Tiered Evaluations for CDF Contaminant Pathways—Upland Testing Manual

Confined disposal facilities (CDFs) are one of the most widely used options for placement of contaminated sediments. Consideration of pathways for migration of contaminants from the site and potential contaminant impacts is required to determine the need for operational or engineered measures to control contaminant releases. The pathways of concern for CDFs include effluent discharges to surface water during filling operations, rainfall surface runoff, leachate into groundwater, volatilization to the atmosphere, and direct uptake by plants and animals on site and subsequent cycling through food webs. During the 1980s and 1990s, a number of evaluation procedures and laboratory tests were developed for CDF pathway evaluations, and these approaches were applied at a number of projects. However, a comprehensive approach for pathway evaluations, considering the level of concern for each pathway and an appropriate level of effort to address the concerns has been lacking. Recently, a tiered approach has been developed for CDF contaminant pathway evaluations, similar to that long used for evaluation of open water placement of dredged material. This tiered approach is being incorporated into a new testing manual for nearshore and upland CDFs, commonly referred to as the "Upland Testing Manual." The Tier I evaluation for CDFs determines the need for pathway evaluations, pathways of concern, contaminants of concern, and which pathways require more detailed evaluations based on existing information. Tier II focuses primarily on screening evaluations and chemically based tests and evaluations. The screening evaluations consist of determining the need for management actions derived from very conservative techniques which use the chemical, physical and biological characteristics of the dredged material and basic information about the CDF. Tier III focuses primarily on definitive evaluations, including pathway testing. Tier IV, which should rarely be needed for navigation projects, includes formal quantitative risk assessment designed to answer specific, well defined questions. This paper describes the tiered evaluation approach and associated testing and modeling procedures for CDFs in the context of the new testing manual.