Nisqually Landing Apts July 2021 Submission Compliance with High Groundwater Hazard Area.docxNisqually Landing Apts July 2021 Submission Compliance with High Groundwater Hazard Area
G. Performance Standards – General Requirements in High Ground Water Hazard Areas.
1. Flood Elevations. The base flood elevation for high ground water flood hazard areas corresponds to the elevation of the outer edge of the high ground water flood hazard area.
-Using geodata (Thurston County) high ground water hazard area polygon & 2 ft contours, the BFE is 339’
2. Delineation of the Base Flood Elevation. Applicants shall submit to the approval authority hydrologic and hydrogeologic studies as necessary to delineate the high ground water flood
hazard area and the base flood elevation.
-studies submitted by applicant showed lower BFE, we are choosing to use the higher number from Thurston County as visual reconnaissance shows that this area does flood frequently
3. No development shall locate within 50 feet, measured on a horizontal plane, from the outer edge of the high ground water hazard area or extending to a ground elevation two feet above
the base flood elevation, whichever is less.
-Thurston county contours show building at 345’, well above the 341’ 2 ft above requirement
-field survey created 242’ contour, and building meets 50’ setback from that contour
4. The bottom of any infiltration facility for stormwater discharge shall be located at least six feet above the base flood elevation.
-2019 SWMMWW requires infiltration facilities to be 5’ above BFE
-using 339’ BFE, 5’ above is 344’ for bottom of sw facilities
-2019 SWMMWW represents best available science regarding infiltration facilities and high gw