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KLEINFELDER Several methods exist to moisture condition the expansive clay soils. Generally, if construction is performed during the winter or early spring months, December through April, the surface and near-surface soils are usually adequately moisture conditioned because of rainfall. However, if moisture conditioning is necessary, long-term sprinkling, with dikes to control runoff, generally produces uniform results. This method can take time however, often on the order of several days. If this alternative is selected, we recommend that moisture conditioning be performed no more than three days prior to the placement of nonexpansive Engineered Fill, floor slabs, and/or exterior concrete flatwork. Moisture tests should be taken prior to placement of the moisture vapor barrier and reinforcing steel to confirm that the elevated moisture content has been achieved. We stress that weather conditions, i.e., temperature, wind, humidity, etc., at the time of moisture conditioning will have an impact on the amount of time allowed between moisture conditioning and floor slab placement. Generally, moisture tests should be taken no more than three days prior to floor slab placement. However, in hot and/or windy weather moisture tests should be taken no more than approximately 24 hours prior to floor slab placement. We recommend our firm be contacted prior to moisture conditioning in order to provide consultation regarding the time frame for moisture testing. It is important that the subgrade soils under exterior concrete flatwork be moisture conditioned in the same manner as recommended for floor slabs. Moisture conditioning should extend at least 2 feet beyond flatwork outlines. It is also recommended that exterior flatwork be placed in approximately square patterns not more than approximately 200 square feet in size. Suitable divider strips or other appropriate methods should be used at placement joints. Positive drainage away from concrete flatwork should also be provided. IX. SUMMARY OF GEOLOGIC HAZARDS The site is not located within a fault rupture hazard zone as delineated by the Alquist-Priolo Earthquake Zoning Act, and no known active faults traverse the site or surrounding area. The California Division of Mines and Geology (DMG) suggests a maximum peak ground acceleration of at least 0.20g be assumed for anywhere in the valley. A "Probabilistic Seismic Hazard Map" published by DMG indicates there is a 10 percent probability that the site will realize a peak horizontal ground acceleration of between .10g and 0.20g within 50 years. On the basis of our experience in this area and on our review of available literature, the residential structures should, as a minimum, be designed to meet seismic requirements stipulated by the current Uniform Building Code(UBC) for Seismic Zone 3. The site coefficient according to UBC Table 16-J is SD- 20-4280-0 I.GO I 12019R 150 D.20-4280-01.G01/2019R150 Page 8 of 12 Copyright 1999 Kleinfelder,Inc. April 14, 1999