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tC-SHADRIFS.6/WPADD.5 <br /> 05/24/90 <br /> An investigation is required at SHAD to define the mechanisms associated <br /> with the movement of arsenic in and out of solution by measuring an <br /> appropriate group of chemical analytes at selected monitor wells. Once <br /> the interdependence of arsenic and other dissolved chemical species is <br /> understood, the pathways of arsenic in groundwater will be better <br /> understood and a reliable model of arsenic dissolution can be used to <br /> design an appropriate remediation process. <br /> Analysis of samples from two rounds of consecutive quarterly water <br /> sampling efforts on a selected group of wells (Table 1) will provide <br /> temporal variations of all measured chemical parameters. Both filtered <br /> and unfiltered aliquots will be analyzed so that suspended and dissolved <br /> species can be compared. The chemical parameters that will be measured <br /> on the samples collected on the first round are listed in Table 2. <br /> Principal component analysis will be used to establish which analytes <br /> are related to the geochemical behavior of arsenic in the SHAD <br /> groundwater. For the second round of sampling, the list of parameters <br /> to be measured will be reduced to analytes relevant to arsenic behavior <br /> ' as determined from the first sampling episode. <br /> A total of 66 A- , B- , C- , and D-zone monitor wells will be sampled. The <br /> ' list includes 56 wells that were already scheduled for sampling, plus <br /> 10 wells that were chosen because they routinely have arsenic <br /> concentrations above 50 ppb. This group of wells is expected to provide <br /> the entire range of arsenic concentrations that have been measured at <br /> SHAD, as well as a wide geographic sample. <br /> 5 <br />