The previous post looked at the 1.5-year-old effort to divert 1,4-Dioxane in the Nuclear Metals, Inc. (NMI) plume before it can reach the public water supply. This post looks at a longer time frame, and asks whether dioxane levels in the Acton public water supply wells have been getting better or worse over the scale of a decade.
Appendix G of the 2017 Groundwater Monitoring Report prepared for W.R. Grace presents time series graphs of 1,4-Dioxane level in dozens of production and monitoring wells in and around the W.R. Grace Superfund site. Let’s start with the familiar Assabet 1A well, which is the one most immediately threatened by the NMI plume and the one referred to in previous posts.
In this and subsequent graphs, the horizontal axis is date, and the vertical axis is concentration of 1,4-Dioxane in micrograms per liter, which is equivalent to parts per billion (ppb). The horizontal blue line represents the MassDEP guideline for 1,4-Dioxane in drinking water, 0.3 parts per billion (ppb). Each data point represents one sample. Samples from Assabet 1A have tended to fall just above the MassDEP guideline.
In contrast, the values from the Assabet 2A well, approximately 700 feet north of Assabet 1A, have almost all fallen safely below the MassDEP guideline. Those lower levels in 1A (and other Acton wells) are what has made it possible for the Acton Water District (AWD) to blend water from multiple wells to produce finished water with dioxane below the MassDEP guideline.
Note that both the Assabet 1A and Assabet 2a values have been been bouncing around quite bit. That means that one shouldn’t read too much significance into any single measurement. It also means that a genuine change — for the better or the worse — will be hard to detect because there is so much natural variability and/or “noise” in the data. More recent data, from July 2018, were shown at the August AWD Commissioners’ meeting. The Assabet 1A well came in at 0.32 ppb, while Assabet 2A came in at <0.20 ppb. In other words, the most recent measurements were on trend with the last five years or so.
The Assabet well field is not the only part of Acton experiencing dioxane problems. Dioxane is also found in the School Street group of wells (see location map). This dioxane is attributed to the W.R. Grace Superfund site, rather than NMI. The School Street well field includes three wells: Lawsbrook, Scribner, and Christofferson.
Christofferson, farthest from the W.R. Grace Superfund site, has been reliably below the MassDEP guideline:
Lawsbrook and Scribner have been bouncing back and forth across the MassDEP guideline, although more often below it than above:
Across all five graphs, for each well, the cloud of data points is basically horizontal, with neither a marked upward, nor downward, trend. In other words, the answer to the question in the headline would seem to be: Acton’s 1,4-Dioxane situation has not been getting better or worse; it has been stable.