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Table 5. Relative leaching or sorption/desorption ranking of well-casing and screen materials <br />for indicated water-quality constituent classes <br />[Applies in general to classes of compounds indicated. Actual amounts and rates of leaching <br />or sorption/desorption of individual constituents can differ within each major constituent class. <br />The tendency of a material to leach compounds can differ from the ability of the materials to <br />sorb constituents or compounds. 1, least leaching or sorptive/desorptive; 5, most leaching or <br />sorptive/desorptive; PTFE, polytetrafluoroethylene; PVC, polyvinylchloride] <br />Water-quality constituent classa <br />Inorganic Organic <br />Material constituents compounds <br />PTFE 1 2-4b <br />PVCC <br />- Flush-threaded joints 1-2 2 <br />- Glued jointsd 3 5 <br />Stainless steel' 4 1-2 <br />Galvanized steel 5 4 <br />Carbon steel 5 4 <br />aIncludes constituents to be analyzed according to the laboratory schedules shown on <br />table 2. <br />bPTFE can be highly sorptive of some organic compounds, although these losses might <br />diminish as equilibrium of casing with ground water is approached (Parker and Ranney, <br />1994; Ranney and Parker, 1994). <br />PVC is the best compromise choice if measuring all constituent classes in table 2. <br />dVolatile organic compounds leached from glue can include THE (tetrahydrofuran), <br />MEK (methylethylketone), MIBK (methylisobutylketone) and cyclohexanone (Sosebee and <br />others, 1983). <br />'Generally, stainless steel 316 is more resistant to corrosion than stainless steel 304. <br />29