4320 THOMSON AVE 2023-08-10 - Laserfiche WebLink

GeoTest Services, Inc. 12,2019 4320 Thomson Avenue, Everett, WA April Project No.19-9-0050050 DCP explorations included advancing a steel rod through the site soils using a 35- pound drop hammer. The number of blows required to drop the rod 4 inches (10 centimeters) was recorded and correlated with the density of granular soil deposits and the consistency of cohesive soils. Soils encountered in the test pits generally consisted of12 inches of loose, silty, organic topsoil overlying native, medium -dense, silty sand (Weathered Advance Outwash) to an approximate depth of 3 to 3.5 feet BGS. Underlying these soils was very dense, gravelly sand' (Advance Outwash) that was encountered to the maximum explored depth of the test pits. Both DCP explorations encountered refusal conditions in the Advance Outwash soils due to the increased gravel content and very dense nature of these soils. General Geologic Conditions Mapped geologic information was obtained from the Geologic map of the Everett 7.5 minute quadrangle, Snohomish County, Washington (Minard,1985), published by the United States Geological Survey. According to Minard, general geologic conditions at the site are mapped as Advance Outwash (Qva) and Till (Qvt) of the Fraser glaciation. The approximate boundary between these two soil units is on or adjacent to the subject property, based on Minard's map. Till (locally referred to Vashon Till or Glacial Till) is a nonsorted mix of all grain sizes deposited directly by the advancing glacier. Advance Outwash is a well stratified sand to aravel deposited h"" meltwater from1 the front of the advancing glacier. Stratigraphically, the Till lies overtheAdvance Outwash. Our on -site explorations indicate that the encountered subsurface soil conditions are in accordance with the Advance Outwash. Based on our site observations and mapped geologic information, GTS expects that Till would be encountered further upslope. Soil Survey According to the United States Department of Agriculture (USDA) Natural Resource Conservation Service website, soils within the property are classified as Alderwood gravelly sandy loam,15 to 30 percent slopes. The Alderwood gravelly sandy loam soils are derived from a parent material of glacial drift and/or outwash over dense glaciomarine deposits. This unit is moderately well - drained and rated as having a low erosion susceptibility and an erosion Kfactor of 0.10. Values of K range from 0.02 to 0.69; the higher the value, the more susceptible the soil is to sheet and rill erosion by water. 3