V4 11 Stormwater Report Rev 3 1 26 2023

DRAINAGE AREA 3 (DA-3) Drainage Area 3 consists of both pervious and impervious surfaces which drain to Basin #2. The pervious area, 5.52 acres, consist primarily of the wooded areas in the rear of the site along with some landscaped area around the proposed parking lot. It also includes the remaining two courtyard areas, both of which have been assumed to be 50% impervious surfaces. The impervious area, 1.38 acres, is mainly comprised of the proposed parking lot and surrounding walkways. A time of concentration of 14.46 minutes was calculated for this drainage area. DRAINAGE AREA 4 (DA-4) Drainage Area 4 consists of both pervious and impervious surfaces which drain to Basin #3. The pervious area, 4.78 acres, consists primarily of the wooded area located to the rear of the site, along with some lawn and landscape areas around the proposed building and parking lot. The impervious area, 1.15 acres, is comprised of some proposed parking lots, drive aisles, sidewalks, and patios. A time of concentration of 14.30 minutes was calculated for this drainage area. GREEN ROOF CALCULATIONS Drainage area 1A and drainage area 1B consist of roof areas that will incorporate green roofs. The green roofs are a modular 24” x 24”, 4” deep tray, pre-vegetated, G5 system by Green Grid Roofs (See attached). To account for the reduced runoff from the green roofs within our analysis, we calculated a reduced curve number for the Phase I roof area and the Phase II/III roof area, separately (See attached calculations). The Phase I building will include a total roof area of 44,933 square feet with 4,492 square feet of green roofs. The Phase II/III building will include a total roof area of 76,224 square feet with 18,366 square feet of green roofs. After calculating the adjusted curve numbers for the 2-yr, 10- yr, and 100-yr storm events, we chose to use the highest value for the models to be conservative. The adjusted curve number for the Phase I roof area was 95 and the adjusted curve number for the Phase II/III roof area was 94. CURVE NUMBERS Table 4 — Curve Number (Proposed Conditions) Description Hydrologic Curve Group Number Woods A 30 Woods Cc 70 Woods D 77 Open Space A 39 Open Space Cc 74 Open Space D 80 Impervious A/B/C/D 98 Phase I Roof Area D 95 Phase II and III Roof Area D 94 x . e