8925 AIRPORT RD MUKILTEO SCHOOL DISTRICT 2022-01-19

GeoTest Services, Inc. Mukilteo SD —Wall Design, Everett, Washington Site Conditions February 26, 2018 Job No. 18-0068 The subject area (proposed wall location vicinity) is located on the south side of an existing asphalt parking lot and along the northern portion of a wetland buffer. The southern edge of the parking lot contained level surfaces and a curb that separated the hardscape from south -facing, 2- to 4-foot tall slopes. A portion of the edge of the parking area, within the subject area, is currently supported by a 2- to 3-foot tall rockery wall. A catch basin and drain pipe existed within the southern portion of the subject area and just south of the proposed retaining wall location (Figure 2). The proposed retaining wall location existed within a vegetated area consisting of juvenile and mature deciduous trees and blackberry briars. A wetland area existed to the south and east of the subject area and retaining wall location. Subsurface Conditions Subsurface conditions were explored by excavating three test pits (TP-1 through TP-3) with a subcontracted tracked excavator/operator subcontracted through GTS and supervised by a staff Engineering Geologist. The test pits were advanced into soils at the location at the base of the proposed retaining wall location (Figure 2). The upper 12 inches of TP-1 consisted of soft, brown, moist, sandy silt with and roots and organics (topsoil). Below the topsoil was approximately 4 feet of medium dense tan to orange -brown, moist, silty sand with gravel (Weathered Glacial Till). Within this layer, a lens of wood debris was present at 2 to 3 feet below ground surface (BGS). Below the weathered layer was hard, gray and slightly sandy with gravels. This is interpreted to be native (Glacial Till). Slight groundwater seepage was encountered at 5 feet BGS in the test pit. The upper 12 inches of TP-2 consisted of soft, brown, moist, sandy silt with and roots and organics (topsoil). Below the topsoil was approximately 4 feet of medium dense tan to orange -brown, moist silty sand with gravel (Weathered Glacial Till). At 2.8 feet BGS, rapid (perched) groundwater seepage was observed in the north side of the excavation. Below the weathered layer was hard, gray, and slightly sandy with gravels (Glacial Till). The upper 6 inches of TP-3 consisted of soft, brown, moist sandy silt with and roots and organics (topsoil). Below the topsoil was approximately 18 inches of medium dense tan to orange -brown, moist, silty sand with gravel (Weathered Glacial Till). Below the layer of Weathered Glacial Till was approximately 20 inches of native soft to medium stiff, gray silt/clay fill (Glacial Till) fill. At approximately 4.5 feet BGS we encountered slightly Weathered Glacial Till followed by native Glacial Till at approximately 7 feet to full depth of our exploration. Please refer to the attached test pit logs for more detail (Figures 9 and 10). Groundwater Slight groundwater seepage was encountered within TP-1 at 5 feet BGS and rapid seepage in TP-2 at 2.8 feet BGS. We anticipate that the groundwater found in these two test pits is in a perched condition at the transition between weathered and un-weathered soil No groundwater was encountered within TP-3 to the full depth of the exploration. Page 2 of 8