Updated · Rapid City, South Dakota

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

  1. Suction point: A hole through the slab into aggregate or soil, or a sealed crawl-space collection point.
  2. Piping: Usually 3–4 inch PVC routed through a closet, garage chase, or exterior wall.
  3. Fan: Continuously runs to maintain sub-slab vacuum.
  4. Exhaust: Discharges outdoors, away from windows and air intakes, typically above the roof eave.
  5. 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.

Pressure Field Extension (PFE) and Diagnostics

Professional radon mitigation relies on scientific diagnostic testing called Pressure Field Extension (PFE). Rather than guessing where to drill suction pits, a certified mitigator drills small test holes through the slab at opposite corners of the home. Using a high-sensitivity micro-manometer, the technician measures how effectively negative air pressure travels through the sub-slab crushed rock, aggregate, or native soil.

If the sub-slab material has low air permeability—such as dense clay common in parts of Rapid Valley or compacted fill—a standard single-pipe installation may fail to depressurize the perimeter. Diagnostics dictate whether the home requires high-flow versus high-suction fan impellers, larger 4-inch trunk lines, or multiple routed suction drops to ensure continuous vacuum beneath 100% of the building footprint.

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

  1. U.S. EPA. Consumer’s Guide to Radon Reduction: How to Fix Your Home (EPA 402/K-10/005). epa.gov/radon/consumers-guide-radon-reduction
  2. ANSI/AARST. Soil Gas Mitigation Standards for Existing Homes (SGM-SF-2023). standards.aarst.org
  3. National Radon Proficiency Program (NRPP). Radon Mitigation System Installation & Inspection Standards. nrpp.info
  4. South Dakota Department of Health. Mitigating Radon in South Dakota Residences. doh.sd.gov/programs/radon

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Need a local next step? Call (605) 600-6282 to talk through testing, real estate timing, or mitigation for your Rapid City–area home.