Re: Radon Migration Through Concrete

[bill_goldsmith@urscorp.com]

Ron:  With a couple of assumptions, maybe I can shed some light on the
subject.  First, I assume that the poured concrete is a floor slab.
Second, I assume that the order of magnitude variations are from a few
pCi/L to a few tens of pCi/L.  If these assumptions are correct, then the
variation you are seeing is normal.
Consider two aspects of radon:
   The concentration of Rn in soil gas is on the order of a few thousands
   of pCi/L under normal circumstances.  Rn will diffuse from the soil
   toward a lower concentration (such as room air of a few pCi/L).  Also,
   soil gas will move through the path of least resistance.  If surface
   soil is wet, Rn rich soil gas will move through cracks in concrete.  Rn
   will diffuse through this path more quickly.  Once it has come out of
   the soil, it isn't going to fight the concentration gradient to go back
   into the soil.
   The removal of Rn from the building is by one of two mechanisms: decay
   or ventilation.  The rate for removal by decay is the decay constant,
   about 0.008 per hour.  A "sealed" building will generally have
   ventilation rates on the order of 0.1 per hour.   Hence, the dominant
   removal is by ventilation, which in turn may be influenced heavily by
   wind speed.
Thus, wet soil would tend to pump Rn into the building and natural
ventilation would tend to pump it out.  You would reach a constant Rn
concentration only when the two mechanisms were roughly equal in their
effect.  So, you could expect to see this kind of variation as one
mechanism dominates the other.  The concentration should be higher, but
steadier in winter when ice covers the ground or the first several inches
of ground are frozen.  Hope this helps.
Bill
Bill Goldsmith
Radian Remediation Services
865.220.8265
bill_goldsmith@urscorp.com



                                                                                                 
                                                                                                 
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                    Sent by:                  Subject:     Radon Migration Through Concrete      
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                    06/21/2000 12:47                                                             
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We have a welded steel lined building that has a substantial amount of
poured concrete inside the building.  The building is about 25 years old.

Can anyone provide information, explanations and/or examples that could
indicate how the airborne radon concentration inside this sealed building
could change by a factor of 10 over an 8 day period ?  The change has been
steady for over a month with little or no variation.

Thank you for your time and consideration.

Ron LaVera
Lavera.r@nypa.gov
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