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$I antec Work Plan for Amended Bioremediation Pilot Study BP Terminal 40T November 10, 2008 was injected into each well at a rate of 0.2 gallons per minute (gpm). Approximately 240 gallons of the solution were pumped into each well over a period of approximately 18 hours. The injection events began on May 25, 2004 and were performed weekly until June 22, 2004. Injections were temporarily stopped after the fifth event because the levels of sulfide exceeded the baseline limits set for monitoring well AR/MW-1A. The injections were restarted in August 2004, following a change in the baseline levels. During the course of the URS pilot study, a total of 11 nitrate/sulfate injection events were performed, during which, approximately 7,920 gallons of the nitrate/sulfate solution were injected. URS concluded that the impact of the nitrate/sulfate injections on the hydrocarbon concentrations only appeared to be significant near the injection points. GRO and benzene concentrations in groundwater monitoring well AR/MW-5A decreased compared to groundwater monitoring wells farther from the point of injection. Therefore, the pilot study indicated that nitrate/sulfate injections may be able to remediate dissolved hydrocarbons at the site (Pilot Study Evaluation Report Enhanced Bioremedation Pilot Study, URS, 2005). Stantec submitted a work plan to the RWQCB on May 7, 2007 for injection of nitrate/sulfate as part of the Enhanced Bioremediation Pilot Study (SECOR, 2007). The RWQCB developed a waste discharge requirement permit using background concentrations the previously established for groundwater based on the URS-2005 study. The problem with the background concentrations were that many of on-site wells contained groundwater with concentrations above background level for the salts proposed for treatment. Due to potential problems associated with determining background level of nitrate, phosphate, and other salts being used as part of the proposed nitrate/sulfate treatment system. Stantec determined that the best approach would be to limit addition to calcium sulfate. Use of calcium sulfate reduced the potential that groundwater concentrations in down gradient point of contingency wells would exceed background levels and require some sort of mitigation. GEOLOGY AND HYDROGEOLOGY Unconsolidated strata beneath the Stockton area consist primarily of interbedded clays, silts, and fine grained sands of the Quaternary age flood basin deposits. The flood basin deposits attain a thickness of approximately 1,000 ft in the Stockton area and were deposited by fluvio- deltaic processes. Based on previous work, the lithology has been generally subdivided into five zones based on the distribution of fine- and coarse-grained sedimentary units defined as the A- zone, the B-zone, the B/C-aquitard, the C-zone, and D-zone. A-zone The A-zone extends from ground surface to a depth of approximately 20 to 25 ft bgs. The A- zone hydraulic gradients vary from 0.001 to 0.005 foot per foot (ft/ft), and the flow is generally toward the southeast. Downward vertical gradients of 0.001 to 0.24 ft/ft were typically observed in the A-zone and B-zone paired monitoring wells during quarterly events. B-zone The B-zone underlies the A-zone and extends to an approximate depth of 40 to 45 ft bgs. Differentiation of the A-zone and B-zone is based on differing aquifer properties of the unconfined A-zone and the confined B-zone, and variation of the general mineral quality parameters. The B-zone hydraulic gradients vary from 0.002 to 0.004 ft/ft and flow toward the 40T Work Plan for Amended Bioremediation Pilot Study.doc 4