Holli LaBrie

Soil, Water, and Environmental Science

Influence of the Nogales International Wastewater Treatment Plant on the Santa Cruz River
     Future water supplies are heavily dependent on the flow and quality of the treated water that leaves wastewater treatment plants. Although this effluent is treated, in some instances the treatment processes do not successfully remove harmful contaminants. The Nogales International Wastewater Treatment Plant releases treated wastewater from both Nogales, Arizona and Nogales, Sonora, Mexico into the Santa Cruz River, potentially putting environmental and human health at risk. Due to the industrial demographic of the region, outdated infrastructure, and lack of data, the treatment facility and the treated effluent are an important area of study.
     To better understand how the treated effluent is affecting the river, data were used from existing water quality databases and effluent flow reports from 2008 to 2015. To address how flow quantity has changed during drought periods, effluent flows were compared to historical flood data produced by the USGS.  To determine any exceedance in water quality standards, given the environmental and recreational use of the river, water quality reports produced by the International Boundary and Water Commission were examined and analyzed to understand the threat of past exceedances of contaminants such as nickel, cadmium, and cyanide.
     Preliminary results showed that spikes in effluent flow corresponded with large rainfall events. This finding indicates that there might have been exfiltration of raw sewage from existing infrastructure into the subsurface during dry periods due to a decline in the water table depth given current drought conditions. Flow totals also showed that the majority of the effluent was produced in Nogales, Sonora, suggesting that the industrial areas of the state could greatly contribute to water quality problems. Although the quality of water has been relatively pristine, recent exceedances in cadmium and nickel could threaten surface soils and wildlife, as well as subsurface water supplies.
     Without proper wastewater treatment for effluent flowing into the Santa Cruz River, the well-being of the river could severely decline. Although outreach to stakeholders across the border and updated infrastructure has improved the quality of water in the river, there are still many areas to improve upon as the demand for treated wastewater increases, including proper disposable of harmful contaminants and continued maintenance of treatment processes. To identify opportunities for improvement, further studies should examine the specific fate of each contaminant present in the effluent.