1111 80TH ST SW BLDG SHELL 2016-01-01 MF Import

Cornerstone Columbia Development Co. W-6984 5 July 1990 Page 4 approximately 2 feet. Below the fill we observed the medium dense silty sand (weathered till) which graded to the dense glacial till at approximately 4 feet in depth. Groundwater or subsurface seepage was observed in Test pit TP-3 at a depth of approximately 9 feet. Seepage zones and a seasonal perched water condition may develop above the dense, gray, glacial till horizon during sustained periods of precipitation, when infiltration vertically is impeded by the relatively impermeable till subsoils. It should be noted that groundwater and moisture conditions will fluctuate due to variations in the season, rainfall, site utilization and other factors. 4.0 CONCLUSIONS AND RECOMMENDATIONS We understand the proposed development will include office structures and associated asphalt paved parking. Based on our subsurface exploration program, the parcel is feasible for development from a geotechnical standpoint. utilizing shallow foundations and conventional construction measures. Due to the silty nature of the site soils, the site will be moisture sensitive and highly susceptible to disturbance. It is therefore suggested that site gracing and footing preparation b�i performed during the dry summer months, if. atall possible. Special attention to wet weather construction techniques would bf: required. During wet weather, use of the silty onsite soils as fill would be difficult or impossible, and the near-surface site soils could become disturbed. These c3nditie^.s could require replacement of the wet on-site soils with import, free-„raining fill. 4.1 Site Pr;paration All building and pavement areas, sidewalks, and areas to be graded or receive fill, should be stripped of trees, brush, top soil, dense root accumulations and any undocumented fill and organics. Based on our test pit explorations, we estimate the average stripping effort would be on the order of t to 2 feet, although deeper local areas may exist, especially for removal of tree stumps. and roots greater than 3/4 inches in diameter. All of the brush and vegetation should be removed from the project site and wasted. The top soil could be stockpiled for use in landscaped areas. The native subgrade soil contains a high percentage of silt and will be very susceptible to disturbance when damp or wet. For this reason, site work, including stripping, should be scheduled for the warm, dry, summer months if at all possible.