Hydrogeology and geochemistry of Horace Springs, Pueblo of Acoma, New Mexico

Horace Springs is the start of a perennial reach of the Rio San Jose at the Pueblo of Acoma, New Mexico. As the meandering Rio San Jose flows through a gap between Horace Mesa to the north and La Ventana Mesa to the south, the alluvial aquifer system lies in the gap, causing a decrease in the alluvial aquifer’s cross-sectional area resulting in groundwater discharging to the streambed. Horace Springs, currently, discharges about 3.5 to 4 cubic feet per second of water into the stream channel and is classified as a rheocrene spring. Geology in the area is characterized by Mesozoic sedimentary rocks that have sandstone and limestone aquifer systems. The San Rafael Fault Zone is a northeast trending fault zone west of Acoma, and rocks have been down-dropped towards the east. Along the fault, the San Andres Limestone and Glorieta Sandstone (Psg), which forms a combined aquifer system, are just below alluvial cover and lava flows west of the fault; east of the fault the aquifer is displaced over 800 feet deeper below ground surface. The groundwater in the Psg, which flows from west to east, is brought to the surface due to juxtaposition of the Psg against the lower permeability Chinle Formation along the fault contact. This water discharges at a spring, Ojo del Gallo, and also recharges the alluvial-basalt aquifer. Horace Springs discharges from the alluvial-basalt aquifer downgradient (east) of the fault. Water chemistry was used to evaluate potential aquifers contributing to Horace Springs. Water that discharges at Horace Spring is predominantly derived from the Psg, with components from aquifers in the alluvial-basalt, Entrada Sandstone and Dakota Sandstone. 397