SITE INFORMATION AND CORRESPONDENCE

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ST Services Stockton Termin� - 3 - 15 May 2007 Monitoring Reports and Char��rization Report reverse was true for the more distant well cluster, ACA-2A and ACA-213. ACA-213 contained TPHg and TPHd at 540 pg/I and 450 pg/I, respectively, but ACA-2A did not contain these COCs. In monitoring conducted during January 2007, TPHg, TPHd, and benzene concentrations increased sharply to 5,200 pg/I, 4,300 pg/I, and 3,000 pg/I, respectively. Table 3 shows the results of monitoring for monitored natural attenuation (MNA) parameters, which is being conducted to evaluate MNA as a potential remedial technology for the Site. Regional Water Board staff conducted a site visit on 19 April 2007 to observe current site conditions. Ms. Wendy Cohen and I were accompanied by Ms. Amanda Spencer of Ash Creek and Mr. Joe Aldridge of NuStar throughout the site visit. I also spoke with Ms. Spencer by telephone on 27 April 2007 about recent monitoring results observed in the newly installed well pairs. Our comments on the Third QMR, the Annual Report, the Report, and the First QMR are presented below. 1 . In the Third QMR and the Annual Report, Figures 7 and 8 show TPHg and TPHd concentration isopleths that represent the horizontal distribution of these CDCs at the Site. SPH is written next to monitoring well PS/MW-14 on Figure 7 of both reports, indicating that the separate phase product observed in the well during the third and fourth quarters is gasoline. However, SPH is not written next to monitoring well PS/MW-14 on Figure 8 in either report. The 28 October 2002 Additional Site Assessment Report prepared by SECOR on behalf of ST Services shows that soil and groundwater from boring ST/SB-8 (advanced in the vicinity of PS/MW-14) contained TPHd at 5,700 mg/kg and 9,000,000 pg/l, respectively. These results show that diesel SPH remains in the subsurface even after ST Services conducted a soil removal action in 2002 to remediate the release from diesel AGT D1503. Unless there is information to the contrary, Ash Creek must note SPH next to monitoring well PS/MW-14 on Figure 8 in future QMRs whenever free product is observed in this well, to disclose that diesel SPH is present at the site. 2. There are seven B-zone wells at the Site. Four of the seven wells contained TPHg and TPHd in excess of WQOs during the most recent monitoring events. However, Ash Creek did not prepare contour maps for this water bearing zone. During my phone conversation with Ms. Spencer on 27 April 2007, she stated that she will include B-zone maps in all future QMRs. 3. During the site visit, Ms. Spencer and Mr. Aldridge stated that they intend to conduct monitoring for about one year after the new well installations in Fall 2006 to evaluate MNA as a remedial technology. This strategy is based on the Regional Water Board's 15 February 2006 letter stating that ST Services needs to conduct additional groundwater characterization to demonstrate decreasing concentration trends before the recommendation for MNA can be properly evaluated. We are concerned, however, that the evaluation presented in the 5 January 2006 Cleanup Plan (Cleanup Plan) that was used to select MNA is incomplete. Given the presence of free product in groundwater, it is unlikely that MNA will achieve WQOs in a reasonable time.