complete drainage report rev 9

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD 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 Rev 7-9-24 Rev 8-30-24 Rev 10-01-24 Rev 10-28-24 R No. 33410 EE STA PAU T L ER S FE S S I CE N S ED G IO N AL E N IN PR O L W Y SE O N F NEW JE E O . AND R __________________________ Paul W. Anderson PE PP CME NJ PE Lic. No. 33410

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD Table of Contents Location Map………………………………………………………………….…………...1 Introduction………………………………….……………………………………………..2 Methodology……………………….…………………………………….………………...2 Discussion……………………………………………………………………………….…2 Existing Conditions POA-1 POA-2 POA-3 Point of Analysis 1 Basin 1 Basin 5 Basin 6 POA-1 Summary Table Point of Analysis 2 Basin 2 Basin 3 Basin 4 Basin 7 Basin 8 Basin 9 Basin 10 Basin 11 POA-2 Summary Table Point of Analysis 3 Proposed POA-3 Summary Table Conclusion

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD Appendix Drainage area maps ( full size maps provided separately) Hydrocad Output Existing Conditions POA-1 POA-2 POA-3 Hydrocad Output POA-1 Basin 1 Basin 5 Basin 6 Hydrocad output POA-2 Existing Conditions Basin 2 Basin 3 Basin 4 Basin 7 Basin 8 Basin 9 Basin 10 Basin 11 Hydrocad output POA-3 Basin 12 Groundwater Mounding Analysis Recharge Spreadsheet Theissens Polygon soil type analysis Pipe sizing calculations Riprap sizing calculations Water Quality MTD’ calculations

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD Location Map 1

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD 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

rge 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 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: E802A2F1-2485-417E-948D-E0A4008C75BD 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 required 80% suspended solid removal rate. Small-scale infiltration basins are paired with a pre-treatment separator to achieve 90% removal rate. Chapter 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. Roof areas with roof leaders connecting directly to the porous pavement systems will have pre-treatment in the form of a cascade separator or leaf guard. The large-scale basin utilizes a green technology approved MTD (filterra) at its inlets to achieve the 80% 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. Existing Conditions The analysis of the existing conditions was completed for the 3 points of analysis on the project. The 3 points are the Canoe Brook, The Canoe Brook Tributary and to the Howell Drive drainage system. Each

analysis of the existing conditions was completed for the 3 points of analysis on the project. The 3 points are the Canoe Brook, The Canoe Brook Tributary and to the Howell Drive drainage system. Each point of analysis assumes the surface condition of wood in good condition. The Tc for each POA drainage area is shown on the existing conditions drainage area map and utilizes type C soils except where a modification of the soil type has been verified by soil testing and reviewed by the NJDEP. In these instances, area of the site have been determined to be type D. The Theissens Polygon soil type map for the soil type determination is included in the appendix of this report. 3

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD POA#1 (Point of Analysis) Existing Conditions Tc Computations. This drainage area has a forested cover with very light underbrush due to deer over browsing. The 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: The Basin 1 contributing area is 395796.5 sf of Woods in good condition. The initial 100 lf (linear feet) is sheet flow with a slope of 4.5% in woods with light underbrush. Tc=14.9 min The next segment is shallow concentrated flow 1625 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 = 7.2 min. Total pre-development Tc= 22.1 minutes POA#2 Existing Conditions Tc Computations. This drainage area is in a forested cover with very light underbrush due to deer over browsing. The path of the existing conditions Tc is shown on the Existing Conditions Drainage Area Map. The Tc is calculated in the Hydrocad program with the factors shown on the map and is as follows. The Basin 2 contributing area is 808221.9 sf of Woods in good condition. The initial 100LF is sheet flow with a slope of 4.5% in woods with light underbrush. Tc=9.0 min The next segment is shallow concentrated flow 564 lf with a slope of 9.2% 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 = 1.9 minutes. Total pre-development Tc= 16.8 minutes POA#3 Existing Conditions Point of analysis 3 discharges to an existing drainage system in Howell Drive. This municipal system flows to the east away from the onsite streams. This drainage area is only for disturbance associated with one half of the emergency access road . Existing Conditions are: woods with light underbrush. The existing Tc is calculated with the following factors. 100 LF. Of sheet flow @ 4% with woods coverage Tc= 15.8 minutes 70 lf of shallow concentrated Flow @ 11.5% woods cover. Tc= .2 Total Tc = 15.8 minutes 4

Docusign Envelope ID: E802A2F1-2485-417E-948D-E0A4008C75BD The summary of the existing conditions discharges is as follows. Hydrocad output for the existing conditions is provided in the appendix of this report. 2 YR 10YR 100 YR POA-1 7.08 15.93 35.21 POA-2 17.53 38.43 83.14 POA-3 .13 .32 .75 Proposed Conditions Point of Analysis 1 (POA#1) POA#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. Large Scale Infiltration Basin #1 This stormwater system collects water from Kusik Drive some new building roof areas and the lawn areas adjacent. 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 to meet the water quality requirement. 5