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submitted and analyzed within the required holding times during the fourth quarter 2009. Review of the historical TDS concentrations indicates that the concentration measured in well AMW-12 during the current monitoring period is within the range of values measured for this well. Based on the results of the laboratory blank and duplicate analyses, it is concluded that generally acceptable QA/QC procedures were exercised and the water quality samples collected from the Austin Unit appear to be representative of water quality at the site. 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 0.00 15 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 0.0015 sec- ft V [(0.04 —)*—]*2835 —� 0.49 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�0.0015 for the site during the current the fourth quarter 2009. n,=Effective porosity(n,=0.35);an estimated value. The groundwater flow rate is calculated to be 0.49 feet/day(177 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the DMP wells for the fourth quarter 2009 are summarized in Table 3-1. As shown in Table 3-1, DCDFM was measured above the PQL, and a trace concentration of 1,2-dichloropropane was measured in the sample collected from well AMW-14; 1,1-DCA, DCDFM, and cis-1,2-DCE were measured at trace concentrations in the sample collected from well AMW-13; PCE was measured at a trace concentration in the sample collected from well AMW-6; PCE and TCE were measured above the PQL and TCFM was measured at trace concentrations in the samples collected from wells AMW-13 and AMW-14. D:\2009_0017TA_4Q09.doc 9 Geologic Associates