Reso13 PC 13-09 2859 Initial Study Mitigated Negative Declaration Kensington

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Proposed Senior Assisted Living Facility PSI Project No. 575-308-2 August 3, 2011 Page 13 include provisions for liberally spaced, vertical control joints to minimize the effects of cosmetic "cracking." We recommend that at the time of excavation for foundation footings, that PSI be retained to observe the exposed soil conditions to verify firm, unyielding bearing conditions. 5.5 Drainaae Considerations Water should not be allowed to collect in the foundation excavations or on prepared subgrades of the construction area during construction. Positive site drainage away from excavation areas should be established to minimize the flow of surface runoff or rain water into the excavations. Undercut or excavated areas should be sloped toward one corner to facilitate removal of any collected rainwater, groundwater, or surface runoff. Following construction, water should not be allowed to pond adjacent to the building foundations or adjacent to concrete flatwork. Positive site drainage of the finish grade should be provided to reduce infiltration of surface water beneath the floor slabs and around the perimeter of foundations for the proposed improvements. The grades should be sloped and surface drainage should be collected and discharged to an acceptable location away from the proposed site improvements. The on-site soils are susceptible to erosion. The contractor should exercise care in creating drainage paths for water during the construction phase of the project. Curbing adjacent to landscaped areas should be designed deep enough to act as a barrier between the landscape irrigation and pavement subgrade soils. Surface run-off from roofs, parking areas, etc., should be tightlined to the storm sewer or other approved disposal areas. 5.6 Floor Slab Support Based on the recommended remedial grading, it is our opinion the proposed floor slab can consist of a conventional slab on-grade supported on a properly prepared low expansive (EI<50) subgrade as described in the site preparation section of this report. It is our opinion that the slab may be designed by the structural engineer using a modulus of subgrade reaction of 100 pci. Based on geotechnical considerations, it is recommended that the interior slabs be at least 4 inches in thickness, and reinforced as specified by the structural engineer. Care should be taken by the contractor to ensure that the reinforcement is placed and maintained at slab mid-height. Floor slabs should be suitably reinforced and jointed so that a small amount of independent movement can occur without causing damage. Due to the presence of low- expansive soil, care should be exercised not to allow these expansive soils to dry back prior to concrete placement. We recommend that the subgrade soils beneath the slab on-grade (and other concrete flatwork) be maintained at a moisture content of about 1 to 3 percent above the soil's optimum moisture content (per ASTM D-1557) to a depth of at least 12 inches. Periodic moisture conditioning may be needed to maintain the proper moisture content of the subgrade soils.