Date of Award

1995

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

P.J. Gerla

Abstract

High levels of indoor radon have been observed in many areas of the Red River Valley and particularly in Grand Forks County of North Dakota. Data from the University of North Dakota (UND) Radon Monitoring Facility indicated more than 80% of the dwellings tested had radon levels greater than the United States Environmental Protection Agency (USEPA) action limit of 4 pCi/l. High radon levels may pose a health threat (USEPA, 1986) to valley residents.

A review of existing data indicates that areas of the Red River Valley in North Dakota with elevated soil salinity also exhibit higher equivalent uranium (eU) concentrations than soils of lesser salinity. This study examined relationship between soil salinity, radon precursors, radon, and radon progeny in Grand Forks County, North Dakota.

Approximately 75 soil-gas samples collected in Grand Forks County were analyzed for radon-222 using in an alpha particle scintillation counter. Radon concentrations observed in the soil gas samples ranged from about 200 to 1700 pCi/l. In addition to the soil gas samples, continuous soil samples were taken from approximately 0-1 meter and 1-2 meters at the location of each soil gas sample. Ninety-two soil samples were analyzed for uranium by fluorimetry, equivalent uranium (eU) by gamma-ray spectrometry, and for soil salinity.

Equivalent uranium, equivalent thorium, potassium-40, and derivative maps were produced using aerial γ-ray data collected during the National Uranium Resource Evaluation (NURE) program in 1979. These maps, when compared to soil survey maps, show several similarities. Areas mapped as saline soils and nearby non-saline soils typically exhibit higher γ-radiation intensities than surrounding areas. Radon concentrations observed in the field appear to be consistent with concentrations predicted by calculations using NURE eU values.

Results suggest that radium-226 is preferentially transported in the saline groundwater that is discharged from bedrock aquifers in Grand Forks County. Radium appears to be more soluble in water with high dissolved solids. In an aquifer with high dissolved solids water, competition for the few available sorption sites is high, and radium solubility is enhanced (Michel, 1990). The bedrock aquifers that discharge to the surface in Grand Forks County have total dissolved solids (TDS) values ranging from 4,000 to 10,000 parts-per-million (ppm); thus, it may be reasonable to expect that radium transport could occur under such conditions.

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