Water quality issues in Flint began with the decision of city officials in 2014 to switch from buying treated drinking water from Detroit to treating Flint River water themselves using a city-owned treatment facility. This was considered a cost saving measure as the utility was insolvent.
The switch was considered a temporary money-saving “fix” to provide the city with drinking water until they were able to join a new regional system. A 10-month engineering effort was undertaken to equip the Flint plant to treat Flint River water before it was put into service.
Sources of drinking water supply, in general, include groundwater and surface waters, such as lakes and rivers. Among those water sources, rivers present the greatest treatment challenge. Relative to groundwater, surface waters contain more particles, microorganisms, organic matter, taste- and odor-causing compounds, and many types of trace contaminants. On average, surface water also tends to be more corrosive than groundwater.
Many utilities treating surface water are under pressure to look for less costly approaches to perform chemical treatment. Yet particle removal, a critical step used to treat surface waters like the Flint River, is a chemical-intensive operation. Iron and aluminum salts are typically coagulants added to water supplies to help aggregate particles so they can be effectively removed through settling and filtration.
Coagulant choice is an important design decision; so the choice of coagulant should not be based only on cost. Each coagulant has to be optimized to enhance removal of organic matter in the source water. If too little organic matter is removed, it will react with chlorine disinfectants in the water to form hazardous by-products (TTHMs etc.)
A switch from sulfate-based to chloride-based aluminum or iron coagulant salts also alters the chloride-to-sulfate ratio in water. It was this ratio that Dr. Marc Edwards, a faculty member at Virginia Tech, linked in 2010 to higher lead concentrations in vulnerable distribution systems with pipes made from lead. The Flint treatment plant relied on iron chloride coagulants, contributed to the corrosivity of the water.
Because of Flint’s method of treating Flint River water, it experienced problems with elevated trihalomethanes (TTHMs), a regulated class of disinfection by-products that are known carcinogens. A domino series of causes and effects were responsible for this problem. The Flint River is naturally high in corrosive chloride. Therefore, iron pipes in the water distribution system began corroding immediately after the initial switch from Detroit water. The iron that was released from the corroding pipes reacted with the residual chlorine that was added to kill microorganisms, making the chlorine unavailable to function as a disinfectant. Because chlorine, which reacted with the iron pipes, could not act as as disinfectant, bacteria levels spiked. When coliform bacteria were detected in distribution system water samples, water utility managers are mandate by law to increase the levels of chlorine. The higher levels of chlorine, while reducing coliform counts, led to the formation of more trihalomethanes.
The science of pipe corrosion in drinking water systems is complex and not completely understood. Corrosion control occurs when naturally forming minerals deposit on pipe walls to protect the iron pipe surfaces from exposure to oxidants in the water. Changes in water quality sometimes dissolve these mineral coatings, exposing the pipe to corrosion. In iron pipe systems, the released iron corrosion particles are visible, causing colored and turbid water. In older distribution systems, where lead service lines are often still in place, corrosion then releases lead and copper.
Because of the uncertainties around leaching, the majority of utilities treating surface water add phosphate corrosion inhibitors to control corrosion. They determine doses based on the water industry’s experience, rather than on rigorous scientific calculations. Empirical tests known as “loop tests” are commonly used to assess the effectiveness of corrosion control strategies applied to a given water distribution system. There is no record that such tests were performed in Flint.
A critical cost-saving decision made by Flint not to use corrosion inhibitors, especially when water previously supplied by Detroit did contain them, should have raised concerns. Evidence to demonstrate that inhibitors were unnecessary was a minimum common-sense requirement. Ignorance among utility personnel and water quality engineers of the importance of corrosion control management and its subtle linkage to decisions made elsewhere in the treatment plant unfortunately also played a role in this fiasco.
By not adding a corrosion inhibitor, Flint was going to save about $140 per day.
Replacement of Flint’s lead service lines, which is the only permanent solution to address its lead vulnerability, is estimated to cost up to $1.5 billion, according to the City of Flint.
One of the reason the water rates in Flint were high compared to the national average was that the water customers who paid their bills were essentially subsidizing the customers who didn’t pay their bills.
