., power (5) Average speed of vehicles on each link or for plants and factories) are usually sufficiently specific each zone. so that the techniques outlined for estimating current (6) Vehicle emission rates. emissions can be applied. That is, emissions are esti- mated from the manufacturing processes to be used. In support of the new indirect source regulations pro- In fact, new point source emissions are strictly regu- mulgated by EPA, a series of documents has been lated by state and local pollution control agencies as prepared specifying approaches to estimating the im- mandated by EPA. pact of indirect (i.e., vehicle-generating) sources." As For proposed residential and commercial develop- a basis for these estimations the manuals provide in- ment, the primary effects are power plant and formation from which calculations for most of the transportation-induced emissions. Procedures for es- above data can be made. However, only traffic pat- timating electrical energy demands of new develop- terns in the immediate vicinity of the facility are con- ments are outlined in another report in this series .21 sidered. In addition, residential developments are ex- These new demands must be translated into addi- cluded. tional fuel consumption and then into increased emis- The chapter on transportation in the public and pri- vate service report13 explicitly treats the issues not 18. Allen S. Kennedy et al., Air Pollution-Land Use Planning covered by the EPA indirect source documents. Project Phase I. Final Report (Argonne, Ill.: Argonne National Methods for estimating trips generated by residential Laboratory, November, 1971). developments and trip distributions for various types 19. The flexibility of community zoning plans is rather no- of land developments are outlined. The spatial distri- torious. Perhaps they can be more appropriately thought of as but one constraint on the pattern of future development. bution of trips is perhaps the most difficult aspect of 20. An overview and critique of land use models can be found in Ira Lowry, "Seven Models of Urban Development: A Structural 22. Scott D. Thayer, Kenneth Axetell, Jr., and Jonathan Cook, Comparison," in Urban Development Models, Highway Research Vehicle Behavior In and Around Complex Sources and Related Board, Report No. 97, 1967; Wiffiarn Goldner, "The Lowry Model Complex Source Characteristics, vols. I-VI (Shopping Centers, Heritage," Journal of the American Institute of Planners (March, Airports, Sports Stadiums, Parking Facilities, Amusement Parks, 1972): 100-09; and California State Air Resources Board, Air Qual- Major Highways, Recreational Areas) (Research Triangle Park, ity, Land Use, and Transportation Models (Sacramento: CSARB, N.C.: EPA, Office of Air and Water Program, Office of Air Quality July 1974). Planning and Standards, August-November, 1973). See also Kevin 21. See the "Energy Services" chapter in: Philip S. Schaenman, G. Croke, et. al., The Relationship of Automobile Pollutants and Dale L. Keyes, and Kathleen Christensen, Estimating Impacts Of Commercial Development, (Argonne, Ill.: Argonne National Labo- Land Development on Public Services (Washington, D.C.: The ratory, 1975). Urban Institute, forthcoming). 23. Schaenman, Keyes, and Christensen, op. cit. 20 Land Development and the Natural Environment these calculations. It requires detailed information below or above preselected standards or targets. On about the future inhabitants and the origins and desti- the other hand, if future emissions will produce am- nations of their trips. In addition, rather complex sim- bient concentrations approaching threshold levels, ulation models are required to assign these trips to then more accuracy may be needed. links in the highway network. Fortunately, only the largeSt24 developments will impact significant portions 3. Measuring/Estimating Current of the entire network. Ambient Concentrations Once the number of new trips has been estimated Although data on emissions constitute a valuable and distributed, emission levels can be projected and necessary base of information, ambient pollutant using the EPA emission factors and knowledge of ve- levels must be measured in order to assess the impact hicle age, speeds, and volumes on specific highway of the new emissions. The measurement of ambient links." concentrations remains a difficult and costly activity, despite continued federal involvement and financial d. Estimation Problems support .27 Although the uncertainty in predictions may be a. Quantitative Measurement high (and in many cases is itself unknown), consid- ering an extension of past trends and/or other plau- Pollutants in the atmosphere show variations in sible futures is useful for estimating future air quality. both time and space. This has important implications However, if growth projections are to be used as any- for the design and operation of an.air monitoring net- thing more than qualitative descriptions they should work. The number and placement of stations and the be generalized spatially and cover a limited interval of frequency of recordings must be planned to capture time, perhaps no more than ten years. the concentration variations. EPA's recommen- However, the primary focus of this report is on dations are a compromise between scientifically individual developments and short-time horizons. based design criteria and the problems of the real Even here, though, considerable uncertainty exists world .28 Recognizing that the costs of an ideal system regarding the factors which will determine ultimate are prohibitive, the EPA guidelines emphasize place- impact-vehicle miles of travel induced and energy ment of the sampling stations where the potential for requirements-which, in turn, are related to a host of pollution problems is the highest. The "hot spot" cri- other factors, such as population density, character- teria include such factors as population distribution, istics of new residents/customers/employees, and suspected ambient levels, location of sources, and building construction features. But even where un- areas of future growth. Other practical considerations certainty exists, a range of estimates can be consid- are presence of power supplies and security fiom ered-the lowest, average, and highest value at each vandalism. Thus, the number and actual location of step in the calculation procedure (if these values are stations may be far from ideal. known). The final estimate can then be expressed in The Clean Air Act defines ambient air as "that por- the same terms (lowest, average, highest) even tion of the atmosphere external to buildings to which though the probability of obtaining these values the general public has access." Thus, measurements cannot be specified. In other words, the sensitivity of of air quality should logically be made at a height of the estimates to the assumptions can be stated .26 five to six feet. EPA suggests a height of three to six I The concern about data precision, valid as it may meters (approximately ten to twenty feet), while be, must be conditioned by the ultimate use of the actual locations are often at roof level. study results. Great accuracy is not needed to predict The literature on monitoring instrumentation is well trends or make initial assessments, especially when developed and will not be reviewed here .29 Worthy of initial assessments show that conditions will be far 27. EPA estimates that approximately ten man-years of effort are required annually to maintain a monitoring network the size of 24. "Large" is a relative term. The size of the development (in the one found in Washington, D.C. (personal communication with terms of the number of trips generated) must be compared with the a member of the Contract Programs Development Division). size of the surrounding community. 28. R. A. McCormick, Air Pollution Measurements (Research 25. EPA, Compilation of Air Pollution Emission Factors (Re- Triangle Park, N.C.: EPA, National Environmental. Research search Triangle Park, N.C.: EPA, Office of Air and Water Pro- Center, February, 1972) (NTIS No. Com-73-10016); and EPA, grams, Office of Air Quality Planning Standard, April, 1973) (Re- Guidelines: Air Quality Surveillance Networks (Research Triangle port No. AP42). Park, N.C.: EPA, Office of Air Programs, May, 1971) (Publication 26. For a good discussion of the way errors propagate through No. AP-98). multistep calculations, with illustration for air quality assessment, 29. For a summary of available methods and techniques, see Na- see Hagevik, Mandelker, and Brail, op. cit. tional Academies of Sciences and Engineering, op. cit., vol. 3. Air Quality: Methodological Approaches 21 note, however, is research on measuring ambient versely, if ambient concentrations at a single station concentrations using airborne sensors. Advances in at a "hot spot" during the worst meteorological con- these techniques may significantly improve the accu- ditions are satisfactory, then probably no part of the racy of the measurements.30 city faces a serious problem. These data may also be useful in answering questions regarding planning at a b. Measurement Problems community-wide level. (E.g., is any additional devel- Despite the existence of more than 7,000 federal, opment within city limits feasible?) But for other as- state, and locally operated monitoring stations sessments there is no substitute for accurate data on throughout the country,31 knowledge of ambient con- the variable conditions found in different parts of the ditions remains rather primitive. Even if all the sta- community, which must be obtained from properly tions recorded each of the major pollutants, there are located, well-maintained, and competently operated simply too few stations to reflect geographical varia- stations. Diffusion models can be used, but their vali- tions adequately. With the possible exception of Chi- dation depends on the existence of a good profile of cago and New York, the number of stations for any current conditions. A series of simple procedures for one city is insufficient to allow satisfactory interpola- calculating the current ambient levels in localized tion between stations and the construction of iso- areas (i.e., several blocks) using simple mathematical pleths Oines of equal concentration). Thus, diffusion relationships is outlined in a recent HUD-sponsored models will be needed in most communities to ob- report.34 tain isopleths of current ambient concentrations or to obtain estimates for areas within the community c. Vegetative Indicators which are not located near monitors. (Diffusion For many communities the quantitative monitoring models are discussed in the next section.) of ambient air quality is simply too expensive, while Aside from problems of location, there remains a serious concern regarding data reliability. Variations for others one or a few sampling points must suffice. In order to obtain an objective, albeit very qualitative in station operation and maintenance, combined with "sense" of community-wide or subarea air quality, poor quality control procedures, especially for sta- strategically placed vegetative test plots may offer tions requiring manual chemical analysis, has ren- one alternative. Although plant damage from air pol- dered the data recorded, for many cities of question- lution remains a poorly understood phenomenon, able accuracy. The inappropriate height of many carefully controlled field studies continue to provide stations ftirther hampers meaningful interpreta- information by which various plant species can be tion.32 rated for sensitivity." Local governments interested There is also some evidence that the EPA- in utilizing plants as pollution indicators should con- recommended sampling frequency is too low for the tact state air pollution agencies for additional infor- desired degree of certainty in the results .33 Compared mation and assistance. with the other problems, however, this seems to be of lesser importance. - What then can be said about the concentration of 4. Estimating Future Ambient Concentrations pollutants in the atmosphere? Certainly the data from The next step in the analytical procedure involves even a single station are useful, not as a definitive the estimation of future ambient concentrations for statement about air quality for a city, but at least as each of the various pollutants. In a sense, this is the an indicator of a potential or general problem. Con- culmination of all preceding calculations. Data on current and future emissions and current ambient 30. L. J. Duncan, E. J. Friedman, E. L. Keitz, and E. A. Ward, levels are combined with meteorological and surface An Airborne Remote Sensing System for Urban Air Quality (Wash- feature inputs to produce the net change in future am- ington, D.C.: The Mitre Corporation, February, 1974). bient levels. The analysis can be performed at varying 31. EPA, Inventory of Air Pollution Monitoring Equipment Operated by State and Local Agencies (Research Triangle Park, levels of sophistication and complexity. Manual tech- N.C.: Air Pollution Technical Information Center, 1971). niques as well as those requiring computer support 32. Even New York has recently recognized the inadequacy of are available. its network. Forty-five new CO monitoring stations placed at a The various techniques for estimating future am- height of five to eight feet above street level will be added to the sixteen presently in operation. See Richard Severo, "City to Aug- ment Monoxide Gauges," New York Times, 20 April 1975, p. 42. 34. T. M. Briggs, Air Pollution Considerations in Residential 33. Harold E. Neustadter and Steven M. Sidik, On Evaluating Planning, vol. I: Manual (Cincinnati: PEDCO-Environmentai Spe- Compliance with Air Pollution Not to be Exceeded More Than cialists, Inc., July, 1974). Once Per Year (Cleveland: Lewis Research Center, June, 1974) 35. See Atle Habjorg, Air Pollution and Vegetation II (Research (NASA No. N74-25879). Triangle Park, N.C.: EPA, June, 1974) (NTIS No. PB-237-880-T). 22 Land Development and the Natural Environment bient concentrations will be discussed both generally Di the change due to turbulent diffusion of i and specifically. The material to be presented is out of the volume partly a synthesis and recombination of information Qi the amount of i emitted directly into the and ideas contained in other overviews .36 However, small volume from outside only the Darling report contains specific information With the improved understanding of the way turbu- on the cost and accuracy of individual dispersion lent diffusion varies with wind speed, temperature, models .37 The information presented here is designed humidity, sunlight, and surface roughness, and with to supplement the Darling report. The emphasis is on the advent of high-speed computers, the mass conser- models which have wide geographic applicability and vation equation is now being used as the basis for which are used routinely by planning or pollution recently developed dispersion models. The obvious control agencies. advantage is that, in theory, all emission sources (including photochemical generation) and time varia- a. Types of Models tions can be represented, along with data on surface There are many ways to differentiate approaches to roughness. The disadvantage is that the theoretical estimating the transport and dispersion of atmo- models tend to be costly to operate. spheric pollutants. The various typologies described The next category (semi-theoretical, semi- below highlight different yet important aspects of dis- empirical) includes a family of models derived from persion models. the Gaussian dispersion equation, which is depicted schematically in Figure 1_1.39 This equation repre- Theoretical versus Empirical Models - "Theoret- sents the concentration at any point in space of a ical" models are those which are grounded on basic single puff of pollutant i which is transported by local principles of the physical sciences. They are rigorous, winds and diffuses three-dimensionally in a Gaussian and only a few purely theoretical models have ad- or normal manner in the process .40 The extent to vanced beyond the research stage. Empirical models which the puff will continue to disperse in horizontal are derived purely from observed patterns over time and vertical directions is related to the stability of the or for different settings. Models which embody em- atmosphere. Turner has developed empirical relation- pirically justified modifications of theoretical relation- ships between stability categories and the standard ships are in the middle. Theoretical air dispersion models are based on the where: Ci = concentration of pollutant i conservation of mass law, which, in simplified mathe- t = time matical terms, is:" V = change with respect to the x, y, and z directions in Ci = Ti + Di + Ri + Qi space a a a where: CI = the change in concentrations of pollutant (ax ay az i over time in a small volume of air V = wind velocity with components in the x, y. and z Ti = the net transport of i into or out of the direction small volume K =turbulent diffusivity with components in the x, y, and Ri = the amount of i created in the volume by Z direction Ri =rate of generation or removal of pollutant i by photo- photochemical reaction chemical reaction Q =rate of emission of pollutant i 39. The mathematical representation is as follows: 36. See Eugene M. Darling, Jr., Computer Modeling of Trans- portation-Generated Air Pollution (Cambridge, Mass.: U.S. De- Q exp (X - ut), + Y, partment of Transportation, Transportation Systems Center, June, C' = T27r) 3/2 O-x Cry (T. 20-,2 1972) (NTIS No. PB-213013); Joe J. Mathis and William L. Grose, 2 2 A Review of Methods for Predicting Air Pollution Dispersion, exp - (Z H) (Z + H) (Washington, D.C.: NASA Langley Research Center, 1973) (NTIS 1 1 20'. 2 1 + exp - @z_2 o-.2 '] I No. N73-20658); Harry Moses, Mathematical Urban Air Pollution where: C, =concentration of pollutant i at time t after emission Models (Argonne, Ill.: Argonne National Laboratory, April, 1969) at any point in space (NTIS No. ANL-ES-RPY-001); R. A. Papetti and F. R. Gilmore, Air Pollution (Santa Monica, Calif.: The Rand Corporation, Feb- Q = amount of pollutant emitted ruary, 1971). XIYIZ =distances in 3-dimensional space 37. Darling surveyed private research and consulting firms u =mean wind speed regarding the mathematical underpinnings and technical aspects of 07X 1 (FY I crZ=standard deviation of the distribution of concentration their dispersion models. in the x, y, and z directions 38. Or more formally: H =height at which the pollutant is emitted exp =e raised to the expression which follows @S = -V - (VCJ + V - (K V CO + Ri + Qi 40. A Gaussian or normal distribution when graphed is the famil- at iar bell-shaped curve. Air Quality: Methodological Approaches 23 FIGURE 1-1 not yet been quantified. The selection of appropriate SCHEMATIC REPRESENTATION OF THE values for a given local situation remains a serious GAUSSIAN MODEL weakness in the utilization' of Gaussian dispersion models. Similarly, the model is not easily adapted to reflect photochemically produced pollutants or pollutant re- moval processes. On the other hand, the puff model retains the conservation of mass model's ability to re- flect changes in wind speed, wind direction, and ernissions over time. X In order for the instantaneous Gaussian puff model to reflect a realistic urban setting (i.e., continuous X, emissions from many sources), the equation is mathe- H matically integrated over time and summed for each source." The result is an integrated puff or a Gaus- X, sian plume model .43 The third category of models embraces those which are empirically derived, that is, those which at- tempt to explain observed data in the simplest way. a. Gaussian Puff Representation The most obvious example is the use of regression equations to relate changes in ambient concentrations with such variables as emission levels, meteorological conditions, and terrain.' In fact, attempts at repro- ducing the results obtained from more sophisticated models have proven quite successful .45 The obvious advantage of such an approach is its simplicity and built-in validation properties. By defi- nition, unless the regression equation "explains" a considerable amount of the variance in the dependent variable, it will not be used. Thus, fairly high agree- ment with observed data is assured. However, since regressions only reveal associations and not causal X, relationships among the data, future patterns may be H significantly different from present ones. X, Another empirically based, simplified dispersion X, 42. Ci Ci dt Q exp - [ Y i] f. 27T 0-Y o-Z u 2o-, b. Gaussian Plume Representation exp (z - H)l + exp, (z + H) 2 0_@2 'I I NOTES: n n = the total number of sources H = height at which emissions are released Ctotal Ci = infinity X = downwind distance 43. These are closely related, yet distinct models. The dif- SOURCE: Modified from Darling, op. cit. ference is that in the integrated puff version, the emission times over which the equation is integrated can be quite short. The re- sulting puffs or segmented plumes (depending on how elongated a deviations of dispersion." However, atmospheric sta- puff can be and still retain the name) can then be tracked sepa- rately. The plume version incorporates the dispersion equation in- bility is but one factor, albeit a very important one, tegrated over an infinite period (the resulting effluent is simply a which influences the degree and rate of dispersion. stream of effluent). It consequently does not retain the ability to re- Mechanical turbulence from surface roughness is an- flect changes in meteorological and emission variables with time. other, but the roughness dispersion relationship has 44. Regression equations are simply mathematical expressions which relate one variable with one or more others, based on a number of observations of each. 41. D. Bruce Turner, Workbook ofAtmospheric Dispersion Esti- 45. Alan Horowitz, William S. Meisel, and David C. Collins, mates (Cincinnati: Department of Health, Education and Welfare, The Application ofRepro-modeling to the Analysis ofa Photochem- Rev. 1970) (NTIS No. PB 191482). The standard deviations are the ical Air Pollution Model, (Washington, D.C.: EPA, December, parameters which determine the rate of puff expansion. 1973) (EPA No. EPA-650/4-4-74-001). 24 Land Development and the Natural Environment model is that known as a "box" model. When the sian point source model can be integrated in both the mixing depth of the atmosphere is roughly equivalent x and y direction. The emission rate (Q) for area to the extent of plume expansion vertically once it sources is expressed in terms of emission level per has begun to disperse, the warm layer of air aloft acts unit time per unit area (e.g., grams/second-meter as a lid on a box, causing the pollutants to be uni- squared). formly dispersed within. Under these conditions Line sources are simulated by mathematically inte- (usually referred to as an inversion aloft), the concen- grating the point source Gaussian plume equation tration can be estimated by a very simple equation: over the length of the line in the y direction (assuming Ci = Qi that the line is perpendicular to the wind direction) .46 u d Furthermore, if the source is on the ground and effec- where: Ci = ambient concentration of pollutant i tively of infinite length (as is the case for most mobile Qi = amount of pollutant i emitted per unit sources), and if the wind is blowing at an angle with of time respect to the source, then the equation is greatly u = average wind speed simplified .41 d = mixing depth Since the conservation of mass model is used with an emission source grid, all sources are in effect area Simple versus Complex Models-The theoretical- sources. This means that point, area, and line sources empirical classification scheme includes most but not must be aggregated on a unit cell basis. The cells can all models. Pressed by legislative and judicial edicts, be as small as several acres or as large as several EPA has begun to use simple linear approximations square miles. to predict future air quality. These can be classified Models Based on.Type of Pollutant-Most of the neither as theoretical nor empirical. They have no theoretical justification except in the most funda- models developed to date treat the relatively inert mental sense (i.e., increases in emissions cause a pro- pollutants-particulates, SO,, and CO. The ambient portional increase in ambient concentrations) and no concentration of these is independent of chemical empirical verification. These models will be discussed reactions, which may occur subsequent to emission .18 in more detail subsequently, since they . are widely Some modelers have also attempted to treat NO, as used and thought to be satisfactory for rough approxi- inert gases, but their success has been limited. mation. Photochemical models are now being developed and validated for specific cities. They are largely Source versus Receptor Models-Some models based on smog chamber and other closed vessel are designed to estimate the concentration levels at experiments. This is an inherent weakness, since the various points due to pollutants emitted from a single atmospheric reactions are not confined by the walls source. Conversely, some models focus on air quality of a container. The extent to which open and closed at single points due to the contributions from many system reactions differ is still largely unknown. sources. The former (source-oriented) are useful when a new development will be a major source (e.g., Models Based on Scale of Application-A scale a new industrial plant), while the latter (receptor- of application has two components: (a) the magni- oriented) are more appropriate for developments tude of the emissions to which the model is sensitive, which may expose additional people or other re- and (b) the degree of spatial disaggregation of the cal- ceptors to existing concentrations and for evaluating culated ambient concentrations. Most models are sen- air quality of comprehensive plans. sitive to any major point source and cumulative Models Based on Type of Source-The nature of the source is another important consideration in 46. C 2Q exp- /2(' model design, especially for the Gaussian dispersion _I. u 11 @@) I f models. exp YJ Y) 2 d (11-) The Gaussian puff and plume models described 2 o'Y previously assume a point emission source. Area where: Q emission level per unit time, per unit length of the line sources can be depicted by the use of an imaginary source (e.g., grams/second-meter) virtual point source located upwind of the area over 47. C 2Q which individual area sources are to be aggregated. sin E) v"2-,T c,,u The plume from the virtual point source is allowed to where: 0 the angle between the source and the wind direction disperse so that by the time it reaches the area in 48. Strictly speaking, this is not true for S02 which is oxidized and hydrolyzed to sulfuric acid. Also, CO may play a role in pho- question the concentration approximates that from tooxidant production. However, for both, the rates of reaction the area sources combined. Alternatively, the Gaus- seem to be small. Air Quality: Methodological Approaches 25 changes in small point sources (i.e., significant most cases these supplement and expand the material changes in area sources). However, the models vary presented here. The EPA document is especially considerably in the spatial disaggregation of the out- useful for comparing the most readily available public put. Some reflect changes in ambient concentrations domain models. at a single point in the community, while others esti- The word "model" as it is used here has a very mate changes for smaller subareas. general definition. It refers to simple numerical form- A few models are sensitive to individual area, line, ulas, the utilization of which requires nothing more and less-than-major point sources. Typically, these than pencil and paper, as well as to highly developed will also specify the change in ambient concentrations packages of complex mathematical expressions re- at a large number of points within the community or quiring the assistance of a digital computer. In other as a continuous function of downwind distance from words, "model" refers equally well to general tech- the source. niques or specific computer programs. Of the mod- Translating this into types of development to which els reviewed here, the first four (rollforward, the models apply is not a straightforward task. Much Miller/Holzworth, Hanna/Gifford, and California High- depends on the size of the development in terms of way) do not require the use of a computer. The source strength. Residential and commercial develop- others do. ments are important primarily as vehicle-trip genera- Roltforward Models-The rollforward models are tors and thus as fine sources. Whether an individual identical to the rollback models (also known as linear development will produce significant changes in air models) advocated by EPA, with one exception. quality will depend on the number and distribution of Rather than being used to estimate the reduction (roll- new trips and whether localized or large area effects back) in emission required to meet the national am- are considered. At least two models, to be reviewed bient standards, they are used to estimate future am- here, will estimate roadside concentrations for single bient levels (rollforward) from various levels of future roads (although the accuracies may be quite low) emissions. ' while others estimate community-wide impacts from EPA has published an excellent description of the changes over the entire road network. basic rollback model and modifications thereof.50 b. Description of Individual Models Other publications report on specific applications in Los Angeles and San Diego." Those readers who would like an initial overview of The rollforward models currently in use can be the models to be discussed here are advised to turn characterized as extremely to moderately simple, first to the Summary and Comparison section of this receptor-oriented, and applicable to all types of chapter. The most salient features of each model are sources but only to inert pollutants (CO, SOX, par- summarized and compared with those of the other ticulates). The models are normally used on a models utilizing a tabular format. .community-wide scale, but with some modification The preceding background material will now be can be used for subarea analysis as well. used to describe specific dispersion models in a con- The basic equation from which all rollforward cise manner. Each model will be characterized ac- models are derived is as folloWS:52 cording to the previously discussed typologies. This will be followed by a description of the type and scale -CaL = K !@P-' of application and an assessment of costs of operation Cfi Efi and accuracy of results where this information is known. Some data on the latter points have been col- 50. Noel H. DeNevers and J. Roger Morris, "Rollback Mod- lected by means of a questionnaire mailed to selected eling-Basic and Modified" (Paper presented at the sixty-sixth Annual Meeting of the Air Pollution Control Association, Chicago, model users. June 24-28, 1973). Several simplified reviews of air quality models 51. William T. Mikolowsky et al., The Regional Impacts of with an orientation toward land use/air quality analy- Near-Term Transportation Alternatives: A Case Study of Los sis and planning have recently been prepared .49 In Angeles (Santa Monica, Calif.: The Rand Corporation, June, 1974); and Mikolowsky, San Diego Clean Air Project, Appendix 2 (Santa Monica, Calif.: The Rand Corporation, December, 1973). 49. California State Air Resources Board, Introduction to Man- 52. More formally, ual Methods for Estimating Air Quality (July, 1974) (NTlS No. n PB-237-871) and Air Quality, Land Use, and Transporation F, [KaijelJfetwe Year Models, Evaluation and Utilization in the Planning Process (July, (Cai b0fw. Year J=@ n 1974) (NTIS No. PB-237-867); and EPA, Guidelines for Air Quality (Caj b0base Year [KaljeiJlbase Year Maintenance Planning and Analysis, vol. 12, Applying Atmo- spheric Simulation Models to Air Quality Maintenance Areas (Re- search Triangle Park, N.C.: EPA, September, 1974) (NTIS No. where: C., = concentration of pollutant i at point a PB-237-750). bi = background concentration of pollutant i (i.e., that 26 Land Development and the Natural Environment where: C,i = present ambient concentration of pollu- sources by sector. The K values are then modified to tant i reflect the frequency with which the wind blows from Cfi = future ambient concentration of i various directions. Thus, those portions of the con- E,1 = present emission level of i centric zones which normally lie upwind from point A Ffi = future emission level of i are weighted more heavily. K = a constant The rollforward models thus far discussed are ap- This is a simple proportional relationship which as- plicable only to nonreactive pollutants where the am- sumes that the ratio of future year to base year am- bient concentration is linearly related to the emission bient concentration is the same as the ratio of future level. For pollutants which undergo photochemical to base year emissions, with emissions broken into reactions this assumption of linearity does not hold. categories so that the importance and growth of each Smog chamber experiments reveal that a complex re- category can be weighted separately. The simple ver- lationship exists between ambient concentrations of sion of this general relationship does not differentiate oxidants and the emission level of their precursors among emission categories and further assumes that (nitrogen oxides and reactive hydrocarbons). How- one geographical point can be selected to represent ever, at least one attempt to apply the rollforward the whole community .53 model to reactive pollutants has been reported .55 In Several modifications to the simple version have other words, proportionality was made slightly non- been proposed in order to render it more theoretically linear for these pollutants. accurate. The semi-diffusion version incorporates the The advantages and disadvantages of the various relationship between height of emission release and rollforward models are as follows: dispersion as estimated by the Gaussian dispersion Advantages equation. The K values are made to reflect the rela- tive contributions of the various emission categories 1. These models are the least complicated and least by specifying average height of release for each cate- expensive to use of all dispersion models. gory.,, 2. Current emissions and meteorological data re- The location version further modifies the K values quired are available from local or state pollution by incorporating the general location of emission cat- control agencies and Weather Bureau stations egories into the mathematical expression. The com- located at all major airports. munity is first subdivided into concentric zones cen- tered about point A. Emissions for each category Disadvantages are then disaggregated by zone and are assumed to be 1. The models are unvalidated. uniformly distributed throughout each zone. The rela- tive contribution to the concentration at point A are 2. The point chosen as being representative of the then made inversely proportional to distance from A. community must be the location of an existing The wind direction version represents yet another monitoring station and, therefore, may not be step in rendering the simple version more realistic. truly representative. Here the effect of differences in wind direction are 3. The lack of spatial disaggregation means that all factored in by further subdividing the community into present emissions are assumed to increase in a wind sectors and further disaggregating the emission proportional manner and maintain their present spatial distribution in the future. (This is some- transported in from other regions and that due to what less of a problem for the location version.) natural sources) 4. Meteorological and surface roughness factors e,j = emissions of pollutant i from category j (categories are either ignored or treated simplistically. can be by industrial activity groupings or by type of source) (Complete atmospheric mixing is assumed.) n = total number of categories 5. The models are not applicable to short-lived K.,j = contribution of a unit emission of pollutant i from pollutants (such as CO) unless their half-life is 53. Thus: category j to the ambient concentration at point a comparable to their travel time across the com- (Ci - b)ftu,e (Kjeofuture munity at the predominant wind velocity.56 (Q - b)b.e Year (Kieobase Year 6. Reactive pollutants have not yet been routinely Here Ci is the average community-wide ambient concentration for some time period (usually one year), ej is the aggregate emissions 55. Mikolowsky, et al., op. cit. As with all applications of the from all sources, and K, is a constant which reflects meteorological roll-forward model to date, the accuracy of the results is unknown. conditions, surface features, and other factors related to dispersion. 56. "Half-life" is the amount of time required for half of the pol- 54. "Release height" is a function of both stack height and lutant to be removed from the atmosphere by deposition, interac- plume rise, the latter due to the buoyant effect of a hot gas. tions with vegetation, or other processes. Air Quality: Methodological Approaches 27 FIGURE 1-2 Gaussian dispersion equation for an infinite cross- SUMMARY OF THE MILLER/HOLZWORTH MODEL wind line source emitting at ground level .51 This is then integrated across the length of the entire commu- nity in the direction of the prevailing wind to obtain line sources the highest ambient concentration (which will occur along the down-wind edge of the community). How- 'Im ... ng ever, it does not assume that the vertical dispersion of the plume is relatively constant with distance trav- 1-1.4 depth eled. Instead, when integrating the basic equation, two terms are produced, one which represents up- wind sources close to the receptor, the plumes from which have not had time to disperse throughout the X, wind mixing layer, and one which represents more distant sources, the plumes from which are uniformly mixed NOTES: within the " box. " 59 In order, to obtain average value s The,community is visualized as being composed of an infinite for the community as a whole (not just at one point), number of infinitely long line sources of uniform strength. the values at all points are averaged by additional in- Pollutants from each line source are presumed to disperse in a tegration. Gaussian manner until the plume reaches the top of the mixing layer. Thereafter, the contribution from that source is uniformly mixed In order to facilitate calculations using their model, in the box. Miller and Holzworth have prepared graphs and These line sources are integrated in the direction of the wind to tables which relate the normalized concentration obtain an aggregate concentration value for the downwind edge. (C/Q)60 to wind speed 61 (the greater the speed, the Average, community-wide values are obtained by a process lower the C/Q value), mixing depth d (the greater the sim ilar to averaging the concentrations of the upwind and downwind depth, the lower the C/Q value), and community size edges. (the smaller the community and thus the fewer the treated by rollforward models, although some sources, the lower the C/Q value). Once these values initial attempts have been made. are specified, the actual C value is then obtained by substituting the appropriate Q value (the estimated In general, the rollforward models are attractive and average emission density previously -computed) for widely used because of their relative simplicity. Gen- the community in question. Actual calculations are eralized emission data inputs and desk calculators are used for computations. However, a reduction in 2Q accuracy is the cost of simplicity. It is worth re- 58. C /2-7r o-@ u peating that these models are completely unverified. Although the rollforward model is typically identi- where: C = the downwind ambient concentration fied with the assumption of linearity, it should be Q= emissions per unit time and per unit length of the source 0-,=standard deviation of vertical dispersion noted that many of the simpler models to follow also ii = average wind speed assume linearity between emissions and ambient con- centrations. Thus, rollforward models should be con- 59. C = ft@ 2Q dt + f a dt sidered as one type of linear model, the distinguishing N/'2-, o-@ t d characteristic of which is its application to commu- where: t. = time to travel from the nearest source nity-wide and long-term estimation problems. td= time necessary for uniform dispersal (at average wind speed) MillerlHolzworth Model-This model is relatively t@ = time to travel the length of the community (at average simple (it does not require. the use of a computer), wind speed theoretical (although based on empirically validated d = mixing depth ,relationships), receptor-oriented, and designed to be Q = emissions per unit time and per unit area of the source used with area sources and most pollutants .57 It also o-@ =standard deviation of vertical dispersion treats line and point sources by assuming they behave The time td is obviously dependent on the mixing depth (i.e., the as uniformly dispersed area sources. higher the Ed on the box, the longer it takes for the plume to dis- A summary and schematic depiction of the model perse upward to it). The travel times for various values of d are obtained from Turner's data as shown in the Miller/Holzworth appears in Figure 1-2. The model is based on the article. 60. This expression relates the average ambient community-wide 57. Marvin E. Miller and George C. Holzworth, "An Atmo- concentration (C) to a unit emission rate (Q). spheric Diffusion Model for Metropolitan Areas," Air Pollution 61. This is the average wind speed throughout the mixing layer Control Association Journal 17 (January, 1967): 46-50. obtained by averaging wind speed at the surface and aloft. 28 Land Development and the Natural Environment thus minimized; most of the work involves finding FIG URE 1-3 values in tables once the input data are assembled. SUMMARY OF THE HANNA/GIFFORD MODEL The limited number of test applications have pro- duced encouraging results. Tests in Los Angeles, Nashville, and Washington for SO, and NOx pro- duced correlations between measured and predicted values above 0.8 once the model was calibrated .62 These results are especially surprising for NO, which undergo photochemical reactions. It must also be remembered that only community-wide averages were estimated. I,n summary, the Miller/Holzworth model is a NOTES: simple, inexpensive -technique which has produced The community is divided into equal sized two-dimensional cells fairly accurate results. However, the limitations are by superimposition of a gird pattern. quite severe. Area source strengths are calculated for each cell. The ambient concentration in the cube above any one cell de- Advantages pends only on the emissions in that cell, the average wind speed, and the category (stable, neutral, unstable) of atmospheric stability. 1. The model is extremely easy and inexpensive to Average, community-wide values are obtained either by averaging use once the emission rates have been deter- the values for all cubes, or expanding the size of the cells until one mined. ceU covers the entire community. 2. The results appear to be quite accurate for S02 . and NO,, (except for situations listed below). prisingly accurate atmospheric dispersion model .63 Disadvantages The model is largely empirical, receptor-oriented, and applicable to both inert and reactive pollutants 1. Emissions from point sources with tall stacks emitted from area sources. are not estimated well since the emission height A summary and schematic representation of the is assumed to be zero everywhere. Hanna/Gifford model appears in Figure 1-3. Although 21. Cities of asymmetrical shape or with nonuni- it is derived from theoretical considerations (largely formly distributed sources present difficult of the Gaussian dispersion type), the model is a result problems and may lead to highly inaccurate re- of empirical observations. Gifford and Hanna argue sults. that for a community which is superimposed by a grid 3. Uniform and symmetrical growth of a commu- of uniform cells, the average ambient concentration nity is necessary in order for the model to ac- for any one cell is a function of the area source emis- curately predictfuture concentrations. sions for that cell plus emissions from surrounding cells, attenuated by their distance from the cell in 4. The smallest spatial unit of analysis is an entire question. (The cells are usually on the order of one to community. several hundred square miles-the entire commu- 5. Although test results for NO,, have been fairly nity.) What they discovered, however, was that the good to date, the model is not designed to treat overwhelming determinant of ambient 'concentration reactive pollutants. is the local (i.e., source cell) emission level. This led HannalGifford Model-Frank Gifford and Steven to the following formulation:64 Hanna of the National Oceanic and Atmospheric Ad- Cj = AQj/u ministration have developed a rather simple but sur- where: Ci = average ambient co ncentration of a 62. Correlations measure the agreement between predicted and measured data. Values of 0 signify no agreement, while values of 63. E. A. Gifford, The Simple ATDL Urban Air Pollution Model 1.0 indicate perfect data agreement. For dispersion modeling, val- (Oak Ridge, Tenn.: National Oceanic and Atmospheric Administra- ues about 0.7 reflect "good" agreement. Correlation coefficients as tion, Atmospheric Turbulence and Dispersion Laboratory, May, applied to data on ambient concentrations must be interpreted with 1973) (File No. 78 rev.); Steven R. Hanna, "A Simple Method of caution. The specific coefficient values are a function of the ade- Calculating Dispersion from Urban Area Sources," Journal of the quacy of the monitoring program (e.g., network design and Air Pollution Control Association, 21 (December, 1971): 774-77; sampling frequency) as well as the accura6y of the model. In addi- Steven R. Hanna, "A Simple Dispersion Model for the Analysis of tion, other measures of validity can, and for some models have, Chemically Reactive Pollutants," Atmospheric Environment, 7 been used. These measures will be discussed in the Summary. (1973): 803-17. (Correlation coefficients cited in this report are the statistic "r- 64. The reader will note the striking similarity to what was pre- unless otherwise noted.) viously called a box model. Air Quality: Methodological Approaches 29 chemically inert pollutant in cell j tory, at least when using correlation coefficients as A = constant the yardstick. For both inert and reactive pollutants Qj = emissions from cell j per unit time per the results are usually as good, and in some cases are unit area better, than those obtained from more complex u = average wind speed models. Furthermore, it was shown that A is a function of the As mentioned previously, the application of the rate of vertical plume expansion, and thus of atmo- Hanna/Gifford model is restricted to area sources. spheric stability." The following values were ob- However, certain types of point sources (i.e., those tained by fitting the equation to empirical observa- with short stacks) and line. sources can be considered tions: as area sources.70 The model is also designed for large area, aggregate level application. However, the use of unstable conditions A = 50 a grid with cells as small as one square mile has been neutral conditions A = 200 reported .71 It was also reported that the model has stable conditions A = 600 been modified to more realistically reflect urban For calculating long-term averages (i.e., annual or meteorology by weighing the relative contribution of seasonal), 225 and 50 are the suggested values for A66 the sources as a function of wind direction .72 How- for particulates and S02, respectively .67 (Further ever, an example of such a modification was not analysis by the EPA has shown that particulates given. can be better estimated by this relationship: Following is an assessment of the Hanna/Gifford C = 52 + 91.7 Q/u). model: The form of the model which treats reactive as well Advantages as nonreactive pollutants is more complicated, 1. The Hanna/Gifford Model is simple and inex- although considerably simplified over other photo- pensive to use. The manual calculations for a chemical models. It is based on a modified form of con- Chicago- test application of the nonreactive ver- servation of mass law and includes terms for mass sion are reported to have consumed approxi- movement out of the area, emission within the area, and mately V2 manhour .72 (This does not include photochemical reactions .611 By a suitable mathematical time needed for data collection.) transformation, the equation is expressed in terms of the original Hanna/Gifford model (C = AQ/u). The 2. The results have been verified in various set- model is then specified by values for u, d (the mixing tings and appear to be quite accurate (at least for depth), the areal extent of the community, and the Q's seasonal and annual averages). for the various reacting substances. Disadvantages The results of Hanna/Gifford model applications 1. The accuracy of the results may not be adequate have been consistently good for the "inert model" when: and mixed for the "reactive model." The correlations between predicted and observed values for SO@, par- a. Neighboring area sources differ in strength ticulates, and CO have been near or above 0.7 for by more than a factor of two. tests in Chicago, Los Angeles, Nashville, San Fran- b. The wind blows predominately in one direc- cisco, and several other cities .61 For NO, and reactive tion. hydrocarbons the tests have been limited to one city 2. Short-term concentration values are not esti- (Los Angeles) and the results have been less satisfac- mated well. 3. The model has not yet been tested for a spatial 65. More specifically, A is a function of o-,, the vertical standard resolution smaller than approximately one deviation of Gaussian dispersion. square mile. 66. Thus, A reflects the average extent to which a,plume, released at ground level, has been able to disperse vertically before im- 4. Only point sources with short smokestacks (plus pacting the "average" receptor. area sources and line sources treated as area 67. EPA, Guidelines for Air Quality Maintenance Planning and sources-mobile area sources) can be modeled. Analysis, vol. 12, op. cit. 68. The turbulent diffusion term in the conservation of mass equation is not included since the atmosphere above the commu- 70. For specific guidelines see, Gifford, "Applications of a nity is assumed to be a large box within which the pollutants are Simple Urban Pollution Model "(Proceedings reprints, American uniformly mixed. The photochemical reaction term is based on a Meteorological Society Conference on Urban Environment and simplified set of smog reactions proposed by Friedlander and Sein- Second Conference on Biorneteorology, Philadelphia, October feld, "A Dynamic Model of Photochemical Smog," Environmental 31-November 2, 1972). Science & Technology, 3 (1969): 1175-81. 71. Hanna, op. cit. (1972). 69. For specific results, see Gifford, op. cit. 72. Ibid. 30 Land Development and the Natural Environment 5. Without additional testing, the reactive version resp ectively. (The base meteorological data are of the model cannot yet be considered opera- manipulated by a specially developed computer tional. program.). On the whole, the model combines the simplicity of Disadvantages the rollforward model with the empirical validity of some of the more complex models. 1. The model is unvalidated. California Highway Model-The California High- 2. Low wind speeds (less than two miles per hour) way Model is the last of the manual techniques produce large overestimates of concentration, to be reviewed .73 This source-oriented "model" is based on the mathematical representations really a series of modified Gaussian equations for es- alone. timating the dispersion of carbon monoxide from line 3. The authors of the model recommend that it not sources over short distances. The equations are modi- be used near interchanges, large aerodynamic fied to incorporate emission, meteorological, and obstructions, or in the vicinity of valley winds, highway design variables. since the meteorological records at the Weather The model depicts a highway as a continuously Bureau may not be sensitive to microscale ef- emitting line source which produces its own mechan- fects near these features. ical mixing from the turbulence created by moving 4. The model only treats CO. vehicles. The partially mixed CO is then dispersed ERTIMARTIK Model (Modified AQDM)-The away from the highway by winds, and the resulting ERT/MARTIK model is a modification of EPA's Air downwind concentration is a result of wind speed and Quality Display Model (AQDM) .71 It is complex, semi- atmospheric stability .74 The effect of highway eleva- empirical, receptor-oriented, spatially disaggregated, tion is also included. and applicable to SO,, CO, NO,,, hydrocarbons, and A series of charts has been prepared relating all of particulates emitted from any type of source. Annual these variables to normalized concentration which, in and seasonal ambient concentration averages are esti- turn, is expressed as a function of distance from the mated. highway (up to 1000 feet). Once values for the various Due to the model's rather complex mathematical inputs have been obtained, ambient concentrations formulation a detailed description is beyond the scope can be determined from the charts. (Concentrations of this review. Instead, a brief description of various are expressed as hourly averages.) Figure 1-4 summa- model components will be given. rizes the above operations. The model is based on the Gaussian plume equa' Unfortunately, the model has not been validated tion, with the following major elaborations and modi- with field measurements. It thus remains unproven, fications: despite the fact that it is widely used by transpor- tation planning organizations. The authors of the user 1. The equation is integrated in both the x and y manual do suggest, however, a series of guidelines to directions for area sources, rather than u 'sing the be used in selecting applications. (These are incorpo- virtual point source approach of the AQDM rated in the assessment below.) model. Advantages 2. Line sources are approximated by a series of virtual point sources. 1. The California model is simple and inexpensive 3. A box model is used when a major part of the to operate. (The manual contains a number of plume has reached the upper boundary of the examples for purposes of self-instruction.) mixing layer. 2. It uses meteorological and transportation data 4. The changing vertical plume dispersion values which are usually available at local Weather with distance traveled are based on an alterna- Bureaus and transportation planning agencies, 75. Byron H. Willis, The Hackensack Meadowlands Air Pollu- 73. California State Division of Highways, Air Quality Manual, tion Study, Summary Report (Lexington, Mass.: Environmental vol. 4: Mathematical Approach to Estimating Highway Impact on Research and Technology, Inc., July, 1973); James R. Mahoney, Air Quality and vol 5: Appendix (Washington, D.C.: Federal Bruce A. Egon, and Edward C. Reigenstein, III, The Hackensack Highway Administration, April, 1972). Meadowlands Air Pollution Study, Task 2 Report: Development 74. The meteorologic data is input as joint frequency distribu- and Validation of a Modeling Technique for Predicting Air Quality tions. That is, the probability of each stability, wind direction and Levels, (Lexington, Mass.: Environmental Research and Technol- wind speed category occurring simultaneously is calculated, based ogy, Inc., July, 1973). For a description of the original AQDM see, on historical records. This part has been computerized to facilitate National Air Pollution Control Administration, Air Quality Display preparation of the input data. Model (Washington, D.C., 1969). Air Quality: Methodological Approaches 31 FIGURE 14 FLOW DIAGRAM OF THE CALIFORNIA HIGHWAY MODEL TRAF IC DATA (VEHICLES PER HOUR) EMISSION FACTORS FOR AVERAGE ROUTE SPEED ANALYSIS OF Determine the atmospheric stabilities METEOROLOGICAL and probabilities with prevailing DATA WITH COMPUTER wind speed and direction. PROGRAMS ARE Estimate concentration NO WINDS YES Estimate concentration within mechanical mixing cell. PARALLEL T within mechanical mixing cell. HIGHWAY ALIGN. ? Estimate ground level concentrations Estimate the concentration build-up depending on the type of highway within the mechanical mixing cell. design and meteorological conditions. Estimate ground level concentrations normal to highway depending on highway design and meteorological conditions. SUMMARIZED RESULTS SOURCE: California State Division of Highways, op. cit. tive empirical relationship rather than on the 8. Ambient concentrations at receptor points are Turner curves. obtained by summing the contributions from all 5. Slight modifications have been introduced to relevant sources (i.e., those that lie upwind partially account for the urban heat-island and based on the wind direction probability distribu- topographical effects. tions). Isopleth maps can thus be generated from 6. The AQDM's equations for plume rise are used concentrations at selected receptors. (to give an effective emission release height) and The model has been applied in only one geographi- special considerations are made for very tall cal area (the Hackensack Meadows in New Jersey). stacks. Since it was carefully calibrated for this area, the gen- , HNO *_YES_@. 7. Wind speed, wind direction, and atmospheric eralizability of the model remains largely unknown. stability joint frequency distributions are used to The results obtained for the Hackensack Meadows estimate time-averaged concentrations. application are reported to be "fairly good." How- 32 Land Development and the Natural Environment ever, the difference between predicted and observed lation Model (TASSIM) is a combination transpqr- values expressed as a percentage of the observed val- tation, vehicle emission, and air diffusion model .77 It ues averaged 45 percent and ranged from 0 to 180 per- is simple, more empirical than theoretical, spatially cent. Although correlation coefficients between ob- disaggregated, and applicable to SO,, CO, NO., hy- served and predicted concentrations (seasonal and drocarbons, and particulates emitted from point and annual averages) were not reported (too few pairs of area sources. (Line sources are treated as mobile area values were used), the results are quite dis- sources.) couraging .76 On this basis alone CO and hydro- The diffusion submodel is a combination of the carbons were underpredicted while S02 and NO, Hanna/Gifford area source model and the AQDM for were overpredicted for all averaging times. Particu- point sources .711 The previously presented descriptive lates were underpredicted for summer and annual and material relating to these models applies equally well overpredicted for winter. However, since the number to TASSIM and will not be repeated again. It should of values compared was extremely low, additional be noted, however, that a more complex version of validation studies are needed. the Hanna/Gifford model is used, rather than the The specific costs of calibrating and operating the simple approximation employed by Hanna and Gif- model have not been reported. However, judging ford. from the complexity of the model and the amount of The transportation and emission submodels are de- data preparation and computation, the costs could be signed for high compatibility with the Department of considerable (i.e., probably in the tens of thousands Transportation's (DOT's) urban transportation plan- of dollars). Although a more detailed listing of advan- ning modeJ79 and with emission data typically found tages and disadvantages is shown below, the primary in urban areas. TASSIM is consequently well suited considerations are cost and spatial resolution. for estimating air quality changes deriving from future Advantages patterns of development. The spatial resolution of TASSIM is presumably 1. The model incorporates numerous modifications that of the Hanna/Gifford model (i.e., approximately of the Gaussian plume equation, which render it one square mile). For the Boston application the city much more theoretically satisfying.' was divided into 122 zones, most if not all of which 2. The spatial resolution is approximately one were considerably larger than one square mile. Of square kilometer (approximately .39 square course, point sources can be located much more pre- mile). cisely. 3. Point, line, and area sources are all modeled. The model has been applied in Boston and Los Angeles. In Boston the results are very encouraging, 4. The model is readily coupled to "planning data" but limited. S02 and particulates were estimated with (e.g., future land use projections). correlation coefficients of over 0.9, while NO,, re- 5. Isopleth maps can be produced by the program corded a value of approximately 0.7. Coefficients for to aid in comprehension of the results. CO and hydrocarbons could not be obtained, how- ever, due to insufficient monitored data. The correla- Disadvantages tion coefficients obtained in the Los Angeles applica- 1. Operating and calibration costs could be quite tion were 0.9, 0.8 and 0.7 for CO, hydrocarbons, and high. NO,,, respectively. The reported cost data relate only 2. Reported accuracy from limited testing has not to the operation of the model ($80 per run, or $30 if been very good. only the mobile sources are modeled). Data collection and coding and model calibration could presumably 3. The model, as currently constructed, is designed push the costs into the tens of thousands of dollars only to estimate long-term averages. for one application. Subsequent applications in the 4. Attempts to simulate reactive pollutants with any "nonreactive" model are always suspect. 77. Gregory K. Ingram and Gary Fauth, TASSIM: A Transpor- TASSIM-The Transportation and Air Shed Simu- tation and Air Shed Simulation Model, vol. 1: Case Study of the Boston Region and vol. 2: Program User's Guide (Washington, D.C.: Department of Transportation, May, 1974). 76. It is often difficult to relate one measure of accuracy, (e.g., 78. As noted previously, the AQDM (also known as the Martin- percent error) with another (e.g., correlation coefficients), and Tikvart model) is applicable to both point and area sources. neither is a completely satisfactory measure of accuracy alone. TASSIM, however, only uses the AQDM formulation for point (See the Summary section for a further discussion of these issues.) sources. However, percent errors as large as the ones reported here are gen- 79. See the transportation chapter in Schaenman, Keyes, and erally interpreted as being unsatisfactory. Christensen, op. cit. Air Quality: Methodological Approaches 33 same community would be less expensive, as much-of the emissions by wind direction, wind speed, the same data could be used again and recalibration and atmospheric stability joint frequency distri- would be unnecessary. butions. In summary, TASSIM would appear to be a prom- 3. The contributions from point sources (up to 200) ising model. However, additional test applications are are calculated separately and again are weighted needed in order to substantiate the reported levels of by the joint frequency distributions of wind accuracy. speed and direction, and atmospheric stability. Advantages 4. A theoretically superior plume rise represent- 1. TASSIM appears to be one of the conceptually ation is used, as compared to the AQDM. In ad- less complex computerized dispersion models dition, winds at the emission height are extrapo- currently available. lated from surface wind. 2. The accuracy appears to be excellent for CO, 5. Pollutant removal processes are simulated by S02, and particulates, and good for the other simple exponential decay functions. pollutants (based on one test). The joint frequency distributions of the metero- 3. The model would appear to be easily adaptable logical data can be obtained from the National Cli- to other communities. (The user manual treats matic Center (NCC) in Asheville, North Carolina. the particularization problem explicitly.) The NCC has developed a program called STAR to 4. Operating costs are reasonable, although cali- collect the appropriate data from each Weather bration and start-up costs may be high. Bureau station (every major urban area has at least one), calculate the joint frequencies, and appropri- Disadvantages ately format the results. The e 'missions data collected per EPA guidelines are also suitable as input. (All line 1. The spatial resolution is limited to about one source emissions must be expressed as mobile area square mile. sources.) 2. The model is designed only to estimate long- The results of attempts to estimate ambient concen- term average concentrations. trations Of S02 and particulates in St. Louis and New York have been very good. Correlation coefficients of Climatological Dispersion Model (CDM)-EPA's approximately 0.8 were reported. Again, however, National Environmental Research Center has been the reader is referred to the Summary and Compari- actively involved in dispersion model development son section for a discussion of other measures of and testing for several years. One of the compu- accuracy. terized models which the center is now making avail- Following is a summary assessment of the CDM. In able through the National Technical Information Ser- general, the model offers improved accuracy and vice (NTIS) as part of the UNAMAP program is the better spatial disaggregation than most of the manual Climatological Dispersion Model.80 Essentially, this is techniques, for an increase in cost. a modification of the previously discussed AQDM. As such, the model is fairly complex, semi-empirical, Advantages receptor-oriented, spatially disaggregated, and simul- taneously applicable to any two nonreactive pollu- 1. The spatial resolution is as good as that of the tants from area and point sources. Long-term (annual emission inventory. or seasonal) averages are estimated for any number of 2. Estimates can be made for an unlimited number receptors desired. of receptors. The characteristics of the model are as follows: 3. The model appears to be quite accurate. 1. Gaussian plume equations are used for both 4. The computing time is approximately three- point and area sources. fourths that of the AQDM. 2. The contributions from area sources are calcu- lated by integrating all area sources surrounding Disadvantages. a receptor (up to 2500 sources) and weighting 1. The cost of calibration and operation, although unknown, is assumed to be quite high, since a 80. Adrian D. Busse and John R. Zimmerman, User's Guide for computer the size of the IBM 360 series is re- Climatalogical Dispersion Model (Research Triangle Park, N.C.- quired for storage and computation. (The com- EPA, December, 1973). For information on other models in the puter program can be purchased from NTIS for UNAMAP series, contact EPA, National Environmental Research Center, Meterology Lab, Research Triangle Park, N.C. 27711. $175.) 34 Land Development and the Natural Environment 2. Only long-term. averages are estimated. by means of the Federal Highway Administration's 3. The incremental contributions of individual suggested procedures .82 sources cannot be easily ascertained. The model output can be expressed as either long- term or short-term concentrations for a few selected APRAC Model-Another member of EPA's locations, usually those representing the worst condi- UNAMAP series of models is APRAC, a transpor- tions. Alternatively, concentrations for one time in- tation model originally developed by Stanford Re- terval can be obtained at up to 625 locations and iso- search Institute."' It is fairly complex, semi-em- pleths derived therefrom. pirical, receptor-oriented, spatially disaggregated, and Based on correlation coefficients alone, the results applicable to CO emitted from mobile area sources. of test applications in St. Louis and San Jose are Both long-term (annual) and short-term (hourly) esti- somewhat disappointing. Correlation coefficients mates can be made. Concentrations can also be esti- between 0.4 and 0.7 have been reported. Even more mated for up to 625 receptors. Characteristics of the disturbing, an application by Argonne National Labo- model are described as follows: ratory in Chicago yielded correlations of approxi- 1. CO transported from surrounding areas (up to mately 0.25.13 However, most other dispersion models approximately 160 miles away) is simulated by a (especially those which only estimate long-term simple box model and generalized emission averages) do not attempt to estimate ground-level data. concentrations. Although these locations are more 2. For intra-community estimates, CO emissions meaningful in terms of human exposure, the concen- from line sources are averaged over segments of trations are more variable and more difficult to esti- sectors which radiate out from each receptor in mate. the direction of the transport wind. In general, the user of APRAC will be purchasing spatial disaggregation and flexibility of application for 3. The contribution from each sector is calculated a moderate price. by using the Gaussian plume equation. 4. For long-term estimates contributions from the Advantages various radial sectors are made proportional to 1. The model can be extremely disaggregated@ spa- the frequency with which the wind blows in that tially. Estimates for up to 625 points can be direction and the average speed with which it made, even for small communities. blows, , 2. With the canyon submodel, APRAC is a much 5. A street canyon submodel simulates ground- more realistic representation of actual micro- level concentrations in streets bordered by high- atmospheric dispersion than other CO models. rise buildings from data on crosswind speeds at 3. The I model can be obtained from EPA (UN- the roof level, the height of the buildings, ve- AMAP) for $175 '114 and the operating cost is hicle usage in the canyon street, and CO trans- quite modest ($50 per run). However, the start- ported from other areas of the city. up and calibration costs run into the tens of The model is compatible with meterological and thousands of dollars. 85 transportation data normally available in urban areas. 4. Both short- and long-term estimates can be The raw transportation data for each street are allo- made. cated to the appropriate radial sector, and emission 5. The model produces isopleth maps derived from levels are generated internally using empirically the 625 receptors to aid in comprehension of the derived emission factors. Data on wind speed, wind results. direction, atmospheric stability, and mixing depth are acquired from the local Weather Bureau. For future projections the model readily accepts forecasts made 82. See transportation chapter in Schaenman, Keyes, and Chris- tensen, op. cit. 83. See L. J. Habegger et al., Dispersion SimulatioaTechniques 81. Walter F. Dabberdt, F. L. Ludwig, and Warren R. Johnson, for Assessing the Air Pollution Impacts of Ground Transportation Jr., "Validation and Applications of an Urban Diffusion Model for Systems (Chicago: Illinois Institute for Environmental Quality, Vehicular Pollutants," Atmospheric Environment, 7 (1973): 603-18; May, 1974). The authors suggest that the low correlations could R. L. Moncuso and F. L. Ludwig, User's Manualfor the APRAC- also be influenced by inaccuracies in the measured ambient con- IA Urban Diffusion Model Computer Program (Menlo Park, Calif.: centrations and windspeeds. Stanford Research Institute, September, 1972); and W. B. Johnson, 84. Contact EPA's National Environmental Research Center, F. L. Ludwig W. F. Dabbcrdt, and R. J. Allen, "An Urban Diffu- Meteorology Lab, Research Triangle Park, N.C. 27711. sion Simulati@n Model for Carbon Monoxide," Air Pollution Con- 85. Based on costs experienced by the Department of Environ- trol Association Journal, 23 (June 6, 1973): 490-98. mental Quality, Portland, Oreg. Air Quality: Methodological Approaches 35 Disadvantages more complex models without a loss in accuracy. 1. Only CO is simulated. However, a purely empirical approach such as this suffers from the old association/causalty enigma. We 2. The accuracy is still questionable. may be able to predict the value of one variable sim- Other Models-Space does not permit a complete ply by knowing the value of another today. But with review of all relevant dispersion models. The reader no understanding of causality, changing values of will note that models based on a complete solution of other related variables may make future predictions the conservation of mass equation have yet to be dis- impossible. cussed. The reasons are two-fold: (1) these models are inherently more complex and considerably more c. Summary and Comparison of Models expensive to operate, and (2) the photochemical In order to make a cost-effective decision when kinetics of open system reactions are still poorly un- choosing a model, reliable information on total cost derstood, so that model accuracies tend to be low. and predictive accuracy must be at hand. The analy- Two "reactive" models, DIFKIN111 and the SAI sis in this section has shown that data on cost and model '17 have been developed and validated with data accuracy are not always precise or comparable. A from the Los Angeles area. Both models track projec- summary of the various models appears in Table 1-4, tions of air parcels over extended distances. Within to aid in comparative assessment. these presumed homogeneously mixed air parcels the Correlation coefficients have been given earlier complex chains of photochemical interaction are which show how well the model reproduces observed simulated. The models differ in the representation of values. Although this is a widely accepted and com- these interactions. Both have shown promising re- monly used indicator, it is but one statistic which sults, although they continue to suffer from limiting measures the tendency of one value to agree with an- assumptions regarding initial conditions and arrange- other. Largest positive or negative errors, error ments of sources. They are expensive to uses" and re- ranges, relative errors, mean absolute errors, 95 per- quire extensive testing before routine utilization. cent confidence intervals, and root mean square Some organizations are developing in-house models errors are others. Correlations alone can be mislead- for application in specific communities. The Bay Area ing, since they are often reported for partially cali- Air Pollution Control District and the New York brated models (models to which correction factors State Department of Transportation are two ex- have been applied to compensate for systematic amples.89 The models tend to be modifications of errors), thereby inflating the correlation coefficients. basic Gaussian plume and box model formulations. In addition, the user may be interested in the error at Another promising but still experimental approach either extremely high or extremely low values. (For is that of "repro-modeling" -the attempt to use air pollution measures concern is usually with high simple equations to relate the input and output data of values.) A recent EPA publication reports the results a complex model. One effort to apply repro-modeling of a comparative analysis of accuracy for three to the SAI model has proven quite successful, models and variations thereof." The models are as although a series of assumptions limits the general- folloWS:92 izability of the results.90 The concept is certainly at- 1. AQDM. tractive-to vastly reduce the complexity and cost of 2. CDM. 3. CDM (Single Stability). (The CDM values are 86. A. Q. Eschenroeder and J. R. Martines, Concepts and Ap- further averaged by using a single average wind plications of Photochemical Smog Models (Santa Barbara, Calif.: General Research Corp., June, 1971). 87. Steven Reynolds, Philip Roth, and John Seinfeld, "Mathe- 91. D. Bruce Turner, John R. Zimmerman, and Adrian D. Busse, matical Modeling of Photochemical Air Pollution-1, Formulation "An Evaluation of Some Climatological Dispersion Models (Paper of the Model," Atmospheric Environment, 7 (1973): 1033-61; and presented at the Third Meeting of the NATO/Committee on the Steven Reynolds et aL, "Mathematical Modeling of Photochemical Challenges of Modern Society, Panel on Modeling, 1972) and in- Air Pollution-III, Evaluation of the Model," Atmospheric Envi- cluded in the CDM users' manual. ronment, 8 (1974): 563-96. 92. Model 3 is simply the result of using averaged input data as 88. W. Brian Crews, Department of Environmental Quality, compared to Model 2. Models 5 and 6 involve structural modifica- Portland, Oreg., reports that the start-up and calibration costs of tions to the Hanna/Gifford model and, as such, have not been dis- DIFKIN are over $50,000. cussed previously. They are included here only to show the effect 89. For further information, contact San Francisco Bay Area Air of the most constraining assumption of the Hanna/Gifford Pollution Control District, 939 Ellis Street, San Francisco, Calif. model-that ambient concentrations for any subarea are solely due 94109, and New York State Department of Transportation, Plan- to emissions in that subarea. The reader should consult the Hanna ning and Research Bureau, State Campus, Albany, N.Y. 12226, and Gifford reference for further information on the more complex 90. Horowitz, Meisel, and Collins, op. cit. formulation of their model. 36 Land Development and the Natural Environment Table 1-4. COMPARISON OF ATMOSPHERIC DISPERSION MODELS Pollutants Modeled Sources Modeled Stationary Mobile Aver- Computing NAME CO SO@ NOs HC 0. Part. Point area area 'Line aged' Inputs Outputs Requirements Cost Accuracy Rol Iforward Current average ambient concen- (1) Average ambient concentration Manual Low Unvalidated Model X X Xt, Xb Xb X X trations, total emissions (for entire for'one or a few representative community or subareas) and future points in the community emissions. For more complex ver- (2) Any averaging time period sions, wind speed, wind direction, and average stack heights Miller/ Average community-wide emission (1) Average ambient concentration Manual (essentially Low Good (r > 0.8 for S02 Holzworth rate, average wind speed through- for the community as a whole referencing of and NO@ for the test Model X X X X out the mixing layer, mixing depth, (2) Hourly or annual averages tables) application community size (along wind length of the urbanized area) Hanna/ Emission rates for area and certain (1) Average ambient concentrations Manual Low (approximately Good for nonreac- Gifford point sources and wind speed (and for areas as small as I square mile, 1/2 hour of calcula- &e version (r - 0.7), Model X X X, XC X X X direction for short-term averages) (ifthe areas are numerous enough, tions for 150 sub- less satisfactory for isopleths can be drawn for the areas in Chicago reactive version community) plus the cost ofemis- based on one applica- (2) Any averaging time period sions data collection tion (r = 0.05-0.97) California Vehicle speeds, volumes, and mixes; (1) Average ambient concentrations Manual (helpful to Low Unvalidated Highway average wind speed, wind direction, as a function of distance from the computerize some . Model X X and atmospheric stability tjoint fre- highway (up to 1000 feet away) meteorological data) quencies), highway elevation (2) Annual averages ERT/MARTIK Average wind speed, wind direction (1) Average ambient concentrations Digital computer Presumably high Initial validation Model X X X X X X X X atmospheric stability ljoint frequen- for areas as small as 1/2 square (probably tens of results were mediocre cies); emission rates for all sources, mile; isopleths can be drawn thousands of background emissions (2) Seasonal or annual averages dollars) TASSIM X X X X X X X X See ERT/MARTIK for point sources (1) Average ambient concentrations Digital computer Presumably High Good (r = 0.7-0.9) for and Hanna/Gifford for area sources. I for areas as small as 1/2 square with 156,000 the various pollutants Distribution of trips and speeds by mile; isopleths can be drawn bytes of storage zone for line sources. (2) Averages by hour, day, year CDM X X X X X Emission rates for point and area (1) Average ambient concentrations Digital computer Presumably High Good (r -- 0.8) sources; joint wind speed, wind at an unlimited number of direction and atmospheric stability locations frequencies; average mixing depth (2) Annual averages APRAC X X X Vehicle speed and volume per link, (1) Average ambient concentrations Digital computer, Presumably High Mediocre (r 0.25- average hourly cloud cover, temper- at up to 625 locations from which 45,000 words of 0.7) ature, atmospheric stability and isopleths can be drawn storage (program mixing depth (2) Hourly or annual averages modification needed for computers except CDC 6400 and IBM 360/50) a. Emissions from all types of sources are averaged together. b. The application of the model to these pollutants has been very limited. c. These pollutants are modeled by the more complex "reactive" version. speed category and selected atmospheric stabil- CDM, two models designed for "off the shelf " appli- ity category.) cation, users have reported the need to recode input 4. Gifford '72. (This is the Hanna/Gifford model data (and in the case of CDM, even to undertake discussed previously.) some reprogramming) before operation.93 This is not 5. Modified Hanna. (This is the Hanna/Gifford intended to dampen enthusiasm for computerized model modified to include contributions to the models. Certainly they are more widely applicable average ambient concentrations within a given and, in most cases, more accurate than the simple area by emissions from surrounding areas as ones. But their calibration and use can be a costly well as by emissions in the area itself.) process. A brief statement regarding general limitations and 6. Modified Hanna including source height. (This is deficiencies is also in order. One need is for the the same as the preceding, with one additional development of regional models which would simu- modification: the average emission height for all late the movement of pollutants over distances of sev- area sources is used rather than a value of zero.) eral hundred miles and thus help to explain the high The results of an evaluation of these models using background levels found in many areas. Synoptic SO, and particulate data from New York City are scale meteorology is poorly modeled as well. On the shown in Tables 1-5 and 1-6, respectively. The con- other extreme is the lack of a model which reflects clusion is that no one model is clearly superior on all urban meteorology and special microclimatic effects. measures. Furthermore, the simpler models per- But probably the greatest and certainly the most per- formed better than might be expected theoretically. vasive deficiency is the lack of field data to be used The results of this test bear directly on the question for model validation. Without better designed moni- of selecting among the models presented in this re- toring networks and a dramatic increase in the port. Certainly for long-term planning purposes or for number of stations, model validation will lag far be- evaluating the cumulative effects of development the hind the development of model theory. simpler models (rollforward, Hanna/Gifford, and Miller-Holzworth) would appear to be more cost- 5. Measuring/Estimating Odor and Smoke effective. Choosing among these would have to be Problems based on the type of pollutant being considered, the Since the assessment of nuisance problems requires availability of required input data, and the level of a slightly different approach, the subject will be given spatial disaggregation (degree of resolution) needed. special, albeit brief, attention. For example, only the California Highway Model and the canyon submodel of APRAC would appear to be a. Odor Problems capable of reproducing microscale effects in the Odors can be localized or widespread, of short- immediate vicinity of a development. APRAC ap- term duration or long-lived, constant or intermittent. pears best suited for evaluations of individual residen- In addition, the extent to which they present a tial and commercial projects, especially if the project problem depends on intensity, distinguishing quality, will change traffic levels throughout the entire and acceptability. 94 As a result, the objective detec- highway network or a large section of it, or if changes tion (to say nothing of the prediction) of odor in traffic will occur within street canyons. However, problems is a difficult task. APRAC is not as comprehensive nor as accurate as As a guide, evaluators might obtain from develop- some of the others. The California Highway Model is ers a component breakdown of future emissions or, appropriate for those situations where individual failing that, a description of the industrial process and developments will cause increases in traffic on only raw materials to be used. (Paper mills, sewage plants, one or a few highways. ERT/MARTIK, TASSIM, meatpacking plants, and chemical firms are of special and CDM (the latter for point and stationary areas concern.) A rough estimation of potential problems sources only) would appear to be appropriate for either very large projects or for area-wide develop- ment in general. ERT/MARTIK and TASSIM have 93. Richard Hawthorne, Department of Environmental Quality, Portland, Oreg., and Steven Albersheim, NUS Corporation, Rock- the further advantage of being designed specifically viRe, Md-respondents to the Urban Institute questionnaire. for planning applications. 94. The Third Karolinska Institute Symposium on Environ- The potential user of any model requiring computer mental Health, "Measuring and Evaluating Odorous Air Pollutants support should remember that the start-up and at the Source and in the Ambient Air" (Report of an International Symposium in Stockholm, June 1-5, 1970). (Available from the "tuning" activities can be expensive, time- Department of Environmental Hygiene, Karolinska Institute, consuming, and frustrating. Even for APRAC and s. -10401, Stockholm, Sweden.) 38 Land Development and the Natural Environment Table 1-5. RESULTS OF MODEL EVALUATION USING S02 DATA LINEAR ERROR AT AVERAGE* NUMBER ROOT CORRELATION POINT OF MAXIMUM*** ESTIMATED OF MEAN MEAN LARGEST LARGEST WITH MAXIMUM ESTIMATED CONCEN- COMPARI- SQUARE ABSOLUTE NEGATIVE POSITIVE ERROR MEASURED MEASURED CONCENTRATION TRATION" SONS ERROR** ERROR** ERROR** ERROR** RANGE** VALUES (r) VALUE" 1. Air Quality Display Model (AQDM) 211 75 121 92 -87 310 397 0.89 112 566 2. Climatological Dispersion Model (CDM) 138 75 52 37 -118 166 284 0.84 -101 368 3. CDM (Single Stability) 206 75 124 89 -112 332 444 0.84 13 577 313. CDM (C Stability) 94 75 56 46 -128 96 224 0.82 -119 307 3C. CDM (C/D Stability) 139 75 64 45 -115 188 303 0.84 -56 423 4. Gifford '72 54 75 82 72 -175 29 204 0.81 -175 180 413. With CDM Point Estimates 79 75 59 50 -137 49 186 0.85 -137 219 5. Modified Hanna 279 75 330 178 -145 1232 1377 0.77 1153 1503 5B. With CDM Point Estimates 305 75 348 193 -120 1270 1390 0.78 1191 1541 6. Modified Hanna Including Source Height 102 75 58 45 -151 190 341 0.84 49 399 6B. With CDM Point Estimates 127 75 56 38 -126 225 351 0.86 87 437 SOURCE: Turner et a]. (1972). The average and standard deviation for the measured values are 135 and 72 micrograms/cubic meter, respectively. In micrograms/cubic meter. The maximum measured concentration was 350 micrograms/cubic meter. Table 1-6. RESULTS OF MODEL EVALUATION USING PARTICULATE DATA LINEAR ERROR AT AVERAGE* NUMBER ROOT CORRELATION POINT OF MAXIMUM*** ESTIMATED OF MEAN MEAN LARGEST LARGEST WITH MAXIMUM ESTIMATED CONCEN- COMPARI- SQUARE ABSOLUTE NEGATIVE POSITIVE ERROR MEASURED MEASURED CONCENTRATION TRATION" SONS ERROR** ERROR** ERROR** ERROR** RANGE" VALUES (r) VALUE" 1. Air Quality Display Model (AQDM) 102 113 36 28 -51 115 166 0.62 5 199 2. Climatological Dispersion Model (CDM) 74 113 22 16 -63 68 131 0.61 -48 135 3. CDM (Single Stability) 88 113 28 21 -60 98 158 0.64 -6 165 3B. CDM (C Stability) 58 113 31 26 -78 59 137 0.57 -71 126 3C. CDM (C/D Stability) 69 113 25 19 -73 75 148 0.61 -43 142 4. Gifford '72 40 113 53 47 -117 46 163 0.63 -56 151 4B. With CDM Point Estimates 51 113 47 40 -111 59 170 0.63 -44 164 5. Modified Hanna 80 113 41 30 -77 177 254 0.64 61 281 513. With CDM Point Estimates 92 113 45 32 -71 190 261 0.64 73 294 6. Modified Hanna Including Source Height 56 113 31 26 -80 25 105 0.66 -58 129 613. With CDM Point Estimates 67 113 25 19 -71 37 108 0.62 -53 141 SOURCE: Turner et a]. (1972). The average and standard deviation for the measured values are 82 and 23 micrograms/cubic meter, respectively. In micrograms/cubic meter. The maximum measured concentration was 169 micrograms/cubic meter. can then be made based on the known odorant prop- may displace or provide an alternative to the con- erties of the material to be emitted. A fairly recent ar- tinued use of existing nuisance sources. ticle on threshold concentrations of fifty-three odorant chemicals would be a starting point, although 6. Measuring/Estimating Exposure of the thresholds reported were developed under con- People to Pollution trolled laboratory conditions .95 In order to determine the dispersion of the odorant material, dispersion Once the spatial distribution of pollutants in the models can be used as demonstrated by HogstroM96 ambient air has been estimated, the next step is at- and Sullivan.91 tempting to relate these concentrations to the popula- For measuring the magnitude of existing odor tion (or other receptors) at risk. There are at least problems a variety of techniques exists.98 The tech- three dimensions to the problem: mques range from subjective evaluations by panels of 1. Specifying the intensity of exposure. experts" to objective assessment made by analytical 2. Specifying the duration (or frequency) of expo- devices, such as the scentometer.100 The subjective approach is attractive because it integrates the sure. various odor characteristics (intensity, distinguishing 3. Specifying the number of people exposed. quality, and acceptability). The hardware approach, Since these dimensions apply to each of the several on the other hand, is more objective and quantita- potential pollutants, and since various combinations tive.101 of intensity, duration, and numbers of people exposed may occur for each pollutant in different areas, the b. Smoke Problems potential amount of data generated by an air quality Smoke problems are typically associated with the analysis is indeed large. opacity and size of smoke plumes. Reference has already been made to the standard opacity measure- a. intensity and Duration ment device-the Ringelmann chart-which can be One way to reduce this volume of information is used to estimate problems caused by existing devel- through the use of intensity-duration indices (or single opments. Future estimations are becoming less of a number scores). As was discussed earlier, index concern since new EPA source regulations are de- scores are typically derived from a comparison of es- signed to elimina 'te smoke problems. All new point timated ambient concentrations to appropriate federal sources will be required to install appropriate control or other standards. equipment. Thus, the assessment of smoke genera- In this case, however, it is suggested that indices tion generally need not be a part of the evaluation Of proposed d Ievelopments, although new developments be used to combine concentrations of one pollutant for various averaging time periods rather than com- bining concentrations of several pollutants for a single 95. G. Leonardos, D. A. Keudoll, and N. J. Barnard, "Odor time period. This mitigates much of the criticism of Threshold Determinations of 53 Odorant Chemicals," Air Pollution Control Association Journal 19 (1969): 91. indices discussed in a previous section.101 In order to 96. U. Hogstrom, Atmospheric Environment 6 (1972): 102. calculate an exposure index, ambient concentrations 97. F. Sullivan and G. Leonardos, "Determination of Odor for various averaging times are needed, since federal Sources for Control" (Presented at Conference on Odors: Evalua- standards are specified for averaging times of one, tion, Utilization, and Control, New York Academy of Sciences, October, 1973). three, eight, and twenty-four hours, and twelve 98. G. Leonardos, "A Critical Review of Regulations for the months. However, most of the simple dispersion Control of Odors," Journal of the Air Pollution Control Associ- models only provide estimates of long-term average ation 24 (1974): 456-68. concentrations. To estimate average concentrations 99. J. DeChioia and L. Koppelman, Planning Design Criteria for any short-time averaging period (i.e., one, eight, (Van Nostrand Reinhold Co., 1969): and A. Dravnieks, "Mea- suring Industrial Odors," Chemical Engineering 8 (October 21, or twenty-four hours), monitored data for several 1974):91-95. years are needed. Larsen has shown that pollutant 100. J. L. Milles, et al., "Quantiative Odor Measurement," concentrations vary in a log normal fashion with time Journal of the-Air Pollution Control Association 13 (1963): 467. (i.e., frequency of occurrence plotted against the 101. In those cases where a new development will remove a source of current odor problems, the techniques mentioned above logarithm of concentration produces a normal or bell- or a survey can be used to establish the severity or perceived shaped curve), which means that average concentra- severity of the current problem. A case in point is the replacement of a rendering plant by an office building in the Georgetown area of Washington, D.C., which produced greatly. improved conditions 102. Indices are discussed in Section A on "Measures, Stan- for thousands of residents, workers, commuters, and visitors. dards, Indices" in Chapter II, Part 1. 40 Land Development and the Natural Environment tions for any averaging time period can be calcu- sions are a way of "summing up" the change in expo- lated.103 This involves calculating (a) certain standard sure level. statistics for the observed frequency distribution, and (b) using the dispersion model estimates of future b. Number of People Exposed concentrations and Larsen's relationships, the same statistics for the time-averaging period in question.104 Once the exposure level has been determined there In addition to annual average values, estimates of the remains the task of identifying the population af- maximum yearly concentrations for any averaging fected. At least two of the dispersion models pre- time can be obtained from the same frequency distri- viously described (ERT/MARTIK and APRAC) and bution. possibly Hanna/Gifford and TASSIM (depending on Some of th Ie more complex dispersion models, such the size of the grid cells used) allow the construction as APRAC, can be used to obtain annual averages of isopleth maps from the output data. At a minimum, and maximum values for short averaging times di- pollution contours can be overlaid on maps of resi- rectly. As yet, no one has made a cost/accuracy com- dential population distributions derived from census parison of simple models and Larsen's relationships data. A more meaningful analysis would compare pol- on the one hand, and a complex model on the other. lutant distribution and population distribution by time Where adequate historical air pollution data are avail- of day or day of the week (e.g., the number of com- able, and where estimates at only a few geographical muters exposed to rush hour traffic or the number of points are desired, the first approach would certainly workers exposed to downtown, daytime pollution seem to be less expensive. levels). Although a search failed to uncover any Another type of exposure index can be calculated studies of this nature, the voluminous amounts of once the frequency distribution of concentration with transportation data collected by most cities should time has been estimated. Since total exposure is a shed some light on the daily activity patterns of at function of both pollution intensity and duration, mul- least certain groups of individuals. tiplying one by the other can give a one-number value In judging the number of people at risk it could be for exposure. That is, each concentration level is mul- argued that the extent to which people are exposed to tiplied by the amount of time that level is reached, interior ambient air should also be considered. Many and the resulting values are summed for all concen- persons spend a considerable portion of the day in- trations. (See Figure 1-5.) If a comparison with stan- side buildings, a large percentage of which are air- dards is desired, the index can be computed for those conditioned and ventilated. However, recent studies concentration values exceeding the standards. A indicate that interior and exterior concentrat 'ion levels format for presenting the results is also illustrated in tend to fluctuate together, with the indoor peak being the notes to Figure 1-5. slightly lower, although much depends on construc- Both types of indices have their drawbacks. The tion, air-conditioning, and ventilation character- first type (i.e., direct comparison with standards) istics.101 For automobile interior spaces the situation relies almost exclusively on somewhat questionable may be even worse, with pollutant levels exceeding standards as the sole measure of damage, while the those outside.101 Thus, estimates of exterior concen- second assumes a linear relationship between expo- trations can be used as representative (and in some sure and damages (i.e., damage from five days at ten cases conservative). indicators of interior concentra- parts per million is assumed equivalent to ten days at tions as well. five parts per million. Nevertheless, these expres- In addition to a comparison of pollutant concentra- tions with population density, it may.be informative to identify impacts on especially susceptible popula- 103. Ralph 1. Larsen, "A New Mathematical Model of Air Pollu- tion groups. Areas with large elderly or adolescent tant Concentration Averaging Time and Frequency," Journal of populations, or where athletic facilities are located, the Air Pollution Control Association 19 (January 1969): 24-30: and Ralph 1. Larsen, A Mathematical Modelfor Relating Air Quality may be more severely affected by the same pollution Measurements to Air Quality Standards (Research Triangle Park, levels than other areas. Some communities may also N.C.: EPA, Office of Air Programs, November, 1971) (Report No. wish to single out already disadvantaged groups and AP-89). 104. More specifically, the geometric mean and standard geo- metric deviation for one averaging time are calculated from the monitored data. The future arithmetic mean for the long-term 105. T. M. Briggs, et al., Air Pollution Considerations in Resi- aver-aging time is obtained from a dispersion model or simpler ana- dential Planning, Volume H: Backup Report (Cincinnati: lytical technique and used to calculate the geometric mean for this PEDCO-Environmental Specialists, Inc., July, 1974). averaging time. The long-term standard deviation is obtained from 106. New York Department of Air Resources, Air Pollution that for the monitored data. These parameters are then used to esti- Variations and Roadway Configurations (New York: September, mate average future concentrations for all other averaging times. 1971). Air Quality: Methodological Approaches . 41 FIGURE 1-5 THE USE OF FREQUENCY DISTRIBUTIONS TO ESTIMATE EXPOSURE INTENSITY AND DURATION Number of days (other units of time can also be used) d. a concentration standard c a b d Concentration in ppm (other units of concentration can also be used) NOTES: The curve is constructed from a histogram of concentration intervals within which short-term (usually one or eight hours) averages are observed. In the example, hourly average concentrations between the values "a" and "b" are observed to occur for a total of c days out of the year. (The distribution is skewed to the right because the logarithm of concentration is related to frequency of occurrence in a normal fashion.) Exposure index calculations: (a) Total exposure = total area under the curve (this is obtained by mathematical integration or approximated by calculating the area of the histogram). (b) Exposure above a standard = area under the curve to the right of standard "d." The units of the exposure index would be ppm-days. The results could be displayed as follows: CLIENTELE GROUP* A B C Total population 15,000 75,000 65,000 Change in exposure level +50 ppm-days + 150 ppm-days +100 ppm-days Change in exposure level above the 1-hour standard + 10 ppm-days +8 ppm-days +5 ppm-days For example, adolescent, elderlyj and others. the areas where they live or work as worthy of spe- data into dollar estimates of damage. A rich literature cial consideration from an equity point of view. has been developed on the subject over the last few years.101 Most studies which attempt to estimate the 7. Measuring/Estimating Damage in Monetary Units 107. See, for example, National Academy of Sciences, op. cit.; Assuming that future concentrations of individual Thomas Waddell, The Economic Damage of Air Pollution (Wash- ington, D.C.: EPA, May, 1974); Allen Kneese and Blair Bower, pollutants have been ascertained and the populations eds. Environmental Quality Analysis (Baltimore: John Hopkins at risk identified, it may be useful to translate this Press, 1972). 42 Land Development and the Natural Environment costs of pollution (or the benefits - of abatement) fall studies suffer both theoretically and empirically. It is into one of three categories-those based on health safe to say that ail estimates are highly approximate. data, those concerned with property values, and No procedures were found that can be recommended those based on vegetation and materials damages. for the salient concern here, evaluating community- The first type attempts to impute monetary values to specific development and individual projects. 1011 How- loss of life and limb or ill health based on foregone ever, current research efforts may soon make esti- earnings or data taken from court decisions. The mates feasible for small areas. property value studies attempt to isolate and measure the effect of air pollution by determining changes in value of property in otherwise "comparable" neigh- 108. Several studies have attempted to allocate national damage borhoods in several communities, each with different estimates to smaller geographical areas. The results are highly air quality. Studies in the third group attempt to attri- speculative, however. See, for example, Leonard P. Gianessi, bute a percentage of crop loss and the consumption of Henry M. Peskin, and Edward Wolff, "The Distributional Implica- tions of National Air Pollution Damage Estimates" (Paper pre- pollutant-damageable goods and related services to pared for the Conference on Research in Income and Wealth, Uni- the presence of airborne pollutants. All of these versity of Michigan, May 15-17, 1974). Air Quality: Methodological Approaches 43 111. CONCLUSIONS AND RECOMMENDATIONS A. PLANNING VERSUS PROJECT REVIEW basis at the point of project proposal. Table 1-7 is a At various points in the discussion we have at- listing of factors to be considered for each of the tempted to relate the evaluation of individual pro- major pollutants, differentiated by the level of analy- posed projects to air quality planning for groups of sis. As shown, both planning and project review are projects or for future development in general. We appropriate for most pollutants and thus most types stressed the need to place each project in the context of developments.. of community-wide or area-wide growth, especially At the planning level, one approach is to work for large projects whose construction would extend backward from desired ambient concentrations to over long periods. Since we view the relationship of allowable emissions for various areas within the com- large area planning to individual project review as one munity. The allowable emissions (perhaps phrased in of the more important issues in the implementation of terms of emission densities) can then be considered an impact evaluation program at the local level, we targets to strive for in achieving acceptable air qual- will now elaborate on these and related points. ity.' Then, as these areas develop at some point in The extent to which a planning, as opposed to a the future, the cumulative effects of individual devel- project review, approach should be utilized is pri- opments can be measured against the target by simply marily dependent upon two factors: (a) the scale of keeping a running sum of emissions from all develop- impact, and (b) the sensitivity of pollutant generation ments to date. Presumably, once the target was to design features of the development. Developments reached, development would stop, emission levels for which will produce. negative community-wide effects some developments would have to decrease, or the (either singly or cumulatively), such as high emission community would accept growth knowing that air rates or the generation of pollutants with slow decay quality would be less than desired. Emission densities rates, are probably best controlled through planning. (e.g., parts per million per acre) could be further As noted before, however, both planning and project translated into traffic volumes or size and types of review may be desirable; proposed projects which are 1. For a more detailed discussion of emission density zoning, consonant with area plans (as revealed by a quick im- see, A. S. Kennedy, et al., Air Pollution-Land Use Planning Proj- pact evaluation) may still need more detailed individ- ect, vol. III (Argonne, Ill.: Argonne National Laboratory, May, ual evaluations as a check on the assumptions used to 1973) (NTIS No. P13-239138); Richard K. Brail and George Hagevik, "Air Quality Management as a Constraint on the Com- make the plan. prehensive Planning Process: Emission Allocation and Emission On the other hand, developments which produce Density Zoning Strategies" (Paper presented at 1974 AIP Confer- only localized effects or which generate pollutants ence in Denver); and J. J. Roberts, E. J. Croke, and S. Booras, "A Critical Review of the Effect of Air Pollution Control Regulation that can be reduced by such design features as buffer and Land Use Planning," Journal of the Air Pollution Control areas are probably best regulated on an individual Association 25 (May, 1975): 500-20. 45 Table 1-7. PLANNING AND PROJECT REVIEW CONSIDERATIONS FOR EACH OF THE MAJOR AIR POLLUTANTS POLLUTANT PLANNING CONSIDERATIONS PROJECT REVIEW CONSIDERATIONS Particulates Industrial sources (singly and collectively) plus generalized Smoke from individual point sources can produce localized wind erosion exacerbated by construction activities can problems. Specific construction practices may reduce wind produce community-wide problems. erosion. Trees and vegetation tend to increase rates of deposition. so. Large point sources and numerous area sources can create No special problems or ameliorating factors at this level. large-scale problems. CO Due to the dispersed nature of the source (i.e., the road net- CO decays rapidly with distance from the source and thus work), CO is a community-wide problem. can produce local concentrations much higher than the com- munity average. Street canyons present special problems. Project design features may affect auto vs. transit use. NO., hydrocar- Since all three participate in long-term photochemical reac- No specialized, localized problems. Project design features bons, and photo- tions and since the sources are highly dispersed, the effects may affect auto vs. transit use. oxidants are experienced community-wide. Odiferous Some highly pungent compounds may be detectable over Most odoriferous materials are primarily localized in effect materials considerable distances. due to rapid rates of dilution. new developments, although the latter assumes fairly rather than absolute values are desired. Again, if the invariant relationships between development charac- relationship between the characteristics of future teristics and emissions, an assumption which is rarely developments and emission levels is tenuous, esti- valid. mates of ambient concentrations are questionable. Different air quality targets for different parts of the In addition to assessing emissions from future community may be desirable, based on population developments for comparison with planning targets, a distributions or socioeconomic and demographic project level analysis could be used to assess local- characteristics of population subgroups (e.g., stricter ized effects and those sensitive to particular project controls in areas characterized by an elderly popula- design features, or, as noted before, to assess large tion). - individual developments as a check on the adequacy If the targets are phrased in terms of emission of the plan. Local accumulation of CO generated by levels, then impact analyses of individual proposed development-associated traffic, for example, can best developments need only to estimate development- be ascertained by scrutinizing the project site plan produced or -related emissions. This insures the flexi- and characteristics of the immediate environment, bility needed to accommodate changes in federal, such as type, amount, and location of vegetation; ter- state, and local requirements and in pollution control rain; and type and location of other manmade struc- technology, as well as to capture the idiosyncracies of tures. The most appropriate dispersion models for individual developments. these small area analyses are those which are sensi- To determine the appropriate target emission levels tive to microscale effects. Of those reviewed, only from maximum desired ambient pollutant concentra- the California Highway Model, the APRAC canyon tions, dispersion models can be operated essentially submodel, and perhaps the individual source-oriented in reverse. For this purpose the most appropriate are models which are part of the EPA's UNAMAP the Hanna/Gifford model, the Miller/Holzworth system qi@alify.2 model, the ERT/MARTIK model, TASSIM, and CDM. B. SPECIFIC RECOMMENDATIONS Another planning level approach is to compare the AND CONCLUSIONS air quality implications of alternative land use plans Following is a list of recommendations and conclu- developed to achieve other objectives. Emission sions based on our investigation of issues and levels determined by using gross emission factors (by land use category) are combined with long-term 2. EPA has two relevant point source models (PTMAX and average meteorological conditions and with a simple PTDIS) which have not been reviewed here due to a lack of docu- mentation. Readers should contact the Meteorology Lab, EPA dispersion model to produce the expected impact on Environmental Research Center, Research Triangle Park, N.C., in air quality. The results can be quite good if relative order to obtain descriptive materials as they become available. 46 Land Development and the Natural Environment methods of analysis relevant to the assessment of air 4. Relatively simple yet reasonably accurate tech- quality impacts from proposed land developments: niques appear to be available for making estimates of long-term (e.g., annual) average 1. Local governments should consider specifying pollutant concentrations from community-wide emission "targets" in their land use or zoning development. These can also be used to establish plans, based on a dispersion analysis of those emission targets in land use plans or to assess pollutants which are community-wide in scale. very large developments. At a minimum, evaluations of individual devel- 5. Some existing air dispersion models estimate opments would estimate the future on-site short-term (e.g., one-hour, eight-hour) max- and off-site emissions associated with each imum concentrations due to emissions from development, add them to the development- single developments or groups of developments generated emissions to date, and compare them but appear to be of questionable accuracy and/or with the target. are costly. 6. Only two models reviewed have the capacity of 2. Where developments would cause emission estimating ambient pollutant concentrations in targets to be exceeded or where the pollutants to the immediate vicinity (i.e., within a few be emitted are localized in scale (or simply as a hundred feet) of a proposed development. check on the assumptions used to determine the 7. Every model reviewed needs additional valida- plan), detailed evaluations of individual develop- tion. Models are typically validated with sparse, ments should be undertaken. and in some cases questionable, field data and under too few differing conditions to allow for 3. The detailed evaluations should focus on both much confidence in the reported accuracies. health and aesthetic/nuisance problems, empha- Even where detailed validation studies have sizing end impacts on man where possible, and been performed, the accuracy of the results is perhaps using the recommended measures. In difficult to measure. Statistical measures are nu- choosing between preferred and fallback mea- merous, and no one measure can reflect accu- sures, the potential magnitude of impact and the racy in a totally satisfactory way. When dif- time and funding available for evaluation will ferent measures are used for different models, probably be the most important considerations. comparison is difficult if not impossible. Air Quality: Conclusions and Recommendations 47 PART 2 WATER QUALITY AND QUANTITY. 1. INTRODUCTION AND BACKGROUND With the increase in population and advance- areas and use these areas for parks or wildlife pre- ment in the level of industrialization have come an in- serves. Not only would damage to any development crease in water use and a simultaneous decrease in in question be eliminated, but increased flooding the availability of clean water for drinking, recrea- downstream caused by the diversion of flood waters tion, and other uses. Man-produced changes in ter- around structures could possibly be reduced. rain and land cover have also affected the likelihood of flooding. Clearly, land use planning and control 2. Water Pollution should consider potential impacts on the quantity and quality of water for various users and changes in As used in this report, "water pollution" refers to flooding hazards. This part of the report discusses the quality of bodies of water, such as wetlands, these water-related impacts and methods for esti- streams, rivers, lakes, and oceans used for purposes mating those caused by land development. other than for the supply of drinking water. The qual- ity of water used for drinking purposes, on the other hand, is mentioned in the water pollution discussion A. HEALTH, SAFETY, AND WELFARE EFFECTS but receives primary consideration under "water con- Since the legal justification for the local application sumption. " of land use controls (and thus, by extension, for the The quality of a body of water is determined by the existence of impact evaluation requirements) usually composition of the earth material over which it lies rests on protecting human health, safety, and welfare, (or in which it is located) and the composition of the it is useful to maintain this categorization in dis- inflow water (precipitation, surface and underground cussing water-related impacts. flow, and wastewater flow.) Urban sources of waste- water include sewage treatment facilities, septic 1. Flooding tanks, and industrial plants. Stormwater runoff and air pollution can also lead to the contamination of sur- Flooding relates most obviously to- man's safety, face and ground waters. but floods are also frequently associated with out- .. The extent to which water can be called polluted is breaks of communicable diseases. Although floods really dependent on the use to which it will be put. occur naturally as a consequence of an uneven distri- The criteria for human consumption will obviously be bution of precipitation and runoff over time, the loca- the most restrictive, while some deterioration may be tion and design of land developments can substan- acceptable for certain agricultural, recreational, tially affect the extent of flood damage. One solution industrial, and wildlife uses. is to eliminate manmade structures from flood-prone The EPA has proposed a series of water quality cri- 51 teria (for bodies of water) pursuant to the Federal eral aesthetic considerations are difficult to quantify, Water Pollution Control Act Amendments of 1972.' although attempts have been made to do so.5 The recommended criteria consist of maximum am- bient concentrations for fifty-seven polluting sub- 3. Water Consumption stances and maximum levels for eight indicators of Land development may affect water consumption water quality. These are based on field and laboratory by changing the quality and/or quantity of available studies which measure the effects of various pollu- water. That is, water supblies can be affected through tants or their surrogates on crops, domestic livestock, the introduction of undesirable substances and by the aquatic life, wildlife, and man. The specified levels or increased consumption demands of the new develop- concentrations applicable to plants and animals re- ment (or decreased demand as previous users are re- flect a margin of safety below the demonstrated moved by development.) The qualitative problem in- response threshold, or below the concentration which cludes both health impacts (from pathogenic and causes death within ninety-six hours to 50 per- toxic substances) and aesthetic impacts (taste, odor, cent of a test group of certain important and sensitive and clarity). The quantitative impact is a problem of animals, or plant species, 2 Standards for human con- major proportions in rapidly growing areas with only @umptionlare based primarily on dose-response,rela- limited access to fresh wate r. such as parts of the and tionships in test animals, modified by a "safety Southwest, the Florida coast, and Washington, D.C. factor.3 'table 2A shows the pollutants covered in the EPA B. APPLICABLE FEDERAL AND STATE LAWS documents and provides a brief description of sorne Current of the more common pollutants, their sources, and federal and state legislation bears directly their effects. Also included is a description of se- on the question of which types of impacts can and, in lecied water quality indicators. some cases, must be evaluated in granting land use The criteria or standards which appear in the EPA changes and/or in developing land use plans. These document have varying confidence levels. Many pol- laws are extremely pertinent to any local government lutants found in pretreatment water sup Iplies have considering an impact evaluation' program. known health effects .4 Numerous others, however, have only suspected deleterious effects when present 1. Flooding in concentrations observed in drinking water. The The National Flood Insurance Act of 1968 and its asbestos-like fibers discharged into Lake Superior successor, the Flood Disaster Protection Act of 1973, and the possibly carcinogenic chlorinated hydro- bear directly on the relationship between land devel- carbons recently found in New Orleans and Cincin- opment and flood hazards .6 Both attempt to encour- nati are cases in point. Likewise for aquatic life, the age the adoption of flood plain zoning and building toxic effects of environmentally significant pollutants codes by local communities, using subsidized flood are usually known only for laboratory conditions. insurance for existing flood plain developments as the Even more difficult is the determination of standards lever. The 1973 act (which has now replaced the 1968 for recreational uses. Although water contact and act) goes one step further by stipulating that no fed- fishing activity standards can be based on aquatic life, erally insured mortgage lender (i.e., almost all and, to some extent, on human health criteria, gen- 5. For primarily non-aesthetic criteria see, for example, R. E. Coughlin, Perception and Use of Streams in Suburban Areas: Ef- 1. EPA, Proposed Criteria for Water Quality (Washing- fects of Water Quality and of Distancefirom Residence to Stream ton, D.C.: Government Printing Office, October, 1973). See also, (Philadelphia: Regional Science Research Institute, March, 1972); EPA, Comparison of NTAC, NAS, and Proposed EPA Numerical and Doyle W. Bishop and Robert Aukermann, Water Quality Cri- Criteria for Water Quality (Washington, D.C.: Government Print- teria for Selected Recreational Uses (Urbana-Champaign: Univer- ing Office, May, 1974) (NTIS No. PB-237586); and David L. Jor- sity of Illinois, September, 1970) (NTIS No. PB195164); and B. J. dening@ Estimating, Water Quality Benefits (Washington, D.C.: Mechalas, An Investigation into Recreational Water Quality, EPA, August, 1974) (EPA-600/5-74-014). Water Quality Criteria Data Book. vol. 4 (Washington, D.C.: EPA, 2. The EPA recognizes that the importance of plant and animal April, 1972). For an example of aesthetic criteria, see L. B. Leo- species varies by geographical area. Local communities should pold, Quantitative Comparison of Some Aesthetic Factors Among thus select and apply the criteria appropriate to their area. Rivers, Geological Survey Circular 620 (Washington, D.C.: Depart- 3. See also HEW,Fublic Health Drinking Water Standards, Re- ment of the Interior, 1969). vised (Washington, D.C.:. Government Printing Office, 1962) and 6. For a more detailed description of these laws see: Peter M. the discussion of water consumption in Part 2, 11, Sec. C. Williams, "Legislation Signals New Approach to Nation's Critical 4. For a summary of the known and suspected health effects of Flood Problem,", Mortgage Banker 34 (March 1974): 18-28; and pollutants identified by the Public Health Service see, Public The League of Women Voters, "Flood Plain Management and the Health Service, Public Health Service Drinking Water Standards National Flood Insurance Program," Environmental Update on 1962 (Washington, D.C.: HEW, 1962). Water, No. 534 (January, 1975). 52 Land Development and the Natural Environment Table 2-1. PRINCIPAL WATER POLLUTANTS AND WATER QUALITY INDICATORS a. Water Pollutants POLLUTANT SOURCE EFFECT Phosphorus (P) Fertilizer, treated' and untreated Occurs predominantly as phosphate (POJ and serves as a plant nutrient which sewage, detergents can lead to eutrophication (a process of overfertilization and overproduction of water plants) which, in turn, can produce algal blooms and other nuisance conditions. Nitrogen (N) Fertilizer, treatedaand untreated As dissolved nitrogen (N2@-and like many dissolved gases at high concentra- sewage, the atmosphere tions-it is toxic to fish. As ammonia (NH3), it interferes with drinking water chlorination. As nitrite (NO2) and nitrate (NO3), it is a plant nutrient and thus can lead to eutrophication. As N03 it can be toxic to humans, especially infants, causing methemoglobinemia. Suspended solids (SS) Soil, street debris, sewage Can reduce sunlight penetration and clog animal and plant surfaces thus reducing biological activity; high levels will also cause water bodies to have a brown or muddy appearance. Heatb Nuclear generators, industrial Can be toxic to fish at high levels while at lower levels, it c 'an increase their plants susceptibility to disease and stress. Decreases dissolved oxygen (see Table 2-1-b). Bacteria Sewage, effluents with high BOD Some forms are disease-causing in man; many cause reduction in dissolved content can induce bacterial oxygen levels through biological degradation of waste (see Table 2-1-b). multiplication (see below) Other (e.g., metals, Industrial effluent, sewage addi- Some are cancer-causing or otherwise toxic to man. Polychlorinated chlorinated com- tives from treatment plants, biphenyls are generally toxic to animals, especially fish and waterfoul. pounds, exotic stormwater runoff from agricul- materials) tural lands, etc. b. Water Quality Indicators (in addition to pollutant levels) INDICATOR DESCRIPTION/COMMENTS. Biological oxygen demand (BOD) BOD is a descriptor of effluent content. It is the amount of oxygen required to completely oxidize a quan- tity of organic matter by biological processee If the organic matter is being discharged into a body of water, then this is the amount of dissolved oxygen which will be depleted from the stream. Dissolved oxygen (DO) Water bodies with high DO levels will have abundant plant and animal life (assuming that other necessary conditions exist). Low DO levels are often the result of the discharge of effluents with high BOD levels! Turbidity This is a measure of suspended solids (SS) concentration. High levels indicate high concentrations of SS and, thus, low light penetration. pH This is a measure of acidity. High quality water can display a range of values depending on natural condi- tions. However, very acidic or very alkaline water will not support much life. a. Treated at the primary or secondary level. b. This is obviously. a physical state of water rather than a pollutant. However, heat can be considered a pollutant in terms of its produc- tion and effects. C. BOD is usually expressed as BOD5 or the amount of oxygen consumed by the decomposition of the organic matter during a five-day period. However, laboratory methods are now available to measure total oxygen demand (TOD) or ultimate BOD without having to wait long periods of time for bacterial decomposition to take place. d. Sewage treatment plants using ozone (03) as a disinfective sometimes supersaturate the receiving water with DO; this can lead to fish kills. Water Quality and Quantity: Introduction and Background 53 lenders) can provide financing for developments in nonnavigable streams from the planning and control flood hazard areas unless the local government provisions. adopts land use controls which zone these areas for Many states have also assumed an active role in re- nondevelopment uses or enacts special building codes ducing water pollution by means of legislation. Where for the few structures allowed .7 Although there is no state standards are stricter than federal ones the requirement that local governments prohibit all flood states' -prevail. Even where the federal standards are plain development once controls are adopted (e.g., used, EPA encourages and to some extent requires variances could be granted), any new development in the states (and local/regional governments) to become a hazardous area will not be covered by subsidized actively involved in the program. flood insurance. This in itself should be a strong de- terrent to any new flood plain development. 3. Water Consumption As a consequence of federal action it now appears Federal and state laws pertinent to water consump- that a major element of the flood problem will be tion are only tangentially related to land develop- greatly reduced-the damage which accrues to new ment. Most laws simply regulate water purification developments in a flood plain. However, the exacer-- procedures. A new federal law (the Safe Drinking bation of existing flood conditions by increased Water Act) extends federal authority slightly by regu- stormwater runoff from new development located lating underground injection of wastes. outside flood plain boundaries is a problem which re- Section 304 of the WPCA does refer to the mains to be addressed. problem of salt water intrusion as the result of groundwater related activities, one of which could be 2. Water Pollution the extraction of water for drinking purposes. How- The federal government has an extensive history of ever, specific land use control requirements which involvement in the area of water pollution. The most would follow from this section are unclear at this recent legislation, the Water Pollution Control Act time. amendments of 1972 (WPCA), provides funds for wastewater facility construction and establishes both C. FUNDAMENTAL HYDROLOGIC PRINCIPLES effluent and water quality. standards.8 The effluent The study of water resources can be approached standards apply to all existing and new point sources from two quite distinct perspectives. One looks at the (primarily municipal sewage plants and industries) mechanical processes of water movement, storage, which discharge into navigable surface waters. The and changes in phase (solid, liquid, gas); the other water quality standards apply to all navigable waters.9 places water in the larger context of aquatic eco- Either one set of standards or the other will be the systems. limiting factor in determining the allowable effluent content from any source. In order to implement these 1. Physical Hydrology" standards an extensive permit system is being estab- The hydrologic cycle, represented schematically in lished to control the effluent content from every Figure 2-1, is a highly variable process requiring vast known point source. Under Section 208 of the act, amounts of solar energy for its operation. In essence, area-wide wastewater planning programs will control the process involves the condensation and precipita- nonpoint sources (e.g., urban and agricultural land) tion of water, the collection, transport, and storage of through land use and other control measures. How- water on and beneath the earth's surface, and the ever, the act excludes groundwater resources and evaporation of water back into the atmosphere. Sur- face and subsurface hydrology is seen to be a com- 7. A "flood hazard area" is any area covered with water (i.e., plex and interrelated series of processes including the flood plain) according to a 100-year flood record; that is to say, rapid surface runoff, surface percolation, subsurface a place where a flood has at least a one-hundredth chance of occur- interflow, and extremely slow groundwater move- ring in any one year. 8. For additional information, see Council on Environmental ment (base flow). Evaporation is accomplished abioti- Quality, Environmental Quality, Fifth Annual Report (Washington, cally (i.e., direct evaporation from surfaces) and bi- D.C., December, 1974); EPA, Draft Guidelines for Areawide otically (transpiration" by plants). Waste Treatment Management (Washington, D.C.: Government Printing Office, May, 1974); and EPA Water Quality Strategy Paper, 2nd ed., (Washington, D.C.: Government Printing Office, 10. For more information see a standard hydrology text, such March 15, 1974). as, R. K. Linsley, M. A. Kohler, and J. L. H. Paulhus, Hydrology 9. The effluent standards reflect secondary treatment of sewage for Engineers (New York: McGraw-Hill, 1975). for all municipal plants and the best practicable technology for 11. Transpiration is a physiological process whereby water is other point sources by July 1, 1977. By July 1, 1983, the standards taken up by plant roots and released as water vapor at the leaf sur- should reflect the best available technology for all point sources. face. 54 Land Development and the Natural Environment FIGURE 2-1 THE HYDROLOGIC CYCLE topographic precipitation divide lit I evapo transpiration interception depression storage unsaturated IS @___ interilOw watertable groundwater see SOURCE: Clark, op. cit. 2. Biological Hydrology12 work for understanding the hydrologic impacts of From the ecologist's point of view water provides land development. the environmental support for aquatic life forms. Not only is it the medium in which life exists, but also it D. WATER-RELATED IMPACTS OF provides transport for life-sustaining nutrients. LAND DEVELOPMENT Figure 2-2 is a flow diagram depicting the dynamics As a watershed becomes increasingly. urbanized, of an aquatic ecosystem. The living members are pri- specific and frequently dramatic impacts on flooding, mary producers, plant eaters, meat eaters, and de- water pollution, and water consumption can be ob- composers. These form a food web, the initial and served. These impacts result from (a) physical final sections of which are "pools" of nutrients. The changes to the land itself, (b) wastes generated by the system is fueled by several forms of energy and by new inhabitants, and (c) demands for water to sup- nutrients imported from surrounding land and water port various economic activities associated with ur- areas. The outputs of the system are energy in altered banization. forms, nutrients, and sediments. Oxygen is produced and consumed internal to the system, and water is the 1. Flooding medium. Development may affect the likelihood of flooding These highly simplified principles of physical and in several ways. First, the ability of the ground to ab- biological hydrology comprise the conceptual frame- sorb water may change due to soil compaction and changes in the amount of impervious ground cover 12. For additional information, see, for example, John Clark, (e.g., asphalt and concrete). This leads directly to Coastal Ecosystems (Washington, D.C.: The Conservation Foun- dation, 1974). Aquatic biology is also touched upon in "Wildlife changes in surface runoff. and Vegetation," Part 3 of this report. Secondly, the vegetative cover may be altered. For Water Quality and Quantity: Introduction and Background 55 FIGURE 2-2 MATERIAL AND ENERGY FLOWS IN AN AQUATIC ECOSYSTEM Inputs Outputs Energy Primary Energy Radiation Producers Thermal (Light) Algae Plant Eaters Chemical Thermal Aquatic Zooplankton (Fixed Org. Mechanical Macrophytes Fish Matter) (Wind) Benthosa Meat Eaters Latent Heat Fixed Org.' Higher animals Zooplankton (Evapor.) Matter (e.g., Duck, Benthos' @_J Muskrat, Fish Man) Man Nutrients Nitrogen __ip Dissolved N Dissolved Phosphorus Nutrient Nutrients C02 Pool Decomposers6 Water Precipitation Streams Detritus Sediments a. Organisms living at or on the bottom of bodies of water. b. Fungi and bacteria. c. Small particles of organic matter. SOURCE: D. C. Watts and 0. L. Loucks, Models for Describing Exchange Within Ecosystems (Madison: Institute for Environmental Studies, University of Wisconsin, 1969). example, deeply rooted plants, such as trees or native humidity and solar radiation may be observed, the grasses, are typically replaced by lawn grass with most relevant effect is on precipitation. Some cities shallow roots. Less frequently, old fields may be re- with large point sources of air pollution have been as- placed by ornamental trees and shrubs. The result is''a sociated with increased precipitation *. 13 ,change in the amount of water stored in the soil and The net effect of these changes will depend on the subsequently transpired by plants, leading in most local hydrology, physiography, and soil conditions, cases to increased amounts of surface runoff. on the extent of urbanization (both absolute and rela- Thirdly, development is frequently accompanied by tive to the watershed), on land uses, and on the spe- topographical changes and often by a reduction in cific. location of the development. It will also depend average slope. These often increase the rate of water on the severity of the storm. (Since surface runoff percolation through soil and decrease the rate of sur- will increase with severity, most precipitation becomes face runoff, although the removal of topsoil may runoff once the soil is 'saturated, relatively reducing negate or reverse the effect. the effect of development.) However, most studies of Urban storm drainage systems may replace natural urbanization have shown that the percentage of pre- drainage channels with culverts and storm sewers. cipitation which appears as surface runoff increases, The net effect is a decrease in the time it takes sur- and the time lag between onset of precipitation and face runoff to reach local streams and lakes. fd jA Finally, as a large area or region becomes urban- 13. Presumably, particulates emitted from these sources act as condensation nuclei for atmospheric moisture. See William P. ized, slight changes in climate may be noticed. Lowry, "Project METROMEX: A Review of Results," Bulletin of Although changes in temperature, wind velocity, the American Meterological Society 55 (February, 1974): 86-121. 56 Land Development and the Natural Environment occurrence of peak stream discharge decreases. Con- ample, urban stormwater runoff contributes from 40 sequently, floods increase in both frequency and to 80 percent of the total national BOD (biological ox- severity. ygen demand) discharged to surface water." Thus, urbanization not only increases the amount 2. Water Pollution of polluting material deposited in developed areas and Water pollution refers to the quality of water ultimately washed off, it also eliminates natural areas bodies which are affected by wastes generated by or where these materials could be "recycled" before associated .with development. Residential and com- reaching bodies of water. Forests and grasslands are mercial developments will produce additional quan- very successful in accomplishing this recycling. tities of sewage and related wastes, while industrial 3. Water Consumption plants often discharge a wide array of harmful wastes associated with various industrial processes. A new development (or urbanization in general) In addition to pollutants discharged from point will place additional demands on a community's or sources (i.e., sewage treatment plants or industrial neighboring households' water supply. Residential plants), water pollution can result from nonpoint and commercial developments will need water for do- source discharge s-general stormwater runoff. This mestic and other uses (e.g., lawn sprinkling), while type of pollution is due to natural processes as well as industries may need large quantities for cooling and human activities. In natural areas the death and sub- related purposes. Since our primary concern is for sequent decay of plants and animals, natural erosion water used for drinking purposes, our interest in processes, leaching of soil minerals, and generation of other uses will extend only insofar as they compete animal wastes account for most pollutants. In agricul- with personal consumption for the same supply. tural areas the use (or overuse) of fertilizers, the hus- Development may also interfere with the replenish- bandry of large numbers of animals, and the exposure ment or inflow of water to underground sources. of soil stripped of natural cover can contribute to a Placing impervious materials on land which pre- substantial increase in pollutant loadings above the viously allowed aquifers to be recharged is an ex- natural condition. In urban areas the'pollutants found ample. Large developments which use underground in runoff derive from such sources as leaf litter, an- sources may also remove water at too great a rate, imal feces, lawn fertilizer, automobile residue, and air causing water levels in surrounding wells to drop and pollution. total available volumes to decrease. On a national basis, the order of land uses (or land Finally, land development may decrease the pre- cover) from most polluting to least polluting based on treatment quality of water due to additional quantities total solids, nitrates, and phosphates is as follows: of pollutants discharged from point sources, from cropland, urban land (considering only residential -stormwater runoff, or from septic tank leach fields. land use), grassland, and forest. Urban stormwater This may either increase the cost of purification or runoff is the major contributor of a variety of pollu- decrease the quality of the water after treatment. The tants during storms, and even on an annual basis it withdrawal of fresh water from underground sources rivals sewage plant effluent in total loadings. 14 For ex- in coastal areas may also lead to salt water intrusion by reducing the hydraulic pressure that formerly 14. James D. Sartor, Gail Boyd, and Franklin J. Agardy, "Water acted as a barrier. Pollution Aspects of Street Surface Contaminants," Journal of Water Pollution Control 46 (1) (March 1974): 458-67; and James D. Sartor and Gail Boyd, Water Pollution Aspects of Street Surface 15. Anne M. Vitale and Pierre M. Sprey, Total Urban Water Contaminants (Washington, D.C.: EPA, November, 1972) Pollution Loads: The Impact of Storm Water (Rockville, Md.: En- (EPA-R2-72-081). viro Control, Inc., 1974) (NTIS No. PB-231 730). Water Quality and Quantity: Introduction and Background 57 11. METHODOLOGICAL APPROACHES The conceptual framework and the individual 1. impact Measures analytical techniques for estimating water quality and Two alternative measures of flood problems are quantity impacts are specific to the various impact suggested:' areas. Thus, flooding, water pollution, and water con- sumption will be discussed separately. 1. Change in the number of people endangered The sections on flooding and water pollution em- by flooding plus the change in the expected phasize the use of generalizable mathematical for- property damage (or the value of property mula.s which relate the areal extent and type of devel- endangered). opment (among other factors) to stormwater runoff. OR A broad range of approaches, from simple linear 2. Change in flood frequency or severity. approximations to complex computerized models, will be discussed. The water pollution section also Measure I best expresses the end impact on man and discusses sewage generation. Finally, the analytical is thus preferred. It is also the most difficult and ex- treatment of water consumption impacts will focus on pensive to obtain values for. Measure 2 is the fallback methods of estimating total supplies and the use of measure. Values for Measure 2 are used to compute coefficients which reflect usage rates for different values for Measure 1, but they can also be used to re- types of development. flect changes in the probability of flooding alone. In this connection one speaks of a flood which can be A. IMPACTS ON FLOODING expected to occur on the average of once in two, five, With the full implementation of the Flood Disaster ten, fifty, 100 or 500 years. (This corresponds to a Protection Act discussed previously the exposure of probability of occurrence of fifty, twenty, ten, two, new structures to flood hazards will be vastly re- one and 0.2 percent for any one year.) Obviously, as duced, although the few future proposals for flood the frequency decreases the magnitude increases. plain development will still require careful review.. Since a number of dimensions are suggested by However, a flood-related problem will remain-the Measure 1, a tabular display of the results may be effect of changes in stormwater runoff patterns suitable. An example is shown in Table 2-2. The re- caused by new development to existing structures sults are expressed as the additional number of peo- within flood hazard areas. This effect can be de- scribed in terms of increased damage to structures 1. A third alternative would be "the amount of impervious already at risk and increased risk to structures cur- ground cover relative to the budgeted amount" where budgets have been prepared for the watershed in question. See section A-3 rently safe, meaning those located just beyond pres- of this chapter and section A of part 2, 111, for a more detailed dis- ent flood plain boundaries. cussion. 59 Table 2-2. AN ILLUSTRATIVE FORMAT FOR PRESENTING THE EFFECT OF A DEVELOPMENT ON RISKS FROM FLOODING FLOOD FREQUENCY ADDITIONAL PEOPLE JEOPARDIZED ADDITIONAL PROPERTY VALUE JEOPARDIZEDa OR MAGNITUDE - Within Outside Within Outside Development Development Development Development (millions of dollars) Floods Worst in 10 years 1,000 0 $10 0 Worst in 50 years 3,000 100 $40 $.5 Worst in 100 years 3,000 100 $40 $.5 a. Alternatively, the expected property damage could be used (this would be less than the total in jeopardy, as in a case where a property worth $ 100,000 is put in jeopardy, but where the likely damage to it may be $25,000). ple at risk and the expected damage caused by floods, The first estimates rainfall/runoff/strearn flow rela- of various frequencies. It may also be desirable to tionships; the second routes the runoff into existing display the maps delineating flood plains for the ten, channels and estimates flood levels for bodies of sur- fifty, 100 and 500- year floods. This is extremely effec- face water in the watershed. A few of the more com- tive in communicating the impact on individual plex models accomplish both types of analyses. properties. The sections to follow present descriptions of alter- native techniques and, where possible, evaluations. of 2. General Analytical Approaches thern.' The last few years have witnessed a dramatic In order to measure the hydrologic changes that proliferation of the more complex hydrologic models. have occurred as a result of urbanization in a given Selection of the techniques reviewed here was based watershed (i.e., retrospective analysis), one can primarily on their current popularity or represent- either trace and relate the hydrologic and develop- ativeness of alternative approaches. Unfortunately, mental changes over time (controlling for all other the dearth of information on input requirements and variables), or compare the changes with those ob- accuracy of the various techniques reduces our ability served in an "identical" watershed which has not to appraise the various approaches. Where possible experienced land development. The first approach is we have attempted to survey both the developers and limited by the difficulty in accounting for all users of particular techniques, in order to gain at least nondevelopment-related factors which could fffect qualitative insights. the watershed's hydrology. This is especially true for 3. Estimating .Impacts on Stream Flow climatic factors, which can display extreme variabil- ity from year to year. In some cases simple models The extent to which a proposed land development have been used to estimate the fraction Of observed will cause significant changes in the flow of local hydrologic changes due to.climatic factors alone, the streams is dependent on numerous characteristics of residual then being attributed to land use changes. both the development and the watershed in which ifis The second approach is limited by a similar to be located. In determining whether a particular problem. No two watersheds are identical. Thus, dif- development is large enough to justify an individual ferences must be carefully measured and accounted assessment, the most meaningful and widely used fac- for. These differences include physiography, soil tor is "percent imperviousness." That is, the amount structure, vegetation, land use, and watershed size, of land to be covered with impervious material, as well as climate. such as concrete or asphalt, is expressed as a per- In assessing the impact of future developments pre- centage of the land on the site and as A percentage of dictive techniques calibrated to local conditions are the entire watershed. However, in order to determine frequently employed. Alternatively, analogies to simi- lar watersheds can be drawn. If the latter approach is used, one must again be careful to account for dif- 2. For more inclusive treatment see, for example, J. W. Brown ferences between the test and the reference situa- et al., Models & Methods Applicable to the Corps of Engineers Urban Studies (Vicksburg, Miss.: Army Corps of Engineers, June, tions, as in retrospective analysis. 1974); and Ray K. Linsley, A Critical Review of Currently Avail- Flood analyses which involve the use of predictive able Hydrologic Models for Analysis of Urban Stormwater Runoff (Palo Alto, Calif. Hydrocomp International, August, 1971). The techniques or models are typically comprised of two first is particularly relevant to the subject here as individual models parts, a hydrologic analysis and a hydraulic analysis. are described and to some degree evaluated systematically. 60 Land Development and the Natural Environment how large these percentages must be to justify an as- Rantz provides rules of thumb and some empirical sessment, the sensitivity to imperviousness of indi- data (from the San Francisco area) which can be used vidual watersheds within the community must be as- to relate various types of development to "percent certained. This can be done through retrospective imperviousness" and thus to determine C.6 A pro- analyses (as discussed above) or by applying analyti- posed development will change the "percent impervi- cal techniques to the watersheds and observing the ous" and thus values for estimated stream flow effect that hypothetical degrees of imperviousness through changes in C. have on estimated stream floW.3 As mentioned previously, the Rational Method is one of the most popular techniques for estimating a. Anaiytical Techniques stream flow, especially for watersheds undergoing ur- The following techniques differ in base data re- banization. It is simple and provides estimates of quired, complexity of computation, type of results peak stream flow-a quantity directly pertinent to generated, and applicability to different types of flooding. However, it is limited in application to small watersheds. The simpler techniques will be presented watersheds of no more than a few square miles and first. Each technique is used to estimate water flow in preferably less, a fact not recognized by all users .7 In streams and/or lakes. addition, there have been few attempts to compare computed with observed values. In at least two vali- Rational Method-One of the most widely but, in dation studies, errors were as large as 60 percent." many cases, inappropriately used techniques is the Another test showed that only 35 percent of the esti- Rational Method.' It is a straightforward and simple mates were within 25 percent of the observed values. computational, procedure applicable to streams and It is thus of dubious utility for anything more than based on the following relationship: gross estimates. Q CiA Flood Frequency Analysis-As the name implies, where: Q peak (short-term) runoff rate (or stream this technique estimates stream flow during flood in- flow) in cubic feet per second cidents from actual flood data.9 These data are then C a c Ionstant dependent on basin character- related by empirical analysis of watersheds in the istics region under study to climatologic, topographical, average precipitation intensity in and if possible, land use characteristics. The impact inches/hour (different values are used for of a new development is then estimated, using these storms of different degrees of severity) empirical relationships. A drainage area in acres Mote specifically, data on peak stream flow are compiled for all streams within the region on which The coefficient C is dependent on many watershed gauging stations are located.10 These data are then variables, such as shape, slope, soil moisture content and capacity, ground cover, and terrain, as well as on the severity of the storm.5 (As noted previously, 6. The relationship between land use categories and "percent imperviousness" for other geographical areas can be found in: development can affect many of these variables.) Suc- Water Resources Engineers and the Hydrologic Engineering cess in assigning appropriate values to C which re- Center, Corps of Engineers, Management of Urban Storm Runoff, flect all of these factors has not been obtained. Typ- (New York: American Society of Civil Engineers, May, 1974); George Dempster, Jr. Effects of Floods in Dallas, Texas Metropoli- ically, the total effect of urbanization is represented tan Area (Austin, Texas: Geological Survey, January, 1975); and by "percent imperviousness," although the extentof Joachin Tourbier and Richard Westmacott, Water Resources Pro- storm sewerization is implicitly included as well. tection Measures in Land Development-A Handbook (Newark: Water Resources Center, University of Delaware, April, 1974). 7. Some have suggested the the upper limit be 200 acres 3. This is further discussed in Part 2, 111, under the heading, (approximately V3 square mile). See Wright-McLaughlin Engineers, "Planning versus Project Review." Urban Storm Drainage Criteria Manual (Denver: Denver Regional 4. For additional information, see American Society of Civil Council of Governments, 1969). Engineers, "Design and Construction of Sanitary and Storm 8. Error values are observed-estimated differences as a percent- Sewers," Manuals and Reports on Engineering Practices, No. 37 age of the observed. These occurrences were for watersheds of less (Washington, D.C., 1969); S. E. Rantz, Suggested Criteria for Hy- than fifty acres. See D. Earl Jones, Jr., "Urban Hydrology-A Re- drologic Design of Storm-Drainage Facilities in the San Fran- direction," Civil Engineering (August, 1967): 58-62; and J. C. cisco Bay Region, California (Menlo Park, Calif.: U.S. Geological Schaake, J. C. Geyes, and J. W. Knopp, "Experimental Examina- Survey, November 24, 1971); and James K. Searcy, Design of tion of the Rational Method," Journal of the Hydraulics Division Roadside Drainage Channels, Hydraulic Design Series #4, Bureau Proceedings of the American Society of Civil Engineers (No- of Public Roads (Washington, D.C.: Government Printing Office, vember, 1967): 353-70. May, 1965). 9. For additional information, see Rantz, op. cit. 5. Runoff as a percent of precipitation increases as the soil be- 10. Gauging stations are manmade structures designed to mea- comes saturated and the surface depressions are filled. sure stream flow. Water Quality and Quantity: Methodological Approaches 61 organized into frequency distributions for each Table2-3. RESULTS OF A FLOOD FREQUENCY ANALYSIS stream according to standard statistical procedures." (For Illustration Purposes Only) Values for stream flow for floods of various recur- RECURRENCE COEFFICIENT rence intervals (typically, two, five, ten, fifty and 100 INTERVAL MULTIPLE REGRESSION OF MULTIPLE years) are then mathematically related to the basin (YEARS) EQUATION CORRELATION characteristics of the test watersheds. 12 If the set of test watersheds shows wide variation in these charac- 2 Q, = 0.069AO.913PL.6@ 0.964 teristics (e.g., the gauged basins include large as well 5 Q5 = 2.00A0.925P1.2D6 0.976 10 Q1, = 7.38AO.922F--928 0.977 as small ones, urbanized as well as natural ones, ones 25 Q21 = 16.5AO-912PO.797 0.950 with high levels of precipitation as well as dry ones), 50 Q50 = 69.6AO.847pO.511 0.902 these factors can be analyzed for their effect on stream flow. If not, relationships developed for other SOURCE: Rantz, op. cit. regions can possibly be substituted if interTegional dif- NOTES: ferences are not too great. The natural basin charac- Q = stream flow, in cubic feet per second teristics and forecasted land use changes (either gen- A = drainage area, in square miles eral growth or single large developments) are then P = mean annual basinwide precipitation, in inches used to estimate flow levels for the stream in ques- These results are specific to the unusual hydrological and climato- tion. Measures of development are typically very logical features of various watersheds in the San Francisco Bay gross, such as "percent urbanization" as measured area. by areal extent of structures, lawns, pavements, etc. Thus, this technique is best applied only where the Other Simple Techniques-Most other techniques new development represents a large increase in a which do not involve the use of computerized hydro- watershed's degree of urbanization. Again, more de- logic models are refinements of the methods already tailed guidelines can be found in the Rantz report.13 presented. 15 For example, the Unit Hydrograph Tech- Table 2-3 shows the results of a Flood Frequency nique expands the Flood Frequency Analysis by esti- Analysis of forty watersheds in the San Francisco mating the time distribution of runoff from a storm region. Storms of various recurrence intervals are re- rather than just peak discharge .16 (A hydrograph for a lated to several basin variables (only precipitation and hypothetical basin is shown in Figure 2-3.) This infor- basin size proved significant) and corTelation coeffi- mation is useful if certain flood control devices are cients reported." As shown, the technique is highly employed in a watershed. Total, rather than just peak successful in reproducing past events, althoughfuture flows, are needed to estimate the effectiveness of events can only be estimated accurately to the extent storage facilities, such as levees and dams. Hydro- that future hydrologic relationships are similar to past graphs are also useful for showing the impact of ur- ones. banization on the timing of peak discharge. In addi- tion, Rantz has reported a slight improvement in accuracy for estimates of peak discharge values as 11. The data are fitted to a Pearson Type III distribution. See compared to the Flood Frequency Analysis, although Water Resources Council, Hydrology Committee, A Uniform Technique for Determining Flood Flow Frequencies, Bulletin No. the computation procedures are considerably more 15 (Washington, D.C.; December, 1967). involved. A recent study sponsored by EPA further 12. These relationships are determined by regression analysis, documents the utility of this method." typically using an equation of the form: Each of the techniques discussed thus far which es- Q = aXbye timate short-term fluctuations in flow (i.e., peak flow) where: Q = flow use a single measure to reflect the hydrologic effects x, y . = are variables such as watershed area and pre- of urbanization. Even though this measure is fre- cipitation a,b,c ... = are constants, the values for which are deter- quently called the "percent of imperviousness" it mined by analyzing the data for Q, x, y, often encompasses the other major hydrologic-related etc., collected for various watersheds 13. Rantz, op. cit. 15. For a discussion.of other simple techniques which may be 14. Correlations measure the agreement between data. Values of used to estimate runoff, see EPA, Water Quality Management for 0 signify no agreement while values of 1.0 indicate perfect agree- Urban Runoff (Washington, D.C.: EPA, December, 1974) (NTIS ment. Values about 0.7 reflect "good" agreement. Correlation PB241689/AS). coefficients as applied to stream flow data must be interpreted with caution. The specific coefficient values are a function of the ade- 16. For much information see Rantz, op. cit., or any standard quacy of the stream gauging program, as well as the accuracy of hydrologic text such as Linsley, Kohler, and Paulhus, op. cit. the technique. In addition, other measures of validity can be, and 17. E. F. Brater and J. D. Sherifl, Rainfall-Runoff Relations on for some techniques have been used. (Correlation coefficient§ cited Urban and Rural Areas (Cincinnati: EPA, Office of Research and in this report are the statistic "r- unless otherwise noted.) Development, May, 1975). 62 Land Development and the Natural Environment FIGURE 2-3 Another factor not accommodated well by these AN EXAMPLE OF HYDROGRAPH FOR A techniques is the influence of site design. Since the HYPOTHETICAL WATERSHED options for diverting or detaining runoff through landscaping and the construction of special facilities Peak discharge are numerous, it is unlikely that the impact of future development on flood potential can ever be estimated with a high degree of certainty using these methods. However, rough approximations of the mitigating ef- U Onset of rain fect of runoff detention devices can be made, using design specifications found in relevant engineering reports.19 Termination of rain Complex Hydrologic Models-The relatively sim- ple techniques discussed so far are simple because TIME they abstract only the more important features of the a. Actual Hydrograph hydrologic cycle while ignoring the rest. The Rational Method, for example, does not treat evapotranspira- tion, soil moisture replenishment, or subsurface water flow explicitly (see Figure 2-1). Rather, it relies on P4 empirical measurements of rainfall intensity and the coefficient C, which presumably encompasses the to- U cally important variables. Likewise, the Flood Fre- quency Analysis attempts to associate presumed causes (e.g., basin configuration, precipitation, and land use) with effects (floods of various severity) but with no direct analysis of hydrologic processes. TIME Complex hydrologic models, on the other hand, at- tempt to simulate more elements in the hydrologic b. Mathematical Abstraction cycle. "Event models" are used to estimate stream flow during single events or storms. They are consid- factor as well-the extent to which natural drainage erably more complex than the simple techniques, but channels have been modified or replaced by storm stop short of simulating the complete hydrologic sewers. It would, of course, be useful to know the cycle. "Continuous models" are based on a detailed relative effect of each so that the proposed develop- accounting procedure which traces the fate of precipi- ment could be characterized by each separately. tation within a given watershed on a daily, hourly, or Luna Leopold has compiled and presented in tabu- even subhourly basis. Figure 2-4 is a flow chart for lar and graph form the results of flood frequency one representative continuous model. In order to studies of the effects of both factors on stream compute stream flow according to this procedure, flows."' Since the individual studies were undertaken short-term data on temperature, precipitation, hours in different geographic regions the combined results of sunlight, topography, vegetation, soil type, and are national averages and may or may not be appli- land cover are necessary. cable to specific areas. However, they could possibly Many of the complex models also employ stream be used to suggest when the other techniques may routing routines which assign surface and subsurface give low or high estimates when applied to specific runoff to natural and artificial channels in various developments. If the new development will be portions of the watershed. The technique used to sewered to an unusually high or low extent when route the flows is one of the main points of differen- compared with the developments used to calibrate or tiation among the various models. particularize the technique, the estimates could be ad- Once the precipitation has been translated into sur- justed up or down, perhaps by a factor equal to those face and subsurface flows, which in turn have been in the Leopold reference. The resulting estimate routed into existing waterways, and the overall model would still be approximate but to a lesser degree. 19. American Public Works Association, Practices in Detention 18. Luna B. Leopold, Hydrology for Urban Land Planning-A of Urban Stormwater Runoff, Special Report No. 43 (Chicago, Guidebook on the Hydrologic Effects of Urban Land Use, Geologi- 1974) (NTIS No. PB-234-554). See also, Tourbier and Westmacott, cal Survey Circular 554 (Washington, D.C.: Geological Survey, op. cit.; and Meta Systems, Inc., Land Use Environmental Quality 1968). Relationships (Washington, D.C.: EPA, forthcoming). Water Quality and Quantity: Methodological Approaches 63 FIGURE 2-4 FLOW CHART OF COMPUTATIONS FOR A COMPLEX HYDROLOGIC MODELa Actual Precipitation, Potential Evapotrans- I Evapotranspiration I piration, Temperature, Radiation L -------- J ----------------------- SNOWMELT Interception < Interception Storage impervious Area Surface Runoff Upper Overland Channel Infiltration Zone Flow inflow Interflow Upper Zone Interflow Channel Storage Inflow - - - - - - - - - - - - - - - - - - --- - - - - - - - Lower one Lower Zone or Upper Zone Storage Ground ater Depletion Stora e Active or Deep Groundwater Storage Groundwater Channel Channel - - - - - - - - - - - - - - - - Storage inflow Routing Deep or Inactive Groundwater r- - - - - - - - - Storage Simulated Streamflow L- - - - - - - - - -j SOURCE: Modified from R. Linsley and N. Crawford, "Continuous Simulation Models in Urban Hydrology, "Geophysical Research Letters, No. I (May, 1974): 59-62. a. This diagram refers to the "lands" module of the Hydrocomp Simulation Program. 64 Land Development and the Natural Environment calibrated for a similar watershed with stream flow tion with less accuracy than the complex ones. The records, estimates of past and/or future flows are almost total lack of reported information on costs and made for the watershed in question. The results are accuracy necessitates reliance on theoretical consid- expressed in terms of continuous stream flow hydro- erations as the basis for appraisal. graphs for each of the stream reaches into which the We have already mentioned the primary difference stream has been divided. The past or future impact of between complex hydrologic models and most simple changes in land cover (e.g., due to development, techniques, but it is worth noting again. It is basically reforestation, conversion to agricultural uses), in the difference between specifying relationships based channel configuration, or in flood control facilities on observed statistical associations and the simula- can then be simulated. tion of underlying, empirically tested processes which This description is generally applicable to all con- are responsible for the observed associations. Both tinuous hydrologic models but especially those based can be equally accurate for reproducing past events on or modified from the Stanford Watershed Model .20 for the calibrated watershed, but the second approach An abbreviated evaluation of complex models, as is theoretically far superior for estimating future well as simple hydrologic techniques, appears in the events, or events in a watershed to which the model next section in tabular form to aid in comparative as- has not been calibrated. Confirmatory empirical evi- sessment .21 dence is generally lacking, however. Table 2-4 repre- In summary, these models are much more satis- sents an attempt to organize and present descriptive fying from a theoretical perspective, although evi- material on the various techniques in a standard dence for purposes of accuracy comparison is format. lacking. Most have the capacity to estimate short- For the planner seeking to select from among the term changes in flow and the effects of site design available techniques (especially in the absence of spe- features, including changes to the drainage system. cific cost and accuracy figures), a very qualitative as- One additional approach worth noting is the simula- sessment may be valuable. All of the simple tech- tion of long-term stream flow by a mathematically niques described can be used in-house by planners produced stochastic process .22 The concept is quite who have some familiarity with them. In addition, simple-hydrologic processes exhibit many features flood frequency studies for individual watersheds of a random series of events and could be simulated may have already been undertaken by the local U.S. by an appropriately synthesized stochastic process. Geological Survey (USGS) field office. The more This requires the use of a digital computer. In addi- complex techniques will require the use of a com- tion, the results have not been as accurate as was puter and often a consultant. These will most likely hoped. For short-term stream flow prediction and for give better results, but to an unknown degree. estimation of the impact of changing land use pat- All of the techniques require climatologic and hy- terns, other approaches seem more desirable. drologic data as input. The National Weather Service (NWS) maintains daily precipitation records for b. Comparison and Summary various periods of time at 10,000 locations nationwide A discussion of the comparative advantages and and hourly records at 2,506 of these. Hourly records disadvantages of hydrologic techniques cannot pro- of a variety of other meterological data for seventy ceed much beyond the obvious. The simple tech- years are available at approximately 600 first-order niques are less expensive and produce less informa- stations .23 Local data, including that produced by the volunteer observer network, may greatly expand the 20. See N. H. Crawford and R. K. Linsley, Digital Simulation in official NWS system. The National Weather Records Hydrology; Stanford Watershed Model IV, Department of Civil Archives are another rich source of meteorological Engineering Technical Report No. 39 (Palo Alto, Calif.: Stanford data .24 University, 1966). 21. Numerous events and continuous models are available. Re- The USGS operates most of the stream-gauging cently, several comprehensive reviews of many of these have been published. See, for example, Marsalek, op. cit.; and A. Brand- stetter, Comparative Analysis of Urban Stormwater Models (Rich- 23. These data are available in the following Weather Bureau land, Wash.: Pacific Northwest Laboratories, Battelle Memorial publications or data sets: regional Hydrological Bulletins, Chmato- Institute, 1974). See also the description of SWMM and STORM logical Data and Hourly Precipitation. These are available at (two federally developed runoff models which can also be used to Weather Bureau offices and at field offices of such agencies as the estimate stormwater runoff quality) in Table 2-4. Corps of Engineers, Bureau of Reclamation, and Soil Conservation 22. Leo R. Beard, Simulation of Daily Strearnflow, Technical Service. Paper No. 6 (Davis, Calif.: Army Corps of Engineers, Hydrologic 24. Environmental Data Services, National Weather Records Engineering Center, 1967); and Linsley, Kohler, and Paulhus, op. Archives, Environmental Science Services Administration, Federal cit. Building, Asheville, N.C. 28801. Water Quality and Quantity: Methodological Approaches 65 ON Table 2-4. COMPARISON. OF TECHNIQUES USED TO ESTIMATE CHANGE IN STREAM FLOWa TYPES OF COMPUTING NAME WATER BODIES WATERSHED REQUIREMENTS INPUT COST OUTPUT ACCURACY Rational Streams Less than Compilation of pre- Precipitation depth- Relatively low Peak stream flow for Some reports of errors Method approximately cipitation tables, frequency-duration storms of various de- as great as 5017b in re- 5 square mi. manual computation tables, percent im- grees of severity producing past pervious ground cover eventse in the watershed Flood Fre- Streams, lakes, No limit Access to a digital Stream flow records Low-medium (since Peak stream flow for High for reproducing quency estuaries computer desirable to for gauged streams, additional time-con- storms of various de- past events once it has Analysis perform regression watershed size and suming calculations grees of severity been calibrated; un- analyses and to fit slope, average annual are necessary) known for future flood data into the ac- precipitation, and land events cepted distributional use for numerous form watersheds for several years Hydrocomp Streams, lakes, No limit Designed for use on Hourly precipitation Approximately Continuous stream High for reproducing Simulation reservoirs the IBM 360 or 370 and evaporation; $10/acre for small flow hydrographs for past events and Program computer extent, location, watersheds, consider- as many points in the "good" for future (HSp)b type of sewerage, and ably less for large ones watershed and for as events as rated by the ground cover in water- many years as desired developers, although shed; channel configura- no documentation is tion (for snowfall-daily available maximum and mini- mum temperatures, CD point, wind velocity, radiation and cloud cover desirable) a. Each of the techniques can estimate flows for almost any number of points within the watershed that is desired. The HSP is limited by the time needed to compute flow within CD river reaches. The smallest reach modeled has been about 1/2 mile in length. @4 sw b. Norman H. Crawford, Studies in the Applications of Digital Simulations to Urban Hydrology (Palo Alto, California: Hydrocomp International, Inc., September, 1971); and Hydrocomp International, Inc., Hydrocomp Simulation Programming Operations Manual (Palo Alto, California, February, 1972). c. D. Earl Jones, op. cit., and J. C. Schaake, et al., op. cit. stations in the United States. Records of stream flow sectional areas at various points along the valley, are maintained at USGS regional offices and at nu- "roughness" or indicators of flow impedance due to merous public libraries. Unfortunately, most gauged vegetation and other factors both in the stream watersheds are located in rural areas. channel and in overflow areas, and characteristics of manmade structures affecting flow. These data are 4. Estimating Impacts on the Extent then used as inputs for calculations of (1) total energy of Flooding of the flowing water at each point where cross- Once the change in runoff, and thus stream flow, sectional areas have been measured, and (2) energy from new land development has been ascertained, the losses due to frictional forces acting on the flowing next step is to translate this change into depth and ex- water between cross-sections. These values are then tent of flooding. This involves construction of water combined with stream flow values for various pat- surface profiles (i.e., the changing elevation of the terns of precipitation for each reach, obtained by water surface over the length of the stream) and the using one of the previously discussed techniques (or a delineation of both flood plains and floodways (areas similar one) and then translated into a water surface within the flood plain over which most of the flood level above the stream bed in each reach. water is discharged). Figure 2-5 contains an example The results can be presented in tabular as well as of a map and a cross-sectional view of streams, flood- graphic or map form, similar to that found in Figure ways, and flood plains. The underlying computa- 2-5. Flood plain maps and diagrams must be prepared tions (usually called backwater calculations) take into from the surface water profiles according to guide- account river channel and valley configuration as well lines found in the guidebook prepared by the Federal as the effect of manmade structures, such as dams, Insurance Administration (FIA) of HUD as part of levees, and bridges. The latter may. or may not be the Flood Disaster Protection Act .27 The program has part of a new development, but even existing flood been written for use (with minor modification) with control devices or stream obstructions must be ac- many high-speed computers .211 counted for in estimating the height and extent of 5. Estimating Impacts in Terms of flood waters. Damages and Risks a. Analytical Techniques Once the additional runoff caused by new develop- Several highly developed computerized models are ment has been calculated and translated into flooding now available for making these calculations. How- depth and extent, this information can be used to esti- ever, the one developed by the Hydrologic Engineer- mate the impact on the community in terms of poten- ing Center (HEC) of the Corps of Engineers is by far tial dollar damage and people at risk (Measure 1). the most widely used. Due to the popularity and rep- FIA has developed a set of actuarial rate insurance resentativeness of this model and to the existence of premium tables based on correlations between flood other, more detailed comparative reviews of hy- severity and property damage in various geographical draulic models, the following discussion is limited to regions and over an extended period of time.'9 From the HEC model .25 these can be estimated the fraction of a structure likely to be damaged, given its location in the flood HEC-2-The Hydrologic Engineering Center has plain and the frequency of flooding. By estimating the been developing and refining models to compute sur- expected damage to all flood-prone property within a face water profiles for a number of years .26 HEC-2 is watershed both with and without the new develop- the most efficient and comprehensive effort thus far ment, the impact attributable to the new development but is only applicable to streams. To prepare inputs can be ascertained. for the model, the river system in question is subdi- The insurance premium rates actually incorporate vided into a number of fairly homogeneous reaches. both the factors of location in the flood plain and of Measurements are made of stream bed slope, cross- frequency of flooding, since they are based on the dif- 25. See Bill S. Eichert, "Survey of Programs for Water-Surface 27. Federal Insurance Administration, Flood Insurance Study, Proffles," Journal of the Hydraulics Division, Proceedings of the Guidelines and Specifications (Washington, D.C.: HUD, January, American Society of Civil Engineers 96 (HY2) (February, 1970): 1975). 547-63. This review article is purely descriptive, however. No at- 28. Memory requirements are approximately 60,000 words and tempt is made to assess relative costs and accuracies. four or more magnetic tapes plus input-output units such as those 26. Hydrologic Engineering Center, water Profiles -Prelim- available on the CDC 6600, IBM 360 or 7094, and GE 625. inary (Davis, Calif.: Corps of Engineers, February, 1969) and 29. For a discussion of the application of these tables in the Hydrologic Engineering Center, HEC-2: Water Surface Profiles construction of Flood Insurance Rate Maps under the Flood Disas- (Davis, Calif.: Corps of Engineers, October, 1973). ter Protection Act, see Federal Insurance Administration, op. cit. Water Quality and Quantity: Methodological Approaches 67 FIGURE 2-5 REPRESENTATIONS OF THE EXTENT AND DEPTH OF FLOODING RIVER 50 yr. flood plain boundary 100 yr. flood plain boundary a. Flood Plain Map 100 YEAR FLOOD PLAIN FLOODWAY FLOODWAY FLOODWAY.,,, FRINGE FRINGE TREAM <-CHANNEL FLOOD ELEVATION WHEN CONFINED WITHIN FLOODWAY ENCROACHMENT ENCROACHMENT C D A B AREA OF FLOOD PLAIN THAT COULD FLOOD ELEVATION BE USED FOR DEVELOPMENT BY BEFORE ENCROACHMENT RAISING GROUND ON FLOOD PLAIN LINE A B IS THE FLOOD ELEVATION BEFORE ENCROACHMENT (LAND FILLING) LINE C D IS THE FLOOD ELEVATION AFTER ENCROACHMENT (LAND FILLING) b. Flood Plain Cross Section SOURCE: Federal Insurance Administration, op. cit. ENCRO @ENCROACHMENT AcHMI3,NrT A B @MILD 68 Land Developm ent and the Natural Environment ference in water depth between the ten-year and 2. Change in the ambient concentration of each 100-year floods .30 The difference in depth can be esti- pollutant (relative to standards). mated for any location in the flood plain directly from the previous analyses. As an approximation of long- Measure I is the preferred measure, as it is more re- term expected damage, the appropriate actuarial rate flective of the end impact on man. "Change in the (in dollars per one thousand dollars of value) can then monetary value of the pollution-caused damage" is perhaps even more desirable as a quantitative mea- be multiplied by the market value of each structure in sure of end impact, although the state of the art is not the flood plain and summed up for all structures ' 31 yet advanced to the point where its routine use could A simpler but less detailed approach is to express expected damage as the number of structures and be recommended, as will be discussed subsequently. their total market value at risk for floods of various Measure 2 is less detailed and probably simpler to es- frequencies. Impact is again the difference (in market timate. It thus can be used where limited resources value) with and without the development. for project evaluation preclude the use of Measure 1. We have also suggested that impact be expressed In order to make the values generated for Measures as numbers of persons at risk. This information 1 and 2 more meaningful, reference must be made to should be obtainable from census tract data. Ex- the relationship of pollutant concentrations to safety pected injury may be much more difficult to deter- and desired water use. At -present, the standards pro- mine, although FIA or other federal agencies adminis- posed by EPA and other organizations reflect the cur- tering disaster relief may have attempted to correlate rent state of knowledge, although local communities data on deaths and injuries due to flooding with flood may decide to use other standards as well .33 Mea- severity, the size of the population exposed, and sures I and 2 may be stated in terms of average other related factors. This would allow the calculation annual concentrations compared to the standard, the of estimates for deaths and injuries. number of times the standard will be exceeded in a year, or some similar expression. B. IMPACTS ON WATER POLLUTION Once changes in values have been measured or es- timated at specific points in a body of water, they can The procedure to be described for assessing the im- be viewed individually or combined to obtain a single pacts of land development on water pollution consists or a few values for the entire body. An index can be of four distinct steps: assessing current discharge used which combines values for each of the pollutants levels, current ambient concentrations, future dis- assessed and/or for each geographical point for which charge levels, and future ambient concentrations. estimates were made. Several indices have been pro- These steps are necessary in order to place the im- posed and applied in numerous communities .34 How- pact of development (either generalized development ever, the use of indices tends to obscure the signifi- or specific projects) in proper perspective. In addi- cance of changes in the concentration of any one tion, the first three steps will generate the requisite pollutant or at any one point. We thus recommend data to be used as input for the analytical techniques that, if indices are used, values for individual pollut- to be used in the fourth step. ants and individual locations also be provided. Measure I further assumes that the summations of 1. Measures, Standards, and Indices changes in ambient concentrations for several pollu- Impacts on water pollution may be assessed by the tants and at several points in a body of water can be following measures :32 interpreted in terms of changes in permissible or tol- erable uses. This interpretation must again rely on 1. Change in the permissible or tolerable usability rules-of-thumb based on observed correlations of the water in question and the number of peo- between ambient concentrations and the behavior ple affected. and/or preferences of water users .35 In order to OR 33. Suggested standards were discussed in Part 2, 1. 30. Floods occurring more often than once every ten years or 34. See, for example, James W. Curlin, National Environmental less than once every 100 years are thus ignored. Policy Act of 1969, Environmental Indices-Status of Development 3 1. For a discussion of using assessment records as indicators of Pursuant to Sections 102 (2) (B) and 204 of the Act (Washington, property value see, Thomas Muller, Estimating the Impacts of Land D.C.: Congressional Research Service, Library of Congress, De- Development on the Private Economy (Washington, D.C.: The cember, 1973); B. J. Berry, et a]., Land Use, Urban Form, and Urban Institute, forthcoming). Environmental Quality (Chicago: University of Chicago, 1974); and 32. An alternative measure is "the quantity of effluent to be The Council on Environmental Quality, Environmental Quality, generated compared to the budgeted amount" where a budget has CEQ's Third Annual Report (Washington, D.C.: CEQ, 1972). been prepared for the water body in question. See Part 2, 111, 35. The most relevant data can be found in Bishop and Auker- Section A, for a more detailed discussion. mann, op. cit. Water Quality and Quantity: Methodological Approaches 69 express the evaluation results using Measure 1, a P = quantity of pollutant discharged by point simple format such as that illustrated in Table 2-5 sources may prove effective. N = quantity of pollutant discharged by non- In some situations it may be desirable to further point sources subdivide the water uses listed in Table 2-5. Since the I = quantity of pollutant in the water en- conditions necessary for trout fishing, for example, tering the area are considerably different from those for bass, sub- S = quantity of pollutant precipitated out of categorizations would be necessary if a trout stream solution in the area were being degraded or improved. D = quantity of pollutant decayed or trans- formed in the area 2. Measuring/Estimating Current Discharge Levels If long-term (i.e., monthly or yearly) pollutant quan- Discharges from point and nonpoint sources need tities are estimated from data on ambient concentra- tions and point source discharge, the relative propor- to be considered in order to establish relationships tion of emissions due to nonpoint sources can be between current discharges and current ambient con- quantified. However, since nonpoint source dis- centrations. From these, relationships between future charges are typically associated with rainfall which, discharges and future ambient levels can be esti- in turn, can produce high ambient concentrations mated. over short-time intervals, their impact far outweighs The assessment of current emissions from point their-relative quantity. These "shock loadings" can sources (i.e., specific identifiable outfalls, such as have disastrous effects on aquatic biology. those found at sewage treatment facilities and certain An alternative approach is to use a predictive industrial plants) is similar to that for air pollution. model to estimate current nonpoint source dis- Direct measurement of effluent content is combined charges. The EPA and Department of Agriculture with analyses of industrial processes, product mixes, have both produced documents on simple tech- the amount of product used, and the types of potlu- niques .36 More complex techniques, some of which tion control devices employed. For water pollution, can estimate "shock loadings," will be discussed in however, the number of sources to consider is much the section on estimating future discharge levels. smaller than for air pollution. Still, wastewater emis- Methods and procedures for conducting point and sion inventories for most areas remain poorly devel- oped. EPA is currently supporting research to refine nonpoint source inventories appear in recently pub- wastewater emission factors for various industrial listed EPA guidelines .31 categories. The assessment of emissions from nonpoint 36. C. H. Wadleigh, Wastes in Relation to Agriculture and For- sources (e.g., runoff from agricultural fields and resi- estry, Miscellaneous Publication No. 1065 (Washington, D.C.: De- partment of Agriculture, March, 1968); and Office of Air and Water dential areas) is much more difficult. One approach is Programs, Methods of Identifying and Evaluating the Nature and to construct a total materials balance or conservation Extent of Nonpoint Sources of Pollutants (Washington, D.C.:. of mass equation for each pollutant: EPA, October, 1973). 37. Office of Water and Hazardous Materials, Guidelines for Q = P + N + I - (S + D) Preparation of Water Quality Management Plans (Washington, D.C.: EPA, September, 1974); and Office of Water and Hazardous where: Q = total quantity of pollutants leaving the Materials, Draft Guidelines for Areawide Waste Treatment Man- water body agement (Washington, D.C.: EPA, May, 1974). Table 2-5. AN ILLUSTRATIVE FORMAT FOR PRESENTING THE EFFECTS OF DEVELOPMENT ON WATER USE' LAKE CLEARWATER SUITABILITY APPROXIMATE WATER CURRENT AFTER NUMBER USE SUITABILITY DEVELOPMENT OF USERS COMMENTS Swimming Suitable Unsuitable 100,000/yr. Rotting seaweed, floating materials and increased turbidity will also Boating Suitable Suitable 20,000/yr. decrease the aesthetic quality. Fishing Suitable Suitable 5,000/yr. NOTES: A much finer categorization of uses will probably be necessary. Data on pollutant concentration levels relative to standards or rough thresholds and for various locations should also be presented. 70 Land Development and the Natural Environment 3. Measuring Current Ambient Concentrations Thus, we will discuss estimation procedures for both Analytical procedures for water sampling and mea- individual developments and generalized growth. surement of pollutant concentrations are now stan- a. Point Sources dardized and widely accepted .38 Although the accu- racy of the methods is generally high, the paucity of Future emissions from point sources depend on historical water quality data in most communities both the magnitude of future growth and the per unit from which patterns and trends could be established generation of pollutants. The discussion of growth is a severe limitation. This is especially significant, projections in Part 1 applies equally well here. since ambient concentrations are dependent on water Although estimates based on considerations of popu- flow and volume, which vary a great deal with lation growth, economic expansion, and in- and changes in rainfall intensity, duration, and spatial dis- outmigration are far superior to assumptions of no tribution in the watershed. Thus, unless a clear pic- growth or constant growth, understanding of growth ture of statistical fluctuations in ambient levels has processes is still primitive and the ability to accu- been established, it may be difficult to estimate the rately predict the future is still very limited. Low and importance of the typically small changes in pollutant high estimates should be used to describe the enve- concentration caused by individual land develop- lope of probable future states. ments or urbanization in general. In determining the quantity of pollutants generated Sampling points should be carefully located so as to by a given level of future development, rates of gen- measure, as far as possible, the effects of specific eration must be applied to the various types of devel- point sources. For example, water upstream as well opment. Although standard rule-of-thumb generation as downstream of point sources should be sampled. rates have been used in numerous communities, the In addition, the timing of sample collection should be suggested "standards" vary considerably for the such as to capture the effect of stormwater runoff and same type of development and are generally reported variations in flow. Continuous monitoring stations are with no documentation of empirical testing." For this desirable, since by definition they record continuous reason it is suggested that the possibility of deter- fluctuations in ambient levels. However, they are mining generation rates locally be explored. For extremely expensive and cannot be recommended for sewage, local wastewater, sanitation, and/or water routine use. The use of aquatic organisms as indi- supply, departmental files may contain information cators of water quality has also been tested .39 By which can be used to determine volumes generated carefully selecting indicator species and measuring per capita or per unit area for various land use cat- population characteristics, such as diversity, esti- egories (residential, commercial, and industrial) and mates of ambient concentrations for various pollu- subcategories (e.g., high-rise apartments, townhouse, tants can be made. Local communities should con- single family detached; strip commercial, shopping sider using a biological monitoring network as a center) .41 The volumes calculated for single or collec- supplement to chemical analysis. tions of individual developments are often multiplied by the concentration of specific constituent pollutants 4. Estimating Future Discharge Levels in the effluent from the local sewage treatment facil- Although the primary interest here is in evaluating ity, modified, of course, by any planned changes in individual developments, it is important to place indi- treatment .42 Information on pollutants generated by vidual development in the context of community-wide individual industries will have to be obtained from an growth. For large projects, whose development will analysis of the types of operations to be undertaken. span several years it is essential in estimating the im- Since this information must be provided in order to pact to add the generated emissions to those expected from growth in general over the intervening years. 40. For example, the suggested coefficients for sewage effluent from residential developments range from 65 to 300 gallons per day per person. For an example of standards for various types of devel- 38. National Training Program, Water Program Operations, opments see E. E. Seelye, Data Book for Civil Engineers: Volume Water Quality Studies Training Manual (Cincinnati: EPA, May, One-Design (New York: John Wiley and Sons, Inc., 1968). A 1974) (NTIS No. PB237586). useful review can also be found in Meta Systems, Inc., op. cit. 39. See, for example, Patrick Ruth, "Use of Algae, Especially 41. If the sanitation department does not maintain data on Diatoms, in the Assessment of Water Quality" and John Cains, Jr., household/industry size and/or structural size, a sample can be K. L. Dickson, and Guy Lanza, "Rapid Biological Monitoring drawn and this information obtained for those properties in the System for Determining Aquatic Community Structure in Re- sample from such sources as the local assessor's office. ceiving Systems" in Biological Methods for the Assessment of 42. Estimated efficiencies for various levels of sewage treatment Water Quality (American Society for Testing and Materials, 1973); can be found in Hydroscience, Inc. and Mitre Corp., Simplified and J. L. Wilhm and T. C. Davis, "Biological Parameters for Mathematical Modeling of Water Quality, (Washington, D.C.: Water Quality Criteria," Bioscience 18(9) (June, 1968): 477-81. EPA, March, 1971) (NTIS No. PB-227866). Water Quality and Quantity: Methodological Approaches 71 obtain a discharge permit under the WPCA, the puter capability is adequate)." HSP, on the other local or state pollution control agency should be con- hand, can only be obtained through a limited but sulted. growing number of consulting firms. b. Nonpoint Sources 5. Estimating Future Ambient Concentrations As an urban area expands in areal extent, vegetated a. General ConsiderationS45 and agricultural land is converted to urban uses. Thus, the nonpoint source pollution impact of urbani- Once current and future emissions and current am- zation (or the construction of a single development) is bient concentrations are known or estimated, the the difference between stormwater runoff quality be- stage is set for estimating the impact of -proposed fore and after development. development on ambient water quality. The newest subset of water models, known as The problem is basically one of estimating the runoff quality or hydrologic transport models, deals assimilative capacity of the hydrologic environment with various aspects of pollution from nonpoint in question, a quantity which is exceedingly variable sources. 43 Although the algorithms (i.e., the set of from one surface water body to another and from one computation-determining equations) differ among the time to another within the same body. Generally, the individual models, they are all based on modeling greater the volume and flow, the greater the assimi- mechanisms of pollutant transport by means of over- lative capacity. Thus, fast-flowing streams and very land and/or subsurface water flow. large lakes have high capacities, the former because The transport models also simulate the manner in the regeneration rate is high (i.e., high flow rates in- which the pollutants interact with water. Nitrate, for crease the rate of reaeration), the latter because example, is transported primarily in a soluble form, the dilution volume is large. However, lakes gener- while sediment is mechanically moved. In addition, ally do not make desirable dumping grounds. Some mechanisms of pollutant decay or transformation tend to become thermally stratified, thus inhibiting while in transport must also be simulated. mixing and allowing pollutants to accumulate in the Of primary interest here are urban runoff quality strata. models, although runoff from the land before devel- Estuaries represent unique problems. The cyclical opment has occurred should be estimated in order to reversal of flow due to the inflow of fresh water and make "before and after" comparisons. These models the action of the tides may trap pollutants and impede estimate the build-up of street contaminants and the dispersal. On the other hand, the turbulence created extent of flush-out by surface flow. Typically, de- by the opposing forces of flow plus the additional clining daily accumulation up to a limiting value and mixing caused by salt gradients may increase the rate an exponential removal are assumed. of regeneration. Table 2-6 is a compilation and description of some The living and nonliving systems interact to deter- of the more well known or widely used transport mine the quality of hydrologic environments. Some models. Again, data on costs and accuracy are pollutants are relatively inert and are assimilated by scarce. This is especially true if accuracy is to be de- water bodies through dilution and deposition in termined by using observations other than those used bottom muds. Others, however, proceed through a to calibrate the model, that is, if accuracy is defined complex and protracted series of chemical and bio- by the ability to reproduce pollutants generated in un- chemical reactions, often being recycled and modified tested watersheds or at future points in time. innumerable times. Figure 2-2 depicts some of the As indicated, each of the models requires computer major biotic pathways for pollutants which are nu- support. However, since the Corps of Engineers and trients (primarily phosphate and nitrate). Water qual- EPA are active in providing a user support service for ity models can likewise be classified according to the STORM and SWMM, respectively, a local commu- level of complexity of the processes they represent. nity may be able to utilize these models without em- But even for the simpler models which treat only the ploying a consultant (assuming the community's com- relationship of dissolved oxygen (DO) to biological 43. The Universal Soil Loss Equation is probably the only 44. Research recently undertaken by Meta Systems, Inc., of simple technique available for estimating water quality from non- Cambridge, Mass., involved an attempt to combine modules from point sources. However, it is only applicable to sediment and to both STORM and SWMM into a model for predicting stormwater agricultural land use. See EPA, Methods of Identifting and Eval- runoff quality and impact on stream quality. Practical experience in uating the Nature and Extent of Non-Point Sources of Pollutants applying the final product to a range of developments and water- (Washington, D.C.: EPA, October, 1973); and Midwest Research sheds will be reported. See Meta Systems, Inc., op. cit. Institute, User's Handbook for Assessment of Water Pollution 45. For more information, see Hydroscience, Inc. and Mitre from Non-Point Sources (EPA, forthcoming). Corporation, op. cit. 72 Land Development and the Natural Environment 10 Table 2-6. URBAN RUNOFF QUALITY MODELS (FOR ESTIMATING DISCHARGES FROM NONPOINT SOURCES) POLLUTANTS COMPUTING NAME MODELED REQUIREMENTS INPUT COST OUTPUT ACCURACY Hydtocomp Simulation BOD, COD,4 organic Same as for HSP, Table See HSP in Table 2-4, No values available Runoff pollutant con- No reported data on Program (HSP), water N, phosphate, total 2-4 (970,000 word core initial dust and dirt centration during all accuracy of pollutant quality (surface runoff solids storage required to run loadings on pervious runoff events as simu- concentrations component)a all hydrologic and and impervious areas lated continuously by quality modules) and upper loading limits HSP CD 5 0 Storage treatment over- Suspended solids, Program available for Hourly rainfall for 10- No values available Runoff pollutant con- No reported data on flow, runoff model settleable solids, IBM 360/50, UNIVAC 30 years, land use type, centration during storm accuracy of pollutant (STORM)e soluble P, Total N, 1108, and CDC 6600 or percent impervious- events (pollutographs) concentrations BOD 7600 machines, core ness, runoff storage and simulated from rainfall storage of 35,000 wor& treatment character- records; also, quality of required plus 1-5 addi- istics, initial dust and runoff after storage and 10 tional tape/disk units dirt loads and upper possible treatment if loading limits applicable CD Storm water manage- BOD, suspended Core storage of 350,000 Hourly rainfall for Effort for input data Runoff pollutant con- Very low accuracy for Ln ment model (SWMM)d solids, settleable solids, bytes is required plus many years, subbasin preparation has been centrations during suspended solids re- BOD, N, P and grease additional tape/disk characteristics (area, described as "moder- storm events (polluto- ported in one test! units; has been used on width, slope, ground ate" and, although graphs) for the whole No other data available IBM 360/70, UNIVAC cover) storm sewerage computing time is 2-3 basin or at specific 1108, and CDC (slope, length, rough- times longer than for points therein 6400/6600 ness and storage capac- similar models, com- ity), initial dust and dirt puting cost is less than loadings and upper $10 per runO loading limits a. Hydrocomp, Inc., Hydrocomp, Simulation Programming, Mathematical Model of Water Quality Indices in.Rivers and Impoundments (Palo Alto, California: Hydrocomp, Inc., n.d.). b. Chemical Oxygen Demand. This is an alternative but not exactly equivalent measure for BOD. c. Water Resources Engineers, Inc., Corps of Engineers (Hydrologic Engineering Center), and City of San Francisco (Department of Public Works), A Modelfor Evaluating Runoff Quality in Metropolitan Master Planning (New York: American Society of Civil Engineers, April, 1974); and Hydrologic Engineering Center, Urban Storm Water Runoff "STORM," Generalized Computer Program, 723-58-12520 (Davis, California: Army Corps of Engineers, May, 1974). d. W. C. Huber, et al., Storm Water Management Model User's Manual, vol. 11 (Cincinnati, Ohio: EPA, Office of Research and Development, March, 1975). e. D. P. Heeps and R. G. Mein, "Independent Comparison of Three Urban Runoff Models," Journal of the Hydraulics Division, Proceeding of the American Society ofCivil Engineers 100 (HY7) (1974): 995-1009; and J. Marsalek, et al., "Comparative Evaluation of Three Urban Runoff Models," Water Resources Bulletin 11 (2), (1975): 306-28. f. N. V. Colstpn, Jr., Characterization and Treatment of Urban Land Runoff (Cincinnati, Ohio: EPA, Office of Research and Development, December, 1974). demand (BOD), the number of physical and biological ment the information presented here." The review by processes involved may number as many as fourteen. J. W. Brown et al. is especially useful in describing Water quality models can also be classified by the characteristics of individual models. Even here, other characteristics. The simpler models represent a through information on cost and accuracy is sparse. hydrologic environment as a steady state system, Streeter-Phelps-A number of water quality thus ignoring the dynamic elements such as changes models have been based on the Streeter-Phelps equa- in water flows, solar insolation, and changes in pollu- tion first published in 1925.11 This is a highly simpli- tant discharge with time. Others are time-varying. fied version of the conservation of mass equation; it Some models represent each event in the water qual- considers only the DO depletion due to the discharge ity system as a probabilistic event, while others are of BOD containing effluent (and subsequent bacterial deterministic and assume that an event will always oxidation) and the replenishment of DO through sur- occur if the precursor conditions are satisfied. Models face reaeration. The model is also time-invariant (i.e., are also characterized by the type of water body to steady-state) and deterministic, and assumes com- which they apply and the extent to which they are plete, instantaneous mixing. DO concentrations are spatially disaggregated. computed as a function of distance downstream from As with several other types of water models, the the outfall. It is basically an easy and inexpensive, fundamental equation upon which most water quality but highly simplistic and inaccurate, approach to esti- models are based is the conservation of mass or mate- mating water quality. rial balance relationship:16 Simplified EPA Model-This model depends on re- Q, = Ni + Si + Ai latively gross or averaged input data, rules-of-thumb, where Qj = the change in the quantity of pollutant i generalized relationships between watershed pa- in a small volume of water over time rameters and water quality, and a "worst condition" Ni = the net movement of i into or out of the philosophy.19 For example, the. degree of stream small volume reaeration is approximated by describing the depth of Si = the summation of sources and sinks water relative to the size of bottom rocks, and analy- (sources of removal) for i in the volume ses are typically made for points near outfalls and Ai the amount of i added directly into the during low flows-the locations and times of lowest small volume from outside (i.e., pollu- quality. tant discharge) Due to the simplicity and manual nature of the The manner and extent to which the various terms model it is very attractive. Unfortunately, it is limited are represented mathematically will determine each in applicability and may be misleading. Only average model's complexity and fidelity to the real world. relationships between watershed parameters and water quality are used and are assumed constant in time and throughout the water body. The EPA has b. Surface Water Models made an effort to limit distribution to those who are Here we are again faced with the difficult task of either knowledgeable in water quality analysis or who selecting among a profusion of water quality models have attended special training courses. developed in recent years. As before, the criteria of Auto-Qual-The EPA's Middle Atlantic Region III representativeness and popularity have been utilized has developed a water quality model which can be for discrimination purposes. In addition, our prefer- ence has been for the better documented models. A number of recent reviews can be used to supple- 47. J. W. Brown, et al., op. cit.; Martin E. Harper, Assessment of Mathematical Models Used in Analysis of Water Quality in Streams and Estuaries (Pullman, Wash.: Washington State Water Research Center, June, 1971); and Pio S. Lombardo, Critical Re- 46. More formally: view of Currently Available Water Quality Models, (Palo Alto, Calif.: Hydrocomp, Inc. July, 1973) (NTIS No. PB-222265); and V, JjjAj + VjSj) + Wjj Systems Control, Inc., Use of Mathematical Models for Water dt Quality Planning (Olympia: Washington Department of Ecology, where: Cj = the concentration of pollutant i in segmenti June, 1974) V, = the volume of segment j 48. H. W. Streeter and E. B. Phelps, "A Study of the Pollution J,j= the net flux of i in segment j and Natural Purification of the Ohio River," Public Health Bulletin Aj= the interfacial area of segment j 146 (Washington, D.C.: Public Health Service, 1925). (reprinted by Sjj = the summation of sources and sinks of i in i HEW, 1958). For a description of other DO-BOD models, see W, = the direct input of i to j, Harper, op. cit. Furthermore, J depends on the diffusion of pollutant i and the ad- 49. For documentation, see Hydroscience, Inc. and Mitre Cor- vective transport of i as determined by the flow velocity. poration, op. cit. 74 Land Development and the Natural Environment run in either a steady-state or a quasi-dynamic formation on accuracy for the quality component is in mode .50 The model has a hydraulic component which hand, although initial applications on the Green River is applicable to any body of water (except stratified in Washington are reported to have produced "rea- lakes or impoundments) whose length is considerably sonable" results .51 The cost of operation is also un- greater than its width (i.e., rivers and many es- known, although it probably is in the neighborhood tuaries). The model estimates values for nonreactive of that reported for the hydrologic component of pollutants and DO-BOD. HSP (up to $10 per acre for small watersheds, less The computations are based on the conservation of for larger ones). mass equation as applied to a series of points or junc- tions evenly dispersed along the direction of flow. Other Models-A number of advanced modeling Quality variables are estimated at each junction, efforts during the 1970s have been undertaken as part while the hydraulic (flow) variables are used to of the International Biological Program and as part of characterize the transport of substances between EPA's research and development. The ongoing EPA- junctions. sponsored projects are listed in Lombardo's review. Although the dynamic mode of operation allows for Although most of these modeling studies are of a changes in pollutant and quality indicator values over purely research nature, significant advances in the time, the use of average or net daily flows "smooths understanding of hydrologic and ecologic processes out" the rapid response of these variables due to should ultimately result in improved operational storm surges or tidal oscillations. However, the loss models. Analysts involved in water-related planning in fine tuning is compensated for by the model's com- and evaluation should contact the sponsoring patibility with EPA's Water Quality Information agencies for descriptive and evaluative information as System .51 it becomes available. HSP, Water Quality Component-This is the set of water quality routines used in conjunction with the c. Groundwater Models HSP hydrologic model described previou Sly.52 Rivers Groundwater hydrologists have been involved with are segmented into an unlimited number of reaches estimating the capacity of underground sources for and lakes or impoundments into several layers. The several decades. The quantitative modeling of water quality within each segment is estimated on a groundwater quality, on the other hand, has received continuous basis, using the conservation of mass only slightly more than passing attention. equation as an organizing framework and laboratory The most dominant factor in explaining the non- estimates of the various reaction rates to predict val- aqueous components of underground water is the ues for individual pollutant or quality indicators. mineral composition of the aquifer (i.e., the water- The model is extremely comprehensive. In addition bearing strata of rock or unconsolidated earth mate- to several nonreactive pollutants, various forms of N rial). Since the movement of groundwater is often and P, temperature, coliform bacteria, and micro- extremely slow (perhaps only a few hundred feet a scopic plant and animal organisms can be modeled. year), the mineral content is usually high despite the The DO-BOD system is also represented comprehen- slow dissolution rate of most minerals. sively. Human factors are increasingly important, Since Since the model is run with a surface runoff compo- surface water and groundwater are most realistically nent (see Table 2-6), the contribution to water pollu- viewed as an interconnected system, degradation of tion from urban and agricultural nonpoint sources can rivers and lakes can also lead to groundwater deterio- be modeled. ration. Pollutants from cropland, septic tank fields, On balance, the HSP system including the water and sanitary landfills are additional sources of degra- quality submodel appears to be a comprehensive and dation. well-integrated package. However, no quantitative in- The degree to which a potential source will be pol- luting is largely dependent on the ground material 50. Robert L. Crim and Norman L. Lovelace, Auto-Qual overlying the aquifer and through which the pollutant- Modelling System, Technical Report No. 54 (Annapolis, Md.: bearing water must pass. Properly managed, a liquid EPA, March, 1973) (NTIS No. PB-227 032). EPA has developed waste disposal site such as a septic tank leach field alternative water quality models as well (e.g., HARO 3 and SNSM). can be used to recycle nutrients with little or no net 51. For more information contact the Monitoring and Data Support Division, Office of Air and Water Programs, EPA, Wash- production of N or P. Soil particles are also effective ington, D.C. in destroying bacteria and viruses. Improperly man- 52. Hydrocomp, Inc., Hydrocomp Simulation Programming Mathematical Model of Water Quality Indices in Rivers and Im- poundments (Palo Alto, Calif.: Hydrocomp, Inc., n.d.). 53. Lombardo, op. cit. Water Quality and Quantity: Methodological Approaches 75 aged or operated in areas with inadequate soil charac- ecological interactions of living organisms and their teristics (e.g., too fast or too slow percolation, too environment should deliver more accurate results. wet, too shallow), liquid or solid waste disposal sites Thus, the more complex models should provide more can be severely polluting. Once polluted, aquifers reliable predictions. Although the available data on may take years or decades to regenerate owing to accuracy tends to bear this out, much more extensive their slow rates of flow. Techniques for estimating testing in a variety of lakes, streams, and estuaries is groundwater quality must consequently consider both needed. The same can be said for operating costs. In the overlying unsaturated material and the water- some cases we have even experienced resistance on filled aquifer, as well as direct communication the part of the model developer to divulging whatever between surface and groundwater. cost and accuracy documentation exists. Unfortunately, the movement of aqueous pollutants Even if reliable operating cost data were available, in media other than surface water is still not well the question of costs for model start-up, validation, enough understood to support the development of and calibration would remain. Lombardo reports that operational models. One of the most ambitious at- these costs for the HSP (quality component) model tempts to further the research in this area was re- were in the neighborhood of $50,000 and $100,000 for cently undertaken by investigators from the Univer- Denver and Seattle, respectively .56 Thus, any com- sity of Florida.51 They coupled a surface water model, munity which contemplates employing a water model an unsaturated zone model, and a groundwater model should be prepared to expend the necessary and con- in an attempt to simulate the entire hydrologic regime siderable funds for preparation. The justification for for a small Florida lake basin. Unfortunately, their set the utilization of any model should be made on its of models could not be validated due to data limita- long-run benefits, in order to capture economies to be tions. realized from long-term application. In the absence of operational predictive techniques, estimates of causal relationships must rest on inferen- 6. Estimating the Number of People Affected tial evidence. Groundwater quality (as measured from well samples) should be correlated with land develop- The number of people engaged in various water- ment activities and associated soil characteristics to related activities can be approximated using either the extent this is possible .5' The relationships gen- direct observation survey techniques or written/ erated will obviously be general and approximate. telephone surveys of likely users. More detailed Most new developments should not present addi- discussions of recreational survey techniques can tional groundwater problems, since the majority will be found in other references .57 be serviced by sanitary sewers. In fact, they may cause an improvement in quality if older housing 7. Estimating Monetary Benefits units with septic tanks are being replaced or if agri- cultural land is being developed. If the estimated water quality impacts of land A unique groundwater problem faced by communi- development appear to be substantial in terms of the ties in coastal areas is that of salt water intrusion. As number of people affected and/or the types of other this is a problem primarily related to water consump- developments impacted, the local government may tion it will be discussed in the next section, Water want to estimate the monetary value of the clean Supply. water benefits being reduced (or the "costs" of the additional deterioration). The principal approaches in- d. Comparison and Summary clude the following: Various aspects of the previously described water (1) Willingness to pay-determining how much the quality models are summarized and compared in affected individuals or firms are willing to pay Table 2-7. These represent only a limited, albeit rep- for clean water. resentative, sampling of extant models. (2) Expenditure method-determining the expendi- As with the other water models discussed in Part 2, tures made by those using clean water. those which are based on or simulate the fundamental (3) Cost method-determining the cost to ame- liorate the pollution-caused damage. 54. Armando 1. Perez, et al., A Water Quality Model for a Con- junctive Surface-Groundwater System (Washington, D.C.: EPA, May, 1974) (EPA-600/5-74-013). 56. Lombardo, op. cit. 55. In the case of confined aquifers with specific recharge areas, 57. See, for example, The Urban Institute, How Effective Are detailed knowledge of the location and nature of the recharge areas Your Community Recreation Services? (Washington, D.C.: Bureau is a prerequisite for any correlation-type analysis. of Outdoor Recreation, Department of the Interior, April, 1973). 76 Land Development and the Natural Environment Table 2-7. ASSESSMENT OF WATER QUALITY MODELS TYPE OF POLLUTANTS COMPUTING ACCURACY AND NAME WATER BODY MODELED REQUIREMENTS INPUT COST OUTPUT COMMENTS Streeter- Streams and DO-BOD Hand calculations although a Effluent content of point Very low if used manually DO concentrations as a func- Low due to the simplifying Phelps reservoirs computer can greatly expand sources, velocity of flow, and tion of distance downstream assumption used in the calcula- number of locations at which ambient DO concentrations from source tions values are calculated EPA's Streams and Chloride, dissolved solids, total Hand calculations Effluent content of point Fairly low Pollutant and indicator values Less than for computerized Simplified estuaries P, bacteria suspended solids, sources, average and low flow as a function of location in models (EPA cautions against Model DO-BOD velocity, general type of flow, streamlestuary its use by those unfamiliar with channel geometry and slope, water quality analysis) ambient water quality Auto-Qua] Streams and DO-BOD based on both carbon Central core storage requirements Flow and velocity, channel con- No figures available Pollutant and indicator values Theoretically higher than the elongated and N compounds, suspended are 105,000-115,000 bytes; has figuration at each junction, as a function of location in simple methods, although com- estuaries solids, temperature, chloride been run on IBM 370 effluent content of point stream/estuary and of time plex and rare events, such as sources, water temperature, storm surges, not represented rates of DO uptake by sedi- well ments, and production by photosynthesis HSP, Streams, lakes, Dissolved solids, temperature, See IISP Table 2-6 Effluent content of point Approximately $101acre for Pollutant and indicator values Subjectively estimated as "rea- water impoundments bacteria, DO-DOB based on sources. (See Table 2-4 for a small watersheds, less for large as a function of stream estuary sonable" and from theoretical quality both carbon and N compounds, description of the HSP non- ones in addition to cost of the location and of time point of view, relatively high; phytoplankton, zooplankton, point source component.) See other USP components HSP is a comprehensive program benthal organisms, various HSP Tables 2-4 and -6 for other so this submodel can be forms of N and P input requirements coupled with surface runoff and hydrologic submodels (4) Local economy method-determining the effect The first measure of water quantity best expresses in terms of reduced output. the various aspects of the impact on man and is thus (5) Property value method-determining the effect preferred. Measure 2 is the fallback measure. It is of clean water in terms of increased property based on a largely qualitative rating of "likelihood" values. and is thus much less difficult to use. The drinking water quality measure is quite similar These methods are obviously not completely or to those suggested for water pollution. The concern perhaps even partially substitutable. Thus, results ob- here is for those health- or aesthetic- (color, odor, tained by using one are not necessarily comparable to taste, clarity) related pollutants generated by the new those obtained by using another. This fact, plus the development which may appear in the community or difficulties involved with deriving reliable data neighboring households' water supply, assuming the regardless of the method employed, makes an eco- same level of purification. (Increased costs for purifi- nomic analysis of water quality impacts a formidable cation necessitated by the development should be task. considered in its fiscal impact analysis.)60 The dis- Discussions of the conceptual and technical cussion of standards and their use which appears in problems, as well as examples of local studies, can be the water pollution chapter applies here as well. found in the references cited. The EPA is actively engaged in benefit research at the present time. Pre- 2. Measuring/Estimating Impacts on sumably, improvements in methodology as well as es- Storage and Yield timates of benefits (or damages) on a regional scale Any analysis of impacts on water supply should will be forthcoming. consider existing and potential supplies. These are C. IMPACTS ON WATER CONSUMPTION most conveniently divided into surface water and Concern for the impact of new development on groundwater categories. community water supplies, by and large, involves a a. Surface Water consideration of quantities available and quantities In many ways the estimation of water supply is consumed. In addition, problems of replenishment analogous to flood prediction. In this case, though, and salt water contamination are of concern for a the rare event to be redicted is low flow (or low vol- small but growing number of communities. p ume) rather than peak flow. Thus, the general discus- 1. Impact Measures sion and many of the specific techniques for esti- mating flood events apply here as well. Following are suggested measures for both the A river/reservoir system introduces a number of quantity and quality aspects of the problem:51 complicating factors, especially if the reservoir is Water Quantity used for purposes in addition to drinking water storage (e.g., flood control, irrigation, power genera- l. Change in the total duration and/or severity of tion, recreation) and if flows in the drainage system expected shortages and the number of people af- are influenced by water rights. Detailed discussions fected. of both conceptual and technical aspects of the OR problem can be found in selected Corps of Engineers 2. Change in the likelihood of a water shortage and publications and many hydrologic texts .61 the number of people affected. Where the probabilities of various low flows or storage volumes have been determined (i.e., the two, Water Quality five, ten, fifty, 100, 500 year low flow/volume), the 1. Change in the concentration of those drinking impacts can also be estimated probabilistically. The water constituents that are important to health expected water use from the new development is and the number of people affected.59 added to the current use levels during the low flow 60. For a detailed discussion of the issues and methods involved 58. An alternative measure is "the amount of water to be con- in fiscal impact analysis, see Thomas Muller, Fiscal Impact Analy- sumed relative to the budgeted amount" where a budget has been sis (Washington, D.C.: The Urban Institute, 1975). prepared for the community. See Part 2, 111, Section A for a more 61. See, for example, Leo R. Beard, Methods for Determination detailed discussion. of Safe Yield and Compensation Waterfrom Storage Reservoirs, 59. For a specification of drinking water standards, see HEW, Technical Paper No. 3 (Davis, Calif.: Army Corps of Engineers, Public Health Drinking Water Standards, Revised, (Washington, Hydrologic Engineering Center, 1965) and Linsley, Kohler, and D.C.: Government Printing Office, 1962). Paulhus, op. cit. 78 Land Development and the Natural Environment period (obtained from the local water utility), and this sive sustained yield does not involve the simple com- new value is compared with the various low flows. parison of inflows with outflows, even assuming that The proposed development could then be said to the characteristics of all recharge and discharge areas cause a shortage during a five-year or greater low and the total amount of withdrawal were known. The flow, for example (or a shortage with occurrence mechanisms of underground water transmission are probability of 20 percent in any one year). Where numerous and complex, and without complete and adequate data on low flow frequency is not available detailed information on the local hydrologic regime or cannot be computed, qualitative descriptors such estimates of the effects of additional withdrawal re- as "most likely" or "unlikely" will have to be used. main of uncertain validity .63 The duration and severity of shortages would ap- This is not to say that approximations cannot be pear to be more difficult to estimate. A rough esti- and are not made. By tracing the relative changes in mate of duration could possibly be based on historical precipitation, groundwater level, total withdrawal records of low flow duration for the various degrees (usually from well logs), and natural discharge of low flow. Severity could be expressed as the pos- (usually by factoring out the surface and interfloW64 sible consequences of a shortage (e.g., no lawn- contributions to stream flow records), estimates of sprinkling, no swimming in pools, rationing of permissive sustained yield can be made .65 Due to the drinking water). Local water utility personnel may delayed response of groundwater systems and the re- have useful data if past shortages have occurred. The sulting difficulty in ascertaining when permissive sus- experience of other communities in similar situations tained yield has been exceeded, the accuracy of this may also be useful. approach is difficult to specify. Once the yield has been determined the impact of a b. Groundwater proposed development is estimated by adding ex- The problem here is conceptually the same as that pected new demand to current demand and com- for surface water. Total inflows, outflows, and paring the total to the estimated yield. However, storage should be estimated with and without the land since aquifer systems may be related to rainfall in a development in question. More realistically, "safe way that is difficult to understand, and since safe yield" from an aquifer is measured against demand yield is difficult to determine, it is unlikely that the with and without the new development. impact can be expressed in probabilistic terms, at "Safe yield" may be defined in several ways :62 least at this time. In addition to the consumptive demand created by 1. Maximum sustained yield-the maximum rate the new development, its location with respect to at which water can be withdrawn perennially groundwater recharge areas should also be consid- from a particular source. ered. These are areas where geologic structures allow 2. Permissive sustained yield-the maximum rate precipitation to reach underground reservoirs. Most at which water can economically and legally be aquifers have rather extensive recharge areas, but for withdrawn perennially from a particular source those confined by impermeable rock layers the areas for beneficial purposes without bringing about of surface/underground communication may be lim- some undesired result, such as salt water intru- ited and must be protected from coverage by imper- sion. meable materials. The local planner must depend on 3. Maximum mining yield-the total volume of geologists from local, state, or federal agencies to water in storage that can be extracted and uti- conduct the requisite surveys of bedrock formations lized. and overlying unconsolidated earth material from 4. Permissive mining yield-the maximum volume which the recharge areas can be mapped. of water in storage that can economically and 3. Measuring/Estimating Salt Water Intrusion legally be extracted and used for beneficial pur- poses, without bringing about some undesired Salt water movement into fresh water aquifers is a result. phenomenon which may occur in coastal areas due to Most communities are interested in maintaining "per- missive sustained yield," since this implies perpetual 63. A brief description of an attempt to couple a surface water, availability. Unfortunately, the calculation of permis- an unsaturated zone, and a groundwater model appears in the sec- tion on water poflution, Part 2, l(B). 64. "Interflow" is water which flows under but close to the sur- 62. American Society of Civil Engineers, Groundwater Basin face and is not considered part of the groundwater. Management, Manual of Engineering Service, No. 40 (Washing- 65. See Patrick A. Domenico, Concepts and Models in Ground- ton, D.C., 1961). water Hydrology (New York: McGraw-Hill, 1972). Water Quality and Quantity: Methodological Approaches 79 FIGURE 2-6 excessive fresh water withdrawal. This is illustrated AN ILLUSTRATION OF SALTWATER INTRUSION in Figure 2-6. The Domenico text contains an excellent descrip- Q tion of the phenomenon and a discussion of various fluid dynamic-based methods of quantifying it.'16 A few examples of applications are also included, Sea level although a discussion of results is lacking. Confining In the absence of information on the accuracy of material specific analytical techniques, a qualitative approach is justified. Where the occurrence of intrusions has been observed it is safe to conclude that additional withdrawal will be exacerbating. However, the ef- fects may possibly be ameliorated if additional cor- (a) Q rective measures are taken, such as :67 1. A reduction or rearrangement of pumping pat- terns elsewhere. Sea level Confining 2. Artificial fresh water recharge of the aquifer. material - - - - - - - 3. Establishment of a pumping trough along the - - - - - - Seawater wedge coast, thus limiting the intrusion to the trough area. Fresh water - - - - - - - - - - 4. Formation of a pressure ridge along the coast. - - - - - - - - - - - - - - 5. Construction of a subsurface barrier imper- miable to salt water. (b) Details of these approaches can be found in the refer- SOURCE: Adapted from Patrick A. Domenico, Concepts and ence cited. Models in Groundwater Hydrology (New York: McGraw-Hill Inc., 1972). (Used with permission of McGraw-Hill Book Co.) 66. Ibid. 67. H. 0. Banks and R. C. Richter, "Sea Water Intrusion Into NOTE: The vertical shaft represents a well and Q, the withdrawal Groundwater Basins Bordering the California Coast and Inland of fresh water. The height of freshwater in the well represents the Bays," Transactions of the American Geophysical Union 34, pressure due to the freshwater in the aquifer. (1953): 575-82. @e @evel ------------ @@Fresh water Fresh water S*eawaEr, w < w w edge 80 Land Development and the Natural Environment 111. CONCLUSIONS AND RECOMMENDATIONS A. PLANNING VERSUS PROJECT REVIEW plans. That is, allowable degrees of "percent impervi- The relationship between planning and project re- ous ground cover" can be specified for different areas view has emerged as one of the key considerations in within a watershed based on acceptable or desirable an impact evaluation program. Planning can greatly degrees of flooding. (One of the simpler stream flow facilitate the evaluation of certain types of impacts re- techniques could be used for this purpose.) These val- sulting from individual developments. On the other ues can then be incorporated in comprehensive plans hand, large-scale planning does not capture the idio- as targets. Once the target had been reached for an syncrasies of single projects, and the approximate re- area the runoff-related problems in the vicinity would lationships between impacts and development charac- have to be investigated in greater detail, and develop- teristics used to produce the plan may not be terribly ment proposals would have to be carefully scrutinized accurate. These and other related points will now be on an individual basis before new development would elaborated on for each of the impact areas. be allowed.' A similar analysis for all hydrologic im- For those hydrologic considerations which are rela- pact areas appears in Table 2-8. tively insensitive to development design character- It is clear that the planning activities outlined for istics (e.g., sewage generation) the planning approach water pollution of surface waters (sewage, industrial is decidedly superior. The review at the proposal effluents, and, to some extent, stormwater runoff) are stage then becomes almost perfunctory-for ex- being or will be assumed by the special area-wide ample, does adequate treatment capacity exist? For planning organizations as established by the WPCA. Existing city, metropolitan area, or county planning water-related project outputs which are more sensi- agencies are expected to cooperate with these special tive to design features the ability to minimize hydro- planning organizations and to implement the plans logic impact through long-range planning is consider- developed. Although individual local governments are ably reduced. Stormwater runoff, for example, is a function of landscaping and retention facilities (e.g., responsible for flood plain planning and control, the ponds) as well as the extent of impervious ground process is controlled by HUD through the Flood cover and the degree of sewerization. Thus, it is diffi- Disaster Protection Act. Development outside the cult to develop zoning classifications based on a single generalizable factor, such as impervious 1. A pervasive problem which typically attends the application of land use controls is the lack of public authority to require detailed ground cover. A rather detailed site plan review is re- site plans from developers at the point of variance or rezoning re- quired in order to ascertain the actual volume and quest. This argues strongly for the inclusion of quantifiable indica- rate of runoff for various types of storms. tors in the general plan as the best way to control negative impacts. Impervious ground cover can be used, however, as The higher the correlation between the indicator and the impact, the better. Thus, in the runoff example, "percent impervious ground an early warning indicator or target in comprehensive cover" is superior to "housing density." 81 Table 2-8. LEVELS OF ANALYSIS APPLIED TO THE VARIOUS HYDROLOGIC IMPACT AREAS PLANNING PROJECT REVIEW Flooding Specification of allowable development intensity based on Assessment of (1) ground cover and sewerization variables, watershed characteristics and expressed in terms of general- (2) mitigating design features such as retention ponds, and izable indicators such as "percent impervious ground cover" (3) potential for localized flooding problems and "percent of the area served by storm sewers" Water pollution: Sewage (1) Specification of allowable effluent volumes based on hy- Assessment of available treatment capacity drologic characteristics of receiving water body, uses to which it is subject, and degree of treatment to be used; (2) possible allocation of remaining volume to future land use categories Industrial Same as for sewage plus specification of additional treatment Same as for sewage plus assessment of special processing levels of unusual pollutants facilities if appropriate Stormwater Specification of allowable development intensity based on Assessment of (1) ground cover variable, (2) mitigating design runoff watershed characteristics and general runoff loadings for features such as retention ponds, and (3) planned management development types, again expressed in terms of general- practices such as street cleaning izable indicators such as "percent impervious ground cover" Water con- Specification of maximum flow available for consumption Assessment of (1) available supply and (2) localized problems sumption (and other uses) and possible allocation of remaining supply such as salt water intrusions or reduced availability of water among future land use categories for those in immediate vicinity floodplain but within the watershed is not covered, hand, where a watershed or other community subarea however. Variance applications for locations within is being developed quite rapidly and potential conse- the flood plain must also be evaluated. In the area of quences may be quite severe, it may be preferable in water consumption, long-range planning is often con- the long run to utilize a complex model to specify ducted by the Corps of Engineers, especially if more accurate targets. For evaluations of individual drinking water is provided by river regulation or im- developments the selection of simple versus complex poundment. methods should be based on the size of the develop- It would thus appear that a complementary ment (or more accurately, the potential severity of its planning/project review system could be designed and impacts) and the ultimate cost of evaluation. Even for implemented. Where planning is based on the specifi- very large developments, the cost of using com- cation of targets, reviews of individual projects could plex, computer-assisted models may not be justified. be significantly simplified. However, their application to watershed-wide Most plans, of course, do not use the target con- evaluations-in a planning analysis-may be justi- cept. Even worse, some comprehensive plans have fied on the basis that the specification of accurate been developed with very little regard for the conse- targets may greatly reduce the need for individual quences of development to water quality and quan- evaluations. tity. In these cases the local government may wish to Although we have not been able to provide suffi- evaluate these or other alternative plans for hydro- cient cost data for the various methods reviewed, we logic impacts. The impact measures we have have tried to indicate which techniques could be used suggested would seem to be applicable to this type of on an "in-house" basis, which ones require'computer evaluation as well. support, which ones would probably necessitate the In selecting techniques and methods to be used in use of a consultant, and which ones are supported to computing values for the measures, we have tried to some extent by the federal government through user offer some general guidance.2 To obtain target figures services. for use in comprehensive plans or to evaluate existing plans the simpler and presumably less accurate large- B. SPECIFIC RECOMMENDATIONS scale techniques are probably adequate. On the other AND CONCLUSIONS 2. Additional assistance in writing requests for proposals and in 1. Local governments should consider specifying negotiating with contractors for the use of water models can be runoff-, emission-, and water consumption- found in Systems Control, Inc., op. cit. related "targets" in their land use or zoning 82 Land Development and the Natural Environment plans, based on analyses of flooding hazards, niques exist for establishing the relationships desired levels of water quality, and available between land development and flooding/water water supply. At a minimum, evaluations of quality on a watershed-wide basis (e.g., for spe- individual developments would simply estimate cifying targets). Calculations of surface water future levels of such things as imperviousness, supply can be made with techniques similar to emissions, and consumption associated with those used for flood hazard calculations. The each development. These values would then be more complex techniques are presumably more added to the running sum kept for all develop- accurate than the simpler ones. ments and compared with the targets. 5. For conducting the detailed evaluations of indi- 2. Where developments will cause targets to be ex- vidual developments the same watershed-wide ceeded or where special localized problems are techniques can be used. "Before and after" ef- likely, (or simply as a check on the assumptions fects are calculated by using the technique to es- used in preparing the plan), detailed evaluations timate flooding/water quality with and without of individual proposals should be undertaken. the development. 3. The detailed evaluations should utilize the pre- 6. Localized effects are estimated using detailed fer-red measures suggested here (or similar ones) engineering procedures and/or experts in the where possible, and the fallback measures at appropriate disciplines. other times. In choosing between the measures, the potential magnitude of impact and the time 7. Every technique reviewed needs additional veri- and funding available for evaluation will prob- ficatioln. Assessment of accuracy for most of the ably be the most important considerations. models has been based on theoretical consider- 4. A variety of both simple and complex tech- ations or on extremely limited validation. Water Quality and Quantity: Conclusions and Recommendations 83 PART 3 WILDLIFE AND VEGETATION I. INTRODUCTION AND BACKGROUND A. HUMAN WELFARE patterns. Vegetation may also help to cleanse air of Although concern for the environmental effects of certain pollutants and is known to have a significant urbanization has frequently focused on air and water effect on the quantity and quality of stormwater run- pollutants, public interest in other environmental- off. Certain types of plants may also serve as noise bar- related problems has been increasing. We now recog- riers. These and other roles which natural areas play nize that many plant and animal species are facing in maintaining high levels of environmental quality national and global extinction at an alarming rate. On a are discussed further in other parts of this report. more local scale, natural areas rich in common plant Estimating impacts on man's opportunity to enjoy species and frequently providing habitat for large wildlife and vegetation will consist in large part of es- numbers of interesting forms of wildlife are rapidly timating how the abundance of various species will disappearing. The concern here extends beyond first- change. However, another important factor to con- hand experiences with wildlife and vegetation. -Some sider is the value of this type of experience to the people feel a moral commitment to furthering the ex- local population. In communities where residents istence of all living things. In this sense the loss of value the nonmanmade environment highly this im- any natural area or wildlife habitat is important, at p .act area should receive additional weight in deci- least for those who hold these values. At the very sions on land development. It must also be recog- least, the maintenance of natural life forms in devel- nized, though, that some types of vegetation and oped areas permits people to become better ac- wildlife in urban areas are undesirable or even a quainted With natural processes which then places health hazard and that some people dislike many them in a better position to make decisions related to forms of natural life.' In these situations decision environmental matters. makers must face the unenviable task of balancing the Although the primary subject of this part of the re- desires of a subset of the current population with port is man's enjoyment of wildlife and vegetation those of other subsets and with the interests of future and the way land development may affect the oppor- populations. tunity for such enjoyment, we should not lose sight of the fact that the presence of natural areas is inti- mately related to airquality, water quality, flooding, 1. See the results of an attitude survey conducted in Wa- and noise. On a local, regional, and even global scale, terloo, Ontario, in Ann Dagg, "Reactions of People to Urban Wild- the extent and distribution of vegetated areas may life," Proceedings of a Symposium on Wildlife in an Urbanizing Environment (Springfield, Mass.: Cooperative Extension Service, have pronounced climatic effects which in turn will November 27-29, 1973) [hereafter cited as Proceedings of Sympo- affect temperature, humidity, precipitation, and wind sium on Wildlife]. 97 B. FUNDAMENTAL ECOLOGICAL PRINCIPLES2 which species will be present during the climax stage. Ecology is most generally the study of the interre- In addition, climax associations are rarely observed, lationships of organisms to one another and to the since succession is frequently interrupted by human environment. All living organisms are seen as existing intervention and such natural disturbances as floods, with their living and nonliving environments in a state fires, droughts, and insect invasions. of dynamic equilibrium, drawing from them suste- Tolerance and adaptation are other key concepts. nance (food and water), shelter, and the opportunity Individual plant and animal species are known to tol- for reproduction and, in turn, being used by other erate a range of environmental conditions. In some components of the system. Within this dynamic equi- situations they have even been known to adapt to librium structure each organism has a position or conditions far beyond the normal range. niche determined by the function it performs. The Ecologists usually characterize an ecosystem by most common and important types of organisms are such features as its productivity (i.e., the amount and the following: food producers (green plants); plant rate of living matter or biomass produced), by the eaters (herbivores); first and second level meat eaters types and magnitudes of energy and chemical flows, (carnivores); plant and meat eaters (omnivoresj; para- and by the abundance and variety of plants and an- sites; dead animal and plant eaters (scavengers); bac- imals. Diversity is the term used to describe the latter teria, yeasts, molds, and fungi which decompose dead and is generally considered to be the best indicator of organic material into basic chemicals (decomposers); ecosystem stability. A diverse ecosystem is one and microorganisms which convert nutrients into which can withstand numerous perturbations because compounds usable by green plants (transformers). many of its species are at least partially substitutable. The complex set of interactions among the con- Thus, elimination of certain components will not sumed and the consumers (sometimes known as the destroy the entire system. food web) can be characterized by the flow of nu- The implications of these principles for impact trients and energy. Nutrients (water, minerals, and evaluation are several. First, the interconnectedness organic compounds) are continuously recycled by an of the ecological system means that secondary and ecosystem. Energy flow, on the other hand, is pyra- tertiary effects are the rule rather than the exception. What at first appears to be the rather innocuous pri- midal. That is, the simple green plants which are the mary impact of land development (e.g., the mowing basic food producers are very efficient at converting of fields or the dredging of a pond) -may result in an the sun's energy into food. From this level on up the unexpected and dramatic reduction or increase in a pyramid of prey and predator relationships there is a particular species (e.g., loss of field 'birds or water- loss of useful energy at every step. By the time food fowl). reaches man at the top of the pyramid large quantities A second but related point is that disturbances of energy have been used in its production. which affect organisms located-near the bottom of the As a result of the interdependence of ecosystem energy pyramid generally have far-reaching effects in components, plants and animals tend to associate in a terms of impact on other organisms. DDT is a case in complementary fashion. Thus, ecologists speak of point. Small organisms ingested and concentrated the associations (groups of species) and communities chemical until levels toxic to susceptible bird species (groups of associations). The type of biotic comrnu- have been reached in insects and other prey. nity found in any area at any given point in time is de- Thirdly, impacts should also be viewed as changes pendent on soil, moisture, and climatic characteristics in the direction or rate of natural succession. In this as well as the biotic history of the area (what lived sense, "environmental p reservation" may be a mis- there in the past). leading term. Lakes, for example, often become over- This leads to another fundamental ecological con- fertilized and fill in as part of natural processes, cept, that of succession. A biotic community changes although thetime scales are usually quite long. If the over time, generally progressing toward an assem- current lake condition is the desired state, then envi- blage of climax species. In theory, the climax life ronmental manipulation may have to be undertaken. forms which occur under a given set of environmental Developments which interfered with the natural pro- conditions will remain, unless disturbed by outside cesses of lake aging would then be considered to have influences. However, it is often difficult to predict favorable impacts. 2. For further information see any standard text on ecology, Finally, the response to a given disturbance should such as, Robert L. Srnith, Ecology and Field Biology (New York: be estimated with regard to the ability of many Harper & Row, 1974). A less technical discussion of general envi- species to adapt to new environments. Ideal and ronmental principles is contained in Kenneth E. F. Watt, Princi- pies of Environmental Science (New York: McGraw-Hill Book tolerable environments may differ substantially. Company, 1973). Squirrels and raccoons are good examples of wild- 88 Land Development and the Natural Environment life species which have adapted quite well to man's 3.'Natural Areas are open spaces which are rela- presence. tively unmanaged. 4. Wildlife Habitats are areas which provide food, C. DEFINITIONS AND TERMS shelter, and general living space for wildlife. The following terms will be used throughout the re- The term "natural area" is used here in a slightly mainder of the discussion: more general way than it appears in some of the liter- ature. That is, "natural area" is used to designate 1. Wildlife is a collective term which refers to all any unmanaged "open space," regardless of quality, nondomestic animals of a size to be seen and while elsewhere it frequently means a high-quality appreciated by the public. We have extended vegetated area of special scientific interest. On the the usual definition to include fish. other hand, "open space" usually includes manmade -2. Open Spaces are areas of the natural or spaces as well as natural ones. Although "wildlife nonbuilt-up environment, including forests, habitat" includes either open spaces or manmade grasslands, deserts, agricultural land, parks, environments which will support a wildlife popula- lawns, and bodies of surface water (with empha- tion, the more desirable species are associated with sis on their living constituents). open spaces. Wildlife and Vegetation: Introduction and Background 89 11. METHODOLOGICAL APPROACHES Although common and well-accepted techniques 2. Change in the extent and quality of vegetation exist for characterizing existing natural areas and (including the number of mature trees added or habitats, the estimation of impacts on wildlife and lost) and wildlife habitat (quality rating by an- vegetation from proposed land development rests imal type). largely on inference. Simple techniques analogous to The first measure most directly reflects the number simple air or water pollution estimation models are of species added or lost and is thus preferred. Diver- not yet available. The explanation lies in man's lim- sity and abundance are the key variables.' The sec- ited knowledge of a very complex subject. In addi- ond measure is obviously simpler and should be used tion, standards (analogous to air and water quality where detailed surveys of vegetation and wildlife are standards) against which impact estimates could be gauged do not exist. Instead, the impacts are viewed not feasible. The change in extent is expressed as the in the context of how highly local residents (or in the number of acres of open space. The impact on wild- case of rare and endangered species, state and na- life is inferred from changes in the quantity of habitat tional citizens) value wildlife and vegetation. of a given quality. The terms "quality" and "diversity" imply that A. MEASURES AND INDICES rating scales and indices are to be considered. As with the pollution indices, these assessment schemes Measures of impact on wildlife and vegetation are designed to combine many factors into one or a should reflect changes in the amount and kind of veg- few numerical scores. Unlike air and water pollution, etation and wildlife added or lost. As indicated, quan- however, there are no commonly accepted standards titative estimates of change are difficult to make. against which the scores can be compared. A more Consequently, a simpler alternative measure is detailed discussion of rating scales and indices ap- suggested together with the preferred one: pears in the following section. 1. Change in the relative abundance and variety of Communities should also consider measuring local vegetation and wildlife expressed as: residents' attitudes toward, and perceptions of, wild- (a) change in the number(s) of rare or life and vegetation. Questions on this subject could endangered species. perhaps be included in a general survey of residents' (b) change in the population size and diversity 1. Other characteristics of vegetation can also be measured, of common species (number of species, such as cover (a product of abundance and massiveness), density, amount of cover, and possibly a diversity dominance (relative areal extent of various species), and productiv- index score). ity (the rate of production of living matter). Diversity is probably a better indicator of changes which will affect the experience of ob- OR serving vegetation and wildlife. 91 perceptions and attitudes. For additional discussions 1. Vegetation of issues and methods of estimating citizen percep- Natural vegetation is important both as habitat tions in the context of a social impact analysis, see a for wildlife and as a resource itself. The latter, in companion report in this series .2 turn, can be considered from a social/psychological A further consideration is the degree of public perspective (i.e., "open" space) and from an access to the areas affected. Total public access aesthetic/educational perspective (i.e., attractive or would imply that the "clientele group" is the commu- interesting combinations of vegetation). nity at large. However, accessibility is usually related to distance of residence from the area in question. It a. Assessment of Areal Extent may thus be useful to identify those people within Measuring the amount of open space is a straight- walking distance separately from those beyond for publicly accessible areas. For private areas the clien- forward operation. Change in cover areas currently in tele group can be more accurately determined. Even a natural state are readily estimated, if all or most of for private areas, however spillover affecting persons the site is to be' altered (e.g., cleared or filled for other than those with acc'ess to the area can occur. home sites). Assessment of the current stock can be This is especially true for bird habitat areas or for pri- made from black and white or color aerial photos of vate areas which are visible to a larger audience. the community and site in question. The segregation Consideration should also be given to the way eval- of open spaces into cover categories (forest, grass- uation results are presented to the decision makers. land, water, etc.) should be performed at this point if Analysis of impacts on open space readily lends itself this information is to be used in the actual evaluation. to map presentation. "Before" and "after" develop- An inventory of mature trees at the site might also be ment maps reflecting open space changes would ap- taken if there are relatively few and an areal descrip- pear to communicate the information well. The loca- tion seems less appropriate. Sources of aerial photos tion of natural areas could be identified on these maps include the National Aeronautics and Space Adminis- together with their quality ratings (if the preferred tration, the Soil Conservation Service and the Agri- measure is used). If species lists have been compiled, cultural Stabilization and Conservation Service a tabula r presentation of impact is probably most suit- (U.S. Department of Agriculture), the U.S. Geolog- able, as illustrated in Figure 3-1. ical Survey (U.S. Department of the Interior), state departments of transportation, and private en- gineering/planning firms. Developers often obtain B. MEASURING/ESTIMATING CURRENT aerial photos for their own use, and these also may be CONDITIONS available. This section discusses ways to inventory predevel- In measuring the extent of open space from aerial opment conditions in and around the proposed devel- photos, a simple planimeter (i.e., an area measuring opment site. This is necessary in order to determine device) can be employed. Alternatively, a slightly the amount and the quality of the resource to be im- more sophisticated and possibly more accurate point pacted. sampling approach can be used but is probably Although the need to utilize experts in the various unnecessary unless open space is interspersed with substantive areas throughout the impact evaluation developed areas.3 process has been noted in other parts of this report, it is especially noteworthy in the areas of wildlife and b. Assessment of Vegetation Quality vegetation. There is no substitute for expertise in and Quantity identifying the various species of plants and animals. A simple' approach to the inventorying of natural What follows, then, is a discussion of key factors areas is to use a quality rating scheme and data taken which may suggest the type and degree of impact from aerial photos andJor obtained from brief field and, to a lesser extent, of techniques used by bi- surveys. When available, color infrared photographs ologists to characterize natural environments. The are especially useful, since the amount of infrared en- latter is included so that the reader may develop an ergy reflected from leaf surfaces during each season appreciation for the detailed types of ecological anal- provides in-formation on the type and general charac- yses which are frequently required to develop quanti- tative estimates of impact. 3. Points are distributed over the photo according to a sampling design. The percentage of points falling on open spaces equals the percentage of land in open space in the community. See Brian J. L. 2. K. Christensen, Estimating the Social Impacts of Land Berry and Alan M. Baker, "Geographical Sampling," in Brian J. Development (Washington, D.C.: The Urban Institute, forthcom- L.' Berry and, Duane F. Marble, Spatial Analysis, (Englewood ing). See also, Dagg, op. cit. Cliffs, N.J.: Pientice-Hall, Inc., 1968). 92 Land Development and the Natural Environment FIGURE 3-1 EXAMPLE FORMATS FOR THE PRESENTATION OF ESTIMATED IMPACTS ON SPECIES ABUNDANCE AND DIVERSITY NATURAL AREA 11X" Species Present Abundance Future Abundance Diversity Trees (Typical entry for one line) (Typical entry for one line) (Typical entry for entire column) 150 individuals probably 25-50 indi- Present Simpson diversity viduals index score is approximately 20, future score is expected or or to be 10-15 (where 20 is Shrubs 'very diverse," 15 is "diverse," very numerous sparse and 10 is "fairly diverse',)a or or or covering 3 acres covering 1/2 acre Many species with evenly Grasses & distributed populations now, sedges fewer species with more uneven distri butions expected Aquatics Others (e.g., mosses, ferns, herbs, etc.) WILDLIFE HABITAT "Y99 Species Present Abundanc e Future Abundance Diversity Birds (See above) (See above) (See above) Mammals Amphibians Reptiles Fish NOTE: It may be desirable to present impacts on terrestrial (land based) and aquatic habitats separately or to discuss the latter as part of the water quality analysis. a. Simpson's index is a mathematical expression of diversity. See footnote 8. teristics of vegetation .4 The identification of types of plants by species, species within plant communities, vegetation (both from photos and brief field assess- and communities within the area can be ascertained. ment) is based primarily on identifying certain indi- This information can be used to either refine the cator species. Where the area under investigation is simple quality assessment previously discussed or to small (e.g., one hundred acres or less), interpretation provide baseline data for quantitatively estimating the of aerial photos may be almost as time-consuming as impact of land development on species' abundance field studies. Judgments of resource quality are based and diversity. on the current general understanding of resource Field surveys can also provide data on the presence value, health, and degree of disturbance. Several of rare or endangered species. Their presence would rating schemes have been proposed for assessing obviously increase the quality rating. the quality of natural areas.' In general, these are If the results of the field investigations are to be based on the following considerations: used for quantitative estimates of diversity, then a (a) The number of distinct plant communities. suitable diversity expression should be used.' The concept of diversity encompasses (a) the number of (b) The uniqueness of each plant community (in species in a community, and (b) the distribution of the locality/region/state/nation). individuals among the species present. The greater (c) The presence of subareas which have been re- the number of species and the more equal the distri- cently disturbed (e.g., by clear cutting, culti- bution of individuals among the species, the higher vating or grazing, burning, bulldozing). the diversity. Although the number of individuals and (d) The accessibility of the area. species can be used alone, it may be useful to employ a mathematical expression which combines both ele- Values for these factors can be presented sepa- ments." For areas with more than one plant commu- rately or, as suggested in references in Footnotes 4 nity the diversity scores for the individual communi- and 5, be combined in order to assign a rank or score ties can be summed. to individual areas. Although the mathematical manip- Since the diversity index scores have little meaning ulations differ among the various schemes, higher by themselves (and indeed can be misleading if popu- scores are generally assigned to areas which (a) have lation sizes are not also specified), it would be useful a greater number of or rarer plant communities, (b) to "calibrate" the index by applying it to a variety of are undisturbed, and (c) are accessible. natural areas in the local community. Subjective Relevant data sources on locally important6 plant ratings of diversity by a trained observer could communities can be obtained from local universities then be compared with the index score for each area and park departments and from state departments of so that a reference scale relating the two could be natural resources or their analogs. The latter should developed. also be consulted regarding the regional and statewide scarcity of community types. c. Methods of Field Measurement A more detailed, more accurate analysis can be Various standard methods of recording the pres- made using field surveys by trained observers. ence of plants and measuring their various character- Through a sampling procedure the population of 7. A useful scheme for organizing the results of a field study is 4. For more information see Michael M. McCarthy, Richard A as follows: trees, shrubs, vines, grasses and sedges, aquatic vegeta- Boots, and Bernard J. Niemann, Jr., "Remote Sensing of Infrared tion, and others (e.g., herbs, mosses, ferns, lichens). Energy: Critical Data for Land-use Decision Makers," Landscape 8. A number of diversity expressions have been developed. See, Architecture (January, 1973): 133-47; D. M. Carneggie and D. T. for example, Isaacson, op. cit.; C. E. Schannon and W. Weiner, Laver, "Uses of Multiband Remote Sensing on Forest and Range The Mathematical Theory of Communication (Urbana: University Inventory," Photogrammeteria 21 (1966): 115-41; and Lewis M. of Illinois Press, 1963); and M. 0. Hill, "Diversity and Evenness: Cowardin and victor 1. Myers, "Remote Sensing for Identification A Unifying Notion and its Consequences," Ecology 54 (1973): and Classification of Wetland Vegetation," Journal of Wildlife 427-32. One of the simplest is Simpson's Index (E. H. Simpson, Management 38 (April, 1974): 308-14. "Measurement of Diversity," Nature 163 [1949]: 688): 5. See, for example, Peter A. Isaacson, "Aquatic and Terrestrial N(N - 1) Consideration in Power Plant Siting" (Albany: Office of Environ- D= m mental Planning, State Department of Public Service, 1974); Ber- no, - 1) nard J. Niemann, et al., Recommendations for a Critical Resource Information Program (CRIP) for Wisconsin, Phase III Report, where D = the diversity index (Madison: Institute for Environmental Studies, University of Wis- N = the total number of individual plants in the community consin, February, 1974); and William Tans, "Priority Ranking of n, = the number of individuals of species i Biotic Natural Areas," The Michigan Botanist 13 (1974): 31-39. M = number of different species 6. Important plant communities are not necessarily rare. Impor- Note: This index was originally presented in an inverted form. It tance refers as well to representativeness, quality, robustness, and has been used in both forms and seems to be more intuitively satis- aesthetic qualities. fying when the numbers increase as diversity increases. 94 Land Development and the Natural Environment istics can be found in the literature.9 Commonalities the Brown-Blanquet scale probably being the most and key differences in those methods appropriate for popular." measuring abundance and diversity will be briefly A thorough and quantitative analysis of a natural highlighted here. Since the accuracy of field inves- area is expensive. For a site of about fifty acres con- tigations is a product of statistical design, consistency taining three or four plant communities, the cost in sample selection, and skill in plant identification could run to $10,000 or $15,000 for a professional (among other factors), any locality contemplating the biologist, depending on the number of times the use of biological field surveys is strongly encouraged site is sampled. 12 (Seasonal sampling is highly recom- to obtain the services of a person appropriately mended.) A simple species list can probably be ob- trained and qualified. tained for a few hundred dollars. 13 In order to ascertain the presence and abundance Aquatic environments produce several distinct of plant species within a geographic area, the site is subenvironments, each of which should be sampled sampled and the sampled plants are identified and separately. Free-floating or submerged plants can be counted. Since both the presence and abundance of sampled directly. Plants attached to submerged ob- specific species are dependent on seasonal climatic jects can only be inventoried by collecting samples of factors, the sampling should preferably be done these objects and then removing the plants. Bottom- during each active season-spring, summer, and fall. dwelling plants are collected by special devices called For terrestrial (i.e., land-based) ecosystems the most bottom samplers. salient considerations involve the manner of sample selection, the sampling intensity, and the techniques 2. Wildlife of plant identification and measurement. The alterna- Local wildlife can be inventoried directly by taking tive sampling units are "quadrats," "transects," and a population census, or indirectly by assessing the "points" (or "point-quadrats"). The first are cir- quality of local habitats. cular or rectangular plots distributed throughout the natural area. The size, number, and location are de- a. Habitat Analysis termined by the density and distribution of vegeta- This is the .simpler of the two approaches, as the tion.10 Within each plot the vegetation is identified analysis can be performed from secondary sources of and individual plants counted. Transects are either information. Again, aerial photography is a prime linear arrangements of quadrats or lines which cross data source .14 The following factors for terrestrial the area of interest at selected intervals. Plants are ecosystems should be considered in such an analysis: identified and counted if they lie under or over or touch the line. Points are individual positions from a. The number of and types of plant communities which plants are identified and counted. per unit area. For simply producing a list of the species present, b. The number of forest openings (i.e., clearings in the entire area is surveyed in a systematic fashion. forested areas). No attempt is made to count the number present. c. The presence of water. The most appropriate method in any situation will d. The presence of movement corridors (e.g., depend largely on the types and heterogeneity of veg- trails, stream valleys). etation characteristic of the area. Regardless of which method is used, the environment should be separated e. The size of the area. into from three to five vertical strata and each mea- f. The rarity of the wildlife for which the habitat is sured separately. appropriate. The time required can be significantly reduced if The analysis should be performed separately for subjective measures of plant abundance are used. (In groups of animals requiring different types of habi- other words, if Measure 2 is used.) A limited number of abundance rating schemes have been tested, with 11. For additional information on abundance rating schemes, see Kershaw, op. cit. 9. See, for example, Robert L. Smith, op. cit., Appendix B; 12. Personal communication with Forest Stearns, Professor of and Kenneth A. Kershaw, Quantitative and Dynamic Plant Ecol- Botany, University of Wisconsin, Milwaukee. ogy, (New York: American Elsevier Publishing Company, Inc., 13. Ibid. 1973). 14. See, for example, R. N. Colwell, "Remote Sensing as a 10. The spatial distribution of vegetation and other natural Means of Determining Ecological Condition," Bioscience 17 resources and the implications for sampling design are discussed in (1967): 444-49; and H. K. Nelson, A. T. Klett, and W. G. Burge, D. Keyes, V. Basoglu, E. Kuhlmey, and M. Rhyner, "A Compari- "Monitoring Migratory Bird Habitat by Remote Sensing son of Several Sampling Designs for Geographical Data," Geo- Methods," Translations of the North American Wildlife Natural graphical Analysis (forthcoming). Resource Conference 35 (1970): 73-83. Wildlife and Vegetation: Methodological Approaches 95 tats. But, in general, the greater the diversity of plant sistance of trained wildlife observers should be communities, the larger the area, and the greater the sought in undertaking a wildlife census. amount of edge or ecotones (i.e., areas of transition Most methods employ either direct observation between communities), the better the habitat. The (sometimes preceded by trapping and tagging animals presence of water and movement corridors further in the area) or the recording of indirect evidence. improves the value of natural areas as wildlife Direct observations of birds include both visual habitats. sighting and the identification of characteristic calls The quality of aquatic habitats is based primarily or songs (usually during mating season) at selected on the quality of the water. For this reason the reader sample points. A modified procedure used to survey is referred to Part 2 of this report for further informa- bird populations in Columbia, Maryland, relied on tion on tolerance limits for various species. Again, traverses rather than sample points, thus overcoming analysis should be performed separately for species the problems of reduced visibility and audibility in ur- requiring different habitat conditions. banized areas."' Mammals and large reptiles are often Wetland areas (i.e., swamps, marshes, bogs) de- "counted" by recording indirect evidence: pellets serve special mention as habitats. Due to the juxtapo- (i.e., fecal material), tracks, active dens and lodges, sition of aquatic and terrestrial ecosystems, wetlands browse areas, and other signs). Due to the difficulties support a rich variety of animal and plant life. Fresh- in relating this evidence to the number of animals water wetlands are especially important as nesting present, indirect methods are less accurate.19 Quanti- areas for waterfowl, many of which have value as tative expressions of their accuracy are usually game species. 15 Saltwater wetlands are of critical im- lacking, however. portance as breeding grounds for a vast array of com- Although the term "wildlife" is normally reserved mercially valuable fin fish, shellfish, and crustaceans. 16 for the more obvious or apparent species, the value of Various schemes have been proposed for com- a study which will be used in an impact analysis may bining the various habitat quality variables into a be increased if data on animals at all levels of the en- single score." Alternatively, subjective ratings can be ergy pyramid have been collected. Of course, the ex- assigned to a given area based generally on these tent to which this data can be used, in combination variables. In either case it is desirable to catalog the With descriptions of the proposed developments, to habitat ratings by type of animal or animal groupings. estimate impact on wildlife will depend on current Figure 3-2 is an example of a format that could be knowledge of such things as pollutant toxicity levels used to record this information. (Only a sampling of and interrelationships among organisms. Where infor- all possible habitat types is included.) The quality of mation of this sort is at hand for certain "nonwild- the area being evaluated would be broken down by life" animals, or where these animals represent a sig- both type of wildlife and type of habitats found in the nificant local resource themselves (e.g., clams in tidal area. Descriptions based on the quality variables areas), a population survey may be justified. would appear in each cell. Measurement techniques for the smaller, less mo- bile organisms are similar to those for vegetation. b. Population Census Quadrats are often used to sample such animals as Since animals are mobile they are obviously harder mollusks and earthworms, while zooplankton and to find and consequently much more difficult to other aquatic organisms are surveyed by taking water survey than plants. In addition the observer may or bottom samples. Insects are collected with nets frighten the observed, thus reducing the accuracy of and populations determined by the intensity of netting the survey. For these reasons, a population census is effort and the number of individuals collected. In frequently used in combination with habitat assess- most cases the statistical accuracy of the results can ment. be determined if care is exercised in the sampling and As in the discussion of vegetation surveys, only the measurement activities. highlights of field methods will be described. The as- 18. Traverses are divided into 100 yard long segments and birds within My yards on either side of the traverse line are counted 15. See Niemann, op. cit. continuously as the segment is walked. See Aelred D. Geis, "Ef- 16. See John Clark, Coastal Ecosystems (Washington, D.C.: fects of Urbanization and Type of Urban Development on Bird The Conservation Foundation, March, 1974) and G. Lauff, ed., Populations," in Proceedings of Symposium on Wildlife. Estuaries (Washington, D.C.: American Association for the Ad- 19. For example, the relationship between number of pellets and vancement of Science, 1967). number of animals is dependent on animal species, age, sex, diet, 17. See, for example, Isaacson, op. cit. and Niemann, et al., season, and type of vegetation present (which may cover the op. cit. pellets, thus reducing visibility). 96 Land Development and the Natural Environment FIGURE 3-2 A CHART FOR CATALOGING BASELINE DATA ON HABITAT QUANTITY HABITAT AREA "A" HABITAT TYPES ON OR NEAR THE DEVELOPMENT SITE Deciduous' Coniferousb Old Field/ Forest Forest Grassland' Wetland Stream Pond/Lake Birds 1. Abundant 2. Absent 3. Common Mammals 1. 2. 3. Reptiles 1 . 2. 3. Amphibians 1. 2. 3. Fish 2. 3. NOTES: For those habitat types which are generally appropriate for the species listed, the quality is described (e.g., excellent-poor) and possibly given a rating based on the factors listed in the text. a. Deciduous trees are those which lose their leaves seasonally. b. Coniferous trees are those which do not lose their leaves. c. old fields are abandoned pastures, while grasslands are areas characterized by native species (i.e., they have not been farmed). Regardless of the method used to survey wildlife able. Quantitative expressions of species diversity populations, it is important to employ them at several similar to those cited for plants can be used .20 points in time. Climatic and other factors often pro- Quantitative animal surveys tend to be expensive. duce yearly as well as seasonal fluctuations. Ideally, Bird populations are the easiest to measure and the baseline values used in impact evaluations would be long-term averages. Unfortunately, the data 20. Again, the Simpson formula (Simpson, op. cit.) is appro- needed to construct such averages are rarely avail- priate. Wildlife and Vegetation: Methodological Approaches 97 would probably cost several hundred dollars, using a serious transportation-related pollutants-photo-oxi- professional biologist for a site of about fifty acres dants. Even where the new source will be a single and containing three or four plant communities.2' point and the emissions are well-specified, accurately Surveys of mammals would probably cost several predicting the effects on plant growth is difficult .25 thousand dollars under similar circumstances .22 Some of these effects will be quite obvious from the developer's plans (e.g., tree-cutting and wetland C. ESTIMATING FUTURE CONDITIONS23 filling). Others are more subtle and will probably re- quire the judgment of local biologists familiar with the Most estimations of future impacts rely on logical environmental requirements and characteristics of deduction and analogy to similar, well-documented plant species found in the local area. situations. We have yet to find specific predictive The effect of a specific development is also depen- techniques for estimating the impacts of land devel- dent on the management practices employed once the opment .24 The discussions to follow will highlight key development is completed. Mowing of common areas considerations, relevant research, and impact evalua- and the elimination of tree seedlings on the periphery tion findings where appropriate. of privately owned parcels will effectively eliminate wildflowers and reduce the effectiveness of buffer 1. Vegetation zones around natural areas, respectively. On the The most direct and usually most significant devel- other hand, new types of trees and shrubs may be in- opment impacts on open spaces and natural areas are troduced by new residents or the developer. Compar- also the most obvious-removal or addition of trees ison with similar types of developments elsewhere in and underbrush, filling of wetlands, grading and re- the community may be helpful here. planting of grasslands or fields. The vegetation left The actual procedures employed in the analysis pri- standing may benefit or suffer from an increased ex- marily involve the comparison of the project site plan posure to wind and sun and from changes in soil with the baseline assessment of the existing open moisture content. Less obvious impacts may be mani- spaces and natural areas in the immediate vicinity. A fest in terms of interruptions in plant reproduction statement of landscaping plans and future manage- mechanisms. Land developments which reduce those ment intentions would be desirable. types of wildlife upon which some plants depend for seed propagation may reduce the ability of these 2. Wildlife plants to compete for space. For example, berry- a. Key Considerations producing plants depend on birds for propagation, while animals with hair or fur often assist in the distri- Land developments can affect wildlife populations bution of thorny seeds. Land development can also in the following ways: cause the introduction of nuisance species (e.g., dan- (a) Dir'e'ct removal of habitats. delio .ns), which compete well with more "natural" (b) Indirect destruction of habitats through the in- species. troduction of air and water pollutants. The effect on vegetation of additional air pollutants (c) Interference with movement, especially by the emitted by, or as a result of, new development should construction of highways through habitat areas. also be considered. Even low levels of certain pollu- tants may have dramatic effects. However, it may be (On the other hand, the clearing of trees in extremely difficult to separate the effects of a single forested areas may actually facilitate move- development from the cumulative effects of urbaniza- ment.) tion in general. This is especially true of the most (d) The introduction of predators, such as cats and dogs. 21. Personal communication with Forest Stearns, Professor of (e) The elimination of natural predators. Botany, University of Wisconsin, Milwaukee. 22. Ibid. 25. Retrospective studies on the impacts from power plants have 23. For a general discussion of urbanization and its effects on underscored the difficulty in controlling for all nondevelopment the natural environment, see D. Gill and P. Bonnett, Nature in the factors and thereby being able to assign the observed changes to Urban Landscape: A Study of City Ecosystems (Baltimore: York the power plant. See, for example, D. E. Willard, Preliminary Press, Inc., 1973). Documentation of Environmental Change Related.to the Columbus 24. Models developed to simulate the interractions of specific Electric Power Generating Site (Madison: Institute for Environ- ecosystems have been used primarily as management tools for mental Studies, University of Wisconsin, May, 1973). However, largely undeveloped areas (e.g., rangeland management). How- the EPA secondary ambient air quality standards are designed to ever, some water quality models incorporating biological param- protect vegetation and materials, and can be used as an indicator of eters and applicable to urbanizing areas are available. See potential impact. (For more information, see "Air Quality," Part 1 "Water Quality and Quantity," Part 2 of this report. of this report.) 98 Land Development and the Natural Environment (f) The introduction of urban-adapted species (c) Urban species (e.g., house sparrows, starlings) which are superior competitors. increased as eaves and vents provided attrac- (g) The infringement on feeding and nesting activi- tive nesting sites. These populations were also ties due to increased noise and disturbance associated with poorly designed or constructed levels. homes. More desirable urban species (e.g., N The addition of new habitats which will cause song sparrow, mockingbird) also increased due to the landscaping around homes. increased populations of certain species. (d) Detached homes in areas where some original trees were retained provided the greatest diver- b. Research Findings sity of species. Since predictive wildlife impact techniques analo- Geis has also reported that populations of individ- gous to air dispersion and water quality models are ual species and overall diversity can be increased by not at hand, the importance of case studies of similar not mowing open spaces, by leaving'water areas in developments in similar environments is greatly in- natural vegetation, and by planting grasses and creased. The results of retrospective analyses must shrubs of high nutritional value to birds .27 be applied with caution. For studies which have mea- A comparison of bird populations across an envi- sured population over time, checks should be made to ronmental gradient in Washington, D.C., by Robert see if proper controls were used. Since wildlife popu- Williamson provides additional information on bird lations can fluctuate dramatically from year to year, populations in urbanizing environments .2' The follow- the measured changes in urbanizing areas should be ing results were obtained from a population census in compared with those in rural areas for the same time each of three city environments-a large, forested period. In addition, if the results of a study in one park; a moderately dense, landscaped townhouse geographical area are to be applied to another, the neighborhood; a denser neighborhood lacking in validity of such a transfer will depend on the similar- landscaping and open spaces: ity of the developments and environments in ques- (a) Mockingbirds and cardinals were associated tion. Care must also be exercised in interpreting the with the number of deciduous trees and the di- results of urban wildlife studies which summarize the versity of yard vegetation. cumulative results of urbanization (e.g., increased air temperatures, increased average noise levels, de- (b) Robins and blue jays were associated with the creased sunlight, increased street lighting, increased percentage of unpaved ground cover and with community-wide pollution levels). The findings are dense housing. often difficult to apply to single developments, which (c) Wood thrushes were associated with the may contribute only infinitesimally to the cumulative number of coniferous trees which provided impact. food and protection. Although the listing of research findings to follow is (d) Catbirds were associated with dense thickets undoubtedly less than exhaustive, it does provide a and water. set of representative findings: (e) Starlings, house sparrows, and. pigeons were Birds-Aelred Geis has monitored the changes in associated with dense housing. bird populations over a period of several years in A third study provides more detailed information Howard County, Maryland. During this time the new on necessary habitats for various species :29 town of Columbia was undergoing development.16 He found: (a) Cardinals need tree cover at least five feet in height and are found in urban areas only when (a) The cropland species (e.g., bobwhite), field trees are above this height. species (e.g., redwinged blackbird), and wood- (b) Bluejays nest only in mature deciduous trees. land species (e.g., wood thrush) all declined due to habitat removal and possibly predation (c) Both bluejays and cardinals are attracted to by cats. feeders in developed areas, even if not to nest. (b) One adaptable species, the cardinal, showed no Mammals-Most pertinent studies of mammals change. Ornamental shrubs and bushes appear to provide a ready supply of food and nesting 27. Personal communication. areas. 28. Robert D. Williamson, "Birds in Washington, D.C.," in Pro- ceedings of Symposium on Wildlife. 29. Darrell L. Cauley, "Urban Habitat Requirements of Four 26. Geis, op. cit. Wildlife Species," in Proceedings of Symposium on Wildlife. Wildlife and Vegetation: Methodological Approaches 99 have concentrated on squirrels and raccoons. The (e) Some amphibians and reptiles may find "artifi- findings are as follows: cial" habitats suitable (e.g., sewers, reservoirs, (a) Squirrels adapt well to urban environments pro- ponds). vided that "mature, uncrowded trees with large canopies" are present .30 Chimneys and attics will provide shelter but are hardly an accept- c. Estimation Procedures able alternative .31 . (b) Raccoons will co-exist with man in urban envi- Although quantitative techniques are not available ronments provided that fallen trees or other for estimating impacts, meaningful conclusions about natural enclosures are available as nesting sites. the effects of future development can be reached. (When forced to seek alternative shelter, These conclusions should be based on baseline garages, attics, and sewers are the preferred studies of local wildlife populations and/or habitat choices.) A supply of water is also required. conditions, information on development character- Garden vegetables can be substituted for natu- istics, and the results of other impact studies similar rally occurring food sources .32 to the ones just described. The analysis can be organized around the primary Amphibians and Reptiles -Because many amphib- mechanisms of impact: (a) removal of habitat, (b) ian and reptile species have water-associated habi- deterioration of water and air quality, (c) interference tats, they are susceptible to alterations in water qual- with wildlife movement, (d) introduction or removal ity as well as to physical changes in their habitat. of predators, (e) introduction of more competitive Craig Campbell has reviewed a number of relevant species, and (f) increase in noise levels. The pro- studies regarding impacts on amphibians and rep- posed development can then be assessed for each of tiles .33 A sampling of these follows: these changes. Special attention should be given to (a) Modification of natural storm drainage systems the proposed design features and management prac- (e.g., channelization of streams, installation of tices. Consideration should be given to the extent to sewers, dredging) reduces habitat for various which original vegetation can be retained, the extent frog, snake, and salamander species. to which grass mowing can be confined to small areas, the extent to which development in general and (b) Frogs are extremely vulnerable to roads, roads in particular can be directed away from key which create barriers to their movement. habitat areas (especially wetlands), the types of vege- Snakes and turtles, which use roadways for tation which will be planted, the types of new water warm resting areas, also exhibit high death areas created (and the intended management prac- rates from cars. tices, thereof), the design of the proposed buildings, (c) Increasing levels of pollution from septic tanks, and, of course, future levels of air, water, and noise municipal sewage facilities, and industrial pollution. Attempts to circumvent probable negative sources have been associated with decreasing impacts (e.g., culverts beneath roadways to facilitate populations of aquatic amphibians and reptiles wildlife movement) should also be noted. in many geographic areas. Once the development-induced changes have been (d) Species which inhabit transitional areas enumerated, they can be related to the wildlife found between plant communities seem to be more in the area. In many cases the probable direction of tolerant to disturbance; land-based species tend impact (e.g., the red winged blackbird population will to survive longer in the face of urbanization be reduced, a high-quality habitat will be disturbed) than do aquatic ones. and, in some cases, the relative magnitude of impact (e.g., mallard ducks will be eliminated from the area, 30. Vagn Flyger, "Tree Squirrels in Urbanizing Environments," the wetland will be totally drained and filled) can be in Proceedings of Symposium on Wildlife. ascertained. In order to translate these into quantita- 31. Cauley, op. cit. tive estimates of impact and areal extent of habitat re- 32. Ibid.; and James R. Schinner and Darrell L. Cauley, "The moval can be estimated. If present wildlife popula- Ecology of Urban Raccoons in Cincinnati, Ohio," in Proceedings tions are known, a range of estimated changes in of Symposium on Wildlife. 33. Craig A. Campbell, "Survival of Reptiles and Amphibians in species populations (high, low, most likely) can be Urban Environments," in Proceedings of Symposium on Wildlife. used to estimate changes in diversity. 100 Land Development and the Natural Environment 111. CONCLUSIONS AND RECOMMENDATIONS A. PLANNING VERSUS PROJECT REVIEW made of selected areas as time and funding permit. Aside from the obvious fact that eliminating devel-' Although most of the prior discussion focused on the evaluation of individual developments, planning opment in and around high quality areas will rnim- for the protection of a community's wildlife'and vege- mize impact, little in the way of generalizations* can tation resources should be coordinated with and sup- be made about types of development and'the p'rob- portive of the project review process. First, the iden- able severity of their impact. Certainly the largest (in tification and assessment of open spaces, natural area) and the most polluting developments Will have areas, and wildlife habitats can be used as the basis the greatest impact, but translating these variables for the application of land use controls and induce- into general types of development is difficult. Even a ments designed to protect these areas (and thus pos- correlation of impact severity with population density sibly eliminate the need for evaluations of individual is tenuous. A well-designed, high-density cluster developments). Secondly, community-wide baseline development can be much more consonant with studies may facilitate individual evaluations when neighboring habitats than a large-lot subdivision with they are necessary. Thirdly, knowledge of alternative its manicured and often fenced-in yards. Perhaps the habitat areas into which wildlife may relocate (car- one general statement which is justified is that zoning rying capacity permitting) and of the total remaining which provides for design flexibility should be used in community resource base will allow more accurate buffer areas. The more important point to be made, estimates of impacts from single projects to be made, however, is that planning can never totally substitute on the one hand, and more meaningful interpreta- for project reviews. Design features and future man- tions of the estimates, on the other. agement practices (e.g., for planned unit develop- Although a few local governments have undertaken ments) are very important considerations which field studies of selected types of natural areas or habi- only the evaluation of individual developments c Ian tats on a community-wide basis,' most planning-type capture. studies are of a reconnaissance nature. Aerial pho- B. ALTERNATIVE DATA COLLECTION tographs are typically employed to inventory all open APPROACHES spaces and to make initial assessments of natural areas and habitats. More detailed studies can thus be Although ecological field studies may be time- consuming and costly, alternative data collection op- 1. Dane County, Wis., for example, has initiated a detailed field tions are available. Any community located near a analyses of all wetlands in the county. college or university should investigate the possibility 101 of employing biology students supervised by appro- C. SPECIFIC RECOMMENDATIONS priate faculty members. Information already collected AND CONCLUSIONS as part of class research projects may be highly rele- Following is a list of recommendations and conclu- vant for the purpose of evaluating impacts. Depart- sions based on our investigation of issues and ments of natural resources or analagous agencies at methods of analysis relevant to the as .sessment -of the state level should also be queried for locally rele- wildlife and vegetation impacts from proposed land vant data. Private environmental interest groups and development: other organizations with knowledge of local resources (e.g., bird-watching groups) are other sources of data. I .Evaluations of individual developments should The possibility of employing the latter on a volunteer include consideration of the expected change in or limited pay basis should also be explored. In many the amount of vegetation and numbers of wild northeastern states active participation by local inter- species; communities should consider using im- est groups and r 'esource experts has been formalized pact measures such as are suggested here. In through the establishment of local environmental con- choosing between the preferred and fallback servation commissions. Some of these commissions measures, the potential magnitude of impact and act purely as an official forum for environmental ad- the time and funding available for evaluation will vocacy groups (and thus the subjects for discussion probably be the most important considerations. extend far beyond maintaining vegetation and wildlife 2. The estimation of impacts. on wildlife and vege- resources), while others are more technically oriented tation must be based on analogies to similar and and attempt to undertake original data collection and well-documented case studies and/or inferences analysis on their own .2 ' made by experts knowledgeable about the local Although the utilization of data sources compiled environmental conditions. Predictive models by volunteers is attractive, a word of caution is nec- analogous to air and water pollution models are essary. In those cases where the data collector may not available. also be a strong adversary (or advocate) regarding re- 3. Communities should consider supplementing lated land use issues, the accuracy of the data may be individual project evaluations conducted by questioned. Without supervision of the data collec- trained observers with data collected by local tion by an independent and reputable expert, it may universities and private naturalist associations. be impossible to resolve this issue. 4. The identification. and characterization of high- quality natural areas and wildlife habitats during 2. For more information on conservation commissions, see the process of developing community-wide plans Charles C. Morrison, Jr., "Local Environmental Conservation Commissions-The Beginning of a National Movement," outdoor would probably facilitate the preparation of indi- 'Recreation Action, No. 29 (Fall, 1973): 7-13. vidual project evaluations. 102 Land Development and the Natural Environment PART 4 NOISE 1. INTRODUCTION AND BACKGROUND Noise has been commonly defined as unwanted fare that may be caused by variations in the magni- sound. A proposed land development, by the nature tude, pitch, and timing of noise. These may be classi- of its design and function, can be a potential source of fied into three broad groups of adverse effects which noise for residents in the surrounding neighborhoods. are known to be caused by noise. These are: This section provides a brief background discussion 1. The physiological effects on human hearing. of the physical properties and measurement of noise, as well as information on a few approaches to esti- 2. The nuisance effects on personal comfort, re- mating noise impacts from proposed developments. sulting in annoyance. In evaluating a proposed land development for 3. The nuisance effects on specific activities (e.g., noise the concern is primarily on how the sounds interference with oral communication and sleep- emitted directly (e.g., from people or machinery at ing). the site) or indirectly (e.g., from increased traffic These findings have been based on extensive epide- flows) will affect people living or working in the sur- miological studies, that is, studies conducted on man rounding areas.' The impact is related to the magni- in real-life situations. tude and pitch of the sounds (together, the perceived There has also been extensive laboratory testing on loudness), the frequency of occurrence of the various animals and humans to ascertain nonauditory physio- noise levels, and the compatibility of new sounds logical responses from noise. These relationships, with existing noise levels .2 however, have not been shown to be causal. That is, the effects may be caused by other factors found in A. HEALTH AND WELFARE CONSIDERATIONS3 noisy environments. It is also not presently possible to generalize these findings to humans exposed to Biomedical research has shown that there are a normal day-to-day noises. There are a number of variety of adverse effects on human health and wel- variables that may affect response (e.g., context, timing of occurrence), although the extent of influ- 1. Although most new developments will increase noise lev- ence is not known. A review of the literature on els, it is conceivable that some could provide barriers and noise absorbing surfaces to decrease levels. 2. Additional background material can be found in EPA, Infor- 3. For further discussion of this topic, see Kryter, op. cit.; EPA, mation on Levels of Environmental Noise Requisite to Protect Information on Levels of Environmental Noise . . . ; and Louis Public Health and Welfare with an Adequate Margin of Safety Sutherland, Marial Braden, and Richard Colman, A Program for ,(Washington, D.C.: EPA, March, 1974) (NTIS No. PB 239-429) the Measurement of Environmental Noise in the Community and (hereafter cited as Information on Levels of Environmental Its Associated Human Response, vol. 1: A Feasibility Test of Mea- Noise . . . J; and Karl D. Kryter, The Effects of Noise on Man surement Techniques (Washington, D.C.: DOT, Office of Noise (New York: Academic Press, 1970). Abatement, December, 1973) (DOT-TST-74-5). 105 human effects suggests that noise exposure, under passes, while frequency reflects how rapidly the pres- controlled situations, can lead to decreased respira- sure fluctuates. Both amplitude and pitch contribute tory rates and cardiovascular changes, constriction of to the loudness or "sound level" as perceived by the blood vessels, changes in blood pressure and man. heart rate when sound reaches seventy decibels Most noise is a combination of many individual (dB) and above. Studies on animals indicate that sounds. That is, it consists of a wide range of pitches ". . . continued exposure leads to imbalance of and amplitudes and is known as '-'broad band noise." blood electrolytes, blood glucose levels, size of adre- "Pure tone" or single pitch noise, when it does exist, nal cortex and ultimately changes in kidneys, liver can be extremely annoying, as in chalk screeching on and gastro-intestinal tissues. 114 Even though re- a blackboard. searchers do not know the full extent of the nonaudi- The pitch of a sound is expressed in cycles per tory physiological responses to noise, many assume second, or Hertz (Hz), while amplitude is measured that if noise control is sufficient to protect persons in decibels (dB). Decibels are calibrated on a from ear damage and hearing loss it is probable that logarithmic scale directly related to air pressure humans will also be protected from other nonauditory levels .7 Man's audible spectrum ranges between physiological impacts.' twenty and 20,000 Hz and between zero and slightly Table 4-1 summarizes some of the findings on nui- more than 140 dB. sance and physiological effects of environmental In order to better reflect the subjective loudness of noise stimulus. different sounds as perceived by man, the A-weighted decibel scale (dBA) has been developed. Values on B. FUNDAMENTAL PRINCIPLES6 this scale reflect amplitude weighted by the pitch at Sound is a vibration or wave conveyed by mole- which the amplitude is measured in a manner which cules of air. As such, it has an amplitude (volume) reflects man's responsiveness. The scale is again and a frequency (pitch). The amplitude is the magni- logarithmic and an increase of 10 dBA corresponds tude of air pressure fluctuations caused by changes roughly to a doubling in perceived loudness. Figure in the concentration of air molecules as the wave 4-1 shows the amplitude of some common sounds. The loudness of noise at any point in space de- pends on features of the source, the distance between 4. Sutherland, op. cit. 5. EPA, Information on Levels of Environmental Noise .... P 6. For additional information, see Kryter, op. cit.; and Theodore 7. More precisely: dB = 20 log,0 Schultz, Noise Assessment Guidelines: Technical Background, HUD Report No. TE/NA 172 (Washington, D.C.: HUD Office of where P = the pressure of the sound in question Research and Technology, 1971). P0 = a reference pressure (usually 20 micronewtons/cm') Table 4-1. A SUMMARY OF HUMAN HEALTH AND NUISANCE RELATIONSHIPS TO ENVIRONMENTAL NOISEa APPROXIMATE SETTINGS WHERE NOISE LEVELS NOISE LEVELSb ARE LIKELY PROBABLE EFFECTS >45dB Urban residential (indoors) Speech interruption indoors (interruptions of normal conversations at distances up to 2 meters) >5513 Urban residential (outdoors) Speech interruption outdoors (interruption of normal conversations at distances up to 2 meters) >60dB Urban residential and residential near airport (outdoors) Average community reaction: Complaints and threats of legal action >70dB Industrial settings (indoors) and very noisy urban Hearing loss residential (outdoors) a. These thresholds are based on the summary findings of the Environmental Protection Agency in Information on Levels of Environ- mental Noise . . . (Washington, D.C.: EPA, March, 1974). b. These noise levels are approximations and may be subject to change given variations in such factors as the frequency of noise and the intermittency of occurrence. These are outdoor day-night noise level averages, or average levels for twenty-four hour periods with night noise given increased weighting due to its sleep interruption characteristics. See p. I I I for a further discussion. 106 Land Development and the Natural Environment FIGURE 4-1 the source and the point in question, and character- LOUDNESS RANGE OF COMMON SOUNDS istics of both the intervening land and atmosphere. (Measured at Source or Indicated Distance) Noise, attenuates in amplitude exponentially with dis- Sound Source dBA Response Criteria tance. A doubling in distance will reduce the ampli- tude by a factor of four, everything else held con- stant. Additional attenuation can be accomplished by Wind and temperature fluctuations and by the pres- Carrier Deck Jet Operation ence of vegetation "screens" and physical barriers.8 Painfully Loud The latter two are by far the most important factors. Limits Amplified Speech The degree of attenuation will depend on the size, type, and location of the screen or barrier with Jet Takeoff (200 feet) respect to the source and receiver. For example, tall Discotheque trees with many branches and thick foliage are quite Auto Horn (3 feet) Maximum Vocal Effort effective in reducing sound levels. Riveting Machine __110 Reverberation from reflecting surfaces, such as Jet Takeoff (2000 feet) highrise buildings found in many central cities, repre- Shout (0.5 feet) __100 sents a complicating factor. Any method used to esti- N.Y. Subway Station Very Annoying mate noise levels in these locations should be care- Heavy Truck (50 feet) -- 90 Hearing Damage (8 hours) fully calibrated in order to account for these effects. Pneumatic Drill (50 feet) -- 80 Annoying 8. For further information on atmospheric effects, see B. A. Kugler and A. C. Piersol, Highway Noise-A Field Evaluation of Freight Train (50 feet) Traffic Noise Reduction Measures, NCHRP Report No. 144 Freeway Traffic (50 feet) -- 70 Telephone Use Difficult (Washington, D.C.: Federal Highway Administration, Highway Research Board, 1973). For further information on vegetation and Intrusive barrier effects, see B. K. Huang, An Ecological Systems Approach Air Conditioning Unit (20 feet) - - 60 to Community Noise Abatement-Phase I (Raleigh: North Caro- lina State University, June, 1974) (NTIS No. PB 234-311). Light Auto Traffic (50 feet) 50 Quiet Living room Bedroom 40 Library Soft Whisper (15 feet) 30 Very Quiet Broadcasting Studio 20 (background level) 10 Just Audible 0 Threshold of Hearing SOURCE: Council on Environmental Quality, Environmental Quality, The First Annual Report (Washington, D.C.: CEQ, August, 1970). Noise: Introduction and Background 107 11. METHODOLOGICAL APPROACHES A. MEASURES, STANDARDS, AND INDICES dards for different types of land uses.' HUD has is- The suggested measure of noise impact is as sued standards applicable to outdoor noise for HUD- follows: sponsored residential developments.' Table 4-2 lists standards suggested by still others. 1. Change in the level of noise, the frequency with One of the basic problems in developing standards which it occurs, and the number of people af- is to capture the most significant aspects of noise fected in the area surrounding the development. variability: pitch, magnitude, frequency of occur- Estimates of noise levels and frequencies of occur- rence, compatibility. Reference has already been rence produced by proposed developments could be made to the dBA scale, which reflects both pitch and based on analogies to other similar developments magnitude. Some sets of standards (e.g., the FHWA (and in similar settings) or on detailed calculations of guidelines) are specified directly in terms of the dBA noise Isources and the subsequent propagations of scale. In order to capture frequency of occurrence, sound into surrounding areas. Since the suggested standards are typically specified in terms of L,O-the measure requires an estimation of the number of peo- level which is exceeded 10 percent of the time .5 T-his is true for the FHWA guideline. The HUD Standards ple affected, noise levels should be estimated for a are in terms of L33 and L, The EPA standards, on the variety of locations around the development. I Noise is a multifaceted problem which resists re- other hand, refer to L,q values. This is a scale which duction to a few simple rules of thumb. Nevertheless, expresses patterns of intermittent noise as equivalent the EPA has attempted to relate hearing damage and constant4evel noise. L,,, is thus dependent on the dis- activity interference to levels of exterior and interior tribution, of noise levels over time and can be easily noise.' Although the recommended standards do not converted to L10 values .6 The compatibility factor has represent inviolable breakpoints, they can and should 3. Sten Ljunggun, A Design Guide for Road Traffic Noise be used as points of reference.' The Swedish National (Stockholm: National Swedish Building Research, 1973) (NTIS No. Board of Urban Planning has also specified interior PB-227-258); and Federal Highway Administration, Interim Noise and exterior standards for various types of structures, Standards and Procedures for Implementing Section 109(i) of Title while the Federal Highway Administration (FHWA) 23, U.S.C., FHWA PPM 90-2 (Washington, D.C., n.d.). 4. HUD, (1390.2 chp. 1). has developed design guidelines which contain stan- 5. Similarly, L.0 and 1_90 are levels which are exceeded 50 and 90 percent of the time, respectively. 6. In order to translate L., to L,, values, the distribution of noise 1. EPA, Information on Levels of Environmental Noise. . . . levels over time and the standard deviation of this distribution must 2. EPA refers to these standards as "guidelines" since they are be known. See EPA, Information on Levels of Environmental not legally binding. Noise. . . . 109 Table 4-2. RECOMMENDATIONS OF SOUND LEVELS IN VARIOUS SPACES KNUDSEN- KOSTEN- SWITZER. CZECHO. HARRIS BERANEK BERANEK LAWRENCE VAN OS ASHRAE DENISOV KRYTER TOKYO USSR BERANEK DOELLE WOOD RETTINGER SWEDEN LAND SLOVAKIA 1950 1953 1957 1962 1962 1962 1%7 1970 1971 1971 1971 1972 1972 1973 1970 1967 dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA dbA RESIDENT Home Bedroom 35-45 35 35-45 25 30 25-35 40 35 34-47 35-45 35 34-42 25 35-45 40 Living Room 35-45 35 40 35 30-40 40 35 38-47 40 25 35-45 40 Apartment 35-45 35-40 30 35-45 18 34-47 38-42 35-50 40 Hotel 35-45 35-40 35-40 35-45 38 35 34-47 35-54 30-46 42 35-50 40 COMMERCIAL Restaurant 50-55 55 55 40-60 50 40-55 55 55 42-52 45-60 45-50 50 40-50 55 Private Office 40-45 50 30-45 35-45 30-45 25-45 40-45 35 38-47 30-45 40-45 46 40 General Office 45-55 40-55 40-60 60 35-65 50-60 35-40 50 42-52 45-55 45-55 50 Transportation 35-55 60 INDUSTRIAL Workshop Light 50 40-60 52-61 55-65 45-55 Heavy 75 60-90 70 85 66-80 60-75 70 50-60 EDUCATION Classroom 35-40 35 35 30-40 30 35-45 35 40 3"7 35 35-45 38 35 35-45 Laboratory 40-50 40-50 40-50 47-46 45-50 42 Library 40-45 40 42-45 35-45 35 35-45 40 38-47 40-45 40-45 42 40 HEALTH Hospital 35-40 40 42 20-35 35 30-45 40 25 34-47 40 40-45 38 25-35 25-35 35-40 RECREATION Swimpool 45-60 50-60 50 Sports 60 30 35-45 60 60 46 60 Gymnasium 55 40-50 55-60 45-55 46 CD CD AUDITORIUM 0 10 Assembly Hall 35-40 35 35-40 40-45 30-40 38 30-42 35-45 35-45 Church 35-40 40 40 35-40 35 25-35 40 35 30-42 35-40 35-40 38-42 (D Concert Hall 30-35 30-35 25-35 25-35 30 25-35 28-35 21-30 25-35 30-35 34 35 Court Room 40-45 40 40-45 40-45 35 40 42 35-40 35-40 Record Studio 25-30 30 25-30 20-30 20 25-35 28 21-34 25-30 30 30 TV Studio 25-30 30 30 25-35 30 25-35 28 21-34 30-35 35 34-38 Mot. Piet. Studio 25-30 30 25-30 25-35 28 21-34 35 25 CD Mot. Piet. z Theater 35-40 40 40 35 35-45 40 40 40 35-40 38 Leg. Theater 30-35 35 30-35 25 30-40 33 30-34 30-35 34 35 OUTSIDE Rural 35-45 35 Suburb 40-50 45 U rban 50-60 Industrial 0 50-60 =1 Res. Areas 55 CD SOURCE: EPA, Information an Levels ofEnvironmental Noise (1974). been used in designing still another scale of noise Table4-4. APPROXIMATE NOISE LEVELS FOR levels-Ldn. This is basically a day-night or 24-hour CONSTRUCTION EQUIPMENT L,, scale with nighttime noises weighted more heavily TYPICAL SOUND LEVEL to reflect their intrusive nature. TYPE OF EQUIPMENT dBA AT 50 FT. Additional indices which attempt to integrate the various noise considerations in other ways include Dump truck 88 Portable air compressors 81 Table 4-3. TABULAR PRESENTATION OF NOISE IMPACTS Concrete mixer (truck) 85 FOR A HYPOTHETICAL DEVELOPMENTa Jackhammer 88 NUMBER OF RESIDENTS EXPOSEI)b Scraper 88 Dozer 87 Paver 89 NOISE LEVEL ELDERLY OTHER TOTAL Generator 70 Piledriver 101 (L10 in dBA) Rock drill 98 >65 50 50 Pump 76 55-65 Pneumatic tools 85 45-55 Backhoe 85 <45 Local standards: SOURCE: Federal Register 39 (121) (June 21, 1974): 22298. >65-clearly unacceptable 55-65-potentially unacceptable noise contour lines can be interpolated. By over- 45-55-normally acceptable laying these on maps showing population by block <45-clearly acceptable or some other spatial unit, approximate values for a. Another table should be prepared showing the levels to which the number of people exposed to various levels of the population groups are currently exposed. Changes in the num- ber of people exposed to the various levels could then be calculated. noise can be obtained. Figure 4-2 illustrates a pop- b. Socioeconomic and demographic data can be obtained from ulation and noise distribution map. the census. Supplemental information on individual units such as Once these values for both the "with" and nursing homes can be used to further refine the population distri- without development" situations have been ob- bution data. tained from such a map overlay process, they could the Community Noise Equivalent Level (CNEL), the be displayed in a tabular format, -as illustrated in Composite Noise Rating Method (CNR), the Noise Table 4-3. It may also be desirable to indicate the Exposure Forecast (NEF), and the Noise Pollution impact on especially susceptible population groups Level (NPL)7 . Although any one of these indices may (e.g., older persons, persons living in poorly insulated be best suited for a given situation, they tend to cor- homes, or, from an equity perspective, disadvantaged relate well with one ,another. They can also be readily groups), as shown. At a minimum, the location of translated into L, values." noise sensitive activities or facilities, such as schools A local government may well desire to use different and hospitals, should be noted in the map presenta- standards in different parts of the community. Citi- tion. zens presumably desire quieter residential than work- ing or shopping environments. Determining the ap- B. ANALYTICAL TECHNIOUES propriate standards, however, is not a trivial task. A new development will generate noise in several Eliciting preferences, assigning levels of accept- different ways. Depending on the type and number of ability, and translating these into statistical values for buildings constructed and the degree of terrain mod- noise levels require a considerable survey effort. ification required, significantly high construction- Regardless of which standards or categories of related noise levels may be attained. After occu- acceptability are used, a map format becomes ex- pancy, commercial and residential developments will tremely useful for an intermediate, if not a final, produce transportation-related noise. Industrial de- display of information. If estimates are made for velopments will also produce various on@site noises enough geographical points (perhaps fifty, 100, specific to each type of industry. 200, and 300 feet back from the roadway and every 100 feet along the roadway), then 1. Construction-Related 7. For further information, see ibid.; and Bolt, Beranek, and The degree to which objectionable levels of noise Newman, Inc., Noise Assessment Guidelines, Technical Back- will be produced during the construction stage is ground, No. TEYNA 172 (Washington, D.C.: HUD, n.d.). 8. See EPA, Information on Levels of Environmental largely dependent on the type of equipment and Noise .... for specific instructions. machinery to be used. Table 4-4 presents average Noise: Methodological Approaches III FIGURE 4-2 MAP PRESENTATION OF NOISE IMPACTS FOR A HYPOTHETICAL DEVELOPMENT" 55 dBA 65 dBA 60 dBA NEW DEVELOPMENT 375 peopleb 350 300 350 400 200 65 dBA 150 350 60 dBA 300 55 dBA Local standards (based on a survey): >65-clearly unacceptable 55-65-potentially unacceptable 45-55-normally acceptable <45-clearly acceptable a. This displays the estimates for noise levels with the proposed development. A similar map should be prepared for the existing condi- tions so that the change in noise levels can be calculated. For this example, the loudness (dBA) estimates are given at the L,@ levels. b. The residents are assumed to be evenly distributed throughout each spatial unit (e.g., the block or block group). noise levels for various types of construction equip- will be used at the same time.' The estimates should ment at a distance of fifty feet. Rough estimates of reflect changes in noise by time of day and by phase total noise generated by the construction of a pro- posed development could be made simply by esti- 9. The noise produced by several sources is calculated by adding mating the number and different types of machinery the sound pressure levels rather than the decibels. Thus, two 3 rOO @@300 cranes each producing 80 dBA of noise would produce 83, not 160 required and adding the noise generated by those that dBA, together. 112 Land Development and the Natural Environment of construction. (The duration of each construction tail space for smaller areas which could be used to phase should also be noted.) Estimates for distances supplement the transportation data. other than fifty feet can be made, based on the fact that sound pressure changes exponentially with a a. Specific Examples change in distance from the source." The effects of The available techniques for making transportation- terrain, barriers, and possibly meteorology can be sim- related noise estimations range from simple approxi- ulated according to techniques found in references mation based on the use of tables and graphs to rather cited in the next section. complex computer models. Three of the more promis- ing and/or popular of these techniques will be dis- 2. Tra nsportati o n-R elated cussed. The discussion here will be limited to vehicular HUD Noise Assessment Guidelines -Bolt, Bera- traffic. Noise from aircraft and trains is covered in nek, and Newman, Inc. have developed a set of numerous other sources." Residential, commercial, simple procedures to estimate the suitability of poten- and industrial developments will all cause an i ncrease tial settings for proposed HUD-sponsored develop- in traffic at least on the surrounding streets, if not on ments." That is, proposed sites are rated for their a significant portion of the entire road network. The current acceptability, based on noise emanating from degree of impact will be determined by the type and the surrounding environment. For estimating noise number of vehicles added (by time of day), the impactsfrom a development on the community, the average speed and "stop-and-go" nature of the trips, same procedures can be used, but at several geo- the physical characteristics of the streets (e.g., eleva- graphic points. Although the guidelines deal with tion, grade, natural or manmade barriers), and the aircraft and railroad as well as with automobile distance from source to receptor. The noise levels and truck noise, our concern is largely with the lat- once the development has been constructed are then ter two. the sum of existing levels and the increment added by In order to use the guidelines the following must be the development. 12 specified: Besides data on traffic generation, information on 1. The mix of cars and trucks. population distribution is needed to select the points 2. The average flow (number per hour) and speed where estimates should be made and to specify the of the vehicles. number of people affected. For residential popula- tions the census provides population data on a census 3. Whether the flow is continuous or "stop and tract, block group, and individual block basis. (In go. most cases the smaller units will allow more accurate 4. The road grade (i.e,, percent slope). estimates.) Population dot maps would also prove 5. The existence and position of large reflective useful if they are available on a large-map scale. For barriers (e.g., billboards, buildings). daytime nonresidential populations local transpor- tation studies of trip origins and destinations are a po- 6. The distance from each of the street lanes to the tential source of information. Rarely, however, is the geographic points where estimates are desired. data available for small areas. (Traffic zones are The noise levels are then estimated by using a usually a square mile or more.) Planning departments series of nomographs and charts. The impact due to or assessment offices may have data on office and re- the new development would thus be based on the ad- ditional number and type of vehicles generated, their 10. Mathematically, the relationship is: effect on traffic speeds and volumes, and changes to P, d22 noise barriers." In order to estimate the total impact P, d@) on the community estimates should be made for a where: P, = pressure level at distance "I" number of points at various distances along each side P2 = pressure level at distance -2- of every street affected, with the points chosen to re- d, = distance "I" flect the distribution of population and the location of d2 = distance -2- especially sensitive facilities, such as hospitals. This translates into an approximate decrease of 6 decibels with a doubling of distance. The results are expressed as one of four levels of 11. See, for example, Bolt, Beranek, and Newman, Inc., op. cit. acceptability (from clearly acceptable to clearly unac- 12. For a discussion of methods for estimating traffic levels as- sociated with proposed developments, see the chapter on transpor- tation in P. Schaenman, D. Keyes, K. Christensen, Estimating the 13. Bolt, Beranek, and Newman, Inc., op. cit. Impacts from Land Developments on Public Services (Washing- 14. The development may also reduce noise levels by adding ton, D.C.: The Urban Institute, forthcoming). barriers or other sound dampening devices. Noise: Methodological Approaches 113 ceptable), rather than in terms of decibels. Thus, the The model is sensitive to such factors as the noise HUD standards are built-in. If desired, the levels of spectrum's of different types of vehicles, the heights acceptability can be adjusted to reflect local stan- of the source and the receptor, and various types of dards. A modification of this type is presumably a ground cover (trees, shrubs, high grass), as well as to straightforward operation. However, we know of no the variables used as input to the simple version. one who has attempted it. 15 Thus, the results should be more accurate than those Unfortunately, no data on accuracy are provided in produced by the simple version. Validation experi- the user manual or supporting document. The only re- ments, however, indicate that the accuracy even of lated notation that does appear concerns the fact that the more complex version is disappointing. (See the the technique does not estimate noise levels from Summary and Comparison section.) more than one source very well. This lack of infor- NCHRP Report 117 Method-Bolt, Beranek, and mation on accuracy levels detracts considerably from Newman, Inc., as part of the National Cooperative what otherwise appears to be an extremely simple ap- Highway Research Program (NCHRP), have devel- proach to noise estimation. oped a guide to be used by highway engineers in de- TSC Methods-Two versions of a technique for es- signing highways for noise minimization.19 Much of timating highway-associated noise have been devel- the input data and many of the relationships under- oped by the FHWA's Transportation Systems Center lying the calculations are the same as those for the (TSC). 16 Similar to the HUD guidelines, the simple HUD noise guidelines. In this case, however, the version of the technique specifies parameters which technique was designed to estimate impacts of in- characterize the traffic and the environment, with es- creased traffic levels due to a proposed development timates being derived from nomographs. However, at selected sights in the surrounding neighborhoods fewer parameters are used and thus the results are rather than existing noise from the neighborhood at a less sensitive to variations in traffic and other vari- proposed site for development. ables. The effects of "stop-and-go" flow and street The analysis involves the use of charts and tables grade are -ignored. to relate the input values to levels of noise at each As with the HUD guidelines, the impact from a point specified, a new analysis being required for development would be described by estimating the each point. One relevant application of this technique noise levels at numerous locations on either side of was the analysis of noise impacts from increased each street where significant additions to traffic vol- traffic levels due to new high-rise office buildings in umes are expected. The actual number of estimates San Francisco .2" A discussion of the advantages and required depends on initial results (i.e., low estimates disadvantages from this and other applications ap- near the street eliminate the need to estimate levels at pears in the Summary and Comparison section. greater distances) and the uniformity of the environ- Other Techniques -Since the degree of roadway, mental and street characteristics. The results of the simple version are L,,, values and traffic, and environmental characterizations neces- are reported to be within 3 dBA of measured values. 17 sary to make accurate noise-level estimates tends to However, validation experiments for the presumably be necessarily large and to involve numerous calcula- more accurate complex version (discussed below and tions, several efforts are now underway to develop in the Summary and Comparison section) would indi- computer models of noise generation and propaga- cate that this is an overstatement of accuracy. tion. One such model, albeit a relatively crude The more complex version allows a greater number one-the TSC model-has already been discussed. of input variables to be used (and thus allows for a Another promising but as yet unverified example is more detailed description of the area), produces esti- the Noise-Environment-Ecology System Model under mates in terms of various statistical measures (e.g., development at North Carolina State University .21 L,O, L,,) and indices (e.g., Noise Pollution' Level), Approximately the same level of detail is required for and increases very little in cost as the number of 18. The noise spectrum is the relative magnitude of noise pro- points at which estimates are to be made increases. duced at various pitches or frequencies. The spectrum of new ve- hicles can presumably be altered in such a fashion that those noises 15. The acceptability categories can be related to statistical ex- which are irritating to man are reduced. pressions of noise levels (dBA) in a general way from Figure 29 in 19. C. G. Gordon et al., Highway Noise-A Design Guide for Bolt, Beranek, and Newman, Inc., op. cit. This graph plus those Highway Engineers, NCHRP, Report 117 (Washington, D.C.: found in Part 4 of this report provide the basis for recalibration to Highway Research Board, 1971). locally determined levels of acceptability. 20. David M. Dornbusch & Co., Inc., Intensive Commercial and 16. J. E. Wesler, Manual for Highway Noise Prediction (Cam- Residential Development Impact Study, San Francisco. Phase I bridge, Mass.: DOT, TSC, March, 1972) (NTIS No. PB 226088). Report (San Francisco: Dornbusch & Company, Inc., n.d.). 17. ibid. 21. Huang, op. cit. 114 Land Development and the Natural Environment descriptive data on roadway and traffic character- Table 4-5. COMPARISON OF PREDICTED AND ACTUAL istics, but the required descriptions of factors af- NOISE LEVELS, AT SELECTED SITES fecting propagation are much more refined. The latter PREDICTIVE include the type and density of grass, shrub, and tree TECHNIQUES zones, atmospheric temperature and -pressure, and wind patterns. The computations are based on rela- MEASURED TSC NCHRP 117 tionships derived from -extensive field studies on the SITEa DISTANCE dBA dBA DEFF. dBA DIFY. effect of these factors on propagation of sound. Noise levels can be expressed as L,O, L50, L90 and Noise Po- 1 50' 77.1 80.3 +3.2 79.0 +1.9 100, 74.7 78.7 +4.0 74.9 +0.2 lution Level values, each of which in turn can. be 200' 71.3 76.5 +5.2 69.6 -1.7 plotted as isopleths on maps of the area under inves- 2 50'. 71.4 76.7 +5.3 74.4 +3.0 tigation. 12 Although the cost of operation is unre- 100, 65.4 75.0 +9.6 71.1 +5.7 ported and the accuracy of the results remains to be 200' 58.4 67.9 +9.5 60.0 + l.'6 determined, the model seems promising. 400' 55.4 67.6 +12.2 57.1 +1.7 3 50' 74.6 79.4 +4.8 76.7 +2.1 100, 68.5 75.8 +73 70.7 +2.2 b. Summary and Comparison 200' 64.8 73.7 +8.9 66.4 +1.6 Three operational techniques for estimating the 400' 60.6 70.9 +10.3 60.6 0 4 50' 75.5 80.1 +4.6 78.5 +3.0 noise impact of increased traffic have been described. 100, 72.0 77.8 +5.8 73.5 +1.5 The key considerations from an application perspec- 200' 68.4 75.0 +6.6 68.4 0 tive are the relative cost and accuracy of these tech- 400' 59.5 70.8 +11.3 61.5 +2.0 niques. SOURCE: E. W. Babin, Highway Noise Study (Baton Rouge, Loui- Perhaps the simplest measure of accuracy is the siana: Louisiana Department of Highways, Research and Develop- difference between estimates from observed values ment Section, May, 1974). under a variety of field conditions. Table 4-5 shows a. Sites are various highways. the results of several such experiments by an inde- pendent organization. As shown, the NCHRP 117 better adapted to making large numbers of estimates Method proved to be considerably more accurate and to situations where roadway geometries became than the computerized version of the TSC Method more complicated (e.g., interchanges). Additional val- (average deviation of 1.8 versus 7.2 dBA) '13 although idation studies of NCHRP 117 produced deviations the investigators report that the TSC model was ±3 dBA or less for observed versus estimated reduc- 22. Isopleths are lines connecting points of equal values. tions in noise levels due to barriers .14 However, the 23. The reader should recall that noise is perceived to double best-drawn line through plots of observed versus esti- with a 10 dBA increase. An error factor of ± 7.2 could easily make a difference between acceptable and unacceptable levels if the esti- 24. The reductions were due to physical shields and to roadway mate is close to a threshold. configurations. Kugler and Piersol, op. cit. Table 4-6. SUMMARY OF THREE NOISE ESTIMATION TECHNIQUES TECHNIQUE OUTPUT COST ACCURACY COMMENTS HUD noise Noise level as one of Inexpensive, although repeated appli- Unreported This is an extremely simple technique assessment four acceptability cations are tedious (a new calculation whose utihty is limited by the unknown guidelines categories is required for each point for which an accuracy and the already interpreted estimate is desired) nature of the estimates. TSC method L,,@ for the manual ver- Same as for the HUD guidelines (for Suspect for the The manual version should be used only sion; L10, L50, L90, the manual version); more expensive simple version,a for very rough approximations; the com- "noise pollution level" for the computerized version but to an fair for the puterized version is probably better than for the more computer- undetermined degree computerized the NCHRP 117 method only for com- ized version version plex roadway configurations. Neither version of TSC is applicable to stop- and-go traffic. NCHRP 117 L,,, L,o, L90, "noise Inexpensive, although the computa- Good This appears to be the most widely pollution level" tions are not as quickly performed as applicable of the three methods with the HUD guidelines reviewed here. a. The accuracy should be less than that for the computerized version but was reported to be fairly good by one investigator. Noise: Methodological Approaches 115 mated values often deviated significantly from the 117 would appear to be the most accurate but TSC ideal 45* line." The authors of the- study report that, (computerized version) the most practical for impact in general, the NCHRP 117 method tends to overpre- evaluation where large numbers of estimates are dict reduction in noise levels due to barriers at points needed. If the TSC method is used, the analyst distant from the roadway and to underpredict reduc- should anticipate a consistent pattern of overpredic- tions for trucks. No validation efforts have been re- tions for continuous traffic and unknown accuracies ported for the HUD guidelines. for stop-and-go traffic." Regardless of which tech- Information from these and other sources is used to nique is employed accuracies should be determined summarize the three methods in Table 4-6. NCHRP locally, since the reported accuracies are only for a limited range of conditions. 25. If on the average the observed and estimated values were equal, then a line drawn through plotted points would be at a 45' 26. Stop and go traffic tends to produce louder but more inter- angle to each axis. mittent noise levels than continuous traffic of the same speed. 116 Land Development and the Natural Environment Ill. CONCLUSIONS AND RECOMMENDATIONS Much has already been said, either implicitly or fully evaluated). Quiet areas can also be identified for explicitly, about the utilization of measures and tech- the purpose of preservation, if this is desired. It is niques for estimating noise impacts. This chapter will worth reemphasizing that in the process of deter- attempt to tie together some loose ends and offer fur- mining problem areas communities may wish to use ther guidance to those in local governments responsi- different standards, or "targets," in different areas. ble for impact evaluation. B. SPECIFIC RECOMMENDATIONS A. PLANNING VERSUS PROJECT REVIEW AND CONCLUSIONS Unlike the situation for many of the other types of Following are recommendations and conclusions impact, advanced planning does not appear to offer regarding the estimation of noise impacts from land great potential for impact mitigation in the case of development: noise. Of course, some areas will be more or less pre- 1. Local governments should consider using im- disposed to noise problems owing to topographical pact measures similar to the ones suggested features or vegetative cover, and planners can here. Where practical, they should be quantita- encourage the segregation of noise-producing activi- tive and reflect the number of people affected. ties. In general, downtown areas will be noisier 2. Standards should be used to interpret the esti- than mixed central city residential/commercial areas, mated noise levels. Standards suggested by which will be noisier than suburban residential areas, various experts (such as the EPA standards) can which will be noisier than rural areas. Noise mitiga- be employed for the purpose, although commu- tion thus lies primarily in source controls and project nities may wish to establish their own levels of design. acceptability, based on surveys of the local resi- Impact evaluations of individual developments can dents. Different areas of the community may be used to (1) assess the seriousness of the additional thus have different standards. increment added by the development (perhaps by ref- 3. Success in reducing noise or in maintaining low erence to some set of standards), and (2) determine levels will probably depend on the incorporation the effect of special design features used to reduce of barriers, buffer zones, and other noise- noise levels (e.g., physical barriers or trees). Baseline abating features in the project design. noise studies (not necessarily part of aplanning activ- ity) can be used to identify those areas where noise is 4. Analytical techniques appear to be available for either currently a severe problem or where noise is an use in quantitatively estimating noise impacts. increasing but not yet severe problem (and thus 5. Much remains to be done in the area of tech- where the impact of new development should be care- nique development and validation. 117 PART 5 OTHER TYPES OF IMPACT: NATURAL DISASTERS AND - SCARCE, RESOURCE PREEMPTION 1. INTRODUCTION Although the discussions in the preceding parts of salient issues have been discussed elsewhere, the this report have been wide-ranging, a few topics have treatment here will be of a summary and reference not been covered fully or have been left untouched. nature. Among the many types of natural disasters, for in- The relatively superficial treatment given these stance, only floods have been mentioned thus far. topics compared to other impact areas in this report (See Part 2.) As for topics not yet broached, problems should not be misinterpreted. Natural disasters and associated with the substitution of development uses scarce resource preemption are extremely serious for other types of land use is an obvious candidate for problems for specific communities. But the quantita- discussion. tive methods for evaluating the impacts occurring to Hence, this part of the report deals with natural or caused by land development is generally less ad- disasters and scarce resource preemption. The man- vanced for these types of impacts. In addition, what ner in which new developments may (a) create dis- we do know about impact estimation is reasonably aster hazards for the occupants or other commu- well documented elsewhere, although this informa- nity residents, or (b) preclude other valuable uses of tion is contained in many diverse documents. We the land will be highlighted. Key considerations for have elected to highlight key considerations and ref- impact evaluation will be noted. Since many of the erence primary sources of information. 121 11. NATURAL DISASTERS ,OTHER THAN FLOODS In spite of improvements in our understanding of It is difficult to specify quantitatively the probability natural processes and in our technical ability to cir- of occurrence for most disasters other than floods cumvent undesirable events, man still is seriously af- and, in some cases, earthquakes. The discussion of fectedby natural disasters, such as earthquakes and data needs and procedures for estimating people and landslides. Many developments are built in or near property at risk which appears in Part 2 applies hazardous areas in the absence of clear identification equally to other types of natural disasters. of the risks involved. Whether to allow development of land when the risks are known is another matter A. LANDSLIDES AND SUBSIDENCE left to local or higher governmental judgment. The Landslides are the result of forces exerted on earth reader should also keep in mind that the subject of material located on sloping bedrock and can be due to this report-estimating the impacts associated with the characteristics of the soil or to weaknesses in the land develooment-is but one small aspect of a com- bedrock. Subsidence is the vertical collapse of the prehensive disaster prevention program. I ground due to underground mining, overpumping of The factors which lead to natural disasters are groundwater,- cavern formation, and other. causes. often localized geographically. Earthquakes occur The scale and location of a development and, to some near fault lines; landslides in areas of steep, unstable extent, the degree of landscape alteration, will largely slopes; forest fires on forested land. In order to esti- determine the potential for landslides or subsidence. mate damage to future inhabitants (and thus to reduce The basic procedure involves determining the haz- the potential monetary impact on the population as a ard potential at the development site from geologic whole), the hazard potential in the locality of the pro- and hydrologic evidence and from records of past posed development should be evaluated. landslides or subsidence episodes in the area or in Impact measures for any type of disaster can be other areas of similar topographic, geologic, hydro- patterned after that suggested for flooding.- logic, and soil characteristics .2 In order to reduce the Change in the likelihood of the disaster and the number of people and the value of the property endangered. 2. For information on specific data requirements and methods of landslide hazard assessment, see E. B. Eckel, ed., Landslides and 1. For a discussion of key issues involved in the design. of Engineering Practice (Washington, D.C.: Highway Research disaster prevention and relief programs, see Gilbert F. White and J. Board, 1958); Building Research Advisory Board, Methodology for Eugene Haas, Assessment of Research on Natural Hazards (Cam- Delineating Mudslide Hazard Areas (Washington, D.C. National bridge, Mass.: The MIT Press, 1975) and Office of Emergency Academies of Sciences and Engineering, 1974); and John H. Preparedness, Disaster Preparedness-A Report to the Congress, Sorensen, et al., Landslide Hazard in the United States: A Re- (Washington, D.C., Executive Office of the President, January, search Assessment (Boulder, Col.: Institute of Behavioral Science, 1972). University of Colorado, 1975). 123 need to evaluate each proposed development on a location of fault lines, soil type and depth, bedrock site-by-site basis, regional hazard maps can be pre- type, and water table conditions. Detailed guidelines pared using similar data and assessment methods but regarding the site-level assessment of risk are found at a smaller geographic scale. For example, a land- in various federal agency publications.6 slide hazard map has been prepared for the San Cle- The estimation of expected damage should be mente area of California based on a geologic model based on detailed information regarding the location, which relates landscape stability to (1) background design, and construction of the proposed develop- factors (e.g., critical angle of natural slope and type ment. Severalreports by various federal government of vegetation), (2) energy factors (e.g., amount of pre- agencies provide relevant information for damage as- cipitation and fire potential), and (3) special factors sessments and hazard reduction through improved (e.g., presence of swelling clays and adverse geologic construction practices .7 structures) .3 This highly abbreviated discussion may create the impression that earthquake hazard assessment is a B.EARTHQUAKES simple, straightforward operation. Quite the contrary Numerous areas within' th& United States are sub- is true.1 These calculations require the collection of ject to earthquakes. The West Coast in particular considerable quantities of data and are fraught with has been the site of significant episodes of seismic uncertainty. The error in estimating the expected activity, Ialthough some of the largest earthquakes damage for a single building may be 100 percent and in history occurred in the Midwest and on the East for several hundred structures, 50 to 75 percent .8 Coast. Before undertaking an assessment of earthquake In conducting an earthquake impact analysis the impacts for proposed developments, it is recom- key questions are these: Will the new development be mended that the USGS be contacted regarding the ex- in a high risk zone? What is the frequency of expected tensive body of research on the subject. Many communities in seismically active areas now earthquakes of various magnitudes? And what is the have special building codes designed to mitigate expected loss of life and property damage? In order to predict . the.frequency and severity of future earth- earthquake damage. New development in these com- quakes, past records of seismic activity are combined munities must meet these, codes, thus reducing some- with geological information in the vicinity of the site what the need for special attention to impact evalua- in question. Future damage is also a function of the tion. However, improved earthquake resistance is size, nature, and method of construction of the pro- only a partial solution.9 posed development. Earthquake risk maps should be a starting point for C. OTHER TYPES OF DISASTERS the analysis. Although the National Seismic Risk Map Hurricanes, tornadoes, avalanches, and forest fires does not contain information on the probability of fu- all extract a toll in human life and property damage. ture earthquakes, it does indicate what the severity In some cases the high risk areas are so widespread may be and can be used where other risk maps are and the forces of destruction so great that few pre- unavailable.4 The U.S. Geological Survey (USGS) is completing a national risk map which incorporates both the frequency and severity factors. This is ex- pected to be available sometime in 1976. Techniques 6. See, for example, Walter W. Hays, et al., Guidelines for have also -been developed by USGS and HUD which Developing Design Earthquake Response Spectra (Champaign, Ill.: provide a basis for more detailed mapping. 5 Army Construction Engineering Lab, June 1975) (NTIS No. Where a proposed, site is located. in a high risk AD-AO12 728/2GA)., 7. See, for example@ The National Bureau of Standards, Building zone@ a site-level evaluation should be conducted. Practices for Disaster Mitigation, NBS Building Science Series This is based on detailed information concerning the #46 (Washington, D.C.: U.S. Government Printing Office, 1973) and National Oceanic and Atmospheric Administration, A Study of Earthquake Losses in the San Francisco Bay Area (Washing- ton, D.C.: Government Printing Office, 1972). Additional informa- 3. California Division of Mines and Geology, "Mudslide and tion can be obtained from Charles Culver at the National Bureau Landslide Prediction," California Geology 25 (June 1975): 136. of Standards. 4. National Seismic Risk Map, Department of Commerce, Envi- 8. Personal communication with Charles Thiel of the National ronmental Science Services Administrution, Coast and Geodetic Science Foundation. Survey, circa 1969 (also contained in HUD's Minimum Property 9. Improvements in our ability to predict earthquakes may re- Standards). duce the' safety hazard 4 not the property damage. See, Frank 5. USGS, Studies for Seismic Zonation of the San Francisco Press, "Earthquake Prediction," Scientific American 232 (May, Bay Region, Professional Paper 941-A (Washington, D.C.: U.S. 1975): 14-23; and Christopher N. Scholtz, "Toward Infallible Department of the Interior, 1975). Earthquake@ Prediction," Natural History 83 (May 1974): 54-59. 124 Land Development and the Natural Environment ventative measures can be taken. Tornadoes are a For hurricanes the key considerations involve build- case in point. 10 Forest fires and avalanches, on the ing strength and potential evacuation problems for other hand, are more localized. Damage from the those likely to be affected. For example, one argument latter can thus be minimized by preventing develop- for limiting development in the Florida Keys is based ment in the high-risk areas and, in the case of forest on potential evacuation problems caused by too few fires, undertaking certain preventative maintenance bridges linking the Keys with the mainland. In order to activities, such as removal of dead plant material in provide local governments in hurricane hazard areas forest fire-prone areas and clear-cutting of trees in with more information on the extent and severity of the corridors to be used as barriers to the propagation of problem, the National Oceanic and Atmospheric Ad- fire. 11 ministration is planning to publish about 185 storm evacuation maps showing the potential flood zone areas. 12 10. Even for tornadoes, attempts at identifying high risk zones have met with some success. See Illinois Emergency Services Tayler, A Fire Hazard Severity Classification System for California Agency, Hazard Analysis for the State of Illinois (Springfield, Ill.: Wildlands (Sacramento: California State Division of Forestry, April October, 1975). 1, 1973) (NTIS No. PB-237 951/9WV). 11. For a discussion of factors which can be used to estimate the 12. Raymond Wilcove, "The Mapping of Hurricane Alley," potential for or risk from forest fires, see R. D. Nelm, B. Neal, and L. Water Spectrum (Summer 1975): 18-25. Other Types of Impact: Natural Disasters Other Than Floods 125 111. SCARCE RESOURCE PREEMPTION For every @parcel of land used for urban develop- reclamation of farmland elsewhere in the country may ment, alternative uses must be foregone. In some render urban preemption relatively insignificant. 13 cases the preemption of alternative uses may carry Still, metropolitan farmland may affect the local price with it significant social costs which are borne by the of certain agricultural products. population as a whole or large portions thereof. This In assessing the value of farmland to be converted, may be the case when certain scarce resources, such the following factors should be considered. 14 as agricultural land, land overlying mineral deposits, 1'. Produ .ctivity-this can be expressed directly as and land with unique natural features are used for res- yield (by crop type) or indirectly as soil fertility, idential, commercial, or industrial development. topography, and available moisture. The suggested impact measure is as follows: 2. Specialty crops-certain land may be uniquely The type and value of the scarce resource suited for the produc ,tion of certain specialty. and the degree of the preemption. products, such as cranberries or seed potatoes. Although the calculation of the costs of preemption in 3. Viability-even productive land is of limited monetary terms is far from a straightforward process value if its size is too small or if support indus- and is not practical for routine evaluations at the tries have left the community or region. present time,'an articulation of the land uses being preempted by development will allow decision These factors could be used to specify a qualitative makers to consciously formulate value judgments measure of resource "value." The impact of develop- about these costs. Descriptions in terms of land area, ment could then be expressed as amount of land of and perhaps qualitative assessments of "value," are the specified value converted to other uses. more practical. 13. For a discussion of these issues, see George E. Peterson and A. AGRICULTURAL LAND Harvey Yampolsky, Urban Development and the Protection of Met- ropolitan Farmland (Washington, D.C.: The Urban Institute, 1975); Recent food shortages in various parts of the world and Richard L. Barrows, et al., Wisconsin Natural Resource Policy have heightened the concern of many for the conver- Issues: An Economic Perspective, Working Paper No. 6 (Madison: Center for Resource Policy Studies and Programs, School of Natural sion of agricultural land to other uses in metropolitan Resources, University of Wisconsin, July 1973). areas. Although much of the land converted to urban 14. For additional elaboration see, Bernard J. Niemann, Jr., et uses tends to be well-suited for crop production, the al., Recommendations for a Critical Resource Information Pro- gram (CRIP) for Wisconsin, Phase III Report, (Madison: Institute impact of these conversions on total food production for Environmental Studies, University of Wisconsin, February, is far from clear. Improvements in technology and the 1974). 127 B. MINERAL DEPOSITS operators may well decide to close their operations Less well-publicized but certainly as important is rather than spend the money necessary to reduce the preemption of mineral extraction by urban devel- the level of noise and pollutant output in a manner opment. The loss of gravel pits on Long Island, for appropriate for residential or commercial areas. Un- example, has reportedly cost New York State less the proposed development will be compatible $30,000,000 per year in increased building Costs. 15 with surface or deep mining operations (e.g., heavy This is not to say that the value to society of develop- industry), a buffer area should be secured sufficient ing land overlying mineral deposits is not equal to or to .screen the mine and to mitigate accompanying even greater than the value of the deposits them- noise and dust. selves. But investigation of this issue prior to devel- opment is certainly in order. C. UNIQUE NATURAL FEATURES Mineral resources encompass nationally scarce fossil and nuclear fuels and metallic minerals, as well Unique natural features are those geologic or physi- as less scarce but locally significant construction min- ographic features which are of scientific, educational, erals, such as sand and gravel. Key considerations in or aesthetic interest. 17 They include such items as any planning study or impact evaluation include scar- waterfalls, canyons, natural bridges, mountain ranges, city, quality, and size of the deposit, ease of extrac- escarpments, or simply combinations of more com- tion, and (usually) the availability of water. 16 Unfortu- mon features which provide a scenic view. nately, an adequate assessment of these variables fre- Many states have undertaken an inventory of these quently requires costly test borings. Even though po- resources as part of critical area or other programs. tential deposits can be inferred from general geologic The relevant state agencies should be consulted for data, only about I percent of potentially valuable this information. If planning or inventory studies have deposits are economically exploitable. Where the po- not been conducted at the state or local level an as- tential mineral is extremely valuable and the pro- sessment of the impacted environment should be posed development represents a sizable investment, made as part of the impact evaluation of individual test borings might be conducted. developments. Criteria to use as basis for these as- The impact of the development should be measured sessments can be found in the literature.18 A further not only by direct physical interference with mining discussion of aesthetic evaluation appears in another activity. Development in close proximity may effec- volume of The Urban Institute's land use series of re- tively preclude future mining activity, since mine ports. 19 17. Biological features (i.e., natural areas and wildlife habitats) 15. E. Dale Trower, "Land Use and Mineral Industry" (Paper have already been discussed. See Part 3 of this report. presented at the Annual Meeting of the American Association for 18. See, for example, Niemann, et al., op. cit. the Advancement of Science, January 30, 1975). 19. K. Christensen, Estimating the Social Impacts of Land 16. For a iurther description of these variables and their applica- Developments (Washington D.C.: The Urban Institute, forthcom- tion to various types of minerals, see Niemann et al., op. cit. ing). 128 Land Development and the Natural Environment THE URBAN INSTITUTE BOARD OF TRUSTEES Charles L. Schultze, Chairman Senior Fellow, The Brookings Institution, Washington, D.C. Kingman Brewster, Jr., President, Yale University, New Haven, Conn. John H. Filer, Chairman, AEtna Life & Casualty, Hartford, Conn. Eugene G. Fubini, President, E. G. Fubini Consultants, Limited, Arlington, Va. William Gorham, President, The Urban Institute, Washington, D.C. Katharine Graham, Chairman of the Board, The Washington Post Company, Washington, D.C. Robert V. Hansberger, Chairman and Chief Executive, Futura Industries Corporations, Boise, Idaho Vernon E. Jordan, Jr., Executive Director, National Urban League, New York, N.Y. Richard Llewelyn-Davies, President, Llewelyn-Davies Associates, New York, N.Y., and London, England Bayless A. Manning, President, The Council on Foreign Relations, New York, N.Y. Stanley Marcus, Executive Vice President, Carter Hawley Hale Stores, Inc., Dallas, Texas Robert S. McNamara, President, International Bank for Reconstruction and Development, Washington, D.C. Arjay Miller, Dean, Graduate School of Business, Stanford University, Stanford, Calif. J. Irwin Miller, Chairman, Cummins Engine Co., Inc., Columbus, Ind. John D. Rockefeller IV, Charleston, West Virginia William D. Ruckelshaus, Partner, Ruckelshaus, Beveridge, Fairbanks & Diamond, Washington, D.C. Herbert Scarf, Professor of Economics, Yale University, New Haven, Conn. Franklin A. Thomas, President, Bedford-Stuyvesant Restoration Corp., Brooklyn, N.Y. Cyrus R. Vance, Partner, Simpson, Thacher & Bartlett, New York, N.Y. James Vorenberg, Professor, School of Law, Harvard University, Cambridge, Mass. kvu 3 6668 0009? 519