J_2024 05 09_West Orange Stormwater Management Plan

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report be operated on an inspect and release basis and will not be discharged during major storm events, the net change in impervious surface area coverage will be a decrease of 15,833 square feet or approximately 0.36 acres. [4] Minimize the decrease in the time of concentration from preconstruction to post construction. By maintaining relatively flat slopes across the yard stone surface coupled with placement of a 4-inch layer of 3/4-inch crushed stone, reductions in the time of concentration have been minimized. [5] Minimize land disturbance including clearing and grading. The area encompassed by the limit of disturbance will total approximately 10.3 acres. This includes a laydown area, which will also fall within the boundaries of the existing switching station. However, due to the proposed expansion of the switching station, grading will be required. Soil erosion controls will be implemented and retaining walls will be constructed to control soil erosion. [6] Minimize soil compaction. Soil compaction will be required for the installation of new foundations, which require structural support, and for construction of the expansion area. Areas targeted for revegetation will be scarified prior to revegetation. [7] Provide low maintenance landscaping that encourages retention and planting of native vegetation and minimizes the use of lawns, fertilizers, and pesticides. The project will not result in the creation of new landscaped areas. Existing landscaped areas falling outside the limits of the switching station expansion area will be returned to predevelopment conditions. As such, the need for fertilizers and pesticides has also been minimized. [8] Provide vegetated open channel conveyance systems discharging into and through stable vegetated areas. A series of bioretention basins and natural drainage swales will be constructed west of the switching station pad expansion area to maintain stable vegetated areas. [9] Provide other source controls to prevent or minimize the use or exposure of pollutants at the site. Secondary containment will be provided for the new 230 kV transformers. Discharge from the containment sumps will be on an inspect and release basis. If transformer oil is suspected to be present in the sumps for any reason, the liquid contents of the sumps will be

rmers. Discharge from the containment sumps will be on an inspect and release basis. If transformer oil is suspected to be present in the sumps for any reason, the liquid contents of the sumps will be transported for off-site disposal at an appropriately licensed treatment facility. TRC Engineers, Inc. 9 March 2012

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report 2. Analysis of Pre-Development Stormwater Runoff This section presents hydrologic data and information to demonstrate that peak stormwater runoff flows under post development conditions will not exceed those under pre-development conditions during the 2-year, 10-year, and 100-year, 24-hour rainfall events. The analysis was performed using the methodology described in Technical Release No. 55, Urban Hydrology for Small Watersheds, published by the United States Department of Agriculture, Soil Conservation Service, dated June 1986. Hydrologic modeling was performed using HydroCad stormwater software developed by HydroCAD Software Solutions LLC. Pre-development runoff rates were determined by subdividing the drainage area into nine smaller drainage areas by land use. Existing land uses are listed in Table III-1. The PreDevelopment Drainage Area Plan is included in Appendix B. Table III-l Pre Development Drainage Areas1,2,3 LAND USE Impervious (Foundations) Gravel Road Gravel Yard Stone Meadow Grass Brush NonContributory Total EXDA 1 (ft2) EXDA2 (ft2) EXDA3 (ft2) EXDA4 (ft2) EXDAS (ft2) EXDA6 (ft2) EXDA? (ft2) EXDAS (ft2) EXDA 9A (ft2) EXDA 9B (ft2) 11158 4190 3042 31370 17517 9501 805 15912 1344 24703 661 0 0 0 53293 14189 0 0 0 0 10038 3705 35019 29686 0 26372 30906 0 5072 12803 8134 0 21568 0 0 0 0 0 2694 0 8481 0 43082 0 57041 27592 2198 0 10157 0 86177 5402 0 0 29261 0 1535 0 0 0 20580 0 0 0 0 670 20336 0 0 0 0 0 1964 0 982 0 0 79301 17933 125025 78947 20211 147661 104739 47690 21924 45709 1) 2) 3) 0 0 0 See Appendix B - Pre-Development Drainage Area Plan The total area within the Limit of Disturbance is 10.3 acres or 448,819 ft2. The total area within the Drainage Area is 15.8 acres or 686,140 ft2. The existing transformer secondary containment basin was assumed to be non-contributory under pre-development conditions. Rainfall totals for each event were obtained from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 for West Orange, NJ and are summarized in Table III- 2. TRC Engineers, Inc. 10 March 2012

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report Table III-2 Precipitation Frequency Estimates with 90% Confidence Intervals (inches)1 Duration 24-hours 1) 2 year 3.42 inches Average Recurrence Interval Vears) 10 year 100 year 5.21 inches 8.72 inches NOAA Atlas 14, Volume 2, Version 3, West Orange, NJ For each drainage area, time of concentration (Tc) was determined using the hydraulically longest flow path. The flow path for the drainage area was extended to “Analysis Point A,” where drainage from the site reaches an existing catch basin, which then carries flow to an unnamed tributary of the Rahway River. The Tc flow paths are identified on the PreDevelopment Drainage Area Plan. Curve numbers (CNs) were generated based on hydrologic soil group and land use cover type. The yard stone surface of the switching station pad, which will consist of a 4-inch thick layer of loosely packed 3/4-inch crushed stone, was assigned a CN value of 85 to reflect available storage capacity within the yard stone prior to the initiation of surface runo ff. HydroCad output for pre-development conditions for the 2-year, 10-year, and 100-year, 24hour storm events is included in Appendix C. Pre-development runoff rates and volumes are summarized in Table III-3. Table III-3 Pre-Development Runoff Rates and Volumes at Analysis Point A Storm Event 100-year, 24-hour Runoff Volume (acre-ft) 2.684 4.777 9.133 Peak Runoff Rate (cfs) 23.25 41.95 79.82 NJDEP 0.541 10.16 2-year, 24-hour 10-year, 24-hour 3. Analysis of Post-Development Stormwater Runoff Post-development runoff rates were determined by subdividing the drainage area into nine smaller drainage areas by land use. The Post-Development Drainage Area Plan is included in Appendix D. The new secondary containment areas for the transformers were determined to be a non­ contributory area during a storm event, since they will be operated on and inspect and release basis. As such, it was excluded from the post development runoff calculations. Thus, the total drainage area under post-development conditions is 689,600 square feet. Proposed land use within the drainage area is summarized in Table III-4. TRC Engineers, Inc. II March 2012

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report Table III-4 *ost Development Drainage Areas LAND USE Impervious (Foundations) Gravel Road Gravel Yard Stone Meadow Grass Brush Non­ contributory Total LAND USE PODA1A (ft2) PODA1B (ft2) PODA1C (ft2) PODA 2 (ft2) PO-DA 3A (ft2) PO-DA 3B (ft2) 11168 2107 1769 4402 0 0 5785 0 0 0 8088 38971 0 0 0 0 10364 0 0 0 0 0 6795 0 0 0 0 0 5534 0 0 0 0 0 19890 9261 0 10141 0 0 10571 0 0 1111 0 0 3792 0 0 0 0 0 0 0 0 0 58227 12471 8564 9936 29151 20712 10688 PO-DA 4 (ft2) PO-DA 5A (ft2) PO-DA 5B (ft2) PO-DA 6 (ft2) PODA 7 (ft2) PODA 8 (ft2) 4334 15734 16509 13009 1868 10980 5398 0 0 15808 14366 0 0 39906 0 0 0 7713 8318 0 2364 34129 0 6800 0 0 2441 0 0 25750 0 0 47083 853 39774 22963 4135 127817 0 0 14410 0 72265 5406 0 93949 0 0 5243 0 0 0 3173 19396 9 Impervious (Foundations) Gravel Road Gravel Yard Stone Meadow Grass Brush Non-contributory Total PODA1 (ft2) PODA 9B (ft2) PODA 9C (ft2) PODA 9D (ft2) 650 5504 1117 1192 1367 0 46220 0 0 0 0 48237 6361 0 30963 0 0 0 0 42828 18457 0 33086 16177 0 37810 0 0 0 0 55179 Impervious (Foundations) Gravel Road Gravel Yard Stone Meadow Grass Brush Non-contributory Total TRC Engineers, Inc. > LAND USE 12 0 0 0 0 52660 March 2012

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report As in the pre-development analysis, the time of concentration (Tc) was determined using the hydraulically longest flow path. The Tc flow paths within the area of disturbance are identified on the Post Development Drainage Area Plan located in Appendix D. Tc flow paths under post-development conditions were also extended to ‘‘Analysis Point A.” HydroCad output under Post-Development conditions for the 2-year, 10-year, and 100-year, 24 hour storm events is included in Appendix E and summarized in Table III-5. Table III-5 Post-Development Runoff Rates and Volumes at Analysis Point A Storm Event Runoff Volume (acre-ft) Peak Runoff Rate (cfs) 2-year, 24-hour 10-year, 24-hour 100-year, 24-hour 2.379 4.371 8.685 21.97 39.70 75.50 NJDEP 0.460 9.30 Table III-6 provides a comparison between pre-development and post-development runoff conditions for each design storm. As shown in Table III-6, projected peak runoff rates and volumes under post development conditions are expected to be less than under pre-development conditions for each storm event. Table III-6 Pre and Post Development Total Runoff Volumes and Peak Rates Storm Event 2-year, 24-hour 10-year, 24-hour 100-year, 24-hour NJDEP Pre - Tota Discharge Volume Peak Runoff [acre-ft] [cfs] 2.684 23.25 41.95 4.777 9.133 79.82 0.541 10.16 Post - Total Discharge Volume Peak Runoff [acre-ft] [cfs] 21.97 2.379 39.70 4.371 8.685 75.50 0.460 9.30 Figure 4 shows the pre and post-development hydrographs for the 2-year, 24-hour, 10year, 24-hour, and 100-year, 24-hour storms at Analysis Point A. The graphs show that runoff flows under post-development conditions do not exceed at any point in time those under pre-development conditions. Table III-6 shows that the 2-year, 24 hour peak runoff for the post development is less than predevelopment. Therefore, at a minimum, 100 percent of the average annual pre­ construction groundwater recharge for the site has been maintained. TRC Engineers, Inc. 13 March 2012

PSE&G West Orange Switching Station West Orange, NJ Stormwater Management Report Figure 4 - Hydrograph Overlays TRC Engineers, Inc. 14 March 2012

10 uu> 15 20 25 - Pre-Development »Post-Development Time (hrs) <H *-l r-l <H <-l <-l <-l <-l M IN (N IN (N (N IN (N IN IN IN IN o h ri n m >t ui ui r ^ r ^ o o o i o * - i » - i < N * H m ' y L n u ' > « - < i ' ' r ~ o o C T > t - i o > - i « - < r M < N m « a - L n L n c M r ^ r ~ o o a > < N O V O r M O O < 3 - m O r M O O ' T l O « 5 r1M 3 -UCI T VU O lfrM tO'trMVDrMOO«a-U1VOfMOO»Te01£>fMOO"3-»-llDrMOO / IO NO O'O J tl O tM J _________________________________________ 1 21.97 i 23.25 Figure 4 - West Orange Switching Station Pre- and Post-Development Flydrographs for the 2-Year, 24-Hour Storm Event

25.0 0.0 5.0 10.0 15.0 .£ 20.0 Qi 30.0 35.0 40.0 45.0 OHH ro ^ cn in ui vip om r O)M 0cn^ 0 vo(7) VO oo(N O) id If) VO fN 0 0 * T 0 0 V D C N 0 0 * T r - l V O f N 0 0 * T « 3 ' V D C N 0 0 « T r ^ oo <3; co oi 0^-iT-irMrMro'^LniDrNir^r>'000^<N CN IN CN CN CM CM CN CM CN CN M fN * Post-Development Time (hrs) h ro ^ m io ri CM VO 04 00 rri « «"! • Pre-Development • l/) (N 00 ip vo vo CM ^ (p VD (N 00 ^ CN O ) i f ) IN cri K oo oi 6 T-i T-l (N | i 39.70 1 41.95 Figure 4 - West Orange Switching Station Pre- and Post-Development Hydrographs for the 10-Year, 24-Hour Storm Event

o o 10 20 30 40 50 60 70 80 90 t h ■Pre-Development h H in cm ini ■ Post-Development MlDMOO'TrllDrlOO^'TlDrjCOTh O OO 'TL DIN V ^V l DNV O OO ^O ' T °P H 0° » T H 4Oi0O IoVO TTIN )^ V i oOr nl N o )O^ O ^ 0^ )TvrqOf V NO OC ) ^Nf sOoO) L OO i NV^Oi nr N fN o! 0m o^ IN iC m in fNm^LnLniNr^r^ooc7)iN O r - i r - i < N en ^ in in K K o o o i O « IN K K co oi « - i o »r s-riM«rHM ii N N fM nj tN <N <N Time (hrs) 75.50 79.82 Figure 4 - West Orange Switching Station Pre- and Post-Development Hydrographs for the 100-Year, 24-Hour Storm Event