Township Council Meeting — Packet

i. Demonstrate through hydrologic and hydraulic analysis that for stormwater leaving the site, post-construction runoff hydrographs for the current and projected 2-, 10-, and 100-year storm events, as defined and determined in § 25-29.5c and 5d respectively, of this ordinance, do not exceed, at any point in time, the pre-construction runoff hydrographs for the same storm events; ii. Demonstrate through hydrologic and hydraulic analysis that there is no increase, as compared to the pre-construction condition, in the peak runoff rates of stormwater leaving the site for the current and projected 2-, 10-, and 100-year storm events, as defined and determined pursuant to § 25-29.5c and 5d respectively, of this ordinance, and that 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; iii. Design stormwater management measures so that the post-construction peak runoff rates for the current and projected 2-, 10-, and 100-year storm events, as defined and determined in § 25-29.5c and 5d, respectively, of this ordinance, are 50, 75 and 80 percent, 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; or iv. In tidal flood hazard areas, stormwater runoff quantity analysis in accordance with § 25-29.4S3(i), (ii), and (iii) above is required unless the design engineer demonstrates through hydrologic and hydraulic analysis that the increased volume, change in timing, or increased rate of the stormwater runoff, or any combination of the three will not result in additional flood damage below the point of discharge of the major development. No analysis is required if the stormwater is discharged directly into any ocean, bay, inlet, or the reach of any watercourse between its confluence with an ocean, bay, or inlet and downstream of the first water control structure. 3. 4. The stormwater runoff quantity standards shall be applied at the site’s boundary to each abutting lot, roadway, watercourse, or receiving storm sewer system. §

he first water control structure. 3. 4. The stormwater runoff quantity standards shall be applied at the site’s boundary to each abutting lot, roadway, watercourse, or receiving storm sewer system. § 25-29.4—. Calculation of Stormwater Runoff and Groundwater Recharge: A. Stormwater runoff shall be calculated in accordance with the following: 1. The design engineer shall calculate runoff using the following method: (a) The USDA Natural Resources Conservation Service (NRCS) methodology, including the NRCS Runoff Equation and Dimensionless Unit Hydrograph, as described in Chapters 7, 9, 10, 15 and 16 Part 630, Hydrology National Engineering Handbook, incorporated herein by reference as amended and supplemented. This methodology is additionally described in Technical Release 55 - Urban Hydrology for Small Watersheds (TR-55), dated June 1986, incorporated herein by reference as amended and supplemented. Information 25

regarding the methodology is available from the Natural Resources Conservation Service website at: https://directives.sc.egov.usda.gov/viewerFS.aspx?hid=21422 or at United States Department of Agriculture Natural Resources Conservation Service, New Jersey State Office. 2. For calculating curve numbers and groundwater recharge, there is a presumption that the pre-construction condition of a site or portion thereof is a wooded land use with good hydrologic condition. The term “curve number” applies to the NRCS methodology above at § 25-29.5A1(a). A curve number 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 has 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). To calculate runoff and groundwater recharge, the preconstruction land cover of a site or portion thereof shall be woods, unless the applicant provides sufficient evidence that another land cover (e.g., farmland) had existed for at least five years without interruption prior to development of the site. Furthermore, the pre-construction condition of the site or portion thereof shall be considered to have been in good hydrologic condition. If more than one land use existed on the site during the five years prior to initial development of the site, the land cover with the lowest runoff potential shall be used for the computations. 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

re-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 impervious area modifications as described in the NRCS Technical Release 55 – Urban Hydrology for Small Watersheds or 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 consider the effects of tailwater in the design of structural stormwater management measures. 26

B. Groundwater recharge may be calculated in accordance with the following: The New Jersey Geological Survey Report GSR-32: A Method for Evaluating Groundwater-Recharge Areas in New Jersey, incorporated herein by reference as amended and supplemented. Information regarding the methodology is available from the New Jersey Stormwater Best Management Practices Manual; at the New Jersey Geological Survey website at: https://www.nj.gov/dep/njgs/pricelst/gsreport/gsr32.pdf or at New Jersey Geological and Water Survey, 29 Arctic Parkway, PO Box 420 Mail Code 29-01, Trenton, New Jersey 08625-0420. C. The precipitation depths of the current two-, 10-, and 100-year storm events shall be determined by multiplying the values determined in accordance with items 1 and 2 below: 1. The applicant shall utilize the National Oceanographic and Atmospheric Administration (NOAA), National Weather Service’s Atlas 14 Point Precipitation Frequency Estimates: NJ, in accordance with the location(s) of the drainage area(s) of the site. This data is available at: https://hdsc.nws.noaa.gov/hdsc/pfds/pfds_map_cont.html?bkmrk=nj; and 2. The applicant shall utilize Table 5: Current Precipitation Adjustment Factors below, which sets forth the applicable multiplier for the drainage area(s) of the site, in accordance with the county or counties where the drainage area(s) of the site is located. Where the major development lies in more than one county, the precipitation values shall be adjusted according to the percentage of the drainage area in each county. Alternately, separate rainfall totals can be developed for each county using the values in the table below. NOTE: The municipality may instead wish to abbreviate this table along with the text in Item 2 above to reflect only the relevant information, depending on the location of the municipality. The current precipitation adjustment factors added to the ordinance shall be those found in N.J.A.C. 7:8-5.7(c) as Table 5-5. Table 5: Current Precipitation Adjustment Factors Current Precipitation Adjustment Factors County Atlantic 2-year Design Storm 1.01 10-year Design Storm 1.02 100-year Design Storm 1.03 Bergen 1.01 1.03 1.06 Burlington 0.99 1.01 1.04 Camden 1.03 1.04 1.05 Cape May 1.03 1.03 1.04 27

Cumberland 1.03 1.03 1.01 Essex 1.01 1.03 1.06 Gloucester 1.05 1.06 1.06 Hudson 1.03 1.05 1.09 Hunterdon 1.02 1.05 1.13 Mercer 1.01 1.02 1.04 Middlesex 1.00 1.01 1.03 Monmouth 1.00 1.01 1.02 Morris 1.01 1.03 1.06 Ocean 1.00 1.01 1.03 Passaic 1.00 1.02 1.05 Salem 1.02 1.03 1.03 Somerset 1.00 1.03 1.09 Sussex 1.03 1.04 1.07 Union 1.01 1.03 1.06 Warren 1.02 1.07 1.15 D. Table 6: Future Precipitation Change Factors provided below sets forth the change factors to be used in determining the projected two-, 10-, and 100year storm events for use in this chapter, which are organized alphabetically by county. The precipitation depth of the projected two-, 10-, and 100-year storm events of a site shall be determined by multiplying the precipitation depth of the two-, 10-, and 100-year storm events determined from the National Weather Service’s Atlas 14 Point Precipitation Frequency Estimates pursuant to (c)1 above, by the change factor in the table below, in accordance with the county or counties where the drainage area(s) of the site is located. Where the major development and/or its drainage area lies in more than one county, the precipitation values shall be adjusted according to the percentage of the drainage area in each county. Alternately, separate rainfall totals can be developed for each county using the values in the table below. NOTE: The municipality may instead wish to abbreviate this table along with the text in Item D above to reflect only the relevant information, depending on the location of the municipality. The future precipitation change factors added to the ordinance shall be those found in N.J.A.C. 7:8-5.7(d) as Table 5-6. Table 6: Future Precipitation Change Factors Future Precipitation Change Factors County Atlantic 2-year Design Storm 1.22 28 10-year Design Storm 1.24 100-year Design Storm 1.39

Bergen 1.20 1.23 1.37 Burlington 1.17 1.18 1.32 Camden 1.18 1.22 1.39 Cape May 1.21 1.24 1.32 Cumberland 1.20 1.21 1.39 Essex 1.19 1.22 1.33 Gloucester 1.19 1.23 1.41 Hudson 1.19 1.19 1.23 Hunterdon 1.19 1.23 1.42 Mercer 1.16 1.17 1.36 Middlesex 1.19 1.21 1.33 Monmouth 1.19 1.19 1.26 Morris 1.23 1.28 1.46 Ocean 1.18 1.19 1.24 Passaic 1.21 1.27 1.50 Salem 1.20 1.23 1.32 Somerset 1.19 1.24 1.48 Sussex 1.24 1.29 1.50 Union 1.20 1.23 1.35 Warren 1.20 1.25 1.37 § 25-29.6—Sources for Technical Guidance: A. Technical guidance for stormwater management measures can be found in the documents listed below, which are available to download from the Department’s website at: https://dep.nj.gov/stormwater/bmp-manual/. 1. Guidelines for stormwater management measures are contained in the New Jersey Stormwater Best Management Practices Manual, as amended and supplemented. Information is provided on stormwater management measures such as, but not limited to, those listed in Tables 1, 2, and 3. 2. Additional maintenance guidance is available on the Department’s website at: https://dep.nj.gov/stormwater/maintenance-guidance/. B. Submissions required for review by the Department should be mailed to: The Division of Watershed Protection and Restoration, New Jersey Department of Environmental Protection, Mail Code 501-02A, PO Box 420, Trenton, New Jersey 08625-0420. 29

§ 25-29.7—Solids and Floatable Materials Control Standards: A. Site design features identified under § 25-29.4G above, or alternative designs in accordance with § 25-29.4H above, to prevent discharge of trash and debris from drainage systems shall comply with the following standard to control passage of solid and floatable materials through storm drain inlets. For purposes of this paragraph, “solid and floatable materials” means sediment, debris, trash, and other floating, suspended, or settleable solids. For exemptions to this standard see § 25-29.7A2 below. 1. Design engineers shall use one of the following grates whenever they use a grate in pavement or another ground surface to collect stormwater from that surface into a storm drain or surface water body under that grate: i. The New Jersey Department of Transportation (NJDOT) bicycle safe grate, which is described in Chapter 2.4 of the NJDOT Bicycle Compatible Roadways and Bikeways Planning and Design Guidelines; or ii. A different grate, if each individual clear space in that grate has an area of no more than seven (7.0) square inches, or is no greater than 0.5 inches across the smallest dimension. Examples of grates subject to this standard include grates in grate inlets, the grate portion (non-curb-opening portion) of combination inlets, grates on storm sewer manholes, ditch grates, trench grates, and grates of spacer bars in slotted drains. Examples of ground surfaces include surfaces of roads (including bridges), driveways, parking areas, bikeways, plazas, sidewalks, lawns, fields, open channels, and stormwater system floors used to collect stormwater from the surface into a storm drain or surface water body. iii. For curb-opening inlets, including curb-opening inlets in combination inlets, the clear space in that curb opening, or each individual clear space if the curb opening has two or more clear spaces, shall have an area of no more than seven (7.0) square inches, or be no greater than two (2.0) inches across the smallest dimension. 2. The standard in A.1. above does not apply: i. Where each individual clear space in the curb opening in existing curbopening inlet does not have an area of more than nine (9.0) square inches; ii. Where the municipality agrees that the standards would cause inadequate hydraulic performance that could not practicably be overcome by using additional or larger storm

n nine (9.0) square inches; ii. Where the municipality agrees that the standards would cause inadequate hydraulic performance that could not practicably be overcome by using additional or larger storm drain inlets; iii. Where flows from the water quality design storm as specified in N.J.A.C. 7:8 are conveyed through any device (e.g., end of pipe netting facility, 30

manufactured treatment device, or a catch basin hood) that is designed, at a minimum, to prevent delivery of all solid and floatable materials that could not pass through one of the following: a. A rectangular space four and five-eighths (4.625) inches long and one and one-half (1.5) inches wide (this option does not apply for outfall netting facilities); or b. A bar screen having a bar spacing of 0.5 inches. Note that these exemptions do not authorize any infringement of requirements in the Residential Site Improvement Standards for bicycle safe grates in new residential development (N.J.A.C. 5:21-4.18(b)2 and 7.4(b)1). iv. Where flows are conveyed through a trash rack that has parallel bars with one inch (1 inch) spacing between the bars, to the elevation of the Water Quality Design Storm as specified in N.J.A.C. 7:8; or v. Where the New Jersey Department of Environmental Protection determines, pursuant to the New Jersey Register of Historic Places Rules at N.J.A.C. 7:47.2(c), that action to meet this standard is an undertaking that constitutes an encroachment or will damage or destroy the New Jersey Register listed historic property. § 25-29.8—Safety Standards for Stormwater Management Basins: A. This section sets forth requirements to protect public safety through the proper design and operation of stormwater management BMPs. This section applies to any new stormwater management BMP. B. The provisions of this section are not intended to preempt more stringent municipal or county safety requirements for new or existing stormwater management BMPs. Municipal and county stormwater management plans and ordinances may, pursuant to their authority, require existing stormwater management BMPs to be retrofitted to meet one or more of the safety standards in § 25-29.8C1, C2, and C3 for trash racks, overflow grates, and escape provisions at outlet structures. C. Requirements for Trash Racks, Overflow Grates and Escape Provisions 1. 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 from the Stormwater management BMP to ensure proper functioning of the BMP outlets in accordance with the following: i. The trash rack shall have parallel bars, with no greater than six-inch spacing between the bars; ii. The trash rack shall be designed so as not to