ANN ARBOR, MI -- As a toxic plume of 1,4-dioxane continues to slowly spread through Ann Arbor's groundwater, inching closer to the Huron River, the biggest concern remains its potential to reach Barton Pond.

That's where the city gets 85 percent of its drinking water, so contamination of that supply could have disastrous consequences.

Michigan Department of Environmental Quality officials discussed the risks posed by the Gelman dioxane plume during a special City Council work session Monday night, attempting to provide some assurances to local officials who still lack trust and confidence in the state and are concerned not enough is being done.

Council Member Chuck Warpehoski, D-5th Ward, asked DEQ officials what would happen in a nightmare scenario if the plume reached Barton Pond and the city had to find an alternate municipal water source.

He wanted to know who would pay for that. The city? The state? The company responsible for the pollution?

Bob Wagner, chief of the DEQ's Remediation and Redevelopment Division, responded first by saying the majority of the plume is moving east, not north toward Barton Pond. Though there is some dispersion to the north, he said, the DEQ doesn't believe the plume is going to head straight toward Barton Pond.

But, Wagner said, it's something the DEQ will be watching closely, and the department shares the city's concerns.

A Google Earth map showing the varying concentrations of the Gelman dioxane plume in Ann Arbor and Scio Township.

"We're concerned about it, too, which is why we've asked for more resources," he said, noting a $700,000 funding request in the DEQ's budget for next fiscal year to better monitor, track and understand the plume.

Gelman Sciences, which was acquired by Pall Corp. in 1997, dumped large amounts of dioxane into the environment along Wagner Road -- on Ann Arbor's western border with Scio Township -- from 1966 to 1986, causing the plume of pollution that local and state officials have spent decades trying to address.

DEQ and local officials are in agreement that the plume is many years away from reaching Barton Pond, if it ever does reach it.

Wagner said Pall Corp. would have to take preemptive action before it ever gets to that point if the threat becomes more real.

"So, whether that is some sort of capture system, whether some kind of barrier system, interception system -- that's what we would go to court to look for so that that never happens," he said.

Wagner said monitoring wells show the plume is still about 11,000 feet away from Barton Pond so there's no imminent threat.

He also told council members there is a natural hydrological barrier around Barton Pond that could keep the plume from ever entering the pond.

"Because Barton Pond is an impoundment, it has a dam," he said. "And we're very familiar with working around impoundments and dams with respect to groundwater contamination. Typically what happens is when you put a dam in, and you have all of this backwater, while a lot of it ponds up and that's what you see on the surface, a lot of it finds its way around the dam through the groundwater, so it creates what we call radial flow subsurface. So, Barton Pond groundwater is moving outward away from Barton Pond, and basically circling around the dam and getting back to the river."

So, if the plume got near Barton Pond, Wagner said, it could meet that radial flow, which he described as water from the pond trying to escape around the dam, and that creates a natural hydraulic barrier.

Some still remain concerned about the westward migration of the plume toward Honey Creek, which flows to the Huron River upstream of Barton Pond.

"What really hits my eye every time I look at this is how closely the plume is following a tributary of Honey Creek and how close it is to Honey Creek now," said Council Member Sabra Briere, D-1st Ward.

Pall Corp. is doing some pump-and-treat remediation of the dioxane-contaminated groundwater, discharging treated water with trace amounts of dioxane into Honey Creek. Because the dioxane entering Honey Creek is at low enough concentrations, it becomes diluted and hasn't been detected at the city's drinking water intake at Barton Pond, which holds 1.5 billion gallons of water.

'We're acting proactively'

In the event that any drinking water sources become contaminated, whether it's Barton Pond or the many residential drinking water wells out in the township areas, some of which already have been contaminated, Wagner said the DEQ will be prepared to intervene. As a short-term solution, he said, the DEQ would provide bottled water to any properties that need an alternate water supply.

And as a long-term solution, he suggested the DEQ would be willing to spend millions of dollars to extend municipal water service.

Wagner said the DEQ is getting closer to proposing new statewide pollution cleanup standards that will lower the permissible level of dioxane in groundwater from 85 parts per billion to somewhere in the single digits.

He promised the state will go to court with a sense of urgency once the new standards are in place to get a consent judgment for the cleanup revised.

"In the meantime, we make a commitment to provide safe drinking water to any resident or business that either exceeds the current criteria, the current standard, or the new proposed standard when it's released," he said.

Ann Arbor Township Supervisor Mike Moran also addressed the council, expressing interest in getting the plume designated as a federal superfund site to get the U.S. Environmental Protection Agency involved in overseeing the cleanup.

If the plume ever reaches Barton Pond in high concentrations, Moran said, the city is going to have to find another source of water, and the topography suggests the city might be looking at going to Ann Arbor Township.

"And if we're able to find water there, then the infrastructure has to be built to get it into the city and back into the distribution system that currently exists," he said.

"It's a very, very long-range and very expensive proposition, and it's not one that you can make a plan when it's already too late, so we're trying to get some engagement here to require this to happen."

Wagner said there have been concerns about the plume moving north for the past few years and there have been increased monitoring efforts.

There are 38 additional wells the DEQ proposes to sample this year on the north side of M-14 east of Wagner Road.

"So know that we're acting proactively, that we are out there planning, collecting samples," Wagner said.

"We'll work with Pall and see what we can get out of them voluntarily to monitor movement of 1,4-dioxane, and know that we're prepared to provide these folks with bottled water, and in the long term a permanent source of water. I can't tell you where that would be right now, but know that we have paid for and developed municipal systems in very rural areas where there previously was no municipal source, so we've actually created municipal systems to make sure the residents of Michigan have safe water, and we will do so here."

'Toxicological information has changed'

Wagner addressed the fact that there have been repeated delays with revising the state's cleanup standards for dioxane to reflect the latest science, which shows the cancer risks to be much greater than previously believed.

The EPA published new findings in 2010 showing cleaning up dioxane to 3.5 ppb in drinking water poses a 1 in 100,000 cancer risk.

The DEQ for the last several years has enforced a cleanup standard of 85 ppb, which was intended to result in the same 1 in 100,000 cancer risk

"I know that you're not seeing the 1,4-dioxane number yet, but you will see it, and you will see at least a 10-fold decrease," Wagner assured city officials. "And the reason we know that is the toxicological information has changed."

State law called for putting forward new standards by December 2013, which the DEQ still has not done, but Wagner said they're getting close.

The reason it didn't happen in 2013, he said, is because there wasn't consensus among a stakeholders group, which included polluters, as well as representatives from public health, academia and the environmental community.

"We had these stakeholder meetings throughout 2013 and when we got to August, we realized we did not have agreement on some major issues," he said, adding they couldn't agree on exposure assumptions for residential drinking water and whether there should be an adult-only standard or a child-only standard or both.

"Now that may seem simple, but I can tell you that we did not have agreement on that," Wagner said. "Additionally, we did not have agreement on what we call developmental toxicants, so we're talking about chemicals, hazardous substances that can either have a one-time or chronic effect upon the unborn and children under the age of six, basically in the developmental years."

Wagner said there also wasn't agreement in 2013 with respect to how to evaluate vapor intrusion as an exposure pathway.

"So, what we're talking about is when certain chemicals are in soil and groundwater and they like to become airborne, and similar to radon they become airborne in enclosed spaces, so we call it vapor intrusion," he said.

Council Member Julie Grand, D-3rd Ward, criticized the DEQ for letting polluters hold up the process for establishing stricter cleanup standards. She said it seems like the DEQ's stakeholders are disproportionately those doing the polluting.

"I just personally find it very troubling that we're depending upon a group who can't agree that children should be a standard," Grand said.

"It's your job at the MDEQ to protect the public, not to protect the polluters, and it just boggles my mind that the group couldn't agree to something as basic as that a child standard should be the standard for pollution."

Wagner defended the DEQ's process, saying he believes there's a balance of interests on the stakeholder group, including representatives from the automotive, chemical, petroleum and mining sectors, as well as state and local public health, local government, academia and the Michigan Environmental Council.

He argued there are likely similar processes at the local government level when adopting new ordinances.

"Not this one," Grand replied, referring to Ann Arbor's government.

Council Member Sumi Kailasapathy, D-1st Ward, also expressed displeasure with the DEQ and its process.

"I just feel so sick in the stomach. I mean, we keep seeing all these Pure Michigan advertisements and see this sickening, dirty standard that is being set by industry," she said, comparing it to asking the airline industry and oil companies how to get a handle on global warming.

"What I have heard from MDEQ, I just feel hopeless."

Though there wasn't consensus among stakeholders in 2013, Wagner said a different stakeholder process in 2014 resulted in consensus, and the DEQ agreed with the stakeholder group's recommendations in early 2015.

He said that includes changing the groundwater or drinking water exposure standard to take into consideration both children and adults, instead of just adults as the current standard does. He said the DEQ had hoped to release the new standards by now, but they're still working out technical problems.

After that's done, it will take an estimated six to nine months to go through the state's administrative rules process.

'Appalling for so many different reasons'

State Rep. Jeff Irwin, D-Ann Arbor, lamented the change in state law in 1995 that moved Michigan away from doing full-scale cleanup of pollution sites to doing risk management, which is the approach to the plume in Ann Arbor.

"The law was changed from really a law that required polluters to clean up their mess to a law that required the department to manage exposure between humans and the pollution that is caused," he said. "And that has been a big part of why it's been so hard to get a good cleanup here in Washtenaw County, why this 1,4-dioxane plume continues to spread. Because not only have we had, I think, an insufficient effort from our regulatory body ... but I also think it's fair to say that our regulatory body is working with a law that isn't very good."

Mayor Christopher Taylor simultaneously criticized state leaders while thanking the DEQ's staff who came to speak Monday night. He said it's clear the DEQ's staff is operating under constraints not within their control.

"It will come as no surprise that many in the community find where we are today appalling for so many different reasons," Taylor said.

"And this is again another instance, from a local government's perspective, in a long line of neglect and broken promises that continues to have very adverse effects to our community and other communities throughout Michigan."

Commenting on the law under which the DEQ must operate, Wagner said court orders from former Washtenaw County Circuit Judge Donald Shelton with respect to managing risks associated with the plume -- through a combination of pump-and-treat remediation and letting the plume migrate east through a groundwater use prohibition zone -- are not inconsistent with state law.

Wagner said he's not sure the DEQ or attorney general have any legal basis to argue for anything greater than what's in state law.

"So, it is a combination today of putting resources toward cleanup, but also protecting public health by managing the risk, and that is how our current statute is designed," he said. "And I believe that's what is basically the situation here."

Matt Naud, the city's environmental coordinator, also shared his latest thoughts at Monday night's meeting.

"The plume continues to expand," he said. "In most cleanups, the plume is contained. In this case, it's migrating both east, west and a little bit to the north, and the area to the north is an area we have the most concern about."

Naud said it's also a concern that both the amount of water being pumped and treated, and the number of samples being taken, are decreasing.

"Pall is allowed to discharge 1,300 gallons a minute into Honey Creek of treated water. That's down around 500," he said. "And even though the plume is expanding, Pall is requesting the amount of sampling they do go down. That concerns us."

Naud said the densest mass of contamination is between Wagner and Maple roads, and most of the pumping is happening at Maple Road.

"So it's not really happening at the core of the mass," he said. "We think there is more that could be done to remove the mass."

If the state's cleanup standard for dioxane goes down to less than 10 ppb, Naud said, Pall Corp. will be required to track and show where the plume is at the new single-digit standard, which will require more monitoring.

"Understand this is a long-term remediation site," he emphasized. "It's not going away in the near future, so we're going to need to be kind of eternally vigilant."

'Unintended consequences'

Another concern raised Monday night is the possibility that dioxane could infiltrate people's homes through vapor intrusion.

"We have a lot of homeowners on the west side ... who have basements that are continuously taking water -- winter, summer, spring -- and what contaminant level are we going to allow in the basements of homes?" said Vince Caruso, a founding member of the local Coalition for Action on the Remediation of Dioxane.

"And who is going to be responsible for cleaning that water collection in the basement? It's in a confined space. The 1,4-dioxane will evaporate with the water. You'll have exposures in that respect."

Warpehoski asked if there is any sampling being done to show if dioxane-contaminated groundwater is springing up to the surface anywhere.

"That's an area where I think we don't know," Naud said. "So what we're worried about is unintended consequences."

Naud noted he lives on top of the plume on the city's far west side and the plume is 150 feet below his house there, so he's not exposed. As the plume gets closer to downtown, he said, there's less certainty about what could happen.

"We don't know whether it's going to hit Allen's Creek first and vent there," Naud said, adding it's also a possibility the dioxane could get closer to the surface as it gets to downtown and get into the environment by other means.

"You've got a building that goes in with a two-story underground parking deck, and they've got sump pumps, and all of a sudden 2,800 ppb is now hitting those sump pumps, and what we thought was discharging clean water into a stormwater system is now discharging 2,800 ppb into a stormwater system," he said, describing a hypothetical scenario. "Those are the things that we just don't know."

Wagner briefly addressed the issue of vapor intrusion Monday night, though not specifically in the context of dioxane getting into Ann Arbor homes. It was in the context of the broader revisions to the state's cleanup standards.

"These chemicals like to become a vapor and they like to enter buildings, and of course they can present a risk when they do that," he said.

Council Member Kirk Westphal, D-2nd Ward, posed the question: "Should we be holding out any hope that a plume like this can be stopped?"

Naud responded by saying the city isn't going to be able to use the contaminated aquifer on the west side of the city for a very long time, but removing more of the mass of the dioxane at the core of the plume needs to be a priority.

"We need to be vigilant and make sure that this doesn't get even close to Barton," he said. "And again, these township wells are going to get hit first. But we need a way to stop this before it gets across M-14."

Briere said she's concerned about the potential cost to taxpayers and disruption to people's lives if the plume spreads and contaminates more drinking water wells, requiring extending municipal water service lines at great expense.

"I'm not really happy about hearing that something magic is going to happen if the water goes north and we don't know what that magic thing is but something magic is going to happen and that's our contingency plan," she said. "So there's a lot here that we're going to have to deal with."

Ryan Stanton covers the city beat for The Ann Arbor News. Reach him at ryanstanton@mlive.com.