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March 14, 2016 <br /> Gully Bank Stability Evaluation <br /> Wright Residence <br /> L&A Job No. 16-023 <br /> 'Page 3 /$ <br /> The deposits of the advance outwash soil unit are composed of stratified sand and gravel <br /> with very minor amount of silt and clay, deposited by the meltwater of advancing glacial <br /> ice of the last glacier then overridden by the still advancing glacier. Due to their <br /> generally granular composition, the advance outwash deposits are of moderately-high <br /> permeability and drains fairly well. The advance outwash deposits are generally dense to <br /> very-dense in their natural, undisturbed state. They are of moderately-high shear strength <br /> and can remain stable in natural slopes or man-made cuts. <br /> Groundwater Condition <br /> The surficial advance outwash soil unit mapped at and in the vicinity of the residence site <br /> is of moderately-high permeability and would allow stormwater to seep through easily. <br /> The advance outwash soil unit is normally underlain by a Transitional Beds soil unit <br /> consisting of very-stiff to hard, fine-sandy to clayey silt. This soil unit is of extremely <br /> low permeability and would perch stonnwater infiltrating into the overlying advance <br /> outwash soil unit. The perched water would flow laterally down-gradient along the <br /> surface of the transitional beds soil unit. This perched groundwater would emerge out <br /> natural slopes or man-made cuts where the underlying transitional beds soil unit is <br /> exposed. Emerging groundwater under high hydraulic head in winter can cause erosion <br /> and prolonged erosion can result in landslides. However, transitional beds soil unit is not <br /> mapped within or in vicinity of the residence site in the above-referenced geologic map. <br /> Therefore, the hazard of erosion-induced landslides does not exist within the residence <br /> site. <br /> LIU & ASSOCIATES, INC. <br />