Revised Stormwater Management Report

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Stormwater Management Report ( formerly Drainage Report) West Essex Highlands Block 179, Lot 32 West Orange NJ March 12, 2023 Rev 1 April 27, 2023 Rev Sept 7, 2023 Rev Oct 3, 2023 Rev October 24, 2023 Rev 10-30-23 Rev 6-24-24 ER EE L IN PR O No. 33410 R S STA PAU T L W Y SE O N F NEW JE E O . AND R FE S S I C E N S ED G IO N AL E N __________________________ Paul W. Anderson PE PP CME NJ PE Lic. No. 33410

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Table of Contents Location Map………………………………………………………………….…………...1 Introduction………………………………….……………………………………………..2 Methodology……………………….…………………………………….………………...2 Discussion……………………………………………………………………………….…2 Point of Analysis 1 Existing Conditions Basin 1 Basin 5 Basin 6 PA-1 Summary Table Point of Analysis 2 Existing Conditions Basin 2 Basin 3 Basin 4 Basin 7 Basin 8 Basin 9 Basin 10 Basin 11 PA-2 Summary Table Point of Analysis 3 Existing Proposed Conclusion

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Appendix Drainage area maps Hydrocad Output PA-1 Existing Conditions Basin 1 Basin 5 Basin 6 Hydrocad output PA-2 Existing Conditions Basin 2 Basin 3 Basin 4 Basin 7 Basin 8 Basin 9 Basin 10 Basin 11 Groundwater Mounding Analysis Recharge Spreadsheet Theissens Polygon soil type analysis Pipe sizing calculations Riprap sizing calculations

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Location Map 1

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Introduction The West Essex Highlands property has been designated as the location for multifamily housing as part of a court approved settlement agreement which is part of the affordable housing requirements for the Township of West Orange. Part of the Settlement Agreement provides that disturbance on the 120-acre parcel is limited to 30 acres leaving the remainder as open space to be utilized as passive recreation in its natural condition. The initial submittal to NJDEP relied heavily on three stormwater basins in the southern area of the property where deeper soil and seasonal high ground water prevailed. Reviews of this submission and subsequent modifications to it found that the NJDEP preferred a design that managed stormwater more broadly over the entire site. Several video conferences were held with NJDEP to review in more detail the existing site soil conditions, the overall soil testing that had been performed to date and to develop a conceptual plan for the re-design of the stormwater management system with stormwater managed neared to it source. The concept plan required new soil testing within the approved soil testing window to establish the seasonal high-water table at each proposed stormwater system. The testing resulted in areas with high water tables, shallow bedrock and poor soil permeability in many of the tested areas. As a result, the site grading design was raised to achieve a greater distance to groundwater and bedrock and soil replacement was used to address permeability issues. A video conference was held with NJDEP to review the new concept and the consensus was to proceed to full design of the new concept. Previous soil testing results reviewed by the NJDEP have resulted in the designation of some areas of the project as type D soils. Thiessens Polygon Method has been utilized to determine the limits of the D soils. The plan showing this analysis is included in the Appendix. The project design includes a stormwater management design in accordance with the concept plan review with NJDEP. It meets state stormwater standards for water quality, groundwater recharge and discharge rate. The drainage design has a combination of small-scale infiltration basins, porous pavement systems and a large scale infiltration basin. The systems have been located throughout the disturbed area

ate. The drainage design has a combination of small-scale infiltration basins, porous pavement systems and a large scale infiltration basin. The systems have been located throughout the disturbed area to manage the stormwater near its source. The calculations utilize Hydrocad, version 9.10, NJDEP approved intensity curves, and the SCS TR20 methodology to calculate the pre-and post-development runoff. 2

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Methodology The drainage for the development area of the property is calculated for the existing and proposed conditions for each of the three Points of Analysis. The proposed analysis is broken down into the overall un-detained in the analysis area and the flow to each of the stormwater management systems. The existing conditions for the site are considered wooded in good conditions per NJDEP guidance documents. Discharge rates for the existing conditions under the 2, 10 and 100-year storm events are calculated with The Hydrocad drainage program and the SCS TR-20 method. Hydrographs for the proposed conditions for areas detained and un-detained are developed. Allowable discharge rates for the detention system are calculated and the proposed hydrograph is routed through a proposed detention system until the desired discharge rate is achieved for each storm. Discussion Water Quality Each Drainage basin uses green technology to achieve the require 80% suspended solid removal rate. Small-scale infiltration basins are paired with a pre-treatment separator to achieve 90% removal rate. Chaptrer 9.8 permits non-GI Approved MTD’s to be used as pre-treatment as noted on page 10. “ Pretreatment may consist of a forebay or an BMPs found in chapter 9 or 11”. Porous pavement systems remove 80% per the BMP manual. The large-scale basin utilizes a green technology approved MTD ( filterra) at its inlets to achieve the water quality requirement. Water Quantity The stormwater system proposed has been designed to reduce the discharge from the site for the 2-, 10- and 100-year storms as required by the stormwater regulations. Each of the drainage/detention areas has been designed to control stormwater to below its current discharge rate. The results of the stormwater analysis for existing and proposed discharge are provided in the summary tables for each point of analysis. Detailed Hydrocad output is also included in the appendix of this report. Point of Analysis 1 (POA#1) PA#1 is the area of the site that drains to the Canoe Brook in the western portion of the property. The stormwater management systems designed for this are Large Scale Basin #1, and porous pavement systems 5&6. POA#1 (Point of Analysis) Existing Conditions Tc Computations. This drainage area is in a forested cover with very light underbrush due to

is are Large Scale Basin #1, and porous pavement systems 5&6. POA#1 (Point of Analysis) Existing Conditions Tc Computations. This drainage area is in a forested cover with very light underbrush due to deer over browsing. path of the existing conditions Tc is shown on the Existing Conditions Drainage Area Map. The Tc (Time of Concentration) is calculated in the Hydrocad program with the factors shown on the map and is as follows. 3 The

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 The Basin 1 contributing area is 414691 sf of Woods in good condition. The initial 100 lf (linear feet) is sheet flow with a slope of 5% in woods with light underbrush. Tc=14.3 min The next segment is shallow concentrated flow 1980 lf with a slope of 5.4% through woods with light underbrush. There is no discernable channel in the field along this path that would change the categorization of the flow type. Tc = 8.8 min. Total pre-development Tc= 23.1 minutes Large Scale Infiltration Basin #1 This stormwater system collects water from Kusik Drive and the lawn areas adjacent. The total contributory area outside the basin itself is 2.5 acres but when the basin area is included the total drainage area is 3.49 Acres. The proposed Tc for the area flowing to Detention 1 uses the following input Sheet flow 59 lf @2% over grass Tc= 9 minutes Shallow concentrated flow 425 lf over pavement @ 6.5% Tc = 1.7 minutes Pipe flow 425 lf pipe , 2.5 fps Tc = 3.4 minutes Total Tc = 14.1 minutes Basin 1 is designed as a large scale basin without exfiltration as an outlet. The Basin details do include soil replacement with a permeable sand to allow infiltration to occur. Water quality is achieved with MTD’s at each inlet location. Porous Pavement system #5 Porous pavement #5 collects stormwater from the Building B parking lot, Building B roof and grass areas around the building. The total drainage area is 1.07 acres with the majority of that area the building roof or the porous pavement surface. The ratio of other contributing areas to the Porous pavement area is .4 : 1 The system will have soil replacement with a permeability of 4 inches per hour with a factor of safety of 2. The proposed Tc for the area flowing to PP5 uses the following input Sheet flow 40 lf @2% over pavement Tc= .6 minutes Pipe flow 182 lf pipe , 2.5 fps Tc = 1.2 minutes Total Tc = 1.8 minutes The porous pavement system is considered green technology for both groundwater recharge and water quality. 4

DocuSign Envelope ID: DB0533B0-B14B-449D-A0A8-3B9C3C0DF5D9 Porous Pavement system #6 Porous pavement #6 collects stormwater from the parking lot between Buildings B and C, Building C roof and grass areas around the building. The majority of the drainage area is the building roof or the porous pavement surface. The ratio of other contributing areas to the Porous pavement area is 1.9 : 1 The system will have soil replacement with a permeability of 4 inches per hour with a factor of safety of 2. The proposed Tc for the area flowing to PP6 uses the following input Sheet flow 40 lf @2% over pavement Tc= .6 minutes Pipe flow 450 lf pipe , 2.5 fps Tc = 3 minutes Total Tc = 3.6 minutes The porous pavement system is considered green technology for both groundwater recharge and water quality. PA-1 Discharge Summary STORM WQ 2 YR 10 YR 100 YR EXISTING 6.84 15.78 35.37 PERMITTED #1 #5 #6 3.43 11.5 28.3 0 .19 .60 1.18 0 0 1.06 4.67 0 .22 2.63 11.67 5 OVERLAND FLOW .42 2.46 5.01 10.26 POA 1 .42 2.46 5.08 10.89