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3.1.2 QA/QC Results The QA/QC program completed for the second quarter 2009 water quality monitoring event at the Austin Unit included analyses of three field blanks, three trip blanks,three laboratory method blanks, and one duplicate sample. The trip, field, and laboratory method 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 trace- levels of methylene chloride and xylenes were measured in one of the QA/QC field blanks during the monitoring period. Review of the primary sample results indicates that a similar concentrations of methylene chloride was detected in the primary sample collected from wells AMW-1 during the monitoring period and was flagged as suspected field/laboratory contaminant. During the second quarter 2009 monitoring event, a duplicate sample was collected from CAP well A -10 and labeled AMW-DUP. Duplicate groundwater results are presented along with the primary data in Table 3-2. With the exception of chloride,nitrate as nitrogen, and cis-1,2-dichloroethene, comparison of the values in the primary sample with the duplicate indicates that there was good agreement(within 10%). Of note, concentrations less than the PQL were not included in the 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 second quarter 2009. Based on the results of the laboratory blank and duplicate analyses,it is concluded that the laboratory data generated for the second quarter 2009 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: V = Ki = [(0.04 cm )* 0.002 1*2835 sec— .� ;t� 0.65 ft /day ne sec 0.35 cm — day MU009 OO17WA 2Q09.doc 9 Geologic Associates