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ENVIRONMENTAL HEALTH DEPARTMENT <br /> P <br /> SAN JOAQUIN COUNTY Program Coordinators <br /> Donna K. Reran, R.E.H.S.Director 304 East Weber Avenue, Third Floor Carl Borgman, R.E.H.S. <br /> Laurie A. Cotulla, R.E.H.S. Stockton, California 95202-2708 Mike Huggins, R.E,H.S., R.D.I.Assistant Director Telephone : (209) 468-3420 Margaret Lagorio, R.E.H.S. <br /> Robert McClellan, R.E.H.S. <br /> Fax : (209) 464-0138 Jeff Carruesco, R.E.H.S. <br /> Website: www.sjgov.org/ehd/ Kasey Foley, R.E.H.S. <br /> DON PRATT JAN12 2007 <br /> ATLANTIC RICHFIELD COMPANY <br /> PO BOX 1257 <br /> SAN RAMON CA 94583 <br /> RE : Arco Station #2130 Site Code 1094 <br /> 7906 N , EI Dorado St, RO#: 035 <br /> Stockton , CA. 95210 <br /> The San Joaquin County Environmental Health Department (EHD ) has reviewed <br /> Additional Site Assessment Report ( Report) and Site Conceptual Model (SCM) <br /> dated October 27, 2006 prepared by Secor for the above referenced site and has the <br /> following comments, <br /> The Report covers the installation of three replacement monitoring wells as required <br /> by the EHD . Monitoring wells " MW- 11 , -12 and -13" were installed in July 2006 . <br /> Minor concentrations of total petroleum hydrocarbons as diesel (TPHd) were <br />{ detected in soil samples collected from the borings where the monitoring wells were <br /> constructed , Ground water samples from these wells were first collected on <br /> September 12 and 14, 2006 and the laboratory data from this event indicates that <br /> 1 , 2-DCA was detected in MW- 11 , MtBE was detected in MW-12 , and TPH (reported <br /> as gasoline range organics-GRO) and 1 ,2-DCA were detected in MW-13 . During <br /> this sampling event, ground water samples were collected from ten ( 10) vapor wells <br /> that contained ground water. All but VW-7 contained GRO concentrations, The <br /> ground water sample from VW-10 detected the highest GRO concentration (21 , 000 <br /> ug/L), Other petroleum constituents were detected in the ground water samples <br /> from all of the other vapor wells sampled . <br /> i. <br /> The SCM was required by the EHD and was to summarize site activities and provide <br /> a guide for future assessment and remediation . Recommendations included in the <br /> SCM included periodic injection of oxygen into the air sparge well and conducting a <br /> soil vapor extraction test with collection of soil vapor samples to calculate the mass <br /> j removal during the test. The EHD concurs with conducting a soil vapor extraction <br /> test, but the residual soil contamination must be evaluated for all routes of exposure <br /> in order to protect human health , safety, and the environment. The San Francisco <br /> Bay Regional Water Quality Control Board Environmental Screening Levels may be <br /> used in this evaluation . If existing data cannot be used to show that the site doesn 't <br /> pose a risk, then a work plan to evaluate the risk must be submitted to the EHD by <br /> February 15 , 2007 . <br /> i <br />