SITE INFORMATION AND CORRESPONDENCE

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Mr. Robert Garcia • - 2- is 1 June 2011— further action. Board staff request Leprino conduct quarterly groundwater monitoring and reporting for one year from the date of system shutdown. 3. Central Valley Water Board staff concur with Leprino's proposal to collect soil samples from the locations of the previous maximum soil concentrations to evaluate remaining soil concentrations. By 1 August 2011, Leprino needs to drill the soil borings, collect the soil samples, and submit a report of findings. Leprino should analyze the soil samples collected from 10 feet below ground surface (bgs) because this corresponds to the depth of the soil samples collected in 1993. In addition, Leprino needs to collect a grab groundwater sample from each of the borings. Soil and groundwater samples should be analyzed for TPHd, TPH as gasoline (TPHg), benzene, toluene, ethylbenzene, xylenes, and naphthalene. 4. Leprino needs to collect soil vapor samples beneath the dry-powder storage building. Additionally, monitoring well MW-6 contains TPHd above the WQOs and is near a building. Leprino needs to also sample soil vapor near MW-6 to evaluate vapor intrusion risks in this area of the Site. By 1 August 2011, Leprino needs to collect soil vapor samples at 5 and 10 feet bgs beneath the dry-powder storage building and near MW-6, and submit a report of findings. Soil vapor samples should be analyzed for TPHd, TPHg, and naphthalene. 5. Leprino needs to follow the 7 February 2005 DTSC Guidance for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(DTSC Guidance) for soil vapor sample collection. Prior to sample collection, Leprino needs to leak test the sampling equipment. In addition, a shroud should be placed over the sampling point and filled with inert leak detection gas. Leprino needs to analyze the soil vapor samples for the leak detection compound to assess whether the sampling setup was airtight. The report of findings needs to tabulate the results of the leak detection gas analysis. 6. The Work Plan proposes using sorbent media tubes for soil vapor sample collection. DTSC guidance recommends using Summa canisters for vapor intrusion analysis and it is not clear whether laboratory analysis with sorbent media tubes will provide sufficient quality data to evaluate the potential for vapor intrusion. Analytical reporting limits and data quality need to be evaluated using the California Regional Water Quality Control Board — Bay Area Region Environmental Screening Levels for indoor air. Leprino needs to clarify whether use of sorbent media tubes will provide sufficient data quality. In summary, by 1 August 2011 please complete the following: • Shut down the product recovery system and begin quarterly monitoring and reporting program; • Drill four soil borings near GP-1 through GP-4 and collect soil and grab groundwater samples and submit report of findings; and • Sample soil vapor at 5 and 10 feet bgs within the dry-powder storage building and near monitoring well MW-6 and submit a report of findings.