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�1 P Z FNMA . Working To Restore Nature 1710 Mala Street Escalon, CA 95320 Phone (209) 838-3507 FAX (209) 838-3509 August 10, 1994 Ms Mary Meays San Joaquin County Public Health Services Environmental Health Division P O. Box 2009 Stockton, CA 95201 Subject Groundwater Monitoring Report, April through June 1994 26056 Thornton, Road, Thornton, CA, Site Code 1864 Ms Meays This letter report summarizes groundwater monitoring activities conducted by RESNA Industries Inc (RESNA) at the subject site (Figure 1) BACKGROUND On September 6, 1989, three underground gasoline storage tanks were removed at the project site by Western Meter Service of Stockton, California Soil samples were collected beneath each tank and the associated piping Soil samples collected from beneath two of the tanks contained moderate to high levels of ethylbenzene and xylenes (1 2 to 70 parts per million [ppm]) as well as total petroleum hydrocarbons as gasoline (TPHg), at 470-830 ppm Due to the presence of elevated concentrations of petroleum hydrocarbons in the tank pit soil samples, further investigation was required by San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD). In a two-phased approach beginning on November 1, 1990, RESNA personnel advanced six soil borings (MW 1-MW6) to depths ranging from 27 to 30 feet below grade at the project site to accomplish the following 1) Define the lateral and vertical extent of hydrocarbon impacted soils, 2) determine soil stratigraphy, and 3) install groundwater monitoring wells within the uppermost aquifer in order to assess groundwater quality The boring/well locations are plotted on Figure 2. Field methodology and analytical results are discussed in detail in RESNA's Interim Problem Assessment Report, dated January 13, 1992 150081/QUARTLY/2QR 1994 FNL