Quantities of hazardous wastes produced each year are not known with certainty
and depend upon the definitions used for such materials. In 1988 the figure for
RCRA-regulated wastes in the U.S. was placed at 290 million tons. However, most
of this material was water, with only a few million tons consisting of solids. Some
high-water-content wastes are generated directly by processes that require large
quantities of water in waste treatment, and other aqueous wastes are produced by
mixing hazardous wastes with wastewater.