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Environmental Health Division
Radon and Operator Safety in Drinking Water Treatment Plants
Radon is a colorless and odorless gas that comes from the soil. The radioactive decay of radium-226 creates radon.
There can be elevated levels of radon in drinking water treatment plants. Radon may be released from areas with radium accumulation, soil gases, sludge, or water. It can travel easily through cracks in concrete or poorly sealed doors. It can then accumulate in the air and become a health concern.
If radium is present in groundwater, it can accumulate on filter media and increase the amount of dissolved radon in the water. Radon can then be released into the air during activities that cause the water to be agitated, such as backwashes, aeration processes, or other agitation.
As a result, water operators may be exposed to elevated concentrations of radon in the air within the treatment plant.
Preventing and reducing operator exposure to Radon at water treatment plants
Assess existing conditions
Water treatment plants should be tested for airborne radon, particularly if the treatment plant meets at least one of the following conditions. These conditions could cause radon to be released by agitating or aerating the water.
- There are open detention tanks, filters, backwash basins, or clearwells in the treatment plant.
- Backwash waste is discharged within the treatment plant (open-to-air sump).
- Radium has accumulated on filter media or sludge. Radium produces radon when it decays. This radon can be released during backwashes.
Test for Radon
As a first step, conduct a screening for radon using short-term radon detectors.
The Minnesota Department of Health (MDH) has partnered with Air Chek, Inc., a manufacturer of short-term test kits. Order online: Air Chek.
Minnesota residents receive a discount. If the water system is a public entity, then it may qualify for a further reduced rate from Air Chek (about $5 per kit).
- MDH recommends using a short-term test kit to measure radon in each room. Rooms should be tested at the same time.
- Detectors should be placed at a normal breathing level in each room, three feet from exterior walls and windows, and in an area where the water operator spends most of their time.
- For large rooms, use 1 test kit per 2,000 square feet.
The MDH Indoor Air Unit provides technical assistance to help systems determine the correct number of test kits (including duplicates and blanks), determine the right times for testing, and interpret test results.
If the radon result is less than 4 picoCuries per liter (pCi/L), the treatment plant meets the U.S. Environmental Protection Agency’s (EPA) action level for radon in homes, where people are likely to spend a lot of their time. This means the amount of occupational exposure is likely limited.
If the source of water or the treatment plant design changes, the water system may want to retest for radon.
If the short-term test result is greater than 4 pCi/L, the plant supervisor should contact the MDH Indoor Air Unit, the MDH Community Public Water Supply Unit, or a licensed radon testing and mitigation professional for information on additional testing.
The Community Public Water Supply and Indoor Air Units have continuous radon monitors that we may bring to help identify when peak radon levels occur and for how long the radon remains elevated. Monitors may be left onsite for several weeks, depending on the facility, the treatment processes, and the number of rooms affected.
Due to the limited availability of monitors and an increased interest in radon testing, the MDH monitors are used to investigate elevated radon levels rather than for an initial screening. This monitoring provides additional information that can help the water system or consultants determine next steps for radon mitigation.
Alternatively, the system may want to hire a licensed radon testing and mitigation professional for continuous radon monitoring.
The Occupational Safety and Health Administration (OSHA) radon exposure limit for adult employees is 30 pCi/L averaged over a 40-hour workweek.
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Reduce water operator exposure
The best ways to reduce exposure are to lower the radon levels or limit the time of exposure. Other ways to reduce water operator exposure to radon in treatment plants:
- Provide ventilation continuously or when the operator is in the treatment plant. Fresh air ventilation should be provided to all work areas.
- Use exhaust fans directly above areas where water is agitated. These fans should run continuously to keep the room or area under constant negative pressure.
- Keep the backwash sump in a well-ventilated room separate from the rest of the plant.
- Replace or clean filter media regularly. This will minimize radium accumulation on the media.
- Limit the time spent in the plant during and shortly after the backwash cycle. Or use automatic backwash controls.
- Educate staff about the risks of radon exposure and how to reduce their risk.
- Use and train staff on standard operating procedures that reduce exposure time.
- Follow the disposal guidelines below.
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Safely dispose of spent filter media or backwash waste containing Radium
Always use best practices for wearing personal protective equipment (PPE) when handling filter media. Proper PPE will minimize inhalation of particulates from dust and prevent skin contact.
Personal clothing that comes in contact with filter media at the treatment plant needs to be washed before the person goes home. Skin that comes in contact with filter media should be washed thoroughly, especially before eating.
Waste that is sent to a landfill or that is land applied must be tested and handled following the Minnesota Pollution Control Agency’s Guidelines-Disposal Methods for Water Filter Backwash Solids (PDF). The entity that generates the waste is responsible for determining what type of waste is it and ensuring proper disposal.
For disposal in unlined landfills, radium-226 cannot exceed 5 picoCuries per gram (pCi/g). For lined landfills, radium-226 cannot exceed 30 pCi/g. If the radium concentration is greater than either limit, it is possible to dilute the filter media or backwash by mixing it with material that has lower radioactivity. If you dilute, you should retest the material before disposing of it.
Dilution example: If you have 10 cubic feet of sand media with radium levels at 15 pCi/g, then it must go to a lined landfill or be diluted. To dilute it, you could mix it with 20 cubic feet of media at 0 pCi/g. This would result in 30 cubic feet of media at 5 pCi/g. This could then be sent to an unlined landfill.
If waste materials are above the limits, they may require a landfill that is specifically for radioactive materials.
- Radiation - Drinking Water Treatment Overview (PDF)
- Radiation Safety Guidance at Water Treatment Facilities (PDF)
- Radioactive Waste Disposal from Water Treatment Facilities (PDF)
- Risks of Radon in Water Treatment Facilities (PDF)
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Background information on Radon
Radon in Minnesota
Radon is a serious public health concern in Minnesota. The average Minnesota radon level is more than three times higher than the average U.S. radon level. Elevated radon levels in Minnesota occur due to our geology and how our buildings are operated.
Health effects of Radon
Radon at water treatment facilities is not likely to have an immediate effect on health. A person has a higher risk of getting cancer if they are exposed to radon every day for many years.
- Contact the Indoor Air Unit at 651-201-4601 or firstname.lastname@example.org for information about occupational exposure and radon testing.
- Contact the Community Public Water Supply Unit at 651-201-4700 or email@example.com for Safe Drinking Water Act-related information.
- Visit Radon in the Workplace, The OSHA Ionizing Radiation Regulations (PDF).
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