By far, the best solution is isolation of a radionuclide source from the water supply. For example, uranium is often associated with shale in sedimentary rock in discrete layers. In some situations, the unit (detectable by analyzing drill cuttings or borehole geophysical logs) can be sealed off with casing and grout.
Among the different types of technologies that treat radionuclides are co-precipitation with barium sulfate, greensand filtration, ion exchange, lime softening, preformed hydrous manganese oxide filtration, and reverse osmosis. Radon is effectively removed by ventilation (see radon section).
Whether or not a particular treatment removes radionuclides from drinking water effectively depends on the contaminant’s chemical and physical characteristics, as well as the water system’s characteristics such as size and water quality.
- Co-precipitation with a barium sulfate is the process of adding a soluble barium salt to radium-contaminated water. It is mainly used in waste water. Data have shown success in removing 95% of the radium.
- Greensand filtration consists of a filter box with manganese greensand replacing the traditional filtration medium. Studies have indicated the sand removes up to 56% of the radium.
- Ion exchange can be used on small systems. It removes 90% of the radionuclides it encounters. The water flow must be regularly monitored, and the resin must be regenerated frequently. Attention must be given to disposal of the brine regeneration wastewater stream, that may contain elevated levels of radionuclide.
- Lime softening can be used to remove radium. It has an efficiency of 80% to 95%. Adding lime to water increases its pH, and can also be a method for treating hard water. This is most often used in public water supply, and resulting lime solids may also have elevated radioactivity.
- Preformed hydrous manganese oxide filtration is a method for radium-contaminated water. It is fairly inexpensive if filters are already in place. It requires proper dosages, and if water quality varies, the dosage must be recalibrated.
- For radon coming primarily from insoluble radioactive minerals in aquifers, especially igneous and metamorphic rock, the gaseous radon is usually removed by active ventilation. Ventilation exhaust should be directed away from human or animal residences.
- Reverse osmosis removes multiple radionuclides, including radium and uranium. It can have a success rate up to 98%. Concentrate streams may have elevated radioactive content and should be managed accordingly.
For all these technologies, waste streams (even ventilation of radon) may be excessively radioactive. There is no “away” that should be ignored.
Treatment technologies must be designed and maintained by professionals familiar with the work. Local health professionals and hydrogeologists will be familiar with the occurrence of radioactivity in natural formations and water. Qualified water well contractors may know about formation sequences associated with radioactivity. If radioactivity is due to contamination incidents such as military, power plant or mining activity, resolution is beyond local action. However, if removal is unlikely, treatment is needed.