25 12 03 Engineering Review Letter 1 rcd 12 4 2025

—_.. Consulting & Municipal ENGINEERS "ASSOCIATES Chairman and Members of the West Orange Township Zoning Board December 3, 2025 Re: 127 Mitchell Street, LLC (ZB-25-08) Our File No. 115.WRZ0154.V01 Preliminary and Final Site Plan with ‘C’ and ‘D’ Variances - Review #1 Page 5 3. The Stormwater Management Report should be revised to indicate that the project is classified as a major development in accordance with the Township’s Stormwater Control Ordinance (Section 25-29). 4. The Stormwater Management Report should be revised to verify compliance with the applicable groundwater recharge standards. 5. The Stormwater Management Report should be revised to indicate how the proposed BMPs comply with the applicable green infrastructure (Gl) standards. 6. The hydrograph routings provided within the Stormwater Management Report should be revised to model impervious areas and pervious areas separately. 7. The Stormwater Management Report should be revised to include a stormwater runoff quantity analysis for the pre-construction and post-construction projected 2-, 10-, 25- and 100-year storm events. 8. The existing and proposed drainage area maps should be revised to label each segment of the time of concentration flow path including indicate the flow type, length of segment and slope of segment. Additionally, existing and proposed time of concentration calculations should be provided for review. 9. Revise the Grading, Drainage, Soil Erosion & Sediment Control Plan (sheet 6) to include invert elevations for all pipes, including roof leaders and at the underground basin connection. 10. Revise the plans to ensure that all inlet grates are set higher than the 100-year water surface elevation within the basins. 11. The proposed inlet located at the bottom of the proposed staircase provides 6” of cover over the top of the pipe. The concrete sidewalk detail on sheet 8 indicates that 4” of concrete and 4” of stone is required for concrete sidewalk installation. Therefore, it appears that additional cover should be provided over the pipe. 12. The design of the proposed underground basin should be clarified. The basin is indicated on the Grading, Drainage, Soil Erosion & Sediment Control Plan (sheet 6) as a detention basin, however, it will be constructed with perforated pipes (infiltration) and is modeled with exfiltration within the hydrograph routings. Our office

& Sediment Control Plan (sheet 6) as a detention basin, however, it will be constructed with perforated pipes (infiltration) and is modeled with exfiltration within the hydrograph routings. Our office notes that underground detention basins are only permitted when granted a waiver or variance from NJAC 7:8- 5.3. 13. Groundwater mounding and duration of infiltration period calculations should be provided for all proposed infiltration systems. 14. Revise the plans to clarify how roof runoff will be pre-treated prior to infiltration.