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What is karst?
Karst is carbonate rock containing solution cavities. It is a geologic condition characterized by sinkholes, underground streams and caves where groundwater has dissolved the sedimentary rock. Where the dissolved rock is on top of a geologic formation high in uranium or radium, radioactive radon gas produced by those formations can more readily move into houses and buildings above.
Karst causes variability
Fissures serve as conduits that channel radon gas to the surface, causing unpredictable flow rates and patterns of movement that can vary with seasons and outside environmental conditions.
Seasonal variations in indoor radon measurements are greater in karst areas than in non-karst areas. Weather and seasonal conditions can cause spikes and dips in radon levels. Short-term tests often show that houses have higher radon levels in colder months (November through February). However, there are houses that do test higher in warmer months (May through September). To account for variability issues, a year-long test will give you the best picture of your home's actual radon level. An Alabama karst variability study has shown that approximately one-third of the homes tested (with short-term tests) in karst areas in the summertime had FALSE negative results and when tested in the winter had a radon problem.
NON-REAL ESTATE TRANSACTION TESTING
(For homeowners testing their own homes, not in the process of buying or selling the home.)
Testing with initial year-long test
Twelve-month radon testing is recommended in state radon program identified karst areas because radon levels in structures located in these areas can vary significantly.
Testing with initial short-term tests.
In karst and non-karst areas, always base your decision to take or not take corrective action on the results of follow-up confirmatory tests, not on a single short-term screening test only.
For further guidance, refer to EPA Region 4 Guidance memo dated Feb. 9, 2005 (PDF document). Additional guidance may also be found in the EPA's A Citizen's Guide to Radon and Home Buyer's and Seller's Guide to Radon when you do follow-up testing or make mitigation decisions.
Further Recommendations
- Periodic retesting is recommended every two years in unmitigated structures.
- If you choose to mitigate based on the results of a short-term test, confirm that the mitigation system is adequate by using a 12-month post-mitigation test.
- If you are planning any renovations with major structural changes, always test the structure before starting the project and after the project is completed. Installing a radon-reduction system before (or during) renovations is less expensive than installing one after renovations are complete.
REAL ESTATE TRANSACTION TESTING
If you choose to base your real estate transaction decisions on a short-term test in karst areas, follow-up with a 12-month confirmatory test immediately (or soon after you move into the home).
Testing recommendations for Real Estate Transaction Testing
Where to test:
- Test in the lowest level of the home suitable for occupancy. This means the lowest level that can be used as living space which is finished or does not require renovations prior to use. (If you decide to finish or renovate an unfinished area of the home in the future, a radon test should be done before starting the project and after the project is finished.)
- Do not:
- test in the bathroom, kitchen, laundry room, crawl space, sumps, cupboards, nooks, or closets.
- place test vial in direct sunlight or near excessive heat sources, such as appliances or fireplaces.
- place test vial near drafts, and do not operate ceiling fans in the room being tested.
How to test:
- Observe closed-house conditions: close windows and outside doors for at least 12 hours before beginning the test.
- Do not test during severe storms or periods of high winds.
- Test for no less than 48 hours and no more than 96 hours.
- Fill out the data form for the exact start and end time and date of the test.
- Place the test vial at least:
- 20 inches above the floor
- 3 feet from exterior windows or doors
- 1 foot from an external wall that has no openings
- 4 inches from other objects
- If you need results quickly, request expedited service with the lab handling the test device.
There are three ways to take a short-term test for Real Estate Transactions:
- Simultaneously take two short-term tests at the same time, in the same location (4-inches apart) for AT LEAST 48 hours. Fix the home if the average of the two tests is 4 pCi/l* or higher.
- Sequentially take an initial short-term test for AT LEAST 48 hours. Immediately upon completing the first test, follow with a second test using an identical test device in the SAME LOCATION as the first test. Fix the home if the average of the two tests is 4 pCi/l* or higher.
- Hire a certified radon tester to test the home with a continuous monitor for at least 48 hours. Fix the home if the average radon level is 4 pCi/l* or higher.
*The EPA recommends reducing radon levels that are 4 pCi/l or higher. One measurement used to determine radon levels is picocuries per liter of air. The higher the radon level in your home, the sooner you should take action to reduce your exposure. Radon levels in most homes can be reduced below 4 pCi/l with mitigation.
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