Radon in Spokane, WA: What the Neighborhood Data Show

Spokane's radon picture changes with the ground under each neighborhood. North of the river, much of the city stands on deep Ice Age flood gravel; downtown, the river falls over basalt, and Five Mile Prairie is a mesa of granite and lava. State test records follow suit: by census tract, the share of high results runs from about one in six to two in three.

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

How it works in Spokane

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 Spokane 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 Spokane

Inside city limits the fan runs on Avista power, and the city, not the state, permits the circuit. North of the river, gravel usually carries suction well under a slab. On Five Mile Prairie's clay or near basalt, a pressure-field test before the quote shows whether one suction point is enough. In older houses, the bigger task is often finding a clean route for the pipe.

Starting prices include the electrical permit and the post-mitigation test. Bold: systems common in Spokane 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 Spokane

Spokane 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.

Gravel, basalt and lake clay under one city

North of the river, much of Spokane is built on Ice Age flood gravel. It fills the deep old channels of the Spokane and Little Spokane rivers several hundred feet thick: a poorly sorted mix of boulders, cobbles, pebbles and sand, from granitic and metamorphic rock like that found locally and in Idaho. In 1993 the U.S. Geological Survey described the city and its eastern suburbs as built on highly permeable glacial outwash, ground that lets soil gas travel freely.

Other parts of the city sit on different ground. Downtown, the river drops over basalt ledges at Spokane Falls. In the northwest corner, Five Mile Prairie is a 3,400-acre mesa of granite and lava that stands 400 feet high, with basalt cliffs on almost every side. Well logs there pass through more than 100 feet of Latah Formation, a soft, finely layered siltstone and claystone laid down in Miocene lakes. Gravel, rock and clay each let gas through in their own way.

State test records show the result. In census tracts within ZIP codes 99201, 99202, 99204, 99205, 99208 and 99218, the share of reported tests at or above 4.0 pCi/L ranges from 16.1% to 66.9%. ZIP 99205 alone has one tract at 16.1% and another at 62.3%. These are tests people chose to run, not a random survey, but the lesson holds: a Spokane address tells you little about a Spokane basement.

of homes above 4 pCi/L in some townships near Spokane, in data the USGS cited in 1993⁵

Spokane questions