Effluent recharge to the upper Santa Cruz River floodplain aquifer, Santa Cruz County, Arizona

Abstract

The Nogales International Wastewater Treatment Plant (NIWTP) discharges treated wastewater to the Upper Santa Cruz River in Santa Cruz County, Arizona. Results of a study designed to estimate effluent recharge to the floodplain aquifer underlying the river are presented. The study's centerpiece comprised two 48-hour synoptics during which intensive data on water budget components were collected. Complimenting these data were periodic water level readings and sample collections through 1995, a seismic refraction survey, and continuous operation of two meteorological towers. These data in conjunction with historical records were used to construct water budgets for the synoptic runs and for 1995, and to estimate effluent recharge for the conditions experienced during the synoptic runs (21.8 acre-feet/day in June and 0.7 acre-feet/day in December), and for 1995 (3,674 acre-feet). An additional effluent recharge estimate for 1995 (5,806 acre-feet), was made using a chloride and boron mass balance approach. The study also provided a basis for recommendations on the monitoring requirements of a long-term effluent recharge estimation program.