5117 23RD AVE W 2016-01-01 MF Import

Geotechnical Enginecring Report 51 17 23rd Ave W � January 2, 2009 RMI File No. 50909 Pagc 3 Literature Review The Distribution and Description of Geologic Units in the Mukiltco Quadrangle by Minard states that Vashon till (Qvt)exists on this site over Transitional beds(Qtb)of clay, silt and sand. Sitc Conditions An earlier geotechnical report (NGA Associates, 2001) states that augered holes encountered the till about 6 feet below the surfacc in the area between the slab and the top of the steep slope. 'Ihe gound surface between the concrete slab and the wooden retaining wall has settic,; about 4 to 5 inches probably due to settlement of the soft fill in this area and probably outwnrd movement of the retaining wall. The slope is at about 41 degrees, which is approximatcly the angle of repose of the till soils and is about ]00 fect high. [31own-down trees and yard debris are on the slope. Hydrologic Conditions Thcre wcrc no signs of ouccropping groundwatcr on thc slopc. Slope Stability The slope comprises glacially compacted deposits of the very dense Vashon till at depth. These deposits typicaL'y have very good strength. We did not observe signs of deep-seated slope failures on these slopes but thc blown-down trees and yard debris should bc ranovcd without damage to the vegr,tation. It is our opinion that there is not a signi(icant potcntial for deep-scated slope instability. (CEOLOGIC HAZARDS Erosion Hazard Thc erosion ha�ard criteria used for determination of affected areas include soil type, slope gadient, vegetn[ion cover and ground water conditions. The erosion sensitivity is related to vegetative cover and the specific surface soil q�pes (group classification), which are related to the underlying geologic soil units. The erosion hazard for [hese soils on Ihe slopcs is listed as bcing high in the weathered till soils strippcd of vegctation. RMI ASSOCIATES LLC 'yl I�°' �