PREDICTING METAL RETENTION IN A CONSTRUCTED MINE DRAINAGE WETLAND

A computer simulation model was developed to predict metal retention in constructed mine drainage wetlands. The model emphasized the processes of advection, diffusion, and precipitation/sedimentation in both surface and subsurface state variables. The model was calibrated and verified using data from five constructed wetlands in Pennsylvania and Ohio, USA. Simulation of metal retention in a proposed mine drainage wetland in southeastern Ohio was performed using baseline data, collected for 18 months prior to wetland construction as model inputs. Predicted retention ranges from 0 to 93% for aluminum and from 50 to 99% for iron for the proposed wetland, depending on season and whether surface or subsurface flow is used. Diffusion of metals from water to sediments limits metal retention in low pH wetlands while metal precipitation rates from the water column limit metal retention in circumneutral wetlands.