Laserfiche WebLink
PUBLIC HEALTH SERVICES <br /> SAN JOAQUIN COUNTY n <br /> ENVIRONMENTAL HEALTH DMSION <br /> Karen Furst, M.D., M.P.H., Health Officer <br /> 304 East Weber Avenue, Third Floor • Stockton, C �Z02� o �/ <br /> 209/468-3420 LL i <br /> PETER J NIEMIEC ESQ <br /> UNOCAL CORPORATION JAN 0 4 ',999 <br /> 376 S VALENCIA AVE <br /> BREA CA 92823 <br /> RE: UNOCAL#6981 SITE CODE: 1217123 <br /> 4707 Pacific Ave. <br /> Stockton, CA <br /> San Joaquin County Public Health Services, Environmental Health Division (PHS/EHD) has <br /> reviewed our files for the above referenced site and provides the following comments. <br /> The vertical extent of soil and groundwater contamination at this site has not been defined. Soil <br /> contamination was evidenced to 50 feet below surface grade (bsg) by analysis of soil samples <br /> from borings B8, B11, B12, B13 and B18. Soil from 56.5 feet bsg in 1318 had benzene at.055 <br /> parts per million (ppm). <br /> In previous correspondence PHS/EHD directed you to install additional monitoring wells to define <br /> the extent of the groundwater contaminant plume, drill soil borings so soil samples could be <br /> collected and analyzed to evaluate the effectiveness of the remediation system and determine the <br /> current radius of influence of the vapor extraction system. <br /> In October 1997, TOSCO, who has not been identified as a responsible party for this site, <br /> requested a case review for closure by the State Water Resources Control Board (SWRCB) <br /> Cleanup Fund Manager. In December 1997, an addendum to a September 1997 work plan was <br /> submitted, performance of the work proposed was contingent on the SWRCB response to the <br /> request for site closure. In December 1997, PHS/EHD requested enforcement action for this site <br /> by the San Joaquin County District Attorney's office. <br /> During 1998 sampling of the monitoring wells and operation of the vapor extraction system has <br /> continued. The vapor extraction system has been operated intermittently the last six months <br /> because influent contaminant concentrations were low. Although, groundwater sample results <br /> from July 1998 are lower than previous sample results there are many variables that can affect <br /> these results and more information is needed to evaluate the extent of contamination remaining at <br /> this site. <br /> Since October 1993, the screened intervals of the monitoring wells have been below first <br /> groundwater. By July 1998 the monitoring well screens were 20 feet below first groundwater. <br /> Groundwater samples have been collected from vapor extraction wells VW1, VW3 and VW4, <br /> which have well screens intersecting first groundwater, several times since July 1996 and the <br /> analytical results have shown lower levels of contamination than those of the groundwater <br /> samples from the monitoring wells. This may be due to the difference in the screened intervals of <br /> the wells and in the filter pack around the well screen. Also the effect of vapor extraction from <br /> VW4 prior to obtaining a groundwater sample is not known. <br /> A Division of San Joaquin County Health Care Sevices <br />