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Mr George Takemon Project OF90-002 04 <br /> October 26, 1995 <br /> • Page 3 <br /> The results of laboratory analyses indicated TPHG and BTEX were not detected in groundwater <br /> samples collected from wells MW-9 through MW-11 TPHG and benzene were detected in the <br /> sample from well MW-14 at concentrations of 470 and 28 parts per billion, respectively <br /> Concentrations of TPHG and benzene are shown on Figure 2 <br /> OPERATION AND MAINTENANCE <br /> In April 1995, EMCON began overseeing the operation and maintenance of the remediation <br /> system The remediation system consists of an EI 250 thermal oxidizer, fitted with a catalytic <br /> insert and rated at 250 cfm, and a vacuum blower The remediation system operates under a <br /> Permit-to-Operate issued by San Joaquin Valley Unified Air Pollution Control District <br /> (SJVUAPCD), No N-841-2-0 <br /> The blower extracts soil vapors from wells MW-13 and MW-14 Extracted soil vapors are <br /> combusted in either thermal or catalytic mode prior to discharge to the atmosphere The <br /> remediation system is currently operating in the catalytic mode An air sparge blower was installed <br /> and started up on June 19, 1995, to remediate dissolved hydrocarbons in groundwater Air is <br /> being infected at the rate of 5 cfm into the groundwater <br /> • During the third quarter of 1995, a technician from EMCON conducted three monthly site visits <br /> During the site visits, system operational parameters were monitored (see field data sheets in <br /> Appendix C), a-Lid air samples were collected m September 1995 for laboratory ar lysis (see <br /> analytical reports and chain-of-custody records in Appendix B) 'fables 2, 3, 4, and 5 summarize <br /> the system performance in the third quarter of 1995 Figure 4 shows the cumulative mass of <br /> petroleum hydrocarbons extracted over time <br /> Percentage Uptime <br /> The system has been operational an average of 94 percent of the time during the thud quarter of <br /> 1995 (see Table 2) The system was down briefly while optimizing the performance of the sparge <br /> blower The sparge blower operated an average of 80 percent of the time in the third quarter <br /> 1995 <br /> Soil Vapor Concentrations and Flow <br /> The average flow rate through the system has been 206 cfm during the third quarter (see Table 3) <br /> Induced vacuums were measured at surrounding monitoring wells to estimate the radius of <br /> influence (ROI) of the extraction system (see Table 4) In the second quarter 1995, EMCON <br /> estimated the ROI to be 65 feet by using induced vacuum data In the third quarter 1995, the ROI <br /> is estimated to be around 60 feet The slight decrease in ROI observed can be attributed to lower <br /> • extraction flow rates The concentration of TPHG in the soil vapors decreased from 1,570 <br /> milligrams per cubic meter (mg/m3) in the second quarter to 810 mg/m3, and benzene <br /> concentrations in the soil vapors decreased from 114 mg/m3 in the second quarter to 4 5 mg/m3 <br /> in the third quarter (see Table 3) A total of 1,270 pounds in the third quarter of TPHG, or <br /> approximately 205 gallons of gasoline, were removed during the third quarter 1995 <br /> SAC%N PJ010F9WF900020 4DS-95 PAS l <br />