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hexavalent chromium and nitrate as nitrogen concentrations reported for well MW-1 are within the historical range of values reported for this well. Based on the results of the laboratory QA/QC analyses, 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 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 C). 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 third 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 0.003 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: Ki cm 0.003 sec– ft V = — = [(0.04 —)* 1*2835 0.972 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�0.003 for the site during the third quarter 2010. ne=Effective porosity(ne=0.35);an estimated value. The groundwater flow rate is calculated to be 0.972 feet/day(355 feet/year). 2.1.4 Detection Monitoring Program Field and laboratory results for the groundwater monitoring wells for the third quarter 2010 are summarized in Table 2-2. In the sample collected from well DW-9690, trans- 1,4-dichloro-2-butene was measured above the practical quantitation limit (PQL); acetone was measured above the PQL in the sample collected from well MW-19; and tetrachloroethane(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-14. D:\20t0 0013\FA_3Q10.doc 5