48 001 STORMWATER REPORT 20240823 Sealed

E. POST-DEVELOPMENT CONDITION: The drainage area in the proposed conditions was divided in three catch basins: Basin 1 has categories as follows: 1. Proposed impervious surface (building & walkways). CN value = 98, area = 0.2217 Ac 2. Open Space (Grass good condition, hydrologic soil group C). CN value = 79, area = 0.19 Ac Weighted CN value for whole drainage area = 96 Basin 2 has categories as follows: 1. Open Space (grass good condition, hydrologic soil group C). CN value = 79, area = 0.0226 Ac 2. Proposed impervious surface (walkway). CN value = 98, area = 0.0099 Ac Weighted CN value for whole drainage area = 84.8 Basin 3 has categories as follows: 1. Open Space (Grass good condition, hydrologic soil group C). CN value = 79, area = 0.0027 Ac Total runoff from the proposed improvements will increase due to the increase of proposed impervious surfaces which will replace the existing grass area. The runoff from walkway and lawn areas will be intercepted by catch basins, which is connected to the proposed underground detention system with HDPE storm drains. Runoff from roof drain system will also be directed to the proposed underground detention system. Runoff from Basin 2 & Basin 3 will overflow outside the site. The peak discharge calculated from the Post-Development drainage area is as indicated in Table No. 2 Drainage Area Basin 1, CN = 96 Table No. 2 Summary of Post-Development Condition (See Exhibit 1 for Stormwater Modeling Report) Peak Discharge (cfs) Runoff Volume (cu ft) Area 1010010100(ac) 2-Year 2-Year Year Year Year Year 0.2479 0.843 1.317 2.231 2,477 3,974 6,907 Basin 2, CN = 84.8 0.0325 0.065 0.111 0.200 179 313 583 Basin 3, CN = 79 0.0027 0.005 0.010 0.020 13.6 27.1 56 This increased runoff volume from proposed conditions will be temporarily stored in an underground detention SYSTEM which has an outlet drainage pipe draining into the existing catch basin which is located on Park Drive N. F. WATER QUALITY VOLUME According to 25-29.4.Q, water quality volume should be calculated for proposed net increase of motor vehicle surface. Since the proposed parking area will be located on the first floor of the proposed building, which is a covered driveway, and new driveway is much smaller than existing (in pre-development conditions), no increase in motor vehicle surface will be provided with new development.