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ENVIRONMENTAL HEALTH DEPAR I NT r SAN JOAQUIN COUNTY G Unit Supervisors Donna K.Heran,R.E.H.S. an,R.E.H.S. - Director 304 East Weber Avenue, Third Floor Carl Bor g Al Olsen R.E.H.S. Stockton California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. ' Douglas W.Wilson,R.E.H.S. Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. Laurie A.CotuIla,R.E.H.S. Program Manager Fax: (209) 464-0138 Robert McClellon,R.E.H.S. Mark Barcellos,R.E.H.S. ROBERT COCHRAN S E p 14 2004 CHEVRON PRODUCTS COMPANY P O BOX 6004 SAN RAMON CA 94583-0844 RE: Chevron Service Station 9-1452 334 East Main Street Ripon, California :; ..................... San Joaquin County Environmental Health Department(EHD) has reviewed the results of the batch groundwater extraction events conducted at the above-referenced site from November 2003 through April 2004. In the monthly reports prepared by Secor International Incorporated (Secor) on your behalf, it is documented that approximately 2,000 gallons of groundwater were extracted from monitoring well MW-8 each month. This is far short of the 8,000 gallons of groundwater extracted per month that EHD approved by letter dated October 16, 2003 for an interim remediation measure to reduce dissolved methyl tertiary-butyl ether(MTBE) at this site. As the MTBE plume appears to be migrating off site toward the west, where the plume is not readily.accessible,you are directed to reinstate the groundwater batch extraction immediately, removing the minimum 8,000 gallons of groundwater from MW-8 each month. Quarterly groundwater results from monitoring wells MW-6S and MW-8 show increasing concentrations of MTBE, tertiary-amyl methyl ether(TAME), and tertiary- butyl alcohol (TBA) from August 2003 through May 2004. This, along with the estimate that only approximately a pound of dissolved MTBE has been removed from the groundwater during the six-month batch extraction events, is an indication that monthly batch extraction, as has been conducted, is not an effective method for controlling the MTBE plume at this site. Therefore, you are directed to conduct a feasibility study that will evaluate at least two alternative methods for restoring groundwater to beneficial use. Provide results from the study, along with your recommendations, to EHD by December 3, 2004. Considering the high concentration of 76,000 micrograms per liter(µg/L) MTBE currently reported for monitoring well MW-6S, you are directed to submit a work plan to EHD by November 1, 2004 to investigate the vertical and lateral extent of contamination in soil and groundwater at this site. This includes assessing the current operating underground storage tank system for leaks and taking corrective action, if appropriate.