IMPLICATIONS OF MANAGED AQUIFER RECHARGE ON COLLOID MOBILIZATION AND CONTAMINANT FATE

Managed aquifer recharge (MAR) approaches are designed to capture and store water in aquifers for subsequent recovery or environmental benefit. However, MAR can sometimes dramatically alter the water status, the geochemistry, dominant metal oxide species, and the microbial community in the vadose zone. These transient conditions can alter contaminant adsorption and desorption, colloid retention and release, colloid-facilitated contaminant transport, and clogging processes. This presentation highlights ongoing field (e.g., use of drywells for MAR on an agricultural field), laboratory, and mathematical modeling studies to better understand and quantify colloid mobilization and contaminant fate during MAR. Illustrative experimental and numerical examples of colloid and contaminant transport are given under various physicochemical conditions. Greater colloid mobility is observed for lower ionic strength, higher pH, higher water velocities, higher water saturations, and coarser textured media, especially when colloids are near 0.5 to 1 micron in size. Field results show that colloid-facilitated transport of some oxyanions can be greater than the dissolved phase.