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2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the fourth quarter 2006 are summarized in Table 2-2 and Appendix D presents time -series charts of select parameters. As shown on Table 2-2, excluding suspected laboratory contaminants, estimated trace VOC constituent concentrations (between the method detection limit [MDL] and the practical quantitation limit [PQL]) of tetrachloroethene (PCE) and trichloroethene (TCE) were measured in the sample collected from well MW -1B; PCE in the sample collected from well MW -10; 1, 1 -dichloroethane (1,1 -DCA) and TCE in the sample collected from well MW 14; and carbon disulfide in the sample collected from well MW -17. In addition, PCE was detected above the PQL in the sample collected from well MW -14. On behalf of Forward Inc., GLA prepared a letter report dated February 14, 2001 (RWQCB Case No. 2209), to assess the source and potential impacts of low- level VOCs in groundwater adjacent to the Forward Landfill. The letter report concluded that the sporadic detection of low-level VOCs in groundwater (and lysimeter samples) at the Forward Unit are most likely due to landfill gas from unlined unit WMU-B. Forward has continued to minimize gas related impacts to groundwater by minimizing interim fill areas that promote ponding of water. Furthermore, in accordance with CCR Title 27, Section 20937, Forward continues to install additional landfill gas extraction wells. New Historical Intrawell Maximum Values During the fourth quarter 2006 monitoring period only a trace concentration of dibromochloromethane was measured at a new historical intrawell maximum values in the sample collected from well MW -1. As discussed in Section 2.1.2, dibromochloromethane is a suspected laboratory contaminant. Concentration Limit Thresholds Data obtained during the fourth quarter 2006 monitoring period were compared to concentration limits (CLs) as specified in the RPCMP for the Forward Landfill. CLs were calculated by Herst & Associates and are included in Appendix D. Table 2-4 summarizes concentration limits that were exceeded in samples collected from groundwater monitoring wells during the fourth quarter 2006. As summarized in this table, CLs were exceeded for wells MW -1B, MW -313, MW -10, MW -13, MW -14, MW -15, MW -16, MW -17, MW -18, MW -19, MW -21, MW -22, and MW -23R. In accordance with the RPCMP, wells with exceedances of CLs will be resampled in February during the first quarter 2007 sampling event and a second independent sample will be collected in March 2007. The results of the retesting events will be submitted to DTSC and RWQCB under separate cover. 2.1.5 Vadose Zone Monitoring n The current vadose-zone monitoring network at the Forward Unit consists of 16 lysimeters. The lysimeter locations are shown on Figure 2-1. Each accessible lysimeter D:\2003_021\ForwardAustin_fO6.doe\ 6 Geologic Associates