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2: <br /> ENVIRONMENTAL HEALTH DEPARTMENT <br /> PCU'" SAN JOAQUIN COUNTY <br /> - <br /> _` '•. '2 Donna K.Heran,R.E.H.S. _Unit Supervisors <br /> `N: 304 East Weber Avenue, Third Floor Carl Borgman,R.E.H.S. <br /> < Director <br /> . _ Mike Huggins,R.E.H.S.,R.D.I. <br /> Al Olsen,R.E.H.S. Stockton, California 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> cq�iFo'R��PProgram Manager Telephone: (209) 468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. Robert McClelion,R.E.H.S. �. <br /> Program Manager Fax: (209) 464-0138 Mark Barcellos,R.E.H.S. <br /> KAREN PETRYNA :AUG 2 6 2004 <br /> i <br /> SHELL OIL PRODUCTS <br /> 20945 S WILMINGTON AVE <br /> CARSON CA 90810 <br /> RE: WATERLOO SHELL SITE CODE: 1760 <br /> 4315 WATERLOO ROAD <br /> STOCKTON CA 95205 <br /> Three groundwater monitoring wells MW-2,MW-3, and MW-4 screened from 47 to 72 feet below <br /> surface grade(bsg),were installed at the above-referenced site in November 2001. A cone <br /> penetrometer(CPT)soil boring was also advanced to approximately 92 feet bsg in an attempt to <br /> define the vertical extent of the dissolved Methyl tertiary butyl ether (MTBE) plume. Analytical } <br /> results of the CPT grab groundwater samples were 57 micrograms per liter(ug/1) of MTBE at <br /> approximately 74 feet bsg, 15 ug/1 at 86 feet bsg,and 33 ug/1 at.92 feet bsg. MTBE and Total I <br /> Petroleum Hydrocarbons as gasoline LITH-g) have been consistently detected in MW-1 (screened <br /> from 60 feet to 75 feet bsg) groundwater samples every quarter. Tertiary butanol (TBA)has.also <br /> been detected in MW-1 samples the last four quarters according to the latest quarterly report <br /> GroundivaterMonitoring Report—First Quarter 2004 dated April 9,2004 prepared by Cambria <br /> Environmental Technology,Inc. In contrast,MTBE was detected irregularly and infrequently in the j <br /> remaining three wells.. The highest concentration of MTBE ever recorded was 3.4 ug/1 for MW-2 in <br /> January 2002. The majority of quarterly groundwater samples from MW-2, V-3 and V-4 were <br /> non detect at a detection limit of 0.50 ug/l. Oxygenates other than MTBE and TBA have not been i <br /> analyzed in quarterly sampling since July 2002. <br /> The vertical extent of the MTBE,TPH-g,and TBA contamination plume has not been defined <br /> based on the groundwater sampling results from the CPT,and MW-1. The lateral extent of the <br /> contamination is also not defined. Although MTBE has been'mosdy non detect in MW-2,MW-3, <br /> and MW-4,there is no groundwater investigation in the northeast downgradient groundwater flow <br /> direction (toward the carwash) of the site. A well receptor survey prepared by Cambria in February <br /> 2002 has identified multiple domestic and municipal wells within 2,000 feet of the site. <br /> Submit a work plan to define the vertical and lateral extent of the contamination to San Joaquin <br /> County Environmental Health Department (EHD) by October 1,2004. You are also directed to <br /> include analyses for all 5 oxygenates starting with the Fall quarter 2004. Please contact Jeffrey Wong <br /> at (209) 468-0335 if you have any questions. <br /> Donna Heran,REHS,Director <br /> Environmental Health Department <br /> Jef�'Nong, nior EHSRV Margaret Lagorio,REHS <br /> LOP/Site Mitigation Unit Supervisor <br /> c: RWQCB,Central Valley Region—James L.L.Barton <br /> c: Cambria—Aubrey Cool <br />