SITE INFORMATION AND CORRESPONDENCE_FILE 2

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Frontier Transportation, Inc. Page 2 425 Larch Road October 11, 2010 Tracy, California 95376 pass the ESLs, CHHSLs, or Johnson and Ettinger model, the EHD approves the advancement of three of the five proposed soil gas sampling point locations. The EHD believes the two proposed soil gas sampling points adjacent to the office building should be omitted since these locations are quite distant from the main source of petroleum hydrocarbon contamination. If it can be demonstrated that preferential pathways (utility conduits or subsurface drains) exist between the source area and the office building, then the EHD will reconsider this matter. AA&A purposes to conduct a purge test of 1, 3, and 10 tubing volumes at borehole SV1 prior to collecting samples and default to 3 purge volumes if contaminant concentrations are not detected while performing the purge test; and either isopropyl alcohol or 1,1-difluoroethane will be used as the tracer compound. AA&A proposes to collect the samples at five feet below surface grade (bsg) using glass syringes and transfer the samples to an on-site mobile laboratory for chemical analysis, resulting in a sample hold-time of 30 minutes. AA&A proposes to backfill the boreholes with hydrated granular bentonite. Instead, the EHD directs that the boreholes be backfilled with neat cement prepared according to the San Joaquin County Well Standards. AA&A proposes to have the soil gas samples analyzed for volatile organic compounds (VOCs) and the tracer compound (isopropyl alcohol or 1,1-difluoroethane) by Environmental Protection Agency (EPA) Method 8260B. It is important that the analyses include total petroleum hydrocarbons as gasoline (TPH-g) as well as benzene, toluene, ethylbenzene, and total xylenes (BTEX); methyl tertiary-butyl ether (MTBE), ethyl tertiary-butyl ether (ETBE), tertiary amyl methyl ether (TAME) di-isopropyl ether (DIPE) and tertiary butyl alcohol (TBA) and the results reported at concentrations at or below the ESLs and CHHSLs. AA&A states that the installation of the soil gas probes and sample collection and handling will be done according to protocols established by the California EPA. In the Department of Toxic Substances Control (DTSC) guidance document Interim Final— Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air, dated December 15, 2004, revised February 7, 2005, it states that "When collecting soil gas samples with glass bulbs or glass syringes and analyzing the gas samples for VOCs by Method 8260B (USEPA, 1996) modified for air analysis with a mobile laboratory, the results of the field work should be independently confirmed through the collection of duplicate soil gas samples in SummaTm canisters. The collection .of duplicates will confirm the mobile laboratory detection limits and identify other potential chemicals-of-concern (COC) at the site. DTSC recommends that ten percent of the soil gas samples collected in the field be confirmed with SummaTM canisters that are analyzed using TO-14A (USEPA, 1999a) or TO-15 (USEPA 1999b), as appropriate." Collection of one duplicate sample in a Summa®canister, preferably in an area of suspected impacted soil gas, would be appropriate for the proposed scope of work if it is determined that additional soil gas samples must be collected. Following completion of the human health risk assessment using soil gas data from 2000, if it is determined that additional soil gas samples must be collected from boreholes, SV1 through SV3, then submit a boring permit application and permittinspection fees of $488 to the EHD. Notify the EHD at least a week prior to the pending fieldwork. Submit the report of findings to the EHD by December 31, 2010.