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August 18, 2014 <br /> Gibson Bluff <br /> L&A Job No. 14-056 <br /> Page 7 <br /> GEOLOGIC HAZARDS AND REMEDIATION <br /> Erosion Hazard <br /> The bench top area of the site is underlain at shallow depth by medium-dense to dense, <br /> fine to medium to coarse sand deposits of the Esperance sand soil unit, overlain by topsoil <br /> and fine sand weathered soil. These soil deposits are all of moderate to high permeability, <br /> and would allow storm runoff to seep through easily. The bench top is very gently sloped. <br /> Therefore, the bench top of the site is not prone to erosion hazard. To further mitigate <br /> erosion hazard, areas disturbed and devoid of vegetation from construction activities <br /> should be vegetated and landscaped as soon as possible for erosion protection. <br /> Concentrated stormwater should not be discharged uncontrolled onto the ground within or <br /> adjacent to the site. Storm runoff over impervious surfaces, such as roofs and paved <br /> road/driveways, should be captured with underground drain lines connected to roof <br /> downspouts and by catch basins installed in the road/driveways. Stormwater collected by <br /> such drain line systems should be tightlined to discharge into a storm sewer or suitable <br /> stormwater disposal facilities. <br /> Landslide Hazard <br /> Where the Whidbey formation soil unit of extremely low permeability is exposed on <br /> slopes or man-made cuts, groundwater seepage would occur. High groundwater seepage <br /> in winter can cause soil erosion in and above the seepage zone. Progressive erosion can <br /> cause soil sloughing and landslides. This is groundwater seepage and erosion induced, <br /> upward working landslides The Whidbey formation soil unit was encountered by only <br /> one of the three test borings at 31.0 feet. Therefore, the Whidbey formation soil unit is <br /> LIU & ASSOCIATES, INC. <br />