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 14 Slabs should be underlain by a capillary break at least 4 inches thick, consisting of clean sand or gravel. In moisture-sensitive flooring areas or areas used to store moisture-sensitive materials, such as carpeted or linoleum covered areas, a 10-mil visqueen moisture retarder should be placed beneath the slab at mid-height within the capillary break material. The visqueen sheet should be sealed along the edges to prevent lateral migration of soil moisture from adjacent non-visqueen areas. Prior to placement of clean sand and slab-on-grade, the visqueen sheet should be thoroughly inspected for cracks, punctures, tears, and holes. If necessary, the visqueen should be replaced or patched to assure a fully functional entity. The contractor should take appropriate curing precautions during the pouring of concrete in hot weather to reduce the potential for the cracking of slabs. We recommend that a slipsheet (or equivalent) be utilized if grouted fill, tile, or other floor sensitive floor covering is planned directly on concrete slabs. All slabs should be designed in accordance with structural considerations. The floor slab should be liberally jointed in accordance with ACI guidelines to help control cracking, resulting from differential movement and concrete shrinkage. 5.7 Pavement Recommendations The subgrade soils for the support of new pavements should be prepared in accordance with the site preparation recommendations (Section 5.1), including scarification and recompaction. Based on assumed pavement loading, we are providing recommendations for both light-duty and medium to heavy-duty pavement sections, which have been successfully utilized for this type of development in the project area with similar traffic loading. For these preliminary pavement sections, we have assumed an R-value of 15 for the subgrade soils. R-value testing should be performed at the time of site grading. Liqht Dutv (Automobile Parkinq), Traffic index of 5.0 • 3 inch Asphalt Concrete • 8 inch Class II Aggregate Base (Caltrans Standard Specs. Section 26) • 12 inches compacted Subgrade Soil Medium to Heavv Dutv (Entrance Lanes and Truck Areas), Traffic index of 6.5 • 3.5 inch Asphalt Concrete • 12.5 inch Class II Aggregate Base • 12 inches compacted subgrade Soil All aggregate base and the upper 12 inches of subgrade should be compacted to at least 95 percent of the maximum dry density as determined by ASTM Designation D1557. All materials and methods of construction should conform to good engineering practices and be in conformance with the requirements of San Mateo County. As an alternate, concrete pavements could also be used at the site. Based on assumed loading, the light duty pavements might be subjected to about 8,000 18-kip equivalent single axle loads (EAL) for a 20-year design life. Medium to heavy duty pavements may receive 65,000 18-kip EAL for a 20-year design life. Both the light duty and medium to heavy duty pavement sections are to be underlain by a minimum of 4 inches of compacted aggregate base.