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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 0.002 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 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 fourth quarter 2011. 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 Austin Unit DMP wells for the fourth quarter 2011 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. In addition,the following VOCs were measured at trace concentrations, PCE in the sample collected from well AMW-6; and 1,1-DCA, cis-1,2-DCE, and TCFM 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 Sanitase, a state-approved statistical software program; the results of the statistical analyses performed by Herst& Associates are presented in Appendix D. Based on a comparison of the data obtained during the fourth quarter 2011 monitoring period, the following analytes were found to exceed a CL. CA2011-00504A 4Q11.doc 9 Geo-Logic Associates