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File No. 20-3514-01 kn KLEINFELDER September 11, 1991 sand should be placed beneath floor slabs. In areas to receive moisture-sensitive floor coverings, we recommend that the gravel or sand be covered by a moistureproofing membrane such as "Moiststop, " or equivalent, to act as a vapor barrier. Care should be exercised to avoid tearing, ripping, or displacing the membrane during construction. If the membrane becomes torn or disturbed, it should be removed and patched, or completely replaced. The membrane should be covered with approximately 1 inch of moist sand to protect it during construction and to aid in curing the concrete. For the structures planned, we recommend that floor slabs be a minimum of 4 inches in thickness and be reinforced with at least wire mesh placed at midpoint in the slabs. The actual floor slab thickness and reinforcing design should be provided by the structural engineer. As noted, if floor slabs are used we recommend that french drain _ systems be constructed around the structures to minimize the flow of water beneath the structures. If raised floors are used over Engineered Fill pads, the drain systems can likely be eliminated. However, if there is any chance that standing water could develop beneath raised floors the drain systems should be constructed. E. Site Preparation and Grading - Site preparation should include the stripping and removal of all structures and their foundations, vegetation and debris from the areas of construction. The stripped vegetation and debris should not be incorporated in any of the structural fills. The actual depth of stripping should be determined in the field by a representative of our firm. Voids left by the removal of foundations, trees and their root systems, irrigation lines and - any other buried objects should be overexcavated and backfilled with Engineered Fill placed as recommended below. After stripping and removal of vegetation and debris and before placement of any Engineered Fill, the exposed surface soil within and to a minimum of 5 feet beyond all building areas should be scarified and recompacted to a minimum depth of 6 inches. The recommended minimum degree of compaction is 90 percent of the maximum dry density as determined by the ASTM D-1557 test procedure, at a moisture content near optimum. Any extremely - loose or soft pockets of soil encountered during this process should be overexcavated and recompacted. Fill required to raise the building pads or any other fill required to reach finished grade should consist of on-site soils or imported granular nonexpansive soil having a maximum percentage Copyright 1991 Kleinfelder, Inc. Page 6 of 13