A Review of NORM/TENORM in Wastes and Waters Associated with Marcellus Shale Gas Development and Production

摘要

Marine black shales have long been known to contain elevated concentrations of uranium, thorium, and associated daughter products, commonly known as Naturally-Occurring Radioactive Material (NORM). Because uranium and thorium are only marginally soluble in near-neutral groundwater and formation waters typically associated with black shales, dissolved concentrations of these elements in produced waters (technologically-enhanced NORM [TENORM]) have not been considered a serious environmental issue. In contrast, radium-226 (~(226)Ra) and radium-228 (~(228)Ra) are much more soluble, particularly in formation waters with high concentrations of total dissolved solids (TDS). Total radium activities in formation and produced waters typically range from 30 to 5,000 picocuries per liter (pCi/L). While total radium activities in waters produced from Marcellus Shale gas wells are commonly less than 5,000 pCi/L, activities as high as 16,000 pCi/L have been reported. When produced water reaches the land surface, changes in pressure and temperature affect the solubility of dissolved gases, and subsequently affect the solubility of calcite, gypsum, and other minerals. These minerals commonly precipitate and form scale and sludges, which can accumulate on the inside surfaces of pipes, tanks, and other water-handling equipment. Radium isotopes co-precipitate and concentrate in these mineral deposits, thereby forming a residue with higher radioactivity values than the original water. The general occurrence and speciation of radionuclides in shale samples, produced waters, scale, and sludges associated with Marcellus Shale are presented and discussed in this paper.