ENWRA Projects
Helicopter Electromagnetic (HEM) Surveys, Pilot Study Sites
The Helicopter Electromagnetic survey is a very rapid and efficient way of remotely sensing geology across an entire site without engaging in extensive drilling. In HEM surveys, a geophysical device containing sensors is suspended beneath a helicopter. An electromagnetic field is continuously transmitted to the land surface (and subsurface) while the helicopter is in flight, and the sensors carried under the helicopter receive the subsequent return of electromagnetic energy from the land surface.
For more information and videos of the HEM data, visit our Media/Downloads page.
Helicopter Electromagnetic (HEM Surveys), Sprague and Swedeburg Areas
Lower Platte South and Lower Platte North have budgeted $240,000 for additional HEM flights outside of the pilot study areas. These areas are of special interest to their Natural Resources Districts because of water quality and quantity issues. The Nebraska Environmental Trust has contributed an additional $200,000 toward processing the data generated by the flights.
Drilling and logging a test hole
Test Hole Drilling
ENWRA drilled approximately 40 test holes total across the three pilot study sites. The test holes provide high-quality geologic data and are required in order to make a direct association between HEM survey results and subsurface geology. Downhole geophysical tools are used to log both electrical resistivity and gamma-ray emissions of the geologic materials encountered in the test holes.
Vadose zone equipment and weather station
Estimating Recharge
ENWRA uses heat-dissipation sensors, soil moisture probes, and weather stations (air and soil temperature, precipitation, humidity, wind speed, solar radiation, and potential evapotranspiration) to continuously collect data regarding groundwater recharge at each of the pilot study sites. This information contributes to understanding the volume of precipitation recharging the underlying aquifer at a specific site, how fast that recharge occurs, and the importance of vertical and horizontal flow paths.
Collecting a water quality sample
Water Chemistry and Age Dates
ENWRA collects water quality samples at monitoring wells and has the samples analyzed to determine general water chemistry. By comparing water chemistry, hydrogeologists can assess the extent of connection between aquifers and surface water and potential flow paths. In cases where general water chemistry does not provide a clear answer regarding connections, additional ground water samples will be collected and age dated. In addition to providing information about aquifer connections and flow paths, water sampling provides site specific information that will likely be useful in the future for water quality conservation purposes.
Aquifer test at Logan East Rural Water System
Aquifer Tests
ENWRA is conducting two aquifer tests, one near Hickman and another near Oakland. Aquifer tests are performed to assess the aquifer extent, amount of water in storage, the rate of water movement, and its potential hydraulic connection to other aquifers. To perform an aquifer test, hydrogeologists use a high-capacity production well installed in the aquifer they are studying. Observation wells are then installed at selected distances and in different directions outward from this pumping well. These observation wells are designed to monitor water levels within, above, or below the pumped aquifer.
Water is pumped from the production well at a constant rate over a period of multiple days. The amount of water level decline in each observation well (drawdown) provides hydrogeologists with the information they need to estimate the transmissivity and storativity of the aquifer. Changes in the rate of water-level decline allow hydrogeologists to assess flow boundaries and the potential connections between aquifers.