Abstract
The longโterm goal of monitored natural recovery (MNR) is to achieve ecological recovery of biological endpoints in order to protect human and ecological health. Insofar as ecological recovery is affected by surfaceโsedimentโcontaminant concentrations, the primary recovery processes for MNR are natural sediment burial and contaminant transformation and weathering to less toxic forms. This paper discusses the overall approach for effective implementation of MNR for contaminated sediment sites. Several lines of evidence that may be used to demonstrate natural recovery processes are summarized, including documentation of source control; evidence of contaminant burial; measurement of surface sediment mixing depths and the active sediment benthic layer; measurement of sediment stability; contaminant transformation and weathering; modeling sediment transport, contaminant transport, and ecological recovery; measuring ecological recovery and longโterm risk reduction; knowledge of future plans for use and development of the site; and watershed and institutional controls. In general, some form of natural recovery is expected and should be included as part of a remedy at virtually all contaminated sediment sites. Further, MNR investigations and an understanding of natural recovery processes provide costโeffective information and support the evaluation of more aggressive remedies such as capping, dredging, and the use of novel amendments. The risk of dredging or capping may be greater than the risk of leaving sediments in place at sites where capping or dredging offer little longโterm environmental gain but pose significant shortโterm risks for workers, local communities, and the environment.