Remedial Actions Triggered
Some Residents of Lake Wingra Watershed Affected
Madison, WI December 1–The Madison Water Utility announced yesterday that “Sodium levels in Well 14 are around 45 mg/L, higher than the recommended limit for people on salt-restricted diets. Chloride, the component of salt that causes the “salty” taste, has been measured at the well at 125 mg/L, or 50 percent of the EPA’s secondary maximum contaminant level (SMCL) for the chemical.”
While the health of most people is not directly impacted by high sodium and chloride levels, elevated salt levels are a concern for those on salt-restricted diets. High sodium and chloride levels do pose a threat to water quality and can contaminate the soil and adversely impact plants and soil organisms.
Contamination Levels Trigger Remediation Actions
The water quality policy of the Madison Water Utility requires that remediation actions be initiated when a contaminant, such as chloride, reaches 50% of its threshold. The water utility outlined a series of remediation steps that include an analysis of the situation to determine which below-ground areas are contributing the most sodium chloride, to re-building the well in order to draw from a deeper aquifer, to on-site desalination, or even abandoning the well altogether.
Dudgeon-Monroe and Vilas Neighborhoods in Lake Wingra Watershed Affected
Well # 14, at 5130 University Avenue, is a major source of water for the near west side of Madison and supplies the following neighborhoods across at least a couple of watersheds: Spring Harbor, Glen Oak Hills, Hill Farms, Sunset Village, Regent, Dudgeon Monroe and Vilas. In addition, Well 14 serves the Village of Shorewood Hills and parts of the University of Wisconsin campus. Although Well #14 is outside of the Lake Wingra Watershed, it supplies two large neighborhoods in the watershed: Dudgeon Monroe and Vilas neighborhoods. Click here to see a map of the location of well #14 and its “wellhead protection zone”.
Source of the salt
The Madison Water Utility points to de-icing salt, as the source of the contamination. The utility cites road salt as a major contributor: “Every winter, about 140 tons of road salt are dumped on the two-mile stretch of University Ave. between Segoe Rd. and Allen Boulevard.” The utility also points to salt applied to sidewalks, parking lots, and driveways of both commercial and residential properties. Even salt from water softeners contributes to the problem.
For a history of road salt use in Madison and chloride concentrations in its lakes, see this earlier blog post.
Other Wells Have Not Escaped a Salt Overdose
According to the Madison Water Utility, “Well #11 on Dempsey Rd., Well #6 on University Ave., and Well #16 on Mineral Point Rd. all show increasing levels of sodium and chloride, albeit at much lower levels than Well 14” (click here for chart). The water utility concludes “It’s possible that if nothing is done to decrease road salt use across our area, we will be looking at costly chloride mitigation efforts at some of those of wells and others in the coming decades.”
Chloride Contamination Concerns Go Beyond Water
As we reported in this blog over three years ago, chloride concentrations are a year-round concern in Madison and the surrounding area. In fact, each spring and summer rain, flushes accumulated salt from the soil and into our freshwater supplies. As we reported then:
“The road salt (usually sodium chloride) applied on our streets, sidewalks, and driveways to make winter driving and walking easier, does not just disappear once the storm is over. It mixes with melt water or rainfall and washes down the storm drain where it ends up in Madison lakes, the groundwater, and eventually our drinking water wells.”
Long-term Solutions Sought
“Rising levels of chloride in our groundwater and lakes should be a cause of concern to all of us,” says Madison Water Utility general manager Tom Heikkinen. “As a region, we are on an unsustainable path with respect to wintertime salt use and we need to figure out how to solve this problem now for the sake of future generations.”
We will report next time on some of these efforts to go on a reduced road-salt diet.