12728 19TH AVE SE BASE FILE Geotech Report 2025-07-29

May 28, 2007 Proposed Office Building ' L&A Job No. 7A053 Page 6 tThe on-site soils contain a high percentage of fines, and are sensitive to moisture. They can also be saturated quickly and result in heavy runoff during extended periods of heavy rainstorms. ' Interceptor trench drains or ditches should be installed along the uphill boundaries of the site, as required, to intercept and drain surface runoff and near-surface groundwater seepage away from construction areas to minimize soil erosion and to facilitate grading and foundation construction work. f GEOLOGIC HAZARDS AND MITIGATION Landslide Hazard The very-dense fresh till soils underlying the site at shallow depth are of very high shear strength and have excellent resistance against slope failures. These competent soils coupled with the generally gentle to very-gentle terrain of the site should make it unlikely for landslides to occur on the site Erosion Hazard The surficial topsoil and medium-dense weathered soils are of low resistance against erosion, 11 while the underlying very-dense fresh till soils are of moderate resistance against erosion. The erosion potential of these weak surficial soils is greatly diminished by the gentle to very-gentle terrain of the site. Therefore, the erosion hazard of the site should be minimal. Nevertheless, exposed unpaved ground within the site resulted from construction activities should be re- vegetated as soon as possible. Stormwater over impervious surfaces, such as roofs and paved parking lot and driveways, should be captured with underground drain line systems connected to 1 roof downspouts and by catch basins installed in paved areas. Water collected by the underground drainage systems should be tightlined to discharge into a storm sewer or a suitable stormwater disposal facility. I LIU & ASSO CIATES, INC. I