IOI leak

Untreated wastewater bubbles up and into Potrero Creek from a broken section of the international sewer line following a rupture in July 2017.

A settlement in an eight-year-old lawsuit will mean nearly $38.8 million in upgrades and protective measures for the aging sewer line that carries millions of gallons of wastewater each day from the U.S.-Mexico border to a treatment plant in Rio Rico, federal and state authorities announced on Tuesday.

The settlement comes as the result of a suit filed by the Arizona Department of Environmental Quality against the U.S. Section of the International Boundary and Water Commission (USIBWC) in 2012 that alleged Clean Water Act violations resulting from the leak-prone sewer line.

According to news releases issued by both agencies, the settlement “sets forth a comprehensive plan to mitigate future discharges of untreated wastewater into the Nogales Wash and Santa Cruz River in Nogales, Ariz.”

The plan includes upgrading the pipeline, known as the International Outfall Interceptor (IOI), from the border to the Nogales International Wastewater Treatment Plant, located approximately nine miles north in Rio Rico. It also calls for installing protective measures for the upgraded IOI in locations vulnerable to damage from stormwater and debris.

“This agreement is a major win for Southern Arizona, helping resolve a decades-old issue that threatened the health and safety of residents and the environment in Nogales and Santa Cruz County,” Gov. Doug Ducey said in the news releases. “Working together, ADEQ and USIBWC have developed a plan that will upgrade this critical infrastructure, reduce hazards from storms and flooding, and protect people and businesses in this border community.”

In one recent example of the hazards caused by storms and flooding, the IOI ruptured just north of city limits in July 2017 when one of its manholes collapsed after a powerful rainstorm. The line break sent untreated waste pouring into Potrero Creek and triggered an emergency declaration from Ducey after elevated levels of the E.Coli bacteria were found in the water.

The USIBWC has reportedly identified $34.2 million of existing funds to immediately begin the upgrades mandated by the new settlement, and has finalized engineering plans and begun negotiating agreements necessary to access the IOI. The construction contract will be put out to bid this fall, the agency said.

“The USIBWC looks forward to getting to work to rehabilitate the IOI as soon as possible,” said USIBWC Commissioner Jayne Harkins.

The project will be bolstered by another $2.59 million in state funds and $1 million from the Freeport McMoRan Foundation.

In addition, the U.S. Environmental Protection Agency will contribute $1 million through the North American Development Bank for a companion project to work on sewer pipelines in Nogales that connect to the IOI, the agencies said.

Meanwhile, ADEQ is “currently working to find funds” to install a metal screen in the IOI near the border to capture large debris that could otherwise cause sewage spills, the news releases said. The cost estimate for installation is estimated at between $2.6 million and $3.3 million, plus $360,000 for yearly maintenance.

The USIBWC is reportedly negotiating to have the Mexican Section of the IBWC contribute to the pipeline rehabilitation as well. 

With funds in place for an overhaul of the IOI, another crucial issue still remains: responsibility for its upkeep.

Maintenance of the pipeline is the shared responsibility of the City of Nogales and the USIBWC as the result of a deal struck back in 1953. In recent years, the city has balked at its 23-percent share, saying Nogales contributes only about 8 percent of the sewage treated in Rio Rico, with the rest coming from Nogales, Sonora. And it has fought the USIBWC in court over the issue.

The Nogales Wastewater Fairness Act, introduced in both houses of Congress in 2017 by then-Sens. John McCain and Jeff Flake and then-Rep. Martha McSally, would require that the city only be charged operation and maintenance costs based on the average daily wastewater that originates from the city. The measure died, but was reintroduced in 2019 by four members of the state’s current delegation in Washington.

The ADEQ-USIBWC settlement announced this week “makes it even more important that Congress acts to provide certainty for maintaining the IOI by passing the Nogales Wastewater Fairness Act,” now-Sen. McSally said in the news releases.

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