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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY Unit Supervisors <br /> Donna K.Heran,R.E.H.S. Carl Borgman,R.E.H.S. <br /> 304 East Weber Avenue, Third Floor <br /> Director Mike Huggins,R.E.H.S.,R.la-I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W. R.E.H.S. <br /> • c-.. �° P <br /> Program Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Fax: (209) 464-013$ Robert McClellon,R.E.H.S. <br /> Program Manager Mark Barcellos,R.E.H.S. <br /> KAREN PETRYNA MG 2 6 2004 <br /> SHELL OIL PRODUCTS <br /> 20945 S WILMINGTON AVE <br /> CARSON CA 90810 <br /> RE: SHELL-BRAND SERVICE STATION <br /> 2375 `VEST GRANT LINE ROAD <br /> TRACY CA 95376 <br /> San Joaquin County Environmental Health Department(EHD) has received and reviewed <br /> Groundwater Monitoring Report—Second.Quarter2004 dated July 27,2004 prepared by Cambria <br /> Environmental Technology,Inc. Four groundwater monitoring welis MW-1,MW-2,MW-3,and <br /> MW-4, all screened from 8 to 23 feet below surface grade (bsg),were installed at the above-referenced <br /> site in January 2003. Methyl tertiary butyl ether(MTBE) has been detected consistently in all 4 wells <br /> since their installation. Concentration of MTBE has risen by an order of magnitude in N1W-1 and <br /> MW-4 since March 2003. The concentration of MTBE has remained relatively constant in the <br /> remaining two wells. Analytical results of the groundwater samples from MtV-1 were 2,800 _ <br /> micrograms per liter(ug/1) of MTBE, 82 ug/l of MTBE for MW-2, 1.4 ug/l for N[W-3, and 120 ug/l <br /> for,MW-4. Groundwater flow direction has been consistently calculated to be in a north-northwest <br /> direction. Tertiary butanol (TBA)was non detect in MW-1 groundwater samples,but the detection <br /> limit was 100 ug/1- Tertiary amyl methyl ether(TAME) was detected at 2.0 ug/1 in MW-1 in the <br /> February 2003 sample,but was non detect at a detection limit of 40 ug/l since February 2003. Other <br /> oxygenates were also non detect at detection limit of 40 ug/l in MW-1. <br /> The lateral and vertical extent of the contamination at this site has not been defined. Submit a work <br /> plan to define the vertical and lateral extent of the contamination to EHD by October 10,2004. <br /> EHD requests that you consult with your laboratory about lowering the detection limit for analyses of <br /> all oxygenates for this investigation and future quarterly sampling events. EHD recommends looking <br /> for a laboratory that could achieve a lower detection limit if your current laboratory could not. <br /> You are also required to conduct a 2,000-foot private/municipal well receptor survey. The survey <br /> should include a properly scaled and labeled map,addresses/locations of the wells,and any well <br /> construction details. Please submit a 2,000-foot well receptor survey by October 31, 2004. EHD <br /> recommends including the receptor survey in the nest quarterly sampling report. <br /> Please contact Jeffrey Wong at (209) 468-0335 if you have any questions. <br /> Donna Heran,REHS,Director <br /> Environmental Health Department <br /> ,�, HS - <br /> JIffe4y%V o Senior REMargaret agorto,RENS <br /> LOP/Site Mitigation Unit Supervisor <br /> c: RWQCB, Central Valley Region—James L.L. Barton <br /> c: Cambria—Aubrey Cool <br />