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GeofogicafTechnics Inc. '•s %ftwl Page 6 City of Escalon Project No. 750.3 February 26,2001 While the blower was in operation, performance parameters were measured which included: vacuum pressure, volumetric airflow, and OVM readings. Vacuum readings were measured and recorded at nearby groundwater monitoring wells (MW-1, MW-2 and MW-3) as well as the vapor extraction wells that were not being used for extraction. This information is summarized in Table 5 of Appendix A. Data obtained from the pilot test was questionable regarding the vacuum influence from wells VEW-3 and VEW-4: • The pneumatic conductivity from shallow extraction well VEW-4 (screened 12-27' bgs) was greater in monitoring well MW-1 than deep extraction well VEW-3, even though the screened interval of MW-1 (55-75' bgs) lies deeper than the screened interval of VEW-3 (39-54' bgs). • The pneumatic conductivity from shallow extraction well VEW-4 was greater in deep extraction well VEW-1 (screened 40-55' bgs) than in shallow extraction well VEW-2 (screened 10-27' bgs). On February 2, 2000, GTI staff visited the site to confirm the labeling of the vapor extraction piping which is currently plumbed to a common traffic box. It was determined that the labeling on wells VEW-3 and VEW-4 were switched. The wells were relabeled to reflect actual site conditions. The data presented in the previously submitted October 10, 2000 Corrective Action Plan has been revised for this work plan. In Table 5, SVE Pilot Test Data, the table headings for VEW-3 and VEW-4 have been switched, and all maps have been updated to reflect actual site conditions (VEW-4 lies 5 feet west of VEW-3). Based on the corrected information for the pilot test, the following conclusions are made: • The site exhibits measurable pneumatic conductivity (vacuum >0.1 inches water) between shallow extraction wells VEW-2 and VEW-4. These wells do not demonstrate pneumatic conductivity to the monitoring wells. • The site exhibits measurable pneumatic conductivity (vacuum >0.1 inches water) between the deep extraction well VEW-1 and monitoring wells MW-1, MW-2 and MW- 3. • Deep extraction well VEW-3 demonstrated pneumatic conductivity to monitoring wells MW-1 and MW-2,but not to well MW-3. • The soil pore spaces are currently full of gasoline vapors with little to no oxygen in the subsurface. This will require that the extraction equipment installed at the site for remediation purposes will need to be run at low flow rates until oxygen is introduced into the subsurface. From experience at other sites, GTI estimates this may take up to a month. • Even though the pilot test was run at low flow rates, 28 to 45 CFM, respectable volumes of contaminants were being removed from the subsurface. When a full extraction system is put into operation with extraction rates of 150 to 200 CFM, removal volumes are estimated to be several hundred pounds per day. • The four vapor extraction wells currently on site should adequately address the vadose zone contamination at the site. The radii of influence demonstrated during the pilot test are illustrated in Figure 8. V �r