ARCHIVED REPORTS_SECOND SEMIANNUAL AND 2014 ANNUAL GROUNDWATER MONITORING REPORT

Home Browse Search

2.RESULTS FOR SECOND SEMIANNUAL PERIOD 2014 Groundwater Analytical Methods Groundwater samples collected from the sampled monitoring wells were submitted to Alpha Analytical,Inc., a California-certified analytical laboratory located in Sparks,Nevada. Copies of the laboratory reports from Alpha Analytical are provided in Appendix B. Groundwater and quality assurance/quality control(QA/QC) samples were analyzed for the following: • Total petroleum hydrocarbons as gasoline (TPHg) and as diesel (TPHd)using United ' States Environmental Protection Agency (EPA) Method 8015 modified • Benzene,toluene, ethylbenzene,and total xylenes (BTEX) using EPA Method 8260B ' The following QA/QC samples were collected: • Duplicate sample from well N-7 (labeled DUP-1) ' • One equipment blank sample (labeled EB-1) • One trip blank sample for the cooler of samples (labeled TB-1) Sample analyses were conducted within a standard 10-day laboratory turnaround time. 2.1.2 Results Groundwater Elevation and Flow Groundwater level data collected on September 10, 2014, are presented in Table 2,and elevation contours for these data are shown in Figure 3.These data are included in the tabulation of the eight most recent historical monitoring events in Appendix C. Hydrographs of the historical data are provided in Appendix D. ' Groundwater Elevations The groundwater elevations and depths to groundwater for the September 10, 2014, data were as follows. • Shallow-interval groundwater monitoring wells are constructed with total depths between 14 and 23.5 feet bgs. Calculated elevations for the shallow-interval groundwater monitoring wells ranged from 3.04 feet above mean sea level(msl) at rwell M-2,located in the north portion of the Site near Trapper Slough,to-12.06 feet msl in well N-8,located in the southeastern portion of the Site. The water level elevations for M-10 and N-8 were anomalously low compared to prior year results. The low water level elevation not including these two wells was-10.66 feet msl at M-8. The depth to groundwater ranged from 2.46 feet bgs at well M-2 to 16.54 feet bgs at well 0-1. • The deeper-interval groundwater monitoring well (N-24) is constructed at a total depth of 42 feet bgs. The calculated groundwater elevation for well N-24 was-8.64 feet msl. The depth to groundwater was at 8.64 feet bgs in the well, above the screened interval. These data are consistent with historical data,as shown in the hydrographs in Appendix D (except for the two anomalous wells,M-10 and N-8). Groundwater Flow Groundwater flow depends on the physical characteristics of the subsurface materials and the groundwater gradients. A detailed analysis of groundwater flow for the fourth quarter ES101214202053SCO 2-3