Missed the 1,4-Dioxane Panel? View it here.

On Oct. 25, 2018, Acton residents benefited from a crash course on 1,4-Dioxane in Acton’s groundwater and drinking water.

From left to right: Moderator Kim Kastens and panelists Matt Mostoller, Dan Groher, and Diane Manganaro. Photo by Norm Strahle.

Moderator Kim Kastens, the Chair of Green Acton’s Water Committee, opened the evening by crediting the organizers of the event, Green Acton and the Acton-Area League of Women Voters, and thanking the Town of Acton for the venue, and ActonTV for recording the event. Then each of three invited experts spoke on a different aspect of Acton’s 1,4-Dioxane situation. Links to the speakers’ slides and the video are at the bottom of this post.

Matt Mostoller, Environmental Compliance Manager at the Acton Water District (AWD), described the two local sources for 1,4-Dioxane: the Nuclear Metals (NMI) Superfund site and the W.R. Grace Superfund site. He explained how water and contaminants travel through interconnected pore spaces between grains of sand, and illustrated the flow paths from the Superfund sites toward the AWD public water supply wells. He shared a historical perspective about how local occurrences of 1,4-Dioxane and other contaminants were first discovered in Acton, how Actonians fought to have the W.R.Grace site remediated, and how knowledge about a second source at the NMI site has emerged in recent years. He concluded with data on 1,4-Dioxane levels in the finished water from the South Acton Water Treatment Plant, showing how the AWD has succeeded in keeping the contaminant level consistently below the MassDEP (Massachusetts Department of Environmental Protection) drinking water guideline of 0.3 micrograms per liter.

Levels of 1,4-dioxane in finished water from the South Acton Water Treatment plant (blue line and dots) relative to the MassDEP guideline (red line). From talk by Matt Mostoller.

Diane Manganaro, of the Office of Research and Standards at MassDEP, helped the audience understand how her office derives an OSRG (Office of Research and Standards Guideline) for drinking water contaminants. Based on animal toxicology studies and human epidemiological studies, staff members consider non-cancer and cancer risks, and set the OSRG to be preventive for the riskier of the two (flow chart below). Documented animal health effects for 1,4-Dioxane, seen in mice and rats, are liver and nasal cancers, and kidney impact. The OSRG for 1,4-Dioxane is 0.3 micrograms per liter. The federal Environmental Protection Agency (EPA) does not have an enforceable standard (also called an MCL, or Maximum Contaminant Level) for 1,4-Dioxane. However, based on those same animal studies, EPA has said that dioxane is a “likely human carcinogen.”

Dan Groher, an Acton resident and environmental engineer, spoke about efforts — both current and future potential — to intercept, divert, and treat 1,4-Dioxane. He described and illustrated how an extraction well has been drilled into the axis of the plume coming from the NMI site. By pumping out dioxane-rich water at a site between the NMI source and the Assabet 1 water supply well, the remediation team is attempting to split the plume (diagram below), thus preventing dioxane upstream from the extraction well from reaching the water supply well. Preliminary data suggest that this approach is beginning to work. Future actions include (definitely) treating the extraction well water with a UV (ultraviolet) advanced oxidation system, and (possibly) removing or treating the actual source of 1,4-Dioxane, which seems to be in the underlying bedrock.

Cross-section into the Earth illustrating the remediation strategy for the NMI plume, from talk by Dan Groher. The Assabet 1A water supply is to the left, the extraction well is in the middle, the Assabet River is to the right, and the NMI site is off screen farther to the right. Groundwater flow direction is from right to left. The pink ovals represent the dioxane plume being split into a small remnant, which will continue toward the water supply well, and a main plume, which will be intercepted by the extraction well.

The auditorium at the Acton Public Safety Building was filled to capacity with an inquisitive, thoughtful audience. After the formal presentations, audience members queued up to ask more than 45 minutes’ worth of substantive questions, ranging from possible effects of 1,4-Dioxane on local food plants, to what has happened when other Massachusetts water suppliers have exceeded the 0.3 µg/L MassDEP guideline, to the likelihood of the MassDEP guideline evolving into an enforceable standard as additional research is completed. The biggest unanswered question is what will happen next at the W.R. Grace site, which does not include remediation for 1,4-Dioxane in its Record of Decision.

Note on units: On the video, you will sometimes hear the concentration of 1,4-Dioxane expressed as “micrograms per liter,” and on many of the speakers’ slides you will see such measurements expressed as µg/L. Elsewhere, including in many Green Acton posts, you will see parts per billion or ppb. Parts per billion (ppb) and micrograms per liter (µg/L) are nearly exactly equivalent, because the density of 1,4-Dioxane is nearly the same as that of water. Parts per billion may be more understandable for a non-specialist audience. The National Environmental Services Center at West Virginia University offers some vivid analogies: one part per billion is like one sheet in a roll of toilet paper stretching from New York to London, or one second in nearly 32 years. 

 

 

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