New Mexico Geological Society Annual Spring Meeting — Abstracts

An increasing number of domestic wells are being drilled in and around the Galisteo Basin south of Santa Fe, New Mexico. Many of these wells encounter the Espinaso Formation and the Galisteo Formation at depths ranging from 20 to 100 feet below ground surface (bgs). In general, data obtained during drilling and well testing indicate that water production in both Formations is limited. However, water capable of sustaining limited development may be found: (1) in fractures within the Espinaso, (2) at the basal contact between the Espinaso and the Galisteo, and (3) fractured channel sands within the Galisteo. Water quality in both Formations is variable, but adequate for drinking water purposes.

The Espinaso Formation is of Oligocene age and consists primarily of red to gray, porphyritic monzonite volcanic and volcaniclastic rocks (Disbrow & Stoll, 1957; Baldridge et aI.,1980). The thickness of this formation is location-dependent and, based on well records and drilling observation, ranges from 100 to 1000 feet. Most wells completed in the Espinaso produce less than five gallons per minute (gpm), although wells located within fracture zones may produc 10 gpm or greater. Limited testing data indicate that limited recharge occurs primarily through tectonic and/or cooling fractures. Near the intersection of State Highway 14 and Santa Fe County Road 42, the contact between the Espinaso and the Galisteo was encountered at approximately 1000 feet bgs. The completed well reportedly produced 100 gpm.

The Galisteo Fonnation is of Eocene/Oligocene age and consists of conglomerates and sands interbedded with thick sequences of red and orange mudstone; the Galisteo Formation is estimated to be in excess of 1000 feet thick in this area (Spiegel & Baldwin, 1963). Fractured channel sands within the Galisteo consist of fine-to medium-grained, angular to sub-angular volcanic and granitic clasts, and may be over 100 feet thick. Galisteo Formation sands can produce water in excess of 40 gpm, but 5 to 10 gpm may be more typical. Transmissivity values for these sands range from 53.5 gpd/ft to 1300 gpd/ft. Where channel sands are not encountered, the Galisteo produces virtually no water and consists of very fme-grained, red and orange mudstones. Some wells drilled to depths of 700 feet have encountered only the red mudstones of the Galisteo Formation.

These formations produce potable water, although water quality varies within each formation. Within the Espinaso Formation, fluoride, barium and copper have been detected above the EPA's maximum contaminant levels (MCLs) for drinking water. Within the Galisteo Formation, fluoride, sulfate and total dissolved solids have been detected above the MCLs. Further study of water availability and regional trends within these formations is needed, as continued development in this area will increase demands on already limited aquifers.