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3.1.2 QA/QC Results The QA/QC program completed for the second quarter 2012 water quality monitoring event at the Austin Unit included analyses of one field blank, two trip blanks, two laboratory method blanks, and one duplicate sample. The trip and field blanks were analyzed for VOCs by EPA Method 8260 and method blanks were analyzed for all required analyses. The results of the QA/QC program indicate that acetone was detected at an estimated trace concentration in the field blank and one of the method blanks during the monitoring period; and with the exception of well AMW-4, acetone was not detected in any of the primary samples collected. A duplicate sample was collected from DMP well AMW-14 and labeled AMW-Duplicate. Duplicate groundwater results are presented along with the primary data in Table 3-1. The duplicate sample analyses yielded good correlation (less than 10%relative percent difference). Review of laboratory analysis dates with required holding times indicates that all samples were submitted and analyzed within the required holding times during the second quarter 2012. 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 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 a hydraulic gradient of approximately 0.001 ft/ft, although a northwest gradient of 0.004 was noted along the western half of the Austin Unit. 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: c:\zoii-oozs\Fn_zQI2.aoo 8 Geo-Logic Associates