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What is NORM?

"NORM" is the acronym for naturally occurring radioactive material. Radiation occurs naturally throughout our environment. In addition to radiation originating from the sun and deep space, NORM originating on earth is found in our bodies, the food we eat, the places we live and work, and the ground we live on.

For the most part, humans have adapted to radiation exposures resulting from background concentrations of NORM (i.e., the normal, ambient concentrations of radiation). Certain industrial processes, however, can cause NORM to accumulate at concentrations greater than natural background levels. The petroleum industry, for example, is one of several industries that generate large volumes of NORM-bearing wastes. The sources of most of the radioactivity in petroleum industry wastes are the isotopes formed from the radioactive decay of uranium-238 (U-238) and thorium-232 (Th-232), which are naturally present in the subsurface formations from which oil and gas are extracted. The primary radionuclide of concern in NORM wastes is radium-226 (Ra-226) of the U-238 decay series. Radium-228 (Ra-228) of the Th-232 decay series also occurs in NORM waste, but usually at lower concentrations. Other radionuclides of concern include those that form from the decay of Ra-226 and Ra-228.

The petroleum industry waste streams most likely to contain elevated radium concentrations include produced water, scale, and sludge. Radium, which is slightly soluble, can be mobilized in the liquid phases of a subsurface formation and transported to the surface in the produced water stream. As the produced water is brought to the surface, some of the dissolved radium precipitates out in solid form. Most commonly, the radium coprecipitates with barium sulfate, a hard and relatively insoluble scale deposit; however, it also can coprecipitate to form other complex sulfates and carbonates.

Several factors affect the degree to which radium in solution in produced water will precipitate out in solid form. As the produced water is brought to the surface, it undergoes temperature and pressure changes that allow solids to precipitate. In general, radium concentrations tend to be highest closest to the wellhead where these physical changes are greatest. The sulfate content of the produced water also is a factor, given the strong correlation between barium sulfate scale and radium precipitation. Wells that do not have significant associated scale formation generally do not have a NORM problem.

Radium that remains in solution is disposed of along with the produced water. Most produced water is disposed of by subsurface injection, and the radium content of reinjected water typically is not regulated. Radium-bearing scales and sludges, however, can pose a waste management issue if the radium content is sufficiently high. Similarly, pieces of equipment that contain residual quantities of NORM-bearing scales and sludges, as well as surface soils affected by these wastes, can present waste management issues to the petroleum industry. Information about the regulatory requirements applicable to NORM-containing wastes can be reviewed in the section of this web site titled Regulations & Guidelines.

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