Though the Madison Water Utility mostly describes the possible carcinogen chromium-6 as "naturally occurring," a study of wellhead protection reports and a close look at neighborhoods around wells that test positive for the pollutant turn up potential man-made sources for the contaminant.
Chromium-6 has been detected in all but three of the 16 public drinking water wells currently in use in Madison. The wells were tested after a national environmental group found the unregulated metal in the wells of 31 cities across the country. The highest level in Madison was found in Well No. 14 near Spring Harbor on the city's West Side.
According to the Environmental Protection Agency, chromium occurs naturally in the Earth's crust. But the agency also warns that chromium-6 can come from a number of other sources, especially industries in which the metal is used in such processes as metal plating, leather tanning and wood preservation. Other studies have shown another major source of chromium-6 is coal ash from coal-burning power plants.
Several such potential sources for the chromium-6 in Madison's wells turn up with a look at the roster of businesses that are operating or have operated in neighborhoods around the wells — information contained in the wellhead protection plans the utility is required to write for each well.
In the vicinity of Well No. 14, for example, the list of businesses that have operated over the years includes lumber yards, gas stations, auto body shops, electrical stores and upholsterers. Some, but not all, of these businesses are listed in the utility's wellhead protection plan, something that bothers Michael Kienitz, a longtime resident of the neighborhood and an activist on water issues.
"Nobody has really studied the neighborhood," said Kienitz. "It seems to me I know more about that parcel of land than the water utility. That's a travesty."
But Joseph Grande, water quality manager for the utility, said while the most recent round of testing showed chromium-6 is widespread in city wells, there appears to be little correlation between wells with the contaminant and neighborhoods with histories of industrial contamination.
"The evidence we have at this point is that the source is more the rock itself. Is that definitive? No. But that's what the data is telling us," Grande said.
Tom Heikkinen, general manager of the water utility, said he hopes to work with the Wisconsin Geological and Natural History Survey to test the rock around affected wells to determine its chromium content.
A more thorough investigation of potential contaminant sources is among the ideas now being discussed by the Madison Water Board in a debate over whether to take a tougher approach to dealing with some pollutants.
Particularly disturbing to Kienitz is that several businesses that have operated in the vicinity of Well No. 14 — especially the auto body shops and gas stations — used industrial degreasers. He said a 2003 study by the Interstate Technology and Regulatory Council found such degreasers, especially when used in metal shops, can be a source of chromium-6.
Other potential chromium-6 sources also show up near other affected wells. The wellhead protection plan for Well No. 9 shows a metal recycling company called Midwest Steel operated near the well. The company had a history of pollution problems and chromium was among the contaminants found by the state Department of Natural Resources.
Another widespread source of chromium-6 in Madison could be the tons of coal ash from coal-burning power plants that were disposed of in landfills. Records kept by the city show several landfills received coal ash, according to Wayne Rippl, a city engineer who maintains a map showing the location and contents of landfills.
Rippl said coal ash also was used extensively to fill marshes, especially in the Isthmus area. He said city workers continually come across layers of coal ash when they dig for street and other construction projects.