Sub - Slab Depressurization Demonstration in Polk County

Six slab-on-grade houses in Polk County, Florida, with indoor radon levels between 19 and 80 pCi/1 were mitigated using sub-slab depressurization systems. With the compacted, moist soil fill under the slabs, sufficient sub-slab communications were difficult to establish. Increasing the suction pit size and using more powerful fans improved the strength of the pressure fields within 3 to 8 m of the suction holes but did little to extend them beyond this radius. The most effective means for extending the field was found to be installing additional suction holes (depressurized by the same fan) in locations where the pressure field was the weakest. Suction holes were placed both in centralized and in near-perimeter locations reached either by interior slab holes or through holes in the exterior stem wall. Indoor radon levels were measured using 2-day charcoal canisters, continuous radon monitors, and long-term (3 mo-1 yr) alpha track detectors. This paper has been reviewed in accordance with the U.S.Environmenta1 Protection Agency's peer and administrative review policies and approved for presentation and publication.