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QA/QC Results The QA/QC program completed for the first quarter 2013 water quality monitoring event at the Austin Unit included analyses of one trip blank, six laboratory method blanks, and one duplicate sample. The trip blank was 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 no VOCs were detected in trip or method blanks. Inorganic constituents including calcium, chloride, copper, hexavalent chromium, sodium, thallium, selenium, sulfate, and total organic carbon(TOC) were measured at trace concentrations in method blanks. These constituents were measured at very low concentrations that generally did not affect the interpretation of primary sample results. However, similar concentrations of selenium were measured in samples collected from wells AMW-12, AMW-13, AMW-14, and AMW-19 and were flagged as a suspected laboratory contaminant on Tables 3-1 and 3-2; TOC was also detected at similar concentrations in several wells and surface water stations and were also flagged accordingly. A duplicate sample was collected from domestic well 8106-A. Duplicate groundwater results are presented along with the primary data in Table 3-3. The duplicate sample analyses generally yielded good correlation with most quantifiable constituents having a relative percent difference (RPD) of less than five percent. Only arsenic had a higher RPD (13 percent). 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 2013. 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. 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 and northeast with a hydraulic gradient of approximately 0.001 to 0.002 ft/ft, although a localized east-southeast gradient of 0.001 was noted along the southern perimeter 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:2013-0021TA_IQ13.aoc 9 Geo-Logic Associates