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Proposed Bank 1465 Union Road West Seneca, NY 14224 Page 2 of 3 2/11/2026 Section 4 – Storm Sewer Service The proposed area of redevelopment was cleared during the first phase of construction and is generally flat. The proposed hydrology for the redevelopment 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. Stormwater runoff generated from the site will enter the pipe network and connect to the existing on-site storm sewer system. Runoff is then conveyed to an existing water quality treatment structure and underground detention located on the east side of the site. The underground detention discharges runoff, at a controlled rate, to an existing catch basin along Center Road.The underground detention system was designed during the initial phase of construction to handle the future development. Since the combined area of disturbance for the existing office building and proposed bank was to be over an acre, a SWPPP was prepared and NYSDEC SPDES Permit was obtained. This Permit has remained open with weekly inspections being suspended until disturbance for Phase 2 begins. The Permit will then be closed out following stabilization of the redevelopment activities. 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 Detention Summary: Event Ex. Runoff (cfs) Prop. Runoff (cfs) Elevation (ft) Storage (cf) 1-yr 2.03 0.96 526.60 1,104 10-yr 3.83 1.69 527.35 2,548 25-yr 4.81 2.05 527.83 3,418 100-yr 6.75 2.85 529.23 5,193 See Appendix C for Storm Water Calculations Section 5 – Erosion Control Summary Stabilization Practices Stabilization practices for this site include: A. Land clearing activities shall be done only in areas where earthwork will be performed and shall progress as earthwork is needed. B. Use of stabilization fabric for all slopes having a slope greater than 1V:3H. C. Permanent seeding and planting of all unpaved areas using the hydromulching grass seeding technique. D. Mulching exposed areas. E. Frequent watering to minimize wind erosion during construction. Structural Practices Structural practices for this site include: A. Inlet protection using a method detailed in the Construction Documents B. Perimeter protection using temporary silt fence C. Temporary stone wash off areas Sequence of Major Activities Page 19 of 65