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0 3.1.2 QA/QC Results L` The QA/QC program completed for the second quarter 2008 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 are included with the laboratory data in Appendix C. Laboratory method blanks were also analyzed for all of the analytes included in the monitoring program. The results of the QA/QC program indicate that no VOCs were detected in QA/QC blanks during the second quarter 2008 monitoring event. Review of the primary sample results indicates that iron, mercury, and manganese are suspected laboratory contaminants since similar concentrations were also detected in the laboratory method blanks for several samples collected at the Austin Unit. A duplicate sample was collected from well A-10 and labeled DUP. Duplicate groundwater results are presented along with the primary data in Table 3-2. Comparison of the values in the primary sample with the duplicate indicates that with the exception of manganese, sulfide, and cis-1,2-DCE there was 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 second quarter 2008. Based on the results of the laboratory blank and duplicate analyses, it is concluded that the laboratory data generated for the second quarter 2008 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 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: D:\2008_0010\FA_2Q08.doc 10 Geologic Associates