SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker . - 2 - • 11 March 2009 Stockton Terminals Technical Committee 82 pg/L, respectively. Except for TPHd, the concentrations of analyzed petroleum hydrocarbons decreased to non-detect (ND) at 160 feet bgs. TPHd was detected at 56 pg/L at this depth. This concentration is below the TPHd water quality objective (WQO) of 100 pg/L. Included in the Assessment Report is a cross-section that graphically depicts STTC's interpretation of the stratigraphy underlying the Site, and the relative location and construction of three of the seven new monitoring wells (PS/MW-20D, OW-3DR, and TS/MW-3D). The cross-section also displays the soil laboratory analytical results for TPHg, benzene, and MTBE for the three well boreholes and the grab groundwater results for TS/MW-3D. Monitoring well TS/MW-3D is screened between 105 to 110 feet bgs. The screened interval is about 35 feet shallower than the depth at which TPHd was detected at 260 pg/L. The Assessment Report concludes that the vertical extent of impacts underlying TS/MW-3D have been defined, that coarse grained units within the D zone do not extend laterally beneath the site and that the pollution observed in OW-5D is not derived from pollution in OW-8D, since OW-8D is screened about 26 feet deeper than OW-5D. During a 10 December 2008 meeting, Regional Water Board staff inquired about the reason for screening TS/MW-3D 15 feet above the maximum contaminant concentrations detected in the borehole. The STTC concurred that TS/MW-3D was too shallow and said that the screen installation resulted from miscommunication with the drilling contractor. Regional Water Board staff stated that a deeper well was needed. STTC agreed and said that a deeper well could be installed based on the outcome of, the preliminary phase of an impending pilot study. The Pilot Study Work Plan was due to be submitted concurrently with the Assessment Report, but the STTC requested and received an extension to 27 January 2009 during the meeting. The STTC's Pilot Study Work Plan proposes to conduct a 1-year oxygen injection pilot study in the D zone. Prior to implementing the pilot study, the STTC is proposing to preliminarily evaluate communication between TS/MW-3D and TS/MW-2D by.injecting a helium-oxygen tracer into TS/MW-3D and monitoring for the presence of the tracer in TSiMW-2D. If there is inadequate communication, the STTC proposes to install two additional wells; replacement injection well TS/MW-3DR, screened from 110 to 115.feet bgs between TS/MW-3D and TS/MW-2D, and TS/MW-4D screened from 125 to 135 , feet bgs. Monthly baseline evaluation groundwater monitoring, consisting of biodegradation data and field parameters including dissolved oxygen (DO), will be conducted monthly for up to three months prior to initiating the oxygen-injection pilot study. The oxygen-injection pilot study will consist of monthly oxygen injections of 150 cubic feet per or 13.35 pounds per injection from oxygen canisters, performed over a 1.2- month period. Biodegradation parameters, DO, and oxygen reduction potential (ORP) levels will be monitored in injection and monitoring wells prior to and following injections. Biodegradation parameters will be collected monthly for the first three months but may be decreased to quarterly as the test continues. Progress reports and evaluations of the pilot study will be summarized in quarterly monitoring reports. After a year of injections,