New Mexico Geological Society Annual Spring Meeting — Abstracts

Subsurface data (lithologic and geophysical logs) collected from three deep municipal supply wells and one exploratory well are used in conjunction with data from long-term (7-day) pumping tests, remote sensing data (aeromagnetic surveys), geologic mapping, and geochemistry data to determine variations in subsurface stratigraphy, chemistry, and aquifer characteristics in a portion of the Albuquerque Basin. City of Rio Rancho Wells 10A, 22, and 23 are completed to depths of between 2000 and 3000 ft in the Santa Fe Group aquifer. Lithologic and geophysical logs from the wells indicate the presence of aerially extensive subsurface units that can be correlated over distances of at least several miles in deep wells. A 3000 ft deep exploratory boring (completed as a 2880 ft deep cased test well) at the Well 23 site was zone sampled for water quality. Significant variations in water quality are recognized in samples collected below 2000 ft vs. samples collected at 2000 ft or less in the test well. Spinner logs conducted in the test well indicate significant upward vertical groundwater gradient in the aquifer. Clays encountered from 2100 ft to 2460 ft in Well 23 act as significant confining beds. The upper portion of these clays are correlative to clays encountered in the bottom of Wells 10A and 22, which are also interpreted as confining beds for the deeper Santa Fe Group sediments. Water quality degrades rapidly (TDS > 4500 mg/L) below the confining beds in the Well 23 test well and composite borehole chemistry in Wells 22 and Well 10A indicate a similar increase in TDS below the clay beds. Although pumping test and chemistry data indicate that faults identified in the area from surface mapping and/or aeromagnetic surveys act as barriers to groundwater flow, stratigraphy and the presence of a regional confining bed are more significant controls on water quality in the deep aquifer system.