Mapping groundwater recharge potential and an assessment of available hydrogeologic data within five selected focus areas in eastern Nebraska

Groundwater recharge potential was mapped using airborne electromagnetic survey data collected over the previously glaciated part of eastern Nebraska. To evaluate the appropriate resolution at which airborne electromagnetic data should be interpolated (or represented), we compared a 500-​meter ​cell ​raster​ and​ a​ filled ​contour​ shapefile​ to ​known​ geologic features, point estimates of groundwater recharge, and selected water-quality data. The median groundwater recharge rate for the estimates collected in areas mapped as having high groundwater recharge potential were higher compared to the groundwater recharge rate estimates collected in areas mapped as having moderate and low recharge potential. Selected water-quality data were examined to determine​ the ​influence of​ near-​surface​ geology​ on​ water​ quality, groundwater geochemistry, and groundwater age. The strongest statistical correlations were produced when examining ​specific​ conductance​ values ​measured​ from​ wells​ in areas mapped as high, moderate, and low groundwater recharge potential. Within till-covered areas, statistically significant​ differences​ existed​ in ​nitrate,​ dissolved ​oxygen,​ manganese, and iron concentrations sampled from wells mapped in high, moderate, and low groundwater recharge potential areas. Boxplots indicate that till-covered areas mapped as low groundwater recharge potential generally have lower concentrations of nitrate and dissolved oxygen, but higher concentrations of manganese and iron.

The Eastern Nebraska Water Resources Assessment project​ sponsors ​have​ identified ​five ​focus​ areas ​as​ locations facing unique and important groundwater resource management issues. These focus areas are experiencing the emergence of groundwater resource issues that include increased groundwater development, nitrate contamination, and the potential expansion of rural water districts. Hydrogeologic assessments were completed for the Dorchester-Sterling paleovalley aquifer, Dodge County, Knox County, Burt County, and the Fremont-Arlington-Leshara focus areas. Potential future studies to address data gaps were identified​ and​ discussed.