SITE INFORMATION AND CORRESPONDENCE_2001-2018

Home Browse Search

Jeff Whitworth • -3 - • 14 September 2007 Shell Stockton Terminal SA with additional costs for more than one SA pilot tests. Based on the differences in soil types underlying each SA, as well as the variability in contaminant concentrations, the Regional Water Board staff believes that pilot testing in all three SAs will be necessary to obtain accurate remedial technology data. Please either revise the WP-FS to specify pilot testing in all three SA or provide the rationale to justify that pilot testing at one SA will provide representative pilot study data. 4. We do not concur with Shell's proposal to use Region 2's ESLs or Risk-Based Corrective Action (RBCA) to establish site-specific cleanup levels. In the Central Valley Region, as described in the Basin Plan, cleanup levels for groundwater are required to be consistent with State Water Resources Control Board (State Water Board) Resolution No. 68-16 (the antidegradation policy) and State Water Board Resolution No. 92-49. Based on these resolutions and the Basin Plan, cleanup levels for groundwater are background concentrations. If background is not technically or economically feasible to achieve, cleanup levels must be consistent with WQOs. Soil cleanup levels are those levels which will not degrade groundwater quality and may be determined by use of the Designated Level Methodology. 5. We concur with Shell's proposal to discharge the treated DPE effluent to the vacant lot north of the facility, if Shell enrolls in Order No. R5-2003-0044 and meets all the requirements of that Order. We agree that implementation of this disposal method will depend the results of infiltration testing to determine capacity of the soil in this area. However, we are concerned about break-through of TBA occurring in the treatment system. If Shell uses this option, Shell will need to ensure the TBA in the treatment system effluent meets permit limits. 6. We concur that additional groundwater data are needed to assess the extent of pollution in the deeper zone and to determine whether the downward vertical gradient is resulting in the downward migration of the plume. However, if pollutants are detected in the deeper zone, an accurate assessment of their extents will require monitoring well installation. The WP-FS needs to be revised to specify that monitoring wells will be installed where grab groundwater samples show that pollution is present in the deep zone. To prevent cross- contamination of deeper zone, dual wall geoprobe borings should be used to complete the exploratory borings, and the wells should be completed using conductor casing. 7. We do not concur that the southwestern edge of the plume is an appropriate location for the four proposed deep borings and/or monitoring wells. The stated purpose of these borings is "to assess the presence and extent of TPHd, TBA and DIPE" in the deeper zone near DW-2, but the proposed borings are distant from DW-2. A single boring advanced downgradient of DW-2 will be sufficient to address this data gap. If pollution is encountered, this boring should be converted into a monitoring well. Additional wells may be needed to further define the extent of pollution. The other three borings should be located at the three SAs to (1) determine the vertical extent of pollution in these areas and (2) evaluate whether a DPE system designed for the shallow zone could effectively address pollution in the deep zones. These borings should The Designated Level Methodology for Waste Classification and Cleanup Level Determination,California Regional Water Quality Control Board Central Valley Region,Updated June 1989.