Abstract

At Slick Rock and Naturita, Colorado, shallow alluvial ground water has been impacted by milling activities downgradient from abandoned uranium mill sites. Surface water from adjacent rivers recharges shallow ground water and is intimately connected with the alluvial systems at both Slick Rock and Naturita. This intimate relationship provides a unique setting to observe the hydrochemical evolution of ground water on a small scale. Contaminants in ground water related to the milling process include sulfate, chloride, sodium, ammonium, and nitrate. Ground water contaminants related to uranium-vanadium ore include uranium, selenium, molybdenum, and major anions. Generally, uranium, chloride, nitrate, and sulfate are highly mobile; molybdenum is moderately mobile and selenium has a low mobility. Ammonium, nitrate, and iron are affected by biological processes in the aquifer. By analyzing bacterially mediated transformation products, it appears that nitrification of ammonium and reductive dissolution of ferric iron is proceeding in ground water. In addition, ferric iron precipitates, which coat the aquifer matrix at oxic-anoxic interfaces, may sorb contaminants and aid in natural remediation of ground water.