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PUBLIC HEALTH SERVICES ,oP �o <br /> SAN JOAQUIN COUNTY <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 /> JUL 2 8 2000 <br /> KAREN PETRYNA <br /> EQUILON ENTERPRISES, LLC <br /> PO BOX 7869 <br /> BURBANK, CA 91501-7869 <br /> RE: INVESTIGATION WORKPLAN APPROVAL SITE CODE: 506313 <br /> SHELL SERVICE STATION <br /> 1071 MAIN ST <br /> MANTECA,CA <br /> San Joaquin County Public Health Services Environmental Health Division(PHS/EHD)has reviewed the <br /> Investigation Work Plan by Cambria Environmental Technology,Incorporated dated June 19,2000. <br /> PHS/EHD provides the following comments and directives. <br /> Analytical data from the site listed above confirms the presence of petroleum hydrocarbons (MtBE) in <br /> groundwater.PHS/EHD has approved the June 19,2000 workplan with the following conditions. <br /> 1) The proposed depth for all pushpoint boreholes are 45 feet below grade surface (bgs) unless a <br /> "competent aquitard is encountered, such as a low permeability clay greater than 3 feet in thickness... ". <br /> Alluvial deposits in the central valley are rarely continuous on a regional scale and as such should not be <br /> considered a barrier to hydraulic flow laterally or vertically. <br /> 2) Soil and groundwater sample collection and analyses proposals may not cost effectively <br /> characterize the plume at this site. The workplan proposes a capillary fringe soil sample and a groundwater <br /> grab sample "a few feet below the top of the water table"from each borehole. PHS/EHD recommends that <br /> boreholes be continuously cored and samples of groundwater and soil be submitted to a certified laboratory <br /> from significantly different stratigraphic units in each borehole to best evaluate contaminant distribution and <br /> transport potential from surface to total depth. From previous investigations a potentially high hydraulic <br /> conductivity(coarse grained sand/gravel)stratigraphic unit is present at approximately 30-35 feet bgs in the <br /> saturated zone. High hydraulic conductivity saturated zones must be sampled and analyzed. <br /> 3) Multi-level discrete length monitor wells may be required to better understand transport <br /> mechanics. Please allow site specific hydrogeologic features to dictate sampling and monitor well <br /> construction detail. <br /> Should you have questions regarding this correspondence please contact Ron Rowe at (209) 468-0342. <br /> Please contact PHS/EHD at least 48 hours in advance to schedule field activities. <br /> Copies of all reports and workplans should be submitted to the CVRWQCB,Attn: Marty Hartzell. <br /> Donna Heran,REHS,Director <br /> Environmental Health Division <br /> 40� <br /> Ronald Rowe g g P Sr.REHS Margaret cu ervisor <br /> Site Mitigation Unit Site Mitigation Unit <br /> CC: Cambria-Stephan Bork <br /> CVRWQCB-Marty Hartzell WORD/1071MAIN/WP2LTR <br /> A Division of San Joaquin County Health Care Services <br />