ABSTRACT
The sources of pollution are many, and they differ from place to place. Manufacturing and industrial wastes have received the greatest notoriety, but other sources are of comparable importance. Agriculture-and mining-related contamination are extensive and likely to become increasingly serious. Defense-related activities have introduced certain types of contaminants specifically in the western U.S. Municipal and industrial landfills have and still let loose a complex collection of pollutants. It has become quite apparent that even "contained" applications and use of chemical compounds such as freons, chlorinated solvents, chromic acid, methyltert-butyl ether, polychlorinated biphenyls, and many others always result in a certain level of discharge into the environment. The total effect from all these different sources of pollutants is to contaminate only about 5% of the aquifers in this country. However, many of these contaminated aquifers are close to large population centers, and thus the environmental impact is disproportionately large. Since nearly 50% of the people of the U.S. depend on groundwater for their drinking water supplies, subsurface contamination in any form has significantly raised the level of public and regulatory concern during the last two to three decades.
