New Mexico Geological Society Annual Spring Meeting — Abstracts

This study was undertaken as a project of the Taos Soil and Water Conservation District, to begin the process of addressing concerns about groundwater resources in Taos County. This is in a geologically complex area within the San Luis rift basin. To provide baseline data for Taos County, nearly 2000 water wells have been accurately located using GPS. Water table elevation maps have been prepared and a depth-to-water map prepared for laymen. Depth-to-water varies, from less than 100 feet along perennial streams along the Sangre de Cristo Mountain front to over 1000 feet in western Taos County. Direction of groundwater flows can be seen on the water table elevation maps and recharge sources can be implied for many areas from these maps. Deeper wells below 500 feet show effects of a downward pressure gradient and were not used for the water table maps.

Structure maps on the Servilleta basalt were made and used in conjunction with aeromagnetic data to map the numerous faults within the study area. Water table differences are seen across faults that impact aquifers below depths of 200 feet. Upward pressure gradients and warm waters are frequently observed along faults. About 500 wells were plotted for major cations and anions and trace inorganics. Contoured maps were prepared on 19 selected constituents, including TDS, HCO3, Br, CI, F, N, SO4, Ca, K, Mg, Na, As, Ba, Cr, Pb, Si, Sr, U, and Zn. High values exceeding EPA drinking standards were mapped mainly along fault traces. Hydrochemical zones are mapped across the County reflecting the geology of recharge source areas and age of groundwater.

The eastern part of the rift basin is gifted with perennial recharge from the mountain front into a large clastic section that serves as a thick aquifer, which provides drinking water for the majority of the population of Taos County. Local groundwater problems include a slight water table drop adjacent to streams during drought periods, rapid draining through fractured dacite lavas, low production rates of fine-grained and volcanoclastic reservoirs in western Taos, County, and cementation of the Picuris Fm. aquifer in southern Taos County.