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Comparison of the quantified values(values above the PQL)in the primary sample with the duplicate indicates that with the exception of arsenic and nitrate as nitrogen, there was good agreement(within 10%). Review of laboratory analysis dates with required holding times indicates that with the exception of the nitrate as nitrogen in the sample collected from surface water station ASW-1,all samples were submitted and analyzed within the required holding times during the second quarter 2007. Based on the results of the laboratory blank and duplicate analyses,it is concluded that the laboratory data generated for the second quarter 2007 monitoring period are generally acceptable. 3.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder, and the static water level was recorded on a well data sheet (Appendix C). 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 Austin Unit are summarized in Table 3-4. The groundwater elevation data obtained during this quarterly monitoring period were used to generate the groundwater elevation contour map shown on Figure 3-1, which indicates that groundwater beneath the Austin Unit generally flows to the north-northwest at an average hydraulic gradient of approximately 0.002 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 cm 0.002 sec– ft V = —_[(0.04—)* 1*2835 0.65 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-0.002 for the site during the current the second quarter 2007. ne=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.65 feet/day(237 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the DMP wells for the second quarter 2007 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, trace levels of PCE were detected in the samples collected from wells AMW-6 and AMW-12; DCDFM and TCE were measured at trace concentrations and PCE was measured above the PQL in the sample collected from well AMW-13, and 1,1- DCA and 1,2-dichloropropane were measured at trace concentrations and DCDFM, PCE, and TCE were measured above the PQL in the sample collected from well AMW-14. D:\2007-0043\ForwardAustin—sPO7.doe 9 Geologic Associates