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July 3, 2017 Single-Family Residence L&A Job No. 17-079 Page 6 laterally down-gradient and emerge out of slopes or tuts where the transitional beds soil unit is exposed. GEOLOGIC HAZARDS AND MITIGATION Erosion and Landslide Hazard The surficial topsoil and weathered soil are of low resistance against erosion, while the underlying dense advance outwash deposit is more resistant against erosion. The topsoil and weathered soil mantling the steep slope flanking the east side of the project site can be gradually eroded if they are devoid of vegetation cover and overly saturated. Surficial erosion may cause shallow skin-type mudflows on the steep slope. To mitigate such surficial hazard, vegetation cover on the steep slope should be protected and maintained. Disturbed and exposed areas caused by construction activities should be covered with plastic tarps during construction and should be re-seeded and re-vegetated as soon as possible. Stormwater can seep into advance outwash deposits of high permeability easily and would perch on the underlying practically-impervious transitional beds soil unit This perched groundwater would emerge out of slopes or cuts where the transitional beds soil unit is exposed. The perched groundwater would accumulate and rise and groundwater seepage would increase substantially in winter. Groundwater seepage under high hydraulic head could cause erosion and prolonged erosion would result in soughing and landslides in and above seepage zone. This is groundwater seepage and erosion induced landslides. According to the above-referenced geologic map, the transitional beds soil LIU & ASSOCIATES, INC.