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correlation(within 10%) with the primary sample results. Review of second quarter 2010 sampling dates and laboratory analytical certificates indicates that the laboratory analyses were completed within required holding times. Based on the results of the laboratory QA/QC analyses, it is concluded that the laboratory data generated for the second quarter 2010 monitoring period are generally acceptable and the water quality samples collected from the Forward Unit appear to be representative of water quality at the site. 2.1.3 Groundwater Elevations and Contours Prior to purging and sampling, each well was sounded for water depth using a weighted electronic sounder to an accuracy of 0.01 foot, 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 Forward Unit is summarized in Table 2-3. The groundwater elevation data obtained during the second quarter 2010 monitoring period were used to generate the groundwater elevation contour map shown on Figure 2-1,which indicates that groundwater generally flows to the northeast towards the Austin Unit, at an average hydraulic gradient of approximately 0.001 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 )* 0.001 ]*2835 sec— f1 0.324 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;w 0.001 for the site during the second quarter 2010. ne=Effective porosity(n,=0.35);an estimated value. The groundwater flow rate is calculated to be 0.324 feet/day(118 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the second quarter 2010 are summarized in Table 2-2. In reviewing the data, several low-level VOCs were detected. In the sample collected from well MW-10, dichlorodifluoromethane (DCDFM) and trichlorofluoromethane (TCFM) were measured above the practical quantitation limit (PQL), and 1,1-dichloroethane (1,1-DCA), cis-l,2-dichloroethene (cis-1,2-DCE), tetrachloroethene (PCE), and trichloroethene (TCE)were detected at estimated trace concentrations (between the method detection limit [MDL] and the PQL). In the sample collected from well MW-2A, toluene was measured above the PQL, and benzene and D:\2010_0013\FA_2Q10.doc 5 Geologic Associates