New town, old soil

Harrisburg is one of the fastest-growing towns in South Dakota, and its housing shows it: whole neighborhoods date from the mid-2000s onward, and framing crews are still working the edges. Most of the stock is new two-stories and ranches with poured-concrete basements, many of them walkouts backing onto ponds and drainage swales, built tight to modern energy code.

None of that newness reaches the dirt. Harrisburg’s subdivisions sit on the same gas-rich glacial ground as the rest of Lincoln County, which the EPA maps as Zone 1, its highest radon-potential category. A 2022 build on a fresh cul-de-sac can test higher than a 1950s house in central Sioux Falls, and the tight envelope that keeps January heating bills down also keeps soil gas in. Fresh concrete even lends a hand in the wrong direction, since new slabs cure, shrink, and open hairline paths at the edges.

Harrisburg’s saving grace is hiding in its mechanical rooms. Because the town was built during the era when radon-resistant construction went mainstream, a real share of its homes carry a passive rough-in: a capped, often labeled vent pipe the builder ran through the framing for exactly this purpose. It’s a builder-by-builder coin flip, not a sure thing, but when the pipe is there, fixing a high test is dramatically simpler work.

No Harrisburg-specific numbers exist. The state program publishes at county grain, and the published picture for this corner of the state lives at radon levels in your area. For your address, the number comes from a test.