Elevated Levels of Naturally Occurring Radioactive Material Associated with Shale Gas Extraction
Sanford Cohen & Associates Inc., Vienna, VA, [email protected]
Naturally occurring radioactive materials, such as radium-226, are ubiquitous in the earth’s crust, and, in some geologic formations and their associated ground waters, the levels of these radionuclides are often elevated. In addition, the extraction and processing of the minerals and ground water associated with these formations can further enhance the concentration of these radionuclides, resulting in products, byproducts, and waste products containing what is referred to as technologically enhanced sources of naturally occurring radioactive materials or TENORM. Examples of TENORM include solids associated with mineral extraction and beneficiation industries, including heap leach extraction, in situ-mineral extraction, thorium and rare earths processing, phosphate industry tailings, sludge at water and wastewater treatment facilities, spent resin from individual water softeners, coal ash, oil and gas production sludge and scale, and geothermal energy production waste.
With respect to shale gas extraction, elevated levels of naturally occurring uranium and radium have been found in rock cuttings and drilling fluid/mud. For example, uranium has been found in shale at 59.4 pCi/g as compared to about 0.85 pCi/g in typical soil. Hydraulic fracturing flowback water (HFFW or cocktail) has been observed to contain up to18,950 pCi/L gross alpha (which consists primarily of radium-226 and its progeny), and produced water has been observed to contain up to 15,000 pCi/L of gross alpha emitters. These concentrations can be compared to the drinking water standards set forth in 40CFR141 of 15 pCi/L gross alpha and 5 pCi/L combined Ra-226 and Ra-228 water.
The industry and state and federal regulatory authorities are currently involved in the analysis of the radionuclide composition of rock cuttings, drilling fluid/mud, HFFW, and produced water for the purpose of evaluating the potential health risks associated with the handling, management, transport, and disposal of these materials. To date, it has been found that the limiting radionuclide is Ra-226, and that its concentration in the various products, byproducts, and waste products associated with the shale gas extraction industry is highly variable depending on location. In addition, investigations to date reveal that under most circumstances TENORM does not pose a hazard to workers, members of the public, or to the environment. However, our understanding of the nature and extent of TENORM associated with this industry is incomplete, and careful attention must be given to characterizing the composition of the products, byproducts, and waste products associated with shale gas extraction in order to ensure that the industry complies with all applicable state and federal regulations and guidelines, many of which are still in the formative stages.
AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012