Atch_3_Radon_Report_0003.pdf

TWENTY-SEVEN YEARS OF RADON MONITORING IN WIND CAVE,

WIND CAVE NATIONAL PARK

Marc Ohms

Physical Science Technician Wind Cave National Park

Background Radon is a naturally occurring radioactive, colorless and odorless gas that in recent years has gained increasing notoriety as a health threat. It is considered to be the leading cause of lung cancer in non-smokers and it is estimated to cause 20,000 deaths a year (Environmental Protection Agency 1992). Radon comes from the natural decay of uranium in the rock and soil. Radon is present in the outside air but is at such low levels that it is not a concern. Where it becomes a problem is in enclosed areas such as buildings, mines, and caves.

The U.S. Geological Survey has determined that the sedimentary rocks surrounding the Black Hills contain uranium deposits, especially the sandstone in the southern Hills. This means that there is the potential for high radon levels. In comparison, the granite core of the Black Hills has a moderate radon potential (U.S.G.S. 2002).

National Park Service Radon History In 1968 the first evidence appeared that radon could be a possible threat to cavers and cave employees. Tests conducted in Carlsbad Caverns suggested a possible health hazard for National Park Service cave employees under existing OSHA uranium mining radiation exposure standards for radon (Yarborough 1977). Following this the NPS launched into a service-wide radon-monitoring program for NPS caves. The problem was the NPS did not have any guidelines on radon exposure and was forced to utilize mining standards.

In 1980 the “Cave Radiation Safety and Occupational Health Management Guideline- NPS 14” was written. It was later revised in 1990 and is now under revision once again by the NPS Occupational Health and Safety Program and will be included in the Director’s Order/ Reference Manual 50B.

Wind Cave Radon History In January of 1976 the department of Mining Enforcement and Safety Administration conducted a radon survey in Wind Cave at the request of the National Park Service. Six sites were sampled along the tour routes. The radon level averaged 0.19 working levels and it was determined that the higher levels were occurring during the summer months (Rapp and Rathbun 1976). It was concluded that the radon level was safe for the visitors as well as the employees. In August of 1976 the National Institute for Occupational Safety and Health conducted a hazard and medical evaluation on NPS cave employees.

At Wind Cave nine employees participated in the study. Sputum samples were taken from each individual and tested for respiratory irregularities. All nine participants produced negative results (Gunter and Meyer 1978).

The park hired a Physical Science Technician in mid-1977 to conduct radon sampling through the end of August 1978. The sampling was conducted weekly along the tour routes including the Caving Tour for a total of 56 sample days. Park employees who worked in the cave were required to keep exposure records. These records included time spent in the cave and where they were in the cave. With this information the park was able to determine each person’s radon exposure. A computer program was written to analyze the data, with an emphasis on determining the causes of radon level fluctuations.

It incorporated barometric pressure, temperature, and humidity in the hopes of discovering some correlation. The results were inconclusive. The Candlelight Tour had the highest radon with an average of 0.42 working levels. The three other tour routes had a combined average of 0.20 working levels (Chord, Farrell, and Finney 1978).

Starting in 1990 the park’s Cave Resource Management staff monitored radon in the cave sporadically through 1997. The sampling was done with a portable pump and was conducted along the tour routes. During this time period the radon level averaged 0.19 working levels (Nepstad and Allison 1997).

Radon Today In the spring of 2002, to continue monitoring Wind Cave’s radon levels, ten RadTrak monitors were purchased from Landauer. The RadTrak is an alpha-track radon gas detector designed to monitor radon exposure for three months to a year. The ten monitors were placed in ten different locations throughout the cave. A monitor was placed on each of the five tour routes, one in an elevator air-lock and the remaining four were placed in off-trail locations along flagged travel routes used by surveyors and researchers. This was the first radon monitoring ever conducted off of the tour routes in Wind Cave. The monitors were left in place for three months. Once the monitors were removed they were sent to Landauer for testing.

2002 Wind Cave Radon

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Figure 1- 2002 radon levels

The ten samples had very little variance in the amount of radon as can be seen in figure 1.

The upper elevator airlock had the lowest level of radon at 0.13 working levels. This can be attributed to air from the surface entering the airlock via the elevator shaft. The highest level at 0.25 working levels was in the Muddle Room along the Caving Tour route. The average radon level was 0.20 working levels.

There does not appear to be any correlation between the level of radon and the distance from an entrance. Many earlier studies concluded that the radon levels are higher the farther you travel into the cave from the entrance. However, the earlier studies did not sample sites beyond the tour routes therefore only represented a small portion of the known extent of the cave.

Wind Cave Radon

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1976 1977 1978 1979 1980 1990's 2002 w or ki ng le ve ls

Figure 2- Wind Cave radon levels

Conclusions Decades of data indicate that the radon levels within Wind Cave appear to be stable, as can be seen in figure 2. The levels are low enough not to pose a threat or concern for those working in the cave or the visiting public. Wind Cave averages around 0.20 working levels. This means that 3.4 out of 1000 non-smoking people could get lung cancer if exposed to this level for a lifetime, which is ten times the risk of dying in an airplane crash (Environmental Protection Agency 2002). However, this is based on a daily dose of at least eight hours. Since park employees rarely are in the cave for eight hours, and surely not every day, and most of the park’s employees do not work in the cave for a lifetime, their risk is greatly reduced. The US Department of Health and Human Services recommends that the annual exposure level for occupational exposures not exceed 1.0 WLM (Working Level Month= radon working level X time spent in exposure area/ 170). If an interpretative ranger at Wind Cave conducts three tours a day for a total of five hours the exposure would be 0.13 WLM, well below the recommended exposure. Since visitors are in the cave for such a short time period their risk is virtually zero.

The cave should be monitored biannually to ensure that radon is not rising above stable conditions seen in the past and to obtain long-term trends of the radon levels within the cave.

References Chord, Casey, Tom Farrell, and Richard Finney. 1978. RADON RADIATION IN

WIND CAVE.

Environmental Protection Agency. 2002. RADON COMPARISON CHARTS.

Environmental Protection Agency. 1992. A CITIZEN’S GUIDE TO RADON.

Gunter, Eileen, and Channing Meyer. 1978. HAZARD EVALUATION AND

TECHNICAL ASSISTANCE REPORT NO. TA 76-54.

Nepstad, Jim, and Stan Allison. 1997. RADON DATA FROM WIND CAVE. Cave Resource Management files.

Rapp, Donald, and Lyle Rathbun. 1976. RADIATION SURVEY OF WIND CAVE NATIONAL PARK. Technical report from the Mining Enforcement and Safety Administration.

U.S. Geological Survey. 2002. RADON POTENTIAL OF THE UPPER MIDWEST.

Yarborough, Keith. 1977. MEASUREMENTS OF SEASONAL AND DAILY RADON

DAUGHTER CONCENTRATION FLUCTUATIONS IN NATIONAL PARK

SERVICE CAVES. Report to Chief of Resource Management, Southwest Region.