New Mexico Geological Society Annual Spring Meeting — Abstracts

Geologic controls on water and solute transport in a heterogeneous vadose zone were investigated in a densely instrumented field plot in central New Mexico. The 30-m by 30-m plot was two miles west of the present day Rio Grande near the New Mexico Tech golf course. Soil cores from 30 boreholes drilled to various depths up to 20-m deep were sampled for particle size distribution and moisture content. Two trenches of depths 1. 5 and 5 m were excavated to present a 2-D view of the geology beneath the plot. The stratigraphy is composed of a fairly
heterogeneous set of seven alluvial fan or piedmont slope units to depth of 4 m, and an underlying, mostly homogeneous ancestral Rio Grande sand facies extending to at least 20 m. A qualitative 3-D reconstruction of the geology beneath the site was prepared as well as a quantitative assessment of the two units' textural and hydrologic properties. Borehole samples were used to create stratigraphic cross-sections and fence diagrams based on the USCS soil classification system. In addition, geostatistical analyses of conductivity and textural data were performed for the geologic units. Geologic structure has been correlated with lateral variability in hydraulic properties. The geologic and hydrologic characterization of such units is important for predicting natural or anthropogenic recharge and contaminant pathways in similar environments elsewhere.