New Mexico Geological Society Annual Spring Meeting — Abstracts

The White Sands National Monument (WHSA), located within the Tularosa Basin in southern New Mexico, occupies a portion of the world’s largest gypsum dune field. The beauty and uniqueness of the dunes along with the numerous plants and animals that have adapted to this strange environment make the monument a valuable natural resource. Within the dune field, depth to groundwater in inter-dunal areas is generally less than three feet below the surface. This shallow groundwater system, which stabilizes the base of the dunes, is thought to be one of the primary controls on the location and extent of the dune field. There is concern that a lowering of the local water table as a result of an increase in groundwater pumping and surface water diversions in surrounding areas may be detrimental to the preservation of the dune field. Therefore, the water sources that recharge the shallow aquifer within the dunes and the degree of connectivity between the shallow and deeper aquifers are of special interest.

The NM Bureau of Geology and Mineral Resources is conducting a hydrologic study at WHSA to investigate these areas of interest by using a variety of hydrologic, geochemical and geophysical techniques. Continuous water level measurements in monitoring wells within the sand dunes respond quickly to individual storm events, indicating the occurrence of local recharge within the dunes. The infiltration of local precipitation through the dunes to recharge the shallow aquifer is also indicated by water chemistry data, and observed hydraulic gradients in the vadose zone. However, electrical resistivity data suggests that the contribution of local recharge within the dunes is small compared to the relative contribution(s) of one or more additional sources. These other water sources are highly brackish waters that probably represent regional groundwater coming from the north and/or east. Additional chemistry, isotope and age dating data will help us to identify other recharge end members and calculate mixing ratios. Future work also includes the installation of wells that penetrate the basin fill below the dune field. These wells will be used to administer a pumping test to evaluate the connectivity between the shallow and deeper aquifers.