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Alabama Testing Recommendations for Karst Areas

Karse Overview

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 is everywhere in the U.S. View the U.S. Geological Survey map of Karst areas in the U.S. 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.

Page last updated: May 13, 2021