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California Regional Water Quality Pontrol Board <br /> vCentral Valley Region <br /> Steven T.Butler,Chep MRR 15 PM 1 07 <br /> Winston H.Hickox Gray Davis <br /> Secreraryfor Sacramento Main Office Governor <br /> Environmental Internet Address: http://w .sv cb.ca.gov/—mgcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,Califomia 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> 14 March 2000 <br /> Ms. Margaret Lagorio <br /> Senior Registered Environmental Health Specialist <br /> San Joaquin County Environmental Health Division <br /> 304 East Weber Avenue <br /> Stockton, CA 95202 <br /> NONCONCURRENCE WITH SAN JOAQUIN COUNTY'S NO FURTHER ACTION <br /> REQUIRED DETERMINATION, ARCO #6100, 25775 PATTERSON PASS ROAD,TRACY <br /> Board staff reviewed San Joaquin County Environmental Health Division's Case Closure Summary for <br /> ARCO#6100 (ARCO), and the 12 October 1998 Hydrocarbon Mass Evaluation with Addendum <br /> prepared by Pinnacle/The IT Group. Based on the findings of TPHg at a maximum concentration of <br /> 28,000 mg/kg in soil, and the lack of groundwater data, San Joaquin County's closure recommendation is <br /> not appropriate at this time (see enclosed memo and Appendix B checklist). ARCO must determine the <br /> hydrogeology beneath the site, and determine whether petroleum hydrocarbons, especially fuel <br /> oxygenates, have impacted groundwater. <br /> As lead agency,please require ARCO to submit a workplan by 1 May 2000 to complete groundwater <br /> sampling and analyses at the subject site. Due to the complexities of the site hydrogeology and unknown <br /> extent of MtBE in groundwater, the threat MtBE poses to the on-site drinking water well and potential <br /> offsite migration, this investigation must be considered high priority. <br /> If you have any questions, please call Marty Hartzell at (916) 255-3115. <br /> AGARYCARLTON <br /> Executive Officer <br /> Enclosures (Memo and Appendix B Checklist) <br /> California Environmental Protection Agency <br /> 0 Recycled Paper <br />