2151002Princeton Hydro West Essex Stormwater Comments to Planning Board 20250310

Stormwater Management Review for Municipal Planning Board Approval West Highlands, Inc. Block No. 179, Lot No.32, West Orange Township, Essex County, New Jersey March 2025 Princeton Hydro, LLC: 2151.002 14 The analysis of the existing drainage area for POA 2 has yet another flaw. The topography within the area delineated for POA 2 has two clear discharge locations in the proposed condition, but it only assumes discharge location at Kuzik Road (see Figure 9). The design maintains both discharge locations, but the modeling assumes they are combined. The flows do eventually combine approximately 600 ft downstream into the adjacent neighborhood, not at the boundary of the site as currently assumed by the model. The drainage area analysis should be redone and the drainage area should be split into two separate drainage areas with two separate points of analysis to ensure the peak flow rate at both locations are compliant. It is difficult to predict how this will impact the site design, but it could be substantial. This re-evaluation is necessary to ensure that the peak flow rate of runoff from the site is compliant with the state and local regulations and to prevent downstream flooding. Figure 9: These are images of DA-1 and DA-2 from the Stormwater Report for the existing condition (left) and proposed condition (right) to demonstrate that the DA for POA 2 should be modeled as two separate DAs because there are two distinct points of discharge. 2.7 SEPARATION OF SANITARY INFRASTRUCTURE AND BMP The design has a sanitary pipe traveling through porous pavement system (Figure 11). While Princeton Hydro could not find a specific rule against a sanitary line traveling through a subsurface basin, there are rules dictating adequate separation between stormwater piping and sanitary piping. Stormwater pipes and sanitary pipes should maintain a minimum horizontal distance of 10 ft and a minimum vertical distance of 1 ft, and the sanitary line should be below the stormwater pipe. The purpose of the separation is to prevent leaking sanitary pipes from entering the stormwater system and potentially causing an illicit discharge of raw wastewater. The design should be modified to relocate the sanitary pipe out of the subsurface system. This may require the project to have additional Flood Hazard and/or Wetlands Permitting depending on how the layout is impacted by

modified to relocate the sanitary pipe out of the subsurface system. This may require the project to have additional Flood Hazard and/or Wetlands Permitting depending on how the layout is impacted by this modification.