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SECOR www secor com INTERNATIONAL S E C O R INCORPORATED i February 6, 2003 Mr Bob Cochran -�� v 200 6001 Bollinger Canyon Road ENVIRON IV,EN Chevron Environmental Management Company PERMIT/$ER ICES P O Box 6004 San Ramon, California 95843 RE Fourth Quarter 2002 Remediation Systems Status Report Chevron Service Station 9-4275 2905 West Benjamin Holt Drive Stockton, California SECOR Project No 77CH 94275 01 0570 Dear Mr Cochran SECOR International Incorporated (SECOR) presents with this letter, 1) operational data for the soil vapor extraction (SVE) and air sparge (AS) systems which are being utilized to remediate soil and groundwater beneath the subject site (Figures 1 and 2), and 2) an evaluation of the remediation systems effectiveness during the fourth quarter of 2002 (4002) Operation of the SVE and AS systems was Initiated at the site in April 1997 The SVE system has • been disabled and the AS continues to operate A brief description and performance evaluation of the remedial system between September 3, and December 2, 2002 are presented below SOIL VAPOR EXTRACTION SYSTEM The inactive SVE system is comprised of ten SVE wells (VW-1 and GM-1 through GM-9), underground mechanical piping, a 5-horsepower (hp) positive displacement blower, and a 100-cubic feet per minute (cfm) catalytic oxidizer (Figure 2) During 4Q02, the SVE system was shut down due to high groundwater levels The SVE system has not operated since February 1998 Depth to water in the monitoring wells at the site ranged from 9 48 to 12 30 feet below ground surface (bgs) on December 17, 2002 The screened intervals in the SVE wells range from 10 to 13 feet bgs, therefore water levels are currently too high for effective operation of the SVE system AIR SPARGING SYSTEM The AS system Is comprised of nine AS wells (GM-1 and GM-9), underground mechanical piping and a 1 5-hp rotary vane air compressor During 4Q02, the AS system was operational 57% for the reporting period, however in October, November, and December power interruptions shut down the system reducing system runtime The AS system operated at an average flow rate of 20 4 standard cubic feet per minute (scfm) and an average injection pressure of 9 0 pounds per square inch gauge (psig) Remediation system field data sheets are presented in Attachment 1 Air sparge operational data, including flow rate and applied pressure data, are presented in Table 1 Dissolved oxygen concentrations for wells MW-1 through MW-9 are presented in Table 2