ARCHIVED REPORTS XR0006976 - Laserfiche WebLink

Home Browse Search

in samples collected from 40 feet bgs 7 4 milligrams per kilogram [mg/Kg]), 49 feet bgs p g ( g p g (9 4 mg/Kg), 85 feet bgs (2 1 mg/Kg), and 95 feet bgs. (1 0 mg/Kg) Benzene and MTBE were not detected in the boring B-17 soil samples The extensive excavation, lack of hydrocarbons in SVE influent samples, and very low concentrations reported in samples from the confirmation boring suggest residual hydrocarbons have been effectively removed from the vadose zone 4.4 Extent of Petroleum Hydrocarbon Impact to Groundwater At the time of the fourth quarter 2005 groundwater sampling event (December 20, 2005), TPHG was reported in wells MW-13 (390 µg/L) and MW-14 (190 gg/L), and 1,2-DCA was reported in wells MW-14 (5 9 µg/L) and AS-1 (12 µg/L) Benzene or MTBE were not reported in any of the wells TPHG, benzene, and MTBE concentrations in all three wells show a decreasing trend The 1,2-DCA concentrations in well MW-14 also indicate a decreasing trend, but the 1,2-DCA concentration in well AS-1 does not appear to be decreasing During the recent CPT investigation, TPHG was reported only in boring CPT-2 at 73 feet bgs (51 pg/L) and 126 feet bgs (180 pg/L) TPHG concentrations in samples collected at 83, 95, and 112 feet bgs in boring CPT-2 were below laboratory reporting limits, and TPHG was not reported in any of the samples form the other CPT borings Benzene and MTBE were not reported in any of the CPT samples 1,2-DCA was reported in samples collected from borings CPT-2 (73 and 83 feet bgs), CPT-3 (71 and 80 feet bgs), CPT-4 (77 and 97 feet bgs), CPT-5 (71 feet bgs), and CPT-8 (62, 72, and 81 feet bgs) The highest 1,2-DCA concentration (140 µg/L) was reported for the sample collected at 72 feet bgs in boring CPT-8 Based on these data and data from the former monitoring well network, the lateral extent of TPHG and MTBE impact appears to be limited to the area in the immediate vicinity of wells ' MW-13, MW-14, and boring CPT-2 (Figure 6) Benzene has also been reported in these wells, but concentrations have shown a decreasing trend, and benzene is currently not reported in the monitoring wells The CPT data suggest the vertical extent of TPHG, benzene, and MTBE impact has been adequately characterized Additional characterization of the TPHG, benzene, and MTBE plumes does not appear warranted iThe lateral extent of the 1,2-DCA impact in groundwater has not been adequately characterized Further characterization of 1,2-DCA east of CPT-5 and east and southeast of CPT-8 appears warranted The vertical extent of 1,2-DCA impact in the vicinity of CPT-2 through CPT-5 has ' been adequately characterized, but further characterization of the vertical extent in the vicinity of CPT-8 is warranted 1 K\Te,ch"IStockton-I111Reportslsc n 04-2006 doc Page 9 STRATUS