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HEALTH% EPARTMENT <br /> ENVIROPAENTAL <br /> a�•t" SAN JOAQUIN COUNTY program Coordinators <br /> .G R.E.H.S. <br /> z a Donna K. Heran, R.E.H.S. 304 East Weber Avenue,Third Floor Mike 1lugg g R.E.H.S.,R.A.I. <br /> Director <br /> Stockton,California 95202-2708 Margaret Lagorio, R.E.H.S. <br /> Laurie A. Cotulla,R.E.H.S. Robert McClellon, R.E.H.S. <br /> •.cq:. :�\p. Assistant Director Telephone: (209)46$-3420 R.E.H.S. <br /> �rFOR Fax: (209)464-0138 Jeff Carruesca, <br /> Website:www.sigOv.org/ehd/ Kasey Foley, RY.H.S. <br /> Nov 0 3 2006 <br /> DON PRATT <br /> ENVIRONMENTAL BUSINESS MANAGER <br /> ATLANTIC RICHFIELD COMPANY <br /> P O BOX 1257 <br /> SAN RAMON CA 94583 <br /> RE: ARCO #5469 SITE CODE: 0710 <br /> 130 S. Wilson Way <br /> Stockton, California <br /> The San Joaquin County Environmental Health Department (EHD) had directed <br /> by letters dated 01 December 2004 and 31 August 2005 preparation of a site <br /> conceptual model (SCM) for your site; the latter letter also directed that an <br /> evaluation of the ozone injection system be made and reported. The SCM was <br /> due 03 January 2006. The SCM has not been submitted, but an ozone sparge <br /> (OS) system effectiveness evaluation was included in Quarterly Groundwater <br /> Monitoring and Remediation Progress Report Second Quarter 2006 (QR), dated <br /> 18 September 2006. <br /> The evaluation of the OS system presented in the QR consisted of comparing the <br /> concentrations of dissolved oxygen (DO) in monitoring wells MW-7 and MW-9, <br /> both located within 10 feet of an ozone injection point (0-5), with the DO <br /> concentrations in the other monitoring wells. It was shown that the DO <br /> concentrations in groundwater in monitoring wells MW-7 and MW-9 were <br /> relatively higher than in the other monitoring wells, and it was concluded that <br /> ozone sparging was affecting the dissolved oxygen concentrations in MW-7 and <br /> MW-9. <br /> No correlation was found between DO concentrations, total iron, chemical <br /> oxygen demand (COD) or gasoline range organics (GRO) in impacted wells <br /> MW4, MW-6 and MW-8. It was noted that the GRO, benzene and/or MTBE <br /> concentrations in impacted wells MW-4, MW-5, MW-6, MW-8 and MW-10 <br /> appeared to have decreased since OS began. <br /> The OS evaluation presented missed the point the 31 August 2005 directive was <br /> intended to address. The EHD doesn't doubt that injection of ozone will modify <br /> the subsurface geochemistry near the point of injection; the directive was issued <br /> to evaluate the effectiveness of the OS system for reducing contaminant <br /> concentrations. It has been the EHD's observation that most sites will exhibit a <br />