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 10 should then be scarified to a depth of about 12 inches, be moisture treated to approximately 1 to 3 percent above the soils optimum moisture content, and then be compacted to at least 90% of the soil's maximum dry density, per ASTM D-1557. The excavated soils and any approved import soil should then be replaced in maximum 8 inch lifts as compacted, engineered fill in accordance with the recommendations of"Section 5.2 — Engineered Fill." In proposed new pavement areas, after site clearing and cutting to subgrade level, the subgrade soils should be proofrolled with a heavy rubber tired piece of construction equipment to look for evidence of subgrade deflections and /or instability (pumping). If excessive deflections or instability are identified during proofrolling, the soils within the affected areas should be removed to expose a suitable subgrade. The exposed subgrade within the pavement areas should then be scarified to a minimum depth of 12 inches, moisture conditioned to 1 to 3 percent above optimum moisture content and recompacted to a minimum 90 percent relative compaction (based on ASTM Test Method D1557). The top one foot of the pavement subgrade should be compacted to at least 95 percent relative compaction prior to pavement construction. We recommend that at the time of initial demolition, site stripping and grading, that PSI be retained to observe the excavations and subgrade conditions to verify that no potentially deleterious soft soils, abandoned foundation elements, buried debris or other unforeseen conditions are present. PSI should observe the bottom of all excavations in order to confirm that all unsuitable materials have been removed. All grading operations should be performed in accordance with our recommendations, the requirements of the current edition of the CBC, and local governmental standards which have jurisdiction over this project. 5.2 Enqineered Fill Fill materials, including both native and import soil, should be free of organic or other deleterious materials, and have a maximum particle size of 3 inches or less. All fill must be "low-expansive" with an Expansion Index of less than 50. Based on our assessment of the site soils it is our opinion that these soils are suitable for use as engineered fill. We recommend that representative samples of any proposed import soils be submitted to PSI for geotechnical characterization testing and approval prior to the start of grading and import of this material. Structural fill should be moisture conditioned to about 1 to 3 percent above optimum moisture content prior to compaction as engineered fill. All structural fill should be compacted to at least 90 percent of the maximum dry density as determined by ASTM Designation D1557. The subgrade soils in all areas to receive fill or support surface improvements should be scarified to a depth of 12 inches, moisture conditioned to about 1 to 3 percent above optimum moisture content and compacted to at least 90% of the soil's maximum dry density, per ASTM D-1557. Fill should be placed in maximum loose lifts of 8 inches, moisture conditioned and compacted as discussed above. If water must be added, it should be uniformly applied and thoroughly mixed into the soil by disking or scarifying. Each lift of compacted, engineered fill should be tested by a