New Mexico Geological Society Annual Spring Meeting — Abstracts

Aquifer heterogeneity has long been an issue in hydrogeologic investigations. For large-scale water supply problems, heterogeneity is often characterized at the formation and stratigraphic group scale. However, with the increasing need to understand the smaller-scale phenomenon of groundwater contaminant migration, hydrogeologists must begin to characterize aquifer heterogeneity at the scale of lithologic facies and architectural elements. Models relating the occurrence and spatial assemblage of lithologic facies to depositional processes offer a powerful tool in assessing heterogeneity. In many of cases interest, the aquifer is of recent geologic origin in which basin evolution and depositional processes are fairly well understood. In such cases, information regarding depositional processes can greatly enhance the ability to quantify statistically the spatial distribution of permeability.

We investigate methods of incorporating depositional process-product models into the statistical characterization of aquifer heterogeneity through an outcrop study of the Pliocene-Pleistocene Sierra Ladrones Formation of the Albuquerque Basin. The Sierra Ladrones crops out along the east-facing Cejita Blanca escarpment of the Llano de Albuquerque west of Belen, New Mexico. The section of the outcrop studied is apeninsular exposure approximately 30 meters high and covering 0.16 km². Four principal architectural elements (Miall, 1985) have been delineated: channel edge deposits, laminated sand sheets, overbank silts and clays, and interfluvial paleosols. These elements are on the order of 1 meter thick and extend horizontally for 100s of meters. Three-dimensional mapping of architectural elements and permeability measurements at surveyed locations provide the database for analysis. This portion of the Sierra Ladrones is interpreted as primarily ancestral Rio Grande floodplain deposits and interfluvial paleosols. The contribution of the western tributaries is also being investigated. The different element types exhibit different mean log-permeability, and the composite geostatistical parameters are controlled by the spatial assemblage of the elements.