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I ?- n <br /> LIM � <br /> PUBLIC HEALTH SERVICtS ,oPQ�,N , <br /> SAN JOAQUIN COUNTY r... <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 /> 209/468-3420 <br /> KAREN PETRYNA MAY 1 9 2000 <br /> C/O EQUIVA LLC <br /> PO BOX 7869 <br /> BURBANK CA 91501-7869 <br /> RE: SHELL STATION SITE CODE: 506313 <br /> 1071 NORTH MAIN STREET <br /> MANTECA CA <br /> San Joaquin County Public Health Services Environmental Health Division (PHS/EHD) has recently <br /> reviewed the files associated with the site referenced above. Although groundwater monitoring is <br /> continuing, the plume is undefined vertically and laterally. PHS/EHD provides the following <br /> recommendations and directives. <br /> Data from cumulative tables document concentrations of MtBE in ground water from monitor well MW-1 <br /> exceeding established Maximum Contaminant Levels (MCL's) for this compound. Concentrations are <br /> variable ranging from<5.0 ug/l to 2000 ug/l since April of 1998. Lower concentrations of MtBE have been <br /> reported from MW-2 and MW-3. Depth to water has varied from 15 to 20 feet bgs. Groundwater flow <br /> direction has remained relatively consistent in a southwesterly direction. MW-1 is located north <br /> (upgradient)of the former UST cavity. Low concentrations of tetrachloroethene (0.644 ug/1)have also been <br /> reported in groundwater from MW-2. No monitor wells are located directly downgradient from MW-1 or <br /> MW-2. <br /> PHS/EHD directs you as the responsible party to fully characterize the hydrocarbon plume at this <br /> site. Off-site access agreements will be necessary. Please submit a workplan and monitor well permit <br /> applications to install additional groundwater monitor wells both on-site and offsite. The workplan <br /> must be submitted to PHS/EHD no later than June 19,2000.Report the results of your investigation <br /> to this agency within 30 days of completion of the approved scope of work. <br /> Boreholes should be continuously cored and sampled focusing on groundwater in high hydraulic <br /> conductivity strata. All wells installed and surveyed shall be referenced to an appropriate and designated <br /> benchmark. Well screen intervals should not exceed 20' in total length and should not create a potential <br /> vertical conduit. <br /> You are requested to properly characterize the hydrogeology and groundwater flow conditions in the <br /> vicinity of your site. We also request that you evaluate local groundwater flow conditions and establish a <br /> site-specific localized flownet that is dependent on hydrogeologic conditions and is reflected on geologic <br /> cross sections and fence diagrams. You are required to complete a well receptor survey in the area <br /> (2000-foot radius). The receptor survey must be completed by July 1, 2000. Additionally, you are <br /> required to prepare a rose diagram for groundwater gradient at this site, plot it on the groundwater contour <br /> maps. Plot and Cross Section drawings shall show the location of former and present UST systems. <br /> A Division of San Joaquin County Health Care Services <br />