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

III. PROPOSED SITE CONDITIONS The proposed improvements consist of the renovation of the existing office building, modifications to the existing parking lot to satisfy current ADA regulations, the expansion of the rear parking area, and other associated site improvements. The proposed site improvements shall result in an increase in impervious coverage of 20,635 SF (0.47 Ac). The existing drainage patterns on-site shall remain relatively unchanged. Stormwater runoff generated by the roof of the renovated building will remain relatively unchanged. Runoff generated by the portions of the site that are not covered with building shall continue to sheet flow west and be collected by various on-site inlets. An aboveground bioretention basin has been designed to detain stormwater runoff generated by the proposed parking lot, parking lot expansion and surrounding wooded areas in accordance with stormwater reduction requirements set forth under NJAC 7:8 and by the Township of West Orange. The proposed site conditions have been evaluated using the following drainage sub-watershed areas as depicted on the Proposed Drainage Area Maps included within the Appendix of this report: DA-1: This area consists of the wooded area to the northeast of the parking lot expansion. Stormwater runoff generated by this area sheet flows overland where it is ultimately collected by a proposed yard inlet, and conveyed to the proposed aboveground stormwater management basin, where it is detained and released at a controlled rate to the existing stormwater management structure (POI-2). A time of concentration of 18.8 minutes has been calculated and utilized for this drainage area. DA-2 Undetained: This area consists of a portion of the existing rear northern parking area. Stormwater runoff generated by this area sheet flows overland to the west and is collected by a proposed inlet, where is it ultimately conveyed to the existing stormwater management structure (POI-2). A minimum time of concentration of six (6) minutes has been utilized for this drainage area. DA-2A Detained: This area consists of a majority of the rear parking lot expansion area and a portion of the rear wooded area. Stormwater runoff generated by this area sheet flows overland to the west and is collected by proposed inlets and conveyed to the proposed aboveground stormwater management basin.

he rear wooded area. Stormwater runoff generated by this area sheet flows overland to the west and is collected by proposed inlets and conveyed to the proposed aboveground stormwater management basin. Stormwater runoff is then detained and released at a controlled rate to the existing stormwater management structure (POI- 2). A time of concentration of 14.7 minutes has been calculated and utilized for this drainage area. DA-2B Detained: This area consists of a portion of the rear remaining parking lot expansion area, the aboveground stormwater management basin and portion of the rear wooded areas. Stormwater runoff generated by this area sheet flows overland to the west and is collected by a proposed inlet and conveyed to the Altera 769, LLC 5 Revised August 2022 DECPC #2530-99-006

proposed aboveground stormwater management basin. Stormwater runoff is then detained and released at a controlled rate to the existing stormwater management structure (POI-2). A time of concentration of 13.3 minutes has been calculated and utilized for this drainage area. DA-3: This area consists of the remainder of the subject site which includes the existing office building, remaining parking areas and open space (lawn) areas. Stormwater runoff generated by this area sheet flows overland in a southerly direction where it is collected by a series of existing inlets. Ultimately, stormwater runoff is conveyed to the existing stormwater conveyance system within Northfield Avenue (CR 508) (POI-3). A minimum time of concentration of six (6) minutes has been utilized for this drainage area. IV. DESIGN METHODOLOGY The intention of the design of the proposed stormwater management facilities is to provide measures as required to address applicable aspects of the Township of West Orange Land Use Ordinance, NJAC 7:8, and the New Jersey SESC standards. In order to prepare the stormwater management design for the subject project, an extensive initial investigation of the property and a topographic survey were performed. On-site review of the tract was performed by Dynamic Engineering Consultants, PC to verify existing site conditions and land cover characteristics. A Boundary, Location & Topographic Survey of the subject site was also prepared by Dynamic Survey, LLC, to depict the existing site conditions. The calculations were established through an examination of the existing site conditions, a review of the topographical survey, and establishing our drainage area maps. The plans were designed to ensure that runoff from the proposed development could be directed to the proposed stormwater management facilities, and designed to meet applicable stormwater quantity and quality requirements set forth by the Township of West Orange and NJAC 7:8. Based on our review of the existing site conditions, review of the survey, and establishment of the Drainage Area Maps for the existing and proposed site conditions, the calculations of this Report were established. A grading plan was also developed for the proposed site improvements with consideration to the existing drainage patterns. The plan was designed to ensure that runoff from the proposed development could

grading plan was also developed for the proposed site improvements with consideration to the existing drainage patterns. The plan was designed to ensure that runoff from the proposed development could be directed to the proposed stormwater management facilities and reduce peak flow rates when compared to existing conditions. The site has been evaluated using the TR-55 ‘Urban Hydrology for Small Watersheds’ standards. Stormwater runoff rates for the subject site were modeled using Hydrology Studio. The 2-, 10-, and 100-year design storms are based upon the New Jersey 24-Hour Rainfall Frequency Data for Essex County as published by the USDA NRCS utilizing a Type D rainfall distribution. Pervious and impervious areas were modeled separately as per the NJ Stormwater Management Best Practices (BMP) Manual. Altera 769, LLC 6 Revised August 2022 DECPC #2530-99-006

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

• The proposed underdrain component consists of three parts – the sand layer, the gravel layer and the network of pipes that collect runoff and transport it to the outflow section of the system. • The capacity of the proposed underdrain is designed to allow the system to drain within 72 hours. • The system has been designed so the seasonal high-water table (SHWT) or bedrock is at least 1 foot below the bottom of the underdrain component. • At least one inspection port, with a removable cap, is proposed in the storage bed at least 3 feet from any edge. • Points of access are designed in such a way as to prevent sediment or other material from entering the system and to prevent the accumulation of standing water, which could lead to mosquito breeding. VI. RUNOFF RATES The following is a comparison of pre and post development runoff rates: PEAK RUNOFF RATES (POI-2) Design Storm Reduction Allowable Existing Runoff Proposed Runoff Difference Required Runoff 2-yr 4.04 CFS 50% 2.02 CFS 1.83 CFS -2.21 CFS 10-yr 7.19 CFS 75% 5.39 CFS 4.09 CFS -3.10 CFS 100-yr 13.54 CFS 80% 10.83 CFS 9.26 CFS -4.28 CFS PEAK RUNOFF RATES (POI-3) Design Storm Existing Runoff Proposed Runoff Difference 2-yr 9.02 CFS 7.40 CFS -1.62 CFS 10-yr 14.76 CFS 12.83 CFS -1.93 CFS 100-yr 26.22 CFS 22.52 CFS -3.70 CFS As can be seen above, the stormwater management system has been designed to not exceed the existing tributary runoff rates for the given design storms. VII. WATER QUALITY The TSS removal rate

As can be seen above, the stormwater management system has been designed to not exceed the existing tributary runoff rates for the given design storms. VII. WATER QUALITY The TSS removal rate requirement set for the Township of West Orange Land Use Ordinance and NJAC 7:8 is 80% for the net increase of motor vehicle surface. Under the proposed conditions, the runoff from the proposed rear parking lot expansion within drainage areas DA-1, DA-2A, and DA-2B will be collected via a Altera 769, LLC 8 Revised August 2022 DECPC #2530-99-006

series of proposed inlets and conveyed to the proposed aboveground bioretention basin. The bioretention basin has been designed with an 18” soil bed and mainly site tolerant vegetation; therefore providing 80% TSS removal rate in accordance with the NJDEP BMP Guidelines for the tributary areas. VIII. GROUNDWATER RECHARGE According to the Stormwater Basin Area Investigation Report, prepared by Dynamic Earth, LLC, dated January 14, 2022, enclosed within the Appendix of this report, the on-site soils do not exhibit permeability to allow for proper infiltration. Therefore, this project is exempt from the Groundwater Recharge requirements of the Township of West Orange and NJAC 7:8. IX. CONCLUSION The proposed project has been designed in a manner that will not adversely impact the existing drainage patterns, adjacent roadways or adjacent parcels. Stormwater runoff rates for the 2, 10, and 100-year design storms will comply with the runoff rate requirements of Township of West Orange and NJAC 7:8. Additionally, stormwater runoff rates to the points of interests shall be reduced compared to existing conditions. Furthermore, the proposed bioretention basin has been designed in accordance with the NJ BMP Manual requirements thereby providing the required 80% TSS removal rate for the net increase in vehicular surface study area. With that stated, it is evident that the proposed development will not have a negative impact on the existing stormwater management system within the vicinity of the subject parcel. Altera 769, LLC 9 Revised August 2022 DECPC #2530-99-006

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