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ANALYTICAL MODELING OF THE INFLUENCE OF DENITRIFYING SEDIMENTS ON NITRATE TRANSPORT IN AQUIFERS WITH SLOPING BEDS
Citation:
Hantush*, M M. AND M. A. Marino. ANALYTICAL MODELING OF THE INFLUENCE OF DENITRIFYING SEDIMENTS ON NITRATE TRANSPORT IN AQUIFERS WITH SLOPING BEDS. WATER RESOURCES 37(12):3177-3192, (2001).
Description:
Denitrification is a significant process for the removal of nitrate transported in groundwater drainage from agricultural watersheds. In this paper analytical solutions are developed for advective-reactive and nonpoint-source contaminant transport in a two-layer unconfined aquifer with inclined bed. In particular, we investigate the impact of denitrification in reducing subsurface sediments on nitrate baseflow loading to streams. The influence of hydrogeologic setup, such as aquifer stratification, aquifer-bed inclination, streambed hydraulic conductance, recharge rate, and transect length is analyzed. In the analysis it is assumed that the dip angle is small, and that groundwaters that enter a redox layer at the base of the aquifer are completely reduced. The general case of partial denitrification, however, requires additional analysis. First, the problem of steady-state groundwater flow in a two-layer inclined unconfined aquifer subject to unifon-n recharge is solved exactly and approximately using a regular perturbation technique. The transport equations, which describe advective-reactive transport in a two-layer aquifer, are then developed using an infinitesimal control volume, and solved in the Lagrangian viewpoint for the particular case of complete denitrification in the redox zone using a similar perturbation technique. Application of the methodology to paired-agricultural watersheds in the Mid-Atlantic coastal plain predicts that the surficial aquifer-bed inclination produced by the regional dip of the strata influences groundwater fluxes in the redox 'layer, thereby significantly affecting nitrate baseflow loadings to two creeks in the paired watersheds. Indices are derived ftom the transport equations, which describe nitrate removal capacity by denitrification in groundwater drainage from agricultural watersheds and in stream riparian zones. The sensitivity of the indices to the hydrogeologic setup is also analyzed.