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1 <br />3 <br />e, <br />October 23, 2007 G-261 1 <br />1030 N Park Drive, Evcrett, WA Page 2 <br />Geologically I lazardous Areas: Geotechnical Letter <br />garage is located, but will extend further to the southwest and southeast. The northwest wall of <br />the proposed new garage, fining the steep slope, will be stepped to maintain a simila, setback <br />from the top of the slope. <br />Geology and Soils <br />According to the area geologic inapt, the soils at the top of the bluff arc mapped as Vashon Till <br />(Qvt), a poorly sorle.!, nonstratified lodgement till consisting of an extremely compact mixture of <br />clay, silt, sand, peb'des, and cobbles that was deposited as ground moraine in the upland areas. <br />'File soils on the bl,AT. below the Vashon Till, arc mapped as the Whidbey Formation (Qw), <br />consisting of nonglacial river (food -plain deposits composed of medium -bedded sand, silt, and <br />clay with generally good sorting within individual beds. <br />The site soils above the top of the slope consist of fine to medium brown sand based on soils <br />exposed in an existing 3-foot cut at the northwest corner of the existing garage. The sand was <br />loose based on probing. The sandy soil is believed to be part of the Whidbey Formation. The <br />Vashon Till soils were not observed. <br />Hydrology <br />Soils of the Whidbey Formation consist of beds of sand, silt and clay. In the upland area, surface <br />water that infiltrates into the ground surface and intersects a silt or clay layer will travel laterally <br />and be exposed as localized seepage or springs on the bluff. A localized area of groundwater <br />seepage was observed about 30 feet below the top of the slope northwest of the house. <br />Slope Stability Evaluation <br />The bluff is classified as a very high/severe landslide hazard area by lire Dames and Moore <br />Methodology for the Inventory, Classification, and Designation of Geologically Hazardous <br />Areas, City of Everett, Washington, July 1, 1991. The slope exceeds 15 percent and the geologic <br />unit is Qw. <br />Smith, M., 1976, Preliminary Surficial Geologic Map of the Mukilteo and Everett Quadrangles, <br />Snohomish Canty, Washington, State of Washington, Department of Natural Resources, Geologic <br />Map GM-20, 1:24,000 <br />GEO Group Northnest, Inc. <br />7/ <br />