Naturally occuring radon-222 concentrations in Antelope Creek - Idaho: Source determination and role of sorpbion on local sediments.

摘要

Radon-222 (222Rn or radon), a known carcinogen, is a naturally occurring radionuclide and the Rocky Mountains' rocks are known to cause radon problems in Idaho. High levels of 222Rn in water can supply indoor airborne 222Rn and approximately 20% Americans use water from domestic wells that are not federally regulated or monitored for 222Rn which is routinely monitored in public water systems nationwide. It is the intent of the study to provide an overall picture of groundwater 222Rn concentrations in Antelope Creek valley of Idaho using measurement, interpolation and assessment of sorption on the local rocks/sediments.;Groundwater samples were collected from eight wells in Antelope Creek valley, Idaho. Seven out of eight locations showed that groundwater 222Rn concentrations were much greater than 11 Bq/L (300 pCi/L), a maximum contaminant level (MCL) proposed by United States Environmental Protection Agency (USEPA). Rock and sediment samples collected near the sampling wells revealed uranium (238U) contents between 0.55 to 6.41 ppm and possessed a potential to generate the observed groundwater 222Rn concentrations. An interpretation technique using a Geographic Information System (GIS) software with available information also suggested a correlation between the rock types and 222Rn concentrations in the groundwater.;Adsorption and desorption experiments were conducted using Revigator water as a standard. Black shale samples exhibited adsorption of 222 Rn while inorganic sands did exhibit a weak sorption phenomenon. Sand grade black shale favored more adsorption than the other two sizes of black shale. The organic carbon content of the samples and initial 222Rn concentration of Revigator water appeared to be the governing factors for sorption. Seven day adsorption-desorption also implied that the black shale samples were better sorbent than the inorganic sands. While different initial concentrations posed limitations and the dynamic nature of the experiments and uncertainties involved were the possible sources of errors, the experiments provided an easy method to quantify adsorption-desorption of 222Rn from water onto sediment surfaces. The information could be useful for remediation purposes as well as modeling and monitoring purposes.