Cleanup of radioactive mud spill U20aa postshot drilling site NTS

Radioactive decontamination of a large rugged terrain on the NTS (Area 20) was undertaken during the Summer of 1976. Several decontamination methods were used and their effectiveness, as measured by the fraction of radioactivity remaining (FR), ranged from 10-1 to 10-3, depending upon the method used and type of terrain. Front end loading was most efficient in large relatively flat areas of fine grain, compact dirt with an FR of about 10-2. Shoveling and bagging achieved FRs of 10-2 in locations of fine grain, compact dirt. However, if dirt was coarse grain or gravel-like, the contaminated mud/water had seeped to considerable depths, making shoveling impractical. Flushing with water was the method chosen for rocky surfaces and was the primary method of decontamination in Area 4. FRs down to 10-3 were achieved on smooth surfaces and about 10-1 in cracks. Vacuuming was very effective in flat areas with fine grain compact dirt achieving FRs down to 10-3, but was a very slow process compared to front end loading. Approximately 900 man days were expended on this cleanup, and 2584 yd3 of contaminated dirt were removed. A similar amount of clean dirt was transported from about two miles away to cover the crater burial site, mud sump, and areas containing residual radiation above 1 mrem/h contact. Total quantity of residual radioactivity present 6 months following the spill and after decontamination was estimated as 900 millicuries of 106 Ru/Rh and 0.034 millicuries 103Ru. No person was exposed to doses of radiation (external or internal) above the maximum allowable limits listed in ERDAM 0524. Estimates based upon hand dose measurements indicate that no individual should have received more than 584 mrem to hands