Influence of the Nogales International Wastewater Treatment Plant on surface water in the Santa Cruz River and local aquifers

Abstract:

As water resources become limited in Arizona due to drought and excessive use of ground water, treated wastewater effluent is becoming essential in creating natural ecosystems and recharging the decreasing groundwater supplies. Therefore, future water supplies are heavily dependent of the flow (quantity) and quality of the treated effluent. The Nogales International Wastewater Treatment Plant (NIWTP) releases treated wastewater from both Nogales, Arizona and Nogales, Sonora, Mexico into the Santa Cruz River. This released effluent not only has the potential to impact surface water, but also groundwater supplies in Southern Arizona. In the recent past, the NIWTP has had reoccurring issues with elevated levels of cadmium, in addition to other, more infrequent, releases of high amounts of other metals. The industrial demographic of the region, as well as limited water quality regulations in Mexico makes the NIWTP and its treated effluent an important area of study. In addition, outdated infrastructure can potentially lead to damaging environmental impacts, as well as human health concerns.

The Santa Cruz River has been monitored and studied in the past, but in recent years, there has been a halt in research regarding the state of the river. Data from existing water quality databases and recent sampling reports are used to address research questions regarding the state of the Santa Cruz River. These questions include:

1) How will change in flow eventually impact surface water and future groundwater supplies

2) What factors influence this flow (such as extreme flooding and drought)

3) What is the impact of effluent on surface water quality

4) Can changes in surface water quality impact groundwater quality

5) How do soil characteristics and surface flow impact the transport of released contaminants

Although outreach to stakeholders across the border and updated infrastructure has improved the quality of water in the river, there are many areas to improve upon as the demand for treated wastewater increases.