New Mexico Geological Society Annual Spring Meeting — Abstracts

A drilling and testing program funded by the Bureau of Reclamation (in progress) carried out with oversight by Glorieta Geoscience, Inc. (GGI) for the Town of Taos and the Bureau of Indian Affairs (BIA) for Taos Pueblo, greatly expands available quantitative aquifer data and water quality data for Tertiary basin fill aquifers underlying the Servilleta Basalts in the Southern San Luis Basin in northern New Mexico. Aquifer testing completed to date on four separate multiple-aquifer well nests provides data on aquifer boundaries, the variability in hydraulic conductivity (k) in Chama-EI Rito vs. Ojo Caliente aquifers, and qualitative data on the variability in vertical k (k') at the different sites. Aquifer testing data indicate that buried structures located near the Picuris and Sangre de Cristo mountain front act as impermeable boundaries, whereas the inferred Town Yard fault, located further from the mountain front, may act as a recharge boundary. Productive sections of Tesuque Formation, Chama-EI Rito Member sediments appear to exhibit order of magnitude higher k than do Ojo Caliente Member sediments (1 to 3 ft/day vs. 0.1 to 0.2 ft/day). The initial testing results and data on vertical gradients indicate that k' between the basin fill aquifers is highly variable, with some tests showing leakage between aquifers and other tests indicating that aquifers remained hydrologically isolated from one another during the period of the pumping test. The Servilleta basalts and overlying eolian mantles plus underlying baked soil horizons act as confining beds, with little or no communication observed between aquifers underlying the Servilleta basalts and the overlying shallow ground water system. Upward vertical gradients are exhibited in some well nests while downward vertical gradients are exhibited in other well nests. Water quality data indicate generally good ground water quality in the deep aquifer system (between 1000 and 2500 ft below land surface), with the exception of high pH, some high fluoride levels, and potentially elevated arsenic levels.