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RM WATER - PL .. ....... t .1 t . ... . ......... Ell jj WALNUT. CREEK VOLUME 2 ERIE COUNTY DEPARTMENT OF PLANNING COMMONWEALTH OF PENNSYLVANIA TD 665 S76 1981 v.2 /* STO NIANAGEMENT N/ OCTOBER 1981 PREPARED 3Y NORTHWEST INSTITUTE OF RESEARCH - WOODRUFF, INC. WATERSHED ADVISORY COMMITTEE Member Representing Joyce Andrews Lake City Borough Delores Bendig Lawrence Park Township Gerald Blanchf ield Harborcreek Township Harold Crane, Jr. Elk Creek Township Frank Fenton North East Township John Gresch Platea Borough LeRoy Gross Erie County Conservation Dist. Ted Guzzy Girard Township Richard P. Hessinger Summit Township John Klier Fairview Township Earl Koon Washington Township Roger C. Latimer Fairview Borough Rose Little McKean Township Jacob Luke Greenfield Township Kenneth Maas North East Borough Paul Martin Millcreek Township Wasinder Mokha Erie City Jeanne O'Brien McKean Borough Wilbur Osborn Waterford Township Lawrence Pieper Franklin Township Norman H. Rabell Conneaut Township Mary B. Ripley Wesleyville Borough Robert Smith Greene Township Ronald VanTassell Springfield Township Larry Wygant Girard Borough ERIE COUNTY DEPARTMENT OF PLANNING David Skellie Acting Director Thomas DeBello Senior Planner Jeffrey Spaulding Transportation Planner Gilbert Rocco Project Planner A. Latif Panhwar Planning Analyst Dolores Oblinski Draftsman II Lori Prody Executive Secretary Kathleen Anderson Secretary This study was financed through a planning assistance grant from the National Oceanic And Atmospheric Administration as administered through the Pennsylvania Department of Environmental Resources Coastal Zone Management Office (Office of Resources Management), and the Erie County Department of Planning. STORM WATER MANAGEMENT PLAN WALNUT CREEK WATERSHED Volume 2 Prepared For Commonwealth of Pennsylvania Department of Environmental Resources and Erie County Department of Planning Prepared By Northwest Institute of Research - Woodruff, Inc. As a Consortium October 1981 TABLE OF CONTENTS Page Section I SUMMARY AND RECOMMENDATIONS 1-1 Section 2 BACKGROUND 2-1 Section 3 DESCRIPTION OF THE WALNUT CREEK WATERSHED 3-1 3.1 Local Input Data 3-1 3.1.1 Signif icant obstructions 3-1 3.1.2 Existing drainage problem areas 3-2 3.1.3 Existing storm sewers 3-2 3.1.4 Proposed storm sewers 3-2 3.1.5 Existing and proposed flood control projects 3-3 3.2 Present and Projected Land Use 3-3 3.3 Soil Types 3-3 3.4 The National Flood Insurance 100-Year Flood Plain 3-3 Section 4 STANDARDS AND CRITERIA FOR STORM WATER MANAGEMENT 4-1 4.1 Definition of Design Storm 4-1 4.2 Definition of Type 1 and Type 2 Channels 4-1 4.3 Criteria for Type I Channels (Main Stream) 4-2 4.4 Criteria for Type 2 Channels (Branch Streams) 4-2 Section 5 IMPLEMENTATION 5-1 5.1 Introduction 5-1 5.2 Special Considerations 5-1 5.3 Building Permit Process 5-2 5.4 Subdivision Review Process 5-3 5.5 Conclusions 5-3 Section 6 THE WALNUT CREEK COMPUTER MODEL 6-1 6.1 Existing Stream Characteristics 6-1 6.2 Post-Development Stream Characteristics 6-1 TABLE OF CONTENTS (Continued) Appendix A Tables and Plates Table 2-1 Significant Obstructions Table 2-2 Storm Drainage Problems Table 2-3 Proposed Storm Water Collection Systems Table 2-4 Storm Water Collection and Control Facilities Table 2-5 Project Development and Construction Schedule and Costs Table 2-6 Existing Flood Control Projects Table 2-7 Proposed Flood Control Projects Table 2-8 Subwatershed Data Table 2-9 Watershed Runoff Data Table 2-10 Watershed Runoff Data (Continued) Table 2-11 Various On-Site Storm Water Control Methods Table 2-12 Advantages and Disadvantages of Various On-Site Storm Water Control Measures Plate 2-1 Walnut Creek Watershed Base Map Plate 2-2 Walnut Creek Watershed Significant Obstructions Map Plate 2-3 Walnut Creek Watershed Drainage Problem Areas Plate 2-4 Walnut Creek Storm Sewer Systems Plate 2-5 Walnut Creek Watershed Flood Control Projects Plate 2-6 Walnut Creek Watershed Existing Land Use Plate 2-7 Walnut Creek Watershed Ultimate Land Use Plate 2-8 Walnut Creek Watershed Soil Map Plate 2-9 Walnut Creek Watershed 100-Year Flood Plain Plate 2-10 Walnut Creek Watershed Subwatershed Map Appendix B Calculations to Determine Increased Runoff and Examples of Specific On-Site Storage Section I SUMMARY AND RECOMMENDATIONS This document has been prepared in accordance with the provisions of the Pennsylvania Storm Water Management Act, P.L. 864, Act 167, October 4, 1978 and is a pilot study under that Act. The Northwest Institute of Research of Erie, Pennsylvania and Woodruff Incorporated, Consulting Engineers of Cleveland, Ohio have formed a consortium for the purpose of developing a pilot storm water management plan for the Lake Erie and Elk Creek Watersheds. This study has been prepared under the direction of the Pennsylvania Department of Environmental Resources, Bureau of Dams and Waterway Management, Division of Storm Water Management and the Erie County Department of Planning. This report is Volume 2 in a series of 14 volumes prepared for the Erie County Department of Planning. The purposes of this report are: 1. To establish as base conditions the existing land use and the existing storm water runoff in the Walnut Creek Watershed against which future conditions can be compared. 2. To calculate the runoff from a projected land use to indicate how much more flow the main stream and its branches would be required to carry. 3. To present a set of criteria and standards for storm water management in this watershed. 4. To recommend the one or more alternative storm water management methods best suited to the needs of the Walnut Creek Watershed. The standards and criteria which are to be applied to storm water runoff have been summarized in Section 4 and are described in complete detail in Volume 1. It is recommended that these standards and criteria be adopted by the committee in the Walnut Creek Watershed Area. The various means of implementing these standards and criteria are discussed in Section 5. It is recommended that the on-site approach to storm water management as described in Section 5 be adopted immediately and included in all future development plans. Immediate steps are to be taken so that the Walnut Creek Watershed Area will be prepared for the tremendous growth that will occur should the U.S. Steel proposal for Springfield Township come to fruition. It should be emphasized that this storm water management plan is intended solely to minimize the creation of new flood problem areas as a result of increased runoff due to development. Also, existing problem areas will not be aggravated by increased runoff. In this way, the municipalities will be able to concentrate on solutions for those flooding problems that presently trouble local property owners. 1-1 Section 2 BACKGROUND The basic approach to storm water management in the past has been to achieve maximum convenience at an individual site by getting rid of any excess surface water after a rainfall as quickly as possible. This removal is accomplished typically by disposal of the water through a storm sewer or other closed system. As the land in a given area becomes more and more developed, this policy has led to the following problems: 1. Flooding due to overland flow. 2. Increasingly frequent downstream flooding. 3. Diminished groundwater supplies. 4. Erosion of stream banks. 5. Siltation and pollution of streams. As land development continues, the percentage of impervious land surface increases as paved roads, sidewalks, parking lots, and other structures are built. The result of this change is to further aggravate the problem. Areas that previously had no flooding begin experiencing problems and areas which might have been prone to flooding earlier now experience an even more severe problem. The solution of passing one's own water problems downstream is no longer acceptable. The potential damage created by such an approach cannot be tolerated as developments continue to move into once rural areas. Clearly, a new approach to handling storm water runoff is needed. A storm water management plan is necessary that protects our land and streams as well as permits reasonable development. The new approach must strike a balance between local convenience and protection against the hazard of flooding. One significant feature of the approach presented in this document will be the planned detention of water on-site in various types of storage facilities. Such structures will hold the water and release it slowly over time, after the danger of flooding is past. In the process, downstream areas will be protected. This concept will be discussed more fully in the following pages and will be applied to the specific requirements of the Walnut Creek Watershed. 2-1 Section 3 DESCRIPnON OF THE WALNUT CREEK WATERSHED On Plate No. 2-10) the base map for the Walnut Creek Watershed Area is presented. On this map, major topographic features of the watershed are shown. The Walnut Creek Watershed is located in the townships of Summit, Greene, McKean, Fairview and Millcreek. It covers an area of approximately 23,500 acres. Walnut Creek has been included in the Scenic Rivers Program inventory and certified as a recreational area. Streams designated as part of the Scenic Rivers System should be preserved or improved as much as possible by both government and private concerns. 3.1 Local Input Data There are five types of local data which have been considered in the description of the Walnut Creek Watershed Area. These include: 1. Significant obstructions 2. Existing drainage problems 3. Location of existing storm sewers 4. Proposed storm sewers 5. Existing and proposed flood control projects Each of these types of data are discussed in the following paragraphs. This information is as complete as possible at the time of writing. Additional information may be added as it becomes available. 3. 1.1 Significant obstructions A significant obstruction is defined as any structure or assembly of materials which might impede, retard or change the flow of storm water runoff. Significant obstructions in the Walnut Creek Watershed were located both by surveys conducted by the consultant and by local input from municipal and county officials as well as the Advisory Committee composed of representatives from the affected municipalities. Those obstructions which were identified are described on Table 2-1 and located on the map presented on Plate No. 2-2. A total of 39 obstructions were mapped. These include many bridge abutments and piers or culverts through which the main stream or side branches pass as they flow under highways, driveways and railroads. While many of these structures do not obstruct normal flow, all may be considered potentially obstructive during severe storms if debris is allowed to collect in culvert openings or around bridge piers. They also serve as potential entrapments for ice floes. (l)For the convenience of the reader and to facilitate locating of tables and maps, all of these illustrations are placed in order in Appendix A at the end of this report. 3-1 The importance of these obstructions is obvious since anything which interferes with the natural flow of the stream can contribute to local flooding under storm conditions. The control of increased runoff due to development that would result from the implementation of this storm water management plan will insure that these structures will operate hydraulically at their present levels. Thus, if a particular structure has no recurrent problems in passing stream flows at the present time, no problems would be expected in the future under the plan as development proceeds. Flooding problems due to structures of insufficient hydraulic capacity will not get worse in the future, nor will they be eliminated by the institution of these storm water management policies. The intent of this plan is to maintain the status quo regarding stream flow. 3.1.2 Existing drainage problem areas There were 18 drainage problems identified in the Walnut Creek Watershed. As indicated in Table 2-2 and shown on Plate No. 2-3, these problems involve primarily either roadways flooding or culvert inlet flooding. Similar problems are noted in Fairview, Millcreek and Summit Townships. Solutions suggested range from increasing culvert size to providing proper drainage. Caution must be taken when incorporating these or any other solutions to insure that no flooding problems are created downstream. As other drainage problems are identified in the Walnut Creek Watershed Area, they can be added to Table 2-2 and Plate No. 2-3. 3.1.3 Existing storm sewers The third type of local input involved the location of all existing storm sewers in the Walnut Creek Watershed Area. This information is shown on Plate No. 2-4. These data can be obtained by consulting the comprehensive plans for Summit, Greene, Fairview, Millcreek and McKean Townships and the Comprehensive Storm Drainage Study for Millcreek Township, Erie County, Pennsylvania. Plate No. 2-4 is provided so that the location of any additional structures may be mapped. At the present time, barring evidence to the contrary, the assumption is made that none of these storm sewers has a significant impact on the management of storm water in this area. 3.1.4 Proposed storm sewers Tables 2-3, 2-4 and 2-5 are provided for the purpose of listing and locating all proposed storm sewers in the Walnut Creek Watershed Area. At the time of writing this report, no new storm sewers are known to have been proposed for the Walnut Creek area. The tables are provided so that information can be added to them and Plate No. 2-4 as it becomes available. Further information on storm sewers can be obtained by consulting the Comprehensive Plans for Summit, Greene, Fairview and McKean Townships and the Comprehensive Storm Drainage Study for Millcreek Township. 3-2 3.1.5 Existing and proposed flood control projects Plate No. 2-5 and Tables 2-6 and 2-7 are provided for the purpose of entering the location and description of all existing and proposed flood control projects. Two existing flood control projects were identified, both in Millcreek Township. In addition a new flood control project on Marshall Run in Millcreek Township is being planned. Additional information can be added to these maps as it becomes available. 3.2 Present and Projected Land Use Present land use is shown on Plate No. 2-6. Existing land use data was taken from the Erie County Land Use Plan Update (June, 1978). It can be seen from the existing land use map that the area is at present largely rural with some residential areas and some small pockets of commercial usage. Projected land use was derived from various Erie County projections. This is shown on Plate No. 2-7. As can be seen, the Walnut Creek Watershed Area is seen as an area of extremely high potential growth. This would be most evident if the proposed U.S. Steel plant is built in Springfield Township. Existing development has brought about the institution of a sewage disposal system in portions of the watershed area. The presence of a public sewer system often has a strong influence on area growth. 3.3 Soil Types The various soil types found within the Walnut Creek Watershed Area are shown on Plate No. 2-8. These soils include the following: 1. Sandy soils of the lake plain (Rimer-Wauseon-Berrien). 2. Gravelly and sandy soils of the beach ridges (Conotton-Ottawa- Fredon). 3. Gravelly soils of the outwash terraces (Howard-Phelps-Fredon-Halsey). 4. Deep, silty and clayey soils of the gently or moderately sloping glaciated upland (Plateau-Birdsall). 5. Deep, medium-textured soils in moderately limy till of the glaciated upland (Erie-Ellery and Alden-Langford). 6. Shallow, medium-textured soils of the glaciated upland and the lake plain (Allis-Ellery and Alden). 3.4 The National Flood Insurance 100-Year Flood Plain The 100-year flood is defined as the highest level of flooding that is likely to occur on the average, every 100 years. The fact that an area has not flooded recently does not mean it will not do so in the future. The probability of such an occurrence is 1 percent in any given year. 3-3 The Flood Plain Management Act, Act 166, October 4, 1978, prohibits development within designated flood plains. No development is allowed in any areas 50 feet or less from the boundaries of designated flood plains. This is intended to reduce flood damage and accumulation of debris due to the 100 year flood and is consistent with the intent of the Storm Water Management Act. On Plate No. 2-9, the flood plain for the basic or 100-year flood is shown. The information was taken from the National Flood Insurance Program Maps (Available for reference at the Erie County Planning Department office). The flood plain in the area 10+00 and 22+00 as indicated on Plate 2-9 is rather wide and comes very close to some mobile home developments. In the area between Station 24+00 and 30+00, the flood plain is quite wide. This latter is a commercially developed area serving an interchange to Interstate 90. The branch that enters Walnut Creek at approximately Station 50+00 floods for several thousand feet upstream. This is a suburban commercial and residential area that should be protected from any increase in flooding in the future. The map also shows that the tributary known as Bear Run which enters the main channel at about Station 108+00 floods a rather extensive area. Since this land is presently undeveloped, any property damage from such a flood would be minimal. With the exception of the Bear Run area cited above, measures should be taken immediately to prevent increased runoff which would result in the 100-year flood plain expanding beyond its present limits. Even in less developed areas, it is beneficial to maintain existing flood plains so that no land is lost for development in the f uture. 3-4 Section 4 STANDARDS AND CRITERIA FOR STORM WATER MANAGEMENT The following are the recommended standards and criteria for storm water management in the Walnut Creek Watershed Area. A complete derivation and justification of these standards are to be found in Volume I of this study report. The recommended standards and criteria may be completely satisfied by use of the on-site approach discussed in Section 5 of this volume. The most fundamental standard of this study is that the amount of flow along Walnut Creek must not be allowed to increase at the data points labeled "I" through 114411 on Plate No. 2-10 above those existing flows indicated on Table 2-9 for each of these points. These flows were obtained from a computer model developed expressly for Walnut Creek using the design storm described below. Flows at positions between the given points must not exceed a straight line interpolation of flow values at adjacent points. This will insure that the flow characteristics of Walnut Creek will remain at their 1981 level for storms equal to or less than the design storm. The objective is to maintain the existing level of flow in the main stream channel for the design storm and to maintain bank-full capacity for the side branches. A policy such as this will not only effectively manage increased runoff as desired, but will help to maintain the sensitive ecological balance of the stream. 4.1 Definition of Design Storm The design storm for this study has been determined to be the 10-year, 24- hour storm. The choice of this storm is justified in Volume 1 of this study. The 10- year, 24-hour storm is that theoretical storm of 24-hour duration that statistically will occur once in 10 years. On the average such a storm would produce 4.8 inches of rain in a 24-hour period. As previously mentioned, this is the storm used to derive the magnitude of flow at the data points described above. 4.2 Definition of Type I and Type 2 Channels Because some of the channels that make up the Walnut Creek drainage systems are more able to carry increased flows than are others, two sets of criteria and standards have been devised for two types of channels. The first, or Type 1 Channels, are characterized as main stream channels. They have a well-defined flood plain and can handle increased flows very easily. These are the shaded portions of the Walnut Creek drainage system shown on Plate No. 2-9, "The One- Hundred-Year Flood Plain." The second are referred to as Type 2 channels. These consist of all the other portions of the Walnut Creek drainage system that are not shaded on Plate No. 2-9. They are characterized as branch stream channels. Plate No. 2-10, the Subwatershed Map for Walnut Creek, indicates those portions of the watershed area whose runoff is initially discharged into Type I Channels and those whose runoff is initially discharged into Type 2 Channels. 4-1 4.3 Criteria for Type I Channels (Main Stream) For those sites which are to discharge their runoff into a Type I Channel, it will be required that the increased runoff after development (due to the design storm) be managed by any of the recommended on-site methods discussed in Section 5. That is to say, the runoff due to the 10-year, 24-hour storm is to be calculated again for the same storm taking into account the specific proposed development. The difference between these two runoffs is that which must be managed. 4.4 Criteria for Type 2 Channels (Branch Streams) For those sites which are to discharge their runoff into a Type 2 Channel, a more stringent standard is to be applied. This is necessary because these channels typically are too small to accommodate increased runoff. They have no flood plain to act as a cushion. In this situation, the amount of storm water that must be stored is the difference in runoff between that due to proposed land use for the 10-year, 24-hour storm and that due to the mean annual storm for existing land use conditions. As defined previously, the mean annual storm (1) is calculated by taking the largest storm for each year on record and averaging them together. Statistically, the mean annual storm is equivalent to a storm with a return frequency of 2.33 years. Whereas side branches are naturally formed to handle the more frequent mean annual storm, this more stringent criterion would now protect them against flooding for all storms up to and including the 10-year, 24-hour storm. MThe concept of a mean annual storm was developed by L. Leopold and referenced in Storm Water Management, 1980. 4-2 Section 5 IMPLEMENTATION 5.1 Introduction Every parcel of land has unique storm water runoff characteristics which inevitably change when the parcel is developed, usually resulting in an increase in storm water runoff from the site. When development takes place the increase in storm water runoff is magnified and serious problems can result. Prior to the development of this Plan there was no established method through which a municipality could require developers to take precautions against causing storm water runof f problems. The purpose of this Plan is to help correct the situation by establishing standards for storm water management and an administrative procedure whereby those standards can be applied by local governments to development within their jurisdiction. The Storm Water Management Plan will be implemented by individual municipalities through the adoption of a storm water management ordinance or through amendments to existing subdivision or zoning regulations. Administration of the storm water management program will be accomplished through a combination of enforcement actions undertaken through the building permit process and through the subdivision review process, both of which are detailed later in this Section. 5.2 Special Considerations Prior to discussing the specifics of the Building Permit Process and the Subdivision Review Process, two subjects which fall outside of the scope of this Plan's evaluation procedures will be discussed. The Building Permit and Subdivision Review evaluation procedures for storm water management apply to all forms of development and land use except development in areas with an existing storm sewer infrastructure and with respect to agricultural land. In situations where development or redevelopment occurs in an area where direct access to an established storm sewer infrastructure is possible, the development or redevelopment is considered sufficient to manage its storm water runoff if its on-site storm drainage network is incorporated into the existing storm water infrastructure. By connecting with the existing storm sewer system, the development would be relieved of further obligations to manage storm water runoff in accordance with this Plan unless the municipal governing body perceives a potential storm water drainage problem or if the governing body wishes to correct an existing storm drainage problem. In these cases where the governing body desires a more stringent application of storm water management controls they may require that a detention/ retention plan be developed which would alleviate the storm water drainage problem. 5-1 Evaluating agricultural land for compliance with storm water management controls is the second topic which falls outside of the scope of the Building Permit and Subdivision Review procedures. With respect to agricultural land, the recommended method of storm water management is to have a Soil Erosion and Sedimentation Control plan and/or permit prepared in accordance with existing State law and reviewed by the Erie County Soil Conservation Service. This applies only to cultivated land; agricultural accessory structures and residential structures should be evaluated by the municipality through the applicable method as outlined in the following sections. 5.3 Building Permit Process If a proposed subdivision is defined by the host municipality's subdivision regulations as a minor subdivision (usually 10 lots or less) or if development is proposed involving no subdivision of property, then storm water management standards and criteria should be evaluated at the time when development is formally proposed via an application for a building permit. This system is designed so that smaller developments may occur without incurring added engineering expense and so that municipalities can implement storm water management requirements without incurring substantial administrative overhead expense. The recommended technique to be followed when evaluating a minor subdivision or a development on an existing lot of record is presented here. First, all developments which fall into the above categories must meet each of the f ollowing: Standard Controls 1. Roof drains are not to be connected to streets, sanitary sewers or roadside ditches. 2. Runoff from the impervious areas must be drained to the pervious areas of the property. 3. Runoff is not to be collected or concentrated into an artificial conveyance and discharged onto adjacent property. Next, the zoning officer must calculate the percentage of the parcel which will be covered by impervious surfaces after development is concluded. In this context impervious surfaces mean all land covered by a house, barn, garage, patio, driveway, etc. Information needed to calculate the percentage of impervious area should be readily available on the building permit application. Once the calculation is made the zoning officer should refer to the following table to determine how many storm water controls in addition to those listed above will be needed to comply with the standards of the Storm Water Management Plan. The additional controls can be found in Table 2-11. 5-2 Determination of Controls Less than 15% impervious Standard controls only 15% - 19.99% impervious - Standard controls only plus one additional control 20% - 24.99% impervious Standard controls plus 2 additional controls 25% - 30% impervious Standard controls plus 3 additional controls The methodology outlined above is designed to be used f or a proposed development which covers 30% or less of the parcel with an impervious surface. Under such circumstances the zoning officer can show the potential developer what storm water management controls are needed in order to receive this building permit. If the proposed development will cover greater than 30% of the parcel with an impervious surface or if the total impervious area exceeds one acre, then a licensed professional must be consulted to prepare a detention/ retention plan which meets the approval of the governing body. An additional fee is recommended to be added to the existing building permit fee to cover the expense of administering the program. 5.4 Subdivision Review Process If a development is defined by the host municipality's subdivision regulations as a major subdivision (usually more than 10 lots), the storm water management standards and criteria should be evaluated during the subdivision review process. This use of the subdivision review process is designed to ensure that large scale developments employ proper techniques to control storm water runoff and that these controls are firmly established prior to municipal or county approval of the subdivision plat. When a preliminary major subdivision plan is submitted for municipal review it shall be accompanied by detailed storm water detention/ retention specifications which meet the criteria of the Plan and which have been prepared by a professional licensed to perform such work in this Commonwealth. The proposed storm water detention/ retention specifications shall be reviewed by the municipality and/or its engineer and shall satisfy the municipality before the major subdivision plan is approved. The municipality may require controls which are more stringent than those which meet the Storm Water Plan's criteria if circumstances dictate that such measures are needed to alleviate a current drainage problem or a suspected future drainage problem. 5.5 Conclusion The L ake Erie and Elk Creek Storm Water Management Plan has been developed in accordance with Act 167 of 1978, the Pennsylvania Storm Water Management Act. Under the provisions of this Act, municipalities are granted certain powers and must assume certain responsibilities. One of the responsibilities which has been assigned to local governments by the Act is the responsibility to adopt implementing ordinances such as those described in this section. Another responsibility assigned to the municipality is that of properly enforcing the storm water management ordinances and regulations. Because of the responsibilities awarded to municipalities under Act 167, each municipality affected by this Plan should consult their municipal solicitor for a briefing about the extent of their obligations under the provisions of Act 167. 5-3 Section 6 THE WALNUT CREEK COMPUTER MODEL As has been discussed previously, a computer model of the Walnut Creek drainage system was developed for the purpose of this study. A complete description of the background and development of this computer model is given in Volume I of this report. The following is a summary of the data used as input for the model and a description of the data it yielded as output. 6.1 Existing Stream Characteristics The existing land use for the Walnut Creek Watershed Area is shown on Plate No. 2-6. This is a base land use against which future development is to be compared upon adoption of this storm water management plan. It can be seen that the area is generally rural with some residential and commercial development. The runoff due to this land use was entered into the computer model. A soil factor derived from the various types of soils found in the Walnut Creek Watershed Area, as shown on Plate No. 2-8, was also taken into account. The results of the computer output are summarized on Table 2-9. The flow characteristics of Walnut Creek due to the runoff from existing land use are shown in the first columns labeled "Existing Runoff" for various data points. These data points are located on Plate No. 2-10. These are the flow characteristics of the stream which must not be altered due to the development of land in the watershed area. 6.2 Post-Development Stream Characteristics A projected ultimate land use for the Walnut Creek Watershed Area was taken from the Erie County Land Use Plan Update (June, 1978). It is shown on Plate No. 2-7. This projection assumed that all of Erie County would develop to its maximum potential, as it would if U.S. Steel were to build the large steel producing facility it has proposed for Springfield Township. Although it is, at present, primarily a rural area, projections indicate major growth in residential usage. The runoff due to this projected land use was entered into the computer model. Again, a soil factor was taken into account. The resultant flow characteristics at the data points are shown in the column labeled "Ultimate Runoff" in Table 2-9. It can be seen that the peak flow of the ultimate runoff is considerably higher at all points than is that of the existing runoff. For example, at Point "A" which is just west of the intersection of Zwilling Road and the Conrail Railroad tracks (see Plate No. 2-10), the peak flow is calculated to be 1426 cubic feet per second (cfs) for existing runoff and 1601 cfs for ultimate runoff. The depth of the ultimate flow is substantially higher at all data points. The increased depth becomes more critical in downstream reaches of the watershed. This implies a great risk of flooding in portions of the channel that will become over-burdened due to projected development along their banks. 6-1 The depth of the ultimate flow is substantially higher at all data points. The increased depth is greater in the upstream reaches of the watershed. This implies a greater need for control in upstream and branch streams locations. The velocity of the flow can also be seen to be much higher for ultimate runoff than for existing runoff. This is an undesirable situation that could result in excessive erosion of the stream bed. The stream channels would eventually widen and deepen beyond their present limits and possibly interfere with development along their banks. Foundations for bridges, culverts or retaining walls might be undermined due to a process known as scour. Scour is the washing away of earth around the footings of piers, bridge abutments retaining walls or the like, and in the process, exposing them. This reduces their structural stability. Water quality would decline due to the inordinant amount of soil particles being carried along by the current. Development would decrease the absorption of rainfall due to the amount of impervious cover it would probably bring with it. This could lower the groundwater table to unacceptable levels. The COWAMP Study Area 7 Report, prepared by the Department of Environmental Resources of the Commonwealth of Pennsylvania does not reveal any of the above to be current problems for the Raccoon Creek Watershed Area. This makes it very important to maintain existing water quality standards related to storm water runoff. In addition, the Clean Streams Law of Pennsylvania regulates activities that affect any stream in the Commonwealth in order to preserve and improve the purity of their water. The Storm Water Management Act will aid in the attainment of these objectives. All work done to manage storm water must be done in compliance with these rules and regulations. 6-2 I I I I I I I I APPENDIX A I TABLES AND PLATES I I I I I I I I I I pi-AN N.(),- SIGNIFICANT OBSTRUCTIONS MAINAGI NO jUN1(!! Lily TYPI Of STRUCTuak Go. MM 0111441 AlAfffl 2 A4,11 C,,@A &Abc '01'rIve 3 -Sr" Avh PwImad ga-it L9 IV I, 3amevAwk 9,mmit 3-AdM r111..,01cd1CWJ-ACSkA2f _ff1_1d9f GM m. Mill Ceh ifflont ar rtm4wiotion AVI CreoA Bi*e, 40',rl25 19 gummIt Railrwdff@dbo &14' Z9 - &Ida*. 50112, 21 Ion __22 onvartmem Or Tmnqp@fo 23 -Ali// C-ek 25@ rVArIA Z4 W,1_1 _CeeA@@@ 91;doe 60@e Villcrepk Zs 'Will C"vk Bl;doo@ Jr' Ar T-0ship of Transaor-latlaa II/ @61-1611 g2!tf' V@rsr Awsylw.,o Okoarf@ni aP Tnv=Aar& &idoe W 5A4c. Alitagr6weat of rrotagwintw -39 4y/ ... @k 5 4@fjllc-k V74 Iran& ov1w'fpf of /on -wvw 404 iwerlw_- 4#r. e*wl@d. 42hio 4411,0 39 cwwt WOODRUFF. ING] WA"ur Cal" T^KA 94 El AN NO, STORM-DRAINAGF4 PROBLEMS _MUNICIPALiTV Pokw-Mra fibinstor1w PROPOSE NOM LOCAYIOU To-li Al-11 66bdieumn Ob-w H-11 R-of) &Awmij rawAshio qw,7 Ifeream Obw?" R@dwwc1bodjb;;:inq3*v#rs Rainsiortm 2 &m"i 7ownsh,,o ill& AV Rau.,# .97 Durinqfe,v@ Abjnj4o,mj rlxy /o/I kuo,m dew- F@11, @IL-s. 3 ale ..... ol (@a,ola@d 4 Floods se@rrf no-sto,mi 0,.-dcb@@ O@ 4' I@A-evk.@ @Dt WillonToo-ILIndeaoi &rnmi 7bw-m-hP- 5 7oksw /41,11 'Q@Y flcl cllve, 6 L194.41 @21'1-1711@--9 lo 7 &#rm", I CavrM@ 0,-,'nq.S*rj-e RoImOo Oro fa.00Flooal D@-V&Ae- Rm@u Size, [email protected]. cvwwarc Relanfan 9 8,@wd Tw-h- R-I'w@ F100CO D@iha,50 VVrj- R01@7$ 1'@" RoodpWrjooo@j oorinqSvvv@# AoinO to Ju@md rowmNo A-pa Ing! /I OreQ. Avenue kfilk-k ro-ho Int.; floodi Dw,@Vje-r, "Moreek To-shw &Ww 0 Inlet Flood3 1 c9eveppRbimt@mt ANA@-k rowm%$160 -Zg,-,Wrt Inlet Flood$ inqJok,,,0 JPip0,."r$ d00p.,.#V- /5 -90@ 4, Xb,& 5 A,16,jholl Run Dutin 4oj@"ofn Re=FeaC5,11flof 14 &IA-.' WPJter1, Rodro0l:@ aALY4brfhll Pun, MZk,,e* row,-AW Cute#, t fniot Ffbods -q jOrer* w6ins.-O-i fe- Aolotek 7bwns% 0.1ve, 0 a 6 0-an wille-ok r Xta.4 D-M, 16 B,4,@A Am F@vww 7.w,,-OP Inlet Flooca pun@q Ralllsl'@M5 -.,to Dit@h Illy - Ca1AS111UC U 0. 1-,, (-,,a e Crook Tqos,?4 95onkJVw14q - rthA@ a/ Mis 1000@@10/7@ more tpvr.)Aobl* if Rains er,"j r-M, M-S, -aAs7i-a Fairview Towwhip apav're.". h,md r,,w,,-h T in, WOODRUFF, INC jwm M9 VALNUT CRUK C. TAILA 3-3 PLAN No-, PROPOSED STORM WATER COLLECTION SYSTEMS fagg MAINTINANCI slopup4lialwiv VV -1 A Qf swm 23;10 WOODRUFF, INC. ALNUT cam STORM WATER COLLECTION AND CONTROL FACILITIES P@A,:T No. Twollu, UIT* CING I ALL PUAREWS U&SLUIrm _ell NIN A 16 I r -A WOODRUFF, INC. ...... V&LNUT Gaiiii -now 'AHEET 2 cr 2- FIR JECrrDEVELOPMENT!AND'CONSTRUCTION'SCHEDULE AND COSTS CUgDULE ESTIMAI Fn maTil COM171 ICTinm,,,,,, --4WJ-lLl No.- -.__jjjWA_ 11GHT-ME-WAY ITART kv A- ir %P ap -3 o% N - Vx- A X 3 x v I :c: @s @Ts WOODRUFF. INC. TAX" EXISTINO: FLOOD CONTROL PROJgCTS A I WA117 Algn,6;@,,.,,,@pA, M A If B, W Mill@ &Qoh.-r,? Amw! h om (b. D= Y@@il R,2,4-ro AA "P. 77 WOODRUFF, IN PLAN NQ PROPOSED FLOOD CONTROL PROJECTS BlUACT LOCATION Ar4Q M VrOCIPAMT n.TF ILWI boa FINAI nw.bb _4 Ob .0 -@h, A/@ folkl k*1,4_ "I W21,rshli?, Mlilleeek 7b-m@A,,p Voj W Der woopitUFF, INC. OWN as:19 @ !7! @ I WALNUT Cat" @u ........ TAMLA 3-1 T@mf wiloAmto CIV otleAftro CIV "w4rcip"ro AREA of foR rcw CONCI#rRATION fxIsrAWLAWUff IIrAMdrftAW�L N-SER @RES mwolfs ASIAN 71 z&V -ism 74 40 Jr4r4v r)I. /Y-. ja 44 IFI.Xi$ a/. 4F Yw6u 7w4o a 5719J7 JA ja MAW 714 d5 7 404J7 4,f. 44 74F Ao .05,140 zo. OP 'A -fo 7700 do. is A 7f Ja#0 74 ij 7A /i AD 10714 it 614 44.01 ?94V It to A.1 /jVjj 70 JI? 71 Zs. 00 7j. 40 14 -14.17 R3. J7 @w. $1. 4 7 /a mou -ir I? /a AM 21 16-108 7990 17 P944 4.e. 90 7,'1;' dA 04.40 AV 9" At 2 0 AQ yj to 404.9# it, R46 Arse ozzi at /SZOR zi. " - Ae.44____ __ _ &.04 21 //C,." 2704 "At -0.101 23 4V?V 7z@ #dI Nor oz.47- 94 481.69 .3b.49 77" also 25 321AP 40. 6V 7A #a 4j. 27 ZZ.Ob 0.07 7a V 0Z so 4Z.492 4a jgj 74 V j/. 219 "14 I.P.,94 Af. 30 jzddz 44.15 70.14F 'pl. 7 J1 1441 7j. tv 01719 1�17S$ P2. ale 7754 da 01 96 VJ. 44 7d. As J1.4)_ 11141f 74@ �4 7415 01,51 11 9072,0 si. is VA01 40 J7 J" 711 4J. 27 MAP J/. Ad 3i /�z 44 IA,?7 iKAO io.T, 50 ZZAA 71 ?JI. ma 71 At AgZ6 40 W14 4474 MN 41 701 H 44.41 AW 40.110 49 ji. 71" at. 1,4 45 sz. 71 Mad 44 AijiAo -JA /* 1141 71 ii 45 /0 ?AP't 44" 4.0 44 440.JS - SWU 25:10 FOX" pArsoiNslo A AN AC.V* WOODRUFF, I C. ZA SSA a WALHVT CREEK WATERSHED WATERSHED RUNOFF DATA EXISTING RUNOFF ULTIMATE RUNOFF ULTIMATE RUNOFF WITH STORAGE LOCATION PEAK FLOW Time Of 0111,711 VaLOCITY F.P.S. VOLUME.MIL. PRAK FLOW Time OF Da"I'll FT V9LOCJTV F.P.S. VOLUME MIL. PEAK FLOW TIME OF DEPTH FT.. VELOCITY F.P.11. VOLUME MIL. C-F & PlAK MR. CU_ FT. Cf.s. PEAK HR. CU. FF. CPS. PEAK HR. CU. Fr. A 140r. Z.3 4. J1 to a i?500 24 5.415. Aa 01 Aq44 UP5 tleOln _____74 r,Q 0!@qq ?.4- 9.31 its* ,_0 Brunch 4611 7/ 7or 6 74 7,9 47. 99,9 78 u-s*,?Lwr 32d5 Zj @%wns 4343 13 a 14- MAL Zronch 76 1" __ ___ 7. Q_ ____ _@4,tq 24 J 7 A. 74 -7.93 /a 50 449f G, gt@oooh t 146 zz. - ___ fo 76 U015 tr t?@rr? 4137 T@l __ ------ 4,9j9 x@r 5.4 _71 u_ Brooch 424 Xx Qpat,eafn 4954 Its 441 Jyz 34 ;?o 914, U. 44 fj 1 .48ro,c @?j 7i - - ___ 7#4 U0,5t'61W" 52?0 74 _14 j20--_@straq,17 5658 %4 4. fdod Alf, 414 74 ro /0 Oawnafr69M - L.D. Are- dve 9 A t4ps tna- D@ tr &Qm 14-1-6 Z I J. s6f ____p@s W t595 u Lam 76 &-stne- 0040 ff. 74 Downstre 7114 X4 AP Cb- 540 X1 ed7 J. 504 wj Sol zz 547 U,P5 1',re 1450 7F Downstripqn PZ &3 9z�j 79 __444 ow-j? 19 _Lk@r?@h_ 379 79 4i's - - -4z 4's traom Xx 2039 Qow,74tr ifl4s Edit 4- 00--_ tk4tr*Q(n 70A 10 @17 An@ -at 74 Ell -A 7.1 A#4 d to- 73 P, 3tr@ !j @0 17ZJ 73 I)oWnatre - ?44 7 -74 7 ji to 7/0 741 OLUMEM"' CU I ulp.1 #Cn ya d p#,,nj @r,_*, %!v,y -4f swid all ar"'NUT Cat" WATERSHED RUNOFF DATA EXISTING RUNOFF ULTIMATE RUNOFF ULTIMATE RUNOFF WITH STORAGE VIIAK FLOW T#M9 Of VOLUM& NIL, MAK FLOW TIM: OF VOLUMS MIL. FEAR FLOW TIM VOLUMB MIL. CIP3. MAR Dan" VaLOCITY F-PS CU. FT. C-F-9 PIA MR. 06" IrT. V5LOCITV F F I CU. C.F.S. owN rv. VBLOCM r m CU. FT. No Y, B-1ch f4y 7 IF 7,0 -7.3 'Ri DOWMt@@ _170a 4.15 Aic-" it .50 i:::::: - a -Z. brovvh -4344 Z4- pAstreom- -- is 7zo Z)u'w@�trqe-- Zo /adz W. .16 k4K1 _Ylil &P rAOV- !A i swu DA WALNUT CJLA" - TA" @ hill Table 2-11 VARIOUS ON-SITE STORM WATER CONTROL METHODS AREA REDUCING RUNOFF DELAYING RUNOFF Large Flat Roof 1. Cistern storage 1. Ponding on roof by 2. Rooftop gardens constricted 3. Pool storage or fountain downspouts storage 2. Increasing roof roughness a. Rippled roof b. Gravelled roof Parking Lots 1. Porous pavement 1. Grassy strips on a. Gravel parking lots parking lots b. Porous or punctured 2. Grassed waterways asphalt draining parking lot 2. Concrete vaults and 3. Ponding and cisterns beneath parking detention measures lots in high value areas for impervious areas 3. Vegetated ponding areas a. Rippled pavement around parking lots b. Depressions 4. Gravel trenches c. Basins Residential 1. Cisterns for individual 1. Reservoir of homes or groups of homes detention basin 2. Gravel driveways (porous) 2. Planting a high 3. Contoured landscape delaying grass (high 4. Ground-water recharge roughness) a. Perforated pipe 3. Gravel driveways b. Gravel (sand) 4. Grassy gutters or c. Trench channels d. Porous pipe 5. Increased length of e. Dry wells travel of runoff by 5. Vegetated depressions means of gutters, diversions, etc. General 1. Gravel alleys 1. Gravel alleys 2. Porous sidewalks 3. Mulched planters Source: Urban Hydrology for Small Watersheds. Technical Release No. 55 Table 2-12 ADVANTAGES AND DISADVANTAGES OF VARIOUS ON-SITE STORM WATER CONTROL METHODS MEASURE ADVANTAGES DISADVANTAGES A. Cisterns and 1. Water may be used for: 1. Expensive to install Covered Ponds a. Fire Protection 2. Cost required may b. Watering lawns be restrictive if the c. Industrial processes cistern must accept d. Cooling purposes water from large 2. Reduce runoff while only drainage areas occupying small area 3. Requires slight 3. Land or space above maintenance cistern may be used for 4. Restricted access other purposes 5. Reduces available space in basements f or other uses B. Roof top 1. Esthetically pleasing I . Higher structural Gardens 2. Runoff reduction loadings on roof and 3. Reduce noise levels building 4. Wildlife enhancement 2. Expensive to install and maintain C. Surface Pond 1. Controls large drainage 1. Requires large areas Storage (usually areas with low release 2. Possible pollution residential 2. Esthetically pleasing from storm water areas) 3. Possible recreation and siltation benef its 3. Possible mosquito a. Boating breeding areas b. Ice skating 4. May have adverse c. Fishing algal blooms as a d. Swimming result of 4. Aquatic life habitat eutrophication 5. Increases land value of 5. Possible drowning adjoining property 6. Maintenance problems Table 2-12 (Continued) D. Ponding on 1. Runoff delay 1. Higher structural Roof by 2. Cooling effect loadings Constricted f or building 2. Clogging of con- Downspouts a. Water on roof stricted inlet re- b. Circulation through quiring maintenance 3. Roof ponding provides fire 3. Freezing during protection for ' building winter (expansion) (roof water may be trapped 4. Waves and wave in case of fire) loading 5. Leakage of roof water into building (water damage) E. Increased Roof 1. Runoff delay and some 1. Somewhat higher Roughness reduction (detention in structural loadings a. Rippled roof ripples or gravel) b. Gravel on root F. Porous I . Runoff reduction (a and b) 1. Clogging of holes or pavement 2. Potential groundwater gravel pores (a and (parking lots recharge (a and b) b) and alleys) 3. Gravel pavements may be 2. Compaction of a. Gravel cheaper than asphalt or earth below parking lot concrete (a) pavement or gravel b. Holes in decreases impervious permeability of soil pavements N, (a and b) in. diam.) 3. Ground-water f illed with pollution from salt sand in winter (a and b) 4. Frost heaving for impervious pavement with holes N 5. Difficult to maintain 6. Grass or weeds could grow in porous pavement (a and b) G. Grassed 1. Runoff delay 1. Sacrifice some land channels and 2. Some runoff reduction area for vegetated vegetated (infiltration recharge strips strips 3. Esthetically pleasing 2. Grassed areas must a. Flowers be mowed or cut b. Trees periodically (maintenance costs) Table 2-12(Continued) H. Ponding and 1. Runoff delay (a, b, and c) 1. Somewhat detention 2. Runoff reduction (a and b) restricted measures on movement of impervious vehicle (a) pavement 2. Interferes with a. Rippled normal use (a and c) pavement 3. Damage to rippled b. Basins pavement during c. Constructed snow removal (a) inlets 4. Depressions collect dirt and debris (a, b, and c) 1. Reservoir or 'I. Runoff delay 1. Considerable detention basin 2. Recreation benef its amount of land is a. Ice Skating necessary b. Baseball, football, etc. 2. Maintenance costs if land is provided a. Mowing grass 3. Esthetically pleasing b. Herbicides 4. Could control large c. Cleaning drainage areas with low periodically (silt release removal) 3. Mosquito breeding area 4. Siltation in basin J. Converted 1. Low installation costs 1. Requires periodic septic tank for 2. Runoff reduction maintenance (silt storage and (infiltration and storage) removal) ground-water 3. Water may be used for: 2. Possible health recharge a. Fire protection hazard b. Watering lawns and 3. Sometimes requires gardens a pump for c. Ground-water recharge emptying after storm K. Ground-water 1. Runoff reduction 1. Clogging of pores or recharge (inf iltration) perforated pipe a. Perforated 2. Ground-water recharge 2. Initial expense of pipe or hose with relatively clean water installation b. French drain 3. May supply water to (materials) c. Porous pipe garden or dry areas d. Dry well 4. Little evaporation loss L. High delay 1. Runoff delay 1. Possible erosion or grass (high 2. Increased infiltration scour roughness) 2. Standing water on lawn in depressions Source: Urban Hydrology for Small Watershed Technical Release No. 55 I10 lp de, Y OFF, INC. WOODR 33 35 36 0% SA. 34 4@. 31 3$ 39 10 7 Is 32 is 13 12 6 17 23 't a 6 N 1A 24 2 4 3 qA a 29 OODRUFF, INC. 13 0 14 xvl- cv.@- oco mo 20W MW WOO RUFF. INC. PROPOSE]) SEWER OL 1@0- CIO -SIX) PROPOSED SEWER FAIRVIEW WOODRUFF, INC. j2o lp b 9 0 ox'@ c @@@@ODRUFF. INC.] los" @z; Wa c Cc 1@1 IC J, O-r) EXIST] CIS WOODRUFF, INC WOODRUFF, INC] ... . ...... 7@ -7 lp . . . ......... lp ......... . NN .............. .... ... . ..... ... ........ -J. ztn _77 2 1- ;r 1 5 F: r ie JI WOODRUFF, INC 120 19 IC -Cll lo -01 45 QD 34 .3a 33 za AVn THC S@ IS WOODRUFF, INC. I I I I I I I I APPENDIX B Calculations To Determine Increased Runoff I And I Examples Of Specific On-Site Storage I I I I I I I I I APPENDIX B CALCULATIONS TO DETERMINE INCREASED RUNOFF AND EXAMPLES OF SPECIFIC ON-SITE STORAGE The procedures presented in this appendix are applicable to all unit developments which contain between 2500 square feet and 43,560 square feet of impervious surface area. Those exempt cases discussed in the text need not make the following calculations. Developments with more than 43,560 square feet of impervious surface area must consult a qualified professional person to aid in determining their excess storm water runoff volume. By following these methods, the non-technical individual can easily determine the amount of excess storm water runoff which he is required to manage. The methods of control presented in this study, or any other approved innovative methods, may be used to manage this calculated runoff volume. Excess Storm Water Runoff Calculation Procedure Step I Determine dimensions of proposed buildings, drives, patios or other impervious areas. These can usually be found on building site plans. Step 2 Calculate impervious area. The more common shapes that will be encountered are rectangles, triangles or circles. Equations to calculate the areas of these shapes are as follows: (all dimensions are assumed to be in f eet) 0 Rectangle: area (sq. ft.) = length (ft.) x width (ft.) ii) Triangle: area (sq. ft.) = 1/2 x base (ft.) x height (ft.) iii) Circle: area (sq. ft.) = 0.785 x diameter2 (ft.) Step 3 Refer to Section 4.2 and plate of volume describing the watershed in which construction is to take place. If construction is found to be along a Type 1 channel, then use Type I criteria. All others use Type 2 criteria. Step 4 Use Figure B-1 to find excess runoff volume to be managed. Example: Figure B-2 shows a typical site plan for proposed residential lot located along a Type I Channel. Determine the amount of excess runoff volume required to be managed. (1) Dimensions as shown on Figure B-2. B-1 (2) Impervious Area: (a) Drive: 141 x 701 = 980 sq. ft. (b) House: 401 x 801 = 3200 sq. ft. (c) Patio: 1/21 x 201 x 201 = 400 sq. ft. Total Impervious Area 6180 sq. ft. (3.) Type I criteria as given. (4.) From Figure B-1, excess runoff volume to be managed is 1150 cubic f eet. Note: One acre contains 43,560 sq. ft. One cubic f oot contains 7.48 gallons of water. B-2 FIGURE B -1 RUNOFF IMPERVIOUSA zo --7- 7:. 7 7@- ...77 '7 7 Ira -.7 YPIE I -Z -7-= 4/50 M 560 A-r-' /0 144 7- 7- 7 77@. -7== ------ =,:-7 =a-Z5;r1MAfRk1l0Uf ARE4 MPL F UP 7-0 4j, S 6 0 L7 tL:,@ 7.777 f7 XCESIS Vow@Ag- F ROM RE, va 'r,rl-,CSS lqUVLlr,= /044 IVIVE /0-00 FIGURE B-2 TYPICAL RESIDENTIAL SITE PLAN 401 House '604 19/w /00, R1W FIGURE B- 3 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO. I SURFACESTORAGE 75 A A-ea A 0ec-tion A -A 4440 House 60' Rlw qlw 1004 L FIGURE B-4 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO. 2 * OVERSIZED STORM SEWER PIPE 40' Houae 60, 54- L?!Lorm 'Yewer pi "oe Oui-147, Rlw /00, Rlw FIGURE B-5 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO.3 POND STORAGE Z4 N, Hou-se 130' Rlw qlw /00, FIGURE B-6 ON-SITE STORM WATER MANAGEMENT ALTERNATE NO. 4 UNDERGROUND TANK STORAGE /0, L -5 'Peep 40$ House 160' Rlw 9/w I I I I I I I I I I I I I I I I I ! - - - - I Immillimm 1 3 6668 14109 4518