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ENVIRONMENTAL HEALTH DEPARTMENT ' SAN JOAQUIN COUNTY • '. � ..OG Ullif Supervi.vors Donna K. Heran,R.E.H.S. Directo), 304 East Weber Avenue, Third Floor Carl Borgman, R,EAKS. Al Olsen,R.E.H.S. Stockton, California 95202-2708 Mike Huggins,R.E.KS ., RD.I. Fragrant mallagwr Douglas W. Wilson,R-13.1-[�S. Laurie A.Cottilla,R.E.H.S. Telephone: (209) 468-3420 Margaret L',jgorjo, R.F.A.S. Progrant Managrr. Fax: (209) 464-0138 Robert McClellan, R.E.1-i-S. Mark Barcellos, R,E,H.S. 0 7 2005 DARIN ROUSE PAUL SUPPLE CHEVRON PRODUCTS COMPANY ATLANTIC RICHFIELD COMPANY PO BOX 6004 BLDG V PO BOX 6549 SAN RAMON CA 94583 MOPLAGA CA 94570 C (apy RE: Chevron #9-4275 and ARCO #2133 2905 and 2908 Ben Holt Drive Stockton CA 95207 The above referenced contaminated underground storage tank sites have applied to the California State Water Resources Control Board (SWRCB) Clean Up Fund for designation as a co-mingled plume. The claim reference number for this application is CP0034. Per the conditions of the application, the claimants are required to have entered into a written agreement to provide for a coordinated corrective action, and are to proceed with that action as soon as practicable. San Joaquin County Environmental Health Department (SJC/EHD) has reviewed the respective files for these two sites and found that neither site has completed definition of their respective contaminant plumes. Neither site has conducted a vertical investigation of the groundwater contamination. Despite repeated directives by this agency to do so, Chevron has declined to investigate the lateral extent of the groundwater contamination reported over the years in monitoring wells MW-4 and MW-3. Review of soil analytical data from the Chevron site indicates widespread contamination onsite, residing primarily from 15 to at least 31 feet below surface grade (bsg). The maximum depth of soil contamination assessed at this site has been in soil boring (VDSB-1), the only one extending to 45 feet bsg. Hydrocarbon contamination in soil samples collected from VDSB-1 at 31.5 feet and deeper was not detectable,' however, soil samples,collected at 35 and 31 feet bsg from monitoring wells MW-1 and MW-2.respectively did report detections of petroleum hydrocarbon contamination. Review of soil analytical data from the ARCO site indicates that vertical definition of the soil contamination was not completed. As previously noted, the vertical' extent of impacted groundwater on the site has not been assessed. CPT data collected offslte indicates the vertical extent of impacted groundwater in that area to be between 40 and 68 feet bsg, but the area assessed has not been demonstrated to be in the predominant contaminant migration pathway from either site. ARCO #2133 conducted interim remediation by groundwater extraction, and has been conducting air sparging since 1995. A conditionally approved draft final remediation plan submitted on behalf of ARCO.to conduct soil vapor extraction was implemented, but could not be continued due to rising groundwater levels. Chevron #9-4275 has been conducting air sparging under a conditionally approved corrective action plan (CAP)that was never fully implemented. As with the ARCO site, rising groundwater levels made soil vapor extraction of the contaminated soil intervals impossible. Plea i se demonstr6te that air sparging without benefit of soil vapor extraction is providing a beneficial result and is not merely spreading and diluting the plume of impacted groundwater.