Is Your Groundwater Corrosive?

Last week Laura Sanchez, editor of our sister publication Water Efficiency, wrote about the state of our nation’s municipal water supplies. A recent survey showed that nearly 2,000 water systems, spanning all 50 states, have shown excessive levels of lead in the past four years, and consumers in some of those areas have not been made aware of it. In the wake of the Flint, MI, situation, she points out, “consumers are mistrustful of the tap water their municipalities provide—and rightly so.”

The problem might be even worse than we realize. A new study from the US Geological Survey reveals that groundwater from certain wells in 25 states could be potentially corrosive. Why is this bad? Corrosivity is what caused the problem in Flint in the first place. The city began taking its drinking water from a new source, the Flint River, and that water contained enough chloride and other chemicals to leach the lead from lead pipes and from the lead solder in copper pipes. Although an oxidation layer builds up in pipes over time, preventing or reducing such leaching, the corrosive Flint River water—and the lack of anti-corrosion agents—stripped away that protective layer.

About half of us in the US rely on groundwater for our drinking water supply. If the groundwater source is corrosive, and if the pipes are old enough to contain lead or lead solder—as many of the pipes in pre-1980 buildings do—then we could see a situation similar to Flint’s. In fact, as Laura’s blog points out, in many areas we already are seeing it.

This USGS website allows you to track changes in the concentrations of pesticides, nutrients, metals, and organic contaminants in groundwater from wells in many locations throughout the country. The National Water-Quality Assessment Project did sampling at periods roughly 10 years apart.

Note that lead is not one of the components listed on the site. The groundwater itself is not a source of lead, but rather of potentially corrosive chemicals that can leach lead from the pipes. The USGS is careful to point out that this study is not directly related to Flint, and that Flint’s water supply came from surface water rather than groundwater. It also notes that corrosive water is not dangerous to drink. However, the agency does note, “Corrosive groundwater, if untreated, can dissolve lead and other metals from pipes and plumbing fixtures.”

The larger question, for those concerned with erosion control and other water-quality practices, is how those contaminants are reaching the groundwater. Some corrosivity may be caused by naturally occurring substances or types of geology—a type of bedrock found throughout the state of Pennsylvania, for example, tends to make the groundwater corrosive. If a water utility properly treats the water, it isn’t necessarily a problem. Other components tracked on the USGS site, though, such as nitrates and total dissolved solids, can enter groundwater as a result of runoff from agricultural and urban areas. Conservation practices and good erosion control methods can help limit the amounts.

Stephen Moulton II, chief of the USGS’s National Water-Quality Assessment Program, noted, “Fortunately, in most areas of the country and with appropriate safeguards, the majority of homeowners can get good quality drinking water from private wells. But this study is a good reminder that prudent, routine testing of the water, including its interaction with the water supply system, is an essential first step so homeowners and their families can confidently drink water from their faucets.”

The USGS report, “Assessing the Potential Corrosivity of U.S. Groundwater,” is available here.

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