ARCHIVED REPORTS XR0006110 - Laserfiche WebLink

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concentrations are associated with the area that was over-excavated contained temporary piezometers PZ1B and PZ2B with 1,800 ug/L and 32 ug/L Benzene respectively on January31, 2003 Newly installed excavation monitor well MW10 contains 1200 ug/L MTBE FIGURE 7A Figure 7A represents the MtBE groundwater in the A zone along with the plume beneath CCFF The Sanchez plume is elongated extending west of the over-excavated area (MW10) out to "Geoprobe" hole P9 were degradation has left only minor TPHg (470 ug/L), Toluene (0 65 ug/L) and tert-Butanol (11 ug/L), the degradation byproduct of MTBE Highest concentrations of MtBE are associated with the areas north and west of MW10 The excavated area (MW10) formerly contained temporary piezometers PZ1A and PZ2A (highest concentration of MtBE 420 ug/L and 72 ug/L respectively on January 31, 2003) The MW 10 area has since reduced to 11 ug/L Newly installed downgradlent well MW9A is below laboratory lower detection limits The CCFF TPHg plume is associated with wells MW1 and MW3 and shows a connection to the Sanchez plume . FIGURE 713 Figure 7B represents the MtBE plume in the B zone Figure 7B resembles figure 7A with the only difference being an increase in MtBE found at wells 6B and 8B Historic water samples obtained from piezometers PZ1B and PZ2B contained 78 and 21 ug/L respectively TBA FIGURE 8A Figure 8A represents the TBA plume in the A zone TBA is only evident in well MW6A at 9 6 ug/L Historically TBA was detected in "Geoprobe" holes P8 and P10 at 11 and 6 ug/L respectively (February 2001) FIGURE 8B Figure 813 represents the TBA plume in the B zone TBA is only evident in wells MW6B and 8B at 12 ug/L Figure 9 illustrates the subsurface lithology and the extent of the A and B zones groundwater plumes within the A and B zones 7 Sanchez QM 1 st 2005