SCERP Project Number: W-16
Principal Investigator: Mark R. Baker
University of Texas at El Paso
Final Report Abstract
Wells were drilled and logged for the NuMex landfill operation permit in 1991. Correlation of strata between these wells proved difficult, and prompted this study of the potential usefulness of geophysical logs to characterization of geologic and hydrologic variability.
We collected both geophysical and geological observations on an escarpment near one of the wells (20 meters distant) with a good log suite. From this data we established that beds interpreted as paleosols, about 1-2 meters thick, could be correlated both to the adjacent well, and to wells around the landfill. Braided stream channel deposits were typically 2 meters thick and could be correlated only on the resistivity log to the nearby well but could not be lithologically correlated to adjacent wells. Gamma ray responses were highly variable and indicative of the distribution of heavy minerals in channel lags and potassium feldspar distribution.
Paleosols were recognized on the basis of either the resistivity or neutron log responses in fine-grained/clay rich strata typically associated with the Bt horizon. The gamma ray response showed an increase with depth through the clay-rich zone that is probably associated with leaching of potassium and uranium during soil development. The paleosols could be traced laterally into fluvial channel deposits, and consequently appear to be good chronologic markers.
Quantitative interpretations of the log readings indicated that zones of partial saturation could be identified, and the depth of drilling mud invasion could be estimated. Discontinuities in profiles of saturation and invasion distance are consistent with the presence of vertical flow barriers that are smaller than could be distinguished as lithologic units in either cuttings or logs. Porosity could not effectively be estimated from the logs due to the mineralogic complexity and uncertainty associated with fluid salinities.
The site of this study did not fulfill the potential we anticipated for teaching purposes due to the lack of stability of the slope. Many of the channel sand deposits were incapable of holding a surface that could be used and we could not obtain as much information as we had hoped.
Results of this study are currently being applied to characterizing variability for Sandia National Laboratory's Environmental Restoration Program.
Last updated 7/1/99