In Nebraska, groundwater is the lifeblood for our homes, our crops and our communities. It’s the water we drink and the foundation of our state’s agriculture. Protecting this vital resource is a top priority, and that protection begins long before contamination ever reaches the deep aquifer. It starts in a critical, often-overlooked layer beneath our feet called the vadose zone: the region between the land surface and the groundwater table.
“This is the part of the system that tells the story before groundwater is impacted,” explained Arindam Malakar, a research assistant professor at the Nebraska Water Center (NWC), a part of Daugherty Water for Food Global Institute (DWFI). “By the time contaminants are detected in groundwater, the water is often already polluted,” he said.
Malakar’s team collects samples of the vadose zone at field sites across Nebraska. The recent efforts by his team represent the final phase of a project that has been underway for nearly three years, but vadose zone monitoring in Nebraska has a much longer history.
“Nebraska is one of the few states with nearly four decades of high-quality vadose zone data,” Arindam noted. “That long-term record is a key reason the state has been a leader in groundwater management.”
By studying this layer of soil, researchers can better understand how contaminants move underground over time and, importantly, anticipate future risks to groundwater quality rather than reacting after damage has occurred, which is hard to remediate.
Why the Vadose Zone Is So Important
Vadose zone data captures how land-use and management practices can influence contaminant movement through soil. It also provides the data needed to forecast what may happen next, offering information for better decision-making.
Traditional groundwater monitoring relies on sampling water directly from wells. Vadose zone research is a shift that allows scientists to observe contaminants like nitrate as they move through soil and before they reach groundwater. This approach gives researchers valuable lead time.
“If we can study the vadose zone quantitatively,” Arindam said, “we can predict when groundwater might become contaminated and take action earlier, rather than responding after the fact.”
This proactive approach is especially important in Nebraska, where groundwater supports agriculture, communities and ecosystems throughout the state.
How Vadose Zone Cores Are Collected
Vadose zone testing is a carefully planned and hands-on process. Each testing site is selected in collaboration with local Natural Resources Districts (NRDs), often based on groundwater nitrate levels and management classifications.
NRDs group areas into different phases depending on the severity of nitrate contamination in groundwater. These designations help determine where samples should be collected, how many samples are needed and how deep researchers must drill. Each sample—or core—is a vertical, cylindrical portion of soil and rock material taken from the vadose zone.
“We plan the coring strategy in advance,” Arindam explained. “The phase designation and the depth to groundwater guide our decisions about equipment and how deep the cores need to go.”
At each site, the team collects cores from the land surface all the way down to the groundwater table. The depth to groundwater can vary significantly across Nebraska. When the water table is relatively shallow, typically around 40 to 50 feet or less, the team uses a Geoprobe Systems direct push technique, which is efficient for reaching those depths. When groundwater lies deeper than that, they switch to a CME auger system, which is better suited for drilling beyond 40 to 50 feet and allows them to safely and effectively reach greater depths.
Cores are collected at five feet intervals. Each soil section is sealed in a liner, capped, labeled by depth and set aside in order. The process continues until the water table is reached. When the cores are laid out side-by-side, they form a visible profile of the subsurface, showing how soil layers change with depth.
What Happens to the Samples
After collection, the cores are transported to the Water Sciences Laboratory at the University of Nebraska–Lincoln (UNL), which is also a part of the NWC and DWFI. There, the sediments are processed and analyzed for nitrate and other forms of nitrogen.
Using these measurements, researchers create depth profiles that show how nitrate concentrations vary throughout the vadose zone. These profiles help reveal how contaminants move through the soil and how long it may take for them to reach the aquifer and begin to affect groundwater quality.
“With enough data, we can use models to estimate when nitrate in the vadose zone will reach groundwater,” Arindam said. “We can also evaluate how changes at the land surface may influence nitrate movement and transformation before it gets there.”
This information supports the development of best management practices and informs long-term groundwater protection efforts across Nebraska.
A Long-Term Commitment to Groundwater Protection
Consistent monitoring of the vadose zone over the past 40 years has allowed researchers to identify trends, improve predictive models and support informed decision-making at both local and state levels. It reflects collaboration among UNL researchers, NWC, DWFI, NRDs and other water managers across the state.
Each core collected adds another piece to a larger picture and helps Nebraska have one of the most comprehensive views of our groundwater quality in the country. By looking beneath the surface today, researchers are helping protect groundwater resources for future generations.
