Ground-water recharge near Santa Fe, north-central New Mexico

Recharge to the basin-fill aquifer near Santa Fe, New Mexico, was investigated using chloride mass-balance methods. Chloride concentrations in water in the unsaturated zone indicate no recharge in areas where runoff and flooding do not occur. The mass of chloride stored in the upper part of the unsaturated zone in these areas would take about 6,000 to 8,000 years to accumulate, assuming the present (1989) chloride fluxes. Chloride concen- trations in water in the unsaturated zone beneath arroyo channels indicate that recharge does occur in these areas; chloride concentrations in this recharge water at two sites ranged from 40 to 60 milligrams per liter. Estimates of mountain-front recharge using a chloride balance in drainage basins are about 2,320 acre-feet per year in the Santa Fe River drainage, 690 acre-feet per year in the Rio Tesuque drainage, and 830 acre-feet per year in the Anoyo Hondo drainage. Stable isotopes of hydrogen and oxygen indicate that little summer precipitation recharges the ground-water system and that winter precipitation results in most of the recharge water. Most hydrogen and oxygen isotope data for ground water in the area coincide with the local meteoric water line on a graph showing the relation between oxygen and hydrogen in ground water. This indicates that, on the basis of the hydrogen and oxygen isotopic composition of ground water and precipi- tation, evaporation of recharge water or ground water does not occur.