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ENVIRONMENTAL HEALTH DEPARTMENT <br /> SAN JOAQUIN COUNTY <br />' <br /> Donna K Heran R Ic.H S Unit Supervisors <br /> 304 East Weber Avenue, Third Floor Carl Borgman,R E H S <br /> Director Mike Huggins,R E H S,R D I <br /> • Al Olsen,R E H S Stockton, California 95202-2108 Douglas W Wilson,R E H S <br /> oR' NSP Program Manager Telephone (209) 468-3420 Margaret Lagorno,R E H S�!aoV Laurie A Cotulla,R E H S <br /> Program Manager Fax (209) 464-0138 Robert McClelton,R E H 5 <br /> 8 Mark Barcellos,R E H S <br /> PAUL SUPPLE APR 0 2 2003 <br /> ARCO PRODUCTS COMP <br /> PO BOX 6549 <br /> MORAGA CA 94570 <br />' RE Arco#6020 SITE CODE 14551 <br /> 1711 E Yosemite Ave(Hwy 120) RO#000665 <br /> Manteca, CA , 95336 <br /> San Joaquin County Environmental Health Department(EHD) has reviewed Quarterly <br /> Groundwater Monitoring Report--First Quarter 2003 and has the following comments <br /> 1 The report covers the groundwater monitoring and sampling event conducted on February 17, <br /> 2003 from the six onsite monitoring wells The depth to first groundwater was approximately 21 <br /> feet below ground surface (' bgs) and the groundwater flow direction and rate was northeasterly <br /> 10 at 0 003ft/ft This pattern has been consistent for this site <br /> MW-6 is located lust northeast and down gradient to the existing underground storage tanks <br /> (UST)and was constructed with a screened interval from 10'bgs to 35' bgs in mostly sands and <br /> some silty sands No other ARCO monitoring wells are located further down gradient from the <br /> USTs or MW-6 <br />' MtBE has been detected in groundwater samples from MW-6 since it's installation in January <br /> 2001 and once only in MW-7, at 0 55 µg11 on November 27, 2002 MtBE concentrations in MW-6 <br /> have varied from a high of 4,200 pg/I in June 2001 to the lowest, 210 pg/i, In March 2002 MtBE <br /> was detected at 340 pg/1 on February 17, 2003 in MW-6 <br /> Nine groundwater sampling events have been conducted for this site since the monitoring wells <br /> have been installed and only MW-6 continues to detect MtBE In the groundwater samples EHD <br /> has determined that the MtBE groundwater plume Is not laterally or vertically defined Please <br /> submit a work plan to Investigate the extent of the MtBE groundwater plume <br /> Please address your submittals and any questions you may have to Michael Infuma, Senior <br /> REHS You may contact Mr Infuma by phone at(209)468-3454 <br /> Donna Heran, REHS, Director <br />' Envlro mental Health De artment <br /> I-11' Michael Infurna, Senior REM Margare agono, REHS <br /> LOP 1 Site Mitigation Unit IV Supervisor <br /> MI/ <br /> c CVRWQCB-James Barton, Sacramento <br /> c SW RCB-CUF--Mark Owens, Sacramento <br /> G ,/ORS Corp-Vernon Elarth, 2870 Gateway Oaks Dr, #300, Sac 95833 <br />