The intervention to divert Nuclear Metal’s 1,4-Dioxane from reaching the public water supply

As discussed in earlier Green Acton posts, there is a plume of 1,4-Dioxane flowing from the Nuclear Metals, Inc. (NMI) Superfund Site, passing under the Assabet River, and impacting the water quality at the Assabet 1 public water supply well. Fortunately, there is a pro-active remediation effort underway to intercept and treat this contaminated water.

To reprise the situation (more detail here), the pink contours on the map below mark the flow path of 1,4-Dioxane from the NMI site in the southeast corner of this map to the Assabet 1 public water supply well at the western edge of the map.

Because 1,4-Dioxane is now recognized by the Environmental Protection Agency (EPA) as a likely human carcinogen, the Record of Decision (ROD), which establishes what the Superfund program must do to clean up the site, has a section on dioxane in groundwater. It states that the “selected remedy also includes extraction and ex situ treatment of volatile organic compounds (VOCs) and 1,4-Dioxane in overburden and bedrock aquifers” (ROD p. 5). “Ex situ” means that the treatment should happen in a treatment plant, not down in the Earth. VOCs are another category of contaminants commonly found in groundwater. VOCs also present human health concerns, but the the techniques for removing contaminants from water are better understood for VOCs than for dioxane. The Record of Decision for the NMI site came out in September, 2015.

To extract the VOCs and dioxane, the remediation contractor for the NMI site, de maximus, inc., drilled and tested an “extraction well” in the axis of the plume just west of the Assabet River, at the location of the yellow star on the map above. The extraction well descends about 80 feet and pulls up water from the core of the plume. In May 2017, de maximus began pumping water out of the extraction well and treating the water in a temporary treatment system. The extraction well is pumping at the rate of 20 gallons per minute; by comparison, a typical household shower spits out about 2 gallons per minute. The idea is to suck contaminant-bearing water toward the extraction well and intercept the contaminants before they can reach the Assabet 1 water well.

Such a remediation effort would typically take many years, and this one has only been operative for a year and half. However, early signs are promising. The map below shows the distribution of 1,4-Dioxane in June 2018. (Download larger scale zoomable pdf).

Comparing the pre-intervention, Sept. 2016 map with the June 2018 map, we can see signs of progress. The earlier map had 40 ppb as its most dioxane-rich contour, while on the more recent map, the highest contour is 20 ppb. In the crucial area between the extraction well and the Assabet 1 water supply well, the area that had been encircled by the 10 ppb contour is now at 5 ppb or less. Data from individual wells show a more-complicated picture, with levels in some wells going consistently down, while others have bounced up and down.

Throughout this extended process of characterizing the problem, planning the remediation, and waiting for it to take effect, the Acton Water District has consistently kept the finished water below the MassDEP drinking water guideline of 0.3 ppb by blending water from more-impacted wells and unaffected wells:

The water pumped from the extraction well is currently being treated for VOCs, but not yet for 1,4-Dioxane. After treatment, the effluent is being released into the Assabet River. The water being discharged into the Assabet has roughly 6–9 ppb of 1,4-Dioxane (data from summer 2017). This is well below the limit of 200 ppb allowed by MassDEP for discharge into the waters of the Commonwealth of Massachusetts. Even upriver from the treatment plant discharge, there is a detectable amount of 1,4-Dioxane in the Assabet River (0.096 ppb in Aug. 2016), which could come from shampoos and other personal care products.

Green Acton and others concerned with the ecosystems of the Assabet and Concord Rivers look forward to the day when the extraction well water will be treated for dioxane before being discharged into the river. Unfortunately, there is no off-the-shelf technology that will remove 1,4-Dioxane down to the desired levels for the volumes of water that come out of the extraction well — or a municipal production well. The remediation team has been experimenting with various combinations of pre-treatment steps followed by an advanced oxidation process, optimized to work with the particular chemistry of the water in the NMI plume. A treatment facility for 1,4-Dioxane is being built and is on track to begin operation in December 2018, according to Bruce Thompson, Project Coordinator. Lessons learned from designing and operating this treatment facility for the extraction well water will provide valuable insights should it ever become necessary to implement dioxane treatment at the Acton Water District’s municipal water treatment plant.

Green Acton has assembled information about 1,4-Dioxane, both general and Acton-specific, which is available here. We will continue to provide information as the treatment plant comes on line and the remediation effort proceeds. In addition, Green Acton and the League of Women Voters are sponsoring an expert panel discussion about 1,4-Dioxane, in groundwater and drinking water, on Thursday, October 25, 2018, 7–9 pm at the Acton Public Safety Building, 371 Main Street, Acton.

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Data/Model Sources:

• de maximus, inc., Demonstration of Compliance Report #11, submitted to EPA May, 2018
• June 2018 dioxane modeling maps, personal communication from Bruce Thompson, de maximus, inc.
• presentation to Community Groups by Bruce Thompson, October 2017
• NMI Pre-design Investigation Report
• Acton Water District website, dioxane page