Geologic hazards in Arizona – Radon

The Arizona Geological Survey has reissued its “Homeowners Guide to Geologic Hazards” which you can download from http://www.azgs.az.gov/homeownersguide.shtml

Among the hazards discussed are floods, earth fissures and subsidence, earthquakes, debris flows, landslides, karst formations, swelling or collapsing soils, volcanic eruptions and residential radon.

There are three publications dealing with hazards. The overview booklet is “A Home Buyer’s Guide to Geologic Hazards in Arizona” originally published in 2002.

The second booklet is “Land Subsidence and Earth Fissures” originally published in 1993.

The third booklet is “Radon Gas, a geologic hazard in Arizona” originally published in 1992 as a result of the EPA’s “radon scare.” The remainder of this article discusses the radon issue.

Radon itself is harmless, but its daughter products can pose some potential hazard. When radon decays it produces an Alpha particle. Among atomic particles, Alpha particles are big and slow; they literally cannot fight their way out of a paper bag. But if inhaled, they can damage lung tissue. Radon has a half-life of 3.8 days.

According to AZGS: “Radon is a colorless, odorless, radioactive gas produced by the decay of uranium, which is present in virtually all rocks and soils, typically at concentrations of 1 to 4 parts per million (ppm). The Earth’s atmosphere contains small amounts of radon derived from radioactive decay of uranium in the ground. During the 1980’s, scientists discovered that radon gas can accumulate inside homes and other buildings at concentrations that are commonly tens of times greater than in outdoor air and, in some cases, may be hundreds or even thousands of times greater. Most indoor radon is derived from uranium in underlying soil and rock and gradually seeps into buildings through cracks or other openings in the ground floor. Houses with anomalous concentrations of indoor radon are typically built on rock and soil that contain anomalous uranium concentrations.”

Besides the Colorado Plateau area, where uranium is mined, anomalous concentrations of uranium have been found in the Verde Valley, in the “Granite Dells” near Prescott, in the Phoenix Mountains and in the Cave Creek area.

Tucson radiation mapThere is one known occurrence in the Tucson area near the intersection of Valencia and Cardinal Avenue. There, limestone contains thin yellow veinlets of the uranium mineral carnotite. A survey of the area with a gamma-ray spectrometer (a uranium-prospecting instrument) revealed that uranium concentrations vary from near the background (normal) level at the edge of the anomalous area to approximately 14 times the background level at the center. Chemical analyses indicate that uranium concentrations are as high as 20 ppm at the center of the anomaly, according to the AZGS. Several dozen houses are built on the limestone, many of which had radon levels greater than the EPA limit of 4 pCi/1(pico-curies per liter when tested in 1987 by the Pima County Health Department. (See map for exact location. The map shows radioactive bismuth, a daughter product of radon decay.)

The actual danger of residential radon has been overblown by the EPA beginning in the 1980s.

According to the CATO Institute, the EPA alarm “is based on 50-year-old studies of uranium miners on the Colorado plateau. Developed after World War II, when the concern with nuclear weapons propelled a search for uranium, the mines were “dog holes”—dusty, poorly ventilated, thick with smoke. The miners themselves smoked, unknowingly increasing the cancer risk. Data were unreliable: levels of exposure, in particular, were uncertain, given the dearth of measurements in the 1940s and 1950s and the questionable value of those that were made, often by the miners themselves.” “The EPA’s approach fanned the flames. Miners who had inhaled radon showed a high incidence of lung cancer, so it was inferred that radon in the home posed a similar threat, despite much lower concentrations and quite different conditions. A generation later, the EPA still was claiming that we know more about radon risks than risks from most other cancer-causing substances because estimates are based on studies of cancer in humans (underground miners). The agency insists that no level of radon is without risk. Scientists and statisticians generally view such a ‘linear, no-threshold’ hypothesis with skepticism.” Read more of CATO report.

According to journalist Michael Fumento, “practically every large epidemiological study on the subject has shown that households with higher levels of radon have no higher incidence of lung cancer or even significantly less than those with considerably lower levels.

For example, University of Pittsburgh radiation physicist Bernard Cohen analyzed the relationship between lung cancer and residential radon levels in more than four-hundred U.S. counties. He found that those with the most household radon exposure had the least cancer. Physicist Ralph Lapp found much the same thing throughout high-radon areas in New Jersey.

Likewise, populous areas with high lung cancer rates where radon levels have been studied have generally been found to have below-average radon levels. This includes the New York City area, the San Francisco area, England, and China. In 1994, a major study of Missourians in the Journal of the National Cancer Institute (JNCI) and of Canadians in the American Journal of Epidemiology found no elevation of lung cancer in areas with high levels of household radon (Source)

A study in Finland found, “Inhaled radon has been shown to cause lung cancer among underground miners exposed to very high radon concentrations, but the results regarding the effects of residential radon have been conflicting…Our results do not indicate increased risk of lung cancer from indoor radon exposure. Indoor radon exposure does not appear to be an important cause of lung cancer.”

A paper printed in Science Direct “examines the methods and the justification of extrapolating such risks from the high 222Rn [radon] levels in mines to the very much lower domestic levels, and summarizes the findings of some recent Swedish studies on domestic radon levels and their correlation with the risk of lung cancer. The case for suggesting that significant positive correlations exist between radon levels in given regions of a country and the onset of leukaemias and other cancers is also critically examined. It is concluded that, on present evidence, the case for such correlation is not proven.”

The actual danger of residential radon appears small, but if homeowners are concerned, the third AZGS publication shows how they can reduce or prevent radon from getting inside (see page 15). The most effective methods involve venting basements and crawl spaces and sealing cracks in a cement slab. New construction may put an impermeable membrane beneath the slab.

According the AZGS, “In the late 1980’s, a church (Santa Cruz Lutheran Church, 6809 S. Cardinal Ave.) was built in southwestern Tucson on an area with elevated uranium levels. To prevent radon entry, the concrete-slab floor was constructed above a sheet of impermeable plastic that, in turn, overlay a layer of gravel. Perforated pipe was placed in the gravel and connected to a pipe that vented aboveground, outside the building. This appears to be an effective method of preventing indoor-radon accumulation.”

A Home buyer’s Guide to Geologic Hazards in Arizona

The Arizona Geological Survey has a 45-page booklet discussing some geologic hazards that home buyers should be aware of. You can download the booklet here. Subjects include floods, earthquakes, problem soils, mass movement, subsidence & fissures, radon, karst (caves), abandoned mines, and volcanic hazards.

“Our purpose is not to say that any particular parcel of land should not be developed. Rather, in those areas where geologic hazards or limitations are known to be present or where they may potentially exist, knowledge of their existence should help guide planning, design, construction, and maintenance. It remains up to property buyers or owners and local government to determine the level of acceptable risk from geologic hazards.”

In the desert, ironically, flooding is the most widespread, common, and damaging of all the geological hazards. This section explains floodplains and “100-year floods” and notes the areas most prone to this hazard.

“Over the past 150 years, more than 20 earthquakes having magnitudes greater than 5 have occurred in or near Arizona, and all of Arizona has experienced at least moderate earthquake shaking. The magnitude 7.4 Sonoran earthquake of 1887, which was centered about 40 miles southeast of Douglas, caused 51 deaths in Sonora and extensive property damage throughout southeastern Arizona. The Yuma area has experienced repeated damage from earthquakes that occurred in southern California or northern Mexico.” This section of the booklet shows maps which rate potential hazards.



















“Damage to structures in Arizona is commonly related to soil characteristics, with expansive (shrink/swell) soils and collapsing soils causing the most problems. Cracking of foundations, walls, driveways, swimming pools, and roads cost millions of dollars each year in repairs.” Such damage is related to the amount and type of clay in the soil.

The section on mass movement deals with landslides and debris flows which occur along mountain fronts and at the base of cliffs.

Land subsidence and earth fissures occur in areas in which groundwater is withdrawn faster than natural recharge.

“Radon gas is a radioactive element that is produced by the decay of uranium, which is present in virtually all rocks and soils, typically at concentrations of 1-4 parts per million.” The hazard is that radon can seep into buildings through cracks in the foundation. A sufficient concentration poses a health hazard. This section explains the danger and shows the areas of Arizona especially prone to radon emissions.

Karst terrain is developed in areas underlain by limestone, especially on the Colorado Plateau. Sinkholes may develop as cave systems mature.

 Old mine workings present a danger of toxic substances as well as falling in them.

Volcanic activity has occurred frequently in Arizona, some just 800 years ago (see ). The San Francisco volcanic field near Flagstaff is considered active. “Hazards associated with volcanic activity include ash and cinders that can overload the weight-bearing capacity of some roofs. Houses built in the Flagstaff area, where snow is routine, are already designed with loading in mind. Volcanic gases include carbon dioxide and sulfur gases that are sometimes at concentrations that may be harmful to breath.”

The AZGS booklet is well-illustrated with maps and other graphics showing the general locations of each hazard and what to expect.