Radon. What does 4pCi/L mean and why is it important?


What does 4.0pCi/L represent?

By Frank J. Delle Donne, Licensed Home Inspector

January 16, 2014

About the author.  I am a NJ Licensed Home Inspector.  I am the owner and Senior Inspector at Regal Home Inspections, LLC.  I have been a volunteer Emergency Medical Technician for over 20 years and was  a past member of the Colts Neck, NJ Board of Health and was Chairman of that Board for 2008 and 2009.    During my studies to become a Home Inspector and earning my NJ Certification to be a Radon Measurement Technician I learned a great deal about Radon and felt compelled to share that information in a manner that is easy to understand and increases awareness.  Every home in New Jersey should be tested for Radon on a regular basis.  Regal Home Inspections, LLC is having a New Year 2014 SPECIAL on Radon testing.  These discounted prices are good through February 28, 2014.  Please call now to schedule your Radon test.

The federal Environmental Protection Agency (EPA) has been leading the effort to make citizens aware of radon and closer to home, the NJ Department of Environmental Protection (NJ-DEP) has been following suit.  Please read our earlier post for general information about radon.   This piece is intended to explain the measured results; When is it an issue and when is it not?


A few points that I’d like to repeat from the earlier article is that radon is everywhere and it is naturally occurring.  It is a radioactive gas which means that it transforms spontaneously and in that transformation it releases tiny bursts of energy.  It is these tiny bursts of energy that cause harm.

Radon, like other radioactive materials, are measured in pCi/L.  This stands for pico Curies per liter of air.  A “pico Curie” is one-trillionths of a Curie.  A Curie is equivalent to 37 Billion radioactive disintegrations per second.  Therefore one pico-Curie works out to 2.2 radioactive disintegrations per minute (dpm) in a liter of air.  A “Curie” is of course named after Marie Curie who lived in the late 1800s to the 1930s.

Action Level

The EPA (and NJ-DEP) refers to 4.0pCi/L as measured over a minimum of 48 hours as the Action Level for radon mitigation.  This applies uniformly to real estate transactions and for the self motivated homeowner who tests for radon, they too should mitigate at this, measured level.

As mentioned in the previous article, the radioactive disintegrations take on three different forms.  There is Alpha radiation, Beta radiation and Gamma radiation.  The result of a, “disintegration” is a new element (Polonium, Lead, Bismuth or Radon) but the process that the atoms change also releases energy in Alpha, Beta or Gamma form.

At 2.22 dpm per pico Curie at 4pCi/L (assuming each one of your lungs holds a liter of air) that’s 16.88 (8.44 per lung) radioactive disintegrations that are occurring inside your lungs!  While these releases of energy are extremely tiny, they have the potential to damage cells and DNA.  This can lead to the events that begin the formation of mutant or cancerous cells.

So is 3.5pCi/L that much better?  Not really but for the real estate transaction, a radon test measurement that reads 4.0pCi/L will result in a letter from the buyer’s attorney to the seller/seller’s attorney stating that the seller must mitigate the radon and provide new test results that show the level is, post mitigation, less than 4.0pCi/L.

At or above 4.0pCi/L and a letter is coming.  A reading of just below 4.0pCi/L may ask for a second test where the two tests might be averaged.  Rest assured that at or above 4.0pCi/L and the seller will be calling a radon mitigation company.


Radon mitigation comprises of a system, usually a vent, that will reduce the measured radon inside at the lowest, “livable” area.

A very common type of mitigation system is a sub soil depressurization system.  In this method, a pipe is placed below the concrete basement floor.  That pipe (usually a 4” PVC pipe) is routed to the outdoor and a fan is placed to draw the air (and radon) from below the basement floor and vent it to the outdoors before it enters the house.  With this system the basement floor has to be sealed which means that sump pits are sealed and French drains are sealed.   Also, any cracks or other basement floor penetrations must also be sealed for the sub soil depressurization system to be most effective.

The white pipe is the radon mitigation system pulling air and radon from below the basement floor, up and outside before the radon gas enters the house. The area of the vent system that bulges out is a fan. The fan runs constantly.

The cost for such a system can be as low as $1500 but based upon many factors could be higher.   After the system is installed and activated, it should be left operation AT ALL TIMES.  It should be operating for at least 12 hours to allow “Dynamic Equilibrium” to occur.  This is a fancy way for saying that the positive effects of the new mitigation system should be set in place after 12 hours.  After this period of time a post-mitigation test must be done to ensure that the mitigation steps were successful.  In some cases secondary or tertiary mitigation steps must be taken to achieve a reading below 4.0pCi/l.  If for example your initial test reading was 8.0pCi/l and the first mitigation effort reduced the radon by 25%, Post-Mitigation test #1 may indicate a 25% drop but that’s still 6.0pCi/L.  A second mitigation system may have to be added which may reduce the radon by another 25%.  6.0pCi/L less 25% is only a 1.5pCi/L reduction so you STILL may be above 4.0pCi/L.  A third mitigation system may be necessary to finally get you below 4.0pCi/L.


Radon is a serious health issue but it can be minimized.  Likely, it cannot be eliminated.  It’s naturally occurring and exists in nature.  It’s not man-made nor can we stop it from existing.  We can, however, minimize its pathways into our homes and help ensure a healthy and safe environment.

Please call today to schedule your  radon test for your family.  Discounted prices are valid for tests started by February 28, 2014.  Please mention, “Radon Discount” when you call.  Also, if you need radon consultation, Regal Home Inspections, LLC can help guide you through the testing and mitigation process.

I would appreciate your comments about this article.  Please email your comments to frank07722@gmail.com .

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