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® to be representative of the water quality conditions measured at the site. Based on the results of the laboratory QA/QC analyses,it is concluded that the laboratory data generated for the third quarter 2008 monitoring period are generally acceptable and the water quality samples collected from the Forward Unit appear to be representative of water quality at the site. 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 third 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 AOL square foot(0.04 sec) and an estimated effective porosity of 35 percent(CH2M Hill qW 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: Ki cm 0.001 sec– ft 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 t--0.001 for the site during the third quarter 2008. ne=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 third 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 (1,1-DCA), acetone, dichlorodifluoromethane(DCDFM), tetrachloroethene(PCE), and trichloroethene(TCE)were measured in the sample collected from wells MW-10; a trace concentration of bromoform was measured in the sample collected from well MW-13; a trace concentration of trichlorofluoromethane (TCFM)was measured in samples collected from wells MW-15 and MW-16; and a trace concentration of bis(2- D:X2008 00101FA 3Q08.doc 5 Geologic Associates