Disposal Options and Problems

Disposal options for hazardous waste include landfills, injection wells, incineration, and bioremediation, as well as several others. The greatest concern with the disposal of hazardous waste in landfills or injection wells is that toxic substances will leak into surrounding groundwater. Groundwater is a major source of drinking water worldwide and once it is contaminated, pollutants are extremely difficult and costly to remove. In some instances, it is impossible to remove groundwater contamination. The ideal disposal method is the destruction and conversion of hazardous waste to a non-hazardous form. New technology for hazardous and mixed low-level radioactive waste conversion includes a high-temperature plasma torch that converts low-level radioactive wastes to environmentally safe glass. Conversion to

Workers wearing hazardous materials suits, neutralizing hazardous materials. (┬ęPete Saloutos/Corbis. Reproduced by permission.)

environmentally safe substances can be very expensive for some types of hazardous wastes and technically impossible for others, creating the need for alternative disposal methods.

The most common form of hazardous waste disposal in the United States is landfilling. Hazardous waste landfills are highly regulated and are required to include clay liners, monitoring wells, and groundwater barriers. The 1984 Hazardous Solid Waste Amendments require the monitoring of groundwater near landfills for thirty years. Injection wells may be used to inject hazardous waste deep into the earth, but problems result with aquifer contamination and the ultimate fate of the hazardous waste after injection is unknown.

Incineration may be an effective way to convert hazardous waste into a nonhazardous form while greatly decreasing its volume. The waste is burned and converted into carbon dioxide, water, and inorganic by-products. The problems associated with incineration are high capital and operating costs, and the disposal of ash, which may contain hazardous substances. In addition, incinerating wastes can cause mercury and dioxin air pollution. Bioremedia-tion may also be used in situ or ex situ to convert hazardous wastes to nontoxic by-products using microorganisms and natural degradation processes. Biodegradation requires very long treatment times and it may be difficult to control or enhance natural degradation processes. Phytoremediation, the process by which plants absorb and in some cases degrade hazardous

Workers wearing hazardous materials suits, neutralizing hazardous materials. (┬ęPete Saloutos/Corbis. Reproduced by permission.)

substances in the environment, is being investigated as an emerging cleanup technology. For example poplar trees have been shown to break down the herbicide atrazine, mustard plants will remove lead from soil, and the alpine pennycress plant will take large amounts of heavy metals and also uranium from soil.

When hazardous waste is to be transported off-site for disposal, the waste generator prepares a shipping document called a manifest. This form must accompany the waste to its final destination and is used to track the waste's movements from "cradle to grave."

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