ARCHIVED REPORTS_2008_20 - Laserfiche WebLink

Home Browse Search

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 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, five new historical intrawell maximum values were measured during the fourth quarter 2008 monitoring event. New Historical Intrawel Maximum Values Well Analyte New Value Previous Value MW-16 Chromium,Hexavalent 9.7 gg/L 9.1 µg/L MW-23R Magnesium 69 mg/L 64 mg/L Nitrate-N 35 mg/L 32 mg/L Strontium 1.700 mg/L 1.600 mg/L Sulfate 330 mg/L 280 mg/L Concentration Limit Thresholds Data obtained during the fourth quarter 2008 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 fourth quarter 2008. As summarized in this table, CLs were exceeded for wells MW-lA, MW-2A, MW-3A, MW-10, MW-13, MW-14, MW-15, MW-16, MW-17, MW-18, MW-19, and MW-21. In accordance with the RPCMP, wells with CL exceedances (other than arsenic,bicarbonate, hexavalent chromium, nitrate as nitrogen, and sulfate, which the RPCMP do not consider impact constituents) will be resampled in February during the first quarter 2009 sampling event and a second independent sample will be collected in March 2009. The results of the retesting events will be submitted to DTSC and RWQCB under separate cover. On behalf of Forward, GLA has submitted a request to the DTSC to update the CLs for 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—10 to—25 inches of mercury on November 13, 2008. On December 9, 2008, the lysimeters were again checked and positive pressure was applied to evacuate the accumulated sample. As recorded in the field notes for lysimeters (Appendix C) and summarized on Table 2-5, lysimeters E-2, W-2, LY-A, and LY-BG1 had a sufficient volume of soil-pore liquid for sample D:U008_0010\FA_4Q08.doc 6 Geologic Associates