Intermittent discharge of a sanitary sewer overflow confirmed in tunnel which transports stormwater from Nogales, Sonora to Nogales, Arizona

January 25, 2019 - 8:05 am

The Arizona Department of Environmental Quality (ADEQ) and local officials confirmed an intermittent sanitary sewer overflow (SSO) in a tunnel under the international border, which transports stormwater from Nogales, Sonora to Nogales, Arizona. A SSO is a release of untreated wastewater and contains raw sewage.  

When flowing, the SSO originates from Nogales, Sonora and is exiting the tunnel into the Nogales Wash about one mile north of the international border. Depending on volume of flow and frequency, the SSO could reach the Santa Cruz River.

ADEQ urges people to avoid these areas. This recommendation is based on potential health risks to people and animals from exposure to raw sewage in the SSO. Untreated sewage carries pathogens that pose a risk to human health and the environment. People and animals that come into contact with untreated sewage are at risk of infection from those pathogens.

The U.S. and Mexico sections of the International Boundary Water Commission (IBWC) are in contact with the utility in Nogales, Sonora to assess the cause of the SSO. ADEQ continues to monitor the situation and is also in contact with IBWC, the utility in Nogales, Sonora, the City of Nogales, Arizona and the Santa Cruz County Health Department.

Recommended Actions:

  • Avoid contact with the water in this area, including wading, drinking and washing. If you have contact with the water, rinse using soap and clean water immediately.
  • If you think that your health or that of your pet or livestock has been affected from exposure to raw sewage, seek medical treatment immediately. Be sure to tell the medical professional about contact with the water. Also, make sure to advise your local county public health department about the exposure details.
  • Take care that pets and livestock do not drink potentially affected water. Pets can be especially susceptible because they tend to drink while in the water and lick their fur after. Rinse pets using soap and clean water.

For more information, visit the resources below:

  • Arizona Department of Environmental Quality (ADEQ) Water Quality Division | View >
  • Report an Environmental Complaint to ADEQ | View >
  • U.S. EPA Sanitary Sewer Overflows | View >
  • Santa Cruz County Health Services Agency | View >
  • About ADEQ
  • Under the Environmental Quality Act of 1986, the Arizona State Legislature established the Arizona Department of Environmental Quality in 1987 as the state agency for protecting and enhancing public health and the environment of Arizona. For more information, visit
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