ARCHIVED REPORTS_SECOND SEMIANNUAL AND 2014 ANNUAL GROUNDWATER MONITORING REPORT

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2.RESULTS FOR SECOND SEMIANNUAL PERIOD 2014 2001 groundwater elevation data is presented in the Final Site Characterization Report ' (CH2M HILL,2002). In general, groundwater flow occurs in the direction of maximum potential hydraulic gradient, or perpendicular to the lines of equipotential head. Groundwater elevation is highest in the clayey sediments northwest of Whiskey Slough r Road (approximately 0 foot msl) and lowest in the sandy sediments southeast of Whiskey Slough Road (approximately-9 feet msl). The horizontal gradient magnitude at the site is characterized by the individual gradients across the following three transects for the September 10, 2014, groundwater elevations, all of which are in a west-to-east alignment: • 0.0034 feet per foot(ft/ft) through clayey sediments from well M-3 to the 0-foot-msl ' elevation contour • 0.18 ft/ft through clayey transition zone from the 0-foot to-9-foot-msl elevation contour ' • 0.0010 ft/ft through sandy sediments from well M-8 to well N-19 Sitewide,horizontal groundwater flow occurs from the recharge areas of Trapper Slough ' and the area with standing water through the clayey sediments northwest of Whiskey 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 0 and-9 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 former 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 Analytical results for the groundwater and blank samples collected on September 10 and 11, 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 (wells 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 and shrinking. The lateral extent of petroleum-affected groundwater is defined by wells M-1,M-8,N-18,N-19,and N-20. Petroleum hydrocarbons were not detected in wells N-18,N-19, and N-20 for the samples collected on September 10,2014, and 2-4 ES101214202053SCO 1