The USACE New England District’s evaluation of dredged material disposal projects has been collaboratively developed over a number of years with guidance from the Disposal Area Monitoring System (DAMOS) as well as input from the U.S. Environmental Protection Agency.
It is based on the tiered approach outlined in the New England Regional Implementation Manual (RIM) which was developed by the Corps and EPA.
The RIM is available for review here.
The Weight of Evidence (WoE) approach involves gathering a number of different types of empirical and descriptive datasets including previous sediment testing data; spill records; watershed history and development; oceanographic variables; and physical, chemical and biological test results, as appropriate.
Formerly, chemical analysis was performed by comparing bulk sediment chemistry results on project sediments to the chemistry data associated with reference sites at the selected open water disposal site.
Biological analysis was performed by assessing the response of test animals incubated with project and control sediments to measure toxicity and bioaccumulation responses.
The New England District is now applying a WoE approach that more completely documents this evaluation process, while still employing the tiered approach outlined in the RIM.
For each suitability determination the various inputs, non-point sources, watershed influences and local concerns are documented as part of a Conceptual Site Model (CSM) to identify potential contaminants of concern and exposure pathways for a given project as a basis for assessing potential risk associated with in-water placement of the material to be dredged, said USACE.
A discussion is included in each suitability determination to address the watershed history, oceanographic setting and specific local project history.
According to USACE, the results are discussed and placed in context of an updated set of reference site chemistry data and established national sediment screening levels. The implementation of this approach is based on an evaluation of the procedure to appropriately determine the suitability of dredged materials for open water placement.