SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker -2 - 16 November 2009 Stockton Terminals Technical Committee As shown in Tables 6 and 7 from the Third QMR, the highest COC concentrations occurred in A zone wells in the BP aboveground tank (AGT) area and on the Tesoro property. The highest concentrations of TPHg and TPHd were in AR/MW-3A and TS/M- 2, at 70,000 micrograms per liter (ug/L) and 420,000 pg/L respectively. The highest concentration of benzene was detected in AR/MW-8A at 9,400 pg/L, which has also had an increasing MTBE concentration trend since 2001. BP conducted MBAS sampling, which has a water quality objective of 500 pg/L, from 29 wells in the A through D zones. , Laboratory analytical results showed that MBAS was detected at concentrations ranging from 130 pg/L to 3,100 pg/L in these wells, with nine wells increasing from the previous quarter. To address the MBAS, BP over-purges up to 10 well casing volumes of groundwater from wells impacted by MBAS before sampling. Eight wells were over-purged during the third quarter and BP recommends over- purging 12 wells with MBAS concentrations above 500 pg/L during the fourth quarter. Central Valley Water Board staff concurs with this recommendation. In the fall of 2004, the STTC began operation of two ozone sparge (OS) systems to clean up groundwater pollution migrating downgradient from the Site. The system, comprised of 57 A zone and 16 B zone wells connected to two 5 pounds-per-day (lbs/day) ozone generators, is divided into a west system downgradient of Tesoro, and an east system downgradient of BP. System performance is evaluated using an array of six remedial observation (RO) wells, two midpoint wells, and four trigger wells. A contingency plan is triggered if the concentrations of BTEX, MTBE, or TBA in any remedial observation wells exceed compliance limits. The TBA concentration in RO well AR/MW-18B has increased from 13 pg/L to 39 pg/L over the last four quarters. These concentrations exceed the compliance limit of 6.6 Ng/L. Pursuant to the terms described on Page 3 of the Revised Contingency Plan (Appendix K of the Third QMR), three consecutive exceedences of an order of magnitude greater than the compliance limit will trigger installation of a second ozone sparge array east of the RO wells. None of the concentrations measured so far has been an order of magnitude above the compliance limit. TPHd, which has displayed an increasing trend in monitoring wells OW-46 and OW-4C, was detected at 1 ,100 pg/L and 2,000 pg/L, respectively. However, neither concentration of TPHd trigger the contingency plan. Between January and March 2009, the STTC estimates that the east system and west system had run times of 50 and 85 percent, respectively. The STTC estimates that historically, about 7,639 pounds of ozone have been injected and 2,546 pounds of hydrocarbons have been destroyed. The Third QMR provides a brief update on an additional helium-tracer, oxygen-injection pilot study that was conducted on the Tesoro facility at monitoring well TS/MW-3D. Technical difficulties delayed the completion of this study after it was started on 3 August and results reportedly were inconclusive. The results of a modified version of the test, which was implemented on 6 October, will be submitted under separate cover. Table 8 in the Third QMR provides the results of the first two quarters of a four-quarter background sampling study for Tesoro's proposed TS-4R hydrogen peroxide pilot test. Background groundwater monitoring is being conducted in four wells including TONT-3,