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• 4 <br /> PUBLIC HtALTH SERVIC-�VS <br /> SAN JOAQUIN COUNTY <br /> -Z <br /> ENVIRONMENTAL HEALTH DIVISION ` <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, CA 95202 <br /> 2091468-3420 FILE <br /> ROBERT BOUST <br /> UNOCAL CORPORATION MAY 0 41999 <br /> 2121 N CALIFORNIA BLVD SUITE 250 <br /> WALNUT CREEK CA 94596 <br /> RE: UNOCAL SITE CODE. 1213 <br /> 1665 Pacific Avenue <br /> Stockton, CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHSIEHD) has <br /> reviewed the "Supplemental Site Characterization Report" dated February 26, 1999, prepared by <br /> ARCADIS Geraghty & Miller, Inc. for the above referenced site. <br /> PHSIEHD does not agree that the Site has been adequately characterized and that the <br /> information provided shows that the Site will attain Basin Plan water quality objectives with no <br /> further action. With growing populations and limited sources of water, the issues of defining <br /> contaminant plumes and restoring groundwater quality are important since it is not known when <br /> the water will be used. <br /> The lateral and vertical extent of soil and groundwater contamination from the unauthorized <br /> release of petroleum from the underground storage tanks formerly operated at this site has not <br /> been adequately identified. Feasibility studies of viable remedial alternatives, given the current <br /> site conditions, have not been conducted. Compliance with the Corrective Action Requirements in <br /> the California Code of Regulations, Title 23, Division 3, Chapter 16, Article 11 has not occurred. <br /> The vertical extent of soil contamination on site has been shown; however further analysis of <br /> water from NPI must be completed to evaluate whether the vertical extent of groundwater <br /> contamination on site has been determined. The downgradient extent of impact to soil and <br /> groundwater has not been shown. Soil samples off site and downgradient from below 40 feet of <br /> surface grade have not been analyzed. Analysis of soil samples off site and downgradient from <br /> below 40 feet of surface grade should be conducted to demonstrate the lateral and vertical extent <br /> of soil contamination. <br /> The levels of contaminants in the groundwater sample from monitoring well (MW) 10 (screened <br /> interval 50—60 feet) obtained on February 4, 1999, are between the level of contaminants found <br /> in the water samples collected from 50 feet and 60 feet below surface grade(bsg) on January 5, <br /> 1999, using the Simulprobe during drilling of NP1. The level of contaminants in the groundwater <br /> sample from MW10 are higher than those found in the groundwater sample from MW2 (screened <br /> interval 20—50 feet). <br /> Downgradient monitoring wells do not extend to the most contaminated depth of 60 feet below <br /> surface grade (bsg); so lateral definition at this depth has not been shown. In addition, there are <br /> no monitoring wells downgradient and off site that are screened at 90 feet bsg or deeper to show <br /> that the petroleum contaminants did not impact the deeper water downgradient and off site. <br /> A Division of San Joaquin Count- Health Care Services <br />