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Multifamily Development 1425 & 1475 Orchard Park Road West Seneca, NY 14224 Page 2 of 4 5/26/2026 Design Parameters: Multifamily Development: 29 units x 220 gpd/unit = 6,380 gpd Since the sanitary sewer extension is designed to convey greater than 2,500 gpd, a downstream sewer capacity analysis was performed to ensure that the existing sewer could handle the additional flow. The hydraulic loading rates per “Design Standard for Wastewater Treatment Works” 2014, NYSDEC. See Appendix B for Sanitary Sewer & Water Calculations See Appendix C for Downstream Sewer Capacity Analysis Report Section 4 – Storm Sewer Service The existing site sheet drains from east to west to a USACE jurisdictional wetland area at the rear of the site. The proposed development will replicate the existing hydrology of the site. The proposed hydrology for the development project area will consist of overland sheet flow and pipe channel flow. The storm sewer system for this site will consist of 6”, 8” and 12” HDPE pipes connected by a series of catch basins and yard drains. Stormwater runoff generated from the site will enter the pipe network and be conveyed to a detention basin on the west side of the site. The detention basin will discharge runoff, at a controlled rate, to the existing wetlands. To meet NYSDEC water quality requirements, runoff will be conveyed to a bioretention areas prior to the detention basin. Runoff that is currently being discharged on to the site from the church parking lot to the east will be collected and piped to the west side of the site. Design Criteria Storm pipes: 10-year storm Detention: Comparison of the existing 1-year vs. the proposed 1-year runoff. Comparison of the existing 10-year vs. the proposed 10-year runoff. Comparison of the existing 10-year vs. the proposed 25-year runoff. Comparison of the existing 100-year vs. the proposed 100-year runoff. Stormwater Runoff Summary: To Detention: Event Prop. Runoff (cfs) Elevation (ft) Storage (cf) 1-yr 1.94 671.04 5,335 10-yr 2.82 672.95 15,013 25-yr 3.10 673.70 21,268 100-yr 3.45 674.73 34,966 Direct: Event Prop. Runoff (cfs) 1-yr 0.38 10-yr 1.12 25-yr 1.57 100-yr 2.52 Total Site: Event Ex. Runoff (cfs) Prop. Runoff (cfs) 1-yr 2.63 2.32 10-yr 8.17 3.94 25-yr 11.66 4.67 100-yr 18.97 5.97 Page 469 of 849