THE AQUIFER MAPPING PROGRAM APPROACH IN THE SOUTHERN SACRAMENTO MOUNTAINS, NEW MEXICO

The Aquifer Mapping Program (AMP), based at the NM Bureau of Geology and Mineral Resources at NM Tech, has a unique approach to hydrogeologic studies in New Mexico. Using multiple datasets, we are able to produce high quality, large-scale interpretations of regional hydrologic systems. The hydrogeologic study of the southern Sacramento Mountains, covering 2400 mi², displays this multidisciplinary approach.

Data collection took place from 2005 to 2009. We mapped 21 geologic maps at 1:24,000-scale (7.5-minute quadrangles) which serve as the foundation for the study. To determine hydrologic properties, every other month we measured depth-to-water in 50 wells, while 9 wells had continuous water level measurements. We collected a variety of samples from over 120 well, spring and stream sites in order to examine groundwater flowpaths, residence time, and geochemical evolution. For comparison with groundwater samples, precipitation was collected from 6 regional sites every 3 months for stable isotope analyses.

Our findings show that the laterally and vertically heterogeneous Yeso Formation is the primary aquifer in the study area. The Yeso Formation includes carbonates, siltstones, sandstones and evaporites, with local and regional fracture networks, breccias and collapse features. Water level fluctuations in response to rainfall events show that the fractured carbonates in the Yeso Formation act as a karstic aquifer system in the high mountains region with shallow perched zones overlying a deeper, regional aquifer. Water sampling in the region indicates that primary recharge occurs in the high elevations above 8200 feet with groundwater moving toward lower elevations in the east and south. The primary recharge is then “recycled” from springs to losing streams where it recharges repeatedly along its flowpath.

The final report for the southern Sacramento Mountains describes our hydrogeologic conceptual model for groundwater flow and recharge within the highly heterogeneous karstic Yeso Formation. The culmination of this project (and all AMP studies) is a publicly available dataset. Large-scale, regional hydrogeology studies performed by the AMP provide the basis for many future research opportunities, as well as benefits to state agencies, water and land managers, federal agencies and local individuals.