ARCHIVED REPORTS_2010_12 - Laserfiche WebLink

Home Browse Search

total xylenes were detected at trace concentrations. In the samples collected from wells MW-14 and MW-16, PCE was measured at trace concentrations. 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 WW-B. The particular VOCs detected in samples during the current monitoring period appear to support this conclusion. Forward has continued to minimize gas related impacts to groundwater by limiting 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, as needed. New Historical Intrawell Maximum Values As shown in the table below,three new historical intrawell maximum values were measured during the second quarter 2010 monitoring event. New Historical Intrawell Maximum Values Well Analyte New Value Previous Value MW-2A Toluene 0.76 0.19' MW-10 DCDFM 1.1 0.97 TCFM 0.96 0.78 Notes: j—Trace value(between the MDL and PQQ. Concentration Limit Thresholds Data obtained during the second quarter 2010 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 CLs that were exceeded in samples collected from groundwater monitoring wells during the second quarter 2010. As summarized in this table, CLs were exceeded for toluene at well MW-2A; for DCDFM and TCFM at well MW-10, and for sulfate at background well MW-22. In accordance with the RPCMP guidelines, CL exceedances for non-impact constituents (arsenic, bicarbonate, hexavalent chromium,nitrate as nitrogen, and sulfate)are not retested, and therefore,retesting for sulfate is not required. In addition, CL exceedances for these low-level VOCs are not retested since similar low- level VOCs have been confirmed at the Forward Unit. 2.1.5 Vadose Zone Monitoring The current vadose-zone monitoring network at the Forward Unit consists of 17 lysimeters. The lysimeter locations are shown on Figure 2-1. Each accessible lysimeter was inspected and vacuums were reset to approximately 20 inches of mercury on June 4,2010. On June 24, 2010,the lysimeters were again checked and positive pressure was D:%2010_0013\FA_2Q10.doc 6 GeoLogic Associates