Disposal of Hazardous materials

Surface impoundment (placing liquid or semiliquid wastes in unlined pits) keeps waste in long-term storage, but it is not considered a method of final disposal. About 8 percent of hazardous waste is injected into deep wells; 21 percent enters landfills (large, unlined pits into which solid wastes are placed) as its ultimate resting place.

Abandoned and particularly serious waste sites may qualify as “Superfund” sites, eligible for cleanup with government funding under legislation passed in 1980. In 1993, of about 38,000 hazardous-waste sites inventoried by the Environmental Protection Agency (EPA), 1407 sites were listed on or proposed for the National Priority List (NPL) for waste cleanup.

In 1995 the EPA estimated that 73 million people lived within 4 miles of a Superfund site in the United States. Before 1995, 3300 emergency removals—urgent cleanups of hazardous wastes because of the immediate hazard they present—were conducted.

The serious problem of underground plumes of hazardous materials leaving the original disposal sites has only partial solutions at this time. The typical method of handling this problem is the drilling of wells around a plume's perimeter.

Hazardous materials are then removed from some wells, and water may be injected into other wells to produce a barrier to the plume's motion. Drilling wells and monitoring holes near a toxic site carries risks; a plume originally confined between strata (horizontal layers of rock) may penetrate vertically through a drilled hole and escape confinement.

A recent method of treatment for shallow plumes of chlorinated solvents depends on their chemical reactivity. A trench is dug around the leaking waste site and filled with a mixture of soil and powdered iron. The iron then reacts with the chlorinated solvents, turning them into simple hydrocarbons, which are less hazardous.