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Mr. Andrew Smith 0 - 2 - • 15 August 2006 removal from the groundwater appears to have reached a plateau and recommends that this interim remedial measure be discontinued. Regional Water Board staff specific review comments on the reports are as follows: Annual Report 1. In Section 2.2.1, Ground Water Pump-and-Treat Operation, the second paragraph states that the field sheets and data are included in Appendix B. These sheets were not included in the document and should be submitted. 2. TPHd and TPHg were reported at shallow well MW-14 and TPHd, TPHg, and BTEX were reported at deep well MW-7 in December 2005. Advanced could not account for these detections in the Annual report. These detections may be anomalous, as TPHd, TPHg, and BTEX have not been reported at these wells since that time. Well MW-7 is located immediately north of extraction well EW-1. Well MW-14 is located about 160 feet north and cross-gradient of well EW-1. Second QMR 1. In 2006, groundwater pump-and-treat system influent TPHg concentrations have fluctuated between non-detect (February, March, and June 2006) and 850 pg/L (May 2006) showing an overall decline from a high of 8,000 pg/L in July 2005. Influent MTBE concentrations decreased from 320 pg/L in December 2005 to non-detect in June 2006. Advanced recommends ceasing operation of the pump-and-treat system because MTBE removal appears to have reached a plateau and contaminants are present in only one well, MW-4. From December 2005 to June 2006, groundwater concentrations in well MW-4 have increased from 1,900 pg/L to 3,000 pg/L TPHg and 11,000 pg/L to 17,000 pg/L TPHd. Regional Water Board staff does not concur with the recommendation to cease remedial system operation based on the increasing concentration trend at well MW-4 which is located upgradient of extraction well EW-1. Continued operation of the remediation system is warranted to capture groundwater pollutants as they migrate downgradient. Advanced may want to consider installing an extraction well near well MW-4 to reduce contaminant concentrations in this area. 2. Advanced recommends destruction of shallow well MW-13 as it has been dry for the past several years. The well is located at the top of the levee upgradient of both the underground and aboveground storage tanks at the site. Regional Water Board staff concurs with the recommendation to destroy this well. Advanced should submit a work plan for destruction of well MW-13 for Regional Water Board review and approval. If you have any questions or comments regarding this letter, you may contact me at (916) 464- 4719 or by email at mcllardy@waterboards.ca.gov. jhl, � /V e4cj Mark W. Clardy, P.G. Engineering Geologist Private Sites Cleanup Unit