||Robert S. Kerr Environmental Research Lab., Ada, OK. ;ManTech Environmental Technology, Inc., Ada, OK. ;Geological Survey, San Diego, CA.
Laboratory columns using contaminated natural aquifer material from Globe, Arizona, were used to investigate the transport of inorganic colloids under saturated flow conditions. Fe2O3 radio-labeled spherical colloids of various diameters were synthesized and introduced into the columns under varying conditions of pH, ionic strength, electrolyte composition, and colloid concentration. Column influent and effluent were evaluated by photon correlation spectroscopy and scintillation-counting techniques. Effluent breakthrough concentrations of the colloid were as high as 57 percent of the influent concentration under conditions. In all cases where significant transport occurred, the colloids arrived at approximately the same time as a conservative tracer, tritium. Conditions favoring colloidal transport in the system were low ionic strength and a pH in the range where the colloids are stable. Arsenate was used as a model reactive contaminant to evaluate its facilitated transport on the Fe2O3 colloids. The calculated sorption capacity of the colloids from batch tests was 1 percent by weight for arsenate. Compared to dissolved arsenate transport in the same columns, the colloids were transported more than 21 times faster.