The science of lead pipe corrosion
The complexities of the water crisis in Flint, MI run deeper than the infrastructure that carried the tainted water to the city’s residents. Clouded by years of political discourse, the events taking place in Flint have been a culmination of many issues, but overall boil down to the degradation of the city’s infrastructure.
There’s one constant at the core of these problems that has been part of the cause, but also has the potential to provide a solution: corrosion science and technology.
Root issues of the water crisis
When the city’s water source changed from the treated water of the Detroit Water and Sewerage System, which pulls from Lake Huron and the Detroit River, to the Flint River in April of 2014, high levels of lead contaminants began coursing through Flint’s water.
While there are many pieces to this puzzle, issues with the water distribution system are at the heart of it all.
“There is an inherent potential liability associated with the design of many water distribution systems in the U.S., certainly in older communities, where water mains are made from cast iron and service lines that come off the water mains are made from lead,” said Gerald Frankel, expert in corrosion science and professor of materials science and engineering at Ohio State University. “There is the overall issue about the degradation of our infrastructure. We have old distribution systems that have finite life and they’re all coming to an end.”
Lead and the water infrastructure
The design of Flint’s water distribution systems was, of course, a main contributor in the crisis that soon followed when the city changed its water source. But lead pipes have a long history in U.S. infrastructure. While congress banned using lead water pipes in new construction 30 years ago, upwards of 10 million older pipes still remain as integral parts of distribution systems.
“You might think lead would be an odd material to use for water distribution,” Frankel, ECS member of 26 years, said. “The truth is, when properly managed, these water systems are not necessarily a concern.”
Typically, lead isn’t highly reactive. Electrochemically, it has an extremely low exchange current density for the hydrogen evolution reaction. This results in the corrosion rate of lead being on the low side.
Lead, however, will begin to corrode at a high rate when it is not managed properly, particularly when it is galvanically coupled to a more-noble metal that supports the cathodic reaction at a high rate. In order to safely transport water through lead pipes, they should be electrically isolated and a protective film on the interior surface of the pipe must be developed. Additionally, the water should be treated with the proper chemicals to protect the pipes.
Flint missed the mark on both the treatment of the water and the preservation of the pipes.
“When the water source changed in Flint, additives should have been included in the water to maintain the integrity of both the cast iron water mains and the lead service lines,” Frankel, technical editor of the Journal of The Electrochemical Society, said. “The reporting indicates that to save money, those corrosion inhibitors were not added.”
These budget cuts led to a domino effect for Flint’s water distribution. From this, the protective corrosion films on the lead pipes were disturbed by the more aggressive water, which had unusually low pH levels and high chloride contents. The consumption of chlorine by the high corrosion rate of the iron mains might have allowed for the growth of Legionella bacteria.
“If you were to start again and design a water distribution system, you wouldn’t use lead,” Frankel said. “The lead is a cause, but the root cause is how the water treatment has been detrimental.”
Revamping the water system
In the past, the EPA made efforts to eliminate lead from the U.S. water infrastructure. The agency appraised the cost to replace lead at $5,000 per pipe, which would total an amount of upwards of $50 billion. However, the EPA justified the cost stating that it would still be a fraction of the $384 billion needed by 2030 for maintenance to just keep drinking water safe in the current infrastructure.
“[The EPA] authorized lead service line replacements,” Frankel said. “The problem is that the water utilities are only responsible for the portion of the line to the boundary of the property.”
This put a burden of responsibility back on the property owners. In order to fully replace the lines, the property owners needed to pay for the pipe replacement from the property line to the house. Many, however, did not due to the cost.
The partial replacement of lead, with new copper pipes connected to the old lead ones, did more harm than good.
“It turns out the galvanic coupling of copper and lead results in drastic increases in the corrosion of lead, and thereby, the contamination of the drinking water by lead,” Frankel said. Partial lead service line replacement has been a problem in many communities, but Flint has agreed to pay for full replacement of lead pipes all the way to the houses.
Future of U.S. water infrastructure
The question now is: can a tragedy such as the Flint water crisis happen in cities all across the country?
“There is a potential for more of these Flint type situations to arise,” Frankel said. “Whether the politicians are interested in funding the required maintenance and engineering is another question.”
According to a March 2016 poll by the Associated Press, only about half of Americans say they are very confident in the safety of the water flowing from their tap. That trust level goes even lower when analyzing minorities and those at lower income levels, reflective of the demographics in Flint.
For Frankel, the answer inevitably lies in the replacement of the infrastructure.
“It’s going to be expensive, but we need to make sure that we are providing safe water,” Frankel said. “We need to be confident in the quality of the water we’re drinking.”
About Gerald Frankel
Gerald Frankel is the current professor DNV designated chair of materials science and engineering at The Ohio State University and director of the Fontana Corrosion Center. He has received degrees from Brown University and MIT, followed by a post-doc in Switzerland and a position at the IBM Thomas J. Watson Research Center. Throughout his career, he has been involved in novel research in corrosion and corrosion protection, with recent emphasis in the proper, safe disposal of nuclear waste and lightweighting in cars to advance the fuel economy.
He is the past chairman of the Corrosion Division of ECS and is currently the technical editor of the Journal of The Electrochemical Society in the area of corrosion science. Frankel is a Fellow of ECS and won the Society’s Corrosion Division H. H. Uhlig Award in 2010.