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laboratory data in Appendix C. The results of the QA/QC program indicate that trace <br /> levels of methylene chloride were detected in several QA/QC field and trip blanks during <br /> 0 the third quarter 2007 monitoring event. Review of the primary sample results indicates <br /> that methylene chloride was detected in two of the primary samples collected and was <br /> flagged as a suspected field/laboratory contaminant. <br /> Duplicate samples were collected from well AMW-7 and labeled AMW-DUP. Duplicate <br /> groundwater results are presented along with the primary data in Table 3-1. Comparison <br /> of the quantified values (values above the PQL) in the primary sample with the duplicate <br /> indicates that with the exception of carbonate,there was good agreement(within 10%). <br /> Review of laboratory analysis dates with required holding times indicates that with the <br /> exception of the carbonate and bicarbonate in the sample collected from well AMW-6, all <br /> samples were submitted and analyzed within the required holding times during the third <br /> quarter 2007. Based on the results of the laboratory blank and duplicate analyses,it is <br /> concluded that the laboratory data generated for the third quarter 2007 monitoring period <br /> are generally acceptable. <br /> 3.1.3 Groundwater Elevations and Contours <br /> Prior to purging and sampling, each well was sounded for water depth using a weighted <br /> electronic sounder, and the static water level was recorded on a well data sheet <br /> (Appendix C). The groundwater elevations were calculated for each well by subtracting <br /> the depth-to-water measurement from the top-of-casing reference elevation. The current <br /> groundwater elevation data for the Austin Unit are summarized in Table 3-5. <br /> The groundwater elevation data obtained during this quarterly monitoring period were <br /> used to generate the groundwater elevation contour map shown on Figure 3-1. <br /> Historically, groundwater beneath the Austin Unit generally flows to the north-northwest <br /> at an average hydraulic gradient of approximately 0.002 ft/ft. However,based on lower <br /> levels associated with observed pumping from adjacent agricultural wells, groundwater <br /> during the third quarter 2007 monitoring period appears to flow west-southwest to <br /> northwest at a gradient of 0.002 ft/ft. <br /> To calculate the approximate linear groundwater flow velocity for the site, conservative <br /> assumptions were used, including a hydraulic conductivity of 875 gallons per day per <br /> square foot(0.04 cm/sec) and an estimated effective porosity of 35 percent(CH2M Hill <br /> 2000). An estimated groundwater flow velocity was calculated using Darcy's Law: <br /> Ki cm 0.002sec– ft <br /> V = — = [(0.04 —)* ]*2835 ;Z� 0.65 ft l day <br /> ne sec 0.35 em – day <br /> where: V=Groundwater flow velocity. <br /> K=Hydraulic conductivity of the water-bearing unit(0.04 cm/sec). <br /> i=Hydraulic gradient: i z 0.002 for the site during the current the third quarter 2007. <br /> ne=Effective porosity(ne=0.35);an estimated value. <br /> D:\2007 M3\FomardAus&suMO7.doc <br /> Geologic Associates <br />