Understanding recharge processes in arid alluvial basins is becoming increasingly important in light of drought and the increasing demand for groundwater as surface water resources become even more scarce. In this study, we investigate recharge to the Pecos Valley Aquifer, one of many alluvial basin aquifers that occur throughout western Texas as well as southwestern United States. The aim of this study is to gain greater understanding of factors controlling (1) spatial distribution of recharge and (2) sources of recharge water in these aquifers. These aims are achieved through investigation of (1) groundwater hydrology, (2) groundwater geochemistry, including isotopes, and (3) results of groundwater flow modeling.

This study found that the common practice of using soil properties to predict recharge rates is potentially unreliable, especially in arid climates. These recharge rate predictions are unreliable because infiltration rate measurements are often based on fully saturated soils, which rarely occur naturally in arid climates. This results in a gross over-estimation of recharge rates.

Groundwater isotopic compositions in the Pecos Valley Aquifer provide information about the source and spatial distribution of recharge to the aquifer. The isotopes analyzed as part of this study are stable deuterium, oxygen-18, and carbon-13, as well as carbon-14 and tritium. These groundwater isotopes indicate that in some parts of the alluvial basin, recharge water is locally-derived and infiltrates throughout the basin through playas. In other parts of the basin, recharge water is derived from adjacent mountains and recharge occurs along the margins of the basin from ephemeral streams.