Capture Zone Analysis of a Wellfield to Assess Contaminant Transport

Abstract

Model Gaps and Recommendation CHAPTER VI: CONCLUSIONS REFERENCES groundwater. Due to the importance of those two isotopes in groundwater, Ra concentrations in groundwater are usually reported with respect to the combined concentration of those two isotopes, 226 Ra and 228 Ra with half-lives of 1600 years and 5.75 years, respectively (Kelly, 2008). Ra concentrations in groundwater differ because of differences in chemical properties of the parent isotopes at the head of the decay series, either 232 Th, 235 U, or 238 U (Stackelberg, 2018). The Thorium isotopes 228 Th 230 Th, and 232 Th, which are said to be insoluble in groundwater, are the immediate radioactive sources for 226 Ra, 228 Ra, and 224 Ra respectively (Stackelberg, 2018). 224 Ra has a half-life of 3.6 days and its concentration declines rapidly after about one half-life, whiles 223 Ra occurs infrequently in the environment at high concentrations (Stackelberg, 2018), hence both are not reported for combined Ra levels in drinking waters. Ra has been identified as the most potentially hazardous naturally occurring radionuclide likely to occur in drinking water (Szabo et al., 2012). Radium in drinking water increases cancer risk, primarily bone and sinus cancers (Szabo et al., 2012). The risk incurred from alpha particle emission depends on the way the body metabolizes the ingested radionuclide (Szabo et al., 2012). The Maximum Contaminant Level (MCL) for combined Ra is 5 picocuries per liter (pCi/L), which is set by the United States Environmental Protection Agency (USEPA) (Stackelberg, 2017). Radium in Northern Illinois The Cambrian-Ordovician aquifer system underlies area of 476,560 km 2 extending across parts of Midwestern states (Stackelberg, 2018). Within the northern part of Illinois, the Cambrian-Ordovician aquifer system is used as an important source of domestic and public water supplies. Concentrations of naturally occurring radioactive isotopes 226 Ra and 228 Ra in excess of the USEPA standard for drinking water has been detected in water from deep bedrock aquifers used for public water supply (Kay, 1999). One of the distinct stratigraphic difference between areas having higher concentration of Ra recorded in drinking water supplies and areas not having higher concentration is the presence of the Maquoketa