In this study, the nitrogen loading of groundwater underlying on-site sewage disposal systems (OSDS) in four different soil/topographic settings in Morgan County, Indiana, was determined by undertaking an intensive program of monitoring in and beneath septic distribution fields at each of the field sites. The sites selected were different from one another in setting and soil texture, and were representative of a broad range of soil types within the county. At each study site, sensors were installed to measure soil-water tension in the unsaturated zone, soil-moisture content, and water-table elevations. Each site was monitored for 10 months (late October 2004 through late August 2005). Samples of water were collected from the saturated or unsaturated zones, or both, at each of the four study sites on 16 separate occasions. Geographic information systems (GIS) software was used to conduct an analysis of similar hydrogeologic settings that would yield an assessment of the suitability of installing on-site sewage disposal systems in different areas of Morgan County. Additional supporting data files (hydrology, micrometeorology, and chemistry data spreadsheets) are available for this open-file study. To request a downloadable data archive, or alternatively a CD-ROM, please contact our publication sales office.