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r MEMORANDUM Richmond, California April 19, 1996 Former Chevron Service Station No. 9-1918 45 East Harding Way Stockton, California Mr. S.L. Hunter San Ramon, CA As you requested, I have reviewed the biologic parameter data recently collected from former Chevron Service Station No. 9-1918, in order to define the degree of naturally occurring subsurface biodegradation characterizing the site. The following comments briefly summarize site conditions, the results of the analysis, and recommendations regarding further activity at the property. A more detailed summary of site conditions, and a review of the former remediation system, is present in a memo dated October 21, 1994. Observations 1) The site is the location of a former Chevron service station which operated from 1953 to February 1988. There are presently eleven monitor wells on-site (MW-1 to -11) , and three wells off- site (MW-12 to -14) (see attached Site Map - Figure 1) . The station was closed in 1988, with the product and waste oil tanks removed at that time. Three additional product tanks (3000, 4000 and 500 gallon capacity) were later discovered and removed in 1988. Another 1000 gallon capacity tank was discovered and removed in 1994. 2) The site is underlain by an interlayered sequence of clayey silt, silty clay, and sandy clay, with discontinuous fine sand layers of variable thickness. Depth to groundwater during the most recent monitoring event (January 23 , 1996) was approximately 41 to 42 feet below ground level (BGL) , with an apparent flow direction to the north/northeast. Following several years of lowered groundwater elevation, the last two years have been characterized by an approximately 8 foot rise in the local water table (see attached '0i Cumulative Table of Well and Analytical Results) . 1