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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 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 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 and northeast with an average hydraulic gradient of 0.003 ft/ft to the north and 0.001 ft/ft to the northeast. 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—)*—]* 2835 —� 0.65 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 At:0.002 for the site during the current the fourth quarter 2010. n,=Effective porosity(n,=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 fourth quarter 2010 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, PCE was measured above the PQL, in the samples collected from wells AMW-13 and AMW-14; and TCE was measured above the PQL in the sample collected from well AMW-13. For the DMP wells at the Austin Unit, CLs are calculated for the water quality protection standards(WQPS). The CLs shown in Table 3-1 were calculated by Herst&Associates using Sanitas®, a state-approved statistical software program. Based on a comparison of the data obtained during the fourth quarter 2010 monitoring period,the following D:U0I0_0013IYA_4QI0.doc 10 GeoLogic Associates