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Frontier Transportation Page 2 <br /> 425 Larch Road February 4, 2011 <br /> Tracy, California 95376 <br /> • Variations in the depth to water, <br /> • Variations in the flow direction of first groundwater, <br /> • Instability of the MTBE plume, and <br /> • Any other potential causes. <br /> Also evaluate the overall concentration/mass trends of MTBE, TPH-g, and benzene and <br /> determine whether the dissolved masses may be declining. The EHD will decide whether to <br /> approve the proposed HVDPE based on this information and the groundwater data submitted <br /> after the installation of proposed monitoring well MW-28. <br /> Upon review of the mass estimate calculations for dissolved total petroleum hydrocarbons as <br /> gasoline (TPH-g), the EHD believes there may have been a computational error and the <br /> masses should be reduced approximately three orders of magnitude. Please review and, if <br /> appropriate, resubmit the revised mass calculations for dissolved TPH-g, benzene, and <br /> MTBE. <br /> By electronic mail on 28 January 2011, the EHD approved one duplicate soil gas sample to be <br /> collected in a 250-milliliter Summa® canister during the soil gas investigation and analyzed by <br /> Environmental Protection Agency (EPA) SW-846 Method 8260, instead of Method TO-14A or <br /> TO-15, by an off-site State-certified environmental laboratory. AA&A had recommended this <br /> change in analytical method following the Department of Toxic Substances Control (DTSC) <br /> Draft-for-review Advisory—Active Soil Gas Investigation, dated March 2010. The EHD further <br /> stipulated that if the laboratory used water-phase standards instead of gas-phase standards <br /> for the calibration curve, that a vapor-phase validation check standard be analyzed that <br /> included the target analytes and that the percent difference for the target analytes be less than <br /> or equal to twenty percent. By electronic mail dated 02 February 2011, the EHD rescinded <br /> the directive for the laboratory to include a vapor-phase validation check standard because of <br /> the cost incurred, and the dependability of reporting accurate soil gas results for benzene, <br /> toluene, ethylbenzene, total xylenes, and methyl tertiary-butyl ether using water-phase <br /> standards for the initial calibration curve, continuing calibration check and associated quality <br /> control by EPA Method 8260. <br /> If you have any questions, please contact Vicki McCartney at (209) 468-9852, or by e-mail at <br /> vmccartney@sjcehd.com. <br /> Sincerely, <br /> Victoria L. McCartney, REHS� Nuel C. Henderson, Jr., PG <br /> Senior Registered Environmental Health Specialist Engineering Geologist <br /> c: Ms. Gabriele Baader, PG, Ami Adini & Associates, Inc., 4130 Cahuenga Blvd., Suite 113, <br /> Los Angeles, California 91602 <br /> Mr. James L.L. Barton, PG, California Regional Water Quality Control Board Central <br /> Valley Region, 11020 Sun Center Drive, Suite 200, Rancho Cordova, California 95670 <br />