MODELING GROUNDWATER QUALITY WITH SURFACE WATERINTERACTION

摘要

A four-layer groundwater model that included unsaturated zone was developed for the West Virginia Ordnance Worksrn(WVOW) to predict the migration of TNT (2,4,6-trinitrotoluene) and DNT (2,4- and 2,6-dinitrotoluene) over time and space.rnComplicated site geology made it difficult to simulate the flow and transport due to high tendency of numerical dispersion of thernmodel. To complicate the situation even more was the incorporation of sixteen surface ponds (lakes), five of which were installedrnwith outflow structures – culverts. The inflow and outflow of the ponds, rainfall, evaporation, and seepage to or recharged fromrngroundwater were accounted for in the water balance. The stage changes over time were predicted for each pond to evaluate thernimpact of existing and potential pumping wells in the close proximity in groundwater. The flow modeling was calibrated with the usernof MODAC and MODFLOW-LAKE software packages.rnModeling results showed that stage in the ponds were very sensitive to the conductance of the bed material, the segmentrnparameters of the inflow stream, the discharge coefficient of the outflow rating equation and most of all, the time step allocation inrnthe flow model. Contaminant transport was modeled with MT3D with consideration of the cell-by-cell fluxes around the ponds. Thernresults showed that the contaminant migration was restricted by the existence of ponds, bedrock boundaries, and the pumping in thernentire study area and that no significant level of contaminant will be detected in the nearby residential areas or in the ponds even inrnthe worst case scenario.