5107 SOUND AVE 2017-01-14 - Laserfiche WebLink

July 21, 2014 Two Single-Fa�riily residences L&A Job No. 14-065 Page 7 formatian and seep out of the slope or cut banks where the Whidbey formation is exposed. Prolonged seepage may cause erosion and soil sloughing, especially in winder and with vegetation cover removed. GEOLOGIC I�AZAI2DS ANI) MITIGATI�N Erosion and Landslide Hazard The toe of the hillside in the s�utheast quadrant of the project site is underlain by a hard clayey silt deposit which is of extremely low permeability. This deposit would perch stormwater infiltrating into the more permeable surficial soils. Rising perched , . _. ?r� t; ,1 1-n-, �E,�, n��,�nj�,j cnilc �.z/�r��71pQ t�1P . , ,. .. , , , _. t��ii�..ii:�� ., �,_. _ _1:�. .__..o .._ _ . � _ ;,, „�... . _ ., _ - .. - , � clayey silt deposit. Also, ihe perched groundwater may emerge out of the toe of the hillside. Groundwater seepage may cause soil erosion if the toe of the hillside is disturbed and the vegetation cover is stripped. Progressive erosion may cause slide to occur over the underlying hard sil# deposit. To mitigate �otential of erosion induced landslides on the toe of hillside, a retaining wall may be constructed along the toe of hillside. Recommendations for such retaining wall are provided under the RETAIl�ING WALL section below. Seismic Ha�ard The Puget Sound region is in an active seismic zone. The site is underlain at shallow depth by either hard sili within the toe of hillside area or by medium-dense to dense advance ouiwash deposit in the gently sloped area. The seismic hazard in the gently sloped area of the site should be minimal. The weak surf cial soils overlying the hard silt LIU & ASSOCIATES, INC.