Ask A Scientist Chemistry Archive

(Created prior to 1993)

Question:  Is radon really that much of a problem in the US, and if so what 
areas have the greatest problem?
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There is some radon seeping out of the earth almost everywhere in 
the country.  There are some areas with higher concentrations of uranium and 
radium, etc., than others.  The region along the Virginia and Tennessee border 
is high because of the clay.  The problem in houses is that with new standards 
of keeping air inside a house longer, to save heating energy, the levels of 
radon can accumulate.  Since we breathe it into our lungs, we are exposed to a 
greater risk from this radiation.  Usual fix is to close cracks into the soil 
around the basement so no gas can come out of the ground and to keep the air 
moving through the house.  I believe the EPA has some information about this 
and expect that Consumer Reports or other popular magazines will have several 
articles from a few years ago.  I think that  $500 for a test is a little 
steep.  There are inexpensive measurement devises that can be bought at 
hardware stores or can be acquired by contacting the state government that 
will assess the level of radon in the house.  
Sam Bowen
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The EPA is not the only government agency which is warning people 
about radon buildup in basements!  The American Lung Cancer Association says 
that radon gas is the second leading cause of lung cancer in the United States 
( after smoking).  Also, the cost of testing for radon should be quite 
inexpensive.   The test should cost about $50 when done by a reliable firm.  I 
would advocate contacting the local office of the EPA and asking about radon 
testing.
Topper
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Radon gas is a problem in any area of the country that has uranium in
the underlying geology and an access pathway to the occupied underground
portions of a building. Radon contamination has nothing to do with
human-made pollution or careless environmental practices because radon
originates in the radioactive decay of uranium found in almost all
soils.
The singular physical property which distinguishes radon from its decay
progeny is, unlike the others which are all solids, radon is a
colorless, odorless, invisible gas. When it decays, it forms tiny solid
particles (atoms, technically referred to as progeny, or Radon Decay
Products (RDPs) in the more familiar vernacular) which are also
radioactive. These attach themselves to airborne dust which can be
inhaled which can be inhaled and imbedded in the epithelium of the lung.
Therein lies its major lung-cancer inducing property.
Radiation from radon and its RDPs has sufficient energy to disrupt
chemical bonds, damage living tissue — and sometimes induce lung cancer.
The cancer-inducing capability of radon and its radioactive decay
products is not being overstated. The question is: At what exposure
level does the risk become significant?

The U.S. EPA has set 4.0 pCi/L as the action level for radon mitigation.
That level was established based on scientific and EPA assessments of
lung cancer incidents which occur in American and European uranium
miners. It matters not at all that other nations may have selected
higher action levels for their populations. Our EPA chose to opt on the
side of greater occupant safety for American citizens.

It should be recognized, although 4.0 pCi/L is the current EPA action
guideline, that level and its estimated associated risk equivalent of 2
lung cancer deaths per 1000 non-smokers, are currently based on the
assumption that one will spend 75 % of a 70 year time span in the
contaminated space.

Those who smoke and occupy radon-contaminated spaces are put increased
risk (about 29 deaths per 1000 at the 4.0 pCi/L level) because smoke
particles act as adsorption nuclei to which radon's decay products — all
but one of which are radioactive — may be attached and transported to
and thereby embedded in the lungs. In addition, children, because they
are growing so rapidly, are more sensitive to the effects of
cancer-inducing radiation than are adults.

In April of 1993, the EPA proposed a set of "voluntary guidelines" for
radon-resistant new construction. Although residential real estate has
been relatively immune from EPA involvement, Washington observers
predict the EPA will ultimately mandate residential properties be tested
for both leaded paint on interior surfaces and radon. So far, that has
not occurred.

Some other Considerations:

Short-term radon levels in structures can be significantly affected by
the weather. In general, other factors being equal, radon levels will be
higher shortly after arrival of a low pressure air mass;
correspondingly, they will be lower shortly after the onset of a high
pressure air mass. Soon after a heavy rain, indoor radon levels tend to
rise when the gas flow is diverted toward the unsaturated soil near the
structure. Radon is relatively soluble in water. If a home has an open
unvented sump-pit, radon can enter the basement at that point.

Environmental and Structural  Influences:

Radon Levels are affected by:

Home design and construction
Structural cracks and pores in basement walls and floors
Sub-soil composition
Sub-soil moisture level
Soil adsorptivity and permeability
The amount, condition, and location of nearby vegetation
The radon content of the home's potable water supply
The radon content of natural gas supply (ordinarily this is
insignificant)
The season (open- vs closed-house conditions)
Indoor / outdoor temperature differences
Barometric pressure
Wind velocity
Rainfall amounts and intervals

How is radon mitigation accomplished?

As mentioned earlier, radon is a radioactive gas generated by the decay
of uranium in the soil surrounding the foundation and basement slab
(floor). If radon is being generated in the deeper underlying geology,
and if there is a relatively unimpeded pathway from its points of origin
to the structure, radon can move quite a distance before entering the
home. Radon enters the home through cracks and holes that may be present
in the basement walls and floor. It can also enter through sump-pits and
exposed earth in crawl spaces.

A variety of complex weather and seasonal factors are involved in the
overall radon entry process. Radon is drawn into (or forced into) a home
whenever the (air) pressure inside the basement is lower than that in
the surrounding soil. If the surrounding atmospheric pressure imbalance
between the soil gases and the interior of the home can be reversed,
radon will be drawn away from the structure.

The most common mitigation approach is referred to as "sub-slab
depressurization." (SSD) In general, SSD operates to establish a
pressure differential that discourages radon entry. Rather than
pressurizing the home to push the radon away — an almost impossible task
— the soil near the home is de-pressurized to draw the radon away before
it has an opportunity to enter.

Typically, a hole (a few inches in diameter) is drilled through the
basement floor, a  small collection cavity  is dug into in the soil or
drainage gravel beneath the slab, and a venting system of plastic pipe
sealed to the hole and terminated with a suction fan is routed through
the home to the outside. The fan is designed to silently and
economically operate 24 hours per day.

If the home has a sump-pump, the pit must be sealed with an approved lid
that enables pump servicing and inspection. Sealing is necessary because
drainage pipes in the underlying and surrounding soil can lead radon as
well as water into the sump pit. Sumps are, therefore, major radon entry
pathways.

If the home has crawl spaces, the exposed soil in them should be covered
with a sturdy plastic membrane (visqueen) which has been sealed to the
walls and, in some cases, power-vented to the outside by the same (or an
additional) SSD system as described earlier.

The overall effect of an SSD radon mitigation is to draw the air out
from under and around the home. In so doing, interior air is swept out
through the same cracks and other entry pathways that formerly allowed
radon entry. At a cost of about a thousand dollars, the process is
almost always able to reduce radon levels to less than the EPA action
guideline of 4 pCi/L Soon after mitigation, the home should be tested to
ensure that the system is operating properly. Inexpensive follow-up
tests can be performed by the occupant yearly thereafter to assure the
system continues to be effective.

Though radon poses a problem worthy of public and professional
attention, effective strategies exist to minimize its impact on public
health.

Mitigation of a radon problem offers two significant benefits:

1.   It improves the home's interior air quality and markedly reduces
the likelihood that occupants will be  exposed to the lung
cancer-inducing effects of radiation.

2.   It adds value to the property and is an assist to the sale of the
home because a known health hazard  has been substantially reduced.

Something to consider before you build a home:

In the design and building stage of the structure, I suggest that you
centrally locate a PVC "passive stack" that originates the gravel under
the slab and terminates through the roof much like the plumbing vent
stack. Such a passive system allows radon beneath the slab to be
convectively vented safely outside. Often, this simple addition to the
home is sufficient to eliminate any radon problem which might have
occurred. If, however, a radon problem is still evident afterward, a
section of pipe in the attic can be removed and replaced with a
specially designed, silent and operationally economical radon fan at an
additional cost of only about $200. The addition of the fan transforms
the passive stack to an active system which greatly increases the
sub-slab airflow. This measure is all but certain to dramatically reduce
the interior radon level.

Considering the low initial cost of a passive stack incorporated during
construction, and the modest cost of adding a fan should one be needed
later, preventative measures taken in the building stage can spare the
builder and homeowner considerable expense and inconvenience when a
concerned buyer enters the picture and a radon problem is discovered
afterward.

If you have more questions about radon, you may contact me by posing
another question on Newton or directly at xenon55@hotmail.com

Regards,
ProfHoff
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