Radon Levels
Radon level of 20 pCi/L: what it means
Short answer
A radon level of 20 pCi/L is very high: five times the action level, and the top row of EPA's risk chart. Confirm it with a second short-term test right away and then fix the home.
Next step: pick the right test for your home. Which test to use
Key takeaways
- 20 pCi/L is 5 times EPA's 4 pCi/L action level.
- More than twice the action level: confirm right away, then fix.
- EPA estimates the average U.S. home at about 1.3 pCi/L; 20 pCi/L is 15.38 times that.
- Confirm a first short-term result this high with a second short-term test immediately.
Where it sits
Is a radon level of 20 pCi/L high?
- 740 Bq/m3
- 20 pCi/L in becquerels per cubic meter, the published figure.
- 5 times
- EPA's 4 pCi/L action level (calculated).
- 15.38 times
- The U.S. indoor average of about 1.3 pCi/L (calculated).
The risk chart puts 20 at about 260 lung cancers per 1,000 people who smoked and about 36 per 1,000 who never smoked, over a lifetime, a smokers' figure about 250 times the risk of drowning. 20 pCi/L is about 740 .
Readings in the 20s are fixable. Even very high levels can be reduced to acceptable levels, and the number and location of suction points a system needs depends partly on the strength of the radon source.
Where 20 pCi/L sits against EPA's and WHO's reference points
Against outdoor air (about 0.4 pCi/L)
50 times the outdoor average (calculated)Against WHO's recommended reference level (100 Bq/m3, 2.7 pCi/L)
Above itEPA's band
More than twice the action level: confirm right away, then fix
What to do
What to do about a radon level of 20 pCi/L
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. For a reading of 20 pCi/L, the steps come to this:
Steps for a reading of 20 pCi/L
Retest right away
20 pCi/L is more than twice the action level, so take a second short-term test immediately rather than wait for a long-term test.Check the first test
Improper testing may give inaccurate results; confirm the device, its placement and closed-house conditions.Fix the home
EPA recommends fixing a home when the radon level is 4 pCi/L or higher. Get estimates from qualified contractors; see radon mitigation.Test after the fix
No sooner than 24 hours and within 30 days after the system starts, then at least every two years.
The full sequence of tests, from a first result to the decision to fix, is drawn on radon testing.
Health risk
The lung cancer risk at 20 pCi/L
EPA's risk chart has a row for 20 pCi/L. It estimates how many people out of 1,000 could get lung cancer if exposed to that level over a lifetime, separately for people who smoked and people who never smoked.
At 20 pCi/L, the chart's lifetime estimate is about 260 in 1,000 people who smoked (250 times the risk of drowning), and about 36 in 1,000 who never smoked (35 times the risk of drowning). The comparisons in parentheses are the ones EPA prints beside the row.
| Radon level | People who smoked | People who never smoked | What to do |
|---|---|---|---|
| 20 pCi/L (740 Bq/m3) | About 260 in 1,000 | About 36 in 1,000 | Fix your home |
These are population estimates from EPA's 2003 assessment of radon risk in homes, not a forecast for any one person. Your own chances depend mostly on how much radon is in your home, how much time you spend there, and whether you smoke or have ever smoked; a former smoker's risk may sit between the two columns. Lung cancer risk is estimated to rise by about 16% per 100 Bq/m3 of long-term average radon.
EPA's whole chart, from outdoor air to 20 pCi/L, is drawn on radon levels.
How sure
How certain is a reading of 20 pCi/L?
One test is a sample of a level that moves. Radon levels tend to vary from day to day and season to season, so a is less likely than a to show the year-round average, and levels can change from hour to hour. A single short-term result of 20 pCi/L is a reading for those days.
Where the test sat matters as much. A test belongs in the lowest lived-in level, and levels are usually higher in basements and rooms in contact with the ground. Testing is the only way to know the radon level in a specific building. Placement and are on radon testing.
With a system
How much a radon system would lower 20 pCi/L
Each technique has a typical reduction range, and with today's technology radon levels in most homes can be reduced to 2 pCi/L or below. Applied to 20 pCi/L, the low end of each range gives the figures below: our arithmetic on the published ranges, not a prediction for your house. Only a test after installation shows what a system achieved.
| Technique | Typical reduction | From 20 pCi/L, about |
|---|---|---|
| Active sub-slab suction (the usual system) | 50 to 99 percent | 10 pCi/L or lower |
| Sump-hole suction | 50 to 99 percent | 10 pCi/L or lower |
| Drain-tile suction | 50 to 99 percent | 10 pCi/L or lower |
| Submembrane suction (crawl spaces) | 50 to 99 percent | 10 pCi/L or lower |
| Passive sub-slab suction (no fan) | 30 to 70 percent | 14 to 6 pCi/L |
Which technique fits depends on the foundation; see radon mitigation systems, and for cost, radon mitigation cost.
Situations
Where people meet a reading of 20 pCi/L
20 pCi/L in three common situations
20 pCi/L on a first test
Check how the test was run. Improper testing may yield inaccurate results and require another test, and disturbing the device or the closed-house conditions may invalidate the result.Designing a system for 20 pCi/L
With a strong radon source, the number and location of suction pipes matter, and the contractor may need to run diagnostic tests during the first phase of the installation.20 pCi/L after a mitigation system
As a post-mitigation result, 4.0 pCi/L or greater means fix the building, and with a system already installed, more work may be needed to lower the radon further. Many contractors guarantee to adjust or modify the system to reach a negotiated level.
Retest
When to retest after 20 pCi/L
20 pCi/L is five times the and the top row of EPA's chart. Take a second short-term test immediately. After the fix, the two- to seven-day test within 30 days of the system starting shows how far it came down.
| When | What to do |
|---|---|
| To confirm the first result | Immediately, with a second short-term test |
| After a system is installed | No sooner than 24 hours and within 30 days, with a two- to seven-day test |
| With a system in place | At least every two years |
| After a remodel | In the lowest lived-in area |
The general answer is on how often should I test for radon.
Questions
Radon level of 20 pCi/L: questions
Is 20 pCi/L of radon safe?
No. 20 pCi/L is at or above EPA's 4 pCi/L action level, where EPA recommends fixing the home once the result is confirmed.
Do I need radon mitigation at 20 pCi/L?
Yes, by EPA's guidance, once a long-term test or the average of two short-term tests confirms the level is 4 pCi/L or more.
What is 20 pCi/L in Bq/m3?
It is 740 Bq/m3, the figure EPA prints for it.
Should I buy a house with a radon level of 20 pCi/L?
A high level is fixable. Buyers and sellers should discuss the timing and costs of radon reduction, and the contract can say when mitigation happens and who pays. See should I buy a house with radon.
Is 20 pCi/L in a basement different from upstairs?
Usually the basement reads higher. Levels are usually highest in basements and rooms in contact with the ground, though considerable levels can occur above the ground floor too. A test belongs in the lowest lived-in level.
How long should I wait to retest after 20 pCi/L?
Do not wait: a first short-term result more than twice the action level calls for a second short-term test immediately.
Can a home at 20 pCi/L get below 4?
Even very high levels can be reduced to acceptable levels. Across the 50 to 99 percent typical of active soil suction, 20 pCi/L would fall to somewhere between 10 and 0.2 pCi/L (our calculation), so the post-mitigation test is what tells you.