Dose Assessment Associated with Landspreading of Petroleum-Industry Naturally Occuring Radioactive Material

As a result of oil and gas production and processing operations, naturally occurring radioactive material (NORM) sometimes accumulates at elevated concentrations in byproduct waste streams. The primary radionuclide of concern in NORM wastes are radium-226 (Ra-226) of the uranium-238 decay series; radium-228 of the thorium-232 decay series is also present, but usually at lower concentrations. The production waste streams most likely to be contaminated by elevated radium concentrations include produced water, scale, and sludge. Scales and sludges removed from production equipment sometimes are disposed of by landspreading, a method in which wastes are spread over the soil surface to allow the hydrocarbon component of the wastes to degrade. The disposal of NORM-contaminated wastes by landspreading was modeled to evaluate potential radiological doses to the general public. A variety of future land use scenarios—including residential, industrial, recreational, and agricultural scenarios—were considered. The waste streams considered included scales and sludges containing NORM above background levels. The RESRAD computer code was used to estimate the radiological doses for the maximally exposed receptor for each scenario. Depending on the land-use scenario, potential exposure pathways evaluated for the general public included external radiation; inhalation of contaminated particulates; inhalation of indoor and outdoor radon-222; inadvertent ingestion of contaminated soil; and ingestion of crops, milk, and meat grown on the property. Potential doses were modeled for a unit concentration of $1\mathrm{Bq}{g}^{-1}$ of Ra-226 in soil. Because dose increases linearly with radium concentration, doses were extrapolated for a range of radium concentrations.