Radiological criteria for unrestricted use of sites containing norm

Natural occurring radioactive materia (NORM) is redistributed in the environment as a result of many mineral recovery and processing industries. There are not federal regulations specifying criteria for NORM contaminated sites; however, several states have promulgated regulations. The regulations promulgated by the states generally focus on NORM from oil and gas production, the primary focus of the assessments for this paper. The criteria for residual NORM in soil are generally (1) 0.18 Bq g-1 in the surface 15 cm of soil and 0.6 Bq g-1 at depth or (2) 1.1 Bq g-1, with a limitation on the radon flux. The primary radiation dose pathways for unrestricted use of land are external gamma exposure and exposure related to indoor radon. Radiation doses vary by over an order of magnitude based on different ratios of 226Ra to 228Ra concentrations, biological uptake parameters related to NORM, and the different radon emanation factors for oil field scale and sludge. A 226Ra criterion of 1.1 Bq g-1 results in a dose of about 2 mSv y-1 from external gamma and about 3 mSv y-1 from radon for a general crawl-space type residence home scenario. The chemical and physical characteristics of the NORM and site-specific factors are important considerations in the assessments. The radon dose would be about 3 times higher for NORM in sludge, vs. the assumption of pipe scale. The structural characteristics of residences (e.g., slab-on-grade, crawl-space, or trailer) also have a significant impact on the potential doses to residences