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dibromochloromethane, and methylene chloride were detected in one or more of the primary samples collected during the monitoring period and were flagged as a suspected field/laboratory contaminants. During the third quarter 2008 monitoring event, a duplicate sample was collected from well AMW-6 and labeled DUP. Duplicate groundwater results are presented along with the primary data in Table 3-1. Comparison of the values in the primary sample with the duplicate indicates that there was good agreement(within 10%). Of note, suspected field/laboratory contaminants and concentrations less than the PQL were not included in the duplicate comparison. Review of laboratory analysis dates with required holding times indicates that all samples were submitted and analyzed within the required holding times during the third quarter 2008. Based on the results of the laboratory blank and duplicate analyses, it is concluded that the laboratory data generated for the third quarter 2008 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 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-northwest at an average hydraulic gradient of approximately 0.002 ft/fl. 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: Ki cm 0.002 sec– ft V = — = [(0.04—)* ]*2835 0.65 ftlday ne sec 0.35 cm – day where: V=Groundwater flow velocity. K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). i=Hydraulic gradient:i=�0.002 for the site during the current the third quarter 2008. ne=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.65 feet/day(237 feet/year). n:M_0010\Fn_3Q0&d9c 10 Geologic Associates