9900 19TH AVE SE Geotech Report 2018-01-02 MF Import

Geotechnical Engineering Report Home Base Warehouse - Everett July 31,1997 NCA File No. 213497 Page 5 Hydrologic Conditions Very slight seepage was encountered in Test Pit 16 at 1.8 feet in depth. Seepage was not encountered in any other test pits. Surface water was observed in the wetland. We expect the surface water is perched on shallow till. We would expect ground water to perch on the less permeable glacial till soils during the wetter portions of the year. Perched water occurs when surface water infiltrates through less dense, more permeable soils and accumulates on top of the underlying, less permeable soils. The perched water does not represent a regional ground water "' ,ble" within the upper soil horizons in our opinion. It should be noted that the local volumes of perched ground water will vary, depending upon the time of year and the upslope recharge conditions. CONCLUSIONS AND RECOMMENDATIONS General The unweathered or weathered glacial deposits will provide adequate support of the planned structure using conventional foundation systems. Foundations should be supported on medium dense to dense soil or structural fill extending to these soils. We should be retained to evaluate the exposed soil conditions in the footings prior to placement of the forms. Some dewatering may be necessary prior to structural fill placement in the wetland area. The till soils would not be suitable for fill in the wetland area due to their high fines content and moisture sensitivity. Till soils could be suitable for structural fill in other areas provided moisture contents are near optimum. The soils likely to be exposed during construction are moderately to highly moisture sensitive and will disturb easily when wet. We recommend that construction take place during the drier summer months. Construction may take place during the wet season; however, additional expenses and delays should be expected due to the wet conditions. Additional expenses could include covering of all foundation subgrade areas with rock or gravel, and importing and exporting additional material. Site Preparation and Grading Site preparation and grading should consist of stripping the vegetation and topsoil layer in pavement and ibuilding areas. This material should be wasted off site, or stockpiled for later use as landscaping fill. ( Cut areas should then be cut to proposed grade. In areas where the exposed surface does not consist of NELSON-COUVRETTE & ASSOCIATES, INC.