Lack of Progress on Remediation of 1,4-Dioxane at WR Grace Superfund Site

The previous post described the recent progress that has been made in reducing the levels of volatile organic compounds (VOCs) at the WR Grace Superfund Site by extracting and treating the groundwater, as called for in the 2005 Record of Decision (ROD). Unfortunately, the same cannot be said for 1,4-Dioxane.

1,4-Dioxane is an organic compound that was widely used in late 20th century industrial processes, but is now known to be a likely human carcinogen. Much has been written recently on the Green Acton website about 1,4-Dioxane — but most of that has dealt with the contaminant plume flowing under the Assabet River from the Nuclear Metals, Inc. (NMI) Superfund Site in Concord. This post focuses on the other relevant, local Superfund site: the 260-acre WR Grace site on the border between Acton and Concord. A map showing the location of the two Superfund sites relative to each other, and to Acton’s town borders, was included in a recent post.

The Superfund Record of Decision (ROD) for groundwater at the WR Grace site, finalized in 2005, does not mention 1,4-Dioxane. At that time, the danger of this contaminant was not well understood, and thus, Grace was given no obligation to remediate. But the scientific understanding of, and the technology for dealing with, 1,4-Dioxane have have come a long way since 2005. The ROD for the NMI Superfund Site, finalized 10 years later in 2015, calls for extraction and ex-situ treatment for 1,4-Dioxane, and explicitly calls for accelerating the cleanup of this particular contaminant.

According to the every-five-years report issued in 2014, the presence of 1,4-Dioxane was first noted on the WR Grace site in 2006, when EPA requested that Grace sample for it. Since then, the concentrations of the compound have been monitored in wells throughout the site. It’s hard to compare concentrations of this contaminant across time, because older measurements are fewer in number and analytical techniques have changed, so this post will address the most recent data, found in the 2018 Monitoring Program Report for Operable Unit 3 (hard copy available in the Acton Memorial Library).

The current MassDEP drinking water guideline for 1,4-Dioxane is 0.3 micrograms per liter. Table 3-4 of the 2018 Monitoring Program Report shows a total of 48 measurements of 1,4-Dioxane from wells throughout the site during 2018. Only six out of 42 of these measurements are below the MassDEP threshold of 0.3 micrograms/L. Until 2011, MassDEP had a less-stringent guideline of 3 micrograms/L. Seventeen of the 48 measurements taken in 2018 would have failed even this more lax standard. The very highest 1,4-Dioxane measurement in the 2018 report, in a sample from the Southeast Landfill Area, was 25 micrograms/L.

It had been thought that the treatment plants originally planned for other contaminants could be modified to help with 1,4-Dioxane, as well (2014 report, p. 4). But the draft 2018 annual report (available in the Acton Memorial Library) has discouraging news on the lack of reliability and efficiency of the removal process. The table below shows the concentration of 1,4-Dioxane in the water coming into the treatment plant (influent) and the water coming out of the plant (effluent) on various sampling dates.

From Table 5-2 in the 2018 annual monitoring report for the WR Grace Superfund Site. Influent and effluent columns show 1,4-Dioxane concentration in micrograms/L. “% Removal Efficiency” is influent minus effluent, divided by influent. NC means “not calculated.”

On a few sampling dates, the effluent concentration is much lower than the influent concentration. But on most dates, there is little improvement from influent to effluent, and on four most-unfortunate dates, the effluent ended up with a higher concentration of 1,4-Dioxane than the influent.

Is this all OK? Reassuringly, the seriously high 1,4-Dioxane levels were found far from the AWD municipal water wells. Grace and the EPA emphasize that “the MassDEP drinking water guideline is not considered an enforceable standard” (2014 report, p. 10), and that “there is currently no federal drinking water standard for 1,4-Dioxane” (2018 draft annual monitoring report, pp. 3–9) .

But local observers can’t help wondering why 1,4-Dioxane is being cleaned up at the NMI site — with similar hydrogeology, proximity to municipal water wells, and contaminant levels — but not at the WR Grace site.

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