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3.1.2 QA/QC Results . The QA/QC program completed for the first quarter 2006 water quality monitoring event at the Austin Unit included analyses of two field blanks,two trip blanks, two laboratory method blanks, and two duplicate samples. The trip, field, and laboratory method blanks were analyzed for VOCs by EPA Method 8260 and are included with the laboratory data in Appendix C. The results of the QA/QC program indicate that no VOCs were detected in blank sample results. A duplicate groundwater samples were collected from well AMW-3 and surface-water monitoring station ASW-2, and were labeled AMW-DUP and ASW-2DUP,respectively. Duplicate groundwater test results are presented along with the primary data in Tables 3-2 and 3-4. As shown on Table 3-2 and 3-4,with the exception of the TDS concentration measured in the surface-water station duplicate, comparison of the primary sample results with the duplicate indicates good agreement(within 10%). Of note, concentrations less than the practical quantitation limit(PQL)were not included in the duplicate comparison since these are estimated values. Review of laboratory analysis dates with required holding times indicates that all samples were submitted and analyzed within the required holding times during the first quarter 2006. It is concluded that the laboratory data generated for the first quarter 2006 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 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 3-5. 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 central and western areas of the Austin Unit flows west to southwest at an average hydraulic gradient of approximately 0.002 ft/ft,while groundwater to the northeast of the site, in the vicinity of the EMP wells, flows 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). The maximum groundwater flow velocity was calculated using Darcy's Law: D:\2003_021\ForwardAustin_w06.doc\4/20/2006 10 Geologic Associates