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Mr. Jeff Baker - 2 - 30 July 2008 Stockton Terminals Technical Committee The Work Plan also 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-81D and OW-51D. PS/MW-20A will only be installed if attempts to locate the existing well PS/MW-20 fail. Regional Water Board staff provided concurrence with these well installations in our 30 May 2008 letter. The Work Plan proposes to relocate the wells 50 feet to the north of the original locations to avoid damage to the wells from activities at the recycling facility. As stated in our 30 May letter, the STTC monitors the operation of an ozone sparge (OS) system in six A and B zone remedial observation wells (PS/MW-18, PS/WC-1S, AR/MW-21A, AR/MW- 18B, AR/MW-21 B, and PS/WC-1 M). A contingency plan would be 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. However, the document does not list the specific hydrocarbons that trigger application of the contingency plan. On behalf of ARCO, Mr. Haeck, said that he would be in touch with me to get a list of trigger constituent concentrations worked out by 19 September 2008. Finally, as discussed in Comment No. 2 of our 30 May letter and during the 5 June meeting, Regional Water Board staff believes that the recent elevated concentrations of TBA observed in remedial observation well AR/MW-18B warrant inclusion of this contaminant in the contingency plan list of trigger hydrocarbons for the OS monitoring program. The Addendum states that this comment will be addressed in a separate letter to the Regional Water Board. Our comments are presented below. 1. During the 5 June meeting, STTC stated that the increasing benzene concentrations observed in OW-3C and mentioned in the Regional Water Board staff's 25 April 2008 letter have recently been characterized by three consecutive non-detects (NDs). The data show that this observation is correct, but OW-3C is still characterized by elevated TPHg concentrations, and this shows that the C zone in the vicinity of this well is polluted. Regional Water Board staff concurs with the STTC's proposal to abandon and relocate monitoring wells OW-3C and OW-31D because the data obtained from these wells are critical to the monitoring program. We also concur with the proposal to install the three B to D zone monitorina wells in the vicinity of PS/MW-20A and to abandon and replace PS/MW-20A, if warranted. By 29 August 2008, STTC needs to submit a schedule to conduct this work and to submit a Report of Findings. 2. Regional Water Board staff cannot concur with Tesoro's proposal to install injection well TS/MW-3D until we have had the opportunity to review the data and rationale used to select this approach. In addition, the vertical extent of the plume in this area is not delineated and is needed in order to perform an adequate evaluation of potential remedial technologies. By 5 September 2008, Tesoro must submit a Feasibility Study (FS) evaluating several remedial technologies and select one or two for pilot testing to mitigate D zone pollution. Following Regional Water Board staff concurrence with the FS, Tesoro will need to submit a pilot study work plan. The FS must contain a strategy for defining the vertical extent of pollution in the vicinity of the proposed TS/MW-3D. 3. By 19 September 2008, STTC needs to submit the proposed list of petroleum hydrocarbons and respective trigger constituent concentrations that will be incorporated into OS monitoring