Minnesota may be hailed as the land of picture postcard lakes and streams, but the waters of the state that can’t be seen or photographed – its underground aquifers – also are important. Now that groundwater, which provides water for drinking, irrigation and other uses, is getting added attention with accelerated funding for mapping as a result of the Clean Water Land and Legacy Amendment approved by voters five years ago this fall.
Making a map of groundwater isn’t quite as simple as mapping the lakes and rivers and streams in an area. It takes several years and gets developed in two phases. The Minnesota Geological Survey at the University of Minnesota gathers information about an area’s bedrock formation and glacial sediments where water is located underground in aquifers. The Minnesota Department of Natural Resources (DNR) then collects water samples from a variety of wells in the area and analyzes them to understand how the groundwater moves, how long the water has been in the aquifer and how sensitive the aquifers may be to pollution.
The analysis can look at a variety of indicators, such as water hardness, the concentration of common contaminants like nitrates, and the presence of indicator isotopes such as tritium. A radioactive isotope of hydrogen, tritium began appearing in increasing amounts in the 1950s and 1960s as a result of nuclear weapons testing. Whether or not it’s present in groundwater can tell researchers if the water entered the aquifer within the past 50 years. Groundwater samples that are believed to have entered the aquifer hundreds or thousands of years ago may be dated by testing for the presence of carbon-14, another radioactive isotope of a common element, often used to find the age of archaeological relics. By learning the age of a groundwater sample, scientists can better understand if the groundwater system is old and relatively protected, or young and relatively sensitive. A shallow groundwater system containing more recently replenished water can be more easily contaminated.
Once the data are compiled and processed using geographic information system computer tools, the result is what’s known as a county geologic atlas: a collection of maps and other information that describe an area’s aquifers, including where and how water moves through them underground. That information is critical for protecting water resources, responding to contamination, and planning for long-term sustainable water use, said Jan Falteisek, a DNR hydrogeological supervisor.
“This is foundational information,” Falteisek said. “Having this information allows us to make intelligent resource management decisions.”
In Benton County, for instance, a recently completed atlas is helping resolve conflicts between groundwater use for irrigation and the health of a groundwater-fed trout stream. In Pine County, information provided by a county geologic atlas helped the city of Askov determine where to locate a new wastewater lagoon (and where not to). In Olmsted County, the atlas helped the city of Rochester determine where to relocate a land fill that was contaminating local aquifers.
The atlas, which identifies where areas of pollution sensitivity may be and where the groundwater might most easily be contaminated, has many uses. It’s critical information for communities to have as they plot their future, said Jason Moeckel, who manages the inventory monitoring and analysis section of the DNR’s Ecological and Water Resources Division. That’s why decision makers have been increasing funding and accelerating the pace at which the atlases can be completed.
Originally paid for from the state’s general fund, the county geologic atlas program has been augmented by lottery proceeds, and more recently the program’s capacity has been enhanced with Legacy funds. The first atlas was published in 1982, covering Scott County. To date, atlases have been completed for 20 counties, and another 19 are underway. Eventually the entire state will be mapped, a process that at current rates could take another 15 years.
The Clean Water Fund receives 33 percent of the sales tax revenue from the Clean Water, Land and Legacy Amendment, approved by voters in November 2008. The Clean Water Fund’s purpose is to protect, enhance and restore water quality in lakes, rivers, streams and groundwater.
For more information on the Legacy Amendment, visit www.mndnr.gov/legacy.