ARCHIVED REPORTS_FIRST SEMIANNUAL AND 2014 ANNUAL GROUNDWATER MONITORING REPORT

Home Browse Search

2.RESULTS FOR FIRST SEMIANNUAL PERIOD 2014 Slough Road toward the sandy sediments southeast of Whiskey Slough Road. The water table drains from the clayey sediments laterally into the sandy sediments at the band shown by water table elevation contours-1 foot msl and-8 feet msl. This flow results in a focusing effect where groundwater in the sandy sediments southeast of Whiskey Slough Road is naturally directed toward a common area in the vicinity of the two formerly operated extraction wells,RW-1 and RW-3. Locally,the former release area is bounded on three sides by a constant head—to the north and west by Trapper Slough and to the south by the area with standing water. These boundaries result in locally focused groundwater flow toward the area between the two access roads(of the former pipeline and the bypass pipeline) that then drains to the southeast. Groundwater Analytical Results t Analytical results for groundwater samples collected on March 5,2014,are presented in Table 3. TPHg and benzene concentration contours for these data are shown in Figures 4 and 5, respectively. These data are further presented as follows: • Appendix C-Tabulated with most recent eight monitoring events • Appendix D- Time series concentrations charts for wells with consistently detectable constituents(M-10, N-7,N-8,0-1,N-15, N-16,N-17, and RW-1) • Appendix E-Long-term trend concentration charts,by expanding the future scale of the charts in Appendix D to 2050 to better see the long-term concentration trends Shallow Groundwater Laboratory analytical results of shallow groundwater samples are consistent with data reported during previous quarters, as shown in the time-series concentration charts in Appendix D. The data indicate that the lateral extent of petroleum-affected shallow groundwater is stable. The downgradient lateral extent of petroleum-affected groundwater is defined by wells N-18,N-19,and N-20 (petroleum hydrocarbons were not present above the laboratory reporting limits in these wells). Compounds detected in shallow groundwater during the first semiannual period 2014 include the following: • TPHg was detected in shallow groundwater at wells N-7,N-8,N-16,N-17, and RW-1. , Reported concentrations of TPHg in these wells ranged from 10.70 milligrams per liter (mg/L) at well N-16 to 12 mg/L at well N-7. • TPHd was detected in shallow groundwater at wells N-7,N-17, and RW-1. Reported concentrations of TPHd in these wells ranged from 1.1 mg/L at well RW-1 to 8.7 mg/L at well N-7. • BTEX compounds were detected in shallow groundwater at wells N-7,N-8,N-15,N-16, N-17,0-1,and RW-1. Reported concentrations of benzene in these wells ranged from 0.61 micrograms per liter (µg/L) at well N-15 to 2,900 gg/L at well N-7. Deeper Groundwater No TPHg, TPHd,or BTEX compounds were detected in samples from deeper well N-24. This is consistent with data reported during previous sampling events. 2-4 ES041514081714SCO/HOLT_1SA14_TEXT_FINAL