Abstract

A survey of radon-222 (Rn) in soil-gas and water at selected locations in Yellowstone National Park was initiated as part of Northwest College's Young Scholars' program. For two weeks in July 1993, four high school students and other researchers collected and analyzed nearly 100 samples of soil-gas and water. The three objectives of our reconnaissance of Rn in soil-gas and water in Yellowstone National Park were: (1) to engage talented high school students in challenging and enjoyable research, (2) to survey the variability of Rn in soil-gas and water in Yellowstone National Park, and (3) to provide the National Park Service with reconnaissance data on Rn in soil-gas and water. The research was conducted in four areas: (1) a study of Rn in water at public water-supply sources and in soil-gas near those sources, (2) a study of Rn in water and in soil gas near thermal areas, (3) a study of hourly and spatial variation of Rn in soil gas at West Thumb, and (4) a study of Rn in soil-gas and in water in the Mammoth area. With the help of National Park Service personnel, samples of soil-gas and water were collected for radon analysis from several public water supplies (Old Faithful, Madison, Norris, Lewis Lake, Mammoth, Lake, Bridge Bay, and South Entrance), West Thumb Geyser Basin, Boiling River, and other thermal areas. In Yellowstone National Park, most values of Rn in sampled supplies of public drinking water were above the range of average values (353-686 pCi/L) for public ground water supplies for the United States.

The study of Rn in water at selected thermal areas indicated an inverse relationship between temperature and Rn concentration, as anticipated thermodynamically. No definitive relationship was noted between Rn concentrations in water and in soil-gas. At West Thumb Geyser Basin, the spatial variation in soil-gas Rn concentration was greater than the hourly variation. In the Mammoth area, an attempt was made to trace the underground course of Boiling River using Rn in soil-gas as an indicator. However, the thin soil overlying the travertine made it impossible to collect adequate samples of soil-gas. Although these studies indicated some variables (temperature, surface area, soil moisture, free exchange of water with air, uranium content of rock, and age of volcanic flow) that are affecting Rn concentrations in soil-gas and water, much work remains to be done on the spatial distribution and temporal variability of Rn concentrations in water and soil-gas in Yellowstone National Park.