Geology and Geochemistry of a Deep Aquifer System, Ruidoso, New Mexico USA

Two deep exploratory wells were drilled in the Sacramento Mountains near Ruidoso, New Mexico to depths greater than 2,500 feet below ground surface for evaluating the potential water supply.  Water rights are administered by the New Mexico Office of the State Engineer, and supply wells are developed in aquifers of Cretaceous and Paleozoic rocks.  The deep aquifer system consists predominantly of poorly characterized Paleozoic San Andres Limestone and Tertiary intrusive rocks.  An important feature of the deep aquifer system is the stratigraphic relationship and lithologic characteristics of limestone and dolomite units relative to the 2,500-foot depth. 

Geology and geochemistry for the deep aquifer system were characterized through the use of borehole geophysics, lithologic and mineralogical descriptions, and water quality analyses.   A full suite of geophysical methods were used to characterize rock types.  Lithology was described from drill cuttings with additional examination using microscope and microprobe analyses.  Water quality analyses included major ions, stable isotopes of oxygen and hydrogen, carbon-14 and tritium.  Water quality samples were also collected from nearby and regional wells completed in the Cretaceous and Paleozoic aquifers.  Surface water samples were also collected.  Results of the data collection effort were integrated to determine geologic units encountered during drilling and their regional hydrogeological and geochemical context.  The chemistry of collected samples reflects water-rock interactions along flow paths; for example, the Ca-Mg-HCO3 type water is associated with the limestone and dolomites of the San Andres Formation, and the Na-Ca-SO4 water is derived from anhydrite dissolution and cation-exchange reactions.  This presentation will provide a review of the exploratory drilling program and interpretation of the data collection efforts described above.