Living on the Edge

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Groundwater—that stuff that trickles through sand, gravel and cracks beneath our feet, that provides 70 percent of the drinking water in this state but is often out-shined by all those beautiful lakes and rivers—is in the news these days. People are not only starting to worry about what’s in it, but how much of it is left. This attention to water is important because of one simple, hard truth: they ain’t making any more of it. Basically water is the ultimate recyclable product, and what we do to it now—quantity and quality wise—will show up centuries from now. That’s why it’s good to see the Minnesota Environmental Quality Board is convening an interagency working group to examine how the booming ethanol industry, among other things, is affecting groundwater. While working on a groundwater article for the current issue of the Minnesota Conservation Volunteer, I talked to rural residents and hydrologists who already know what impact ethanol plants can have on water in a localized region. One problem is most of those plants are being built in parts of the state that are corn rich, but water poor. But one bit of good news related to groundwater that I stumbled across while researching the story came out of Rochester. There, officials have figured out how to remove dangerous levels of one common pollutant from water without breaking the bank. A bonus of this system is that it relies on protecting natural landscapes in the area—one of those win-win situations people like so much. Once the EQB gets done looking at what thirsty industries like ethanol are doing to our groundwater, they and others concerned about the future of the wet stuff would do well to examine Rochester’s experience. It’s a lesson in learning from history and using that education to ensure a better future.

Rochester’s experience with groundwater recharge shows that even when water is plentiful, studying its comings and goings can pay off. For decades the city drew on the Galena aquifer, a shallow system just below the surface. It produced plenty of water but, like a lot of shallow aquifers in southeast Minnesota, was easily contaminated.

By 1960 the city had abandoned the aquifer completely because of nitrate and fecal coliform bacteria. Now the city drills hundreds of feet to draw presettlement water out of two aquifers: the St. Peter Sandstone and Prairie du Chien-Jordan. But geological studies in the 1980s showed that there was a ticking time bomb buried below the surface. It turns out that half of Olmsted County’s water was recharging from the Galena down to the aquifers below it. That shouldn’t have been a problem, because typically on its way down through the soil profile the water would hit an impervious layer of shale called the Decorah Edge.

It would then run along the top of the shale and trickle over the edge at places where the shale is exposed on a hillside. At that exposed edge, grass, trees and soil filter out contaminants such as nitrates, making it so they don’t accompany the water the rest of the way down into the aquifers.

In fact, one study showed that nitrate levels decreased from 9.8 parts per million to 0.7 parts per million as recharge water flowed over the Decorah Edge. The drinking water standard for nitrate is 10 parts per million—higher levels can be toxic for infants. The problem is, as Rochester’s population has grown and spread out, the area of the Decorah Edge has been threatened with development—particularly residential housing. One estimate is that the entire area could be developed by 2045, eliminating deep-rooted grasses and trees and basically eliminating the ability of the Decorah Edge to filter water.

“When you convert land from something like permanent pasture and hay, you disrupt the hydrology,” Jeff Green, a Department of Natural Resources karst expert in southeast Minnesota, recently told me. “You can manage the impacts of land uses such as animal agriculture, but land conversion into housing developments and parking lots is different.”

Nitrogen contamination in southeast Minnesota is a big problem, particularly as more pasture, hay and timber has been replaced by corn fields, which rely on nitrogen fertilizer to be productive. Using technology to replace the Decorah Edge’s ability to remove nitrogen from water would cost the city an estimated $5 million annually. That’s one reason why in 2006 city officials passed zoning ordinances keeping parts of the Decorah Edge from being developed. Lake City, Wabasha and Redwing are now looking into using similar buffering to filter water recharging along the St. Lawrence Edge adjacent to the Mississippi River.

“It’s one of the most sophisticated water protection ordinances in the country,” says Terry Lee, Environmental Services Coordinator for Olmsted County. Lee credits widespread geological mapping and water testing with providing the information needed to take advantage of this natural filtration system. “It has wide ranging applications. You’re using an ecological approach to reach your water quality goals.”

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