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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOA UIN COUNTY <br /> �••��'•.0 1C Unit Supervisors <br /> H <br /> Donna K. eran R. . . . <br /> EHS304 East Weber Avenue, Third Floor <br /> Director Carl Horgman,R.E.H.S. <br />' Mike Huggins,RE-H.S.,R.D.J. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H_S. <br /> c4 =a�P • Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> C o Laurie A.Cotulla,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McClellan,R.E.H.S. <br />' Program Manager Mark Barcellos,R.E.H_S: <br /> TOM BARBOUR SEP 2 2l OZ _ <br /> 3271 MADROAN AVE <br /> MERCED CA 95340 <br /> RE: Bobs Muffler & Radiator SITE CODE: 2247 <br />' 466 Moffat Blvd. <br /> Manteca CA 95336 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has reviewed the most <br />'. recent site investigation and quarterly groundwater monitoring reports that have been <br /> prepared by Advanced GeoEnvironmental, Inc. (AGE) on your behalf and has the <br /> ' following comments- <br /> In October 2001 and February 2002 a total of five additional monitoring wells were <br /> installed to further investigate the vertical and lateral extent of petroleum hydrocarbon <br /> ' . contamination in groundwater at this site. Monitoring wells MW-7, MW-8, MW-9 and MW- <br /> 10 were built to total depth of 35 feet below surface grade (bsg),with 20 feet of screened <br /> casing. These wells were installed to monitor the lateral extent of the shallow plume. <br /> ' Monitoring well MW-6 was built to total depth of 50 feet bsg, with 5 feet of screened <br /> casing. This well was installed to monitor the vertical extent of the plume. Subsequent - <br /> quarterly groundwater monitoring and sampling events indicate that the vertical extent of <br /> ' the dissolved contaminant plume has been defined, and that the lateral extent has been <br /> mostly defined, except towards the north/northwest. SJCIEHD has noted that while the <br /> overall analyte concentrations across the site have been declining, the detection limits for <br /> ' the tertiary butyl alcohol (TBA) analysis have been going up. With the overall reduction in <br /> concentrations, less matrix interference and a reduced detection limit-would be expected, <br /> rather than an increased detection limit. Does AGE have any comments on or <br /> ' explanation for this? <br /> Review of soil sample analyses from this site indicates that soil contamination exists to a <br /> depth of approximately 25 feet bsg at various sample locations across the site.- The <br /> ' maximum concentration detected was 670 milligrams.per kilogram (mg/kg) total petroleum <br /> hydrocarbons as gasoline (TPHg) in the 20-foot bsg sample from boring B-2,which was <br /> located in the former underground gasoline storage tank pit area. Soil samples.collected <br /> ' from below 25 feet bsg have contained low contaminant concentration or have been non- <br /> detect for constituents analyzed, suggesting that the contaminants in the 20-foot samples <br /> are capillary fringe/smear zone contaminants of limited vertical extent. <br /> Per California Code of Regulations, Title 23, Division 3, Chapter 16, Article 11, Section <br /> . 2725, responsible parties for contaminated underground storage tank sites must complete <br /> ' a corrective action pian that includes an assessment of the potential impacts from their <br /> site and a feasibility study to determine the most cost effective remedial alternative for <br />