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United States District Court, District of Maine, 221 pp, 2018

Beginning in 1967, a chlor-alkali facility located in Orrington, Maine, released mercury into the Penobscot River Estuary. Hg releases at overall declining concentrations continued throughout facility operation and ceased with facility closure in 2000. The slow rate of Hg concentrations decline in the area is attributable, in part, to the presence in the Estuary of a large pool of Hg-affected mobile sediment, which is retained in the Estuary by natural processes that result in the landward flow of both bottom water and associated sediment under the influence of tides. Following several extensive studies of this contamination issue, six remedial alternatives were evaluated for this report: (1) monitored natural recovery; (2) enhanced monitored natural recovery; (3) dredging; (4) thin layer capping in Mendall Marsh; (5) amendment application in Mendall Marsh; (6) dredging in intertidal and subtidal zones plus thin layer capping in Mendall Marsh. Bench-scale treatability studies were conducted to provide data for the development and evaluation of alternatives. The subsequent Phase III Engineering Study recommended a suite of remedies—thin layer capping, dredging, and long-term monitoring—to address various portions of the river. For more information, including the appendices to this report, see the Penobscot Study website:

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