Radioactivity of Fossil Fuel Waste Products and Associated Environmental Implications

Abstract

Extraction of energy resources and energy production can redistribute and concentrate naturally occurring radioactive materials (NORM), particularly from the uranium (238U t1/2=4.5 x 109 yr) and thorium (232Th t1/2=1.4 x 1010 yr) decay series, posing potential human and environmental health risks if not managed properly. In particular, elevated activities of NORM have been measured in coal combustion residuals (CCRs) generated from coal combustion and oil and gas wastewater (OGW) drawn from both conventional and unconventional oil and gas producing wells. This dissertation characterizes the radioactivity associated with CCRs and OGW and further investigates the use of this radioactivity as a tracer and timer of contamination, particularly from OGW following its accidental or intentional release to the environment. 232Th and its decay product 228Ra and 238U and its decay products 226Ra and 210Pb were measured in coals and CCRs from the majors coal producing basins in the United States as well as in coals and CCRs from high-U coal producing basins in China. 228Ra and 226Ra were measured in OGW from the Appalachian Basin in the United States. Finally, 228Ra, 228Th, 226Ra, and 210Pb were measured in soils and sediments impacted by spills of OGW and the permitted release of treated OGW to surface water. Characteristic 228Ra and 226Ra activities 228Ra/226Ra activity ratios were found in CCRs and OGW derived from distinct formations, suggesting that the radioactivity can serve as a potential fingerprint of for contamination when CCRs and OGW are accidentally or intentionally released to the environment. Additionally, the decay of 226Ra and 228Ra into their respective decay products 210Pb and 228Th offers the ability to source and age date contamination from OGW. The 228Th/228Ra activity ratio in particular is useful for age dating contamination in impacted sediments up to about 10 years old, which is ideal for age dating recent contamination. The 228Ra/226Ra and 228Th/228Ra activity ratios were successfully used to constrain the age and source of contamination from two scenarios including OGW spills and treated OGW disposal to surface water.