ARCHIVED REPORTS XR0006662 - Laserfiche WebLink

Home Browse Search

S ESC ® R concentrations of GRO since November 2002, with a maximum concentration detected at 370 pg/L during the third quarter 2005 The laboratory, however, indicated that this value was an estimated value Evaluation of dissolved concentrations through the fourth quarter 2005 indicates that the highest concentrations of petroleum hydrocarbons continue to be detected off-site in the vicinity of Shell wells S-1 and S-2 During the fourth quarter 2005, with the exception of a concentration of GRO (2,800 pg/L) in well MW-3, GRO and BTEX were not detected at or above laboratory MRLs, maximum concentrations of GRO and benzene were detected in Shell wells S-2 (12,000 pg/L) and S-1 (290 pg/L) respectively The constituents of concern at the site include dissolved MtBE and TBA MtBE has historically been detected in the majority of the site wells, with the highest concentrations reported in wells MW-3 and MW-7 at site maximum concentrations of 198,000 pg/L (MW-3) and 233,000 pg/L (MW-7) in 2001 MtBE has significantly declined in the site wells over time since 2001, which is likely due to the metabolism of MtBE into TBA by natural attenuation and/or as a result of active remediation through the operation of the OS system During the fourth quarter 2005, MtBE was detected in wells MW-4 through MW-6 and MW-11 up to a maximum concentration of 28 pg/L Split samples collected from Shell wells S-5 and S-6 this quarter contained MtBE at respective concentrations of 260 pg/L and 300 pg/L Other site wells and Shell wells did not contain MtBE at or above laboratory MRLs Since the initiation of consistent TBA sampling during the first quarter 2002, TBA peaked in wells MW-3 (240,000 pg/L), and MW-7 (220,000 pg/L) in 2002, and although elevated concentrations continue to be detected in these wells, TBA levels have since declined in these wells over time During the fourth quarter 2005, wells MW-3 and MW-7 contained TBA at respective concentrations of 22,000 pg/L and 24,000 pglL, respectively TBA levels in wells MW-1, MW-4 through MW-6, MW-8 through MW-10, MWA 2, and MWA 3 have either decreased to relatively minor to non-detectable concentrations, or have generally been non-detectable Deeper well MWA 1, which has contained relatively minor levels of MtBE, contained elevated concentrations of TBA with the highest levels reported during the third quarter 2005 (16,000 pg/L) A generally increasing TBA trend has been observed in the well since November 2002 Historical analysis of TBA in the off-site Shell wells indicated that the highest concentrations have historically been detected in on-site well S-2 (1,700 pg/L, split samples collected by TRC in November ' 2004 and February 2005), and in off-site well S-5 (1,400 pg/L, November 2004) TBA was present in wells S-2 (950 pg/L), S-5 (21 pg/L) and S-6 (93 pg/L) during the fourth ' quarter 2005 Other fuel oxygenates and the analyte acetone (MW-3 and MW-7 only), were not detected in the site wells at or above laboratory MRLs during the fourth quarter 2005 Low levels of 1,2-DCA were detected in wells MW-3 (15 pg/L) and MW-12 (0 63 pg/L) The samples collected from the Shell wells did not contain other fuel oxygenates, 1,2- DCA, and EDB at or above laboratory MRLs, with the exception of the following DIPE in wells S-1 (43 pg/L) and S-3 (61 pg/L), 1,2-DCA in well S-3 (3 8 pg/L), and TAME in wells S-5 (1 6 pg/L) and S-6 (1 9 pg/L) 11BP-ARC01191921Reporls\QMR-Q RPS1200514Q2005 QS SR and QRPS doc K