Featured article: Sediment Capping
Capping is an in situ
remedial technology for contaminated sediments that involves placement of a clean substrate on the sediment surface. Capping serves to contain contaminated sediment solids, isolate contaminants from benthic organisms and reduce contaminant transport to the sediment surface and overlying water. The clean substrate may be an inert material such as sand, a natural sorbing material such as other sediments or clays, or be amended with an active/reactive material to enhance the isolation of the contaminants. Amendments to enhance contaminant isolation include permeability reduction agents to divert groundwater flow, sorbents to retard contaminant migration through the capping layer or provide greater accumulation capacity, or reagents to encourage degradation or transformation of the contaminants. Depending upon the erosive forces to which the cap may be subjected, the surface layer may be composed of relatively coarse material to withstand those erosive forces. In addition to providing chemical isolation and containment, a cap can also be used to provide improvements for organisms by enhancing the habitat characteristics of the bottom substrate. As a result of its flexibility, simplicity and low cost relative to its effectiveness, capping is one of the most prevalent remedial technologies for sediments.