That which we do not see will not hurt us. Perhaps a way of living in decades past, this idea simply does not hold today, particularly when it comes to the millions of liters and cubic meters of hazardous and radioactive waste materials currently being stored across the United States.
 
Long-standing debates over the nation’s ability to clean up, or remediate, hazardous and radioactive materials at U.S. sites are seeing some resolution. However, the outcome is not as clear-cut as once hoped: that the waste at these sites could be completely remediated or removed and the sites could be restored to pristine conditions. The hope was that these sites would be safe for any use, including the construction of parks, homes, hospitals or schools.
 
We now know the outcome is actually one of degrees. This realization evolves from a significant shift in thinking, and a recognition that  we cannot just walk away from a site after the cleanup is complete. Traditionally, waste is removed or remediated to meet regulatory mandates, within the confines of budgetary and technological limitations. However, residual contamination frequently remains at the sites after the cleanup, and this contaminated material must be monitored and managed to ensure long-term protection of human health and the environment. Past thinking focused more on short-term solutions, including temporary on-site storage, which may ultimately introduce more contaminants into a site’s surroundings.
 
As we become increasingly aware of the potential health and environmental risks these wastes pose, the federal agencies responsible for their cleanup have come under growing pressure not only to clean up those wastes, but also to ensure long-term protection from their effects. The federal agencies charged with these tasks are primarily the U.S. Department of Energy (DOE), the U.S. Department of Defense (DOD) and the U.S. Environmental Protection Agency (EPA). All these agencies have established programs that address long-term stewardship.
 
Long-term stewardship includes measures put in place at a site after cleanup is complete, or when remediation ends, to ensure protection in perpetuity. Examples include:

• regular and continuous monitoring of groundwater and soil to evaluate the migration (if any) and attenuation of contaminants;
• institutional controls, such as restricted worker and public access to keep people away from contaminants;
• maintaining technologies for isolating and reducing contaminants;
• planning land use;
• overseeing the site and enforcing regulations;
• managing information; and
• periodically evaluating systems by considering new technologies or understandings of the environment.

Contamination from hazardous and radioactive materials is widespread across the United States. The large volumes of materials currently being stored at numerous sites come from a variety of practices, including industry and the military.

The activities that produced these hazardous materials, and the resulting groundwater and soil contamination, go as far back as the 1940s — in the case of nuclear weapons production — or even earlier, in the case of military waste disposal, agricultural runoff and disposal of industrial chemicals. During those times, little thought was given to the consequences these materials might pose to future generations and the environment.
 
Common waste disposal methods have been discharge materials into lakes, rivers or streams; landfills or other shallow burials; direct injection into groundwater. The health and environmental ramifications of these practices have come to light in the past 30 years. That recognition has laid the groundwork for what has become a complicated and expensive national history of trying to remediate the problem and thus find an effective way of protecting human health and the environment for current, as well as future, generations.
 
Not only is the disposal problem complex, but so too are the contaminants themselves. Contaminated sites at major DOD and DOE sites, as well as many industrial facilities, may contain complex mixtures of chlorinated solvents, fuels, metals and, at DOE facilities, radioactive materials. Storage tanks at Hanford, the former nuclear weapons production facility in Richland, Wash., not only contain a mixture of the radioactive materials cesium and strontium, but also host dissolved chemicals — primarily sodium nitrate, nitrite and hydroxide.
 
Once these mixtures are released into the environment, their fate or migration is difficult to predict. The contaminated liquids will flow preferentially through pathways that offer the least resistance, but the locations of these pathways is not easy to determine. Also, contaminants may absorb to the soil or may be trapped in soil pores, leaving residual contaminants that can migrate downward to the water table, and leaving long-term sources of groundwater contamination.

Another threat is that contaminants from the source may dissolve very slowly into the groundwater, forming a plume that can migrate large distances and contaminate groundwater far away from the source.

The human factor

Evaluating the potential environmental and health risks from hazardous and radioactive wastes poses a complex problem. The magnitude of these risks remains highly uncertain.
 
Health risks are expressed as probabilities that people who come in contact with the contaminant could, as a result, suffer from cancer, have children with birth defects, experience genetic damage or suffer premature death. But the symptoms of cancers may not appear until long after a person has been exposed. Or a genetic disorder might not manifest itself for several generations. Furthermore, dose-response relations based on epidemiological evidence is lacking for low-dose exposures.
 
Also, we do not fully understand the complexity of environmental contamination and transport. The physical parameters of waste sites vary considerably, depending on the source of contamination and on the geologic conditions at the site. The underground geologic environment may be highly variable, consisting of differing grain sizes, soil and rock permeabilities and fractures, which make the flow of water and other liquids through the subsurface difficult to predict.
 
Few studies have quantified the hazard that these contaminated sites pose. However, the fact that thousands of U.S. waste disposal sites have leaked, or have the potential to leak, hazardous and radioactive materials into the environment has prompted a number of regulations and laws over the past 20 years mandating specific cleanup responsibilities to DOE, DOD and EPA. The U.S. Nuclear Regulatory Commission maintains regulatory oversight of nuclear materials. Examples of such regulations are the EPA and USNRC groundwater standards, which are based on the level of contaminant they deem to be safe in groundwater that may eventually reach drinking water.
 
Other groups, such as the Agency for Toxic Substances and Disease Registry (ATSDR), conduct public health assessments of some select hazardous and radioactive waste sites across the country. The ATSDR evaluates contaminants and determines whether exposure to them has public health significance. For instance, a study of an equipment maintenance area at Hanford concluded that both the soil and groundwater may be contaminated with arsenic, lead, chromium and trichloroethylene.

Monitoring and isolation

Key to the success of long-term stewardship is environmental monitoring, traditionally done with sampling from monitoring wells. Monitoring provides early warning strategies that could alert site managers to potential leakage, migration or contamination that may threaten human health and the environment either now or in future generations. Such monitoring must detect the smallest release of contaminants from the site, as well as any environmental changes that could affect the fate and transport of potentially leaked or spilled materials. Groundwater monitoring is necessary to verify compliance with federal regulations, as well as any environmental commitments or safety measures.
 
Our recent shift in thinking about disposal recognizes the need for a long-term solution. Decades of scientific and technical research point to geologic isolation as the only credible long-term solution for disposal of hazardous materials. The idea is that waste would be placed in a repository located in a dry and geologically stable environment, such as salt formations or volcanic tuff.
 
In this and other long-term stewardship challenges, geoscientists have a key role to play.

Long-Term Stewards Three U.S. federal agencies are charged with long-term stewardship of contaminants and contaminated areas. Department of Energy (DOE) DOE manages about 24 million cubic meters of waste containing about 900 million curies from the production of nuclear weapons. Starting in the 1940s, DOE generated wastes and contaminated media from practices related to the production of nuclear weapons. Contaminants entered the environment through a number of pathways, including direct disposal into the groundwater through injection wells, disposal pits and settling ponds; through accidental spills and leaks from storage tanks; and from atmospheric releases. DOE’s Office of Long-Term Stewardship, established in 1999, was the first federal office devoted to protecting human health and the environment after the cleanup or stabilization of radioactive waste. Although most nuclear-weapon production has ceased, a large volume of groundwater, soil, sediment and bedrock contamination exists at more than 100 DOE waste sites across the country, and DOE has determined that long-term stewardship programs will need to begin at these sites within the next 70 years. Department of Defense (DOD) Since the early 1900s, the military has stored weapons and conducted military exercises at its installations, which have left contaminated soil and groundwater at more than 1,700 sites. DOD practices long-term stewardship within its Office of Environmental Cleanup, which focuses on reducing risk to human health and the environment at active, formerly used and closing bases from pollutants due to past practices. DOD operates cleanup activities at about 9,000 locations identified as Formerly Used Defense Sites (FUDS) and at active military installations. FUDS include sites containing industrial waste, such as fuels and solvents in groundwater or ordnance and explosive waste. FUDS are also sites that require building demolition and debris removal. DOD estimates that more than 2,500 FUDS require some further action to remove this waste or reduce the risk from residual waste. Environmental Protection Agency (EPA) EPA administers the Superfund program, established by Congress in 1980 to locate, investigate and clean up the nation’s worst hazardous waste sites that are abandoned or uncontrolled. After a site is identified by various sources, including state agencies or citizens, EPA evaluates the potential for a release of a hazardous substance from the site. It then decides whether to place the site on the National Priority List (NPL), a roster that identifies the most serious sites in need of long-term cleanup. As of 2000, more than 1,500 hazardous sites were on the NPL, including some large DOE and DOD sites. After remedial actions are completed at a site, EPA practices long-term stewardship through a program that includes groundwater sampling and monitoring to ensure that all actions are effective and operating properly. EPA and state environmental agencies have joint responsibility to regulate cleanup, monitoring and long-term stewardship of the NPL sites. S.B. Mockler

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