Clean Watershed Campaign

Arsenic and Old DNAPL

The EPA and Dow Chemical have agreed on an initial clean-up plan for Segment One of the Tittabawassee River Superfund project. This section, which runs through the Dow plant in Midland, is one of the more contaminated sections of the river. At one point this section of the river had over 1,100 outfalls carrying waste water and other pollutants from the plant and into the river. Where most of the project on the Tittabawassee focuses on dioxin and furans, this section has been contaminated with a range of chemicals which include such substances as ethyl parathion (a potent insecticide) and chlorinated solvents.

There are two portions of this recommendation which pose particular quandaries. The first is the decision by Dow and the EPA to leave a sizeable contamination of arsenic in the riverbed of the first section of Segment One. Dow would have historically produced arsenic-based compounds which are used as wood preservatives or herbicides. The protocol chosen leaves the arsenic in place under the premise that the habitat in that area is unique and the small crustaceans have adapted well to the contaminated environment. Dow has also indicated that “new information” on arsenic has changed perceptions on how it acts in the environment. Considering there is over 2000 years of using it as a biocide and poison in advance of this information is apparently irrelevant in this case. From the standpoint of human health, ecological stewardship, public perception or good common sense, there does not seem to be a good reason to leave the arsenic in place and untreated.

The second issue relates to a substance that has been named DNAPL (Dense Non-Aqueous Phase Liquid). DNAPL is a thick chlorinated substance that has accumulated in between the sediment and the till in several places along Segment One. Aside from the potential hazards of this material to the environment, there is real concern that there is no clear understanding of the source of the material and how it migrated to the areas in which it has accumulated. In most instances the EPA is going to attempt to pump out as much DNAPL as possible without causing a disturbance to the river bed or causing additional toxins to migrate downstream. Regardless of the remediation suggested or its potential effectiveness, the existence of a “mystery material” with these characteristics in a site that has been studied so thoroughly is a concern in the near term, as this Segment is remediated, and in the future, as without a known mechanism, re-contamination is a concern.

Stayed tuned for more information as work on this Segment commences.

Matt de Heus
Chemical Engineer