A Study of Improved Quality Effluent Discharged From Agua Nueva Water Reclamation Facility to the Lower Santa Cruz River

Abstract

Reclaimed water is an important renewable resource because it mitigates the use of potable supplies to meet outdoor water demand. In Tucson, reclaimed water is managed through aquifer storage and recovery. Some recharge is done directly in the Santa Cruz River where credits are earned for water that infiltrates in a permitted stretch. The new Pima County water treatment facility, Agua Nueva, releases high quality Class A effluent, which infiltrates the river at higher rates than water from the previous facility. This study monitored the discharge from Agua Nueva and aimed to quantify instream recharge rates. Gaining higher spatial resolution on recharge is important for verifying current recharge credits, and modeling water demand of future effluent-use projects. Water level was continually measured at four river monitoring stations. A mass balance method was used to estimate recharge by calculating differences in streamflow between upstream and downstream stations. Because of the highly variable outflow from Agua Nueva, this method’s results were inconclusive. The study resulted in development of an effective way to temporarily deploy divers in highly variable Southwest streams experiencing intense monsoons. The water level data gathered provided new insight to patterns of effluent flow in the Lower Santa Cruz River.