ENWRA: Accessing Groundwater Resources in Eastern Nebraska

By Julie Wragge
Lower Elkhorn Natural Resources District

UNL Conservation and Survey Division drilling manager Matt Marxsen, hydrogeologist Sue Lackey and research technician Waylon Hullinger retrieve geologic samples near Oakland. Test holes are typically drilled into the top of bedrock, which in the Oakland area generally occurs between 60 and 260 feet below ground surface (LENRD photo).

The Eastern Nebraska Water Resources Assessment (ENWRA) project recently finished a second round of test hole drilling at each of the three pilot study sites. The pilot study sites are located near Oakland, Ashland, and Firth.

The geologic information collected from the test holes will be used by the U.S Geological Survey (USGS) to help interpret maps produced by helicopter flyovers performed earlier this year. Geologists will also install ground water monitoring wells at some of the test hole locations. The water levels in these wells will be continuously monitored to assess the water table response to precipitation. Additionally, water samples will be collected from the wells to determine how long the water has been in the ground and its chemical composition.

The next step in the project will be evaluating the usefulness of a new geophysical technology to determine depth to bedrock beneath glacial till. These tests will be conducted, in conjunction with USGS, at some of the same locations where they have previously drilled test holes.

The geophysical equipment is about the size of a coffee can, so no heavy trucks will be needed and no additional test holes will be made. The equipment sits on the ground surface and records ambient vibrations from passing vehicles, wind in trees, etc.

Theoretically, geologists can analyze the movement of these vibrations through the subsurface and estimate depth to bedrock. Geologists will be assessing this technology at locations where depth to bedrock is known from test holes. These known depths will be used to evaluate how well the technology works in eastern Nebraska.

The overarching goal of ENWRA is to assess the ground water resources in eastern Nebraska so that Natural Resources Districts can successfully balance ground water supply and demand now and in the future.