A successful groundwater exploration and development program was conducted in the Pampa Lagunillas and Pampa Lirima groundwater basins, in the Prealtiplano of northern Chile. The objective of the program was to develop a wellfield capable of providing 120 liters per second of good quality groundwater for industrial use at the Cerro Colorado copper mining complex for an estimated mine life of 30 years. Wellfield development of the Pampa Lagunillas basin consisted of construction and testing of four large-diameter high-yield production water wells. Results of the exploration and development programs indicated that large quantities of recoverable groundwater are stored in the aquifer systems in each basin. The most favorable conditions for development of a large and reliable groundwater supply occur in the Pampa Lagunillas basin, where groundwater storage in the saturated alluvial sediments in the Pampa Lagunillas basin is in the magnitude of 450 million cubic meters.