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suspected laboratory contaminants. During the fourth quarter 2010 monitoring event, a duplicate sample was collected from wells MW-22 and labeled DUP. As shown on Table 2-2, with the exception of chloride, the duplicate sample analyses yielded good correlation(within 10%)with the primary sample results. Review of fourth quarter 2010 sampling dates and laboratory analytical certificates indicates that with the exception of hexavalent chromium the laboratory analyses were completed within required holding times. Since the holding time for hexavalent chromium is 24 hours, the laboratory has been instructed to review the COC and respond more quickly to avoid missing the holding time for hexavalent chromium. Based on the results of the laboratory QA/QC analyses, it is concluded that the laboratory data generated for the fourth 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 fourth 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 0.002 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). An estimated 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=Hydraulic gradient: i�0.002 for the site during the fourth quarter 2010. n,=Effective porosity(n,=0.35);an estimated value. The groundwater flow rate is calculated to be 0.648 feet/day(237 feet/year). 2.1.4 Detection Monitoring Program As summarized in Table 2-2,the following VOCs were measured above the practical quantitation limit(PQL) during the fourth quarter 2010 monitoring period, acetone and 2- D:\2010-0013\FA-4QIO.doc 5 GeoLogic Associates