6101 23RD DR W NORPRO Geotech Report 2025-07-29

I June 3, 2011 Project No. T-6578 3.2 Soils In general, soil conditions at the site consist of approximately 6 to 18 inches of forest duff overlying weathered becoming unweathered horizons of glacial till occasionally overlying a mixture of outwash sand and gravel with I silt deposits. The glacial till consists of silty sand with gravel, increasing in density with depth, and often cemented. The outwash deposits consist of dense to very dense sand with varying amounts of silt, gravel, and cobbles. Fill soils were found in a shallow (three-foot deep) test pit excavated at the edge of the water line easement. Fill depths on the order of 6 inches to 18 inches are anticipated on either side of the trench along the length of the a corridor. The fill soils, consisting of silty sand with gravel, overly the original organic surface soils. The fill is it most likely the result of grading out the trench spoils from the excavation for installation of the utility. More detailed descriptions of the subsurface conditions we observed are summarized on the Test Pit Logs in Appendix A. The approximate locations of the test pits are shown on Figure 2. The Distribution and Description of Geologic Units in the M/lukilteo Quadrangle, Washington, by James P. I Minard (1982), indicates the site is underlain by Vashon Till (Qvt). This published description is consistent with the deposits observed in the test pits excavated at the site. Based on our test pits and the presence of sands and gravels below a layer of glacial till silty sand with gravel, we believe the western extent of the site may more III accurately be described as Advanced outwash(Qva). I3.3 Groundwater I We did not observe groundwater seepage in any of the test pits advanced on-site. Reddish colored soils were observed in the upper weathered glacial till as well as within the upper one to two feet of the unweathered horizon. Oxidized or reddish soils are an indication of the presence of groundwater flow at some point in time. I The development of a perched groundwater table is typical for sites underlain by glacial till, particularly during the wet winter and spring months. In general, surface water that infiltrates through the upper weathered soil zone becomes perched on the underlying, dense,cemented till. The cemented till has a relatively low permeability that impedes the downward migration of the infiltrated surface water. As a result, groundwater will accumulate, and when combined with a positive gradient, will tend to flow laterally along the till contact. Locally, such Yseepage is referred to as interflow. IGroundwater seepage from the discontinuous outwash pockets and layers may be encountered and will be greatest during mid-winter and early spring months. If encountered, it is likely that flow rates will be moderate Iwhen first exposed with flows diminishing as storage is depleted. 4.0 GEOLOGICALLY HAZARDOUS AREAS The City of Everett Municipal Code (EMC) describes geologically hazardous areas as erosion, Iandslide and Iseismic or liquefaction hazard areas. For determination of these areas, the EMC refers to classifications as stated in the "Dames and Moore Methodology for the Inventory. Classification and Designation of Geologically Hazardous Areas,City of Everett,Washington: July 1, 1991". i iPage No. 3 •