History of Radon in Santa
Barbara
Elevated indoor radon was a surprise and high levels of
radon in the air of Santa Barbara homes are a real surprise! It was just not
expected, and somewhat counterintuitive.
|
At the end of World War II, it was clear that uranium was
important. A national survey found that there was uranium everywhere, albeit at
only a few parts per million in a typical sample of dirt or rock. It was known
that there were areas of elevated uranium in Southern California, but the
associated geologic formations were not determined. In 1984 in Pennsylvania, there was the first big surprise. The home of a nuclear plant worker was found to have background radiation levels that greatly exceeded the limits imposed on the nuclear plant itself. In fact, it was found that this was a rather common occurrence. Houses naturally act as a stack and draw gases from the soil. Two to ten percent of their inadvertent ventilation comes filtered through the soil! |
|
Outside levels of radon are
rarely greater than a few 0.1 radon units, but inside, an average level is
usually about 1 unit and, if the soil is uranium rich, it can be 10 or 20 units
or even 100’s of units.
|
|
Don Carlisle of the Geology Department at UCLA knew about
high uranium in soil levels from the 1950’s. Because of this, he believed that
is was possible that there were high levels in the indoor air of California
homes. Sure enough, he found that the Rincon Shale Formation of the Western
Plate was a uranium-rich formation. Assays of soil and rock from this formation
show that it 20-30 part per million uranium while samples from other formations
typically show a little less than 1 part per million. Most of the populated
areas on this formation are in southern Santa Barbara County. Coincidentally,
the air in homes built on the formation has radon concentrations that are about
the same magnitude as the uranium concentration, 5 to 30 radon units. The soils associated with the Rincon Shale are very distinct. They are a black expansive adobe soil. When they dry in the summer, they form deep cracks. |
This cracking may increase their
surface area and enhance the emission of radon. The shale-derived soils usually
will also include small chips of the brittle shale rock.
The biggest surprise relates to the fact that the high
levels of radon gas are found in Santa Barbara even with its very mild climate.
The EPA has established an action level of 4 units of
radon. If a house is determined to have an annual average higher than this, then
mitigation work should be performed. Various surveys (by UCLA, UCSB, and the
California DHS) have shown that about 70% of homes on the Rincon Shale have
radon levels above this action level. This is in dramatic contrast with other
geologic formations in Southern California; only 1-2% of those houses have
elevated levels of radon.
To see if you live on or near the Rincon Shale formation, please see the map.
