Updated Statement on Radon Levels
in Household Water
Purpose
The purpose of this document is to provide an accurate information base upon which decisions can be made regarding whether to install equipment to remove radon from household water. All of the research is not in at this point in time and there are a number of opinions.
Overview
Radon is an odorless and colorless radioactive gas that generally occurs in drinking water derived from groundwater as a result of the decay of naturally-occurring radioactive rock underground. It is considered by the National Academy of Sciences and other health officials to be a "known human carcinogen".
Radioactive drinking water contaminated with radon flows from the taps and shower heads of over 19 million households at levels in excess of the USEPA's proposed (and still not final) standard.
There is no enforceable standard for radon in tap water. For several years, Congress has prohibited the USEPA from issuing a final rule for radon in tap water.
A New York Times article on 9-16-98 by Warren Leary reported the latest conclusions drawn by a 12-member panel of experts convened by the National Research Council which is the research branch of the National Academy of Sciences. Following are the key statements from that article:
- Consuming water containing radon is much less a health risk than inhaling the radioactive gas.
- When radon from drinking water passes into the bloodstream from the stomach, it typically is eliminated from the body before it harms other organs
- Radon in water does increase people's overall exposure to the gas but radon in indoor air is the biggest public health threat.
The latest proposed EPA ruling (October 99) is complex and based on a "multimedia mitigation program." The way I understand it, translated for private well systems, as long as your indoor air radon levels are within EPA limits (4pCi/L air) then the limit on water radon is 4000pCi/L.
In conclusion, it appears that the most recent research suggests that the primary risk is from breathing radon. Colorado Water Wizard, Inc,. at this point, is of the opinion that if your level of radon in water is above 3000pCi/L, especially if you have young children in the household, you should explore the options for radon removal for the whole house. A good reverse osmosis unit with a carbon prefilter should remove a large percentage of the radon from your drinking water.
NSF International, the major certification agency for the water treatment industry, is now in the process of certifying reverse osmosis systems for radon removal and concurrently, the product manufacturers are designing the systems so they will pass the NSF certification.
High indoor air radon levels can be caused either by high sub-slab dirt levels leaching into the house or by high water-born radon or both. High water-born radon can increase household air born radon, especially in the bathroom during showering and bathing. It is suggested that you test for both air and water levels. It is further suggested that when you test the air levels, you get professional advice on how best to test - in what locations and over what time periods - in order to get the most accurate results.
Removal of Radon from Well Water Supplies
There are several primary methods of removing radon:
- Water storage for 24-48 hours (cistern) will reduce radon levels by 50% or more.
- Granular activated carbon (GAC) can effectively reduce radon levels. It is generally suggested that GAC not be used with a level of greater than 5,000pCi/L. The issue with GAC is that radioactive "daughter" elements are produced and held on the GAC. Therefore, the GAC bed becomes more and more loaded with radioactivity. Spent GAC can be disposed of by the homeowner in the trash, but legally, a dealer can't dispose of it because it is considered a low level radioactive waste.
- Aeration technology.
Discussion on Aeration Technologies
There are a number of air stripping or de-gasification technologies available. It should be pointed out that aeration is a process of introducing oxygen to the water. An aerator is not necessarily a good device for removing radon although some radon will be removed in the process. Similarly, an air stripper is not the best device for introducing oxygen into the water. The cost of an air stripping system generally reflects its efficiency. Following are some of the air stripping technologies being used:
- Spray-type: water is sprayed into a tank and an air stream is passed through the tank. Removal efficiency is approximately 50-70% unless there is a recirculating system in which case the efficiency can be raised to ~85%.
- Packed tower: water is trickled down through a bed of packing beads while a stream of air is directed up through the bed. Typical efficiency is ~92%.
- Venturi nozzles: water is forced into a thin jet stream which pulls air into the stream. A single-nozzle system produces an efficiency of ~70%.
- Diffused bubble aeration: air is bubbled by diffusers through a tank of water. The more air bubbled and the smaller the bubbles, the more efficient the system. Efficiency ranges between 70-99.9%.
- Sieve tray (shallow tray): a large amount of air is bubbled through water which runs along a tray. Removal efficiencies are usually 99-99.
Table of Radon Removal Efficiencies
| Incoming Radon Level (pCi/L) | Product Radon Level @ Various % Efficiency (pCi/L) | ||||
| 70% | 80% | 92% | 99% | 99.9% | |
| 2000 | 600 | 400 | 160 | 20 | 2 |
| 5000 | 1500 | 1000 | 400 | 50 | 5 |
| 10000 | 3000 | 2000 | 800 | 100 | 10 |
| 25000 | 7500 | 5000 | 2000 | 250 | 25 |
| 50000 | 15000 | 10000 | 4000 | 500 | 50 |
- All require installation of a vent line, typically 4" PVC, and ideally the vent should be directed through the roof line so that the vented air is not drawn back into the house. The vent line needs to be free of leaks. Exhaust air can contain as much as several thousand pCi/L of radon; however, studies have shown that within 5-6 feet of the vent opening, radon levels dissipate back to background levels.
- All require repressurization, namely a jet pump and additional pressure tank.
- Other parameters in the raw water need to be considered, for example, high hardness, iron, or manganese. These can cause fouling of aerator and venturi nozzles, diffusers, and shallow trays although shallow trays are the most resistant to problems because of the large size of the holes involved.
- All of these systems require maintenance to insure that the solenoid valves are working correctly, that the system does not become bacteriologically fouled, and to remove any deposits.
- It is important to bear in mind that radon levels vary throughout the year for most wells. If you have only a single test result, it would be wise to be conservative with the numbers above and realize that the average level for the well could be double the single test level.
- It is highly recommended that you repeat radon tests on a periodic basis to ensure that your system is operating well.
If you have questions about your water or are concerned about your known radon levels, please contact Colorado Water Wizard.
