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ST Services Stockton Ter. - 4 - 15 May 2007 Monitoring Reports and C terization Report The evaluation in the Cleanup Plan consisted of a discussion of remedial technologies, two of which were conducted at an adjacent site, four that have been tried at other sites, and one (Recirculation/Bioaugmentation) that was tested in an 8-month Pilot Study between November 2003 and July 2004. The network of Pilot Study wells included two extraction wells, three injection wells, and six monitoring wells. The Pilot Study was successful in reducing COCs. However, increases in groundwater amendments in excess of concentrations permitted by the Waste Discharge Requirements (WDR) Order No. R5- 2003-0165 also occurred. ST Service's payments for WDR Order No. R5-2003-016 are current and the infrastructure, including three extraction wells, remains on-site. During the Recirculation/Bioaugmentation Pilot Study, groundwater was extracted at about 0.35 gpm2 from the two 4-inch diameter wells, which have 5-foot screens. These results show that the A-zone is capable of supporting a pump and treat system. However, the Cleanup Plan did not include an evaluation of a groundwater pump and treat system. By 9 July 2007, we request that ST Services submit an amendment to the Cleanup Plan by preparing an evaluation of a groundwater pump and treat system to address COC concentrations in the vicinity of gasoline ALTs G 3301 and G 3302 and diesel AGT D 5301. 4. ST Services should resume monitoring of the Recirculation/Bioaugmentation Pilot Study wells to assess the long-term effects of the Pilot Study on the gasoline concentrations in groundwater in the area of gasoline AGT G 3302. 5. Petroleum hydrocarbon releases, including MTBE, have occurred from both the KMEP and ST Services facilities at different times throughout the operation of the facilities. St Services acknowledges that the fuel hydrocarbon plumes in the vicinity of the tank farms have intermingled but maintains the distinction that the source for the MTBE concentrations in monitoring well PS/WC-313 can only be attributed to a release from the KMEP facility. While this may be the case, the 44 pg/L and 97 pg/L of MTBE in ACA-26 in September 2006 and January 2007 indicate that MTBE from ST Services has probably now commingled with the KMEP release in the downgradient PS/WC wells. In future QMRs, B-zone plume maps should be drawn to show that the diesel and MTBE plumes mapped at the KMEP and ST Services facilities are continuous with the plume observed in PS/WC-3B. 6. Ash Creek flagged the order of magnitude increases observed for TPHg, TPHd, and benzene in monitoring well ACA-213 during January 2007, and stated that confirmation sampling will be conducted in the second quarter to confirm the observed increases. However, Regional Water Board staff are unclear on how groundwater sampling conducted three months later can be used to confirm groundwater monitoring results at a site where COC concentrations routinely fluctuate by 1 ,000s of pg/L. Ash Creek does not apply this procedure to concentration decreases, such as the fourth quarter 2006 to first quarter 2007 decrease in TPHd in monitoring well PS/MW-15 from 2,100 pg/L to 160 pg/L. Regional Water Board staff interprets the first quarter 2007 monitoring results as confirmation that the hydrocarbon plume emanating from the ST Services site greatly exceeds WQOs and requires active remediation to accomplish cleanup in a reasonable time. 2 Hart Crowser, Enhanced Bioremediation Pilot Study Evaluation Report, September 23,2004