2211 GIBSON PL Geotech Report 2023-04-06

• August 18, 2014 Gibson Bluff L&A Job No. 14-056 Page 18 Runoff over Impervious Surfaces Storm runoff over impervious surface, such as roofs and paved road/driveways, should be collected by underground drain line systems connected to downspouts and by catch basins installed in the road/driveways. Stormwater thus collected should be tightlined to discharge into a storm sewer or suitable stormwater disposal facilities. Building Footing Drains A subdrain should be installed, as required, around the perimeter footings of each building. The subdrains should consist of a 4-inch-minimum-diameter, perforated, rigid, drain pipe, laid a few inches below bottom of the perimeter footings. The trenches and the drain lines should have a sufficient gradient (0.5% minimum) to generate flow by gravity. The drain lines should be embedded in washed gravel completely wrapped in non-woven filter fabric to within about 12 inches of finish grade. The remaining trenches may be backfilled with clean on-site soils. Water collected by the perimeter footing subdrain systems should be tightlined, separately from the roof and surface stormwater drain line systems, to discharge into a storm sewer or a suitable stormwater disposal facility. Surface Drainage Water should not be allowed to stand in any areas where footings, on-grade-slabs, or pavement is to be constructed. Finish ground surface should be graded to direct surface runoff away from the proposed buildings. We recommend the finish ground be sloped at LIU & ASSOCIATES, INC.