New Jersey stormwater management program

[From the U.S. Government Printing Office, www.gpo.gov]

New Jersey
Stormwater Program

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10JQ7

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657.5
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1987

New Jersey Department of Environmental Protection

NEW JERSEY STORMWATER MANAGEMENT

PROGRAM U - S . DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
2234 SOUTH HOR'SON AVENUE
CHARLESTON SC 29405-24

TABLE OF CONTENTS

PAGE

Introduction 1

Nonpoint Source Pollution and Hydrocarbons 3

Conventional Stormwater Management 5

Planning and Institutional Aspects 7

Water Quality Control in Stormwater Management 8

Background

Concept 9

Control of Particulate Pollution 11

Summary 12

The New Jersey Program 13

Priorities 14

Grant Programs 15

Watershed Planning Study

Technical Interface Problems 18

Wetlands

Groundwater 19

Shellfish and Estuary Preservation 20

Conclusion 21
Proparty of CSC Library
References 23

NEW JERSEY'S STORMWATER MANAGEMENT'PROGRAM

INTRODUCTION

In New Jersey, stormwater management is a dual purpose program,

which provides for removal of particuldte pollutants as well as

controlling floods. This is in accordance with the New Jersey

Stormwater Management Act (1), which called for a program to

improve the quality of stormwater runoff, and to restrain erosion

damages downstream, as well as to control the extra flooding

caused by development. A pilot program of this nature was

initiated in'fbur counties of the state early in 1980. More

recently, a sophisticated planning exercise in stormwater

management was conducted in Hunterdon County with funds

contributed by the U. S. Soil Conservation Service, the state,

and the county itself. The report on this demonstration project

is available (2). Whereas, nationally, stormwater management is

still generally designed for flood control onlv, our New Jersey

regulations established in 1983 (3) that water quality aspects

would be provided for as well, in the form of retention and of

settlement particulate pollution. Although the statewide

application of the new standards is not yet mandatory, funds are

now being made available to counties and municipalities to plan

on this basis. Details are given later in this paper.

New Jersey established a program of this nature because of the

great concern with nonpoint source pollution and the

environmental degradation which has been observed in New Jersey

streams in urban and urbanizing areas. Within the past year, the

state has become particularly concerned with pollution of coastal

area waterways. For this reason, the stormwater management

program is now being extended to coastal areas, even where no

riverine floods are involved. In such areas, only limited

retention storage is to be provided, sufficient to provide for

settlement of particulate pollutants, without going to the

extreme of providing extra storage for the major flood flows.

The ke*w Jersey stormwater management regulations make it clear

that various alternative types of detention facilities can be

used. The EPA has researched a wide variety of types of retention

facility, in various states and various conditions nationwide.

In New Jersey, the municipalities, counties and land developers

have in most cases used detention basins, or infiltration basins.

To put the stormwater management program in proper context,

particularly in coastal areas, it must be remembered that its

contribution to improving water quality conditions relates almost

entirely to runoff from new facilities. The institutional

arrangements for stormwater management are effected through the

land-use laws, applied to developers. Therefore, if existing

towns and developments are to have runoff pollution completely

controlled, this must be done by some entirely different program.

For coastal areas, the stormwater management program may not be

sufficient, even for controlling polluting runoff from new

development. Some pollutants are found dissolved in stormwater,
or remain in colloidal form, which settles only slowly.

Therefore, complete control of urban runoff pollution, even in

newly developed areas, may require measures other than new

stormwater management.

NONPOINT SOURCE POLLUTION OCCURRENCE AND HYDROCARBONS

It is difficult to relate the characteristic biological

degradation of urban streams to the pollution concentrations

actually observed. In some cases, planned or unplanned releases

of industrial waste may be responsible; but widespread similar

degradation in non-industrial areas may be attributable largely

to hydrocarbons. Hydrocarbons usually occur in concentrations of

from 2 to 4 mg/l in urban runoff, mainly in particulate form, the

remainder being dissolved (4). Although runoff from streets and

parking lots has perceptible oil sheens on the surface, which are

in liquid form, petroleum hydrocarbons are quickly sorbed on the

particulates in runoff; so that storm sewers rarely contain

hydrocarbons in liquid form unless substantial quantities havb

been spilled or deliberately released in the catchment area.

Relatively little attention has been given by government agencies

to petroleum hydrocarbons in urban runoff, because this pollutant

is not a scientifically definable substance but rather a complex

and variable mixture, not included in C.S. EPA's listing of

priority pollutants, and not among the parameters measured and

reported routinely by the U. S. Geological Survey.

The potential for biological damage by hydrocarbons has been

given little attention; but a studv of petroleum impacts in the

Delaware Estuary showed that concentrations of 1 mg/1 of

petroleum in water, when sorbed on particulates, had serious

adverse effects upon filter-feeding biota (5). In view of this

finding, the regular presence of several times these

concentrations of hydrocarbons in urban runoff is highly suspect,

as a.cause of biological damage. Also, in water which is

ultimately to be chlorinated, the presence of hydrocarbons is

obviously undesirable, because of the trihalomethane problem.

Pollution in stormwater runoff, like the flood peaks in small

streams, originates widely throughout the drainage area. Whether

the runoff is conveyed to the stream by a storm sewer or by an

open channel is immaterial to the fate of the pollutants.

However sheet flow at moderate slope over grass not only slows

down the velocity, but also removes most of the particulates.

Unfortunately for the quality of our small streams, most

developers (other than in single-family large-lot subdivisions)

collect storm drainage systematically and route it through curbs,

gutters and storm drains, which deliver a full load of runoff

pollution to the streams.

It is not too much to say that the pollution in storm runoff from

urban and urbanizing areas is a major environmental problem,

which is more important to the quality of most of our small

streams than point source pollution from the effluent of wastewater

treatment facilities.

CONVENTIONAL STORMWATER MANAGEMENT

Conventional stormwater management differs from flood control in

that it is preventive in nature rather than remedial. Instead of

remedying existing conditions, it is required to be carried out

as a condition of new development, by the developer himself, or

on his behalf. The basic rationale for stormwater management is

that new development, whether for housing, commercial, industrial

or highway facilities, greatly increases the rate and the volume

of storm runoff from given precipitation. This results in

creased flood damages downstream. More recently it has also been

noted that the increased rate and volume of runoff from

development also contributes to increasing stream erosion

downstream. New development also generally results in increased

pollution downstream, as has already been referred to. In the

past, reduction of this runoff pollution and stream erosion have

not been among the objects of conventional stormwater management.

Stormwater management is sometimes cartied out by means of roof

top storage, underground pits or tunnels, porous pavement, or

grassy swales, designed to prevent the desired retention,

retardation or infiltration of flow. However, in New Jersey, the

approach usually relies on detention basins or infiltration

basins.

The main hydraulic criterion for conventional stormwater

detention is that a specified design storm occurring after

development should produce no higher peak rate of runoff than the

peak rate which would occur from the same storm prior to

development, measured at the site itself. Obviously, if the

volume of runoff from the site is increased by the development,

peak flood flows further downstream will generally be increased

by the development, even though peak flows at the site may not be

increased. In many of the older stormwater management systems, a

single design storm was specified, frequently the 100 year

frequency storm. Control of 100 year storms or any other single

design storm on a small drainage area requires relatively little

detention storage; but is very ineffective in controlling the

peaks of smaller floods, and in'reducing erosion damage.

Moreover, it has been shown that the effect of such programs in

controlling floods disappears rapidly- downstream (6,7). It is

now clear that stormwater management detention programs are only

effective in controlling flood and erosion damage downstream

when the post-development peaks of any of several design floods

can be held to their pre-development ldvel. To meet New Jersey

standards, control of flood hydrographs of 2 year, 10 year and

100 year floods to pre-development levels at site is required.

Even so, when the flood flows of many contributing drainage areas

are to be aggregated into a river, the stormwater detention

programs will seldom reduce resulting peak flood flows as much as

the increased volume of stormwater runoff will increase them.

Planning and Institutional Aspects

The conventional stormwater management plan is simple in concept.

The municipality passes an ordinance requiring developers to

submit a stormwater detention plan for each proposed new

development. These plans must be reviewed and approved by the

municipal engineer or other appropriate local authoritv; and the

developer or owner must then construct the necessary retention

facility on his own property. Except in the case of large

developments, where master detention basins (or regional basins)

may be built for control of relatively large areas, such a

program usually results in a small detention basins on each of

many lots, in what ha� been referred to scornfully as the

"chicken pox" pattern. The disadvantages of a multitude of small

detention basins at-site, such as usually results from

conventional stormwater management, include the excessive amount

of land required, the difficulty of maintenance, and the planning

and regulatory burden entailed by such a large number of

facilities.

Although simple in principle, implementation of stormwater

management programs presents some difficulties. In their desire

to encourage economic development, municipalities are under

pressure to waive any requirements adding to developers costs.

Most municipal engineers are structure-oriented; and the hvdraulic

and hydrologic analysis of stormwater management plans may be

beyond their personal competence. Therefore, hiring of

additional staff or retention of consultants is generally required.

Difficult maintenance problems arise; which are covered in a

later section.

WATER QUALITY CONTROL IN STORMWATER MANAGEMENT

Background

In stormwater management, water quality control is usuallv

obtained through dual purpose detention basins designed, first,

to reduce flood damages downstream and, second, to reduce

nonpoint source pollution from storm runoff. Although somewhat

similar in concept to the much earlier sediment control and flood

retention programs of the U. S. Soil Conservation Service, the

idea of using stormwater detention basins to reduce environmental

pollution in streams of urbanizing areas first gained currency

through the Section 208 water quality planning studies started in

1975, under Federal authority (8). Section 208 studies in several

states, including New Jersey and Virginia, reported favorably

upon this concept. However, definitive action could only be

taken later; as needs for such a program were recognized more

generally; and as plans were implemented under various local and

state authorities.

Concept

The underlying principle of dual purpose detention is that the

detention of flood flows, for reduction of damages downstream,

and.the retardation of flood flows, for settlement of

particulates, can advantageously be combined in the same

structure, with little loss in effectiveness of either program.

Flood damages are almost entirely due to floods of magnitude

greater than two year frequency, with most of the damages due to

a few very large floods; whereas the harmful pollution occurs

mainly as the cumulative effect of a large number of small

storms, most of which are not larger than one year frequency. It

is also true that the prolonged retention of a given amount of

retention storage, even though it does not contribute to reduce

peak flows from large storms at site, does contribute to reduce

peak flows further downstream, since, for the larger streams,

total volume of water released over a 24 hour period is more

important to flooding conditions than the peak flow at various

development sites. Therefore, in order to be-fully effective, a

dual purpose detention basin must hold runoff from the frequent

small storms over a prolonged period of time; but it must operate

effectively for flood control when a larger storm occurs.

Outlet Design

Dual purpose, long-time retention is accomplished by a small

outlet called aletention outlet, at the low point of the detention

storage, sized for slow release of the runoff from the designated

small storm. See Figure 1. This designated small storm is

referred to as the settleability design storm.

Above the level of the detention storage needed to control the

settleability design storm will be the main outlet, or the lowest

of two or more main outlets. The main outlets are designed so as

to provide the necessary degree of control of specified design

storms (for flood control). Although stormwater management

ordinances usually specify requirements in terms of flow effects

at site only, effective control downstream requires that designs

are adequate to control any of several different frequency design

storms. For example, when a series of 400 detention basins were

modeled, covering an 8000 acre main watershed, with each basin

designed to control peak flow from 100 year post-development

floods at site to the level of the 100 year pre-development peak

at that site, the 100 year watershed, post-development peak flow

at the outlet of the main was reduced by only 2%, and the two

year and ten year peaks were reduced not at all. By contrast, a

similar series of detention basins each designed to control

particulate pollution from small floods, and to hold either a

two, ten, or hundred year flood at site to its pre-development

peak, reduced the post-development peak of hundred year floods of

the main watershed by 20%, and the peaks of ten and two year

floods by 24% and 44% respectively (4). It is apparent that a

stormwater management detention criterion only designed to

control a hundred year frequency storm at site to pre-development

levels, would be of only minor effect downstream. Whereas a

detention basin designed to control any of three design storms

would be quite effective.

Control of Particulate Pollution

In New Jersey, the settleability design storm is 1 1/4 inches in

2 hours or the one year 24 hour storm. The South Florida Flood

Control District uses a settleability design storm of 1.0 inch of

runoff or the runoff from a three year frequency storm, whichever

is greater. The New Jersey standard requires slow emptying of

the retained settleability detention over a 36 hour period,

except for residential area, where evacuation of an 18 hour

period is acceptable. It has been estimated that this degree of

retention will remove about 60% of the total suspended sediments

in urban runoff, a similar proportion of the petroleum

hydrocarbons, and lead, and perhaps 451 of the BOD, copper and

phosphates. of course, dissolved pollutants such as nitrates

should be unaffected by retention. Such special retention

provisions are referred to as the water quality storage

provisions of stormwater management.

Summary

Although water quality storage provisions of stormwater

management are not sufficient to eliminate entirely the increase

in particulate pollution caused by various forms of econmic

development, they are capable of greatly reducing it, thereby

correspondingly reducing the unfavorable environmental effects.

The water quality storage provisions have the incidental effect

of extending the flood control effects of the detention basins

further downstream. As previously mentioned, even greater

effects in removing particulate pollutants from urban runoff can

be obtained by passing the runoff in sheet flow over lawns or

other thick vegetation; and virtually complete elimination of

particulate pollution can be obtained through infiltration

basins.

THE NEW JERSEY PROGRAM

The New Jersey Stormwater Management Act (1) required all

municipalities to prepare and implement a stormwater management

plan and ordinance within one year from the date of promulgation

of comprehensive stormwater management regulations by the New

Jersey Department of Environmental Protection, or by the next

reexamination of the municipal master plan as required by the

Municipal Land Use Law (9). However, the mandatory provisions of

the law were made contingent upon the State providing to

municipalities 90% of the cost of preparing stormwater management

plans.

For implementation of the law, Stormwater Management Regulations

(3) were adopted by the Department of Environmental Protection in

1983. These regulations define Phase I planning for

municipalities, which involves the adoption of a stormwater

management ordinance after only administrative planning. Phase

II planning for counties or municipalities consists of detailed

watershed studies to encourage a broader approach to stormwater

management. For both phases of planning,, design standards

require the construction of dual purpose detention basins rather

than the conventional type, described above.

Because the funding required by the law to be made available to

municipalities to offset the cost of developing a Phase I plan

was not appropriated initially, there has been a delay in

implementing the regulations. In the interim, the stormwater

management regulations have been enforced only where adopted

voluntarily by sub-state agencies, or,--within-the flood hazard

area, by special provisions in the Flood Hazard Area regulations

(10).

Priorities

Each of the 567.municipalities in New Jersey has been assigned a

priority classification based on its need for stormwater

management planning. Areas relatively undeveloped but

experiencing development pressures have been identified as high

priority. Also classified as high priority are the Passaic River

basin communities (a high flood risk area) as well as those

communities whose uncontrolled runoff is impacting the water

quality in reservoirs, shellfishery beds and beaches. Urban

communities, rural areas that are not experiencing development

and areas that would not benefit from stormwater manaqement have

been assigned low priority status. The remaining municipalities

are in the medium priority category. The significance of the

priority is that funds will not be offered nor will application

of the regulations be made mandatory in low or medium priority

areas.

Grant Programs

Two grant programs have been established to administer the

stormwater management program. High ptiority municipalities were

invited in 1986 to apply for grants of $5000 each to cover 90% of

the cost of preparing and adopting a stormwater management

ordinance (Phase I). Sixty applications were received and the

Department of Environmental Protection is preparing for a second

round of applications. Cost sharing grants were also made

available to counties for the development of a comprehensive

county stormwater management plan and/or a detailed watershed

planning study (Phase 11). Six grants have been approved and

these studies are scheduled to be completed within the next two

years. Limited funds remain; and, through a cooperative effort

with the U.S. Soil Conservation Service, the cost of two

additional watershed studies will be shared by the Department of

Environmental Protection and the U.S. Soil Conservation Service.

The main purpose of the Phase II grants is to allow for an

engineered watershed plan to be developed to replace the

ubiquitous small basins, one for each building site, which

usually develop from a Phase I ordinance.

Watershed Planning Study

It is widely acknowledged that planning of stormwater management

at the watershed level will produce more effective control of

runoff than the conventional site-by-site approach.

However, such planning, which usually results in decisions to

build master detention basins, is not often utilized, because of

the cost of planning, requiring use of complex models such as

the U.S. Soil Conservation Service Hydrologic Model TR-20, and

because of the institutional problems involved.

In order to encourage watershed level stormwater management

planning, the New Jersey Department of Environmental Protection

co-sponsored a demonstration study with the U.S. Soil

Conservation Service and Hunterdon County, on the South Branch

Rockawav Creek. Close cooperation was obtained from the

municipalities and other agencies involved, both in conducting

the study and in preparing the final report.

The recommended plan developed by this study (2) requires each

new development to provide on-site water quality controls, and to

contribute a fee towards two regional detention basins designed

to provide flood control for the watershed. The water quality

controls must provide retention storage sufficient to comply with

the State's Stormwater Management regulations.

The fee is to be levied in lieu of the on-site control of the 10

year and 100 year storms, as otherwise required by state

regulation. In each case, the fee is to be levied is

proportionate to the increased runoff volume in the 100 year

storm which is contributed bv that development. The fee, per

unit volume of increased runoff, is to be determined by dividing

the total estimated costs of the two r6gional basins by the total

increase in runoff volume from the 100 year storm with the

watershed fully developed. A detailed description of the

financial aspects of the plan can be found in the study report.

The recommended stormwater management plan, with its combination

of on-site and regional controls, was found to be far more

effective than any other strategy in attenuating downstream flood

peaks for all storm frequencies investigated. When on site

controls were used exclusively, downstream peaks could not be

effectively reduced. This was true whether the on-site basins

were designed for single or multiple frequency peak control (i.e.

2-year, 10-year, and 100-year). The exclusive use of master

detention basins also failed to match the effectiveness of the

recommended plan, in addition to leaving the stream upstream of

the master detention basins exposed to the added floods, erosion

and pollution caused by development.

When quality controls at site are used in conjunction with master

detention basins designed to control the larger floods, the

system meets fully the runoff pollution control objectives of the

regulations throughout the watershed. As regards the flood

control effects, the recommended plan sacrifices a good deal of

control in the reaches between the development sites and the

regional basins, but has a much greater control than the

regulation's standard further downstream, as well as being more

economical to construct and to maintain. All participating

agencies ended in concurrence.

TECHNICAL INTERFACE PROBLEMS

Among the various kinds of water programs, stormwater management

is unusually beset with interfaces, which include both

well-defined programs and certain emerging problems which may be

poorly defined but cannot be disregarded. The four major

interfaces involve, respectively, freshwater wetlands,

groundwater recharge, shellfish and estuary preservation, and

nonpoint source pollution generally.

Wetlands

The site chosen for a detention basin often includes land

classified as wetlands; and the preservation of freshwater

wetlands is a matter of prime environmental interest. Such

preservation has achieved legal sanction nationally through the

permit processes of the Corps of Engineers, which is backed in

this endeavor by the Fish and Wildlife Service and the

Environmental Protection Agency. State laws to preserve wetlands

are pending in various states, including New Jersey. A high

proportion of major land developments involve wetlands, either in

the area to be developed economically or at the site of a

proposed detention basin. In evaluating stormwater management

interfaces with a wetlands program, it"is usually not clear what

the specific wetlands attributes are which are being protected,

or whether the need for protection is absolute or can be traded

off for other values. In some cases, as where endangered species

are involved, the attribute protected may be clearly identified

and the degree of protection afforded may be virtually absolute.

However, in most cases the wetland is identified only by the

presence of swamp-tolerant vegetation or by hydric soils. In

such cases, it may usually be assumed that, as regards wetlands

values, the intermittent impoundment characterizing a detention

basin constitutes a non-significant variation from the less

frequent flooding which already exists.

Groundwater

The control of groundwater is an extremely complex and rapidly

evolving field, with which most stormwater management programs

need have little to do. However, in areas of aquifer recharge,

in order to sustain the aquifer, it is usually considered

desirable to use infiltration basins for stormwater management,

rather than the more usual dry detention basins. In various

areas, including Nassau County (New York) and parts of Few Jersey

and Florida, it has sometimes been found that the desired

infiltration of surface runoff has served to contaminate the

aquifer with nutrients, pesticides, or other undesirables. This

is a problem difficult to handle, on account of the large number

of structures involved, the wide variation in pollutant

concentrations, both temporarily and from one drainage basin to

another, and the practical difficulty of evaluating the degree of

runoff pollutioft at any site and its subsequent fate in

groundwater. In general terms, infiltration basins to handle the

less polluted runoff are desirable, while the more polluted

runoff should be handled otherwise.

Shellfish and Estuary Preservation

This potentially important interface with stormwater management

is reduced in incidence by the fact that most small streams

draining directly to vital waters in coastal zones suffer little

damage due to floods. In such areas, rainfall from even rather

severe storms usually infiltrates directly into the ground.

Bays, estuaries and the ocean seacoast itself usually have

important shellfish and finfish and recreational resources, and

require a high degree of protection, which is different in kind

as well as in degree from that of normal upland streams.

Infectious bacteria, virus and fungi are of primary importance to

both bathing beaches and the maintenance of shellfish beds7 and

pesticides are also of great importance. The protection afforded

to normal inland streams by well-planned stormwater management

programs cannot be assumed to be equally effective in coastal

areas. Normal type stormwater retention of particulates is a

desirable step for protection of shellfish and estuaries, but not

necessarily a sufficient one. For more adequate protection,

control of pollution from existing facilities will usually be

required.

Conclusion

The water quality stormwater control program provides only a

partial answer to the nonpoint source control problems; but it

has the great advantage that it can be readily implemented. All

it takes is the passage of a local ordinance, under authority of

the Stormwater Management Act and the State's regulations. to

require local developers to incorporate such stormwater retention

provisions in the plans which they submit for municipal site plan

and subdivision approval. This is not an unfair burden upon

developers; because the program only requires them to take a ction

to reduce the environmental damage which their developments would

otherwise create. Where river floods are involved developers

have to provide dual purpose detention basins; but in other

coastal areas only the water quality detention provision are

necessary.

Department staff contacts on the program include the following:

William Whipple, Jr., Assistant Director ..... (609) 292-7219

Narinder Ahuja, Acting Bureau Chief .......... (609) 292-2373

Clark Gilman, Section Chief .................. (609) 292-2296

Susan Burke, Program Engineer ................ (609) 292-2402

REFERENCES

1. State of New Jersey, Stormwater Management Act (P.L. 1981,

c. 32).

2. State of New Jersey, Department of Environmental Protection

South Branch Rockaway Creek Stormwater Management Study,

April 1986.

3. State of New Jersey, Stormwater Management Regulations

(N.J.A.C. 7:8-1.1 et seq.).

4. Whipple, Wt., Jr., "Dual-Purpose Detention Basins" Journal

of Water Resources Planning and Management Division, ASCE,

Proc. Paper 14860, September 1979, W.R. 2, p. 404.

5. Haskin, Harold in "Petroleum Industry in the Delaware

Estuary, a report to the National Science Foundation by

Whipple, Wm., Jr. and Patrick Ruth RANN Program, Grant No.

E.N.V. 74-14810 - A03, January 1987, pp. 251-301.

6. Whipple, Wt., Jr., DiLouis, James M., and Pytlar, Theodore

S., Jr., "Erosional Potential of Streams in Urbanizing

Areas," Water Resources Bulletin, AWRA, Vol. 17, No. 1,

7. Whipple, Wm., et al., I'Stormwater Manaaement in Urbanizing

Areas," Prentice Hall, 1983, Chapter 7.

8. U.S. Government, Water Pollution Control Amendments, 1972

(P.L. 92-500).

9. State of New Jersey, Municipal Land Use Law (P.L. 1975,

c. 291).

10. State of New Jersey, Flood Hazard Area Regulations, (N.J.A.C.

7:13-1.1 et seq.).

ACKNOWLED;G.EMENT: This paper is largely based upon apaper by

William Whipple, Jr., to be presented at the American Society of

Civil Engineers Planning and Management Conference in Kansas

City, MO, March 17, 1987.

DUAL PURPOSE DETENTION BASIN OUTLETS

LEGEND

A - Volume to Control 100 Year Storm

8 - Volume to Control Settleability Storm

C- Flood Control Outlet

D - Retention Outlet

E - Trash Racks

F - Downstream Outlet

DATE DUE

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