Use of 2D and 3D GIS in well selection and interpretation of nitrate data, central Nebraska, USA

Nonpoint-source contamination of the principal aquifers in an area of central Nebraska was evaluated utilizing aquifer condition, well depth, soil type, and physiographical and land use settings. A two-dimensional geographical information system linked with a three-dimensional geological visualization and analytical program was used in the random selection of acceptable wells for the monitoring of nitrate concentrations in groundwater. Locations of existing wells were superimposed on the three-dimensional geological block diagram and more than 200 wells randomly were selected for monitoring. The three-dimensional system also was used to show three-dimensional contours of nitrate concentrations. The two-dimensional geographical information system was used in comparing nitrate concentrations in differing physiographical, soil, and land use settings.Nonpoint-source contamination of the principal aquifers in a 7800 km2 area of central Nebraska was evaluated utilizing aquifer condition, well depth, soil type, and physiographical and land use settings. A two-dimensional geographical information system linked with a three-dimensional geological visualization and analytical program was used in the random selection of acceptable wells for the monitoring of nitrate concentrations in groundwater. Locations of existing wells were super-imposed on the three-dimensional geological block diagram and more than 200 wells randomly were selected for monitoring. The three-dimensional system also was used to show three-dimensional contours of nitrate concentrations that can be used interactively to determine the volumetric percentage of an aquifer that contains nitrate concentrations exceeding a specified threshold. The two-dimensional geographical information system was used in comparing nitrate concentrations in differing physiographical, soil, and land use settings. Preliminary results suggest that approximately 6% (volumetric) of water in the High Plains aquifer has nitrate concentrations above the US Environmental Protection Agency Maximum Contaminant Level of 10 mg-1 as N.