Radium and radon in water supplies from the Texas Gulf Coastal aquifer

Abstract

A sampling of the domestic water for two isotopes of the uranium (U)-238 series, radium (Ra)-226 and radon (Rn)-222, was conducted in parts of the Texas Gulf Coast (in and around Greater Houston and Harris County) to better understand the distribution patterns of these radioisotopes in residential and commercial water supplies. Samples were obtained from consumers' taps, as well as at well heads to evaluate variation due to location and depth of water sources. Analyses were conducted at the University of Texas, School of Public Health (UTSPH) in Houston. Computer mapping and statistical analyses were used to depict patterns of Ra and Rn distribution. The concentrations varied depending on water source. No measurable Ra or Rn were found in surface water supplies, whereas up to 23 pCi l −1 of Ra and 3300 pCi l −1 of Rn were observed in some of the wells in northwest and southwest Harris County. The Rn concentrations were observed to increase with depth, but for Ra peak concentrations were found between 180 and 320 m below the surface (at depths roughly corresponding to the top of the Evangeline aquifer). High concentrations of Ra and Rn were associated with wells developed on the flanks of piercement-type salt domes, along faults, and near streams. This study documents high Ra in Tertiary clastic coastal aquifers and suggests that it may be external sources, e.g. salt domes, uranium, or leaky faults, and not the bulk mineralogy of the aquifer which cause elevated concentrations. This is an important consideration when decisions are made about sites for drilling water wells.