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A 1117 Lone Palm Avenue, Suite B (YVATC Modesto, CA 95351 www.atcassociates.com 209-579-2221 A s s o c i a T e s I N C . Fax 209-579-2225 Environmental, Geotechnical and Materials Engineers bgs. Sandy clay was encountered from approximately 80 to 85 feet bgs. While drilling the borehole for MW15, sand was encountered from approximately 85 to 136 feet bgs and was underlain by clay from approximately 136 to 141 feet bgs. Sand was encountered from approximately 141 to 154 feet bgs . 2 . Groundwater in the uppermost water bearing zone appears to be semi-confined. Groundwater flow in the shallow zone beneath the site tends to be somewhat variable with eastward and northward components, but generally trends northeasterly. The magnitude of groundwater flow in the shallow zone has been calculated to range between 0.001 ft/ft to 0 .0017 ft/ft, or approximately 5 to 9 ft/mile. Groundwater flow in the intermediate zone beneath the site tends to be toward the south. The magnitude of groundwater flow in the intermediate zone has been calculated to range between 0.0003 ft/ft to 0.016 ft/ft, or approximately 2 to 84 ft/mile. A summary of groundwater monitoring data is presented in Table I and laboratory analytical results of groundwater samples are summarized in Table 2 . 3 . According to technical reports previously prepared by WIC, Inc. , petroleum hydrocarbon- affected soils are generally present in the vicinity of the former USTs and the locations of MWl through MW4. Petroleum hydrocarbon-affected soils (low concentrations) are present at locations away from the former USTs primarily in the vicinity of the capillary fringe at approximately 50 feet bgs, based on water table conditions in November 2004. The horizontal extent of petroleum hydrocarbons and the presence of these contaminants in the capillary fringe are indicative of groundwater impact and advection. A summary of laboratory analytical results of soil samples collected by ATC is presented in Table 3 . 4 . The shallow groundwater plume appears to be adequately defined in all directions except to the south. Benzene is periodically detected in groundwater samples collected from MW3, and MTBE and 1 ,2-DCA have always been detected in the groundwater samples collected from MW3 and MW9 . These wells are located in the southern portion of the site. Monitoring wells MWl and MW8 continue to be the most impacted with respect to BTEX constituents, and MW2 and MW3 are the most impacted with respect to MTBE and 1 ,2-DCA. The intermediate groundwater plume appears to be generally defined to the northwest in the vicinity of MW12 and MW4, but not well defined in other directions . Monitoring well MW4 is slightly impacted, and MW5 and MW6 continue to be the most impacted wells. The vertical extent of impacted groundwater appears to be less than 120 feet bgs. The locations of the monitoring wells are shown on Figure 3 . 3.0 REMEDIAL ALTERNATIVES Based on the results of previous investigations and professional experience, ATC recommends for consideration one remedial alternative for soil remediation, and two remedial alternatives for groundwater remediation at this site. The selected soil remedial alternative is soil vapor extraction (SVE). The selected groundwater remedial alternatives groundwater extraction and ozone sparging. A summary of each alternative is presented below: s:\environmental\28349\reports\feasibility.doe 3