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results of the QA/QC program indicate that no VOCs were detected in any of the QA/QC blanks during the monitoring period. Review of laboratory analysis dates with the required holding times indicates that all of the samples were submitted and analyzed within the required holding times during the third quarter 2010. Based on the QA/QC results, it is concluded that the laboratory data generated for the third quarter 2010 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 3-4. 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 east with an average hydraulic gradient of 0.002 ft/ft to the north and 0.001 ft/ft to the east. 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 —)* 1* 2835 � 0.65 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=Hydraulic gradient: i;z�0.002 for the site during the current the third quarter 2010. ne=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.65 feet/day(237 feet/year). 3.1.4 Detection Monitoring Program Field and laboratory results for the DMP wells for the third quarter 2010 are summarized in Table 3-1 and time-series plots are presented in Appendix D. As shown in Table 3-1, a trace concentration of PCE was measured in the sample collected from well AMW-6; PCE was measured above the PQL, in the samples collected from wells AMW-13 and AMW-14; and TCE was measured above the PQL in the sample collected from well AMW-13. D:\?0 t0_00 t 3\FA_3Q t 0.doc 9