Environmental Tritium as a Hydrometeorologic Tool in the Roswell Basin, New Mexico

Tritium analysis of precipitation and ground water samples taken over 13 years, together with geohydrologic and meteorologic data, has led to the construction of a tritium input function for the Roswell artesian basin. This recharge function. rather than tritium concentrations in precipitation, was correlated with tritium-time profiles of seven wells. The profiles of these wells also were correlated among each other. Correlation was greatly facilitated by the slug-flow characteristics of the recharge and the sharp periodicity of precipitation in the recharge area of this semi-arid basin. It was found that recharge is not a linear function of precipitation but proportional to an annual fraction of the mean.

Two distinct subregions, characterized by different circulation patterns, were recognized in the basin. The residence time of water in the northern subregion (Roswell) is about four years. It is larger than seven years in the central region (Artesia). Tritium input characteristics vary from north to south along the western flank of the basin. In the recharge area of the northern subregion, percolation from surface to water table takes between 4-12 months.

Hydrological parameters computed on the basis of tritium data were correlated with lithologic and structural features in the basin. In the northern part of the basin average ground water velocity, porosity, effective thickness of the aquifer, and the dispersion constant were found to be of the order of 70 ft/day, 1%, 2 ft, and 70 ft, respectively. A one-dimensional dispersion model was succes6fully used to test the precipitation/ recharge relation using tritium as a tracer.

Project No. A-037-NMEX