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FILE COPY <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY Unit supervisors <br /> Donna K.Heran,R.E.H.S. <br /> Carl 13orgman,R.E.H.S. <br /> 304 East Weber Avenue, Third Floor <br /> y DirectorMike Huggins,R.E.H.S.,R.D.I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> P• Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S_ <br /> egZiFOR`' Laurie A.Cotulla,R.E.H.S. Robert McClellon,R.E.H.S. <br /> Program Manager Fax: {209) 464-0138 Mark Barceilos,R.E.H.S. <br /> DONALD SINCLAIR MAR 0 3 2003 <br /> SHIRLEY THOMPSON <br /> 3780 WEST LINNE ROAD <br /> TRACY CA 95376 <br /> RE: Sinclair Trucking SITE CODE: 1916 <br /> 3780 W. Linne Road <br /> Tracy CA 95376 <br /> San Joaquin County Environmental Health Department (SJCIEHD) has reviewed the <br /> "REPORT Groundwater Monitoring 3rd Quarter 2002" dated September 30, 2002 that <br /> was submitted on your behalf by Geological Technics Inc. (GTI) and has the following <br /> comments. <br /> The report documents a routine quarterly groundwater monitoring and sampling event <br /> that took place on August 6, 2002. Analytical results from the groundwater samples <br /> were consistent with previous events, showing consistently high concentrations of <br /> petroleum hydrocarbon contaminants in the shallow monitoring well MW-1, which is <br /> located near the former underground storage tank pit area. The deeper screened <br /> MW-101 was free of contaminants for the second quarter in a row, indicating that the <br /> contamination may not have penetrated the clay interval logged onsite at approximately <br /> 20 feet below surface grade (bsg). The report also presents a comparison of natural <br /> attenuation parameters collected from the five monitoring wells onsite. <br /> The report recommends that the site be considered for closure, based on the apparent <br /> definition of the plume vertically, and laterally in the up- to cross gradient direction. <br /> SJCIEHD does not agree with this recommendation at this time. The concentrations of <br /> benzene in MW-1 are consistently high, and a true down gradient well has not been <br /> installed. In addition, very high concentrations of soil contamination remain onsite. <br /> Analytical results from soil samples collected above 15 feet bsg in MW-1, MW-101 and <br /> MW-4 were all significant. <br /> SJCIEHD notes the occurrence of sand at 10 feet bsg in MW-1 and SB-1. This may <br /> indicate the presence of a thin NNW-SSE trenching channel sand that is close to the <br /> water table. If actually present, the sand stringer may have provided a preferred <br /> migration route toward the NNW or the SSE. SJCIEHD recommends placing borings <br /> 25-30 feet NNW of MW-1 and approximately 20 feet WSW of SB-1, and obtaining soil <br /> and grab grand water samples at approximately 10 feet, 15 feet and 30 feet bsg to <br /> evaluate this potential pathway and the deeper sands in the down- to cross gradient <br /> directions. A 30 foot bsg grab groundwater sample in the area of MW-4 would also be <br /> useful. SJCIEHD recommends consideration of an active remediation at this site. <br /> Please note that choosing a passive remediation alternative, such as monitored natural <br />