INTRODUCTION
On July 16, 1979, a break in the tailings dam of the United Nuclear Corporation's {UNC) Church Rock, New Mexico, mill occurred. Approximately 94 million gallons of the tailings liquid which had been impounded behind this dam were released into an adjacent arroyo. An estimated 1100 tons of tailings solids also emptied from the dam into the adjoining toe dam and subsequently into the adjacent arroyo. A typical composition of the UNC tailings pond solution is listed in Table 1. The spilled solution traveled down the so-called "pipeline arroyo" and into the north branch of the Rio Puerco arroyo. Beyond this point it continued past the location where the north and south branches of the Rio Puerco join immediately northeast of Gallup, New Mexico, continued across the remainder of the state of New Mexico, and extended into the state of Arizona for ~20 to 25 miles. At that point the flow of the Rio Puerco terminates. Figure 1 shows the location of the Rio Puerco in New Mexico.
Subsequent to the release of this tailings pond solution several organizations began environmental sampling and monitoring programs. These organizations include the U.S. Environmental Protection Agency, the New Mexico Environmental Improvement Division (NME1D), and personnel from the United Nuclear Corporation mine and mill at Church Rock. Intermittent samplings of soil, water, and air were performed by these organizations between July 16, 1979, and the middle of September, 1979. At that time Pacific Northwest Laboratory (PNL) responded to a request from the U.S. Nuclear Regulatory Commission to provide immediate on-site sampling and radionuclide analysis capability. The principal objective of PNL's work on-site at the United Nuclear Corporation mill was to provide capabilities for immediate analyses of samples which had been collected from the Rio Puerco environment. tance and advice on sampling methodology were requested.
Secondarily, assistance and advice on sampling methodology were requested. The conditions for sample preparation and sample analysis were optimized so that the total amount of time required from the time the sample was collected until the data regarding radionuclide concentrations for that sample were available could be less
