Waste Injection Wells
Waste Injection Wells
Increasingly since the 1930s, various industries around the world that generate large volumes of liquid byproducts have disposed of their wastes by injecting them into the subsurface of sedimentary basins. In the United States, according to a 1985 survey by Brower et al. (1989), 411 “Class I” wells were licensed to inject hazardous and nonhazardous waste into deep strata, and 48 more were proposed or under construction. Legal restrictions on the practice vary geographically, as does the suitability of geologic conditions. Nonetheless, the practice of deep-well injection had increased over time, partly in response to environmental laws that emphasize protection of surface water and shallow groundwater. More restrictive regulations introduced in the late 1980s and 1990s have begun to cause a decrease in the number of operating Class I wells. Some injected wastes are persistent health hazards that need to be isolated from the biosphere indefinitely. For this reason, and because of the environmental and operational problems posed by loss of permeability or formation caving, well operators seek to avoid deterioration of the formation accepting the wastes and its confining layers. When wastes are injected, they are commonly far from chemical equilibrium with the minerals in the formation and, therefore, can be expected to react extensively with them (Boulding, 1990). The potential for subsurface damage by chemical reaction, nonetheless, has seldom been considered in the design of injection wells. According to Brower et al. (1989; Fig. 21.1), nine wells at seven industrial sites throughout the state of Illinois were in use in the late 1980s for injecting industrial wastes into deeply buried formations; these wells accepted about 300 million gallons of liquid wastes per year. In this chapter, we look at difficulties stemming from reaction between waste water and rocks of the host formation at several of these wells and consider how geochemical modeling might be used to help predict deterioration and prevent blowouts. Velsicol Chemical Corporation maintained two injection wells at its plant near Marshall, Illinois, to dispose of caustic wastes from pesticide production, as well as contaminated surface runoff. In September 1965, the company began to inject the wastes into Devonian dolomites of the Grand Tower Formation at a depth of about 2600 feet.
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