Supervising Scientist Division

Results of gamma dose rate surveys at remediated, former uranium mining and milling sites in the South Alligator River Valley

Internal Report 586
Doering C, Ryan B, Bollhöfer A, Sellwood J, Fox T & Pfitzner J
Department of Sustainability, Environment, Water, Population and Communities, 2010


Executive summary

Gamma dose rate surveys have been conducted at the former Rockhole Residues, Palette and El Sherana uranium mining and milling site in the South Alligator River Valley. These locations were rehabilitated during the 2009 dry season. The survey results show that the absorbed gamma dose rates at the sites have been reduced to a level which, on average, is less than the agreed guideline value of 1.25 ± 0.25 µGy∙h-1 for site clean-up.

The estimated annual effective dose from external gamma radiation for an adult and a child, assuming the unlikely scenario of one month occupancy per year during the dry season, is less than 1 mSv at all sites. The estimated annual effective dose to an individual from all exposure pathways under the assumed occupancy scenario potentially approaches 1 mSv at the Palette and El Sherana sites. The Australian Radiation Protection and Nuclear Safety Agency (ARPANSA) has imposed a total annual radiation dose reference level of less than 10 mSv for people in the South Alligator River Valley. Based on this reference value, there is presently no unacceptable radiation risk to a member of the general public accessing the remediated sites for the period of the assumed conservative occupancy scenario.