IDENTIFICATION OF GROUNDWATER SOURCES USING GEOCHEMICAL DATA ON THE PLATTE RIVER ALLUVIAL AQUIFER AND UNDERLYING LIMESTONE AT THE LINCOLN WATER WELL FIELD NEAR ASHLAND NEBRASKA

Groundwater exploitation during drought can cause energy gradients to pull water from underlying aquifers due to heavy pumping. This study has focused on characterizing water type in the Platte alluvial aquifer system to determine if water from the underlying limestone aquifer is being pumped during dry periods. The data set used is from three different years, 2008 representing a wet year and 2012-2013 representing dry years. Water chemistry data collected from wells in the Lincoln Water Well Field near Ashland Nebraska has shown that especially during the dry summer months there has been an increase in manganese, iron and bromide ions and an unexpected increase in the winter months. The increase in ions during the summer is attributed heavy pumping causing up-coning and retrieving water from the limestone aquifer. The increase in ion concentration in the winter months is attributed to the water viscosity increasing with decreasing temperature. This cause’s greater drawdown’s in pumping wells resulting in greater yields from the underlying aquifer. Ionic ratios, with decreasing alluvial thickness, also show increases in concentration for manganese in the summer and winter. Piper plot’s, also show that groundwater mixing is occurring between the Platte River alluvial aquifer at the Lincoln Water Well Field and the underlying limestone aquifer.