Simulation of the Transport of Ion‐Exchanging Solutes Using Laboratory‐Determined Chemical Parameter Values

Abstract

ABSTRACTThe practical application of simulation models of the movement of chemically reacting contaminants requires the evaluation of several chemical parameters in addition to those basic hydrogeologic and hydrodynamic parameters required to model conservative constituents. This paper deals with the use of laboratory‐determined chemical parameter values in the simulation of the transport of ion‐exchanging solutes governed by local chemical equilibrium. The transport model has been applied to a field operation involving the injection of advanced‐treated municipal waste water into an alluvial aquifer in the Palo Alto (California) Baylands region.Basic hydrogeologic parameters, such as porosity, bulk density, and aquifer thickness, were determined by analysis of observation well logs and core samples. Data on the breakthrough of a conservative tracer at various observation wells were utilized to determine an approximate velocity field and the dispersivity values. The chemical parameters (selectivity coefficients and cation‐exchange capacity) were determined using standard batch experiments conducted in the laboratory using aquifer core material. With these parameter values, the model was run to predict the breakthrough of major cations at the observation wells. The predicted results agree very closely with the actual field data. This agreement suggests that laboratory‐determined chemical parameters can be successfully used in field‐scale transport simulations.