API PUBL 7105-1997

The objective of the work described in this report was the preparation of a brief technical document evaluating the concentration limit of 30 pCi/g Ra-226 in pipe scale and sludge left near the surface of remediated oil field sites and returned to unrestricted public access. Radiation survey protocols used by the oil companies and the variability of radioactivity in the NORM material ensure that only small isolated areas may contain Ra-226 at the concentration limit, while the concentration throughout most of the site is well below the limit. Analysis was based on estimates (by modeling) of the potential transfer of radioactivity through environmental pathways and of potential exposures to people using the remediated site. The scope of work included an assessment of potential dose from radioactivity in pipe scale and sludge to users of remediated pits, tank battery sites, and land firms. In this assessment, an estimated distribution of radium concentration in NORM material, ranging from 30 pCi/g down to natural background levels (based on Otto's data 1989), was included as an integral component of the pathways and exposure models. This fundamental difference in waste characterization sets this assessment apart horn all previous work. The probabilistic method used for calculating the potential doses and indoor radon concentrations is consistent with the new policy announced by EPA's Science Policy Council in February 1997 which recommends application of such methods.