SITE INFORMATION AND CORRESPONDENCE

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r Mr. Joe Aldridge -4 - 22 April 2009 NuStar Terminals Stockton Facia,, the deep water bearing unit in which it was detected. Given this conceptual model of vertical penetration through aquitards, it is unclear to us why lateral migration along horizontal beds would more inhibited. The data at NS-21 provide evidence that it is not. The geometry of the water bearing units underlying the Site vicinity can be interpreted in many ways, with none necessarily less correct than another. Therefore, NuStar is free to re-classify the water bearing units as it wishes. However, Central Valley Water Board staff does not concur that re-classification or renaming is necessary or increases in any substantial way the understanding of the migratory pathways underlying the Site. 4. The data that show elevated TPHd concentrations in groundwater in C- and D-zones in borings NS-11, NS-7, NS-3, NS-10 NS-14, and NS-21 can be explained by the existence of the continuous migratory pathways identified by NuStar in the first paragraph on Page 16. NS-11 is downgradient of the location of a 1,000-gallon spill that occurred in 2002 from Tank 1503. The TPHd concentrations in these borings downgradient from NS-11 are some of the highest observed at the Site and vary from 1,500 to 54,000 mg/L. This indicates that the key to controlling the migration of a significant mass of petroleum hydrocarbons to areas downgradient of the Site is to fully delineate and mitigate the source area indicated by NS-11 and monitoring wells PS/MW-14 and PS/P-12. The data, which did not include laboratory analytical results from soil sampling at NS-21, do not support NuStar's recommendation that a source exists to the east at MacSteel or any other facility east of Stork Road. 5. The contaminant concentration trends in the Annual Report verify the comments in our 26 March 2000 letter, which state that active remediation is necessary at this Site due to the extended time that would be required to remediate by MNA. Separate phase hydrocarbons are no longer detected in ST/MW-1, and the dissolved plume data show that TPHg concentrations have decreased during this year. Other constituents are stable or increasing. Historical results of wells which typically exhibit elevated.dissolved phase concentrations (PS/P-11, PS/P-12, PS/MW-14, and PS/WC-2S, PS/MW-15) exhibit mixed trends. 6. Regional Water Board staff do not allow the use of silica gel cleanup before analysis. Silica gel cleanup is a tool that is used to separate polar organics from normally non-polar petroleum hydrocarbons in water samples, but silica gel can also filter out non-polar petroleum hydrocarbons. In addition, the polar organics may be early breakdown products of petroleum hydrocarbons and should not be ignored. NuStar may not use the silica gel cleanup for future sampling events. We concur with the B- and C-zone well installations proposed in the Investigation Report. By 19 June 2009, NuStar must submit a work plan to perform the proposed well installations. The Work Plan must incorporate our requirements to vertically delineate and install monitor wells to ND for all CDCs at all proposed locations (P-A through P-D). This will require the installation of D-zone wells. In addition, Location D must be moved to the area of NS-11.