A Tool for Predicting Fate and Transport of Microbial and Chemical Contaminants in Managed Aquifer Recharge Systems.

Treated wastewater discharged into the subsurface for reuse or for environmental benefits through Managed Aquifer Recharge (MAR) systems contains chemical constituents such as nitrogen, pharmaceuticals and personal care products, and biological constituents. During the infiltration process, the contaminants may be partially or totally removed in the unsaturated zone before reaching the water table. Once reaching the water table, contaminants may travel laterally to nearby surface water resources or to drinking water wells down gradient.  A modeling tool for estimating concentration along the flow path needs to consider fate and transport of contaminants as influenced by the soil characteristics and contaminant behavior. The Soil Treatment Unit Model for MAR Systems (STUMOD-MAR) is a tool  for predicting fate and transport of dissolved organic carbon (DOC),  contaminants of emerging concerns (CECs), nitrogen and pathogens. The objective of the study was to develop a practical tool for assessing attenuation of chemicals and pathogens in soil systems that is simple to use for practitioners but detailed enough to include relevant fate and transport  processes.  The tool considers advective movement, sorption, dispersion, biodegradation and inactivation rate for pathogens.  The tool was evaluated using field data collected at Montebello Forebay Spreading Facility operated by the Water Replenishment District of Southern California and laboratory data from Colorado School of Mines. The modeling and experimental study provides an insight into the attenuation behavior of the contaminant and capacity of the soil to treat contaminants to protect downstream water resources.  STUMOD-MAR can be used as an effective screening tool to evaluate if impact from MAR systems is a potential concern.