skip navigation
Arizona Department of Environmental Quality Arizona's Official Website
Office of Border Environmental Protection: Water

Nogales, Sonora Pretreatment Program

Within the cross-border neighboring cities of Nogales, Arizona, and Nogales, Sonora, or Ambos Nogales, wastewater from both countries is treated at the Nogales International Wastewater Treatment Plant (NIWWTP). Located in Rio Rico, Arizona, the NIWWTP discharges treated effluent to the Santa Cruz River. The Office of Border Environmental Protection (OBEP) currently provides material and technical support to the wastewater utility in Nogales, Sonora (OOMAPAS-NS) for the purpose of improving the quality of wastewater discharges originating in Mexico. This helps protect investments in infrastructure and water resources in both countries.

Through a memorandum of understanding with Sonora, ADEQ has in the past provided financial support for analyses of wastewater samples collected from industrial discharge points in Nogales, Sonora. Samples are analyzed in laboratories certified by the state of Arizona and the results are incorporated into a database for generation of an annual pretreatment report by Nogales, Sonora.

With partial assistance from a grant through EPA's U.S.-Mexico Border 2012 Environmental Program, Nogales, Sonora, has constructed a water quality laboratory for analyses of wastewater samples collected in Sonora. The laboratory is undergoing Mexican certification for metals analyses. Once certified, results generated by the lab will be legally defensible and may be used for compliance purposes. This laboratory will be the first of its kind along the entire Arizona-Sonora border region, and may serve the analytical needs of other border communities in Sonora.

In December 2007, OBEP acted as a liaison between representatives from the city of Phoenix pretreatment program and the Nogales, Sonora wastewater utility in facilitating the donation of two autosamplers, flow meters, and flumes for the purpose of characterizing water quality in the broader Nogales wastewater collection system. OBEP's bilingual staff has provided training in the use of this kind of equipment. During the last four years, the legitimacy of Nogales, Sonora's pretreatment program has steadily improved within the regulated community it serves. The municipality has also successfully modified local implementation of state laws to improve the sustainability and effectiveness of the program.

Nogales Wash Coordination Committee Meetings

Nogales Wash is the main drainage conveyance for the Ambos Nogales watershed. During periods of heavy rain, surface runoff may introduce sand, oil and grease, and/or garbage into the wastewater infrastructure of Nogales, Sonora. The obstructions cause sanitary-sewer overflows (SSOs) that may create sewage problems in Nogales Wash, which flows northward into Arizona.

OBEP has taken the leadership role in coordinating binational meetings between local, state, and federal stakeholders impacted by sanitary sewer overflows within the wash. Outcomes of these meetings include generation of historical metrics related to water quality in Nogales Wash and formalized communication protocols for responding to abnormal flows within the wash.

As of June 2009, the Arizona Department of Emergency and Military Affairs coordinates meetings of city, county, state and federal stakeholders for consensus on incident planning and emergency response related to the flooding of Nogales Wash. OBEP provides technical support through hydrologic analyses and mapping of critical infrastructure.

OBEP also supports the Arizona-Sonora Border 2012 Water Task Force in identifying and developing projects that may help diminish the flooding affecting the watershed. Through a Border 2012 grant, Arizona State University is currently developing strategies for offsetting flood peaks within the watershed.

Friends of the Santa Cruz River - River Watch Volunteer Monitoring Support

ADEQ regularly monitors the quality of surface waters in Arizona. This is done in order to meet federal Clean Water Act requirements to develop a Water Quality Inventory Report for Congress every two years. Due to funding shortages, ADEQ frequently relies on data collection activities of volunteer monitoring organizations. One such organization is the river watch monitoring group based in Rio Rico, Arizona, Friends of the Santa Cruz River (FOSCR). This group regularly monitors six sites located along the Santa Cruz River and Nogales Wash near Arizona's border with Sonora.

OBEP works closely with FOSCR volunteers on data collection activities for integration into the ADEQ water quality database. Most recently, OBEP assisted FOSCR in revising its sampling protocols to ensure that the data it collects reflects the needs of ADEQ with respect to its water quality assessment. The ADEQ Water Quality Division currently provides financial assistance for quarterly monitoring of metals, nutrients, and microbiological content in samples collected by FOSCR volunteers.

Technical Assistance to Sonoran Wastewater Utilities

The border region is unique in that binational watersheds share binational wastewater infrastructure. OBEP provides technical assistance on an as needed basis to Sonora wastewater utilities to ensure that wastewater is of an adequate quality to protect investments in shared wastewater infrastructure.

Border Infrastructure Review

In response to many transboundary infrastructure needs, border communities are the recipient of Border Environment Infrastructure Funding (BEIF) provided by the U.S. Environmental Protection Agency. The funding assists with rehabilitation and replacement of deteriorating infrastructure within border communities in the United States and Mexico.

In Rio Rico, Arizona, the Nogales International Wastewater Treatment Plant (NIWTP) received funding for rehabilitation of its treatment works. Construction was initiated in July 2006 and the new plant was inaugurated in June 2009. OBEP supported technical meetings and provided engineering review that contributed to the success of this project.

In Nogales, Sonora, the municipality is in the process of establishing a new wastewater treatment plant with partial BEIF support. The Los Alisos wastewater treatment plant and associated infrastructure will relieve excess flows of wastewater currently being delivered to the NIWTP. This will ensure the NIWTP operates within its design specifications, thus protecting water quality in Arizona. For projects in Mexico, the Mexican Federal Department of Water Resources (CONAGUA) provides a matching grant.

Improvements in border infrastructure contribute to the sustainability of the growing industrial sector. This benefits U.S. companies operating in Mexico as well as citizens living on both sides of the border. In order to ensure Arizona's priorities and concerns are addressed, OBEP staff review and comment on projects facilitated by the BEIF.

For more information on ADEQ participation, please visit, Border Potable and Wastewater Infrastructure Support.


The Nogales, Sonora Wastewater Utility (OOMAPAS-NS) is developing a monitoring program for the broader wastewater collection system in order to identify sources of contamination not captured during its oversight monitoring of specific industrial discharges. This focus has been encouraged through an Arizona-Mexico Commission action item within the Environment and Water committees. Given that Sonoran wastewater is treated in Rio Rico, Arizona and discharged to the Santa Cruz River, OBEP will continue to assist as needed.

OBEP will continue to support FOSCR river watch monitoring given its importance for tracking changes in water quality both on the Santa Cruz River as well as on the Nogales Wash in Arizona. A model and database for web-based submission of water quality data collected by volunteer water quality monitoring organizations has been developed. Facilitating data submissions via the Internet will ensure that volunteer data is reflected in water quality assessment reports to Congress. Progress has been shared with the University of Arizona Non-point Education for Municipal Officials (NEMO) program to ensure efforts are leveraged. If successful, the model can be extended to other volunteer monitoring organizations in Arizona.

OBEP will continue to coordinate and support binational meetings related to Nogales Wash and the Arizona-Sonora Border 2012 Water Task Force. These meetings will ensure that binational stakeholders are engaged in the unique environmental challenges faced on the border and that resources are made available for mitigation.

Back to the OBEP Main Page