It’s August of 2013, and I’m standing on a hillside in northwest Lancaster County, gazing into the distance through morning haze and waiting to hear that distinctive chopping sound made by large helicopters. In front of me a few feet downhill is something that looks like a gigantic Hula-Hoop with a metal box attached to one side of its curve.
The helicopter and the hoop represent a sea change in the way geohydrologists will go about the work of finding and defining aquifers. This technology won’t make drilling test holes obsolete. There will always be a need for human beings and drill rigs to establish the “ground truth” for what lies underneath a specific point on earth’s surface. But the equipment in that metal box does represent a revolution in how geologists will put together the descriptions and cross sections of the earth’s crust in a level of detail not previously possible. With ever-increasing certainty, geologists will be able to map the positions and compositions of previously “unseeable” layers of rock.
Over the decades, many people, often very skeptical, have asked me, “How do you really know what’s going on with aquifers?” The first part of my answer starts with a definition: An aquifer is any naturally occurring subsurface material that stores and transmits water in usable amounts.
The more detailed answers to that question have direct relevance to economic development and public well-being. For determining everything from choosing where to drill irrigation and/or domestic wells to calculating how a pipeline leak would impact an aquifer to designing integrated management systems for groundwater and surface water, the state’s residents deserve access to the best available science. This article is a brief introduction to the test-drilling program as it relates to water supplies. It touches on the ways that geologists identify these supplies and develop conclusions about aquifer features. Issues related to water quality, such as identifying what materials are dissolved in the water and how safe it is for human and agricultural use, can best be covered in another article, preferably by a geochemist.
Starting at the Surface
The nineteenth-century geologists who explored the central Plains and Rocky Mountains deduced much of the basic story about the earth processes that created these regions. They rode horses over long distances, hiked through canyons and over prairies, and rafted down rivers. Each day, they kept careful notes describing what they had seen and where items of particular interest could be located on a map. Although no one at that time understood exactly how and why mountains rose from shallow seas, it soon became clear that the rivers rushing off the eastern flanks of those rising Rockies had carried with them massive amounts of eroded rocks, which were eventually deposited onto the Plains. The sedimentary rocks cropping out in eastern Wyoming and western Kansas and Nebraska were layers of debris from the mountains interspersed with layers of ash from massive volcanoes even farther to the west. There was still much to learn about the different phases of deposition dependent upon pulses of mountain building, climate changes, and time. There was clearly much more to learn about the layers beneath the Plains, but the basics of Great Plains geology were available by the late 1800s.
During the summer of 1898, N. H. Darton, a self-educated earth scientist from New York, was on horseback trotting toward a cliff of buff-colored rocks some seventy-five to eighty feet high. Darton had been curious about how much water was available for settlers coming west, especially in the semiarid regions of the Great Plains. He knew enough regional geology to suspect that the buff-colored outcrop ahead could hold the key to his research. As Darton got close enough to examine its features in detail, he saw multiple layers of ash, gravels, silts, sandstones, and conglomerates. Some layers were loosely held together and porous enough to let water flow through them; other layers were so fine-grained and tightly cemented that water wouldn’t be able to penetrate easily, if at all. Furthermore, up, down, left, right, and angled, the characteristics of these layered sediments transitioned from one type to another. He christened this major geological unit the Ogallala formation, named after a nearby small but booming cattle town.
Examining the Ogallala above ground allowed Darton to see firsthand its composition and structure. But what he didn’t know was how far that gently tilting formation extended to the east or how deep it was beneath the surface or, least of all, how much water was held within the pores and cracks of those buried rock layers. So he did what so many of his geological descendants have done since then—he drilled a test hole. Using horsepower and human power to turn the crank of the rig, he and his crew drilled holes some six inches in diameter into the earth. In one case, he reports, he actually got two thousand feet deep. What they found surprised him: The great American desert lay over millions of gallons of water held within the layers of the Ogallala. It was free for whoever managed to put a well into those water-bearing rocks.
“Impractical for Almost Any Purpose” or Water Riches beyond Imagining?
The perception of the Plains as a “great desert” came from reports and descriptions written by various explorers who traversed the region during the late eighteenth and early nineteenth century. James Mackay, an employee of a French trapping company during the 1790s, led an expedition through what is now western Nebraska and included these words in his report: “It is a great desert of drifting sand, without trees, soil, rock, water or animals of any kind.” Later explorers expressed similar thoughts. One of these was Lieutenant G. K. Warren, who covered the Nebraska Territories in 1857. He had this to say: “We have now traced the Loup River from end to end and found it impractical for almost any purpose. It seems like a great waste of time to have made the exertion we have. Our greatest wish is to get away from it as soon as possible and never return.”
Taking the opposite view was Lewis Hicks, who joined the faculty of the University of Nebraska in the late 1880s as state geologist. Early on he recognized the potential for significant water resources here. He encouraged the US Geological Survey (USGS) to partner with the university in these investigations, marking the beginning of a long and fruitful partnership between the two scientific organizations. Manley’s Centennial History of the University of Nebraska, I. Frontier University (1869–1919), states that it was from Hicks’s investigation in the late 1880s that “…the people of Nebraska learned of the great water resources in the state” and that “…as both a scientist and a promoter of irrigation, Professor Hicks deserves the gratitude of Nebraskans.”
Professor Hicks also deserves a salute from me for his intuition, especially as it relates to Nebraska groundwater. My personal most dramatic moment of insight came on a day when I was measuring water levels in southeast Chase County. I had a blanket permission letter from the Upper Republican NRD to measure previously identified wells. As I was calculating the water level in an irrigation well, a gentleman came up and asked what I was doing. I explained the work and how the results would be used. “But why are you measuring that well?” he asked. “It only pumps 750 gallons per minute. The well in the next quarter north pumps three thousand GPMs.” The man was Jack Maddux; he became a good friend and supporter of our program. I was astounded by his comments; he considered 750 GPMs a bad well! One week earlier, I’d been in Lincoln talking to a man who had built a home just north of I-80. He realized he’d be lucky to get a well that pumped 10 GPM. Clearly west-central Nebraska and the Ogallala Aquifer had water riches beyond what the imagination could grasp.
Drill Rigs Define the Ogallala
Test holes have been the standard way for geohydrologists to discover what subsurface materials hold usable amounts of groundwater. Structural geology and geophysics calculations help clarify some of the specifics of the rock layers. But it is the samples brought up during the test-hole drilling process that show, with certainty, the composition of the various layers of materials that make up the crust of the planet. There can be fragments of granites, sandstones, shales, and metamorphic rocks. There can be fragments of plants and animals long dead that once lived in the surface environments that hardened into buried rock. These fragments help define specific layers, or horizons, and can be used to correlate layers from one test hole to the next.
Since the time of George Condra, who drilled CSD’s first test hole in 1930, there has been a dramatically increasing number of test holes and monitoring wells across the state. In 1940 there were 728 test holes concentrated in Richardson County, the eastern half of the Republican Valley, the Platte Valley, and the North Platte Valley in Scotts Bluff County. In the 1950s the total was 2,450 test holes, and by the 1970s there were 3,522 test holes. Then came the proliferation of center-pivot irrigation and the number of test holes again rapidly expanded. By the early 2000s Nebraska had 5,436 test holes.
Up until 1970, however, very few CSD test holes had been drilled in the Sandhills. I like to say that CSD saved the best for last—exploring the Sandhills and the Ogallala Aquifer beneath them. My colleague Jim Swinehart was given responsibility for deciphering the history of the Sandhills themselves, and I was the fortunate geologist who got to lead the effort and get a firsthand feel for the full extent of the water riches beneath.
During the process of drilling into aquifers, we measure such things as the depth to water, the movement of that water through the earth materials, and the amount of water that would flow out of a well in terms of gallons per minute. A typical drill rig uses a rotary drill, which is the method that has been used throughout most of the years of CSD research. More recently, geologists have used the reverse rotary technique, which is more expensive but especially effective when test holes are deep.
Waiting for that helicopter last fall brought back memories of my earliest years of drilling in the Sandhills. I was still new to the region and the families that lived there. Wariness was the word among many of the ranchers and people whom I’d approached about doing research on their land. It must have seemed odd that this big guy from the university just wanted to drill a hole in their ground, collect samples in little bags, and take them back to Lincoln. But we explained what we were doing and the benefits of gaining knowledge about the aquifer that fed their springs, wet meadows, and watering troughs. What might have appeared to be a threat was soon accepted by a majority of the ranchers as a reasonable thing to do.
Standing on the hillside in northwest Lancaster County, my thoughts were some 275 miles to the west. I reflected on another helicopter in the early 1980s. We were drilling in Garden County on the Eldred Ranch. It was a vast spread making up much of the northern section of the county. Vic Eldred was initially hesitant to agree to my requests, but he soon became a good friend once he learned more about what we were doing. He had a helicopter that he flew to check on his extensive holdings. On one particular day we were drilling north of Oshkosh. Vic had his pilot fly him out to our site and hover over our rig, just hanging in the sky watching us drill and acting as a fan for us on a hot day. On a later occasion, when we were at another site on his land, Vic sent over his helicopter with instructions to fly me around the county so that I could get a feel for the whole landscape. We flew over the headwaters of Blue Creek and over Gusher Springs. We flew over the Crescent Lake National Wildlife Refuge, and I remember being struck by the different colors of the lakes and being able to see the linear tracks on the shallow lake beds made by large snapping turtles.
Whenever we drilled on private land, I always sent the landowner samples of the subsurface materials and summary logs of our drilling so that they could see the evidence of our efforts and better understand what we were doing. Vic liked talking about local geology with me. He and his wife, Martha, are gone now. I often wish, when people ask, “How do you really know what’s down there?” that I could take them onto the Eldred ranch and let them experience firsthand the drill rigs and the samples of various rock formations and the gushing, pure water from many hundreds of feet below. Then I’d whisk them into a helicopter so they could see for themselves the ripples on the dunes at sunset, the interdunal fens and marshes, and the places were groundwater seeps out from sandy hillsides and becomes the start of a small stream that eventually leads to a Nebraska river.
Water Riches Grace Nebraska, But…
If those early explorers could see Nebraska now, they would be astounded. Thanks to those nearly constantly flowing springs, the Loup and Elkhorn rivers feed into the Platte and assure a steady supply of water for communities and ecosystems downstream. Farther west, diversion dams and hundreds of miles of irrigation canals give farmers water for fields of corn, beans, beets, and other crops. With the mid-twentieth century invention and expansion of center-pivot irrigation, ranchers and farmers throughout the state are able to tap into those vast supplies of groundwater to nourish their crops and cattle and to make their land more productive.
This increased accessibility to the state’s water has created a kind of agricultural paradise. But unlimited access to water is a thing of the past. Nebraskans are experiencing conflicting demands on their water supply: Urban versus rural, state versus state, surface water versus groundwater, domestic versus agricultural. All these describe ways in which various interested parties end up in conflict with each other.
I have faith (some people might say naively) that we can work through these conflicts by developing a better understanding of where the water comes from, how much of it is in storage, where the water goes, and how surface and groundwater are inexorably interconnected. I’m intrigued and entranced by new methods of gathering data. That helicopter last fall landed on the hillside, picked up the hoop with the attached box, and used geophysical signals to scan the subsurface across dozens of square miles. By the end of this year that data will be turned into detailed cross sections of aquifers with a level of accuracy beyond what can be provided by extrapolating between test holes. Geologic subsurface research will continue to give Nebraskans the science they need to manage their water in a fair and sustainable way.
Next time, details of how the science of aquifers is used for public policy and water management.
Watch the Video
Nebraska Educational Telecommunications producer and writer Gary Hochman has recently completed a seven-minute video showing the topics this article covers—the definition of an aquifer (with the Ogallala in a starring role), a test hole in progress, and the helicopter-borne electromagnetic mapping process. It’s a must-see if you want to get the full picture of how geologists map and track underground water riches: