A study of improved quality effluent discharged from Agua Nueva Water Reclamation Facility to the Lower Santa Cruz River

Mehka Pereira1, Dick L. Thompson2

1Department of Hydrology and Atmospheric Sciences, The University of Arizona, Tucson, Arizona

2Tucson Water, Tucson, Arizona

Reclaimed water is an important renewable resource in Tucson and helps conserve potable water used to meet outdoor water demand. Pima County’s water treatment facilities discharge effluent (highly treated wastewater) to the Santa Cruz River where it contributes to a managed aquifer recharge project. Water that infiltrates in-stream earns recharge credits, which are withdrawn from the reclaim system when needed. Since 2014, an upgraded facility- Agua Nueva (AN)- produces Class-A effluent, which infiltrates quickly due to its improved quality. This study aimed to gain better resolution on infiltration rate of the effluent as it progressed downstream in order to verify recharge credits. Such data is also important for modeling water demand of future projects utilizing effluent.

Divers (pressure transducers with integrated data loggers) were used to monitor surface water conditions. A mass balance approach using flow measurements, used to find difference in discharge between transects, was used to estimate recharge. Because of high temporal variability in AN outflow, this downscaled mass balance provided inconclusive results. The study resulted in an effective way to temporarily deploy divers to monitor surface water in streams with unstable flow conditions. The hydraulic head data gathered provided insight to the unique nature of effluent flow in the river.

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