ARCHIVED REPORTS_QUARTERLY REPORT - SECOND QUARTER 2008

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dichloropropane,tetrachloroethene, 1,2,3-trichloropropane, methylene chloride, benzene, toluene and xylene detected during this monitoring event. In general,the groundwater plume size appears stable with relatively consistent analytical results over time. Concentration trends appear to be generally stable. Two wells in the interior of the plume (MW-3B and MW-4B) have historically experienced significant variability in carbon tetrachloride concentrations over time. However, MW-3B appears to be relatively stable since the fourth quarter 2003. MRP R5-2007-0826 now requires semi-annual monitoring for select inorganic parameters in the groundwater plume monitoring wells. During the 18 June 2008 sampling event wells wells MW- 3B, MW-9B and EW-11B were analyzed for chloride; while wells MW-3B MW-4B, MW-5B, MW-913, MW-IOB, and EW-11B were analyzed for nitrate. Concentrations for nitrate, which is not required by the MPR, but used to monitor aquifer conditions favorable to carbon tetrachloride reduction, ranged between 22 mg/L and 46 mg/L and chloride ranged between 94 mg/L and 120 mg/L. Changes in chloride conentrations over time will provide information on the reduction of carbon tetrachloride to chlorides. Dissolved iron was not detected in any of the three wells sampled during the June 2008 sampling event. Total organic carbon was not analyzed during this monitoring event. Results from the analysis of inorganic parameters are presented in Table 6. 3.2 Recirculation Pilot Study Results During the 5 May 2008 pre-startup monitoring event, potentiometric elevations for the intermediate wells varied from 9.20 to 9.76 ft below mean sea level. Based on the water level data collected on 05 May 2008 the groundwater flow direction is interpreted to be variable with a hydraulic mound near well MW-9B. This hydraulic mound has consistently occurred since well MW-9B was installed near the zero valent iron injections. Carbon tetrachloride and chloroform was detected in all six monitoring wells sampled; concentrations ranged from 120 ug/1 to 740 ug/1 for carbon tetrachloride, and 23 ug/I to 120 ug/1 for chloroform. There were also low levels (less than 15 µg/1) of 1,2-dichloroethane, 1,2- dichloropropane, tetrachloroethene, 1,2,3-trichloropropane, methylene chloride, benzene, toluene, ehtylbenzene and xylene detected during this monitoring event. Groundwater samples collected in May and June 2008 from wells MW-313, MW-4B, MW-5B, MW-9B MW-IOB and MW-13B were analyzed for chloride with concentrations ranging between 100 mg/L to 130 mg/L. Nitrate and dissolved iron were not analyzed in May 2008. Results from the analysis of inorganic parameters are presented in Table 5. The groundwater recirculation pilot study was started on 19 May 2008 utilizing paired groundwater extraction and injection wells EW-11B and IW-BH2A. Extraction well EW-11B is located in the northwestern portion of the site, while injection well IW-BH2A is located 9