Dr. James Wilde speaking about potential road damage by trucks hauling loads of sand.
Dr. James Wilde speaking about potential road damage by trucks hauling loads of sand.
Houston County Commissioners convened their first public meeting on frac (silica) sand at the La Crescent High School Fine Arts Center on March 19.

Many of the same persons who asked questions at a Planning Commission meeting last month attended. Since that time, commissioners have enacted a one-year moratorium on new frac sand mining permits, while they look at the issues involved.

Monday's meeting was educational. Three experts on the geology of the sand deposits, groundwater and highways spoke.

Why sand in Houston County?

University of Minnesota Geologist Dale Setterholm touched on the sand which mining companies are seeking, and how sand mines operate.

"The mid-continent is the best place to find this sand," Setterholm said. "We have had active silica sand mines in Minnesota in the past, but there's a much greater demand for this material now."

While silica sand from the upper Midwest has had many historical uses, including windshield glass for automobiles, hydrofracking is driving a large increase in new mining, Setterholm noted.

The purity of the large, nearly spherical grains of sand found in prime deposits makes them strong and chemically inert. That's ideal for gas and oil mine fracking, where cracks in petroleum-bearing rock need to be "propped open" with permeable material, allowing extraction.

Setterholm said the most desirable sand in Houston County is from the Jordan layer, which is mostly exposed in bluffs along the Mississippi and Root rivers. Jordan sandstone is also exposed on the floors of some limestone mines, where overlying strata has been stripped off.

"Where the Prairie du Chien limestone has been removed, the Jordan would be exposed," Setterholm said.

Most of the questions directed to Setterholm had to do with water, which he said is "not my area of expertise," but answered from his perspective as a geologist.

Setterholm was asked if "dewatering" sand mines could draw down wells. He answered that it could, although sand mines that go into dry layers (above the waterline of the aquifer) won't need to pump away ground water to operate.

When asked about chemicals used to process sand, Setterholm said, "Physically removing the sand is not going to change the quality of the water, but we want to be aware of the materials that we're introducing into the environment."

Setterholm said mining around the bluffs has not yet been proposed, but is possible. In theory, underground mining is also possible, he noted.

Reclamation, Setterholm said, "doesn't mean making what you had (before mining a site)... There are as many ways to do it as there are mines."

What about the water?

Minnesota Department of Natural Resources Hydrologist Jeff Green spoke about aquifers and how mining could impact water quality.

He said southeastern Minnesota contains karst topography, which allows surface water to "take a short cut" into wells. "That's the system that makes up a big chunk of Houston County," Green said.

"The Jordan lies below the karst," Green said. He added that contour mining of the bluffs has not yet been proposed in the area, and that "In Wisconsin, the sand is easier to get to. Proximity to transportation will be a big issue (in siting new mines)."

"DNR's regulatory purview is water use," Green said. "For us, that's nothing new." Describing the permit process for large wells (over 10,000 gallons per day or 1 million gallons per year), Green said, "We require a lot of information. We take this pretty seriously."

Citing a pair of springs named "Big" in Fillmore County, Green told how quarries had impacted their rate of flow, temperature and turbidity. "That's the kind of thing we want to avoid," he stated.

"A domestic well has the highest priority in Minnesota," Green said.

When asked about municipal wells for Caledonia and Spring Grove, Green said that it's true that those are pulling water out of the Jordan, but said he didn't expect sand mines to draw down the aquifer.

More water will be used in the sand washing process, Green said. "That is being done along the Mississippi River. As a hydrologist, to me that's a good place to do it in terms of water levels."

Roads will be ipacted

Dr. James Wilde, professor of Civil Engineering at the University of Minnesota, Mankato, gave a presentation entitled, "The effect of heavy loads on pavements."

Wilde described roadway bending, or deflection, as a primary factor in road damage.

"Doubling the load does 16 times as much damage to the road," Wilde stated. He said that one semi-truck can do as much damage as 2,000-3,000 passenger cars.

Wilde said a single sand mine may produce 270,000 tons of sand a year. That translates into 11,740 trucks per year at 23 tons per truckload.

A typical roadway in Houston County could be designed for 50,000 trucks over its entire lifetime, according to the presentation.

Putting the impact of more trucks on a given road into perspective, Wilde said a common roadway would be engineered to last about 20 years.

Milling and overlays can extend the life of a highway, but never return the base of the road to pristine condition. A 20-year road can be worn out in as little as five years if heavy truck traffic jumps a great deal beyond original estimates, Wilde said.

Showing videos of actual road deflection by heavy tandem axles, Wilde compared the bending to "a ripple effect."

Board Chairman Jack Miller told residents that Houston County had to pay the city of Caledonia for damage done to streets when concrete was hauled to the Justice Center site.

"This isn't a completely new issue only involving sand mining," he noted.

What next in the process?

Further frac sand meetings will be held so the public can keep up on what Houston County decides to do, Miller stated.

When asked how citizens should contact the board, Miller said commissioners would be happy to take calls, emails or speak to those who "get on the agenda" at weekly board meetings.

Kermit McRae asked how the county planned to proceed?

Miller said a study group will soon be established to advise the board. In addition, "All of us on the county board are going to visit an actual operating mine in Trempealeau County, where they have been at it for some time," Miller said.

"We need to gather as much information as possible," Miller stated, but added that surrounding cities and counties are already working on the same questions.

"Why re-invent the wheel? They are willing to share what they've learned with us... but we also want to take into account the fact that Houston County as its own unique topography."