1710 W MARINE VIEW DR 2024-01-03

Full infiltration was deemed to be infeasible due to high groundwater elevations and inadequate separation between any infiltration facility and the groundwater table. The groundwater elevation at the site mirrors tidal elevations. Anticipated sea level rise over the next 100 years ranges between +1' to +5'. The current Mean Higher -High Water elevation is 11.011 (NOAA Tides and Currents) and with an estimated 1'-5' due to sea level rise, a future groundwater elevation of 12' to 16' is expected. The average proposed finished grade on site is 18.26'. 7.6. MR #6 — Runoff Treatment Site runoff will be treated through the use of a Filterra Bioscape treatment system located at the downstream end of system A. The BMP was selected through the use of the DOE Runoff Treatment BMP Selection flow chart, see Figure 3 below. See Appendix G for treatment vault information. According to the SWi/MMWW, oil control BMPs are required for commercial sites subject to an expected average daily traffic (ADT) count equal to or greater than 100 vehicles per 1,000 square feet of gross building area, or 300 total trip ends per day. The project site is expected to exceed this ADT threshold due to the high traffic turnover associated with the coffee shop and brewery and therefore require an Oil Control BMP. The Filterra Bioscape vault meets the DOE performance standard for Oil Control BMPs. Sizing of the treatment vault is based on treating 91% of the entire runoff volume over a multi -decade period. The flowrate for this volume was calculated in MGS Flood using a 15-minute timestep and determined to be 0.061 cfs. See Appendix F for MGS Flood Results. The vault treatment flowrate is 0.069 cfs.