SITE INFORMATION AND CORRESPONDENCE

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Mr. Jeff Baker . -4 - • 11 March 2009 Stockton Terminals Technical Committee Our comments are presented below. 1. The Revised Contingency Plan incorporates changes to the original text, prepared in 2003, that clarifies the identities of monitoring wells and compliance limits, and adds TBA to the list of volatile organic compounds monitored in remedial observation wells. Regional Water Board staff concur with the terms of the Revised Contingency Plan for the perimeter ozone injection systems. 2.. The 2 July 2008 Addendum to Work Plan for Additional Monitoring Well Installation specified that grab groundwater sampling would be conducted at 5-foot intervals during installation of the seven new monitoring wells. However, grab groundwater sampling was not conducted in the fine grained units at 140 and 150 feet bgs in boring TS/MW-2D. In addition, there is no evidence that any grab groundwater sampling was conducted in the other six boreholes. The lack of groundwater data from these boreholes and the petroleum hydrocarbons detected in the wells installed in the boreholes is evidence that the vertical and lateral extent of petroleum hydrocarbon pollution downgradient of the site remains undelineated. 3. The cross-section in the Assessment Report shows there is a fine grained unit at about 125 feet bgs in boreholes TS/MW-3D, OW-8D, and OW-3DR, indicating that this D zone unit is laterally continuous for about 1,100 feet downgradient of the source area. The STTC arbitrarily has depicted this bed as a pinch-out layer between TS/MW-3D and OW-8D. In addition, the base of the cross-section schematic is truncated below PS/MW-20D where the coarse grained bed should be connected between OW-8D and OW-3DR. STTC needs to explain why this D zone coarse grained unit was not interpreted as laterally continuous where similar data were used to show that shallower units (A, B and C) are continuous. 4. The cross-section also shows that monitoring well OW-5D, which is located about 1,500 feet downgradient from source area well TS/MW-2D and screened in the same fine grained stratum, contains similar detections as TS/MW-2D. The three D zone monitoring wells (OW-8D, PS/MW-20D, and OW-3DR) located in between these two wells are not screened in the same fine grained unit but also contain similar detections of TPHg, TPHd, and benzene. The borehole data provide evidence that individual fine and coarse grained strata within the D-zone do not occur at uniform depths throughout the entire site. However, this geometry is commonplace since local fluvial processes that deposited the beds rarely, if ever, superposition individual strata within a bed like a layer cake. As discussed in the previous comment, the D zone unit as a whole is laterally continuous and transmits contaminants well downgradient of the source area. Therefore, contrary to statements in the Assessment Report, any wells screened within any depth of the D zone water bearing unit, including OW-81D and OW-5D, are in communication with each other. The similar contaminant concentrations observed in OW-5D and TS/MW-2D call into question whether the proposed communication test is warranted. It does show, however, that adequate communication exists within and between individual D zone strata.