Bureau of Mines engineers have investigated the feasibility and limitations of the underground injection of industrial wastes by observing installations at industrial plants, cities, and oil fields. The chemical industry is using about 175 deep wells to inject approximately 30 million gal per day of waste solutions. The wastes are (1) inorganic salts, (2) mineral and organic acids, (3) basic solutions, (4) chlorinated and oxygenated hydrocarbons, and (5) municipal sewage.

The wells, ranging from 1,000 to 8,000 ft (300-2,440 m) deep, are completed in three general types of formations: (1) unconsolidated sand, (2) consolidated sandstone, and (3) vugular carbonate rock. The chemical and physical characteristics of the formation and waste dictate the design of the injection system and govern its operation.

Commonly, underground injection is the most economical method for disposal of liquid wastes that are not amenable to surface treatment. Operating costs are lower for pretreatment and subsurface disposal than for surface treatment systems, and plant area requirements are less. Chemical treatment is minimal, and generally the only physical treatment required for underground injection is filtration.