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 EPA/625/6-91/029


Sub-Slab Depressurization for Low-Permeability Fill Material

Radon, a radioactive gas, comes from the natural decay of uranium. It moves to the earth's surface through tiny openings and cracks in soil and rocks. In outdoor air, radon is diluted to such low concentrations that it is usually nothing to worry about. However, radon can accumulate inside an enclosed space, such as a home, posing a threat to people. Radon can seep into the home in numerous ways, e.g., dirt floors, sumps, joints, and tiny cracks or pores in some hollow-block walls. Since radon is a colorless, odorless, and tasteless gas, the only way to detect its presence is to sample and analyze an area's air using a conventional radon measurement test. The higher the level of radon in a home, the more likely an active radon reduction system (such as sub-slab depressurization) may be required. Even though there are other methods available for reducing radon concentrations in the home, sub-slab depressurization is the most common and most effective radon reduction strategy in basement and slab-on-grade houses. Sub-slab depressurization reduces the pressure in the sub-slab environment by exhausting sub-slab gases before they move through floor cracks or openings. A sub-slab depressurization system consists of one or more pipes attached to a fan or blower thereby creating a suction. ub-slab depressurization system can reduce indoor radon levels by 80 to 99+%. Since much of the existing literature about sub-slab depressurization systems addresses slabs poured over gravel or other more permeable materials, this handbook addresses designing and installing sub-slab depressurization systems to work in less permeable fill material.

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Office of Research & Development | National Risk Management Research Laboratory


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