ANN ARBOR, MI - As a toxic plume continues to spread through the area's groundwater, Ann Arbor officials are considering the possibility that the city's water plant might need to be equipped to treat for 1,4-dioxane someday.

Dioxane is the chemical that has been slowly spreading toward the Huron River from the former Gelman Sciences property on Wagner Road for decades. It isn't in the city's drinking water at this time, but it remains a long-term threat.

At a recent City Council work session, city officials discussed the future possibility of adding new technology at the city's water treatment plant on Sunset Road to be able to remove dioxane before drinking water is delivered to city customers, if that should become necessary in the years ahead.

It's estimated it would cost tens of millions of dollars to do that, according to city reports obtained by The Ann Arbor News.

While dioxane never has been detected in Barton Pond -- an impoundment on the Huron River where the city gets most of its drinking water -- city officials are unable to rule out the possibility of that happening in the future.

There still are high levels of dioxane in the area's groundwater and the plume continues to spread. The plume already forced the city to shut down a municipal supply well on the city's west side several years ago.

Dioxane is classified by the U.S. Environmental Protection Agency as likely to be carcinogenic to humans by all routes of exposure. It also can cause kidney and liver damage, and respiratory problems.

Just a few parts per billion in drinking water, with long-term exposure, poses a 1 in 100,000 cancer risk, according to the EPA.

City officials believe a $90 million upgrade planned for the city's water plant -- an upgrade aimed at replacing aging facilities and not directly related to dioxane concerns -- would have the added benefit of freeing up the west portion of the property for future water treatment needs, including potentially new facilities that could treat for contaminants such as 1,4-dioxane.

Council Member Sumi Kailasapathy, D-1st Ward, raised the question, asking what if in 10 to 15 years the plume has reached the city's drinking water sources? Would the plant have to be abandoned? Or could the city treat for it?

"That's a big issue," Kailasapathy said.

City officials responded by acknowledging it could be possible to add new technology to remove dioxane.

"We're continuing obviously on a regular basis to monitor the progress of the plume and what potential impacts could be from a treatment perspective," said Brian Steglitz, the city's water treatment manager.

"So, as we manage that issue, I think we will make sure that we position ourselves to be able to deal with it, whether it's treatment onsite or whether it's being able to intercept the plume before it reached the river."

He added, "I mean, there are a lot of tools we would be able to use in our toolbox before I think we got to a point where we would be even considering remotely about not being able to utilize our water treatment plant."

Craig Hupy, the city's public services administrator, said if the city goes through with the $90 million project that's proposed now, "That gives us the space that, if there is an additional need for a different treatment technique, we have the space to construct and operate that."

He said the whole west side of the site would be freed up for potential addition of new technology.

"We would have a place to put the technology that could treat and remove the contaminants or any other contaminant that comes up in the future that we haven't even thought of," Hupy said.

Aside from concerns about dioxane, Steglitz said it's expected increased drinking water regulations will be coming in the future.

"As we're learning more about the ability to detect contaminants that are down into the parts per trillion -- so nanograms-per-liter level, as we're seeing with some of the emerging pathogens and things that we're facing -- it's very likely in the next decade to two decades we are going to see increased regulation on things that we don't even know what they are currently," he said.

"And we will probably need additional processes to address that. And with the need for additional processes, we're going to need additional footprint."

Because the footprint of the Sunset Road property is so limited, Steglitz said, the city is struggling right now with where new facilities could go. But the $90 million plant upgrade would make room for some of those future needs.

In response to Kailasapathy's questions about whether it makes sense to upgrade the plant, City Administrator Howard Lazarus said, "Even if dioxane were to find its way into the water, we still have to treat what's in the water now."

City officials did not discuss specific treatment techniques or costs for removing dioxane at the recent meeting, but that has been explored in the past.

In 2006, the city completed a study that found it would be feasible to treat dioxane if it appeared in the city's source water, though it would be expensive.

One of the technical reports from consultant CH2M Hill in 2006 stated that a review of treatment technologies for removal of dioxane indicated a combination of ultraviolet light and hydrogen peroxide might be effective.

Potential removal of dioxane at the water plant with existing treatment processes also was reviewed and found to be ineffective, with current treatment processes able to remove only about 40 to 70 percent of the dioxane.

"To achieve a high degree of removal (90 to 99 percent), additional processes, such as UV light and hydrogen peroxide, would be needed," the report stated.

"Adding these processes to the water treatment plant would be costly (order of magnitude construction cost estimates around $30 million)."

In addition to potentially up to $30 million in construction costs for a UV/hydrogen peroxide treatment system for dioxane removal, the report cited annual operating and maintenance costs of about $1.5 million to $2 million.

The study concluded it might be more cost effective to obtain drinking water sources that do not require dioxane treatment and to prevent dioxane from entering drinking water sources, as opposed to treating for its removal. However, another consultant report produced last year suggested it could cost $250-$300 million to connect to Detroit's water system.

Steglitz said in June the city had not completed any additional investigations into the options for dioxane treatment and associated cost since it was studied in 2006. He said the city believes the contents of the 2006 study remain valid.

A report prepared for the city by a consultant in August 2015 does briefly discuss treatment options for dioxane and other contaminants.

The report from Black and Veatch noted the Safe Drinking Water Act requires the EPA to publish a Contaminant Candidate List every five years, identifying contaminants that are currently not subject to regulations but are known or anticipated to occur in public water systems.

The report stated there were 96 trace organic contaminants under review for possible future regulation in drinking water.

"Ozone oxidation followed by BAC filtration is an effective multi-barrier control strategy for a wide range of trace organic contaminants. However, there are a number of chemically diverse organic compounds that are not effectively removed from drinking water by these treatment technologies," the report stated.

"The cyclic ether compound 1,4-dioxane is of particular concern because of known contamination in a groundwater aquifer adjacent to the city's Huron River surface water supply. Additional advanced oxidation or high-pressure membrane (NF/RO) processes may be required in response to changes in source water quality or to comply with future drinking water standards."

The report identified "advanced oxidation" as the preferred treatment process for contaminants such as dioxane, saying it can completely destroy the contaminants while other advanced treatment processes are ineffective.

The $90 million project the city is planning now is intended to replace aging pre-treatment facilities, some that date back to late 1930s.

After pre-treatment, the city disinfects and filters the water. As far as the disinfection and filtration aspects of the process, Steglitz said, there aren't any major infrastructure replacement projects envisioned on the near horizon.

"I think it was in 1996 when we added our new disinfection facility, so it's becoming almost 20 years old," he said.

"We've already started to replace components, but we're not looking at a major investment of this magnitude in the next 10-20 years."

Council Member Sabra Briere, D-1st Ward, brought up other water-related concerns, noting there are areas of Ann Arbor where the city deals with both low pressure and rusty water. Briere asked how the city will address those.

Steglitz said the city has a process that it goes through annually to assess where there are issues and water quality problems in the system.

"And we evaluate those against all of the other needs," he said. "We have a prioritization system. That's how we capture those issues and that's how we get them programmed into our capital improvement plan."

As the city looks to increase the rate at which it replaces underground pipes, he said, hopefully the city will address those issues sooner than it has been.

He estimated about 40 percent of the city's water distribution system is comprised of cast iron unlined pipes, which is part of the difficulty. He said the city's challenge in the coming decades is to systematically go through and try to get rid of water mains that are causing issues and impacting water quality for customers.

As for water pressure, that's a little more difficult, Steglitz said, because the city doesn't have the ability to change the elevation of people's homes.

"We have some ability to control the pressure in some areas of the city, but because of the topography in Ann Arbor it's quite challenging," he said.

"Because you have some areas that are really low, like the hospital, and then you have some other areas that are in the same pressure district that are really high, like the top of Geddes hill," he said. "And they're all managed together. So, if you're going to increase the pressure for one, you're increasing the pressure for the other. And we're trying to operate in sort of this sweet spot."