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| Fig. 1: An example of scale buildup in a pipe. (Source: Wikimedia Commons) |
With recent development of shale oil and gas resources in the United States, the petroleum industry has come under increasing public scrutiny. Environmentalists are concerned with potential side effects of shale development, namely hydraulic fracturing. While the focus of the environmental debate concerns itself with this so-called "fracking," another issue tends to go unaddressed. With the increase of any type of petroleum production comes an increase of production-related waste. Certain production activities cause naturally occurring radioactive materials (NORM) to be concentrated at higher levels than what is typically found in nature. It may seem strange that this discussion is not at the forefront of environmental concerns, especially when radioactive waste from other sources, like nuclear power plants, is so highly publicized. This report will outline why this issue has taken a back seat to fracking and why it should stay there.
The radioactive isotope of greatest concern is Ra-226 and Ra-228, an isotope that appears in the decay chain of U-238. This NORM is found most commonly in produced formation water as dissolved radium. This formation water is brought to the surface along with oil and gas, where its temperature is lowered, allowing solids to precipitate out of solution and form scale deposits on pipe and sludge that accumulates on storage vessels. [1] It is not the water, but the precipitation of radium in the aforementioned scale deposits or sludge that raises the largest concern as the radium concentrations in scale and sludge are much higher than in the formation water. Because the radium in the formation water is dilute, it is typically not much of a concern. The radiation levels in the produced waste varies geographically, but scale consistently has higher radium concentration. A NORM survey conducted in Michigan measured radium concentrations in waste scale at levels around 50 pCi/g. For reference, the radium concentration found in soil range from 0.5 to 3 pCi/g. [2]
As mentioned, the radiation levels in the produced water are not the main source of concern. Radium that remains in solution in the produced water is typically disposed of along with the rest of the produced water: back into the subsurface formation from which it came. The radium content in the re-injected water is not regulated since its properties are still very similar to the water that is already in the formation. [1] It is worth noting, however, that injection of fluid into a formation is regulated and should not affect potable groundwater in any way. It is also worth noting that the disposal of the NORM affected solids has only recently been regulated.
Accumulation of radioactive scale inside and on oilfield equipment does eventually warrant removal. This scale waste, as well as entire pieces of equipment affected by the scale buildup present various issues in waste management. Perhaps surprisingly, the United States government does not specifically address NORM as it does not meet the requirements of waste under the Atomic Energy Act or of the Low Level Radioactive Waste Policy Act. [1] Instead, this regulation has been left to the states. Some states have chosen to enact regulations, others have determined that existing regulations are sufficient. This lack of consistency may be a cause of alarm and begs the question of whether regulations should be put in place or not.
In 1996, the state of Michigan enacted disposal guidelines that would allow the disposal of petroleum industry Ra-226 waste in non-hazardous solid waste landfills. [1] For the petroleum industry, this would be a much cheaper alternative as it would not require specialized disposal or handling procedures. A study by Argonne National Laboratory in 2003 assessed the risk of this disposal method. The study was conducted to address the main concerns. First, there was investigation into how disposing Ra-226 waste in municipal dumps might affect groundwater in the case of a leak. Second, the exposure of this waste to workers and everyday citizens was analyzed. In the leakage case, both a realistic case and a worst case were considered. Computer simulations showed that even if there was no geomembrane liners in the landfill and if the groundwater aquifer was in direct contact with the base of the landfill, the radioactivity would be a negligible 3.3 × 10-4 pCi/L. [1] This is a significantly different figure than what was originally stated for the solid waste. This drop off can be attributed to the fact that only rain that acts as a leaching agent could possibly seep through the liners and into the groundwater. Furthermore, it was determined that an operational-phase worker would only receive less than 0.02 mSv/yr of radiation while all other human exposure could be considered negligible. Even future use of landfill sites was determined to have a negligible effect on any future users. The study determined that potential doses for future land use would be unacceptably high if the waste was shallower than 3 meters or if the landfill cap were breached during construction.
In summary, NORM waste can be disposed of like municipal waste with minimal risk. It may appear strange to some that environmentalists have not expressed greater concern over this issue but it may be largely due to the fact that there simply have not been problems related to NORM disposal. The Environmental Protection Agency is aware of petroleum industry NORM and is currently conducting further studies on its affects. In the meantime, equipment affected by radioactivity is often isolated and not recycled and NORM regulations are left to individual states.
© Thomas Logan. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] K. P. Smith et al., "Assessment of the Disposal of Radioactive Petroleum Industry Waste in Nonhazardous Landfills Using Risk-Based Modeling," Environ. Sci. Technol. 37, 2060 (2003).
[2] K. P. Smith, "An Overview of Naturally Occurring Radioactive Materials (NORM) in the Petroleum Industry," Argonne National Laboratory, ANL/EAIS-7, December 1992.
