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Pacific Ridge — DRH, LLC ES-8528.01 July 18, 2022 Page 5 The very dense and unweathered glacial till soils (hardpan) observed at depths beginning at about one to eight feet bgs generally exhibit very poor soil infiltration characteristics. In our opinion, the unweathered glacial soils should be considered impermeable for design purposes, and the use of full infiltration systems for stormwater control is not recommended. If determined necessary to satisfy design objectives, small-scale (limited) infiltration devices incorporating overflow provisions may be feasible pending further geotechnical assessment, upon request. Site Preparation and Earthwork Site preparation activities should consist of installing temporary erosion control measures and performing site stripping within the designated clearing limits. Subsequent earthwork activities would likely involve mass grading and installation of new infrastructure and utilities. Temporary Erosion Control The following temporary erosion control measures should be considered: • Temporary construction entrances and drive lanes, consisting of at least six inches of quarry spalls, should be considered to both minimize off-site soil tracking and provide stable surfaces at site entrances. Placing geotextile fabric underneath the quarry spalls will provide greater stability if needed. • Silt fencing should be placed around the appropriate portions of the site perimeter. • When not in use, soil stockpiles should be covered or otherwise protected to reduce the potential for soil erosion, especially during periods of wet weather. • Temporary measures for controlling surface water runoff, such as interceptor trenches, sumps, or interceptor swales, should be installed prior to beginning earthwork activities. • Dry soils disturbed during construction should be wetted to minimize dust and airborne soil erosion. • When appropriate, permanent planting or hydroseeding will help to stabilize site soils. Additional Best Management Practices (BMPs), as specified by the project civil engineer and indicated on the plans, should be incorporated into construction activities. Temporary erosion control measures may be modified during construction as site conditions require and as approved by the site erosion control lead. Stripping Topsoil was encountered generally within the upper 3 to 16 inches of existing grades at the test pit locations. As such, the upper topsoil should be stripped prior to reworking the underlying existing fill and placing new structural fill. Earth Solutions NW, LLC