MOBILITY OF NATURAL ORGANIC-MATTER IN A SANDY AQUIFER

Field-scale transport of natural organic matter (NOM) was studied in a two-well tracer test by injecting 80 000 L of ''brown water'' (66 mg of C L-1) from a wetlands pond into a shallow, sandy, coastal plain aquifer. The basic features of NOM breakthrough observed in laboratory column studies (extending tailing and rapid decline in concentrations when NOM inputs are terminated) were observed in the field. Retardation of NOM in the field agreed with predictions from laboratory studies. In spite of natural heterogeneities, fractionation of NOM subcomponents occurred in transport. Smaller (<3000 MW) and more hydrophilic (by XAD-8 chromatography) components of NOM were more mobile than were larger (3-100K MW), more hydrophobic components. However, over the 2-week injection, the solid and solution phase reached an apparent steady state with respect to NOM adsorption, resulting in the unretarded transport of even the hydrophobic and macromolecular NOM. The results indicate that NOM can exhibit considerable mobility in an aquifer and suggest that NOM could alter the transport of contaminants in groundwater.