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2 . <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br /> ?.'� •o Unit Supervisors <br /> H <br /> Donna K. eran,R.E.H.S. 304 East Weber Avenue, Third Floor caul Bargman,R.E.H.S.H: { ;< Director <br /> _ - California 95202-2708 Mike Huggins,R.E.H.S.,R.D.I. <br /> t Al Olsen,R.E.H.S. Stockton, Douglas W.Wilson,R.E.H.S. <br /> • C9;�:-='� <br /> V. • Program Manager Telephone: (209) 468-3420 Margaret Lagono,R.E.H.S. <br /> <«oa Laurie A.C otulla,R.E.H.S. <br /> Fax: (209) 464-0138 Robert McCleilon,R.E.H.S. <br /> Program Manager Mark Barceilos,R.E.H.S. <br /> TOM BARBOUR SEP 2 5 Z�OZ <br /> t3271 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 northlnorthwest. SJC/EHD 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 3-2, 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 2725, responsible parties for contaminated underground storage tank sites must complete <br /> a corrective action plan 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 />