Nick Krieger (@nckrieger):
High levels of lead are showing up in Flint's municipal water. But what, exactly, is causing this problem? One of the possible causes might surprise you.
Although the city of Flint formerly purchased its water supply from Detroit, it now draws its municipal water from the Flint River. The lead isn't present in the Flint River, itself. Instead, the lead leaches into the Flint River water as it passes through old water-service lines and pipes.
Any Michigan community that draws its municipal water from a river or inland source rather than from one of the Great Lakes will likely face this problem to some extent. River and inland-source water contains higher concentrations of chloride ions than does water pumped directly from one of the Great Lakes. Why? Perhaps surprisingly, one of the primary reasons is the overuse of salt to deice our roads in the winter. As salt molecules dissolve in water, the negative chloride ions are separated from the positive metal ions. These chloride ions become concentrated in runoff, which makes its way into our streams, rivers, and other waterways.
The negative chloride ions are corrosive, so when the high-chloride water is pumped through lead pipes (or iron and copper pipes joined together with lead solder), lead leaches into the water. It's as simple as that.
Why isn't this happening to the same degree in other places, like Detroit for example? Surely Detroit has old lead pipes, too. Right? Absolutely. But Detroit draws its municipal water directly from the Great Lakes, and water pumped from the big lakes simply isn't as corrosive.
Because the Flint River (with its concentration of chloride ions) flows into the Saginaw River, which in turn empties into Saginaw Bay and Lake Huron, it naturally follows that there are chloride ions in Lake Huron as well. However, the Great Lakes are huge, containing quadrillions of gallons of freshwater. With so much water in the big lakes, the existing chloride ions are greatly diluted and much less concentrated than they are in the water of smaller, inland streams like the Flint River. Sometimes dilution really is a solution to pollution.
Flint and Genesee County will eventually purchase their municipal water from the embryonic Karegnondi Water Authority, which will draw its water directly from Lake Huron (by the way, the Karegnondi Water Authority has many of its own, unrelated problems). This will ultimately help with the lead problem. But Michigan must look at safer alternatives to corrosive road salt. The salt isn't only damaging our cars; it's also making our water more corrosive.
Professor Marc Edwards of Virginia Tech, a leading researcher on municipal drinking water, has confirmed that "there is nine times more chloride, which is the key ingredient in the corrosive water. . . in the Flint River than in Lake Huron water." Dr. Edwards suspects that road salt is at least partially to blame for this. Similarly, the Unites States Geological Survey has determined that concentrations of chloride ions have increased dramatically in urban rivers and streams in recent years. The USGS study found that "de-icing activity was the primary source of environmental chloride in urban areas of the northern US. . . ." As Dr. Edwards notes, these high concentrations of chloride ions are simply not present in Lake Huron water.