1125 80TH ST SW 2016-01-01 MF Import

Cornerstone Columbia D• 3lopment Co. W-6984 5 July 1990 Page 8 4.4 Slab On Grade Floors We anticipate that development of this parcel would include slab on grade floor construction. The subgrade to support the grourp levei floor slab should be prepared in accordance with the previous Site Preparation recommendations (Section 4.1). The slab on grade should be founded on a prerolled medium dense native soil or structural fill compacted to at least 90 percent density (ASTM:D-1557). We recommend that the floor slab be underlain by at least 4 inches of clean, washed rock, or pea gravel to serve as a capillary break and working surface. Additionally, an under slab impervious moisture barrier should be utilized to protect the slab from dampness. If the base of the floor slab is set at or below adjacent exterior grades, perforated pipe perimeter drains should be installed around the building foundations as outlined in the following Drainage Considerations (Section 4.5) of this report. i I 4.5 Drainage Considerations At this site, the silty, glacially consolidated soils at depth may result in development of a "perched" grcundwater condition. Additionally, traffic across the soils when they are damp or wet will lead to the disturbance of the otherwise firm strata. Therefore, prior to site work and construction, the contractor should be prepared to divert surface water runoff around exposed ground surfaces. This should include diversion of water runoff from the adjacent property west of the site, which presently drains onto the subject property. Additionally, if areas of spring activity or seepage are encountered during construction in excavations; culverts, subdrains, or pump sump installation may be necessary to transport the water pass the area being developed. In planning, grades should be set so that water does not collect adjacent to the buildings. Instead, the ground should be sloped downward away from the structures so that runoff may be carried to a suitable discharge. The base of all retaining walls, and building locations where the floor level is at or below adjacent outside grade, should be protected from seepage or groundwater by a perforated footing drain pipe at the base elevation. With the sloping site and possible perched ground water, we anticipate that i footing drains could be required for most buildings on the site. The perforated drain pipe should be totally surrounded by at least 6 inches of pea gravel. This foundation drain system should be installed to discharge via tight line by gravity to a storm sewer or other