501 RIVERSIDE RD REGIONAL DISPOSAL COMPANY EVT TRANSFER FACILITY PHASE 1 SITE IMP Geotech Report 2025-07-28

RDC EVERETT TRANSFER FACILITY r,, Everett,Washington The exposed subgrade should be recompacted to at least 95 percent of the maximum dry density(MDD) per ASTM D 1557 prior to placing the geogrid and base course material. The base course should be compacted to at least 95 percent of the MDD per ASTM D 1557. We recommend that a proof-roll of the subgrade and compacted base course be observed by a representative from our firm prior to placing the geogrid or base course and also prior to paving. Soft or yielding areas observed during proof-rolling may require over-excavation and replacement with compacted structural fill. The pavement should be constructed in accordance with Section 5-04 of the 2012 Washington State Department of Transportation (WSDOT) Standard Specifications or similar method. The underlying very soft to soft native alluvial deposits have a high potential for settlement. To reduce potential settlement of these soils due to new loads, we recommend that the finished grade be constructed at approximately equal to the existing site grades. GeoEngineers should evaluate the settlement potential of the underlaying soils if new fills or loads are planned at the site. In addition, organic matter and lenses of peat were observed within the soft native soils. The presence of the peat and other compressible soils below the pavement can cause cracking due to long-term settlement of the pavement. If fill is planned at the site potential long-term settlement and cracking of the pavement can be reduced by surcharging or preloading the pavement areas. Earthwork Based on the subsurface soil conditions encountered in the explorations, we anticipate the soils at the site may be excavated using conventional construction equipment. The materials we encountered include existing asphalt/concrete pavement overlying medium dense to dense sand and gravel fill overlying soft native soils. Ideally, earthwork should be undertaken during extended periods of dry weather (June through September) when the surficial soils will be less susceptible to disturbance and provide better support for construction equipment. Dry weather construction will help reduce earthwork costs and increase the potential for reusing the glacial soils as structural fill. If earthwork is to occur during the wet season, it may be possible to use an asphalt-treated base (ATB) to protect the subgrade prior to constructing the pavement sections. GeoEngineers should be consulted to revise the pavement section design if ATB is planned. We recommend that the contractor leave at least 2 feet of the existing fill above the native alluvial soils. If the existing fill is removed, the contractor should be prepared for poor trafficability and support of construction equipment. All paved and landscaped areas should be graded so surface drainage is directed to appropriate catch basins. IClearing and Site Preparation Areas to be developed or graded should be cleared of surface and subsurface deleterious matter including any debris, existing asphalt and concrete pavement, shrubs,trees and associated stumps and roots. Graded areas should be stripped of organic soils. Based on our observations, stripping depths on the order of 6 to 14 inches will be needed to remove existing pavement sections in most Page 6 June 18,2013 ? GeoEngineers,Inc. File No.4322-002-00