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_ ENVIRON*-LvIENTAL HEALTH DEPARTMENT SAN JOAQUIN COUNTY ¢: Fg--v Donna K. Heran, R.E.H.S. Unit Supervisors < Director 304 East Weber Avenue,Third Floor Carl Borgman,R.E.H.S. Laurie A. Cotulla, R.E.H.S. Stockton,California 95202-2708 Mike Huggins, R.E.H.S., R.D.I. Program Manager Douglas W. Wilson, R.E.H.S. Telephone: (209)468-3420 g < Fax: (209) 464-0138 Robert McClellon, R.E.H.S. Website: www.sjgov.org/ehd/ Jeff Carruesco, R.E.H.S. APR 2 4 2006 CARL KNOWLES P O Box 640 WOODBRIDGE CA 95258 RE: 1140 W HAMMER LANE SITE CODE: 1124 STOCKTON CA San Joaquin County Environmental Health Department (EHD) is the lead agency providing the oversight of the investigation and cleanup of releases from underground storage tanks (UST) within San Joaquin County. EHD has a contract with California State Water Resources Control Board (SWRCB) to conduct a UST corrective action program. Your site was placed in the Local Oversight Program on 15 August 1989. Your site previously operated as a retail gasoline service station until 1986. In 1987, 6 USTs and the associated product piping and dispensers were removed under EHD permit and inspection. An unauthorized release was discovered at the time of the UST system removal. To mitigate the release, approximately 3000 cubic yards of contaminated soil was excavated and treated on-site. After treatment and soil confirmation sampling, the material was replaced and used to bring the excavation up to grade. Nine monitoring wells (MWs) have been installed to investigate the lateral extent of the soil and groundwater plumes. Historically, MW-5 has evidenced the highest groundwater contaminant concentrations. In addition to the 9 MWs,four soil borings in the area of MW-5 have been completed. Soil and groundwater grab samples were also collected from these borings. The vertical extent of impacted groundwater at your site has not been completed. Soil boring DB1a demonstrated the presence of poorly graded sand at 95 and 98 feet below ground surface (bgs). Due to the high concentrations of gasoline contaminants in the groundwater in the area of MW-5, site closure cannot be granted without further vertical investigation and necessary groundwater cleanup. EHD reviewed Feasibility Study Report. prepared by Ground Zero Analysis, Inc. with staff from the California Regional Water Quality Control Board (CRWQCB). In that report, four remedial alternatives for groundwater cleanup were evaluated. The remedial alternative selected by Ground Zero Analysis was use of Oxygen Release Compound (ORC). It has not been demonstrated to EHD that ORC has been effective for groundwater cleanup in a reasonable amount of time. In an EHD letter dated November 7, 2001, EHD recommended that you consider remedial alternatives other than ORC. On December 21, 2005, EHD and CVRWQCB staff met with Mr. John Dunlap, on behalf of Mr. Carl Knowles, and with Ground Zero Analysis. The site history and soil and groundwater assessment results were reviewed, and the need for additional vertical groundwater assessment and groundwater corrective action was discussed. EHD has recently completed a review of Workplan for Vertical Groundwater Investigation and Bench Test for In-situ Oxidation prepared by Ground Zero Analysis, dated 1 March, 2006. EHD offers the following comments regarding that work plan for your site.