NOGALES, Arizona (Border Report) – The U.S. and Mexico share natural resources such as rivers and underground water supplies. So, when poorly treated sewage started flowing across the border wall from Mexico, environmentalists in Southern Arizona raised a red flag.

“The effluent from a new subdivision in Mexico is coming across the border and it seems to be highly contaminated, very poorly treated. It smells as you walk up to it,” said Ben Lomeli, president of Friends of the Santa Cruz River.

The group monitors water quality and environmental threats in the region. Its members a few weeks ago detected refuse and nauseating smells in a flood plain called Oso Wash next to the border wall east of Nogales. Group members took samples and detected E. coli coming from a Mexican wastewater plant in Nogales, Sonora.

The group says that’s likely the result of “not sufficiently treated” or chlorinated wastewater, which fosters the growth of algae, protozoa, fungi, bacteria, worms and leeches. Lomeli is also concerned about chemicals and possibly metals that may be present in poorly treated effluent and may find their way to underground water supplies.

“There are several ranches and homes and other wells in that area that would use that water. The closer you are to the source the heavier the contamination potential,” Lomeli said.

The International Boundary and Water Commission and the Arizona Department of Environmental Quality verified the E. coli findings.

Officials on both sides of the border said treated wastewater from Mexico often flows across the border but attributed the contamination to equipment failure or shortcomings at the Nogales, Sonora, treatment plant.

Maria Elena Giner, the U.S. Commissioner of the IBWC, said efforts are ongoing to get the Sonora plant parts from Arizona to solve the problem in the short term, and funding from the North American Development Bank and other entities for a long-term solution.

Maria Elena Giner, U.S. Commissioner of the IBWC, talks with her Mexican counterpart. (Courtesy IBWC)

“The Commission has received specifications for equipment that is needed at the plant and is reaching out to entities in Arizona to see if equipment is available that could be installed in Mexico on a temporary basis until the Mexican equipment is repaired or replaced. We are also exploring longer term options related to needed infrastructure on the Mexican side,” said Lori Kuczmanski, a spokeswoman for the IBWC.

Nogales, Sonora Mayor Juan Francisco Gim told local news media the Los Alisos plant treats about 220 liters (58 gallons) of wastewater per second but would need to double its capacity to prevent contaminated liquid from flowing downhill to the border wall and Arizona.

Guardians of the river

Lomeli this week took Border Report to the site of the sewage spill east of Nogales. It’s a hard drive over loose gravel on a road going up and down hills that usually only U.S. Border Patrol agents dare travel on four-wheel-drive vehicles.

The smell of wastewater is evident going down the last hill toward Oso Wash. There, the effluent comes across from Mexico like a stream that picks up speed as it enters the flood plain.

“There are several ranches and homes and wells in that area that would use that water. The closer you are to that source, the greater the contamination potential,” Lomeli said.

The flow sinks or dries up with the afternoon triple-digit heat about a quarter-mile from the border wall. But Lomeli, a hydrologist, says any amount of rain can take it farther.

“The water flows toward us (Arizona) because of the topography. We are downstream, so we are going to receive runoff when it rains and we’re going to keep receiving effluent that is released. Hopefully, it will be clean in the future,” he said.

Friends of the Santa Cruz River is a nonprofit formed in 1991 to protect an area known as the San Rafael Valley that straddles the Two Nogales. Their main concerns are protection and education. The group puts out newsletters and hosts community clean-ups.

Ben Lomeli, president of Friends of the Santa Cruz River, walks along a nature trail near Rio Rico, Arizona. (Julian Resendiz/Border Report)

“We have outreach and education. We go to the schools; we bring kids to (natural attractions). And we do environmental advocacy,” Lomeli said. “There’s a lot of natural attractions here in Santa Cruz County, there’s a lot of cultural and historical attractions. As far as nature, we have the river, we have the mountains, we have the Chihuahuan Desert, the Sonoran Desert, we have wildlife – anything from jaguars to the gray wolf. Birding is a big attraction.”

But with the population growing on both sides of the border, safeguarding water supplies is a top priority for the local environmentalists.