Ten years ago, a team of geologists sent one-seat planes on a magnetic-radiometric survey of the farm counties of northeast Iowa. They were searching for rare earth elements (REEs) in the Precambrian basement rock, or craton, which lies buried 2,000 feet beneath the surface. What they found were rings of iron-rich minerals known as layered mafic intrusions.
Over a billion years ago, a swell of hot rock, or pluton, rose into the craton bearing a wealth of REEs once trapped in the mantle. Over the millions of years the pluton took to cool, those elements mineralized at different temperatures, leaving concentric rings with different magnetic signatures. Erosion wore down the surface of the craton and exposed them in cross-section. They have been buried only recently, geologically speaking, by shallow seas, the carriage of glaciers, and corn.
This is how Ryan Clark of the Iowa Geological Survey explained the “northeast Iowa intrusive complex.” From his office in Iowa City, Clark is one of several coordinators of the first new magnetic-radiometric survey of the Upper Mississippi Valley in decades. The same technology that searched for minerals north of Cedar Rapids will map the valley from Wisconsin to central Missouri. They are searching for features of the Precambrian basement that have been hidden by old and imperfect data. Scott County is up for inspection.
“We would like to learn more about what the Precambrian basement geology is,” Clark said, “and then see if that is somehow affecting the overlying strata, and how they’re folded or faulted a little bit from a structural standpoint.”
Sometime in the new year the United States Geological Survey (USGS) will dispatch planes from Dubuque Airport. They will cut rows 200 yards wide just 80 yards above the ground, sweeping the country like a combine. The effort is part of the Earth Mapping Resource Initiative, or Earth “MRI.” It aims to combine and fill gaps in scientists’ knowledge of the ground. It is also searching for more of the rare earth elements that lie buried an hour north of Scott County.
Chelsea Amaral, who works at the USGS federal center in Denver, Colo., is the lead scientist on the project.
“This is a national priority that’s actually funded by Congress,” she explained, “that we’re leading to modernize the nation’s mapping, and to better understand the underlying geologic framework and the knowledge of our domestic mineral resources.”
It is an ascendant truth of our current political world that everything we need must come from the ground beneath our feet. China controls 90% of the world’s output of REEs, and that figure has scared hundreds of millions of government dollars into rare-earth research and refining. REEs are essential in the batteries and magnets on which modern military and energy technology depends.
“Earth MRI is mapping the critical minerals needed to drive the U.S. economy and bolster national security,” Jamey Jones, Earth MRI’s science coordinator, said in a November press release. “Partnering with the state geological surveys of Illinois, Iowa, Missouri, and Wisconsin helps with the work of the nation—and adds to state knowledge crucial to the resource economy, as well as water resources, and natural hazards.”
Since I moved to Iowa six months ago, a refrain has echoed in my head: “Find the cost of freedom / buried in the ground.” It comes from Crosby, Stills, Nash, and Young. No doubt Stephen Stills was reflecting on the dead come home from Vietnam, “buried in the ground.” The song’s only other lyric is: “Mother Earth will swallow you / lay your body down.”
But like all good poetry, it means something more. It means that what lies beneath our feet sets the contours of our lives and freedoms. The modern world has worked tirelessly to contest this idea, to prove that people and ideas and economies can be rescued from circumstance and the natural world, and in many ways, it has made its point. It is a fabulous irony that as the stalks of wind turbines have hoisted neodymium magnets into the skies above cornfields, we have been sent back to dig in the ground for filings of stardust.
Yet life in Iowa has never been so far from the ground. Now, blanketed by snow, the soil sleeps. It is some of the richest in the world. The ebb and flow of Pleistocene glaciers washed the ground with Canadian magnesium, potassium, and calcium. Then, in the Holocene, the prairie began to wake. It rose up and drove down. Ten-thousand years ago its roots reached twelve feet deep and cracked the bedrock. The first Europeans to reach Iowa found a foot of topsoil; they spent half of it in less than two centuries.
Life here depends on a history that spans the geologic and the human: a history of the ground. It raises the corn and soy. The water we drink every day lies trapped in the bedrock, layer upon layer of limestone and shale and sandstone left by old dead seas. That water is awash in the nitrogen that we spray in the spring and fall as a replacement for the richness of lost soil. Running through the ground like veins are natural gas and transmission lines, and new life blooms where they intersect. The smokestack of a power plant sprouts in the field.
It has become my job to present the bill for this way of life. As Stills warned, every freedom has a cost, and these are ours. They are often reasonable ones, good ones, that we should be ready and willing to pay—we cannot be afraid of our own lives. When we are, we can only reflect on what we have missed, and what we can change.
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The Mississippi River Valley is home to its own sort of mineral deposits, known as Mississippi Valley Type (MVT) deposits, or carbonate-hosted lead-zinc ore deposits. While lead and zinc are not REEs, they are still listed among the USGS’s 60 critical minerals. Ammunition remains a critical use of lead, the USGS reports.
You will reach MVT deposits if you travel by river just north of Scott County, which drew the first white settlers to Iowa two hundred and fifty years ago. There the fur trapper Julien Dubuque mined galena, the common ore of lead, with the Sauk and Meskwaki native tribes. In a few decades, the region would produce more lead than any other in the world. In bullets, that lead murdered the Sauk and Meskwaki during the Black Hawk War, commemorated in a plaque by my Davenport apartment. The U.S. Army demanded 10% of all lead mined.
Iowa’s lead mines have long been exhausted, but understanding how MVT deposits landed in the Mississippi Valley could “give us more insight into where we can find them in other places,” Amaral explained.
The leading theory links MVT deposits in Iowa to the Illinois basin across the river to the east. There the craton dips thousands of feet lower than it does here, and so the layers of sedimentary bedrock run especially deep. The bedrock is porous. Liquid flows in from across tens of thousands of square miles, forming what geologists call a “basinal brine.” Somehow, the movement and heat of the craton can force the brine up through the layers of sediment. Hot and saline, it dissolves minerals on its way, and these precipitate when the brine reaches the surface.
“They travel through permeable and porous rock spaces or fractures and things like that, and then get deposited wherever they’re deposited,” Amaral said of lead, zinc, and other minerals. “And so, part of what the magnetics help us to understand are the underlying geologic structure. That helps with that fluid flow.”
Geologists speculate that these brines may have begun their journey to Iowa from as far south and east as present-day Appalachia, Amaral said: a “continental scale migration of mineral-rich fluids.” They would have been pushed westward by the succession of mountain-building events, or orogenies, that built and warped the eastern seaboard.
The origin may have been more recent, with the oceans that deposited marine sediment across the continent.
“The mag surveys will tell us more about the structure of how the basement is shaped and formed, and then we can use that to inform our theories,” Clark explained. “Maybe the basin structure itself affected how the ocean was circulating, and then that affected the deposition of the sedimentary rocks that we’re seeing, say, in the Dubuque area, Jackson County.”
“We know where a lot of these minerals are, generally, already, in this survey area. But what this is helping us do is to better understand kind of why they are where they are,” she said.
For every dollar of lead or zinc the USGS can trace, every ounce of an REE it finds buried beneath the sediments of the River Valley, Earth MRI promises a wealth of geologic knowledge. Geological discovery has always been an accident of prospecting.
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Once the prospect of geology out here was a struggle. In 1852, the geologist David D. Owen wrote that students of the Iowan ground “must be content to travel for half a day together without seeing aught but a rich, black soil, covered, as far as the eye can reach, even down to the very edge of the small streams… He may consider it a special instance of good luck, if, in return, he can catch a glimpse of a rock exposure once or twice a day.”
In eastern Iowa, the rocks chanced on were probably emplaced during the Silurian period, between 444 million years and 419 million years ago, give or take. A wide, shallow sea covered Iowa, and its fossil records lie exposed in limestone and dolomite across the state. Now the sea lies underground. Most of the municipal wells in Scott County draw from the Silurian aquifer, water held in the uppermost stratum of bedrock, just beneath the rich, black soil.
Each of the two wells in Princeton draws from the Silurian. Both run 455 feet deep and they are less than a mile apart. While water from the old well is safe to use and consume, water from the new well is not: it is overloaded with nitrate. Over a year ago, it breached the state drinking water maximum of 10 mg/L nitrate and was severed from the city’s water supply.
Iowans lather nitrate on their fields over the course of the growing season, and even afterward: along with phosphorus, it feeds the corn and soy. Yet nitrate is water soluble, and if it is not taken up by crops, it will run into surface water streams and leach into groundwater.
Ryan Clark, the geologist coordinating Earth MRI from Iowa City, has consulted with the city of Princeton on their struggles with water quality.
“There are many places where the Silurian aquifer is exposed at, or very near, the land surface,” Clark wrote in an email. “This makes it highly susceptible to contamination from agricultural chemicals, what’s commonly referred to as ‘non-point source pollution.’”
“For this reason, large portions of the Silurian aquifer in eastern Iowa have elevated nitrate levels,” he continued.
Nitrate overexposure most scandalously risks methemoglobinemia, or “blue baby syndrome,” in which nitrate strangles the blood’s ability to carry oxygen. It occurs in infants and can be fatal. Nitrate overexposure also correlates with certain forms of adult and childhood cancer, and difficulties during pregnancy.
On the advice of consulting geologists and water quality experts, including Clark, the city of Princeton leased approximately 20 acres of agricultural land surrounding the Lost Grove Well and removed it from production. In six months, nitrate levels have dipped, but never dropped below 10 mg/L. They must remain below that level for twelve consecutive months before the city can restore the well water to Princeton homes and businesses.
“I am not convinced that setting aside a small amount of land directly around the new well… is going to solve the problem,” Clark wrote. He said non-point source pollution could span well beyond the leased land. “However, I agreed that this approach was probably the simplest and cheapest option to start with.”
Aaron Schroeder, water protection specialist at the Iowa Rural Water Association, said it was too early to know whether the city has made progress restoring its water quality.
“I would expect a few months of data to be inconclusive,” he said. “One growing season isn’t going to give you anything conclusive.”
Nitrates may be the result of recent production, but chemical fertilizers have been applied at scale in Iowa since the 1960s. We are living with this history. Months ago, Schroeder sent groundwater samples from the Lost Grove well to a Nebraska laboratory that can test for the origin of the nitrate and the age of the water. They have yet to return results.
Origin tests will indicate whether the nitrate is from organic sources, like a sewage leak or manure fertilizers, or a synthetic source, like anhydrous ammonia. Schroeder said the tests were likely to reveal a mix of both: “groundwater issues like this tend to be nebulous.” That is why it is called nonpoint pollution. The age tests will indicate whether the well is drawing water supplies more or less subject to current production and pollution.
Each point of data is like the point of a constellation, from which you can draw several pictures.
“The more data you acquire, the more decisions you can make and guide, and the more effectively you can evaluate the success of things,” Schroeder said.
At least, that is the hope, he said. “Once we get those samples, maybe there’s something, maybe they’re totally inconclusive.”
The sickness of the Lost Grove Well is not without remedy. Further drilling can plunge the well deeper, through the Silurian aquifer and into one of the aquifers below, such as the Cambrian-Ordovician. Alternately, reverse-osmosis machines can pull nitrate directly from the water, as they do in Des Moines to treat water from the Raccoon River. They produce a stream of nitrate-rich wastewater that the city must pay to ship out.
Either solution is likely to cost hundreds of thousands of dollars just a few years after the well project was completed. So an old bill would land with the city, the charges on decades of agricultural prosperity.
“Those are two real options; they’re just both cost prohibitive,” Schroeder said.
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Scott County takes pride in its ground. In its defense it wields the Comprehensive Plan and the strictures it has laid on land use since the 1980s. Its first land use objective is to encourage development “within the boundaries of existing cities”. Its third is to discourage development “from locating on productive agricultural soils and other agricultural areas”. The glaciers pummeled the ground, and the prairies built the loam, but it requires the law to stymie the cul-de-sac and strip mall.
The soil hides the county plumbing. Tile drains the soil and rushes excess nutrients out of the field. Electricity hurries through transmission lines and will pay for the carriage of the Internet along fiber optics. East-west through Maysville and north-south along the river run a pair of natural gas pipelines.
Nearly four months ago, the Central Iowa Power Cooperative (CIPCO) debuted its plan to build a 240 MW natural gas “peaking” plant at the intersection of the east-west pipeline and transmission lines about a mile east of Maysville, in prime agricultural soil. I visited Barb Holtz, the project’s closest residential neighbor, in the days after the project was announced. She told me that she had noticed men in the field, rooting around in the ground; now she knew they were finding the pipeline, sampling the soil, seeing if the site could hold the steel generators and concrete housing the plant would demand.
Why here? Holtz asked. She was not the only one. The answer was soon clear: mere accident. Here the lines crossed. The county could make that intersection the condition of an exemption to its code and principles, an exemption so narrow as to be nearly singular.
To date, that exemption has been the site of the battle between CIPCO’s project, backed by the Planning and Development Office and Planning and Zoning Commission, and the project’s Maysville neighbors. Planning and development director Greg Schaapveld has repeated that the authors of the Comprehensive Plan did not anticipate the arrival of a power plant. Neighbors have insisted that that silence is a warrant for opposition, especially when the Plan was mounted as a defense of the county’s agricultural character.
“My family farmed near the proposed power plant for four generations,” Dave Golinghorst, one of the project’s neighbors, told the county board of supervisors in October. “I never imagined that the county would ever support a power plant here, where we have the most productive farmland. I never thought I would look out our window and see the industrial stacks, and wonder how power plant emissions would affect my family and crops.”
“It just seems like a sin to own and be the steward of any amount of this amazing land and not use it to grow something,” echoed Carolyn Bauer, another neighbor.
“I recognize the need for power, but putting it on prime ag ground is not the answer,” she said.
The Concerned Citizens of Scott County, organized by Dave and Linda Golinghorst, have consistently raised up the productivity of the soil as evidence of the need for conservation. They have proposed new protections for land with a corn suitability rating (CSR) above a certain benchmark.
For centuries the ground has organized the life of the place; the power plant is at once an attack on that life and a symptom of its disappearance. Engineer Tom Quiram of Durant works for the regional energy cooperative (REC) Eastern Iowa Light and Power. He put the point clearly if accidentally in his defense of CIPCO’s project before the supervisors.
“In the 90 years that Eastern Iowa REC has been in existence, we have seen electricity transform farming from a labor-intensive occupation to a highly mechanized agricultural business,” Quiram said. “To preserve modern agriculture, we strive to provide our members reliable and economic electricity, 24/7, 365 days a year, as does CIPCO, our power provider.”
He continued: “In my opinion, passing this ordinance to allow further electric generation is in itself a form of ag preservation. Tonight, I ask you to pass this ordinance so we can continue to power and preserve modern agriculture now and into the future.”
The gas lines, the transmission lines, the power plant they feed: these are the cost of freedom. Corn may grow from the soil but no one works it with their hands. Farmers rise at dawn to sit behind the wheel of capital and energy and reap the fortune of millions of years of geologic history. Farming is not an easy life but nor is it the life it was, though we would like to think it is, and certainly we would like to look out on the fields of corn which have been its mark on the world for two hundred years. It is a beautiful picture though it is not the whole truth. That honor goes to the smokestack and the rare earth magnets in the generator at its heart.
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Right now Scott County lies buried beneath the snow. Blanketed, the soil sleeps. There are no USGS planes flying out of Dubuque because the radiometers suspended from the back of the plane cannot read through water. They detect traces of radioactive elements in the first few inches of topsoil, which may or may not suggest deposits deeper in the ground.
“If there’s any kind of like flooding or surface water or snow on the ground, we lose the signal,” Amaral said. “So they can’t fly the planes.”
It will take until the end of next year for the USGS to complete their survey. It may be a year before planes cross Scott County. Geologists do not hurry; neither do their subjects. The ground changes very little.