N.J. Admin. Code § 7:45-8.7
Current through Register Vol. 56, No. 24, December 18, 2024
Section 7:45-8.7 - Specific water quality standards(a) Stormwater management measures shall be designed to reduce the post-construction load of total suspended solids (TSS) in stormwater runoff generated from the water quality design storm by 80 percent of the anticipated load from the developed site, expressed as an annual average. The water quality design storm is 1.25 inches of rainfall in two hours. Water quality calculations shall take into account the distribution of rain from the water quality design storm, as reflected in Table 1 below. The calculation of the volume of runoff may take into account the implementation of non-structural and structural stormwater management measures. Table 1
Water Quality Design Storm Distribution
| Time | Cumulative | Time | Cumulative |
|---|
| (Minutes) | Rainfall (Inches) | (Minutes) | Rainfall (Inches) |
|---|
| 0 | 0.0000 | 65 | 0.8917 |
| 5 | 0.0083 | 70 | 0.9917 |
| 10 | 0.0166 | 75 | 1.0500 |
| 15 | 0.0250 | 80 | 1.0840 |
| 20 | 0.0500 | 85 | 1.1170 |
| 25 | 0.0750 | 90 | 1.1500 |
| 30 | 0.1000 | 95 | 1.1750 |
| 35 | 0.1330 | 100 | 1.2000 |
| 40 | 0.1660 | 105 | 1.2250 |
| 45 | 0.2000 | 110 | 1.2334 |
| 50 | 0.2583 | 115 | 1.2417 |
| 55 | 0.3583 | 120 | 1.2500 |
| 60 | 0.6250 |
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 Pollutant Discharge Elimination System (NJPDES) rules, N.J.A.C. 7:14A, or in a discharge specifically exempt under a NJPDES permit from this requirement.
(b) For purposes of TSS reduction calculations, Table 2 below is the presumed removal rates for certain BMPs designed in accordance with the New Jersey Stormwater Best Management Practices Manual. The BMP manual may be obtained from the Commission's website at http://www.nj.gov/dep/drcc/. TSS reduction shall be calculated based on the removal rates for the BMPs in Table 2 below. 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 Commission.(c) If more than one BMP in series is necessary to achieve the required 80 percent 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
Table 2
TSS Removal Rates for BMPs
| Best Management Practice TSS Percent Removal Rate |
| Bioretention Systems | 90 |
| Constructed Stormwater Wetland | 90 |
| Extended Detention Basin | 40-60 |
| Infiltration Structure | 80 |
| Manufactured Treatment Devices | 50-80 |
| See certification by NJCATS on njstormwater.org |
| Sand Filter | 80 |
| Vegetative Filter Strip | 60-80 |
| Wet Pond | 50-90 |
(d) If there is more than one onsite drainage area, the 80 percent 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.(e) Additional information and examples are contained in the New Jersey Stormwater Best Management Practices Manual.N.J. Admin. Code § 7:45-8.7
Amended by 55 N.J.R. 746(a), effective 4/17/2023