Insoluble solid wastes can be buried at shallow depths in locations where they are safe from exhumation. If any parts are soluble, the solution must be managed as with any similar liquid waste. Programs for the management of waste liquids must be tailored to the chemical and physical characteristics of the liquids.
Geologic requisites for successful underground management of liquid wastes include: (1) porous and permeable reservoir rocks, in which the storage space may be caverns, intergranular pores, or fracture crevices; (2) impermeable seals to prevent escape of fluid wastes; (3) adequate understanding of hydrologie parameters and planning to prevent undesirable migration of fluids; (4) compatibility between waste materials and the reservoir rocks and their natural fluids.
Layered sedimentary rocks, rather than igneous or metamorphic rocks, provide the most suitable reservoir space, for both geologic and hydrologie reasons. If the wastes are hazardous to the biosphere, objective reservoir formations must be deep enough to provide permanent protection to groundwater aquifers.
The site must be reasonably stable seismically and not actively moving along, or broken by, faults.
Choice of a suitable underground disposal site can be made only after a thorough investigation of available subsurface data, supplemented by drilling and various other processes of subsurface exploration if sufficient data are not already available. Preliminary investigations and later subsurface operations will be expensive, but they cannot be avoided. Public insistence on an end to pollution must be accompanied by public understanding that a clean environment can be purchased only by higher taxes, if government managed, or by higher prices for consumer goods, if industry managed, plus individual awareness and practices.
As waste-management costs rise, it will become more economical to convert wastes into usable products, in effect eliminating, rather than managing, wastes.
Figures & Tables
This publication consists of papers based on oral presentations at a symposium of the same name co-sponsored by the United States Geological Survey and the American Association of Petroleum Geologists. A wide range of technical issues are covered, as well as regulatory and liability concerns. Documentation of two areas in Colorado where earthquakes had resulted from subsurface fluid injection set the stage for modern debates regarding possible similar results elsewhere. A wide range of fluid compositions are subject to subsurface waste disposal. The largest volumes are brines separated during the production of oil and gas wells, but acid-water and industrial wastes of all types can be disposed in significant quantities in local areas. Large hydraulic fracture treatments never recover all of the injected fluids, and the chemical additives in the fluid that remains underground can be a concern. The subsurface injection of radioactive waste is a topic for three of the papers. The possible need for sequestration of carbon dioxide was not a significant concern at the time and was not covered, but many of the papers provide insight into the issues related to modern proposals. When fluids are injected under pressure into subsurface aquifers, they interact in numerous ways. The fluids can potentially migrate for long distances and potentially interfere with other uses for the native aquifer fluids. If the aquifer cannot transport all of the fluids away, the buildup in pressure can cause fracturing of the rock. Differences in composition between the injected and native fluids can cause chemical reactions to occur; in some cases these can be desirable in that they can immobilize certain solutes in mineral form. The long-term environmental consequences are a common theme in many of the papers because of the recognition that the disposed fluids would become a permanent fixture in subsurface aquifers and could have long-term consequences for their future utilization.