Radionuclides in Drinking Water
Waste Disposal Options
The disposal options for each type of waste stream will depend not only on the type of waste but also on federal, state, and local regulations; landfill and treatment plant requirements; and location of the plant in relation to disposal options.
In general, landfills are the primary disposal method for solid wastes, except for lime softening plants that spread their sludge as an agriculture soil amendment. The type of landfill required will depend on the characteristics of the waste, local requirements, and landfill requirements. Systems can refer to a listing of municipal solid waste landfills (for non-hazardous waste).
There are several options available for disposal of liquid wastes. These include discharge to a body of water, discharge to a wastewater treatment plant (WWTP) via a sewer connection or transport of liquid residuals to a WWTP and underground injection.
Sludge is a mixture of solids and liquids. It can be disposed of in landfills, although some landfills may not allow sludge if there is a free liquid content. The Paint Filter Liquids Test is a method used to determine the presence of free liquids in a representative sample of waste (9095A- 1 Revisions 1 – December 1996). Sludge, because it also has some liquids and can therefore be somewhat fluid, can be disposed of by diluting it with liquids and discharging to an underground injection well or wastewater treatment plant. Underground injection may not be an ideal choice for sludge because it may require increased pressures which can fracture geologic formations used for disposal.
The table below summarizes disposal options for each type of waste.
Direct discharge may be an option for liquid residual disposal if the system has an accessible and appropriate receiving body. The Clean Water Act (CWA) requires anybody discharging pollutants into U.S. waters through a point source to obtain a National Pollutant Discharge Elimination System (NPDES) permit from the state or EPA Region (CWA, Title IV, Section 402). These permits set limits on the amount of certain pollutants that can be discharged. They also set monitoring and reporting requirements, and they may include other provisions that protect water quality and public health.
Federal NPDES regulations do not set specific limits on radionuclides in discharges. States have the authority to establish these limits, and state anti-degradation policies designed to protect the quality of certain water bodies and support source water protection efforts might restrict the levels of radionuclides in discharged waste. It is very unlikely that a state will allow many discharges from treatment systems removing radionuclides, where the radionuclides are highly concentrated. Treatment technologies designated for radionuclide removal also remove co-occurring contaminants for which NPDES regulations set limits, further restricting disposal options.
Discharge to Wastewater Treatment Plant
Liquids and sludge may be discharged to a wastewater treatment plant generally through a connection to the sewer. There are no current federal regulations concerning disposal of radionuclides to the sewer. Liquid wastes that are mixed with domestic sewage and discharged to the sewer are not considered hazardous wastes, although wastes trucked to a wastewater treatment plant might be. There are strict conditions for disposal if a system should have high enough concentrations to be considered source material in the case of uranium. Then the system must ensure the waste is soluble and there are limits on the average and total amounts discharged (10 CFR 20). The amount and type of waste that can be discharged are largely determined by local requirements. Discharges to the sewer must meet technically based local limits (TBLL) established by either the state or the wastewater treatment plant to ensure that the wastewater treatment plant can meet its NPDES permit requirements without upsetting the treatment process. The wastewater treatment plant has the right to refuse any waste that will cause violation of its permit conditions, upset the treatment process, or hamper its ability to recycle or reuse its biosolids. In general, to dispose of liquid waste to a wastewater treatment plant, the system will need to obtain a permit or enter into a contract specifying terms of disposal. Some states will have Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) regulations that must also be followed. EPA has published guidelines based on U.S. Nuclear Regulatory Commission (NRC) requirements that discharges with greater than 600 pCi/L of radium-226 and radium-228 and 3,000 pCi/L of uranium should not be discharged to the sewer. There is also a requirement that the total be less than unity. In other words, the following equation should be true:
Ra226/600 + Ra228/600 + U/3000 < 1
For example, for residuals containing 30 pCi/L of radium-226, 30 pCi/L of radium-228, and 150 pCi/L of uranium, the fraction contributed by radium-226 is 30/60 pCi/L, or 0.5; the fraction contributed by radium-228 is 30/60 pCi/L, or 0.5; and the fraction contributed by uranium is 150/300 pCi/L, or 0.5. As the sum of these fractions is 1.5, underground injection of the material would be prohibited.
Under the Resource Conservation and Recovery Act’s (RCRA’s) “domestic sewage exclusion” (40 CFR 261.4(a)(1)) liquid wastes mixed with domestic sewage and discharged to a wastewater treatment plant are not regulated under RCRA, because they are subject to the Clean Water Act. Hazardous waste that is accumulated, managed, or transported (e.g., by truck) prior to introduction into the sewer system, however, would still be subject to regulation as a hazardous waste. State regulators and local wastewater treatment plants should be contacted to ensure that wastes are properly managed.
In the unlikely event that the treatment technology generates enough source material to require a specific license from the NRC, there are strict conditions set for disposal into any sanitary sewer system (10 CFR 20.2003):
States that have adopted Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) regulations that apply to water treatment facilities may also have placed radionuclide discharge requirements on wastewater treatment plants.
Injection to Class I or Class V Underground Injection Control Wells
Underground injection into geologic formations through injection wells may be an option for liquids and sludge. It may not be a good option for sludge as the higher pressures required may damage the confining layer of the geologic formation and allow for migration out of the injection zone which is not allowed under Underground Injection Control (UIC) regulations. Class I UIC wells may be used for disposal of hazardous, radioactive, or other wastes. Radioactive waste in this instance is defined as more than 60pCi/L for radium and 300 pCi/L for uranium. Other contaminants in the waste may make it hazardous. These would include toxic chemicals (e.g. arsenic) or a pH less than 2 or greater than 12. Class I wells have strict requirements for monitoring of the well and for maintenance of the well to prevent migration of contaminants out of the injection zone. States may also impose other more strict requirements. As a result, injection to a Class I well can be very expensive. Very few Class I wells accept waste generated off site.
It may be possible for systems to inject through a Class V well, which are generally shallower. To inject into a Class V well the system must demonstrate that an underground source of drinking water is not endangered. This generally involves demonstrating no maximum contaminant levels (MCLs) will be exceeded in the source. This may be a very difficult requirement to meet for systems disposing of radionuclides. Also, if a waste is determined to be radioactive based on the NRC definitions it is strictly prohibited from using Class V wells for disposal.
These requirements do not currently apply to single-family residential waste disposal systems (e.g., single-family septic systems) and non-residential septic systems that are used solely for sanitary waste and have the capacity to serve fewer than 20 persons a day. However, the EPA can take action on a residential waste disposal system if the system introduces contaminants into an underground source of drinking water, the presence or likely presence of which causes an imminent and substantial endangerment to public health (SDWA Section 1431).
While Class I injection may be an option for disposal of hazardous and radioactive liquid wastes, there are several limitations:
Injection to a Class V well may be an option for a limited number of systems. Class V wells are generally shallow wells (e.g., large capacity septic systems and dry wells) used to place a variety of non-hazardous liquid wastes into or above underground sources of drinking water.
Injection of hazardous liquid wastes into Class V wells is prohibited. In addition, use of Class V wells is prohibited if it will endanger an underground source of drinking water per 40 CFR 144.12 (cause an exceedance of any primary drinking water standard or otherwise adversely affect public health). Therefore, Class V well injection will most likely not be an option for radioactive liquid wastes, as demonstration of the non-endangerment standard would be difficult.
Solid waste is generally sent to landfills. Prior to landfill disposal, it must be determined whether the waste is hazardous (through process knowledge and/or analytical testing) and whether the waste contains any free liquids (using the Paint Filter Liquids Test). Landfills cannot accept wastes containing free liquids. Generally, wastes with greater than 20 percent solids will not have free liquids. If the waste contains free liquids, an intermediate processing method (such as dewatering) should be used to remove any liquids. An appropriate method for disposing of the liquid residuals generated by the intermediate processing must also be determined.
There is no federal requirement to test radionuclide concentrations in solid residuals prior to disposal. However, there are restrictions on the transport of waste that exceeds certain radioactivity thresholds and states and disposal facilities may have requirements for testing or disposal of TENORM. A determination of whether waste is exempt from NRC licensing requirements for source material should also be conducted.
There are several types of landfills that may provide protective disposal for solid residuals containing radionuclides. The appropriate landfill can depend on the amount, concentration, and physical and chemical attributes of the radiologically-contaminated material, the mobility of radionuclides and their decay products, the consideration of future controls and future land use, and state and local regulations.
Disposal at a municipal or industrial solid waste landfill may be an option for systems disposing of non-hazardous waste. These landfills are regulated under RCRA Subtitle D. Municipal solid waste landfills may have restrictions on the amount of radioactivity they accept. These landfills may accept non-hazardous, solid, and TENORM wastes from all water systems, and hazardous waste from Conditionally Exempt Small Quantity Generators (CESQG) (40 CFR 258). Industrial solid waste landfills may also accept non-hazardous solid TENORM waste, and may be better equipped to handle such waste as it is more like the waste that industrial landfills typically handle (e.g., sludge and ash). Generally, wastes containing less than 3 pCi/g of radium or 30 pCi/g of uranium can be disposed of in these landfills – treatment residuals will likely exceed these concentrations, however.
As disposal facility owners become more aware of issues surrounding disposal of radioactive materials, more landfills are using monitors to scan incoming trucks for radiation. In some cases, wastes that had previously been accepted were found to contain elevated levels of TENORM. If the monitors are triggered, the source must be identified and evaluated. Note that gamma monitors will not detect uranium residuals that do not contain significant radium.
Hazardous waste landfills (regulated under RCRA Subtitle C) may accept hazardous waste (though not mixed waste) from all generator classes. However, they vary in their ability to accept Technologically Enhanced Naturally Occurring Radioactive Materials (TENORM) wastes. Some hazardous waste landfills have explicit permit conditions while others may have to request state approval before accepting TENORM wastes. Systems should check with the disposal facility to determine whether their TENORM waste is eligible for disposal at a particular hazardous waste landfill.
Low Level Radioactive Waste (LLRW) or mixed waste landfills may be an option for systems generating wastes with radionuclide concentrations deemed to be unacceptable for disposal at municipal, industrial, or hazardous waste landfills.
LLRW landfills are licensed by the U.S. Nuclear Regulatory Commission (NRC) or by a state under agreement with NRC. Guidelines for disposing of radioactive sludge and solids are more stringent than in a standard landfill. These facilities are licensed based on projected performance and have packaging and burial requirements that are progressively stricter as the radionuclide concentrations increase.
Some states allow land spreading or soil mixing as an alternative to landfill disposal for water treatment residuals (for example, as a soil amendment on farm fields). One central concern with land application is the potential for build-up or movement of radionuclides to create contaminated sites that would require remediation and/or use of institutional and engineering controls. Other factors to take into account include the physical and chemical attributes of the material, the amount of radiation introduced into the soil over time, the mobility of the radionuclides and their decay products along multiple pathways of exposure, and the consideration of future controls and future land use. However, some States have been spreading lime sludges on agricultural lands for years and their studies have shown that this can be a viable and beneficial disposal method.