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arsenic had a higher RPDs of 12.8 percent. Review of laboratory analysis dates and required holding times indicates that all samples were submitted and analyzed within the required holding times during the third quarter 2013. Based on the results of the laboratory blank and duplicate analyses, it is concluded that generally acceptable QA/QC procedures were exercised and the water quality samples collected from the Austin Unit appear to be representative of water quality at the site. 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. In addition, each accessible EMP well was also sounded for depth to water. 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 southern and eastern areas of the Austin Unit generally flow to the northeast at a hydraulic gradient ranging from 0.001 to 0.002 ft/ft, while an eastern flow direction was noted in the central and northern portions of the Austin Unit. As presented in Table 3-4 and Figure 3-1, groundwater elevation data was also collected from 17 offsite EMP wells,the results of the additional data points shows a westerly hydraulic gradient in the easternmost EMP wells and is believed to be related to groundwater mounding, as a result of agricultural activities east of the site. 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 0.001 sec– ft V = — _ [(0.04 —)* 1*2835 ;t: .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;:z 0.001 for the site during the third quarter 2013. n,=Effective porosity(n,=0.35);an estimated value. The estimated groundwater flow rate is calculated to be 0.324 feet/day(118 feet/year). Detection Monitoring Program Field and laboratory results for the Austin Unit DMP wells for the third quarter 2013 are summarized in Table 3-1. C:\2013-0021\FA_3Q13.doc 9 Geo-Logic Associates