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J. H. KLEINFELDER & ASSOCI"ATES <br /> File: 5-1008-21/12 : 337 <br /> Revised: July 8, 1986 <br /> Page 6 <br /> gradient well will be placed far enough away from the .- landfill <br /> that it would not pick up any leachate from the landfill if it <br /> were to occur . <br /> Selection of the casing material must consider the influence <br /> and effects the casing material have on the integrity of the <br /> sample and the long-term effect the contaminants may have on the <br /> casing material . Available well casing materials include PVC 21 <br /> (unplasticized) , galvanized steel , carbon steel , low-carbon <br /> steel, stainless steel 304, stainless steel 316, and teflon. Of <br /> these materials, teflon is considered the best material under all <br /> circumstances except that its cost makes its use as a casing <br /> material impractical . Stainless steel is considered the next <br /> best alternative and its use is recommended at hazardous waste <br /> sites containing high levels of organic contaminants. PVC 1 is <br /> probably the most predominantly used material, primarily for cost <br /> reasons, and is considered an acceptable casing material for <br /> general applications . <br /> In comparing stainless steel to PVC, the following chart <br /> indicates PVC would be more compatible against mineral acid/high <br /> solids, and buffered weak acid conditions: <br /> RELATIVE COMPATIBILITY OF RIGID WELL-CASING MATERIAL <br /> (The values represent % compatibility) <br /> Lo- Stainless Stainless <br /> PVC Galy. Carbon Carbon Steel Steel <br /> 1 Steel Steel Steel 304 316 *Teflon <br /> Buffered 100 56 51 59 97 100 100 <br /> Weak Acid <br /> Weak Acid 98 59 43 47 96 100 100 <br /> Mineral Acid/ 100 48 57 60 80 82 100 <br /> High Solids <br /> Aqueous/Organic 64 69 73 73 98 100 100 <br /> Mixtures <br /> Percent Overall 91 58 56 59 93 96 100 <br /> Rating <br /> * Trademark of Dupont <br />