Treated wastewater from Nogales, Sonora has reportedly been flowing across the border at the location seen here for several years.

A federal environmental team was dispatched to Santa Cruz County this week in response to a report of wastewater flowing across the border from Mexico in an area several miles east of Nogales.

Sally Spener, spokeswoman for the International Boundary and Water Commission, said the investigators found bacteria in treated effluent flowing across the border at a rate of 80 liters per second, but determined that it wasn’t raw sewage.

According to U.S. officials, treated wastewater from a housing development on the east side of Nogales, Sonora has been flowing into Arizona for years.

The water is discharged by a pair of sewage treatment plants at the Lomas de Anza housing development, then enters a creek that flows across the border in the area of Brickwood Canyon and Oso Wash, Spener said.

Brickwood Canyon is located in a remote section of the U.S.-Mexico border just west of the Santa Cruz River. It’s several miles south of the Kino Springs Golf Course in an area long used for cattle ranching.

Jeff Terrell, the county’s environmental health director, said he hadn’t heard about the cross-border flow in that area, but his department recommends people stay out of any water coming across the border.

“It’s lower risk than if it was untreated,” he said, “but there’s still always a risk, because you’re not going to kill every microorganism that there is.”

Terrell added that people should keep their animals out of water, and anyone with a well in the area should consider getting the water checked.

The wastewater flow might not continue year-round due to seasonal rainfall and other factors, Spener said, but she added that the effluent has been flowing “regularly” across the border since the two treatment plants started operating several years ago.

She said the plants were constructed by the builder behind the housing development, but are now operated by OOMAPAS, the municipal water utility in Nogales, Sonora.

The IBWC was notified about the issue by the Arizona Department of Environmental Quality, which received a report of water flowing across the border in the Oso Wash earlier this week, ADEQ spokeswoman Erin Jordan said.

Spener said that the IBWC’s Mexican section had “reached out to the Nogales, Sonora utility to request any updated information they may have about the Mexican treatment plants.”

The north-flowing Santa Cruz River, which crosses the border approximately a mile east of Oso Wash, is recharged with treated effluent in Rio Rico, where the Nogales International Wastewater Treatment Plant processes millions of gallons of wastewater every day – much of it piped across the border from Nogales, Sonora.

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