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ENVIRONMENTAL HEAL'T'H DEPARTMENT <br /> SAN JOA UIN COUNTY <br /> P <br /> Unit Srtpervrsors <br /> Donna K Heran,R E H S <br /> N 304 East Weber Avenue, Third Floor Carl Borgman,R E H S <br /> Dt►eelor — 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 /> Program Manager Telephone (209) 468-3420 Margaret Lagorso,R E H S <br /> tr <br /> Foa Laurie A Cotulla,R E H S <br /> Program Manager Fax (209) 464-0138 Robert BMcCleliSnR E S $ <br /> �lAR� �. ���� <br /> PAUL SUPPLE KITTY WALKER <br /> ATLANTIC RICHFIELD COMPANY COS REDEVELOPMENT AGENCY <br /> PO BOK 6549 305 Ir EL DORADO STREET <br /> MORAGA --SCA '94570 STOCK-TON CA 95202 <br /> RE ARCO Station #4493 <br /> 205 N Center Street <br /> Stockton CA 95202 <br /> San Joaquin County Environmental Health Department (SJC/EHD) has received the"Monitoring Well <br /> Installation Report"dated February 4, 2003 and the"Quarterly Groundwater Monitoring Report" (QMR) <br /> dated February 5, 2003 that were submitted on your behalf by URS Group, Inc (URS)and has the <br /> following comments <br /> A work plan prepared by URS to install two dual-completion, down-gradient groundwater monitoring <br /> wells at this site was conditionally approved by SJCIEHD in correspondence dated October 23,2002 <br /> The installation of two wells had been agreed upon at a site meeting in June 2002 During fieldwork to <br /> install these wells in November 2002, extensive underground utilities at one selected location <br /> prevented the installation of one of the wells at that time However, it was always the understanding of <br /> SJCIEHD that an alternative location would be selected and the well would be installed at a later date <br /> The Monitoring Well Installation Report documents the installation of one dual-completed groundwater <br /> monitoring well (MW-11-M/D)located to investigate the lateral and vertical extent of the plume in the <br /> down gradient direction As the gradient at this site has historically shifted east to northeast, two dual- <br /> completed wells were to have been installed to cover this area The report states that MW-1 I-MID <br /> was sampled on December 5,2002 However, Table 2-Fuel Oxygenates Analytical Data MW-1I-MID <br /> reports two sample dates and analytical results for this well One of these sample dates is listed at <br /> September 16, 2002,which is before the wells were installed Please have URS explain this <br /> discrepancy and/or correct the data table in this and all future reports <br /> SJC/EHD will evaluate URS's conclusion that the vertical extent of impacted groundwater has been <br /> delineated in the area of MW-11-MID after additional monitoring events However, both the lateral <br /> extent of impacted groundwater and the vertical extent in the areas of MW-8-M/D and MW-9-MID still <br /> need to be delineated Please submit a work plan to continue the investigation at this site and to <br /> install the additional dual-completed well The work plan is due May 16, 2003 <br /> Donna Heran, REHS, Director <br /> Environmental Health Department <br /> . Lori Duncan, Senior REHS Nuel C Henderson, Jr, RG <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit iV <br /> cc James L L Barton, CVRWQCB <br /> VBrown, Daley& Heft <br /> ernon Elarth, URS <br />