On July 25, 2017, during an inspection of the International Outfall Interceptor (IOI), the City of Nogales public works reported a partial breach of the IOI approximately 200 yards north of the intersection of Old Tucson Rd. and the Nogales Wash.
A dislodged section of cement that encases one of the manhole accesses to the IOI, partially sheared the pipe below the waterline causing discharge of untreated wastewater into the Nogales Wash. The location of the partial breach is in a sparsely populated area of the county.
At 2 a.m. on August 2, crews in Nogales, Arizona completed installation of a bypass system to divert sewage that had been leaking from the partial breach. The sewage is now being conveyed for treatment at the Nogales International Wastewater Treatment Plant and is no longer flowing into the Nogales Wash.
The heavy flows from summer monsoon storms have continued to erode embankments at a number of locations within Nogales Wash, exposing and threatening critical infrastructure and property. The U.S. Army Corps of Engineers, the Arizona Army National Guard, and the Arizona Department of Transportation continue to work to stabilize banks along the Nogales Wash and face challenges in stabilizing construction efforts at the worksites.
High flow volume within the International Outfall Interceptor (IOI), which includes heavy debris, temporarily complicated the efforts to plug the IOI, which supports the bypass of the breached section. Crews were able to quickly correct the issue and have installed additional measures to support bypass efforts.
Public Health and Safety
Officials ask that the public refrain from entering this area to allow agency representatives to conduct their surveys and for the safety of the employees working in the area. The public is also asked to refrain from entering into areas where repair work is underway. Drivers should be especially careful in areas where repair crews are working near roadways.
Santa Cruz County Health Services and the Arizona Department of Health Services are advising the public to stay out of the Nogales Wash and the Santa Cruz River. Even in the absence of untreated wastewater, stormflows are typically high in pollutants that can be harmful to human health such as bacteria and pathogens. The state water quality standard E. coli for full body contact is 235 colony-forming units per 100 milliliters of water (235 CFU/100 mL) for full body contact. Water near and downstream of the IOI partial breach is of particular concern and should be avoided.
The Arizona Department of Environmental Quality (ADEQ) initiated daily water quality sampling on July 26, 2017. ADEQ’s initial testing covered a variety of contaminants of concern, including heavy metals. Ongoing testing is focused on E. coli and nutrients because heavy metals were not detected in initial test results.
Due to the evolving conditions in the Nogales Wash, the Arizona Department of Environmental Quality is implementing a longer-term water quality monitoring plan for the duration of the IOI repair. This includes water quality sampling and testing both upstream, at and downstream of the IOI at Manhole 89, in response to developing conditions.
- Map of testing locations
- Test results:
ADEQ’s recent test results in response to the IOI breach confirm both elevated levels of E. coli upstream of the IOI breach, and substantially elevated levels of E. coli downstream of the IOI breach and, as such, ADEQ recommends the public avoid contact with this water.
ADEQ data analysis is ongoing and focused on determining the extent of the increase in E. coli levels from the IOI breach because all sampling locations in Santa Cruz County are located within an area designated as “impaired” for E. coli, meaning water quality in the area known as the Nogales Wash, historically and consistently contains levels of E. coli in excess of state surface water quality standards.
As the Nogales Wash flows into the Santa Cruz River, E. coli levels remain higher than state standards, but lower than immediately downstream of the IOI breach.
Pima County has also conducted water quality sampling in the Santa Cruz River. The sampling is consistent with the results acquired by the Arizona Department of Environmental Quality in earlier tests. The risk of contamination of the river may have been elevated due to the partial breach of the IOI. However, pollutant concentrations within the Santa Cruz River normally spike with storm water runoff.
Santa Cruz County Health Services is recommending to those who live within the county, along the Santa Cruz River, and have a private well within 100 ft. of the waterway have their wells tested for contamination. Even in the absence of untreated wastewater, storm flows are typically high in pollutants that can be harmful.
- Protect your health: a guide of private well owners in Arizona (English)
- Arizona Labs Certified for Drinking Water Samples (English)
- Proteja Su Salud: Una guía para dueños de pozos privados en Arizona (Español)
- Laboratorios de Arizona Certificados para Tomar Muestras de Agua Potable (Español)
The Department of Agriculture shares the concerns of livestock owners and farmers in the region. Until there is more information about the extent of the situation, it is recommend not using water from the Santa Cruz River to water food crops or gardens.
Santa Cruz County
News release 14: Flood control efforts continue in the Nogales Wash
News release 13: Santa Cruz County reminds public of Nogales Wash health concerns
News release 12: Bypass Completed at IOI Partial Breach
News release 11: Santa Cruz County Receives Water Quality Test Results
News release 10: Nogales Wash IOI Partial Breach Monday update
News release 9: Nogales Wash IOI Partial Breach Sunday update
News release 8: Nogales Wash IOI Partial Breach Update; Public advised to avoid the Nogales Wash
News release 7: Nogales Wash IOI Partial Breach Update
News release 6: U.S. Army Corps of Engineers Assists Under the Flood Control and Coastal Emergency Act
News release 5: U.S. Army Corps of Engineers assisting in plan development for IOI partial breach
News release 4: Santa Cruz County Declares State of Emergency
News release 3: Progress Continues on Partial Breach of the International Outfall Interceptor
News release 2: Santa Cruz County and Stakeholders await testing of water samples from Nogales Wash
News release 1: City of Nogales reports a partial breach of the International Outfall Interceptor
Additional response agencies
8/07/17: Los Angeles District, US Army Corps of Engineers: Nogales Wash Emergency Flood Fight Operational Details
8/02/17: Pima County conducts water quality tests in Santa Cruz River
7/28/17: International Boundary and Water Commission hires construction firm to perform sewer pipe repairs
7/28/17: Pinal County Issues Warning to Those Living Near Santa Cruz River
7/27/17: Governor Ducey Declares State of Emergency for pipe rupture in Santa Cruz County
The Nogales Wash is the main surface water drainage for the Ambos [both] Nogales watershed. Nogales Wash runs perennially from Sonora to Arizona with a base flow of 2-3 cubic feet per second, much of which is supplemented by potable- and wastewater-infrastructure leaks in Sonora.
The International Outfall Interceptor (IOI) is the infrastructure that conveys wastewater from Sonora and Arizona to the Nogales International Wastewater Treatment Plant (NIWTP.) The IOI covers a distance of approximately 8.5 miles from the border to the NIWTP. The treated effluent is discharged into the Santa Cruz River, where it provides a perennial surface water source to recharge groundwater levels and sustain riparian habitat.
The U.S. International Boundary and Water Commission (IBWC) and the City of Nogales are co-owners of the Nogales International Wastewater Treatment Plant (NIWTP), which is located in Rio Rico, Arizona, and provides treatment of sewage for both Nogales, Arizona, and Nogales, Sonora.
The NIWTP is designed to treat 14.74 million gallons of wastewater per day (mgd). 9.9 mgd is allocated to Nogales, Sonora under IBWC minute 276. The remaining capacity (4.84 million gallons per day) is allocated to Nogales and Rio Rico, Arizona. The plant does have the ability to handle wastewater flows in excess of 14.74 mgd for limited periods of time.
Additional information on the Nogales Wash and International Outfall Interceptor Fact Sheet.