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Frontier Transportation Page 2 425 Larch Road January 18, 2011 Tracy, California 95376 The EHD also reviewed Limited Groundwater Investigation Report (report), dated 11 November 2010, submitted by AA&A. In the report, AA&A presents the results from the collection of grab groundwater samples from the advancement of eight soil borings on the two parcels west and down gradient of the petroleum hydrocarbon source. Of the eight grab groundwater samples collected at total depth of approximately 20 feet below surface grade, only groundwater collected from soil boring B8 contained significant concentrations of MTBE at 49.5 micrograms per liter(Ng/L). Based on these results and prior to deciding the location to install an additional well, AA&A recommends that four or five additional soil borings be advanced to the southwest of this site to further define the contaminant groundwater plume. The EHD believes that the lateral extent of the MTBE plume is now adequately defined based on the results from this investigation and directs that one additional monitoring well be installed adjacent to soil boring 68. Since the EHD has already received a copy of the access agreement for Parcel ID APN #212-200-05 where the EHD recommends that monitoring well MW-28 be installed, and has issued the permit for the well installation, you are to complete the installation of MW-28 adjacent to borehole B8 by 31 March 2011. AA&A has prepared and submitted Corrective Action Plan(CAP), dated 18 October 2010. In the CAP, AA&A compared six remedial technologies to determine the appropriate remedial technology based on site conditions and cost-effectiveness to mitigate soil and groundwater contamination at the above-referenced subject site. Included in the remedial alternatives were: • Excavation and soil removal • Soil vapor extraction combined with air sparging • Bioremediation • Monitored Natural Attenuation • High vacuum dual-phase extraction (HVDPE), and • In-situ chemical oxidation AA&A concludes, based on the evaluation of the above-listed methods, that HVDPE would be the most suitable and cost-effective remedial alternative for this site. The EHD is currently reviewing the mass estimates, site conditions, and plotting the progress of the high concentration waves; comments concerning the CAP will be forthcoming. If you have any questions, please contact Vicki McCartney at(209) 468-9852, or by e-mail at vmccartney@sjcehd.com. Sincerely, Y' -- Victoria L. McCartney, REHS Nuel C. Henderson, Jr., PG Senior Registered Environmental Health Specialist Engineering Geologist c: Ms. Gabriele Baader, PG, Ami Adini & Associates; Inc., 4130 Cahuengs Blvd., Suite 113, Los Angeles, California 91602 Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670