MINERALOGICAL AND BULK-ROCK GEOCHEMICAL SIGNATURES OF RINGOLD AND HANFORD FORMATION SEDIMENTS

The Ringold Formation and post-Ringold sediments (including cataclysmic flood deposits of the Hanford formation) constitute the primary aquifer and vadose zone sediments beneath the U.S. Department of Energy’s Hanford Site. Although much is known about these formations from over 50 years of study, quantitative methods for classifying these materials in support of flow and transport models have not been developed. The purpose of this study was to explore the possibility of using statistical methods to classify sediment samples belonging to the Hanford or Ringold formations using mineralogy and geochemistry data. To this end, existing electron microprobe (EM), petrographic (Petro), and x-ray fluorescence (XRF) data, were compiled into a central, digital database. Descriptive statistics, tests of difference (e.g. ANOVA), principal component analysis, and various classification analyses were applied to the data as a whole, as well as for subgroups comprised of samples from the two principal formations and for the two primary sampling locations (200 West Area and 200 East Area). We were able to use several statistical techniques to generate effective classifiers for distinguishing between Hanford and Ringold formation samples using mineralogical and geochemical data. Classifiers for the 200 West Area that were generated using discriminant function analysis show good performance for the EM, Petro, and XRF datasets. However, spatial variability and the lack of stringent validation data suggest that generalization of the classification rules to areas outside of 200 West Area may be premature.