DEVELOPMENT OF HYDROGEL TRACER BEADS TO MONITOR CONTAMINANT TRANSPORT IN KARST AQUIFERS

Karst aquifers are susceptible to pollution, but how they transport contaminants is poorly understood. Soluble tracers such as cations, anions, and dyes help to understand the complexities of karst hydrology, but do not reflect the fate and transport of all classes of contaminants. To better mimic particulate and non-aqueous phase liquid contaminant movement, hydrogel tracer beads were developed and tested in conjunction with more traditional tracers.

Hydrogel tracer beads contain 96-98% water and are made using alginate, an anionic polysaccharide extracted from marine algae, which gels in the presence of divalent cations. Calcium alginate gel beads form when the alginate solution is dropped into a calcium curing solution. The beads are environmentally benign, easily made, and can be experimentally altered to possess different physical and chemical properties such as density, size, color, and fluorescence.

This research focuses on the development of methods for bead optimization, alteration, and quantification. Experiments included the determination of the optimal ranges of percent alginate solution, molar concentration of calcium in the curing solution, drop heights for bead formation, curing time, and temperature of the solutions. Additives to the alginate, such as microscopic glass bubbles and high density mineral powders, were used to alter the density of the tracer beads. Methods for determining bead density were also tested and compared. Stability experiments were conducted in Marcellus brine, acid mine drainage, and cave water to determine short- and long-term bead stability in different natural waters. Methods of collection and quantification of tracer beads under field conditions were explored.

Field testing of the beads will be conducted in conjunction with soluble tracers in the stream in Buckeye Creek Cave, near Lewisburg, WV in the spring of 2012. Research at the cave will examine how bead movement varies relative to flow velocity and alternative tracers.