Township of Riverside, NJ Grading/Drainage

Purpose. The purpose of this section is to establish minimum stormwater management requirements and controls for land development in the Township.

Applicability. The stormwater management design standards and requirements of this section shall apply to land development that will ultimately disturb more than one acre or increase impervious surfaces by more than 10,890 square feet.

Design objectives. The State of New Jersey has adopted Stormwater Management Regulations (N.J.A.C. 7:8 et seq.) that establish the design objectives of stormwater management throughout the state. These regulations require the use of nonstructural best management practices (BMPs) and structural BMPs to achieve specific performance standards. The stormwater management design objectives can be summarized as follows:

(1)

Nonstructural BMPs or low impact techniques should be considered for flood control, groundwater recharge, and pollutant reduction before the use of structural BMPs;

(2)

Structural BMPs should be integrated with nonstructural stormwater management measures and proper maintenance plans;

(3)

Multiple stormwater management BMPS may be necessary to achieve the established performance standards for water quality, water quantity, and groundwater recharge;

(4)

Nonstructural measures include both environmentally sensitive site design and source controls that prevent pollutants from being placed on the site;

(5)

Source control plans should be developed based upon physical site conditions and the origin, nature, and anticipated loading, of potential pollutants.

Technical guidance. The design engineer shall rely on the following documents for technical guidance in the preparation of the stormwater management system design:

(1)

New Jersey Stormwater Best Practices Manual, as amended, prepared by the New Jersey Department of Environmental Protection.

(2)

Stormwater Management Facilities Maintenance Manual, as amended, prepared by the New Jersey Department of Environmental Protection.

(3)

Standards for Soil Erosion and Sediment Control in New Jersey, promulgated by the State Soil Conservation Committee and incorporated into N.J.A.C. 2:90.

(4)

GSR-32 A Method for Evaluating Ground Water Recharge Areas in New Jersey, prepared by the New Jersey Geological Survey.

General design and performance standards. Stormwater management measures for land development shall be developed to meet the stormwater management standards of this section. The stormwater management standards are intended to minimize the impact of stormwater runoff on water quality and water quantity in receiving water bodies and to maintain groundwater recharge in accordance with the following standards:

(1)

To the maximum extent feasible, these standards shall be met by incorporating nonstructural stormwater management strategies into the design. If these strategies alone are not sufficient to meet the specified standards, structural stormwater management measures necessary to meet these standards shall be incorporated into the design.

(2)

Residential land development that is regulated under the Residential Site Improvement Standards (RSIS) at N.J.A.C. 5:21 shall be governed by RSIS except to the extent that the RSIS are superseded by the stormwater management regulations (N.J.A.C. 7:8 et seq.) that are the basis of this section.

(3)

Stormwater management measures shall avoid adverse impacts of concentrated flow on habitat for threatened and endangered species as documented in the environmental impact statement, particularly with regard to Helonias bullata (swamp pink) and/or Clemmys muhlenbergii (bog turtle).

Stormwater management standards. This section contains minimum design and performance standards to control erosion, encourage and control infiltration and groundwater recharge, and to control stormwater runoff quantity and quality impacts.

(1)

Erosion control standard. The minimum design and performance standards for erosion control are those established under the Soil Erosion and Sediment Control Act, N.J.S.A. 4:24-39 et seq. and implementing rules.

(2)

Groundwater recharge standards. The land development shall be designed to provide for groundwater recharge in accordance with the following requirements:

(a)

Recharge standard. The design engineer shall, using the assumptions and factors for stormwater runoff and groundwater recharge calculations specified in this section, either demonstrate that the site and its stormwater management measures maintain 100% of the average annual pre-construction groundwater recharge volume for the site or demonstrate that the increase of stormwater runoff volume from pre-construction to post-construction for the two-year storm is infiltrated.

(b)

Impact. The design engineer shall assess the hydraulic impact of the groundwater recharge measures on the groundwater table and site design so as to avoid adverse hydraulic impacts. Potential adverse hydraulic impacts include, but are not limited to, exacerbating a naturally or seasonally high-water table so as to cause surficial ponding, flooding of basements, or interference with the proper operation or subsurface sewage disposal systems and other subsurface structures in the vicinity or down gradient of the groundwater recharge area.

(c)

Exemptions. This groundwater recharge standard does not apply to:

[1]

Projects that qualify as "urban redevelopment";

[2]

Stormwater from areas of high pollutant loading [high pollutant loading areas are areas in industrial and commercial developments where solvents and/or petroleum products are loaded/unloaded, stored, or applied, areas where pesticides are loaded/unloaded or stored; areas where hazardous materials are expected to be present in greater than reportable quantities' as defined by the United State Environmental Protection Agency (EPA) at 40 CFR 302.4; areas where recharge would be inconsistent with Department approved remedial action work plan or landfill closure plan and areas with high risks for spills of toxic materials, such as gas stations and vehicle maintenance facilities]; and

[3]

Industrial stormwater exposed to source material ["source material" means any material(s) or machinery, located at an industrial facility, that is directly or indirectly related to process, manufacturing or other industrial activities, which could be a source of pollutants in any industrial stormwater discharge to groundwater. Source materials include, but are not limited to, raw materials; intermediate products; final products; waste materials; by-products; industrial machinery and fuels, and lubricants, solvents, and detergents that are related to industrial activities that are exposed to stormwater].

(3)

Stormwater runoff standard. In order to control stormwater runoff quantity impacts, the site design shall comply with one of the following requirements:

(a)

The post-construction runoff hydrographs for the two-, ten- and 100-year storm events for stormwater leaving the site do not exceed, at any point in time, the pre-construction runoff hydrographs for the same storm events;

(b)

There is no increase, as compared to the pre-construction condition, in the peak runoff rates of stormwater leaving the site for the two-, ten-, and 100-year storm events and the increased volume or change in timing of stormwater runoff will not increase flood damage at or downstream of the site. This analysis shall include the analysis of impacts of existing land uses and projected land uses assuming full development under existing zoning and land use ordinances in the drainage area; or

(c)

The post-construction peak runoff rates for the two-, ten- and 100-year storm events are designed to be 50%, 75% and 80%, respectively, of the pre-construction peak runoff rates. The percentages apply only to the post-construction stormwater runoff that is attributable to the portion of the site on which the proposed development or project is to be constructed. The percentages shall not be applied to post-construction stormwater runoff into tidal flood hazard areas if the increased volume of stormwater runoff will not increase flood damage below the point of discharge.

(4)

Stormwater runoff quality standards. The stormwater management measures shall be designed to reduce the post-construction load of total suspended solids (TSS) in stormwater runoff by 80% of the anticipated load from the developed site, expressed as an annual average in accordance with the following requirements:

(a)

Stormwater management measures shall only be required for water quality control if an additional 1/4 acre of impervious surface is being proposed on a development site.

(b)

The requirement to reduce TSS does not apply to any stormwater runoff in a discharge regulated under a numeric effluent limitation for TSS imposed under the New Jersey Pollution Discharge Elimination System (NJPDES) rules, N.J.A.C. 7:14A, or in a discharge specifically exempt under a NJPDES permit from this requirement.

(c)

Water quality calculations. The water quality design storm is defined as 1.25 inches of rainfall in two hours distributed in the manner reflected in Table 255-148F(4)(c). The calculation of the volume of runoff may take into account the implementation of nonstructural and structural stormwater management measures.

Table 255-148F(4)(c), Water Quality Design Storm Distribution
Time (minutes)	Cumulative Rainfall (inches)	Time (minutes)	Cumulative Rainfall (inches)
0	0.000	65	0.891
5	0.008	70	0.991
10	0.016	75	1.0500
15	0.025	80	1.0840
20	0.050	85	1.1170
25	0.075	90	1.1500
30	0.100	95	1.1750
35	0.133	100	1.2000
40	0.166	105	1.2250
45	0.200	110	1.2334
50	0.258	115	1.2417
55	0.358	120	1.2500
60	0.625

(d)

Total suspended solid (TSS) reduction calculations. The presumed removal rates for certain BMPs designed in accordance with the New Jersey Stormwater Best Management Practices Manual are presented in Table 255-148F(4)(d). TSS reduction shall be calculated based on the specified removal rates for the BMPs. Alternative removal rates and methods of calculating removal rates may be used if the design engineer provides documentation demonstrating the capability of these alternative rates and methods to the satisfaction of the Board Engineer.

Table 255-148F(4)(d), TSS Removal Rates for BMPs
Best Management Practice	TSS % Removal Rate
Bioretention systems	90%
Constructed stormwater wetland	90%
Extended detention basin	40% to 60%
Infiltration structure	80%
Manufactured treatment device	See Section 5.C[1]
Sand filter	80%
Vegetative filter strip	60% to 80%
Wet pond	50% to 90%

[1]

Editor's Note: So in original.

(e)

If more than one BMP in series is necessary to achieve the required 80% TSS reduction for a site, the applicant shall utilize the following formula to calculate TSS reduction:

R = A+ B- (AXB)/100

Where:
R	=	Total TSS percent load removal from application of both BMPs
A	=	The TSS percent removal rate applicable to the first BMP
B	=	The TSS percent removal rate applicable to the second BMP

(f)

If there is more than one on-site drainage area, the 80% TSS removal rate shall apply to each drainage area, unless the runoff from the subareas converge on site in which case the removal rate can be demonstrated through a calculation using a weighted average.

(g)

Stormwater management measures shall also be designed to reduce, to the maximum extent feasible, the post-construction nutrient load of the anticipated load from the developed site in stormwater runoff generated from the water quality design storm. In achieving reduction of nutrients to the maximum extent feasible, the design of the site shall include nonstructural strategies and structural measures that optimize nutrient removal while still achieving the stormwater management standards.

Calculation of stormwater runoff and groundwater recharge. Stormwater runoff and groundwater recharge shall be calculated in accordance with the following:

(1)

The design engineer shall calculate stormwater runoff using one of the following methods:

(a)

The USDA Natural Resources Conservation Service (NRCS) methodology, including the NRCS Runoff Equation and Dimensionless Unit Hydrograph, as described in the NRCS National Engineering Handbook Section 4, Hydrology, and Technical Release 55, Urban Hydrology for Small Watersheds; or

(b)

The rational method for peak flow and the modified rational method for hydrograph computations.

(2)

Runoff coefficients. For the purpose of calculating runoff coefficients and groundwater recharge, the design engineer shall presume that the pre-construction condition of a site or the portion thereof has a wooded land use with good hydrologic condition. A runoff coefficient or a groundwater recharge land cover for an existing condition may be used on all or a portion of the site if the design engineer verifies that the hydrologic condition has existed on the site or portion of the site for at least five years without interruption prior to the time of application. If more than one land cover have existed on the site during the five years immediately prior to the time of application, the land cover with the lowest runoff potential shall be used for the computations. In addition, there is the presumption that the site is in good hydrologic condition (if the land use type is pasture, lawn, or park), with good cover (if the land use type is woods), or with good hydrologic condition and conservation treatment (if the land use type is cultivation).

(3)

In computing pre-construction stormwater runoff, the design engineer shall account for all significant land features and structures, such as ponds, wetlands, depressions, hedgerows, or culverts, that may reduce pre-construction stormwater runoff rates and volumes.

(4)

In computing stormwater runoff from all design storms, the design engineer shall consider the relative stormwater runoff rates and/or volumes of pervious and impervious surfaces separately to accurately compute the rates and volume of stormwater runoff from the site. To calculate runoff from unconnected impervious cover, urban imperious area modifications as described in the NRCS Technical Release 55, Urban Hydrology for Small Watersheds, and other methods may be employed.

(5)

If the invert of the outlet structure of a stormwater management measure is below the flood hazard design flood elevation as defined at N.J.A.C. 7:13, the design engineer shall take into account the effects of tail water in the design of structural stormwater management measures.

(6)

Groundwater recharge shall be calculated in accordance with the New Jersey Geological Survey Geological Survey Report GSR-32 A Method for Evaluating Groundwater Recharge Areas in New Jersey, incorporated herein by reference, as amended and supplemented.

Stormwater management exemptions.

(1)

Exemption. The following linear development projects are exempt from conforming to the stormwater management standards:

(a)

The construction of an underground utility line, provided that the disturbed areas are revegetated upon completion;

(b)

The construction of an aboveground utility line provided that the existing conditions are maintained to the maximum extent practicable; and

(c)

The construction of a public pedestrian accessway, such as a sidewalk or trail with a maximum width of 14 feet, provided that the accessway is made of permeable material.

(2)

Design waiver. A waiver from strict compliance from the stormwater management standards may be granted for the enlargement of an existing public roadway or railroad; or the construction or enlargement of a public pedestrian accessway, provided that the following conditions are met:

(a)

The applicant demonstrates that there is a public need for the project that cannot be accomplished by any other means;

(b)

The applicant demonstrates through an alternatives analysis, that through the use of nonstructural and structural stormwater management strategies and measures, the option selected complies with the stormwater management standards to the maximum extent practicable;

(c)

The applicant demonstrates that, in order to meet the stormwater management standards, existing structures currently in use, such as homes and buildings would need to be condemned; and

(d)

The applicant demonstrates that it does not own or have other rights to areas, including the potential to obtain through condemnation lands within the upstream drainage area of the receiving stream that would provide additional opportunities to mitigate for the stormwater management standards that were not achievable on-site.

Nonstructural stormwater management strategies. To the maximum extent practicable, the stormwater management standards shall be met by incorporating nonstructural stormwater management strategies into the design in accordance with the following:

(1)

The applicant shall identify the nonstructural measures incorporated into the site design in the stormwater management report.

(2)

If the applicant contends that it is not feasible for engineering, environmental, or safety reasons to incorporate any nonstructural stormwater management measures into the site design, the applicant shall identify the strategies considered and provide a basis for the contention that these strategies did not apply.

(3)

Nonstructural stormwater management measures incorporated into site design shall:

(a)

Protect areas that provide water quality benefits or areas particularly susceptible to erosion and sediment loss;

(b)

Minimize impervious surfaces and break up or disconnect the flow of runoff over impervious surfaces;

(c)

Maximize the protection of natural drainage features and vegetation;

(d)

Minimize the decrease in the time of concentration from pre-construction to post-construction ("time of concentration" is defined as the time it takes for runoff to travel from the hydraulically most distant point of the watershed to the point of interest within a watershed);

(e)

Minimize land disturbance including clearing and grading;

(f)

Minimize soil compaction;

(g)

Provide low-maintenance landscaping that encourages retention and planting of native vegetation and minimizes the use of lawns, fertilizers and pesticides;

(h)

Provide vegetated open-channel conveyance systems discharging into and through stable vegetated areas;

(i)

Provide other source controls to prevent or minimize the use of exposure of pollutants at the site in order to prevent or minimize the release of those pollutants into stormwater runoff including, but not limited to:

[1]

Site design features that help to prevent accumulation of trash and debris in drainage systems;

[2]

Site design features that help to prevent discharge of trash and debris from drainage systems;

[3]

Site design features that help to prevent and/or contain spills or other harmful accumulations of pollutants at industrial or commercial developments;

[4]

When establishing vegetation after land disturbance, applying fertilizer in accordance with the requirements established under the Soil Erosion and Sediment Control Act, N.J.S.A. 4:24-39 et seq., and implementing rules;

[5]

Any land area used as a nonstructural stormwater management measure to meet the stormwater management standards shall be dedicated to the Township, subject to a conservation easement filed with the County Clerk, or subject to an approved equivalent restriction that ensures that measure or an equivalent stormwater management measure approved by the Planning Board is maintained in perpetuity.

Structural stormwater management measure standards. Structural stormwater management measures shall be designed in accordance with the following requirements:

(1)

The structural measures shall be designed to account for existing site conditions, including, environmentally critical areas; wetlands; flood-prone areas; slopes; depth to seasonal high-water table; soil type, permeability and texture; drainage area and drainage patterns; and the presence of solution-prone carbonate rocks (limestone).

(2)

The structural measures shall be designed to minimize maintenance, to facilitate maintenance and repairs and to ensure proper functioning.

(3)

Structural measures shall be designed, constructed, and installed to be strong, durable, and corrosion-resistant. Measures that are consistent with the relevant portions of the Residential Site Improvement Standards at N.J.A.C. 5:21-7.3, 5:21-7.4, and 5:21-7.5 shall be deemed to meet this requirement.

(4)

Trash racks shall be installed at the intake to the outlet structure and shall be designed in accordance with Subsection J of this section.

(5)

At the intake to the outlet from the stormwater management basin, the orifice size shall be a minimum of 2 1/2 inches in diameter.

(6)

Manufactured treatment devices may be used to meet the requirements of this subsection, provided the pollutant removal rates are verified by the New Jersey Corporation for Advanced Technology and certified by the Department.

Stormwater management basin safety standards. Stormwater water management basins shall be designed in accordance with the following requirements to protect public safety:

(1)

Trash racks. A "trash rack" is a device designed to catch trash and debris and prevent the clogging of outlet structures. Trash racks shall be installed at the intake to the outlet structure to ensure proper functioning of the basin outlets in accordance with the following design requirements:

(a)

Trash racks shall have parallel bars with one-inch spacing between the bars to the elevation of the water quality design storm. For elevations higher than the water quality design storm, the parallel bars at the outlet structure shall be spaced no greater than 1/3 the width of the diameter of the orifice or 1/3 the width of the weir, with a minimum spacing between bars of one inch and a maximum spacing between bars of six inches.

(b)

The trash rack shall be designed so as not to adversely affect the hydraulic performance of the outlet pipe or structure.

(c)

The average velocity of flow through a clean trash rack is not to exceed 2.5 feet per second under the full range of stage and discharge. Velocity is to be computed on the basin of the net area of opening through the rack.

(d)

The trash rack shall be constructed and installed to be rigid, durable, and corrosion-resistant, and shall be designed to withstand a perpendicular live loading of 300 lbs/sq. ft.

(2)

Overflow grate. An overflow grate is designed to prevent obstruction of the overflow structure. If an outlet structure has an overflow grate, such grate shall meet the following requirements:

(a)

The overflow grate shall be secured to the outlet structure but removable for emergencies and maintenance.

(b)

The overflow grate spacing shall be no less than two inches across the smallest dimension.

(c)

The overflow grate shall be constructed and installed to be rigid, durable, and corrosion resistant, and shall be designed to withstand a perpendicular live loading of 300 lbs/sq.ft.

(3)

Escape provisions. Escape provisions means the permanent installation of ladders, steps, rungs, or other features that provide easily accessible means of egress from stormwater management basins. Stormwater management basins shall include escape provisions as follows:

(a)

If a stormwater management basin has an outlet structure, escape provisions shall be incorporated in, or on, the structure. A freestanding outlet structure may be exempted from this requirement with the approval of the Board Engineer.

(b)

Safety ledges shall be constructed on the slopes of all new stormwater management basins having a permanent pool of water deeper than 2 1/2 feet. Such safety ledges shall be comprised of two steps. Each step shall be four to six feet in width. One step shall be located approximately 2 1/2 feet below the permanent water surface, and the second step shall be located one to 1 1/2 feet above the permanent water surface. See Section 7.E[2] for an illustration of safety ledges in a stormwater management basin.

[2]

Editor's Note: So in original.

(c)

In new stormwater management basins, the maximum interior slope for an earthen dam, embankment, or berm shall not be steeper than three horizontal to one vertical.

(d)

Design waiver from safety standards. A variance or exemption from the safety standards for stormwater management basins may be granted only upon a written finding by the Board Engineer that the variance or exemption will not constitute a threat to public safety. This finding shall be included in any resolution of approval.

Stormwater management measure maintenance and repair. All land development shall incorporate a maintenance plan for the stormwater management measures that are to be incorporated into the site design. Maintenance guidelines for stormwater management measures are available in the New Jersey Stormwater Best Management Practices Manual. The design engineer shall submit a maintenance plan for the stormwater management measures for review and approval by the Board Engineer that adheres to the following requirements:

(1)

The maintenance plan shall contain specific preventative maintenance tasks and schedules; cost estimates, including estimated cost of sediment, debris, or trash removal.

(2)

The maintenance plan shall identify the name, address, and telephone number of the person or persons responsible for preventative and corrective maintenance and equipment replacement, referred to herein as the "stormwater system operator."

(3)

If the maintenance plan identifies a stormwater system operator other than the developer (for example, a public agency or homeowners' association), the plan shall include documentation of such person's agreement to assume this responsibility, or of the developer's obligation to dedicate a stormwater management facility to such stormwater system operator under an applicable ordinance or regulation.

(4)

Maintenance responsibility shall not be assigned or transferred to the owner or tenant of an individual property in a residential development or project, unless such owner or tenant owns or leases the entire residential development or project.

(5)

If the stormwater system operator is not a public agency, the maintenance plan and any future revisions shall be recorded upon the deed of record for each property on which the maintenance described in the maintenance plan must be undertaken.

(6)

Preventative and corrective maintenance shall be performed to maintain the function of the stormwater management measure, including repairs or replacement to the structure; removal of sediment, debris, or trash; restoration of eroded areas; snow and ice removal; fence repair or replacement; restoration of vegetation; and repair or replacement of nonvegetated linings.

(7)

The stormwater system operator shall maintain a detailed log of all preventative and corrective maintenance for the structural stormwater management measures incorporated into the design of the development, including a record of all inspections and copies of all maintenance-related work orders. The maintenance plan and the required documentation shall be made available, upon request, by any public entity with administrative, health, environmental, or safety authority over the site.

(8)

The stormwater system operator shall evaluate the effectiveness of the maintenance plan at least once per year and adjust the plan and the deed as needed.

(9)

In the event that the stormwater management facility becomes a danger to public safety or public health, or if it is in need of maintenance, the municipality shall so notify the stormwater system operator, in writing. Upon receipt of that notice, the stormwater system operator shall have 14 days to effect maintenance and repair of the facility in a manner that is approved by the Township Engineer. If the responsible person fails or refuses to perform such maintenance and repair, the Township may immediately proceed to do so and shall bill the cost thereof to the stormwater system operator.

(10)

The Planning Board shall require the posting of a performance and maintenance bond for all drainage and stormwater management improvements. The Township shall have the option of calling the bond to ensure that any necessary repairs are undertaken during the term of the maintenance bond.