As cars whiz by on University Avenue, Pete Chase stands inside a small white brick building and pulls a metal tube just a bit longer than he is tall from a 715-foot-deep borehole beneath Madison Water Utility Well 14.
The $3,500 tube has captured a liter of water from below the well, where the utility has found elevated amounts of chloride and sodium, the components of road salt. The chemicals don’t make the water unsafe but the salty taste could make it unpleasant to drink if nothing changes in the next 15 years or so.
Chase, a geotechnician with UW-Extension’s Wisconsin Geological and Natural History Survey, last week used the tool to draw water samples from various depths to help the utility learn what areas below ground contribute the most chloride and sodium to water taken from the well, which is located near the intersection of University Avenue and Whitney Way.
Next, Joe Grande, who leads the utility’s water quality department, and others will analyze samples and other data from probes into the borehole with the hop e of finding a solution to protect the well, which pumps 750 million gallons into Madison’s water supply annually.
The study will provide insight into what part of the sandstone aquifer contributes the greatest amount of water to the well, and the salt levels in the layers of the aquifer, utility general manager Tom Heikkinen said. That information will guide the decision about whether to modify the well’s borehole.
Options, all costly and challenging, include rebuilding part of the well to draw water from deeper in the aquifer, treating the water at the well, and even abandoning the well. Drilled in 1960, Well 14 has a pumping capacity of 2,400 gallons a minute and serves the University Avenue corridor roughly from Whitney Way to Middleton.
“We’re getting a head start,” Grande said. “In the long term, we see this as a problem that’s going to require a fix.”
gets to water’
Chloride and sodium levels have been increasing at Well 14 for many years and have reached a threshold where local policies require investigation, Grande said.
The rising levels are caused by road salt, an inexpensive way to address icy streets and protect municipal governments against liability for crashes. A report from Public Health Madison Dane County said nearly 30,000 tons of salt was dumped on Madison and Dane County roads in the winter of 2014-15, not including what’s spread on county highways, parking lots, sidewalks and driveways.
“The salt eventually gets to water,” Grande said. “None of it goes away.”
Road salt is an increasing problem at several of the utility’s 22 wells, but the biggest challenge is at Well 14, where chloride levels have more than doubled in the last 15 years with no sign of subsiding.
In 2000, the chloride level at Well 14 measured 58 milligrams per liter, and by last fall it had risen to 135 milligrams, more than half way to the 250-milligram level at which the Environmental Protection Agency says contamination significantly affects taste and appearance. In 2015, the sodium level measured 42 milligrams per liter, more than double an EPA guideline that recommends drinking water not exceed 20 milligrams to protect higher-risk populations such as people with high blood pressure.
“There’s no one telling us to do this. It’s our own internal policy,” utility spokeswoman Amy Barrilleaux said of the testing. If nothing’s done, in 15 years or so, “people will be rejecting the water because it won’t taste very good.”
The utility is shutting the well down for roughly a month to do the testing and also some needed maintenance, creating a slight drop in pressure for users in the area.
The Wisconsin Geological and Natural History Survey, which helps municipalities and private well owners when they have problems, brings unique and expensive tools to help measure everything from temperature to conductivity.
One day last week, Chase repeatedly sent the 6½-foot metal tube down the borehole to collect samples at multiple depths, each time a small winch lowering and raising the instrument with a nearby laptop recording the depth and other data. For the last few feet, Chase removed the tube by hand as if pulling a northern pike from a hole in the ice.
One key is determining where the water is drawn from below the end of a metal pipe that extends down the first 117 feet of the 715-foot borehole.
“My hunch is, a lot of water pumped from the well is coming from fairly shallow, between 117 feet and 250 feet,” Chase said, adding that the chloride is most likely to be occurring at shallow levels.
If verified by data analysis, that means the utility may be able to use a liner to extend the borehole’s seal and draw deeper water likely to have lower chloride and sodium levels.
But the utility has only begun to analyze the data and samples, and it could be months or even years before the utility develops a long-range plan, Grande said.