Hazardous Wastes in the Geosphere

FIGURE 15.5 Sources and movement of hazardous wastes in the geosphere. 

Spread on land for disposal or as a means of treatment can contaminate the geosphere and ground-water. In some cases, wastes are pumped into deep wells as a means of disposal. 

Several important properties of the solid determine the degree of sorption. One obvious factor is surface area. The chanical nature of the surface is also important. Among the important chemical factors are presence of sorptive clays, hydrous metal oxides, and humus (particularly important for the sorption of organic substances). 

In general, sorption of hazardous waste solutes is higher above the water table in the unsatu-rated zone of soil. This region tends to have a higher surface area and to favor oxic biodegradation processes. 

The chemical nature of the leachate is important in sorptive processes of hazardous substances in the geosphere. Organic solvents or detergents in leachates will solubilize organic materials, preventing their retention by solids. Acidic leachates tend to dissolve metal oxides 

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Unfortunate cases of the improper disposal of hazardous wastes into the geosphere have occurred throughout the world. This often occurs in poorer countries where wastes are dumped from concerns in more developed conntries. 

In past years, many hazardons solid and liquid wastes have been improperly disposed of to sites in the geosphere, giving rise to a large number of hazardous waste sites, which is the subject of Superfund activity in the United States. The practice of industrial ecology seeks to totally eliminate any such wastes that would require disposal. Ideally, such wastes simply represent material resources that are not properly utilized, a fact that can serve as a gnideline for the prevention of snch wastes. 

The movement of hazardous-waste constituents in the geosphere is largely by the action of flowing water in a waste plume, as shown in Figure 21.4. The speed and degree of waste flow depend upon numerous factors. Hydrologic factors such as... 

These principles currently provide a rigorous geochemical framework within which to design experiments and interpret field observations on the redox-related performance of a deep geological repository for spent nuclear fuel. They can be extended to consider other types of hazardous waste and containment barriers in the geosphere. Of particular interest may be active containment barriers where redox-transformations of mobile contaminants are desirable. 

The overriding aim of this volume is to assess the extent to which chemical processes might contribute to the confinement of a particular waste within the geosphere. In any type of waste containment, it is not necessary to ensure that no waste will ever leak from the disposal site. Rather, it is required to show that for as long as the waste remains hazardous it poses an acceptably low risk to the biosphere. Thus, this volume is really concerned with the degree to which chemical processes will restrict the movement of contaminants through the geosphere. 

The best way to manage hazardous waste disposal to the geosphere is to render all wastes non-hazardous before disposal. Unlike radioactive wastes that eventually decay (see later in this section), some hazardous chemical wastes never degrade and no secure landfill can be assumed to be secure forever. Organic wastes, such as refractory organochlorine compounds, should be destroyed by thermal process, and toxic heavy metals should be separated and recycled. 

The distribution of hazardous waste compounds between the atmosphere and the geosphere or hydrosphere is largely a function of compound volatility. Usually, in the hydrosphere, and often in soil, hazardous waste compounds are dissolved in water therefore, the tendency of water to hold the compound is a factor in its mobility. For example, although ethyl alcohol has a higher vapor pressure and lower boiling temperature (77.8°C) than toluene (1 lO-b C), vapor of the latter compound is more... 

Although it is far better to find uses for hazardous waste constituents and put them into a nonhazard-ous form, in the past, and even today, wastes were disposed of to the geosphere, usually in landfill. This requires treatment of wastes to get them into a form that is suitable for long-term disposal. 

One of the more pressing matters pertaining to geospheric disposal of wastes involves radioactive wastes. Most of these wastes are low-level wastes, including discarded radioactive laboratory chemicals and pharmaceuticals, filters used in nuclear reactors, and ion-exchange resins used to remove small quantities of radionuclides from nuclear reactor cooler water. When disposed of in properly designed landfills, such wastes pose minimal hazards. 

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