SITE INFORMATION AND CORRESPONDENCE_FILE 2

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San Joaquin County DIRECTOR Donna Heran,REHS P° 'N Environmental Health Department ASSISTANT DIRECTOR �O- f �o 600 East Main Street Laurie Cotulla,REHS , StocktonCalifornia 95202-3029 y � PROGRAM COORDINATORS Cad Borgman,REHS Mike Huggins,REHS,RDI • C .,_ -- �P Website: www•sjgov.org/ehd Margaret Lagorio,REHS Fo84 Phone: (209)468-3420 Robert McClellon,REHS Fax: (209)464-0138 ,teff Carruesco,REHS, RDI Kasey Foley,REHS August 22, 2008 Stephanie Furgal Chevron Environmental Management Company 6111 Bollinger Canyon Road Room 3652 San Ramon CA 94583 Subject: Former Unocal #0187 437 E. Miner Street Stockton, CA The San Joaquin County Environmental Health Department (EHD) has reviewed the "Membrane Interface Probe (MIP) and Cone Penetrometer Testing (CPT) Subsurface Assessment" (Assessment) dated July 2008, prepared by ENSR and the EHD file for the above subject site and provides the following comments. In the Assessment, ENSR discusses the MIP/CPT investigation, provides laboratory results of soil samples collected by Geoprobe equipment, provides the MIP data logs, CPT logs and Geoprobe logs, provides the survey data of on-site wells, MIP/CPT locations and Geoprobe locations, discusses monitoring well U-17 status, and provides an investigation summary, but does not provide any recommendations for the site based on the information in the report. The information from this investigation shows that there is residual soil contamination that continues to leach into the groundwater. The EHD staff was present when Geoprobe SB-15 was drilled and observed globules of what appeared to be free product in the soil collected at 45 feet below grade. A soil sample was not collected and analyzed from SB-15 at 45 feet and the boring log for SB-15 only indicates odor at this depth. A soil sample was collected from SB15 at 20 below grade, analyzed by the laboratory and found to have 18,000 mg/kg of total petroleum hydrocarbons as gasoline (TPH- g). This sample had the highest contaminant concentrations of the five soil samples that were analyzed during this investigation. Soil boring UL was drilled in this same area in July 1994 and the soil sample collected and analyzed from 45.5 feet below grade in that boring had 19,000 mg/kg of TPH-g. The Assessment states that a comparison of the BTEX concentrations with the TPH-g concentrations in the soil from the borings is indicative that intrinsic biodegradation is occurring. Even if this is the case, the contaminant concentrations must reach water quality objectives in a reasonable time. The Central Valley Regional Water Quality Control Board has suggested that a reasonable time might be 10 years. The contamination in this area is from underground storage tanks that were removed in 1967 so it has existed for over 40 years. In comparing the