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Mr. Eric Jenks • -2- 17 May 2012 2. During the 2011 monitoring and sampling events, the average depth to groundwater was inconsistent with the historical data. Continued monitoring and comparison of 1,2,3-TCP levels in relation to groundwater level is needed. Wilbur-Ellis also needs to examine the groundwater levels with respect to the nearby land development projects. This could include examining any upgradient dewatering activities, or groundwater extraction activities that could affect the downgradient water levels at the JTF Site and plume migration. 3. Staff notes that chloroform was detected between 2.3 to 2.4 pg/L in the groundwater samples collected from MW-1 during the 2011 monitoring events. The Report does not provide the cause(s) of these detections. Chloroform was not detected in groundwater before March 2006. In a letter dated 7 May 2009, Central Valley Water Board staff requested Wilbur-Ellis to determine the cause for high chloroform levels in the groundwater. As of today, no explanations have been provided for the presence of chloroform in MW-1. In 2009, Central Valley Water Board staff contacted the California Water Service Company, which informed the staff that there was no water supply well within the 2000-foot radius of the Site, and no leakage or malfunction had been reported from the water distribution system. Therefore, staff concludes that Wilbur-Ellis needs to conduct further investigation to discover the cause of chloroform pollution in the groundwater. This investigation could include examining water usage by the nearby land development projects, and examining nearby landscape irrigation, planters irrigation, leaking pipes or sewer lines in the vicinity of the Site. Please include the results from the investigation studies in the next semi-annual groundwater monitoring report due by 1 November 2012. 4. Table 2 in the MRP No. R5-2010-0803 states that , "if all constituents in an analytical suite are not detected in any deep monitoring well during the first two consecutive events, that analytical suite may be removed from the sampling schedule with Central Valley Water Board staff concurrence." In the Report, Wilbur-Ellis recommends to remove organophosphorous pesticides (OPP) from the sampling schedule for monitoring well MW-11. Central Valley Water Board staff concurs with the recommendation to remove OPP from the sampling schedule for existing on-site deeper groundwater well MW-11. Please note, all future deeper groundwater wells must follow the current MRP requirements, and OPP must be analyzed for two consecutive monitoring cycles from all future deeper groundwater monitoring wells. If you have questions or comments, please contact me at 916-464-4658, or by E-mail at ssewaliaCa)-waterboards ca qov i Siddharth Sewalia Water Resource Control Engineer Private Sites Cleanup Unit KAR_ E. LONGLEY SCD, P.E., CHAIR I PAMELA C. CREEDON P.E.. BCEE, EXECUTIVE OFFICER 11020 Sun Center Drive 17200,Rancno Cordova,CA 95670 i wwwwaterboards.ca.gov/centralvalley Qi—cvc110 rnrLn