6101 ASSOCIATED BLVD BASE FILE 2017-06-05

Underwood Gartland Everett, LLC ES-2232.02 February 6, 2015 Page 8 If the above slope gradients cannot be achieved, temporary shoring may be required. Permanent slopes should maintain a gradient of 2H:1 V, or flatter, and should be planted with an appropriate species of vegetation to enhance stability and to minimize erosion. Drainage Relatively shallow and perched zones of groundwater seepage were observed at-depth within the existing fill deposits. As such, the presence of groundwater seepage should be anticipated, especially in deeper site and utility trench excavations. Based on the soil and groundwater conditions observed at the test sites, temporary construction dewatering of excavations will may be necessary at some locations, depending on the time of year. In our opinion, a perimeter footing drain should be installed around the building foundations. Depending on the height of the building pads relative to finish exterior grades, elimination of the footing drain at some locations may be possible. However, the geotechnical engineer should be consulted prior to considering eliminating footing drains. A typical footing drain detail is provided as Plate 3 of this study. Utility Support and Trench Backfill In our opinion, the existing soils observed throughout the site are generally suitable for support of utilities. The geotechnical engineer should be onsite during utility trench excavation activities to confirm stability along the base of trench excavations. Organic or highly compressible soils encountered in the trench excavations should not be used for supporting utilities. Additionally, large rubble encountered along the base of trench excavations should be removed and replaced with structural fill, if necessary. Utility trench backfill should be placed and compacted to the specifications of structural fill provided in this report, or to the applicable city of utility district specifications. Pavement Sections The performance of site pavements is largely related to the condition of the underlying subgrade. To ensure adequate pavement performance, the subgrade should be in a firm and unyielding condition when subjected to proofrolling with a loaded dump truck. Structural fill in pavement areas should be compacted to the specifications detailed in the "Site Preparation and Earthwork" section of this report. It is possible that soft, wet, or otherwise unsuitable subgrade areas may still exist after base grading activities. Any areas containing unsuitable or yielding subgrade conditions will require remedial measures such as cement treatment, overexcavation and thicker crushed rock or structural fill sections prior to pavement. For relatively high volume, heavily loaded pavements subjected to moderate to high, loaded truck traffic, the following preliminary pavement sections can be considered: • Three inches of hot-mix asphalt (HMA) placed over six inches of crushed rock base (CRB), or; • Three inches of HMA placed over four and one half inches of asphalt treated base (ATB). Earth Solutions NW, LLC