The Town of Normal is trying to figure out a way to use less chlorine to treat its drinking water.
The town's well water has some ammonia in it. By itself, the ammonia is not a problem for people. It’s only when it interacts with chlorine, used to treat the water, that it becomes an issue.
Ammonia naturally occurs in groundwater, generally a byproduct of agriculture. Among the town’s numerous wells are four near Stanford and Danvers in farming areas. That is where the ammonia levels are highest, said John Burkhardt, the town water department director.
“Town wells generally don't have a number that's really high,” said Burkhardt. “This is a common occurrence for anyone who pumps water out of the Mahomet Aquifer.”
Burkhardt said the town tries to maintain .7-.8 parts per million (ppm) of ammonia that bonds with chlorine in the water.
“Once you get above one part per million residual level in the water, it can become a problem. It will consume excess chlorine that we have. So, we have to feed more chlorine, to keep chlorine levels up or just have to flush more often,” said Burkhardt.
And Burkhardt said if there isn't enough chlorine left, there’s a potential safety issue.
"It could cause bacteria to become present, which could get people sick," he said.
The town adds extra chlorine to compensate and then flushes mains when tests show chlorine levels fall enough to get close to the Environmental Protection Agency minimum standard of 1 ppm. The town tries to keep a chlorine residual of 3-4 ppm.
There are a couple ways to deal with the ammonia other than with more chlorine. One is really expensive. The town is going to test the other method for the better part of a year. Burkhardt said that removal mechanism is biological.
"Essentially, we'll grow what that industry calls 'bugs,' bacteria in the water that consume the ammonia. And then after the excess ammonia is removed then we can treat it with chlorine to kill those bugs," said Burkhardt.
Costs and benefits
If the ammonia-eating bacteria works at scale, the town could save some money by reducing the chlorine it uses and labor expense.
The other method — the one that costs big bucks — is something called reverse osmosis, basically shooting water at high pressure through really tiny filters.
Another factor is looming regulation of the allowable amount of so-called forever chemicals in water supplies. They're known as PFAS.
"We have detectable levels of PFAS in our water, the EPA has found out," said Burkhardt.
He said reverse osmosis would require the town to build a whole new water treatment plant.
“Our current facility really can't be retrofitted. That's not what it was originally built for. And there's not room at our site. We haven't even started really looking into that,” said Burkhardt.
In a couple years the town staff and council will have to have a dialog about which method to use long term, he said.
"Reverse osmosis can take care of everything, all current regulations and future regulations. So, do we go that route, or just deal with the ammonia now?" said Burkhardt.
The town averages about four million gallons of water use per day. He said generally smaller communities use that method, or some larger ones than Normal, but not a lot of comparably sized municipalities use it.
“You can remove some chemical costs. Electricity costs are generally higher. It takes a lot of energy to push water through those really tight, tight filters. But we have not done any research on the cost side of reverse osmosis at this time,” said Burkhardt.
He said the town can take the time to figure it out because the amount of PFAS in town water is lower than the levels the federal government is talking about regulating. The town may have all the information needed for a policy discussion in 2025 or 2026.
