An intensive site survey and on-site analysis program were conducted to evaluate the distribution of four radionuclides in the general vicinity of Gallup, Mew Mexico, subsequent to the accidental breach of a uranium mill tailings pond dam and the release of a large quantity of tailings pond materials. The objective of this work was to determine the distribution and concentration levels of 210Pb, 226Ra, 230Th , and U in the arroyo that is immediately adjacent to the uranium tailings pond (pipeline arroyo) and in the Rio Puerco arroyo into which the pipeline arroyo drains. An intensive survey between the United Nuclear Corporation (UNC) Church Rock Mill site and the Hew MexicoArizona state border was performed. Sampling locations were established at approximately 50O-ft intervals along the arroyo. During the weeks of September 24 through October 5, 1979, a series of samples was collected from alternate sampling locations along the arroyo. The purpose of this collection of samples and their subsequent analysis was to provide an immediate evaluation of the extent and the levels of radioactive contamination. The data obtained from this extensive survey were then compared to action levels which had been proposed by the Muclear Regulatory Commission and were adapted by the New Mexico Environmental Improvement Division (NMEID) for Th and Ra concentrations that would require site cleanup.
The Pacific Northwest Laboratory/Nuclear Regulatory Commission mobile laboratory van was on-site at the UNC Church Rock Mill from September 22, 1979, through December 13, 1979, and was manned by one or more PNL personnel for all but four weeks of this time period. Approximately 1200 samples associated with the Rio Puerco survey were analyzed in the laboratory. An additional 1200 samples related to the Rio Puerco cleanup operations which the United Nuclear Corporation was conducting were analyzed on-site in the mobile laboratory. The purpose of these analyses was to determine the effectiveness of the cleanup operations that were ongoing and to evaluate what additional cleanup would be required. This on-site analysis of radioactive contamination constituted the principal task of this project, with the identification of those portions of the arroyo exceeding the NMEID proposed cleanup criteria being the
