Project Summary (1995-2000)

The specific aim of this project is to determine the reactions and rate controlling processes of the mobilization of Mn(II) and trace metals (specifically, Cd, Zn, Pb and Cu) due to interactions of an acid mine plume (low pH and high Fe(II)) with Mn(IV)- containing subsurface media and the subsequent Mn(II)/Mn(IV) chemistry in Pinal Creek, Arizona, a state Superfund site. The current hypotheses for the reactions controlling Mn transport in groundwater are that the oxidation state of manganese is dictated by the available reductants (soil organic matter and Fe(II)) in the groundwater system and adsorption/surface precipitation reactions. Once the Mn(II)-laden groundwater reaches the stream, the stream bed materials play a key role in the reoxidation of Mn(II) and surface catalyzed oxidation occurs. As the Mn(IV) is deposited and heavy metals have been adsorbed, photoreduction of the Mn(IV) releases Mn(II) and any other heavy metals sorbed on the Mn(IV) solids. Scientists are testing these hypotheses by a combination of laboratory and field studies in cooperation with the U.S. Geological Survey at Pinal Creek.