New Mexico Geological Society Annual Spring Meeting — Abstracts

As part of the southern Sacramento Mountains Hydrogeology Study, funded by the Otero Soil and Water Conservation District, the New Mexico Bureau of Geology and Mineral Resources has sampled 42 springs and 77 wells for ion chemistry and trace metals, as well as other constituents. Overall, spring and well samples indicate that ground water is dominated by calcium and magnesium as the cations and bicarbonate and sulfate as the main anions. These results support that carbonate dissolution is the dominant chemical process influencing the water chemistry.

Springs, located mostly within the high mountains region of the study area, are typically cool waters (on average 10°C) and are dominantly calcium-bicarbonate or calcium-magnesium bicarbonate water types. Springs found in the northern regions of the study area have higher TDS and concentrations of sulfate, chloride, strontium, sodium, magnesium, silica. Well water samples, which were collected from sites over a larger region, have higher specific conductance and higher ion concentrations, in general, compared to springs. Also, well water temperatures are warmer than springs at an average of 15.4°C. About 32% of the well water types are calcium-bicarbonate or calcium-magnesium bicarbonate (similar to springs), but also have slightly more “evolved” water types, with about 65% calcium-magnesium bicarbonatesulfate, or sulfate-bicarbonate water types. Similar to springs, well water samples show increases in ion concentrations towards the north, but the dominant increases are found towards the east.

The trends of our water chemistry, with some ground water ages, suggest regional ground water flow paths exist, despite multiple perched aquifers in the highly heterogeneous Yeso Formation. Ground water is recharged in the high mountains, and flows to the east and north. Most springs and wells with fairly young, fresh meteoric waters are found in the high mountains area, while wells further east along the Pecos Slope have older, more chemically evolved signatures due to longer water-rock interactions. These chemical changes in the ground water may also be affected by lithologic changes within the Yeso and San Andres Formations.