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In a dark, dank room on Kansas University’s West Campus, you can find some of the best-kept, hard-won and most thoroughly analyzed mud in the state of Kansas.
The room houses row after row of meterlong tubes, which resemble the long fluorescent light bulbs of office buildings, but they are a translucent, super-hard plastic, fatter than bulbs, and the stuff inside has known only the dark of underground, until now.
Each tube holds a meterlong piece of a sample from the sediment below Harvey County in central Kansas. Each tells a small part of the story of not only geologic history but also, scientists hope, the future of the subterranean water system on which the region’s economy, farmers and communities depend.
The filling in some tubes is so fine and sandy it looks as if it was taken from a beach. And in some sense, it was. Ancestral rivers to modern river systems in central and western Kansas dumped the sand onto the plains hundreds of thousands or even millions of years ago.
Greg Ludvigson, a sedimentary geologist with the Kansas Geological Survey, points to a tube holding a heavy granular sand, with bright auburn grains mixed in with browns and grays. “That’s almost something you could put in an aquarium,” Ludvigson said.
Fish might like that sort of sediment, but humans do, too, whether they realize it or not. Water moves more easily through grainy sediment, which makes the wells above it more productive.
Unearthing the Ogallala
It takes a geologist to glean much knowledge from mud, sand and rock. Two years into a five-year project, Ludvigson and the survey team can already tell us more than we have ever known about the layers of earth that house aquifers in the state.
This vertically preserved sample of sediment, which the team calls a “core” sample, was taken from the Ogallala Aquifer, a massive underground water system stretching from Nebraska to Texas.
The Ogallala is hugely important to the economy and communities of the Midwest. Farmers have long tapped it to irrigate their crops. As corn, a very water-needy crop, has gained popularity among farmers because of its market value, the Ogallala has been under more pressure than ever.
In 2012 the aquifer’s water tables in Kansas dropped by three and a half feet, the second highest dip on record. With the the depletion rate so much higher than what nature can replenish through the precipitation cycle, parts of the aquifer could be tapped out in fewer than 25 years.
But such projections are not as precise as they could be. They are based on a limited understanding of the sediment that houses the underground reservoir. Ludvigson notes that previous studies have used techniques that smash up the sediment in the process of extracting it. Extrapolating from broken sediment yields results with high margins of error. And that adds vagueness to those very important projections about the Ogallala’s ability to produce water.
That’s where Ludvigson and the Kansas Geological Survey team come in. Using two drills, they have been able to extract preserved core samples from central and southwestern Kansas. The drills, great gear-filled mechanical beasts that vaguely resemble oil rigs, were imported from Europe because the technology isn’t produced anywhere in the U.S. To give you an idea of the kind of sophisticated technology needed to get a core sample, one of the drills uses sonic vibrations to help cut through the deepest layers of sediment, which helps keep them intact.
Two big drills
The difficulty and expense of doing this is why it hasn’t been done before. It’s also why our understanding of the Ogallala and other aquifers in the plains region is so incomplete. As Ludvigson puts it, “The point of doing a core sample is to stop guessing and start knowing.”
Extracting core samples is a time-, labor- and money-intensive endeavor. The team began drilling the Harvey sample in 2011 and has come away with 98 meters, with 100 feet of harder rock left to go. They have a multimillion-dollar budget, cobbled together from the survey’s budget plus grants from the U.S. Geological Survey, the U.S. Bureau of Reclamation, the National Science Foundation and the Kansas Water Office. All of that to produce five or six core samples, which Ludvigson says is a pretty good start.
Drilling is not where the labor and expense end. From there, the team has, as Ludvigson says, “thrown the kitchen sink” at the samples it has collected. They ran the sediment through a battery of tests to analyze everything they could think of and afford: isotope records, calcium carbonates, gamma radiation and signs of weathering during the sediment’s life.
From all these tests, researchers can learn about the layers of earth, where they came from and how old they are, as well as the composition down to the finest detail. All this goes to providing an incredibly precise description of the sediment’s layers that researchers can then compare to samples from other areas.
Already, the team has made important findings about the state’s aquifer system. Along with the Harvey sample, the team extracted most of a core from Haskell County in southwestern Kansas, an area most had assumed was part of the Ogallala, though an especially low-flowing section of it.
But the survey team found a problem with that assumption. Their samples found that the age of that sediment was tens of millions of years older than everyone thought, meaning that it probably couldn’t have been formed at the same time as the Ogallala. By getting a precise gauge on the core’s age, the team found that the sediment from Haskell might belong to a completely different water system, the White River Group that extends to Nebraska.
These are all fairly big discoveries in the world of geology and hydrology. More modest discoveries found through comparing samples can yield a more detailed picture of the sedimentary makeup of the aquifers under the plains and how it all connects. That information can then be used to make more accurate and specific predictions about the Ogallala and aquifers under the Great Plains.
The promise of the research is that it can be of direct use to water managers and farmers in central and western Kansas. Understanding the Ogallala more deeply can lead to better decisions about pumping from it. Or so Ludvigson and his fellow geologists hope.