Who’s excited about the Deep Borehole Field Test proposed for Spink County? Dr. Larry D. Stetler, professor of geological engineering at the South Dakota School of Mines and Technology.
Dr. Stetler was among the experts at the public meeting hosted by Battelle and the United States Department of Energy last night at the Spink County 4-H Building in Redfield to discuss the Deep Borehole Field Test, a science and engineering experiment that may take place in Spink County, if locals approve. The Energy Department wants to explore the feasibility of drilling 5,000-meter holes to dispose of some forms of nuclear waste in bedrock. Officials from Energy, Battelle, and Mines emphasized repeatedly throughout last night’s meeting and a similar session in Tulare Wednesday night that the Deep Borehole Field Test site in Spink County would not and cannot be used for nuclear waste.
Stetler thought he’d missed his chance to be involved with the Deep Borehole Field Test. His school had joined Parsons Brinckerhoff in a bid for the Borehole, but last January, Parsons Brinckerhoff lost out to Battelle, which proposed Rugby, North Dakota, for its drill site. But when local residents and county officials in Rugby declined to host the Borehole, Battelle went to the next good geological site on its list, and that’s the Benson Block of Milbank Granite under northeastern South Dakota. Battelle contacted the School of Mines in March and asked the school to serve as local experts for the initial public discussions about the Borehole. Stetler says Mines and Battelle have no contract in place yet, but if Spink County green-lights the project, he anticipates the school were serve the same scientific role as it would have partnering with Parsons Brinckerhoff.
Stetler said the most important science that he, his colleagues, and his students would do in the Borehole would be studying the rock brought up by the drill. He said the deepest recorded well hole in the area hit granite at 1,050 feet; the 16,400-foot/5,000-meter borehole would take us into uncharted geology in northeastern South Dakota.
The Borehole will produce a huge new geological dataset that Stetler says could produce new insights on the geological stability of the entire continent. Stetler expects the granite under Spink County is solid—after all, there is no tectonic activity, no seismic activity, no volcanic activity that could disrupt the bedrock. But if we find fractures, Stetler gets to ask all sorts of big geological questions, like what caused those fractures, are there any fluids in the fractures, how old are the fracturing and the fluids, and where do those fluids go?
Fractured bedrock would complicate the engineering of the project. Using boreholes to dispose of nuclear waste depends on drilling a hole as straight as possible so that waste canisters would slide all the way to the bottom. Engineers have dug deeper holes—over 31,000 feet in Oklahoma, past 40,000 feet in Russia—but never this straight. Stetler says we don’t even know if we can do it. A straight hole will be tricky enough in solid bedrock; fractured rock makes the bit veer and shake and gives less integrity to the Borehole wall.
Fractures would also raise the possibility of water infiltrating the disposal zone. Stetler hopes his department would also be involved in the hydrology testing planned once the hole is dug. He and his colleagues would test the age and composition of any fluids found in fractured rock to determine if those fluids are isolated deposits or if they match fluids found at higher levels. Any such mingling would mean a borehole would be an absolute no-go for waste disposal—remember, the whole point of this experiment is to determine whether we can dig a straight hole far enough down to isolate nuclear waste in bedrock, where even after its canister degrades, it will never come in contact with anything we might drink or touch or use.
For Stetler, the ideal science project would be to take core samples all the way down to 5,000 meters. Solid cylinders of rock would give him and his fellow geologists the most complete information about the composition of the bedrock. Conducting complete coring all the way down to 5,000 meters would take much more time and money than the six to eight months and $35 million Battelle’s Borehole project will take. Coring requires sending down the coring bit, grinding out a cylinder, breaking the core loose (think about that challenge: you can’t send a guy down that skinny hole to reach under the cut core and whack it free sideways with a chisel), hauling it to the surface, then sending the bit back down to drill some more. Stetler says the Borehole drill will likely send down the non-core bit to grind the bedrock into granite chips for most of the distance, with breaks at short intervals to take core samples to check for fractures.
We’ll discuss the political implications of this project in coming posts. But regardless of the politics, the Deep Borehole Field Test offers Stetler and his School of Mines colleagues a great opportunity to do the most basic and exciting science: to go where we haven’t gone and find out what’s there.