SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker - 2 - 31 August 2010 Stockton Terminals Technical Committee During the second quarter 2010, the highest dissolved COC concentrations generally occurred in A zone wells in the BP aboveground tank (AGT) area and in the southeast corner of the Tesoro property. In the deeper zones, maximum concentrations were encountered on the Tesoro property. The highest concentrations of TPHg and TPHd were in AR/MW-24A and TS/M-2, at 69,000 micrograms per liter (Ng/L) and 160,000 pg/L, respectively. The highest concentration of benzene was detected in AR/MW-813 at 15,000 pg/L. The highest concentrations of MTBE and TBA were detected in TO/T-2 and AR/MW-50 at 15,000 pg/L and 2,400 pg/L, respectively. Groundwater at the BP facility is polluted with MBAS. BP believes the pollution originates from a November 2008 fire suppression foam release. The water quality objective (WQO) for MBAS is 500 pg/L. To address the concentrations, BP over-purges up to 10 well casing volumes from wells containing MBAS before sampling. BP describes over-purging as the process of removing 10 well casing volumes from a monitoring well prior to sampling. Table 6 shows that the maximum MBAS detection was 16,000 pg/L in AR/MW-21 C. During the second quarter 2010, BP over-purged 20 wells and, due to groundwater volume limitations, unsuccessfully attempted to over- purge an additional four wells. The Second QMR states that over-purging removed about 4,370 gallons of groundwater during the second quarter. As we requested in our 11 March 2010 letter, during the second quarter BP sampled for MBAS in all BP wells and in select downgradient Port of Stockton wells, including PS/MW-20C, OW-3CR, OW-4C, and OW-9C. MBAS was detected in all of the wells. Concentrations in two wells exceeded the WQO of 500 pg/L. 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 is comprised of 57 A zone and 16 B zone wells connected to two 2 pounds-per-day (Ibs/day) ozone generators. The OS system is divided into two portions. The west system is downgradient of Tesoro, and the east system is downgradient of BP. During the second quarter, the STTC estimates that the east system and west system had ozone sparge run times of about 95 and 91 percent, respectively. The STTC estimates that historically, about 8,800 pounds of ozone have been injected and 2,950 pounds of hydrocarbons have been destroyed. The STTC monitors the ozone injection system using an array of six remedial observation (RO) wells, two midpoint wells, and four trigger wells. A contingency plan is triggered if the concentration of BTEX, MTBE or TBA in any RO well exceeds compliance limits. Table 7 shows that the TBA concentration in RO well AR/MW-18B decreased from 44 pg/L during the first quarter to 18 pg/L during the second quarter. These concentrations exceed the compliance limit of 6.6 pg/L. Pursuant to the terms. described on Page 3 of the Revised Contingency Plan (Appendix K of the First 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.