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DEPARTMENTENVIRONENTAL HEALTn <br /> SAN JOAQUIN COUNTY Program Coordinators <br /> Bar man, R.E.H.S. <br /> Donna K. Heran, R.E'U.S. 304 East WeberAvenue,Tbird Floor Carl B E.H.S.,R.D.I. <br /> Mike Huggins,R <br /> Director Stockton, 95202-2708 Margaret Lagorio, R,E.H.S. <br /> kton,California <br /> Laurie A. Cotulla,R.E.H.S. <br /> Telephone: (209)468-3420 Robert McClellon,R-E-ES. <br /> Assistant Director Fax: (209)464-0138 jeff Carruesco, R.E.H.S. <br /> Kasey Foley,R.E.HS. <br /> Website:www.sjgov.Org/ebd/ <br /> JOHN FRARY <br /> UNION OIL COMPANY rJUL 0 2005 <br /> 270 TANK FARM ROAD <br /> P 0 BOX 1069 <br /> SAN LUIS OBISPO CA 93406 <br /> RE: Former Unocal #2859 <br /> 1665 Pacific Avenue <br /> Stockton, CA <br /> San Joaquin County Environmental Health Department (EHD) has reviewed the "Conceptual <br /> Site Model" (CSM) dated April 25, 2006 and the "Quarterly Groundwater Monitoring and Ozone <br /> Microsparge System Status Report, First Quarter 2006" dated March 29, 2006, prepared by <br /> ENSR for the above referenced site and provides the following comments. <br /> The CSM contains a sensitive receptor survey that identifies a well northeast and downgradient <br /> of the site as a USGS well. This well is located at the corner of Wyandotte and Commerce <br /> Streets and is owned by the California Water Service, a public water system <br /> inactive b . The well is <br /> but may be used if there is a major disaster. There is also a California Water Service" <br /> well at the corner of Ellis and Bonnie Streets that is shown on the map in the sensitive receptor <br /> survey. This well is a standby well that may be used if needed. <br /> In the CSM it states "Contaminant delineation of the soil and groundwater is complete." EHD <br /> agrees that good definition of contamination exists, but the 1,2 DCA in the water samples from <br /> the most down-gradient, deep screened well, MWI 9 (screened from 85 to 90 feet), shows the <br /> groundwater contamination is not completely defined. The maximum contaminant level (MCL) <br /> for 1,2 DCA in Public drinking water is .5 ug/l. Complete delineation of the 1,2 DCA <br /> contamination must be provided before a "No Further-Action Required" determination will be <br /> made. <br /> In the CSM there is discussion about the soil impacted with contaminants at the site. The CSM <br /> did not include a table of all soil sample results from the site. There is a table of soil results in <br /> the "Monitoring Well and Sparge Point Installation Report" dated August 19, 2002 for all the soil <br /> data collected prior to that date. The amount of soil excavated from the location of <br /> underground storage tanks (UST's) removed in 1988 continues to be undocumented.the There are <br /> differing statements in previous site reports on the amount of soil excavated from the UST.area, <br /> one estimate is 1300 to 1400 cubic yards and another is 1100 cubic yards, but maps show only <br /> the west side of the former UST area was over <br /> -excavated and the only report of off-site <br /> transport of soil was 350 cubic yards. Soil samples were not collected beneath the piping <br /> removed in 1988. After review of all the concentrations of contaminants in the soil samples <br /> collected from the site, it appears the soil in the area of former pump islands had higher <br /> concentrations of contaminants than the soil beneath the UST's. This,is shown by the <br /> concentration of contamination in samples from boring 1310 that was completed as vapor well <br /> VW2 (TPH-g at 12,000 mg/kg and benzene at 28 mg/kg at 21 feet) which was drilled in the <br />