Page:Survey of Radionuclide Distributions Resulting from the Church Rock, New Mexico, Uranium Mill Tailings Pond Dam Failure OCR.pdf/8

 1. On-site use of planar intrinsic germanium detectors provides adequate sensitivity and short analysis times for quantitation of 210Pb, 226Ra, 230Th, and 238U in sediments/sails.

2. The original sampling plan, which consisted of collecting surface soil/sediment samples at 1000-ft intervals, was adequate to determine those areas which were contaminated and required cleanup.

3. Clustering of samples within arroyo reaches defined by physical (morphological) features would provide a better estimation of the radionuclide spatial variability than did the sampling pattern which was used and which was based on equal distance increments.

4. The revised Rio Puerco cleanup criteria proposed by the NMEID are statistically adequate.

5. Concentrations of Pb, Ra, and U in samples throughout the length of the arroyo are not distinguishable from natural background concentrations, 6. Concentrations of 230Th range from background levels to levels elevated considerably greater than background. Plots of 230Th concentrations versus distance from the tailings pond show high variability, Therefore, a statistical smoothing function was applied to the data to facilitate interpretation,

7. Sediment samples from two site-variability studies indicate that there is considerable 230Th concentration variability within even limited areas of the arroyo (i.e, 5-ft square grids and 25-ft square grids).

8. The concentrations of 230Th in the Rio Puerco show an apparent periodicity as a function of distance. This period is ~2.5 km.

9. The estimated total inventory of 230Th in the Rio Puerco from sampling stake 0-491 is 26.8 Ci, based on aata from the upper two feet of the core samples. The inventory based on data from the first-terrace and second-terrace samples (upper two inches) is 4.9 Ci. The