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PUBLIC HEALTH SERVICES <br />SAN JOAQUIN COUNTY <br />JOGI KHANNA MD , M.P.H <br />Health Officer <br />P.O. Box 2009 • (1601 East HazeIton Avenue) • Stockton, California 95201 <br />(209) 468-3400 <br />DONNA SANTINI GARDNER <br />1206 STRUCK <br />ORANGE CA 92667 NEW 0 6 1992 <br />RE: Donna Gardner Property SITE CODE: 1864 <br />26056 Thornton Rd. <br />Thornton, CA 95686 <br />San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) <br />has completed review of the "Quarterly Monitoring Report, July through September <br />1992" dated October 13, 1992 prepared by RESNA. PHS/EHD has the following <br />comments for your consideration. <br />Residual soil contamination provides a source of contamination to groundwater. <br />Therefore, any postponement of soil remediation may increase the volume of <br />groundwater which is contaminated. Furthermore, once contaminants reach the water <br />table, they generally float on top of the water and migrate with the water as it moves in <br />its gradient direction. The contaminates may also move vertically up and down with <br />corresponding fluctuations in the water table. The migration and subsequent disposition <br />of contamination may increase the extent of soil contamination, providing a secondary <br />source of contamination to groundwater. <br />The extent of soil contamination has not been adequately defined, since soil samples <br />collected during the installation of monitoring wells, MW1, MW2, and MW3, were not <br />analyzed. These monitoring wells are located closest to the primary source of <br />contamination, the former underground storage tanks. <br />The extent of groundwater contamination has not been defined in the down gradient <br />direction. The most downgradient well, MW4, is also the most highly contaminated with <br />38 ppb benzene and 40,000 ppb TPH-gas. This monitoring well is within 30 feet of the <br />Thornton Water Well #2 which has 203 service connections. <br />Additional investigation will be necessary to determine the boundaries and extent of soil <br />and groundwater contamination. The effect which Thornton Water Well #2 may have <br />on the movement of contamination within the subsurface environment should also be <br />studied. <br />A Division of an Joaquin ( aunty Health Care Services c,