Radon Mitigation on Spokane's South Hill

The South Hill is basalt country, and plenty of owners assume rock means low radon. The state's test records say otherwise. In census tracts within the 99203 and 99223 ZIP areas, between about a quarter and a half of reported tests reached the EPA action level. That is lower than much of Spokane, but far from rare.

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48-hour test from $195 · Systems from $1,295 · Post-mitigation test included

How it works in South Hill

1. STEP 1
   Test

   A 48-hour continuous monitor in your lowest living level, under closed-house conditions. Report the same day it comes out.

2. STEP 2
   Look and quote

   We check the foundation, run a suction test and plan the pipe route for South Hill winters. You get a fixed price in writing.

3. STEP 3
   Install

   Most systems take one day: suction point, sealing, fan, manometer and the electrical permit.

4. STEP 4
   Re-test

   A post-mitigation test at least 24 hours after the fan starts shows the new number. The guarantee is below 4.0 pCi/L.

Radon mitigation cost in South Hill

Basalt close under a slab can keep suction from spreading, so a pressure-field test comes before the quote, and some South Hill houses need a second suction point. On finished older homes, routing is usually the harder question: an interior chase or a tidy run up the back wall. The fan runs on Avista power inside the city.

Starting prices include the electrical permit and the post-mitigation test. Bold: systems common in South Hill homes. Estimate your system →

for a typical 60-watt fan running around the clock. Energy charge only, at 2026 residential rates.

A 20-watt fan costs about a third of that, a 90-watt fan half again as much.

Permits and local rules in South Hill

South Hill at a glance

Area figures describe the neighborhood, not your home. Only a test tells you your number. Sources are listed at the end of this page.

What's under the South Hill

HistoryLink describes Spokane's first fine neighborhoods as rising on the basalt-strewn heights above downtown, and the rock is still in plain view. In Rockwood it breaks the surface all over the neighborhood; it set where streets and lots went a century ago, and native rock walls are everywhere. In Lincoln Heights, outcrops and ridgelines bend streets into curves and dead ends.

Under the southern part of the hill and the High Drive bluff, the state's geologic map shows something more layered than solid rock. Dense Columbia River basalt flows alternate with soft, poorly cemented Latah Formation siltstone and claystone, some of it saturated with water. Over that lies a cap of wind-blown silt, mostly montmorillonite and illite clay, usually just 1 to 2 feet thick here and thicker to the south, where the Ice Age floods scoured less.

Even the hill isn't uniform. In the 1880s a clay deposit turned up where Cannon Hill Park is now; it was dug for bricks, and the pit became the park's wading pool. State test records for census tracts within ZIP codes 99203 and 99223 range from 25.7% to 52.7% at or above 4.0 pCi/L, and 9 of the 11 tracts fall below the county-wide 47.0%. Below average still means about one test in four or more came back high.

typical thickness of the clay-rich wind-blown silt over basalt and Latah beds on the southern hill⁷

South Hill questions