Naturally-occurring radioactive material can be a substantial source of radiation exposure to the public, especially in ground-derived drinking water. Two radionuclides from the uranium decay series (lead-210; Pb-210 and polonium-210; Po-210) are of particular concern because their characteristic properties combine to present potential carcinogenic risks to human. These radionuclides are present in subsurface geological deposits where a great deal of drinking water in the state of Iowa is derived. While the potential carcinogenicities are known, concentrations of Pb-210 and Po-210 are not well characterized in Iowa aquifers. This study proposes to determine the concentrations of Pb-210 and Po-210 in 50 privately-owned wells across the state to develop an understanding of the potential contribution to increased lifetime cancer risk to Iowans.It is expected that success in these studies will result in a more detailed understanding of the biogeochemical relationship of increased levels of Po-210 and Pb-210 to other natural radionuclides found in Iowa's well water, and will provide preliminary data for understanding potential risk of natural radioactivity in Iowa's well water.