HYDROGEOLOGY OF THE SANTA FE GROUP AQUIFER SYSTEM, SOUTHERN ESPANOLA BASIN,NEW MEXICO--REPORT ON RECENT DEEP TEST WELLS IN THE SANTA FE COMMUNITY COLLEGE DISTRICT

Recent (2001-2002) sample and geophysical logging of a 1,500-ft exploration well in the “type” Santa Fe Group (SFG), and concurrent hydrogeologic studies throughout the Santa Fe embayment area are providing significant new insights on basin-fill aquifers of the southern Espańola Basin, New Mexico. Primary study sites include stratigraphic and production test-wells near the Santa Fe Community College and adjacent parts of the Rancho Viejo de Santa Fe, Inc. development. As in other Rio Grande rift basins (e.g. Hawley and Kernodle, 2000, NMWRRI Rept. 312), our conceptual model of the area’s hydrogeologic framework is here defined in terms of 1) lithofacies assemblages that are grouped into informal (lower, middle and upper) SFG hydrostratigraphic units, and 2) basin-boundary and intra-basin structural controls. Our work confirms both the “type” Santa Fe Group lithostratigraphic model (Ancha Fm/ Tesuque Fm) of Spiegel and Baldwin (1963, USGS WSP 1575) and recent revisions proposed by Koning and others (2002, NM Geology, v. 24). Borehole logs of Community College District Exploratory Well #1 (CCDX1), however, provide a much clearer subsurface view of this previously unexplored part of the Santa Fe embayment. At the CCDX1 site, about 200 ft of the Pliocene Ancha Fm, with a veneer of arroyo deposits, are underlain by 1,300+ ft of the Miocene Tesuque Fm. The vadose zone is about 260 ft thick. The Upper Santa Fe—Ancha Fm is composed of arkosic (Sangre de Cristo-derived) piedmont alluvium, but this facies is a subordinate Tesuque Fm component. The dominant lithofacies assemblage in the main body of the Tesuque (middle SFG hydrostratigraphic unit) is a basin-floor sequence of sandy channel and silty overbank deposits. Hydraulic testing is consistent with a heterogeneous system of stacked channel deposits. This unit is about 1,100 ft thick at the CCDX1 site and has significant groundwater-production potential.