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PUBLIC tEALTH SERVICES OpAUIy <br /> SAN JOAQUIN COUNTY �'c <br /> ENVIRONMENTAL HEALTH DIVISION <br /> Karen Furst, M.D., M.P.H., Health OfficerP`' <br /> 304 East Weber Avenue, Third Floor• Stockton, CA 95202 '�%Foams <br /> 209/468-3420 FILE COP Y <br /> ROBERT BOUST <br /> UNOCAL—DBG/AMG <br /> 2121 NORTH CALIFORNIA BLVD STE 250 NOV 2 01998 <br /> WALNUT CREEK CA 94596 <br /> RE: Former Unocal #5098 SITE CODE: 2162 <br /> 5606Pacific Ave., <br /> Stockton, CA. 95207 <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS- <br /> EHD) has reviewed the "Work Plan for Supplement Environmental Investigation" <br /> submitted by Environmental Resolutions Inc.,(ERI) on November 12, 1998 and has <br /> the following comments. <br /> Missing from the plan are monitoring well construction details. Diagrams and <br /> specifications are to be included for the wells that detail the size, length, placement <br /> depths, intervals, and materials to be included in the construction of the well. The <br /> "deep" screened monitoring wells proposed in the plan shall not have screened <br /> intervals greater than 5 feet long. In addition, the screened interval of these deep <br /> monitoring wells shall be placed in the most permeable soil layer closest to the <br /> historical deepest (drought) depth to groundwater (-60 feet below grade) during Fall- <br /> 1978. <br /> Soil samples collected from the monitoring well installations shall be additionally <br /> analyzed for the seven oxygenates listed in the enclosed PHS-EHD policy. The <br /> presence of these constituents has not been investigated and is required by PHS- <br /> EHD. All groundwater samples collected from all monitoring wells (new and <br /> existing) are to have all seven oxygenates analyzed by EPA Method 8260 and are to <br /> be in the report due at PHS-EHD at the end of this phase of investigation. Ethanol <br /> and Methanol groundwater samples may be analyzed by EPA Method 8015m direct <br /> injection. Oxygenate detection limits should be in the 1.0 to 50.0 ug/I range. <br /> Soil samples are to be collected and analyzed from at least the current <br /> vadose/saturated zone interface and the historical deepest depth to first <br /> groundwater. Additional soil samples may be required to be analyzed as determined <br /> by PHS-EHD staff during the well construction. Only consecutive five-foot soil <br /> samples that are non-detect for petroleum and oxygenates at LUFT detection limits <br /> can be used for supporting vertical delineation conclusions. <br /> Please report all soil sample data in "mg/kg" only. The detection limit for Total <br /> Petroleum as Gasoline (TPH-G) is 10.0 mg/kg or less. The detection limit for <br /> Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) soil samples is 0.005 mg/kg. <br /> Reports that contain sample data using elevated detection limits should list results <br /> as "less than elevated detection limits" instead of"non-detect'. <br /> A Division of San Joaquin Counry Health Care Services <br />