Flooding could contaminate more Wisconsin groundwater
Wisconsin scientists helped pioneer the study of bacteria and viruses in groundwater. Their research has discovered that microorganisms can occur deeper underground and live longer than previously assumed. They’ve also analyzed whether more people get sick when utilities don't disinfect their drinking water — and they do, especially children.
A Florida State University professor looked to Wisconsin for another first in this line of inquiry — investigating how climate change might make people more vulnerable to groundwater-borne pathogens in the decades ahead.
In an article published in the January 2017 issue of Hydrogeology Journal, FSU geography professor Christopher Uejio and his collaborators reported how they used computer modeling to project how higher levels of precipitation and non-disinfection of groundwater might affect gastrointestinal illness in children between the years 2046 and 2065 in five communities in Rusk County in northern Wisconsin: Ladysmith, Bruce, Tony, Glen Flora and Hawkins. In the worst case, Uejio found the rate of GI illnesses among children in these areas could grow by a little over four percent — a marginal increase, but an indication that an existing public health problem will persist over the long run where communities don't disinfect their water.
"In my opinion, really the big story is that we have an existing health disparity and we have the tools and knowledge to address it, and we don't have to wait for something to be invented," Uejio said. "Climate change is really a secondary or even a tertiary effect here."
Several dozen municipal water utilities around Wisconsin serving nearly 65,000 people do not disinfect their drinking water — nearly all rely on groundwater. The U.S. Environmental Protection Agency requires that utilities drawing water from lakes or rivers disinfect their water, but there are no such federal or state requirements for groundwater. Most of the public drinking water utilities in the state are small, serving only a few thousand, a few hundred or even a few score people.
In Uejio's study, the largest utility included, Ladysmith's, serves a little over 3,600 people, while the smallest, Glen Flora's, serves just over 90. With a small number of ratepayers, a utility doesn't have much money to upgrade its treatment processes. Some don't even have a full-time water manager. Modest budgets, public aversion to treatment chemicals, and a lack of regulation all help explain why some utilities don't use disinfection processes to kill pathogens.
To compound the problem, rural areas around the state, including Rusk County, are in the midst of a long-term population decline. This change will decrease the number of households paying water bills in rural communities. However, according to Uejio's projections, even with a shrinking population, the rate of water-borne illnesses won't decrease.
Climate change plays a role in drinking-water safety because climatologists project rainfall levels to gradually increase in Wisconsin as the atmosphere warms, as well as a greater frequency of extreme rain events.
Uejio studied several scenarios based on varying projections of just how much rainfall in the area will increase over the next few decades. These projections factored in different levels of fossil-fuel consumption, greenhouse gas emissions and economic growth to anticipate how human activity might make conditions conducive to more precipitation in the future.
"There's fair agreement that rainfall and particularly heavy rainfall events are going to increase across the Midwest and Northeast," he said. "We needed to look at such a long period of time to essentially smooth out some of the natural variability in weather patterns."
When there's more rain, it flushes more pathogens into groundwater, especially from livestock manure as well as leaky septic tanks and sewer pipes.
In fact, Wisconsin officials warned residents about how flooding can threaten groundwater supplies after heavy rains struck northwestern Wisconsin in July 2016.
Plentiful and vulnerable groundwater
Groundwater is among Wisconsin's most abundant resources, but it's more vulnerable to contamination from the surface than elsewhere. Much of the state, including parts of northeast and northwest Wisconsin, have a geology called karst, in which limestone or dolomite bedrock is shot through with cracks and fissures. These fractures are great for groundwater levels, because they allow a lot of rainwater and snowmelt inflow that recharges the supply. But the downside is that pollutants can get into groundwater with similar ease.
In places like Kewaunee County, karst geology provides conditions for a concentration of large dairy farms to contaminate water. As more precipitation seeps into the ground, it also overwhelms natural filtration that soil and sand provide, a process emulated in household water filters and municipal drinking-water treatment.
"It's of the right chemical constituency that actually de-sorbs pathogens from soil," said Mark Borchardt, a Wisconsin-based microbiologist with the U.S. Department of Agriculture, about rainwater. He has collaborated with Uejio and led some of the key research the new report builds on.
"Bugs that are hung up and stuck [in the soil] would remain stuck, and once precipitation changes, they are released," Borchardt added.
Accelerating that process could have significant public health consequences. Uejio combined previous data on waterborne illnesses with several different models projecting how climate change might increase precipitation levels in northern Wisconsin. He found that if the studied utilities don't disinfect the groundwater they source, children who drink it are likely to have higher incidences of gastrointestinal illnesses. He also examined models in which utilities add disinfection at either modest or rapid rates. The study concluded that disinfection treatment could reduce the amount of gastrointestinal illness attributed to more precipitation by as much as 82 percent.
Uejio’s study built on previous groundbreaking research, including work to which he contributed, that looked at pathogens in drinking water and their effect on public health. Most of the illnesses people get from tainted drinking water are nasty but non-life-threatening bugs like norovirus. But they can be dangerous to specific groups of people, Borchardt noted.
"For young children, for elderly people, for people that have their immune systems compromised or suppressed for various reason,cancer treatment of whatever, acute GI illness is very very serious," he said.
Even if an individual patient suffers no more than a day or two of diarrhea, vomiting and general misery, a greater incidence of such illness can have a broader economic impact, creating costs in the form of emergency room visits and lost work days. And even a small increase in illnesses in children could have a significant public health impact.
"A 3 percent increase … for most people it is more of an inconvenience, but for children that might already be sick or have pre-existing conditions, they're some of the most vulnerable and at increased risk," Uejio said.
A warming climate could also encourage more bacterial growth, including among those that occur in soil without human help, Borchardt said. Still, he sees increased precipitation as the greatest connection between climate change and waterborne illnesses.
"The projections for Wisconsin are that we're a wetter state, but how much wetter is not entirely known," he said.
Pushing for a cleaner future
Borchardt has encountered some resistance to disinfection in his own work in small Wisconsin communities, and also has found that many people erroneously believe groundwater is inherently more pure than surface water. But he thinks these attitudes are slowly changing as the body of research and broader understanding about pathogens in groundwater grows.
"I think Wisconsinites are really getting a much better sense and appreciation of the quality of groundwater and how it can be vulnerable," Borchardt said.
Uejio acknowledges challenges small communities face in improving their drinking water quality, and hopes research like his will help people think differently about preparedness for climate change.
"Looking at health problems gives climate change a human face," he said. "It's not just an abstract phenom that might hurt us further down the line, but actually there are some existing structural inequalities that are harming human health now, and if we can address those now, we'll actually be more able to cope with any future climate changes."