U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings
of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993,
Water-Resources Investigations Report 94-4015
Processes Controlling Dissolved Copper Concentrations during
an Instream pH-Modification Experiment
Kathleen S. Smith (U.S. Geological Survey, Denver, Colo.)
Changes in dissolved copper (Cu) concentrations as a function of pH were
observed during an instream pH-modification experiment conducted in St.
Kevin Gulch, Colorado, a stream affected by acidic mine drainage. Understanding
the processes that control dissolved Cu concentrations is important because
dissolved Cu can pose health risks and contaminate receiving waters. Comparison
of dissolved Cu concentrations during the instream experiment with changes
in dissolved Cu concentrations in inbottle simulation experiments performed
with streamwater in the absence of streambed sediment shows good agreement.
These data indicate that processes controlling Cu attenuation with increasing
pH occur primarily in the water column. Sorption reactions and (or) coprecipitation
reactions with iron and (or) aluminum precipitates forming in the water
column in response to increasing pH may be the processes controlling Cu
partitioning in these systems. Predictive computer modeling of Cu sorption
onto hydrous ferric oxide slightly underestimates Cu attenuation observed
in the instream system.