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Mr. Jeff Baker . - 2 - 30 May 2008 Stockton Terminals Technical Committee wells contained SPH. The highest COC concentrations typically underlie the BP and Time Oil facilities. During the first quarter 2008, the highest COC concentrations were generally in A zone wells on the Time Oil property. The highest concentrations of TPHg and TPHd were in TS-4 at 100,000 micrograms per liter (Ng/L) and 360,000 pg/L, respectively. The highest concentration of TBA, however, was in the D zone at 1,700 pg/L in well TS/MW-2D. The OS system installed in 2004 is divided into two portions. The west system is downgradient of Tesoro and the east system is downgradient of BP. Between December 2007 and March 2008, the STTC estimates that the east system and west system had run times of 81 and 64 percent, respectively. The STTC estimates that collectively 241 pounds of hydrocarbons were destroyed during this period. The STTC conducts an OS system monitoring program in six A and B zone remedial observation wells (PS/MW-18, PS/WC-1 S, AR/MW-21 A. AR/MW-18B, AR/MW-21 B, PS/WC-1 M). A contingency plan is triggered if petroleum hydrocarbon concentrations (excluding TPH) exceed historical concentrations by one order of magnitude for three consecutive quarters in any of these six wells. This condition was not observed in any remedial observation wells during the first quarter of 2008. The Work Plan proposes to install four monitoring wells (PS/MW-20A through PS/MW-20D) to address a gap in the monitoring well network between wells OW-8D and OW-51D. PS/MW-20A will only be installed if attempts to locate the existing well PS/MW-20 fail. The STTC anticipates that a report describing the installation will be submitted to Regional Water Board staff within six to eight weeks following receipt of the final laboratory analytical data. Our comments are presented below. 1. The STTC had originally recommended installing a single D-zone monitoring well. However, Regional Water Board staff concur with the STTC's recommendation for installing B, C and D zone wells, and if necessary, an A-zone monitoring well if PS/MW-20 cannot be located. By 19 September 2008, please submit a report on the well installations. 2. A copy of the ozone injection monitoring program contingency plan is included as Attachment 3 in the Work Plan. The ozone injection monitoring program, which was formulated by the STTC in June 2003, does not specify which petroleum hydrocarbons increases in the remedial observation wells will be monitored to trigger implementation of the contingency plan. The data trends for remedial observation well AR/MW-18B are tabulated in Appendix I of the first QMR. Historical concentration data for benzene, MTBE, and TPHg in AR/MW-18B show increasing concentration trends over the two quarters preceding the first quarter of 2008. Because the concentration increases for these three constituents did not exceed historical averages or were not part of the list of"trigger" hydrocarbons, implementation of the contingency plan was not warranted. The data trends show that TBA sustained concentration increases over three consecutive quarters, in excess of the only existing historical data point of<5.0 pg/L, from May 2006 to November 2006, and from August 2007 to February 2008. The February 2008 detection of 9.4 pg/L is the highest TBA concentration ever observed in AR/MW-18B However, TBA is not among the list of trigger hydrocarbons in the ozone injection monitoring program. The recent