SITE INFORMATION AND CORRESPONDENCE

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Chevron Chevron , Chevron U.S.A.Products'Companp 6001 Bollinger Canyon Road May 20, 1996 Building L San Ramon,CA 94583 P.O.Box 50049 Ms.Mary Meays San Ramon,CA 94583-0804 San Joaquin County Environmental Health Marketing—Northwest Region P.O. Box 388 Phone 510 842 9500 Stockton, CA 95201-0388 Re: Former Chevron Station#9-1918 45 East Harding Way, Stockton CA Attached groundwater monitoring report(Blaine Tech, 5/16/96) Attached Summary of Biodegradation Analysis(CRTC, 4/19/96) Dear Ms.Meays: Please find attached a report dated May 16, 1996,which was prepared by Chevron's consultant,Blaine Tech Services Inc. (Blaine Tech),to describe the results of groundwater monitoring that was performed at the subject site on April 30, 1996. During their April site visit,Blaine Tech gauged fourteen and sampled thirteen of the fourteen site-related wells. Well MW-7 did not contain enough water to be sampled. Groundwater elevations beneath the site were high enough such that, wells MW-I,MW-3 through MW-6, and MW-8 could be sampled. These wells had not been sampled over the past seven years due to the depth of groundwater being below their screened intervals. All groundwater samples were analyzed for the presence of TPHGas and BTEX constituents. In April,the measured direction of groundwater flow was variable.Previous measurements have shown a consistent direction of east-northeasterly. Detectable concentrations of dissolved hydrocarbons were measured at wells MW-4, MW-6,and MW-13. The groundwater results at all other wells were non-detect. The measured concentrations at well MW-f 3 were consistent with those detected during previous site monitoring events. The measured levels at wells MW-4 and MW-6 were significantly lower than the levels last measured in 1989. The concentrations measured at the same depth in MW-4 during 1989 were the highest concentrations ever measured in groundwater beneath the site. The observed decrease in contaminant concentrations at MW-4 (and other wells)provides conclusive evidence for the effectiveness of the previous remediation efforts. As such, no further active remediation is warranted. Attached you will also find, a document which was prepared by Chevron Research and Technology Company(CRTC),that was provided to you during our meeting at your office on April 25, 1996. The contents included an evaluation of groundwater data that were collected at the subject site to measure the occurrence and potential for intrinsic bioremediation, a summary of findings, and recommendations for groundwater remediation and monitoring. The summary report by CRTC noted that significant hydrocarbon mass reduction has been achieved in vadose zone soils. The mass reduction resulted from nearly two years of soil vapor extraction. In a separate study reported on October 21, 1994, CRTC calculated that 12,000 pounds of hydrocarbons were removed as a result of soil vapor extraction. According to Pacific Environmental Group, in their Corrective Action Plan dated November 30, 1995, eighty five percent of the original hydrocarbon mass beneath the site has been removed. Of the estimated 26,000 pounds of hydrocarbons thought to be