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ENVIRONMENTAL HEALThkEPARTMENT <br /> °U'" SAN JOAQUIN COUNTY <br /> Unit Supervisors <br /> Donna K.Heran,R.E.H.S. 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 95202-2708 Douglas W.Wilson,R.E.H.S. <br /> • cq` FOR��c • Program Manager Telephone: (209)468-3420 Margaret Lagorio,R.E.H.S. <br /> Laurie A.Cotulla,R.E.H.S. <br /> Program Manager Fax: (209) 464-0138 Robert McClellon,R.E.H.S. <br /> Mark Barcellos,R.E.H.S. <br /> JOHN FRARY APR 2 9 2005 <br /> UNION OIL COMPANY <br /> 276 TANK FARM ROAD <br /> P O BOX 1069 <br /> SAN LUIS OBISPO CA 93406 <br /> RE: Former Unocal #2859 and Former Unocal #0187 <br /> 1665 Pacific Avenue 437 E. Miner Street <br /> Stockton, CA Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the "Response to <br /> Agency Request for Additional Subsurface Data" (Response) dated August 30, 2004, prepared <br /> by ENSR International (ENSR) for the 1665 Pacific Avenue site. In addition, Nuel Henderson <br /> and myself from EHD and James Barton from the Central Valley Regional Water Quality Control <br /> Board met with Ryan Harding from ENSR on April 5, 2005, to discuss the above referenced <br /> sites. <br /> The August 30, 2004, Response did not provide any information about the source of the 1,2- <br /> DCA found in the groundwater samples collected from monitoring wells on site and off site. In <br /> fact, the response focused on lead sampling of the soil instead of 1,2-DCA. Since the April 5, <br /> 2005, meeting I have reviewed information in EHD files on other sites in this area to determine if <br /> there is information indicating another possible source of origination of the 1,2-DCA and have <br /> not identified any, so I would conclude that the 1665 Pacific Avenue site is the source of the 1,2- <br /> DCA contamination. <br /> At the April 5, 2005, meeting, Ryan Harding explained that the above referenced sites were on <br /> the Union Oil Company (UOC) 'Portfolio of Reduction Sites'. Apparently these are sites that <br /> UOC wants to aggressively remediate and get closed as soon as possible. It was also <br /> explained that since there have been problems with operation of the ozone remedial systems at <br /> the sites (i.e. tubing conveying the ozone to the wells breaks down and some ozone injection <br /> wells being screened at too great of a depth for the compressor to force the ozone injection), <br /> use of the ozone remedial systems are being re-evaluated. ENSR on behalf of UOC may <br /> propose air sparging as a remedial alternative. It was discussed that vapor extraction should be <br /> performed in conjunction with air sparging and that feasibility tests should be conducted after <br /> installation of some initial air sparge and vapor extraction wells. It was also discussed that both <br /> sites have existing vapor extraction wells but that they may not be in the right location or <br /> screened in appropriate intervals. It was also discussed that vapor extraction and air sparge <br /> wells should be constructed in separate borings. It was discussed that a work plan for any <br /> proposed site work must be submitted to EHD for evaluation and comment/approval. <br /> Remediation of the 1,2-DCA contaminant plume at 1665 Pacific Avenue must be included in as <br /> well as evaluated in choosing the remedial action to be performed at the site. <br />