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Issues of the Environment: New study highlights exposure risks in Ann Arbor basements from the Gelman Sciences 1,4 dioxane plume

Dr. Rita Loch-Caruso
University of Michigan
Dr. Rita Loch-Caruso


  • Residual dioxane from Gelman Sciences operations decades ago continues to migrate in waterways reaching out from the former business site. Historically, the plant manufactured filter devices and used dioxane as a solvent. Thousands of pounds of 1,4-dioxane were discharged to soil, surface water, and groundwater through seepage lagoons, land spray irrigation, and direct discharges at the site.
  • According to the EPA, 1,4-dioxane is hazardous to human health and repeated exposures increase the risks of kidney and liver damage, miscarriage or fetal death, and possibly cancer. The chemical enters the body via contaminated air, food, or water. The 1,4-dioxane groundwater plume, which currently is about four miles long and one mile wide, has polluted local lakes, creeks, residential drinking water wells, and a City of Ann Arbor municipal water supply well.
  • Because dioxane exposure can occur with even low levels of exposure from contaminated vapor, it has long been hypothesized that risk could be associated with spring flooding seeping into wet basements. In April 2020, Ann Arbor City Council authorized funding to sample flooded basements for 1,4-dioxane in low-lying areas intersecting the Gelman plume. See Ann Arbor City Wet Basement Testing for 1,4-dioxane. (More info: https://www.a2gov.org/departments/water-treatment/Pages/1,4-Dioxane-Wet-Basement-Testing-.aspx)
  • Co-authors Dr. Bob Bailey (lead author, principal and owner of Bailey Associates, Environmental Chemistry Consultants, member of CARD) and Dr. Rita Loch-Caruso (a toxicologist at the University of Michigan and Professor Emerita, Department of Environmental Health Sciences, School of Public Health, and Professor Emerita of Program in the Environment, School for Environment and Sustainability, also a member of CARD) recently completed a paper (seen below) that examined this question, and published their findings in Current Opinion in Environmental Science and Health. The study highlights are: 
    • Analysis suggests exposure risk if 1,4-dioxane in shallow groundwater is > 150 μg/L.
    • 1,4-Dioxane intrusion in water could lead to hazardous air in damp basements.
    • 1,4-Dioxane risk may occur even if vapor intrusion calculations indicate low risk.
  • The underground and surface migration of dioxane in groundwater has faced greater scrutiny and testing in recent years as concerns about the plume reaching the city’s main drinking water source (Barton Pond on the Huron River) grow. According to MLive in December, “The city recently moved forward with installing more monitoring wells in northwest Ann Arbor to better track the spread of the plume and stay on the lookout for any dioxane headed toward Barton Pond.” 
  • Neighborhoods on Ann Arbor’s Old West Side, near Veterans Park, West Park, and in Scio Township have shown increasing levels of dioxane, and many homes in the area have a history of flooding with the spring thaws. As the plume concentrations in residential area rise, understanding how and where people are exposed is a top priority for members of CARD (Coalition for the Remediation of Dioxane) and the Washtenaw County Water Resources Department and Department of Public Health, and Ann Arbor City Council. The WCWR points out that surface water from thawing snow or rain is not a source of dioxane, and the risk comes only from contaminated groundwater. 


David Fair: This is 89 one WEMU. And, today, we revisit the Gelman Sciences one-four dioxane plume, but with some new and different focus. I'm David Fair, and I'd like to welcome you to this week's edition of Issues of the Environment. While decisions about how to seek federal EPA Superfund cleanup status for the decades-old remains under discussion, the reality of dealing with the expanding plume is a day-to-day endeavor. And until lately, the primary source of concern when it comes to public health is direct exposure, either by direct contact with contaminated groundwater, contaminated water wells, and by consumption of contaminated water. Now, the prospect of exposure by vapor is being studied. What happens when the spring thaw hits and basements begin to flood or at least get wet or moist? Is it a danger? Well, that's part of a new report coauthored by our guest. Dr. Rita Loch-Caruso is a toxicologist and environmental professor at the University of Michigan. And thank you for making time today.

Dr. Rita Loch-Caruso: Hey, David.

David Fair: Before we get deep into the basement issue, I want to take a moment to review. The old Gelman Sciences Company began using one-four dioxane as far back as 1966. Then the contamination was detected in 1984. It was already a significant issue at that point. Now, here we are, 39 years later, and it's still a significant environmental issue. Certainly, there's been some remediation, and, of course, the monitoring continues. In your examination, how significant do you assess the spread of the contamination to be at this juncture?

Dr. Rita Loch-Caruso: The spread of the contamination is part of a review article that is a companion to the article with Dr. Bob Bailey that deals with the vapor exposure. So, the spread of the contamination now is, I think, unacceptable. There's been an estimated less than 15% of the amount of one-four dioxane that was used by Gelman that has been removed. And yet, the concentrations at the core are going down. And one has to ask, where is it going? And we have documented now through various means that it's spreading. And it's continuing to spread.

David Fair: And do you have a sense of if or when it might reach the Huron River and Ann Arbor municipal water supply at Barton Pond?

Dr. Rita Loch-Caruso: Well, well testing--residential wells in Scio Township--detected one-four dioxane in residential wells that were, what, less than a thousand feet from the Huron River above Barton Pond, above the water intake, for the Ann Arbor municipal water supply.

David Fair: So, with that in mind, is it the potential assessment or conclusion of the companion report that seeking federal Superfund designation is the best opportunity of actually cleaning up the contamination and trying to protect the groundwater and Huron River watershed?

Dr. Rita Loch-Caruso: Yes. Just simply, yes. EPA is our best solution.

David Fair: This is 89 one WEMU, and our Issues of the Environment conversation with Dr. Rita Loch-Caruso from the University of Michigan continues. Now, it had been my assumption that exposure to one-four dioxane came from either physical exposure or consumption. At what point did you and your colleagues begin to consider the potential of vapor exposure?

Dr. Rita Loch-Caruso: Well, the state of Michigan has published vapor intrusion values, and they're a little bit ahead of the game, quite frankly, and the country on that, where they're interested in estimating risk from hazardous substances, volatilizing into the air spaces in soil, and then moving as a gas or vapor from those air spaces into basements. And this has always traditionally been done for solvents like trichloroethylene or percorethylene, which is a common dry cleaning solvent. And when Dr. Bob Bailey saw the vapor intrusion value for one-four dioxane, he got to thinking about it because one-four dioxane is not like these volatile organic chemicals. Like trichloroethylene and percorethylene because one-four dioxane likes water, loves water, partitions into water preferentially, and has a lot of complete miscibility and water.

David Fair: So, there are parts of Ann Arbor that are more susceptible to flooding than others, and that leads to a lot of flooded or at least very wet or moist basements. Where are the areas of the community most likely to potentially have that vapor exposure because of that?

Dr. Rita Loch-Caruso: So, the vapor exposure that...the question we asked was is there a risk for harmful exposure to homeowners when one-four dioxane contaminate groundwater makes its way into basements and then evaporates in basements? So, Dr. Bailey asked a different kind of question. He asked, "Is there a different risk for one-four dioxane contaminated, shallow groundwater because the one-four dioxane will move as water into homes with damp basements?

David Fair: And the conclusion was?

Dr. Rita Loch-Caruso: And the conclusion is yes, that, in fact, his calculation--our calculations--do show that there is a risk when there is a sufficient concentration of one-four dioxane in contaminated, shallow groundwater, and it can lead to a hazardous level of concentration of one-four dioxane in the air if your basements damp, if you've got damp walls.

David Fair: And is that a different standard than what the EPA and the state of Michigan have set forth as for safe, acceptable levels of one-four dioxane in the groundwater?

Dr. Rita Loch-Caruso: Absolutely. So, there's several different levels of one-four dioxane that are considered acceptable or actionable in groundwater in the state of Michigan. One of them is for drinking water. One of them is for when groundwater comes in contact with surface water, which would be, for example, when this plume hits the Huron River. Except the problem is that it looks like it's already coming in contact with the pond, perhaps in West Park, because they've detected one-four dioxane now in the pond in West Park. But that's a different standard. The current Michigan standard for that is 280 parts per billion. The drinking water standard is 7.2 parts per billion, and the vapor intrusion, again, assuming that the volatilization is occurring outside of the house, that is 1900 parts per billion. So, what Dr. Bailey and I did was we made some assumptions, and we calculated what would happen if one-four dioxane comes into the basement as water, not as a gas, not as vapor, but as water, and then vaporizes or evaporates inside the house.

David Fair: We're talking with University of Michigan professor and toxicologist Dr. Rita Loch-Caruso on WEMU's Issues of the Environment. So, now looking to next steps. Is there established protocol for testing to ensure the health and safety of potentially affected residents?

Dr. Rita Loch-Caruso: Unfortunately, no. What we know is that current levels in the shallow water are not potentially having risk because we estimated that 150 parts per billion in shallow groundwater, that is ground water that's within ten feet of the surface level, that would be about 150 parts per billion should be a trigger level for studying it. We don't have that yet, where the groundwater is coming to the surface, where it's meeting the surface. But that area is happening in the West Park and the waterworks park areas, because that's where the ground elevation is declining. As we're approaching the Huron River from the Gelman site. The Gelman site is kind of up on a ridge. And so, the ground is actually coming down. The ground surface is actually coming down to where the plume is rather than the plume kind of bubbling up.

David Fair: So, if I were a homeowner in that area, what preventative measures, if any, might I be able to take within the boundaries of the dioxane plume to prevent water or vapor exposure in my basement?

Dr. Rita Loch-Caruso: There aren't good options. Quite frankly, the best option is that action be taken to remediate the groundwater contamination. So, these higher level concentrations that are upgradient don't keep flowing down gradient towards these neighborhoods where their basements will be in contact with the plume. So, the best thing to happen would be let's remediate more aggressively. Let's stop this, so that we don't find ourselves in this situation. Now, if you do have a home where the groundwater concentrations are high, the groundwater concentrations of one-four dioxane are high, you know, probably the best thing to do is to try to prevent groundwater from coming into your basement, Keep your basement dry. It's expensive. It may or may not work because some basements have a high water table in certain residential areas of Ann Arbor. So, it may or may not work. Certainly, a regular humidifier, residential humidifier--dehumidifier, excuse me--will not work.

David Fair: We know the court system and ongoing legal challenges to the current remediation plan are ongoing. And fact of the matter is it hasn't advanced much in the decades that we've known of the problem. As environmental regulators and elected officials at all levels of government read the findings of your report, what actions do you hope it inspires?

Dr. Rita Loch-Caruso: Oh, thank you for asking that question. What we really wanted to do with this paper was to get people to take action on it, to think about it, to work on it. Certainly, we see our analysis as being a first step, not the ultimate last word, on this potential exposure pathway. Basically, it identifies that, hey, this is a new exposure pathway. You ought to be thinking about it. We hope the regulators will now start paying attention to it and will include it in their estimates of acceptable, actionable levels of one-four dioxane in shallow groundwater.

David Fair: Thank you so much for the time today. Dr. in explaining some of the findings in your report. We could talk for hours, but we've put a lot into a very short period of time. And it's much appreciated.

Dr. Rita Loch-Caruso: Thank you. It was a pleasure to speak with you today.

David Fair: That is Dr. Rita Loch-Caruso, a toxicologist and professor in the University of Michigan's School of Environment and Sustainability. For more information on Dr. Caruso's work and the latest information on the Gelman Sciences one-four dioxane plume, visit our website at WEMU dot org. Issues of the Environment is brought to you every Wednesday and is produced in partnership with the office of the Washtenaw County Water Resources Commissioner. I'm David Fair, and this is your community NPR station, 89 one WEMU FM Ypsilanti.

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