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envxroso February 29, 1996 Ms. Mary Meays San Joaquin County Public Health Services Environmental Health Division P.O. Box 388 Stockton, California 95201-0388 RE: Work Plan Addendum Former Shell Service Station 141 North El Dorado Avenue Stockton, California WIC No. 204-7524-1509 Site Code: 2436 Dear Ms. Meays: Enviros, Inc. (Enviros) has prepared this addendum to the previously submitted "Remediation Summary, System Shut-Off Request, and Confirmation Soil Boring Workplan" dated September 29, 1995, prepared by Fugro West, Inc. on behalf of Shell Oil Products Company to describe subsurface investigation activities at the subject site (Figure 1 and Plate 2). This addendum was prepared to address issues raised in San Joaquin County Public Health Services (SJCPHS) correspondence dated January 25, 1996. Activities will be performed in accordance with SJCPHS and Central Valley Regional Water Quality Control Board (CVRWQCB) guidelines. Site Description and Background The site is currently occupied by an automotive repair shop and parking lot. The subject site is located on the southwest corner of the intersection of El Dorado Street and Channel Street in Stockton, California. The former fuel underground storage tanks (5 total), were removed from the site in 1981 and the waste oil tank was removed in 1991. Between September 1990 and November 1991, a total of 21 exploratory soil borings (SB-1 through SB-9, MW-1 through MW-5, ASB-1, VP-I through VP-4 and RW-1 and RW-2), were drilled, lithlogged and sampled to evaluate soil quality beneath the subject site {refer to Figure 2 in Fugro Request for Case Closure document dated December 20, 1995). Soil samples were analyzed for Total Petroleum Hydrocarbons calculated as Gasoline (TPH-G) and Benzene, Toluene, Ethylbenzene and Xylenes (BTEX). Detectable TPH-G concentrations ranged from 5,100 to 14,000 parts per million (ppm). Benzene concentrations ranged from ND to 0.9 ppm (Table 1 - Analytical Results: Soil, excerpt from Request for Case Closure). In January 1992, Shell began soil vapor extraction remediation at the subject property to remove residual petroleum hydrocarbons from soil and groundwater. Following approximately 6 months of soil vapor extraction operations, nine confirmation soil borings (designated CB-1 through CB-9), were drilled and sampled to verify soil quality conditions (Plate 2). TPH-G was detected in two of the confirmation borings (CB-8 and CB-9), at concentrations ranging from 200 to 4600 ppm. Benzene was not detected in any of the Enviros, Inc. 270 Perkins Street Sonoma, California Tel 707/935-4850 P.O. Box 259 95476-0259 Fax 707 1.935-6649