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ENVIRONMENTAL HEALTH DEPARTMENT <br /> ° SAN JOAQUIN COUNTY <br /> ° <br /> N <br /> Program Coordinumrs a Donna K. Reran, R.H.H.S' g <br /> Director 304 East WeberAvenne, Third Floor Carl Bergman, R.E.H.S. <br /> $ <br /> Laurie A. Cotulla, R.C.H.S. Stockton, California 95202-2708 Mike Huggins, R. E.H.S. , R.W. <br /> ♦ �4• � ; ;. �-' ' �P , dssis(mu Direcmr Margaret Lagorio, R.E.H.S. <br /> c Foaa Telephone: (209) 468-3420 Robert Mcclellon, R.E.H.S. <br /> Fax: (209) 464-0138 Jeff Carruesco, R.E.H.S. <br /> Website: wwxv.sjilov.org/ehd/ Kasey Foley, R.E. H.S. <br /> Ali DON PRATT <br /> J" 12 2001 <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 /> 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 /> 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. fr C <br /> �Vl JAN A 5 2001 <br /> e <br />