California Geological Survey Maps
Hazardous Gas for Department of Health Services

Picking up where they left off eight years ago, the California Geological Survey and Department of Health Services are teaming up to investigate the potential hazard of radon gas to California citizens.

Radon gas is a naturally occurring, invisible and odorless radioactive gas. As Ron Churchill, a senior geologist for CGS’ Mineral Resources Program put it, radon is a “daughter” of uranium. Over time, the naturally radioactive uranium decays, striving to become the stable, non-radioactive element lead. One of the many different radioactive stages it goes through on the way involves becoming radon gas.

The U.S. Environmental Protection Agency lists radon as the second-leading cause of lung cancer in the United States behind smoking, responsible for up to 30,000 deaths per year.

“A lot of the radon you breathe in, you breathe right out, so it’s not harmful,” Churchill explained. “But if you’re exposed to it over a long period of time – if it collects in your home -- you could inhale enough material to pose a cancer risk.”

Ron Churchill
Ron Churchill
The Department of Health Services contracted with CGS to create radon maps of Ventura and Santa Barbara counties in the mid-1990s and wants to expand that work. Churchill is creating a map for the northwest part of Los Angeles County.

The Ventura and Santa Barbara maps were developed after DHS testing showed that some houses built on a certain type of rock formation had up to 25 times more radon than deemed healthy by the U.S. EPA. The maps show zones where there is elevated radon potential, similar to liquefaction/landslide maps produced by      CGS’ Seismic Hazard Mapping Program or the occurring asbestos map of El Dorado County that Mineral Resources created a couple of years ago.

“Uranium is naturally present in all kinds of rocks and soils,” Churchill said. “There’s just more of it in some places than others.”

CGS’ radon mapping work is built in large part on data from a study of uranium resources commissioned in the 1970s by the since-abolished Atomic Energy Commission. Helicopters were hired to fly over grid lines established across the country. East-west lines are three miles apart and north-south lines are 12 miles apart. Gamma ray detectors were pointed at the ground from 100 to 600 feet up to determine the radioactivity level. Readings were taken every couple of hundred feet along the grid line. Soil samples were also taken at various locations in a related study.

“The detectors couldn’t identify radon directly, but instead looked for a uranium daughter element closely related to radon called bismuth 214,” Churchill explained. “If you see higher levels of bismuth 214, there’s a pretty good chance there will be more radon at that location.”

There’s an eight-year gap between the first two radon maps and the new project not because CGS and Health Services lost interest but because Health Services was unable to provide funding for additional CGS work. This past year Health Services again had funds available. Additionally, the decades-old National Uranium Resources Evaluation (NURE) needed for the radon mapping project only recently became available to CGS in a useful digital format – and only then because of a chance meeting.

Last February, a Palos Verdes High School freshman, Lauren Fukumoto, decided to test for radon at local schools as a science project (it didn’t hurt that her father, Dr. Joseph Fukumoto, is a physics engineer with Raytheon). Her tests showed elevated levels of radon at three campuses.

Churchill was dispatched to Palos Verdes to discuss the radon issue with the Fukumotos and the school district and to observe and provide assistance to a special USGS study measuring bismuth 214 levels in school-site soils. He met geophysicist Joe Duval, USGS’ top radon expert. Churchill mentioned the difficulty CGS had accessing the NURE data. Duval arranged for CGS to receive 34 digital data files that Henry Mumm of DOC's Office of Technology Services painstakingly converted into more useful Microsoft Access files. With the NURE data in its GIS system, CGS is in a position to more easily help Health Services with its radon research.

“Henry was an instrumental part of us being able to use that data,” Churchill said.

CGS is also helping out Health Services with two other radon-related projects.

Churchill, with assistance from Les Youngs and Milton Fonseca of CGS, is providing geological information as DHS conducts a radon survey of Amador, Calaveras and Tuolumne counties. Health Services wants to find volunteers willing to put DHS-supplied radon detectors in their homes. The detectors are simple and inexpensive: a piece of foam surrounding activated charcoal that absorbs radon. The volunteers will leave the detectors in their homes for about a week, then seal them up and mail them to a lab where the level of radioactivity is determined.

Health Services is also looking into the radiation levels at the Burro Flats rocket testing site in the hills south of the San Fernando Valley. There was a hushed-up nuclear incident there in the 1950s, and now CGS is being asked to help determine what the natural background levels of the area should be. The 1970s NURE flyover data of the area looked fairly normal – except for two radiation spikes near a couple of buildings in the abandoned test site.

“There’s been some cleanup activity,” Churchill said. “I’m not sure of all the details, but I believe that Health Services hopes to demonstrate to the local public that things are cleaned up.”

Like its predecessors, the northwestern Los Angeles County radon map will be informational only. Ultimately, however, Health Services or local government could determine that regulatory maps are needed. Property sellers would have to do radon testing if a property was in a radon risk zone, and developers would be required to build mediation steps into new construction.

Because radon is a gas, it can move through soil, cracks in building slabs and basement walls. However, remediation doesn’t involve anything as extreme as lead shielding.

“The cost isn’t bad compared to some other environmental risks, maybe a couple of thousand dollars in an existing home and less than that during the construction phase,” Churchill said. “The builders can install pipes to ventilate the gas from under the house out through the roof, install vapor barriers and seal gaps around the pipes going through the floor. Those steps should lower radon levels to acceptable levels in almost every situation.”