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' MW8, MW9, MW 11, UVB-MW 1, and RW I were confirmed using EPA Method 8260, this was done at the request of Harlin Knoll of the San Joaquin County Environmental Health Services The analytical results for the samples are presented in boldface type in Table 1, along with previous data The laboratory analytical report and chain-of-custody documentation are included in Appendix B Detectable concentrations of TPH-g in the groundwater samples ranged from 160 E.cgIL (MW2) ' to 160,000µglL (V2) The concentration of TPH-g in the groundwater sample collected from MW8, located upgradient of the site and adjacent to the Shell service station, was 36,000;ug/L Detectable benzene concentrations ranged from 1 8 ,ug/L (MW 10) ' to 12,000 kzg/L (V2) MTBE, by EPA Method 8020, was detected in groundwater samples at concentrations ranging from 3 1 gglL (MW 10) to 3,500,ug/1-(V2) The laboratory results for MTBE using EPA Method 8260 ranged from 69,ug/L (MW8) to 180 pg/L (MW9) ' Groundwater sample analytical results are shown in Figures 1 and 2 ' 3. GROUNDWATER TREATMENT SYSTEM A vacuum vaporizer well system, known as UVB (Unterdruck Verdampfer Brunnen) has been ' operating at the site since 6 February 1997 A description of the UVB system is included in an installation report issued in June 1997 Between I I September 1997 and 14 November 1997 the UVB system operated a total of 1,626 20 hours Since the start-up of the UVB system, approximately 586 pounds of TPH-g have been stripped from the groundwater Table 2 provides a summary of field data and laboratory analytical results for the UVB system A graphic ' representation of the UVB system performance to date is shown in Figure 4 ' 4 WORK PROPOSED FOR NEXT QUARTER Groundwater elevations will be measured and groundwater samples will be collected in February ' 1998 The samples will be analyzed for TPH-g, BTEX, and MTBE Five wells (P1, MW 1, MW2,MW 12, and MW 13) are subject to a less frequent sampling ' Because of the proximity of wells IW1 and MW4, well P1 is sampled only twice a year Similarly, because of the proximity of wells IW 1 and RW2, well MW2 is sampled only twice a year On the same basis, well MW 1 is sampled only twice a year, because of its proximity to well P2 Petroleum hydrocarbons have not been detected in groundwater samples from well MW 12 since April 1992 Petroleum hydrocarbons were last detected in well MW 13 in August 1994 Therefore, the sampling frequency for both of these wells will be modified to once a year During the February 1998 sampling event, wells PI, MW I, MW2, MW 12, and MW 13 will not be sampled All the other wells will be sampled on a quarterly basis IThe UVB system will be operated and monitored and results reported in the next quarterly report A one-year progress report with an assessment of the remediation accomplished by the UVB ' system will be submitted during the next quarter WPGI 73942 Q1197 TX 2 2