Most common system: Active Soil Depressurization (ASD)—a PVC pipe and inline fan that pull radon-bearing soil gas from beneath the home and exhaust it above the roofline.1
The basic ASD layout
- Suction point: A hole through the slab into aggregate or soil, or a sealed crawl-space collection point.
- Piping: Usually 3–4 inch PVC routed through a closet, garage chase, or exterior wall.
- Fan: Continuously runs to maintain sub-slab vacuum.
- Exhaust: Discharges outdoors, away from windows and air intakes, typically above the roof eave.
- Manometer: U-tube gauge shows the system is pulling.
Sealing still matters
Mitigation is not only a fan. Sealing accessible slab cracks, open sumps (with gasketed lids), and large crawl-space gaps improves vacuum and reduces indoor pathways. Sealing alone rarely replaces an active system when levels are high—but it makes ASD more efficient.
Crawl spaces vs basements
Black Hills homes include full basements, partial basements, and ventilated or encapsulated crawl spaces. Crawl spaces often get a heavy vapor barrier sealed to walls and piers, with suction under the plastic. Mixed foundations may need multiple suction points.
What “success” means
Post-mitigation testing should confirm levels below the action level—ideally as low as practical. Fans wear out after years; plan on occasional fan replacement and periodic retesting. Details for homeowners: mitigation service page.
Sources
- U.S. EPA. Consumer’s Guide to Radon Reduction.
- AARST soil gas mitigation standards (ASD design principles).
Need a local next step? Call (605) 600-6282 to talk through testing, real estate timing, or mitigation for your Rapid City–area home.