2201 100TH ST SW AD SYSTEMS 2022-03-07

GeoTest Services, Inc. April 25, 2017 2201 100th Street Southwest, Everett,WA Job No. 17-0186 consisted of an approximate 1-foot thickness of medium-dense, gravelly sand. Underlying the asphalt or fill was native, loose to medium-dense, silty sand with variable sand contents (weathered till). Very dense, gravelly, silty sand was encountered at an approximate depth of 4 to 8.5 feet BGS (unweathered till). These native soils have been glacially compressed and are locally referred to as Vashon till or glacial till. With the exception of B-1, these very dense soils were encountered to the maximum explored depth of the borings. In B-1, very dense sand (Advance Outwash) was encountered at an approximate depth of 23 feet BGS and was encountered to the maximum explored depth of the boring. General Geologic Conditions Geologic information for the project site was obtained from the geologic map entitled, Distribution and description of geologic units in the Mukilteo quadrangle, Washington (Minard, 1982), published by the U.S. Geological Survey. According to Minard, the near-surface soil deposits in the vicinity of the project site consist of Vashon till (Qvt) from the Fraser Glaciation. The till is a non-sorted mixture of clay, sand pebbles, cobbles, and boulders (diamicton), all in variable amounts. It typically is hard lodgement till and is often referred to as "hardpan". The soils encountered in our subsurface explorations are generally consistent with the published geological information and our experience with projects in the nearby vicinity. Groundwater Seepage and Seasonal Groundwater For the purposes of this report, observed groundwater seepage represents either the existing surface of a widespread, regional groundwater table or the surface of perched seepage. The groundwater table is referred to as the atmospheric pressure surface that coincides with the top of the zone of saturation and is the surface that dictates the development design recommendations in this report. Perched seepage is referred to as a saturated zone that develops where a restrictive surface (i.e. dense, fine grained soils or bedrock) limits the vertical, downward migration of near-surface water. This surface should be considered when determining methods of earthwork construction but is not used to dictate development design. However, if perched seepage at the subject property is ponded above a restrictive surface (i.e. bedrock) and no groundwater table exists, then the perched seepage dictates development design recommendations herein. Groundwater Observations At the time of our visit on March 28, 2017, groundwater seepage was generally encountered at an approximate depth of 2 to 2.5 feet below ground surface (BGS) in the borings. The groundwater seepage was generally found perched atop the unweathered glacial till soils and is not considered to be representative of a regional aquifer. Seepage was also encountered at depth of 15 to 25 feet in pockets within the till, and within the outwash soils. The groundwater conditions reported on the boring logs are for the specific locations and dates indicated, and therefore may not necessarily be indicative of other locations and/or times. Please consider that groundwater levels are generally higher (at shallower depths) during the wetter months (October through May). The presence of perched groundwater encountered atop the unweathered glacial till is consistent with our experience with projects in the vicinity of the subject site. Page 3 of 13