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2.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder to an accuracy of 0.01 foot, and the static water level was recorded on a Well Data Sheet(Appendix Q. The groundwater elevations were calculated for each well by subtracting the depth-to-water measurement from the top-of-casing reference elevation. The current groundwater elevation data for the Forward Unit is summarized in Table 2-3. The groundwater elevation data obtained during the fourth quarter 2008 monitoring period were used to generate the groundwater elevation contour map shown on Figure 2-1,which indicates that groundwater generally flows to the north-northeast towards the Austin Unit, at an average hydraulic gradient of approximately 0.001 ft/ft. To calculate the approximate linear groundwater flow velocity for the site, conservative assumptions were used, including a hydraulic conductivity of 875 gallons per day per square foot(0.04 cm/sec) and an estimated effective porosity of 35 percent (CH2M Hill 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: Ki C177 0.001 sec- fit V = —= [(0.04 —)*—]* 2835 � 0.324 ft/day ne sec 0.35 cm - day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). i=Hydraulic gradient: i�0.001 for the site during the fourth quarter 2008. n,=Effective porosity(n,=0.35);an estimated value. The groundwater flow rate is calculated to be 0.324 feet/day(118 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the fourth quarter 2008 are summarized in Table 2-2 and Appendix D presents time-series charts of select parameters. As shown on Table 2-2, estimated trace concentrations (between the method detection limit [MDL] and the practical quantitation limit [PQL]) of 1,1-dichloroethane (I,I-DCA), dichlorodifluoromethane (DCDFM), tetrachloroethene(PCE), trichloroethene (TCE), and trichlorofluoromethane(TCFM) were measured in the sample collected from wells MW-10; a trace concentration of TCE was measured in samples collected from wells MW-14; and a trace concentration of bis(2- ethylhexyl)phthalate, a confirmed laboratory contaminant, was measured at a trace concentration in the sample collected from well MW-24. In addition, PCE was measured above the PQL in the sample collected from well MW-14. On behalf of Forward Inc., GLA prepared a letter report dated February 14, 2001 (RWQCB Case No. 2209), to assess the source and potential impacts of low-level VOCs D:\2008_0010\FA_4Q08.doc 5 GeoLogic Associates