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Engineer’s Report December 2025 C. Stormwater Management 1. Existing Conditions The project site (0.70± acres) currently contains an 1,860± ft² commercial building, 11 parking spaces, and grass/wooded area surrounding the building and parking area. The topography of the project site is sloped towards Quaker Road (US 20A). Stormwater generally flows to the existing storm sewer system or to the south of the site. The project site consists of 0.57± acres of pervious area and 0.14± acres of impervious area (0.01± acres within the Quaker Road ROW (US 20A)). According to the New York State Department of Environmental Conservation (NYSDEC) Environmental Resource Mapper, no portion of the project site contains any state regulated or federal wetlands. See Exhibit 2 – NYSDEC Environmental Resource Mapper. The Federal Insurance Rate Maps (FIRM) for the Town of Aurora, Erie County, New York prepared by the Federal Emergency Management Agency Community Panel No. FM36029C0369H dated June 7th, 2019, indicates that the proposed project site contains no area within the 100- year floodplain. See Exhibit 3 – FEMA Firmette. Based on the USDA Web Soil Survey, the site is considered to contain 97% Niagara silt loam (NfA) and 3% Canandaigua silt loam (Cc). It is assumed that this soil type has a hydraulic classification of “C/D” and the site is described as 100% poorly drained soil (See Exhibit 4 – Site Soil Map). 2. Post Developed Conditions The post developed watershed boundary includes the same total drainage area as the pre-developed watershed. The stormwater from the proposed building and parking area will be conveyed to the new catch basins within the proposed parking area which drains to the NYSDOT existing catch basin within the Quaker Road ROW (US 20A). Within the proposed stormwater conveyance system, a two (2) foot deep flat bottom swale is proposed to mitigate some of the stormwater runoff from a portion of the building and the southern parking area. The catch basins within the southern parking area and most of the building’s roof leaders are tributary to the proposed swale which will detain a portion of the runoff prior to discharging the excess stormwater into the northern part of the proposed stormwater conveyance system which ultimately discharges into the existing stormwater conveyance system within Quaker Road (US 20A). The proposed swale daylights the stormwater runoff and creates a delay in the peak runoff from the southern portion entering the northern portion of the proposed stormwater conveyance system. This delay allows for the existing storm sewers within Quaker Road (US 20A) to contain a lesser flow rate during the peaks of the storm events reducing the probability of flooding. The watershed delineation maps can be found Greenman-Pedersen, Inc. GPI No. WNY-2500056.00 Page 6