New Mexico Geological Society Annual Spring Meeting — Abstracts

Hydrologic sections consisting of observation-well groups and a river-stage gage were established along the Rio Grande near Las Cruces, Mesquite, and Canutillo as part of a study to better define the hydrologic system of the Mesilla ground-water basin. The wells were completed . in the Quaternary flood-plain alluvium and in the Quaternary and Tertiary Santa Fe Group at depths ranging from 35 to 801 feet.

Downward, vertical hydraulic gradients exist at all observation-well groups. Water levels in wells near the Rio Grande correspond to changes in river stage. Hydraulic gradients indicate the Rio Grande is recharging the aquifer at each section. Seasonal water-level trends in wells less than 60 feet deep generally correspond to recharge during the irrigation season; water. levels in deeper wells (60 to 350 feet) generally indicate similar trends.

Water-quality analyses indicate that freshwater zones are overlain by zones of slightly saline to saline water. Near the Rio Grande and irrigation canals, the shallow, slightly saline to saline water is flushed from the aquifer by surface-water recharge.