ARCHIVED REPORTS_20100427 ATC 1Q2010 GWMR COMPLETE

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Ms.Amy Terrell April 27,2010 Page 9 of 10 • A review of reactive zone indicators indicates that microbial activity may not be sufficient for reductive dechlorination. Indicators suggest that microbial activity is minimal. SUMMARY AND FUTURE WORK Sampling for the 2010 annual groundwater and remediation pilot monitoring event will be conducted in the Third Quarter 2010, and the report will be submitted to RWQCB by November 1, 2010. A review of reactive zone indicators indicates that microbial activity may not be sufficient for reductive dechlorination. Indicators suggest that microbial activity is minimal. The projected effectiveness of HRC-X® treatment at this Site was two to four years. It has been 2.5 years since the injection of HRC-X® for the expanded pilot test. A review of dissolved phase COC trends within the Onsite Expanded Pilot Test Area (MW-6R) suggests that TON concentrations (116 mg/L) have been increasing since the 2007 injection event and are greater than the MCL (10 mg/L). Dissolved phase 1,2,3-TCP (3.3 µg/L) and 1,2-DCP (38 µg/L) concentrations have not significantly changed since the 2007 injection event and these concentrations remain above the California Notification Level (0.005 pg/L) and MCL (5 pg/L), respectively. EDB (0.51 µg/L) has steadily been decreasing since the 2007 injection event; however, EDB concentrations remain above the local background level of 0.26µg/L (Geosyntec, 1998). A review of dissolved phase COC trends immediately downgradient of the Onsite Expanded Pilot Test Area (MW-2 and MW-7) indicate that dissolved phase TON, 1,2,3-TCP and 1,2-DCP concentrations exceed their respective MCL or California Notification Level. Dissolved phase 1,2,3- TCP concentrations in MW-2 and MW-7 (0.38 pg/L and 0.43 pg/L, respectively) have slightly decreased since the 2007 injection event. Dissolved phase 1,2-DCP concentrations in MW-2 and MW-7 (9.3 pg/L and 29 µg/L, respectively) have not changed significantly since the 2007 injection event. Dissolved phase TON concentrations in MW-7 (21 µg/L) have not changed significantly since the 2007 injection event. Dissolved phase TON concentrations in MW-2 appear to be increasing, with elevated TON concentrations observed during third quarter groundwater sampling activities. A review of dissolved phase COC trends immediately downgradient of the Offsite Expanded Pilot Test Area (MW-5) indicate that dissolved phase 1,2,3-TCP and 1,2-DCP concentrations exceed their respective California Notification Level or MCL. Dissolved phase 1,2,3-TCP concentrations (0.15 µg/L) have not changed since the 2007 injection event. Dissolved phase 1,2-DCP concentrations (9.3 µg/L) have slightly increased since the 2007 injection event. Dissolved phase TON (2.52 mg/L) and EDB (0.11 µg/L) concentrations are below the MCL (10 mg/L) and background local level (0.26 µg/L; Geosyntec, 1998), respectively; however, dissolved phase TON concentrations appear to be increasing since the 2007 injection event. ATC will continue to monitor the efficacy of the HRC-X® treatment. Based on the declining reactive zone indicators and observed COC trends since the 2007 injection event, ATC is evaluating the need for an alternative remediation strategy for this Site.