Investigation of Background Radiation Levels and Geologic Unit Profiles in Durango, Colorado.

摘要

As part of the Uranium Mill Tailings Remedial Action (UMTRA) Project, Oak Ridge National Laboratory (ORNL) has performed radiological surveys on 435 vicinity properties (VPs) in the Durango area. This study was undertaken to establish the background radiation levels and geologic unit profiles in the Durango VP area. During the months of May through June, 1986, extensive radiometric measurements and surface soil samples were collected in the Durango VP area by personnel from ORNL's Grand Junction Office. A majority of the Durango VP surveys were conducted at sites underlain by Quaternary alluvium, older Quaternary gravels, and Cretaceous Lewis and Mancos shales. These four geologic units were selected to be evaluated. The data indicated no formation anomalies and established regional background radiation levels. Durango background radionuclide concentrations in surface soil were determined to be 20.3 (plus minus) 3.4 pCi/g for (sup 40)K, 1.6 (plus minus) 0.5 pCi/g for (sup 226)Ra, and 1.2 (plus minus) 0.3 pCi/g for (sup 232)Th. The Durango background gamma exposure rate was found to be 16.5 (plus minus) 1.3 (mu)R/h. Average gamma spectral count rate measurements for (sup 40)K, (sup 226)Ra and (sup 232)Th were determined to be 553, 150, and 98 counts per minute (cpm), respectively. Geologic unit profiles and Durango background radiation measurements are presented and compared with other areas. 19 refs., 15 figs., 5 tabs. (ERA citation 15:009441)