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it is concluded that the laboratory data generated for the second quarter 2010 monitoring period are generally acceptable 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 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 —)* ]*2835 0.65 ft l 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 2010. 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 2010 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, a trace concentration of DCDFM was measured in the sample collected from well AMW-6; PCE was measure at a trace concentration in the sample collected from well AMW-12;trace concentrations of 1,1-DCA, DCDFM, and TCFM were measured in the sample collected from well AMW-13; and trace concentrations of 1,2- dichloropropane (1,2-DCP), DCDFM, and TCE were measured in the sample collected from well AMW-14. In addition,PCE was measured above the PQL, in the samples collected from wells AMW-6 and AMW-14; and PCE and TCE were measured above the PQL in the sample collected from well AMW-13. DA2010_0013\1FA 2Q10.doc 9 GeoLogic Associates