Post by Jenny Seifert with significant input from Eric Booth
While a season has set since this summer’s decision to allow the City of Waukesha to use Lake Michigan water, the Great Lakes region may bob from its ripple effects for seasons more. A point it makes clear is that, despite its water richness, Wisconsin grapples with localized challenges to water sustainability due to municipal groundwater pumping, and solutions will require a long-term lens.
Many Wisconsin municipalities get their water from the ground, and the demands people put on these supplies, if too much, can create public health risks and negatively impact aquatic ecosystems.
Madison is among the state’s groundwater-drinking cities, and it is not without its own challenges. Even though it lies outside the Great Lakes Basin, hydroecological parallels between the state capital and Waukesha—and many other dairy state municipalities, for that matter—highlight implications that transcend basin boundaries.
The first parallel lies in the geochemical makeup of the ground beneath each city.
Deep in Waukesha’s subterranean layers, there are rocks laced with radium, a naturally occurring, but carcinogenic element. Growing awareness of radium’s presence in the water supply created the thorny public health risk that drove the city to seek another source.
Madison has its own naturally occurring heavy metals to deal with: manganese, chromium and iron.
The city is not currently facing a public health threat, however. Regular testing shows the concentrations of chromium are not high enough to pose a problem, and Madison Water Utility filters the manganese and iron out of our drinking water.
Moreover, Madison can do things to offset potential risks down the road.
One such risk is the potential for unnatural mixing of “old” and “new” groundwater.
When people first built wells in Wisconsin in the late 1800s, they tapped into water that had seeped into the ground thousands of years ago. That old water lies deep in the aquifer and contains less oxygen than the new water closer to the ground’s surface.
As Madison works to quench the thirst of a growing population, that younger, higher-oxygen groundwater could mix with its older counterpart. This intermingling of aquifer generations could change underground geochemical conditions, causing some of those unfavorable elements to leach into the water supply. New research at UW-Madison is looking into exactly how this risk could play out.
Adding to the importance of precaution is the risk of contamination by human-caused pollutants, like road salt and industrial waste, which could also enter the geochemical mix.
To be clear, Madison hasn’t reached such a geochemical threshold. Citywide conservation efforts, like more efficient toilets, mean it is pumping less water despite its population growth, and there is evidence the city’s aquifer is rebounding as a result of these efforts.
Continued efforts to avoid crossing that threshold will be crucial for keeping our drinking water clean and safe.
Groundwater pumping presents potential impacts affecting not just people, however, bringing us to the second parallel between Madison and Waukesha.
Extracting groundwater for people takes from aquatic ecosystems, such as lakes, streams, rivers, wetlands and springs. As a result, over time surface water levels drop, which can disrupt important ecological functions.
In Madison today, there is enough groundwater pumping in the city’s denser areas, such as the west side and the isthmus, that Lake Mendota’s water is being sucked into the aquifer, reversing the natural flow of water from the aquifer to the lake. And several of the natural springs around Lake Wingra have even dried up.
Similarly, Waukesha’s pumping has depleted water from the city’s surrounding springs and wetlands. Now that it is set to end its use of groundwater, however, there may be a unique opportunity to witness an eventual recovery of the flow to some of its wetlands.
Perhaps the bottom line of highlighting these parallels is there are long-term risks associated with our use of groundwater resources, and avoiding these risks is largely within our control. Continued prudence with this invaluable natural benefit at both the citywide and household levels will help us ensure its sustainability for generations to come.
*The Water Sustainability and Climate project takes no position on the Waukesha water diversion. This post is intended only to highlight some of the science surrounding it.