2025 12 08_West Orange SMP Memorandum

Stormwater Management Plan Memorandum 2.4 Revision A Hydrology and Hydraulics Results The post-developed watersheds PO-DA A and PO-DA I, which discharge into the existing onsite stormwater pipe network that drains to the AquaShield, will be a reduction in size from the pre-developed watersheds PO-DA 6 and PO-DA 8, thus providing no adverse impact to the original AquaShield design or outfall. As summarized in Section 2.3, an underground detention basin will be utilized to address the water quantity for the peak discharge for the newly developed areas associated with the switching station expansion, specifically post-developed watersheds PO-DA C, PO-DA D, PO-DA E, PO-DA F, and PODA H. The peak post-developed runoff rates do not exceed the peak pre-developed runoff rates for 50% of the 2-year, 75% of the 10-year, and 80% of the 100-year storm events. Runoff from the noncontributory post-developed watershed PO-DA J drains to the same outfall, O-2, as pre-developed watershed PO-DA 1 and should result in minimal change of the peak flowrates. Table 2.5 below summarizes the stormwater flow conditions for the project. Table 2.5: Site Flow Results Pre Q(2-YR) Current (cfs) 4.09 3.60<4.09 OK 2.09 Q(2-YR) Future (cfs) 5.27 4.62<5.27 OK 2.84 Q(10-YR) Current (cfs) 7.37 6.46<7.37 OK 4.20 Q(10-YR) Future (cfs) 9.33 8.15<9.33 OK 5.49 Q(100-YR) Current (cfs) 14.11 12.29<14.11 OK 8.61 Q(100-YR) Future (cfs) 18.67 16.20<18.67 OK 11.65 Post 2.09 2.84 4.20 5.49 8.61 11.65 Outfall Discharge Point O-AquaShield (PO-DA 6 / A, DA 8 / I) O-1A (PO-DA B, PODA G) O-1Bb (Detention Basin Areas (PO-DA 7 / C, D, E, F, H)) Pre Post 2.66*50% = 3.49*50% = 5.20*75% = 6.61*75% = 10.52*80% = 13.89*80% = 1.33 1.75 3.90 4.96 8.42 11.11 0.64<1.33 1.48<1.75 3.66<3.90 4.92<4.96 7.15<8.42 8.71<11.11 Post OK OK OK OK OK OK Pre 2.45 3.19 4.81 6.07 9.80 12.86 O-2 2.36<2.45 3.10<3.19 4.48<4.81 5.72<6.07 8.86<9.80 11.77<12.86 (PO-DA 1 / J) Post OK OK OK OK OK OK b N.J.A.C. 7:8-5.6 requires post-construction peak runoff rates for the 2-, 10-, and 100-year storm events to be 50%, 75%, and 80%, respectively, of the pre-construction peak runoff rates. Pre Public Service Electric & Gas Company TOC-2-3 Burns & McDonnell