2410 RAILWAY AVE Geotech Report 2023-04-06

Penske Truck Leasing-Proposed Service Facility,2410 Railway Ave,Everett,WA Mar.8,2019/Rev.Feb.25,2020 Geotechnical Engineering Report P1493-T18 soils. At depths of 50 feet, the borings had blow counts of 43 in B-12 and 41 in B-14, and minimal amounts of organics. Exploration logs from a previous study prepared by Aspect Consulting, dated June 17, 2009, indicates that underlying site soils generally consist of lower channel deposits comprised of dense sand, silty sand and gravelly sand extending from about 25 to 70 feet or more. In the Geologic Map of the Everett 7.5-Minute Quadrangle, Snohomish County, Washington,published by the United States Department of the Interior(USDI) (1985), the project area is mapped as Qyal, or younger alluvium deposited during the Holocene. These deposits lie in and along present streams and are partly subject to seasonal flooding. The sediments consist mostly of unconsolidated, stratified,gray to brown clay,silt,and very fine sand to fine sand,with abundant organic material. The younger alluvium can be anywhere from 1 meter to possibly 20 meters thick and is mostly poorly drained. Peat deposits and buried logs and stumps are common in the flood plain of the Snohomish River. Our field observations generally conform with the site classifications prepared by the USDI. The enclosed exploration logs (Appendix A) provide a detailed description of the soil strata encountered in our subsurface explorations. 3.3 Groundwater Conditions We encountered groundwater seepage in each of our explorations at depths between 5 and 71/2 feet. Exploration B-6 did not have a clear groundwater horizon due to ponding at the surface during drilling; all samples acquired from that exploration were saturated. Given that our explorations were performed during what is generally considered the"rainy season",we do not anticipate that groundwater levels will rise higher than that which we observed. Regional groundwater levels will fluctuate with localized precipitation and geological conditions. 3.4 Infiltration Conditions As indicated in the Soil Conditions section of this report, the project area is generally underlain by silty alluvial soils;with groundwater seepage typically being encountered at depths of 5 to 71/2 feet. Given the hydrogeologic conditions present within this region,and the proximity to the Snohomish River, infiltration would likely not be feasible. Site produced stormwater should be diverted to a planned storm line to be built alongside a proposed northward extension of Railway Avenue. Native soils and import fill soils are not suitable for implementation of BMP T5-10.A—Downspout Full Infiltration. 3.5 Seismic Conditions Based on our analysis of subsurface exploration logs and our review of published geologic maps, we interpret the onsite soil conditions to generally correspond with site class E, as defined by Table 20.3-1 in ASCE 7, per the 2018 International Building Code(IBC). Using 2018 IBC information on the USGS Design Summary Report website, Risk Category I/II/III seismic parameters for the site are as follows (page 6): Migizi Group, Inc. Page 5 of 17