A Crumbling Sewage Pipe Divides Arizona, Mexico

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By Brenna Goth and Emily Pickrell

Wastewater flowing from Mexico into Arizona fills a stretch of the lower Santa Cruz River through the state’s southern desert—but keeping the water clean and sewer pipe repaired rankles both sides of the border.

The 8.5-mile sewer pipeline has caused issues for at least a decade and leaked raw sewage last year, prompting Gov. Doug Ducey (R) to briefly declare a state of emergency. But long-term fixes are complicated by a watershed that crosses borders, roping in a range of local, state, and federal regulators.

Settlement talks underway between state and federal officials in the U.S. could end years of litigation over aging infrastructure that threatens to contaminate water in the area.


An agreement has to benefit both countries to preserve a flow that’s integral to the surrounding community and environment, said Claire Zugmeyer, an ecologist with the nonprofit Sonoran Institute who leads its Santa Cruz River Initiative. Mexico needs the pipeline to wash away its waste, while Arizona relies on the treated water to keep the Santa Cruz River and nearby wetlands lush.

“It’s our lifeblood,” Zugmeyer told Bloomberg Environment.

The pipeline, called the International Outfall Interceptor, takes sewage from the small Arizona city of Nogales and the abutting industrial city of Nogales, Sonora, Mexico, to a treatment plant north of the border. Millions of gallons flow to the Nogales International Wastewater Treatment Plant each day to be discharged into the river.

In service since the early 1970s, the pipeline is eroding and allows water to seep in or escape through the cracks. Tens of thousands of feet of the pipeline need to be rehabilitated, but funding and making those improvements has become caught in a cross-border tangle of agencies and back-and-forth lawsuits.

Tangled Jurisdiction

The U.S. Section of the International Boundary and Water Commission and its Mexican counterpart govern the Arizona-Sonora watershed. The Arizona Department of Environmental Quality regulates the treatment plant that discharges effluent, with Nogales, Ariz., and the boundary commission listed on the permit.

Local governments are without a voice when it comes to the international flow of water, Luis Parra, city attorney for the American Nogales, told Bloomberg Environment. The boundary water commission is trying to pass the cost and maintenance of the treatment plant to the city, even though it doesn’t benefit from the water that then goes upstream to other places in Arizona, he said.

“What they have offered to do is point the finger at the municipality,” Parra said.

Years of Citations

Arizona regulators began citing the treatment plant a decade ago for releasing effluent with too much cadmium, cyanide, and other harmful substances from Mexico’s industrial waste carried by the pipeline.

Settlement talks aim to address the funding gap to rehabilitate the pipeline and ensure the Clean Water Act violations stop “to the greatest extent possible,” Arizona Department of Environmental Quality spokeswoman Erin Jordan told Bloomberg Environment in an email.

A proposal up for debate outlines a 22 percent local match for repairs, according to a July presentation from the agency.

The design for the five-phase rehabilitation project is already completed, boundary and water commission spokeswoman Lori Kuczmanski said in a statement emailed to Bloomberg Environment. The commission has $21 million available contingent on a cost-sharing agreement, Kuczmanski said.

Nogales, Ariz., wants to see the federal government take a more active role in the infrastructure issue “so that a calamity could be avoided in the future,” Parra said. He also said the Mexican government should do more to stop pollutants from being dumped into wastewater.

Mexico Could Divert Water

Mexico, though, doesn’t have to send its wastewater to Arizona under the governing treaty.

Nogales, Sonora, delivers roughly twice as much wastewater to the treatment plant as does Nogales, Ariz. Mexico is sending more than contracted due to population growth, Sulma Brenda Cantu Robles, who runs day-to-day operations at the wastewater plant in Nogales, Sonora, told Bloomberg Environment.

Processing that water in Mexico instead of Arizona would shrink the amount flowing into the Santa Cruz River. Arizona regulators want the federal government to consider an international agreement that would secure the Mexican water, Jordan said.

“They are under no legal obligation to send that water to the U.S.,” she said.

Mexican water officials, including representatives of the Nogales treatment plant and water utility OOMAPAS, didn’t respond to multiple requests for comment by Bloomberg Environment.

Effluent Impacts River Health

Making those pipeline upgrades is also vital to keeping the Santa Cruz River healthy, environmental groups said. The fate of a deal to repair the pipeline could cement or roll back that progress, they said.

Earlier wastewater quality improvements have already helped the Santa Cruz River’s health.

A decade ago, a survey of fish in the river found only one species and two individual fish in the portion recharged by the Nogales wastewater, Zugmeyer said.

A few years after treatment plant upgrades, an endangered native species returned to the river, she said.

“Almost right away, the fish were back in bigger numbers,” Zugmeyer said.

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