solidsurfacealliance.org Blog

June 10th, 2008
Major break through today on setting safe levels for granite countertops. A few weeks ago, Christina, my better half, contacted the EPA asking about granite slabs with specific levels of radiation.

They responded by asking for more time, then about a week ago, they responded by changing their online position on Radon and granite countertops, recommending that granite countertop owners have their homes tested for Radon.

Today, we received further information, including some info on what is considered a safe level of radiation in granite.

Below are some exerts from the letter, with the entire letter posted at the end of the article.

“The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.
While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.”
So there it is, official proof that high radiation level granite countertop slabs can be qualified as containing Uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mine able zones to ensure that current and potentially future economic resources are captured by the operation.

Dr. Hans Hensel stated on Garden Web a few days ago, that granite with veining pegatites were in high demand as countertop slabs, and that they were distinctive and unusual looking. The rest of the paragraph talks about the normal process of drilling core holes and mapping the Uranium deposits so that maximum use of the mining claim is taken. Outliers are dykes or veins that continue outside the main areas of ore.

“See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen. “

The link seems to be broken for now, but here is the granite portion of that table.

All data in pCi/g
EPA average content for granite in table 1.3 in your Uranium Report.
EPA figures RA 226 1.3 U 238 1.3 TH 1.3 K 40 22
————————————————————————————-
Sample M RA 226 986.95 U 235 37.83 TH 144.76 K 40 53.96

Sample N RA 226 312.82 U 235 13.145 TH 36.92 K 40 30.139
Sample O RA 226 156.6 U 235 5.143 TH 22.458 K 40 37.912

Samples M through O are content levels in samples tested from a Bordeaux countertop that was removed earlier this year due to Radon hazards.

As you can see, all three samples from that Bordeaux countertop were much, much, higher than what the EPA said is average. Hundreds of times higher in some cases. You can also see that despite MIA expert Dr. Hans Hensel claims that most of the radiation in granite countertops comes from Potassium 40 ( K 40), in fact most of the radiation comes from Radon and Thorium.

“Assuming that the readings were accurate, a measurement of 7 micro Roentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk. “

The readings are accurate, we had three of the same meter measuring the Niagara Gold slab, and all read the same. A check source came with our Leni Geiger counter, and the meter was calibrated before shipping by an expert in the field. In addition, a radiation enthusiast used his other methods of measurement to confirm that our meters were accurate and calibrated correctly. We find the questioning of the levels understandable, in this case, this expert had no idea that such radioactive granite countertop slabs were being imported. Note that the EPA expert said that “could, under certain circumstances, pose a problem however for some people.

“Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe. “

So there it is, even the EPA says that the radiation risks are unknown…… This is not good.

“Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop. “

Early on, after getting our meters, I chose 20 uR/hr as an arbitrary level of radiation that a hunch told me was the dividing line between good granite and dangerous granite. Turns out that I was pretty close. Much of the “hunch” came from reading for months on this subject, some of it must have soaked in.

Twenty microRems per hour is written as 20uR/hr. In the coming days, as our radioactive granite data gets posted, you can use this figure to put readings in perspective. One thing, though, they using this figure not on contact as we are, they are holding the meter about 3 feet off the ground. So to get exact figures, we will need to start measuring 3 feet away from the slab. And some granites will exceed this, as much as 150 uR/hr at three feet in the case of Four Seasons.

The rest of the letter is about fabrication shops like ours, the dangers from working a high level granite and the steps we should take to prevent problems. After reading that section, one wonders why the granite industry generally wants to derail the testing effort. It seems they and their employees have more to be afraid of than homeowners in most cases.
We will be replying tomorrow, outlining our check sources and quality control methods used in testing, as well as asking if the Juparana Bordeaux countertop was a risk to the homeowners before it was removed.

Here is the emai from the EPA, I removed the authors contact info so he doesn’t get a bunch of hate mail.

Dear Ms. Weigel,
Thanks for sending all this research information. I will try and address your concerns.

Uranium, radium, and thorium are natural constituents of the wide number of mineral species occurring as crystals which can be found in granites from around the world. Some granites are more radioactive than others, depending on the geothermal fluids present in the matrix which then cooled to form the mineral grains.
The presence of radium and thorium in the mineral matrices can decay into radon which may be released over time through radioactive decay. The presence of these minerals in an igneous rock matrix (which includes granites) rather than sediment acts to decrease the radon flux rate however. The available data on the contribution of radon emissions from granite countertops to the indoor air level in homes is too inadequate to allow us to comment about it at this time.

While most granites used for building stone may not be considered harmful from a radiological viewpoint, some granitic deposits in the U.S., Canada, and elsewhere in the world, as you pointed out, host economically recoverable concentrations of uranium ore.

Due to the economics of extraction, miners searching for uranium in granitic rock tend to look for concentrations primarily in intrusive veins or pegmatites. These ore bodies tend to be distinctive looking and separate from other parts of the surrounding “country rock” granite–this is the case for Namibian deposits for example. It is possible that enrichment could be found in adjacent host rocks, as either outliers of the commercial ore zones or an increase in naturally occurring radioactive minerals in the “country rock” used by quarries. However, most prudent mine claims, leases, or license boundaries are located if possible outside the mineable zones to ensure that current and potentially future economic resources are captured by the operation.

See Table 1.3 of our uranium report, volume 1, http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1.pdf which illustrates the average naturally occurring radionuclide concentration values for igneous and sedimentary rocks, but this does not include the variations in range for each. The numbers below would not cause concern in a well-ventilated kitchen.

Radiological testing of imported, or domestic, granite is not a common practice. There have been numerous studies on the contribution of building stones to background radiation, and some limited studies on comparisons of radiological levels between different granites.

One problem in conducting the research you cited is that radiation detectors must be checked against a source of a known radiation level (check source) to verify that its readings are accurate. The divergence in numbers you cited for the Brazilian sample using different machines suggests checking their accuracy might be useful. Assistance from geologists, health physicists, or other licensed radiation professionals would be helpful in this instance–you might want to inquire at Oklahoma State University, or the Oklahoma Department of Environmental Quality’s Radiation Management Section, both in Oklahoma City, for example.

Assuming that the readings were accurate, a measurement of 7 microRoentgens (microR) per hour would be considered a background reading from average soil and rock samples as naturally occurring radionuclides are found in most everything. The much higher readings you cite from the Brazilian sample and Tacoma slab, if accurate, could, under certain circumstances, pose a problem however for some people. The exposures would have to be continuous (e.g., hours per day) and prolonged (e.g., years) in order for there to be a significant increase in risk. The higher the exposure, the less time would be needed to create a higher risk.

The dose of radiation an individual receives is based on the amount and types of radiation (gamma, alpha, beta for example), distance to the radiation source, shielding (useful primarily for alpha or beta radiation, not so much for gamma), and time of exposure. When measuring the dose rate with a meter, health physicists will examine the radiation level both at the source, and at a distance (in a room’s center for example, with the measurement at waist level) to more objectively portray the likely exposure of an individual. Data at this time is inadequate to characterize the radiation risk posed to individuals who spend extended periods of time in close proximity to countertops with the elevated levels of radiation as you describe.

Federal and state agencies generally provide controls for exposures of members of the public to radioactive substances. Without going into a lot of detail on this topic, EPA and some State agencies have used an exposure of 20 microR/hour as a remediation action level for entire rooms, homes or buildings. Any review of the contribution of countertops to overall dose from radiation and radon in a home would examine, among other factors, time spent in a kitchen versus other living and sleeping areas, which minimizes the exposure from a single source such as a countertop.

Occupational exposures to stone cutters, cabinet or carpentry employees is another concern. In such instances, the potential for increased direct radiation, inhalation, and ingestion of particles as well as radon gas might be increased in shops where large amounts of stone with elevated levels of radiation are stored and worked. There are a few immediate courses of action you may be able to take. The first would be to take radon measurements in the workplace with charcoal canisters (generally available at larger hardware stores or online) or other radon detectors. If so, place them in accordance with the manufacturer’s/laboratory instructions in locations likely to be accessed by workers (though probably not on top of one of the suspect granite slabs). Also, carefully follow the instructions on handling, packaging and returning the devices for analysis. Although EPA does recommend an action level of 4 picocuries/liter of air for homes, schools, and a few industries (drinking water treatment and sewage treatment plants), you may wish to consider the advisability of increasing indoor ventilation should your own readings equal or exceed that level. Secondly, consider having a licensed health physicist conduct a radiation survey of your shop and make recommendations on health and safety practices to minimize worker exposures to radiation. Again, the Oklahoma Department of Environmental Quality’s Radiation Management Section may be able to provide you with some additional guidance or list of qualified radiation specialists.

I hope this information is helpful. Please contact me if you have any further questions.

(Mr.) L S

Geologist
U.S. Environmental Protection Agency

1200 Pennsylvania Ave., NW
Washington, DC 20460