New technologies are introduced regularly while other ideas once thought promising are being dropped. However, through all these changes, the broad categories are likely to remain the same. New dredging tools may be developed, but they will probably all fall within the categories of mechanical or hydraulic. New treatments will most likely be new versions of such existing forms as solvent extraction or bioremediation. The use of non-removal technologies is feasible only if dredging is not required for navigation reasons and if the contaminated area is in waters where storms will not wash away capping material.
Material is placed on top of the contaminated sediments.
The simplest and cheapest caps are sand, gravel, or clean sediment thick enough to prevent benthic organisms from burrowing into the contaminated layers. More expensive caps use special materials called geotextiles. In the Sheboygan River in Wisconsin, an area heavily contaminated with PCBs was capped with alternating layers of gravel and geotextiles topped with a layer of larger rocks. This method isolates a portion of a waterway by enclosing it within cofferdams, dikes, or other structures. In Waukegan Harbor in Illinois, a boat slip was walled off in this way, additional contaminated sediments were placed inside the walls, and the whole mess was then capped like a hazardous waste landfill.