Simulation of the regional geohydrology of the Tesuque aquifer system near Santa Fe, New Mexico

Declining ground-water levels resulting from ground-water withdrawals in the Santa Fe, New Mexico, area have caused concern about the future availability of water from the Tesuque aquifer system (includes the Tesuque, Puye, and Ancha Formations of Tertiary age).This report describes the geohydrology of the Tesuque aquifer system in the Santa Fe area and presents a three-dimensional regional ground-water flow model with which the effects of existing and possible future ground-water withdrawals on the regional aquifer system were assessed.The model was calibrated using simulations of the predevelopment steadystate condition and the 1947-82 historical period.The response of the aquifer to two scenarios of future ground-water withdrawals from 1983 to 2020 was simulated.The maximum projected decline in hydraulic head from 1983 to 2020 was 174 feet for both the large and small water-demand scenarios and occurred in the area of the Santa Fe well field.Simulated discharge to the Pojoaque River and its tributaries was 7.0 cubic feet per second at the end of the simulation with the small water demand and 6.9 cubic feet per second with the large water demand, compared to 7.3 cubic feet per second for the steady-state simulation and 7.1 cubic feet per second at the end of the historical transient simulation.Simulated discharge to the Rio Grande was 36.0 cubic feet per second at the end of the simulation with the small water demand and 34.3 cubic feet per second with the large water demand, compared to 39.3 cubic feet per second for the steady-state simulation and 37.2 cubic feet per second at the end of the historical transient simulation.The sensitivity of the model to changes in aquifer thickness, hydraulic conductivity, specific yield, storage coefficient, and vertical anisotropy ratio was tested.The sensitivity analyses indicated that maximum simulated decline in hydraulic head is most sensitive to specific yield.Average change in hydraulic head is most sensitive to hydraulic conductivity.Simulated discharge to the rivers is most sensitive to the changes in hydraulic conductivity.1