SITE INFORMATION AND CORRESPONDENCE

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Mr. Steve Osborne - 3 - 20 June 2011 KMEP Stockton Terminal elevated photoionization detector (PID) readings were recorded in soil below the first encountered groundwater (A zone). KMEP suggests there may be a shallow source zone in the vicinity of SP/M-10. Monitoring well SP/M-10 consistently contains the greatest benzene concentrations at the Site. Wells closer to the manifold area contain lower benzene concentrations than SP/M-10. This suggests that SP/M-10 is near a source of petroleum hydrocarbons other than the manifold area. In addition, the benzene and MTBE concentrations in SP/M-10 are similar to NuStar wells PS/MW-14 and ST/MW-1. Finally, KMEP analyzed groundwater samples at the Site for additional volatile organic compounds (VOCs); SP/M-10 was the only well to contain detections of trimethylbenzene and naphthalene, which are less mobile than benzene and MTBE and are typically found near the source area. Central Valley Water Board staff concur with KMEP that petroleum hydrocarbons in monitoring well SP/M-10 likely originated from a source on the NuStar property and not from the manifold area, which is approximately 200 feet upgradient. 6. The estimated time for MTBE to reach WQOs has increased since the 2008 Estimated Time to Reach Water Quality Objectives report. The Comment Letter clarifies that the 2008 estimates were prepared using very few data points. Central Valley Water Board staff concur with the Comment Letter's conclusion to provide updated trend analysis for Site monitoring wells and evaluate remedial alternatives beyond MNA in the next monitoring report. 7. The Well Installation Report summarizes the installation of wells SP/M-9B and SP/M-9C. KMEP needs to add these wells to the quarterly monitoring program and include the data in future monitoring reports. In summary, KMEP needs to include the following information in future monitoring reports: Tabulated EC, ORP, and DO data; Mann-Kendall statistical tests for trend analysis, estimates of attenuation rates, and estimate of time to reach WQOs for benzene for wells SP/M-1, SP/M-9 and SP/M-10; Mann-Kendall statistical tests for trend analysis, estimate of attenuation rates, and estimate of time to reach WQOs for TPHg in all monitoring wells; Further clarification on considering wells SP/M-3, SP/M-4, and SP/M-6 as commingled wells with the adjacent Tesoro Site; Updated estimate for MTBE concentrations to reach WQOs; Evaluation of the effectiveness of MNA and recommendations for additional work, if necessary; and Monitoring data for newly installed wells SP/M-9B and SP/M-9C.