PB 22 10 Altera 769 LLC Filed Application with Exhibits Final Site Plan Phase 2

V. ABOVEGROUND STORMWATER MANAGEMENT BASIN DESIGN The proposed stormwater management basin has been designed to meet the applicable standards set forth by the Township of West Orange, NJAC 7:8, and NJ SESC through the use of an aboveground stormwater bioretention basin. Specifically, the basin has been designed to accommodate the 100-yr design storm while providing the requisite stormwater quantity reductions without negatively impacting downstream conditions. Associated calculations are included within the Appendix of this report and details have been provided on the accompanying engineering drawings. The proposed basin has been designed as a Small-Scale Bioretention Basin with an underdrain which will provide treatment of runoff generated by the Water Quality Design Storm. The design of the bioretention basin complies with the standards set forth by the NJ Best Management Practices Manual, thereby providing a TSS Removal Rate of 80%, thereby satisfying the water quality aspect of NJAC 7:8. The area above the Bioretention Basin will be used to utilized to store and attenuate runoff generated by the larger storm events and provide water quantity control for same. The bottom of the gravel storage bed for the proposed basin is at elevation 459.50 ft. As noted in the Stormwater Basin Area Investigation Report provided within the Appendix of this report, two (2) test pits were dug in the vicinity of the proposed bioretention basin location. The pits were excavated to depths at elevation 458.00 where the test was terminated at bedrock and no seasonal high-water table was observed. Therefore, the proposed basin has been designed such that the underdrain system is set a minimum of one (1’) foot above the seasonal high-water table or bedrock. As noted in the hydrograph summary included within the appendix, the volume of the runoff generated by the water quality design storm that is tributary to the bioretention basin is equal to approximately 4,996 CF. This equates to an elevation of 461.99 within the basin. The lowest quantity control orifice in the outlet control structure is proposed at elevation 462.00 in order to allow the entirety of the Water Quality Design Storm to infiltrate through the proposed soil bed and sand layer before being collected by the proposed underdrain system. Runoff generated by larger design storms will be discharged through an

Design Storm to infiltrate through the proposed soil bed and sand layer before being collected by the proposed underdrain system. Runoff generated by larger design storms will be discharged through an outlet control structure and ultimately conveyed to the existing underground stormwater management basin (POI-2). In accordance with the New Jersey Stormwater Best Management Practices Manual, the following design considerations have been satisfied: • Filter fabric is proposed along the sides and the bottom of the system to prevent migration of fines from the surrounding soil. Altera 769, LLC 7 Revised August 2022 DECPC #2530-99-006