GROUND-WATER MONITORING IN THE MIDDLE RIO GRANDE BASIN, CENTRAL NEW MEXICO—IMPLICATIONS OF WATER-LEVEL VARIATIONS IN NESTED PIEZOMETERS

The U.S. Geological Survey, in cooperation with the City of Albuquerque, Bernalillo County, and the New Mexico Office of the State Engineer, has installed a network of 60 nested piezometers throughout the Middle Rio Grande Basin (MRGB) since 1996. The purpose of the piezometer network is to improve understanding of the hydrogeology of the MRGB; information gained from this project includes detailed geologic information from well cuttings and geophysical well logs and water-level and water-quality data for various depths of the aquifer. Piezometers within the city of Albuquerque are generally located at least 1 mile from major production wells to minimize effects of city pumpage. To measure vertical variations in hydraulic head and allow for water-quality sampling at discrete intervals, individual piezometers in a nest are screened at various depths within the aquifer. Typical screen placement includes a 20- to 100-foot screen at the water table, a 5-foot screen in the city’s production zone, and a 5-foot screen below the production zone. Hydraulic head is recorded hourly at all piezometers; manual measurements are made every 4 to 8 weeks for quality control. Analysis of hourly hydraulic-head data provides researchers with valuable information, such as: (1) directions and magnitudes of vertical hydraulic gradients; (2) effects of barometric pressure on water levels; (3) effects of recharge on water levels in different parts of the aquifer; (4) effects of ground-water withdrawals on water levels in the aquifer; (5) extent to which various depths of the aquifer are hydraulically connected; and (6) regional water-level trends.