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r ENVIROIIENTAL HEALTH <br /> WEPARTMENT <br /> ppU1ly <br /> c SAN JOAQUIN COUNTY <br /> Donna K. Heran, R.E.H.S. Program Coordinators <br /> IX 304 East Weber Avenue Third Floor <br /> Director 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.D1 <br /> >..:.1 i4 Assistant Director Margaret Lagorio,R.E.H.S. <br /> <<Fp� Telephone: (209}468-3420 Robert McClellon,R.E.H.S. <br /> Fax: (209) 464-0138 Jeff Carruesco, R.E.H.S. <br /> Website:www.sigov.org/chd/ Kasey Foley,R.E.H.S. <br /> JOHN FRARY <br /> UNION OIL COMPANY <br /> 270 TANK FARM ROAD (J u L 0 3 2006 <br /> P O 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. The well is <br /> inactive but may be used if there is a major disaster. There is also a California Water Service <br /> well at the corner of Elfis 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, MW19 (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 the <br /> underground storage tanks (UST's) removed in 1988 continues to be undocumented. 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-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 B10 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 />