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A duplicate groundwater sample was collected from well AMW-13 and was labeled • AMW-DUP. Duplicate groundwater test results are presented along with the primary data in Table 3-1. As shown in Table 3-1, comparison of the primary sample results with the duplicate indicates good agreement(within 5%). 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 with the exception of non-volatile organic carbon analyses for surface water all samples were submitted and analyzed within the required holding times during the third quarter 2006. It is concluded that the laboratory data generated for the third 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 Austin Unit generally flows 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). The maximum groundwater flow velocity was calculated using Darcy's Law: Ki cm 0.002 sec– ft V _ —_ [(0.04—)* ]*2835 .. 0.648 ft/day ne sec 0.35 cm –day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). i=Average hydraulic gradient: i-0.002 for the site during the current(third quarter 2006)monitoring period. nc=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.648 feet/day(237 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the DMP wells for the third quarter 2006 are summarized in Table 3-1 and time-series plots are presented in Appendix D. Excluding confirmed • laboratory contaminants, four VOCs were measured in DMP wells with the greatest D:0003_0211ForwerdA =mKdoc 10 Geologic Associates