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r <br /> I <br /> A Groundwater Monitoring Frequency Decision Tree,Figure 4,is used to evaluate the <br /> frequency of sampling for each monitoring well at the site,based upon the location of the <br /> { well with respect to the plume and gradient direction. <br /> The decision tree organizes the monitoring wells as upgradient,downgradient, <br /> crossgradient,or within the plume as follows: <br /> • Upgradient wells: MW-DIS-4,-5,-6,-7S,-7D,-8S, and-8D. <br /> • Downgradient wells: Currently,no downgradient wells exist. <br /> 0 Crossgradient:MW-DIS.-3,-9,and-10 <br /> • Within Plume:MW-DIS-1, -2,NP-1-70',-80',-90',SVE-South,and SVE-North. <br /> Table 7 presents the updated recommended sampling frequency for all wells at the Disco <br /> site. The sampling event was the fourth consecutive quarter to analyze all wells for presence <br /> j of 1,2-DCA, and EDB. 1,2-DCA, and EDB was not detected in 4 quarters of sampling in <br /> monitoring wells MW-DIS-2, -3,-4,-6,-7S,-7D,-8S,-8D,-9, and-10. Sampling for 1,2-DCA, <br /> EDB, and TBA in these wells will be discontinued. <br /> Monitoring wells MW-DIS-1,MW-DIS-2,NP-1-70,-80,-90,SVE-South,and SVE-North will <br /> continue to be sampled semi-annually for TPH-gas and BTEX compounds. TBA will <br /> continue to be analyzed in SVE-North on a semi-annual basis. <br /> Note: In order to continue the accurate assessment of the groundwater flow direction, <br /> water level measurements in all wells and evaluation of the groundwater gradient will <br /> continue to be performed on a quarterly basis. <br /> The Second Quarter 2001 monitoring event will consist of collecting water level <br /> measurements only. <br /> i <br /> I <br /> I <br /> i <br /> t <br /> r <br /> f <br /> I <br />