The Sierra Nevada boasts world-class ski areas, epic snow packs, and unparalleled recreation opportunities. Unfortunately, it also boasts some of the highest levels of radon in California and Nevada.

When you think ‘radon,’ a low-budget sci-fi movie might pop into mind. But radon is a naturally occurring radioactive gas produced by the decay of uranium, an element present in granite, the very rock that forms much of the Sierra’s spectacular scenery. Radon is colorless, odorless, and according to the surgeon general, a Class A carcinogen.

Normally, radon filters up through the soil and disperses at low levels into the atmosphere. Out of doors, this doesn’t present a problem. But if radon surfaces underneath a building, it can seep inside the structure and become trapped, rising to levels hundreds of times higher than those outdoors. In the U.S., radon exposure is believed to cause an estimated 20,000 lung cancer deaths per year, a toll second only to cigarette smoking.


Radon-producing soils are not unique to Tahoe, or even to mountainous areas. The degree of risk depends on many factors, including the soil type (granites, shales, and phosphates are primary sources), soil permeability, moisture content, and presence of faults or cracks. In 2009, the California Geological Survey published a study assessing radon risk on the California side of Lake Tahoe. Included in the study was a map of Radon Potential Zones, with areas of very high risk colored a bright, ketchup red.

Looking at the map, it’s obvious that Lake Tahoe sits on extensive granitic soils: The Truckee area is predominately ‘high’ radon risk, with some red patches of ‘very high’ risk that look as if someone dripped a few blobs of ketchup onto the map. South Lake Tahoe, though, looks like someone emptied the entire bottle.

There are few people more familiar with the local radon issue than Jeff Miner. A resident of South Lake Tahoe, Miner tested his own house in 2004 and found unhealthy levels of radon. He took measures to fix the problem, and since then has become a one-man radon activist and spokesperson. His goal now is to raise awareness and encourage everyone to test their homes.

‘The more you know about the risks,’ he says, ‘the more likely you’ll take action.’

Health Risks

‘If radon is inhaled into the lungs,’ explains Miner, ‘it can damage a particular gene that makes the cell unable to protect you from cancer.’ No one can say with certainty how long it takes for radon exposure to manifest as lung cancer — maybe half a lifetime. But the higher the radon levels, the fewer the years it’s estimated to take.

‘The risk of lung cancer is multiplied if you smoke,’ says Susan Howe, director of University of Nevada Cooperative Extension (UNCE) Radon Education Program.

There are no symptoms of excessive radon exposure until late in the game. Once lung cancer is diagnosed, victims often have less than a year to live. ‘Testing is the only way to find out if you have a problem,’ says Howe.

How Tahoe Measures Up

Radon is measured in picocuries per liter of air, or pCi/L. Indoor levels average around 1.3 pCi/L. The EPA recommends taking action if a home measures 4 pCi/L or higher, but the World Health Organization takes a more conservative stance, advising mitigation if a building measures above 2.7.

When Miner tested his own home, he was concerned to find levels of 6 pCi/L. ‘For 24 years I had high levels of radon gas in my house, and didn’t know it.’ Miner isn’t alone; by simple virtue of where we live, many of us are at high risk.

In 2006 and 2007, the California Department of Health (CDH) tested radon levels in 1,700 homes throughout El Dorado, Placer, and Nevada counties; 38 percent registered above the EPA action level.

Among the 392 homes tested in Truckee, 27 percent measured 4 pCi/L or higher. In South Lake Tahoe, almost 40 percent of homes measured at those levels.

In Nevada, the most recent test results compiled by UNCE show that 32 percent of Incline Village homes measured 4 pCi/L or higher. Some of the highest percentages occurred on the East Shore: Out of the 91 homes tested in Zephyr Cove, 60 exceeded EPA action levels. The community of Glenbrook, just north of Cave Rock, carries the dubious distinction of having the highest reading in the entire state of Nevada, at 117 pCi/L.

Despite our area’s risk, only a small fraction of the population has tested its homes. Out of 33,000 residences in South Lake Tahoe, only 1,465 have performed radon tests. ‘Radon is not an immediate problem, and people have a lot on their plates, so they tend to put it off,’ says Miner.

Radon & Your Home

Regardless of whether your house is new or old, radon can find its way inside through cracks in walls and foundations, and around plumbing and utility openings. Radon particles are drawn into a home’s living space by the ‘stack effect’: Since air inside the home is usually warmer than outside air, and because heat rises, a house can literally pull radon out of the earth.

‘Houses are like huge vacuum cleaners,’ says Howe. ‘Fireplaces and kitchen and bathroom fans depressurize your living space. Your house compensates by pulling air from the ground up into the house.’ To put it bluntly, says Howe, ‘your house sucks.’ The problem is compounded in winter, when windows remain closed and less fresh air circulates inside the home.

If your neighbor tests for radon and finds low levels, that doesn’t necessarily mean you will, too. Your house might sit over porous soils, or features such as cracks or faults, which could vent radon directly under your home. In Miner’s neighborhood, one house measured 17 pCi/L while the rest on the block measured 6.

Larger commercial buildings are not immune; any structure can be high in radon, including schools and office complexes. In 2007, parts of Zephyr Cove Elementary tested above 4 pCi/L. Mitigation was successful in reducing concentrations to acceptable levels.

Testing for Radon

The easiest and cheapest way to test the radon level in your home is to purchase a single-use radon test kit for $11 to $20 (see sidebar). These kits measure radon levels over the short term (a few days) or long term (three months to a year), and get mailed back to the company for analysis. Radon detection units are also available; these cost about $120 but are reusable and provide a digital readout over any length of time desired. Another option, often reserved for real estate transactions, is to hire a certified professional tester.

If a short-term test reveals a reading of 4pCi/L or higher, the EPA suggests a follow-up test. For results between 4 and 8 pCi/L, Howe recommends a long-term test. (Since radon levels fluctuate daily and seasonally, a long-term test provides a more definitive result.)

If your initial reading is 8 pCi/L or above, Howe says you should immediately do another short-term test; don’t wait three to 12 months for a long-term confirmation. Average the two short-terms tests, and mitigate if levels are above 4 pCi/L. How dangerous are readings over 4? The EPA estimates that living with 10 pCi/L is equivalent to smoking one pack of cigarettes a day.

Fixing the Problem

The good news is that it’s possible to mitigate radon exposure in your home. Methods vary, depending on the type and square footage of the foundation, but most involve an Active Soil Depressurization system that collects radon particles in pipes and draws them out of the home.

If your home has a crawl space, perforated pipes are placed directly on the soil and connect to a PVC pipe that vents outside the home, preferably at roof level. The entire crawl space area is covered with radon barrier plastic and sealed along piers and the concrete stem wall with a special adhesive. A fan is installed to draw the radon particles into the perforated pipe and outside the house.

Miner installed such a system in his home, and within a week his radon levels dropped from 6 pCi/L to 1.
The cost of mitigation ranges from $800 to $5,000, depending upon the construction of your house, but averages around $1,200 nationwide.

Unfortunately, bare ground can’t be tested, and there’s no way to predict if, or how much, radon will accumulate in a home. That’s why in high radon areas the EPA recommends building in radon resistance during a home’s construction. Radon-resistant new construction is estimated to run between $500 and $800 per home, though cost depends on whether the owner, general contractor, or certified mitigator does the work.

Derrick Carpenter, a certified mitigator based in Gardnerville, Nev., says he can retrofit a home in about three days. During new construction, however, Carpenter has to make multiple trips to install segments of the system as the home’s walls and roof are built.

Carpenter stresses the importance of using high quality, EPA-recommended materials that will resist tears and punctures, and last the life of the home. ‘Not all mitigators use high-quality materials,’ he says. ‘And be wary if a mitigator only wants to install a fan in the crawl space.’ This technique is strongly discouraged by the EPA.

You can save money by doing the work yourself, says Miner, who is certified in radon mitigation, but it’s important to know what you’re doing and take the necessary health precautions. Since mitigation de-pressurizes the crawl space, it can change the pressure inside the home, in some cases causing gas appliances to backdraft carbon monoxide into the living space. Before attempting do-it-yourself mitigation, Miner emphasizes reading Doug Kladder’s book, ‘Protecting Your House From Radon,’ available from UNCE or Miner’s website, (see Radon Test Kits, at left).

Miner has proposed that a local radon ordinance be adopted for new construction, but so far he’s met resistance. He’d also like to see testing and disclosure during real estate transactions. Currently, the Natural Hazard Report provided to buyers lists radon risk in Tahoe as ‘moderate,’ an assessment based on 30-year-old EPA data. The more recent 2009 California Geologic Survey report, however, confirms that radon risks in Tahoe are much higher. In the survey’s study area, which spans from Truckee to South Lake Tahoe, an estimated 28,000 people live in ‘very high’ risk zones, and another 9,100 in ‘high’ risk zones.

The U.S. Green Building Council’s LEED certification program even considers Tahoe a ‘moderate’ radon area and does not require radon mitigation to be built into LEED-certified homes. David Gemme, local realtor and vice president of the Sierra Green Building Association says, ‘Everyone should be aware that radon exists, and should test for it. But I can’t see the town jumping on board and creating legislation around it.’ When it comes to radon, Gemme says, ‘We should educate before we legislate.’

~ Comment on this story below. If you’ve had your home or office tested, share your results with us.


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