Groundwater is threatened by both overuse and contamination from pollutants. Polluted groundwater often is unsuitable for drinking, and it’s usually very expensive to remove pollutants from drinking water. In areas with groundwater contamination, residents and businesses may spend more to dig deeper water-supply wells that tap uncontaminated aquifers.
Agricultural activities, particularly the use of nitrogen fertilizers on crops, can affect the nitrate (a form of nitrogen) concentrations in groundwater. Nitrates from cropland runoff can seep into groundwater, particularly into shallow wells drilled in sand-and-gravel soils.
The salt applied to pavement during our icy winters contains chloride, a water pollutant. Some precipitation percolates into the soil and recharges the groundwater, carrying chloride with it. It takes only one teaspoon of road salt to permanently pollute five gallons of water. Once in the water, there is no way to remove the chloride, and it can cause drinking water to taste salty. Chloride is toxic to some forms of aquatic life, including trout, frogs, and some native aquatic plants. Some groundwater is discharged into streams, lakes, and wetlands, and if it’s contaminated with chloride, it can adversely affect plants and animals.
Land that is contaminated by hazardous substances and industrial pollutants — such as Superfund sites — may affect groundwater nearby. If pollutants get into the groundwater, they can be released as vapors into soils and even buildings in the surrounding area.
In general, water is being drawn out the state’s aquifers faster than it is being replenished. If this overuse continues, groundwater may not be available as needed in the future. And groundwater availability is not only an issue for people; discharge of groundwater to surface waters allows streams to flow beyond rain and snowmelt periods and sustains lake levels during dry spells. The sustained lakes and streams in turn support a variety of plants and animals.
The increasing demand for groundwater
The primary source of clean water in the Twin Cities metro area has shifted from surface water in the 1940s to groundwater. Over time, the level of the region’s most plentiful and most-used aquifer, the Prairie du Chien, has steadily declined in selected regions, as the metropolitan area has become more populated.