Shallow groundwaters in the western U.S. often contain elevated levels of trace oxyanions such as selenate, chromate, and uranyl. A potential remediation method is to react the water with zero-valent iron. Both in-situ permeable reactive barrier walls and pump-n-treat technologies are being used for to treat these contaminated waters (Wilson, 1995) . In this reaction, the iron serves as both an electron source and as a catalyst. The objectives of this research were to determine the factors that

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... affect the rate of reaction and the types of secondary products formed, including the iron hydroxide mineralogy and the fate of the trace elements. Variables that we studied included pH, ionic strength, 02, competitive ions and forms of iron.