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

Nogales, Sonora Pretreatment Programs

Wastewater quality along the U.S.-Mexico border is critical for protecting infrastructure and water resource investments in both countries. Wastewater from Nogales, Arizona, and Nogales, Sonora, is treated at the Nogales International Wastewater Treatment Plant (NIWTP). Located in Rio Rico, Arizona, the NIWTP discharges effluent into the Santa Cruz River. The Office of Border Environmental Protection (OBEP) supports projects focused on protecting wastewater quality so that impacts on infrastructure and the environment are minimized. Most recently:

  • By working with the Arizona-Mexico Commission’s Environment and Water Committee, OBEP organized the donation of water-quality monitoring equipment to the Ambos Nogales communities. This equipment is being used by both cities to identify metals and cyanide in wastewater. OBEP provided training on the equipment’s installation and use.
  • In conjunction with the EPA’s U.S.-Mexico Border 2020 Environmental Program (Border 2020), OBEP is working with the Nogales, Sonora chapter of the Association of Environmental Safety Professionals (APSA) to enact bi-national training for the pretreatment of industrial wastewater. OBEP assists APSA in coordinating peer-to-peer trainings between metal-plating facilities in Nogales, Sonora and Tucson, Arizona. To encourage participation, facilities that partake in the free workshops receive recognition through APSA, which also serves as a subcommittee of the Association of Maquiladoras of Sonora.
  • OBEP attends bi-national technical committee (BTC) meetings hosted by the U.S. International Boundary and Water Commission, and reports progress that's associated with border environmental projects to ADEQ's Water Quality Division. The BTC is a bi-national venue that raises concerns about and proposes solutions to environmental challenges in shared watersheds. OBEP often supports action items developed by the committee.
  • In 2013, ADEQ renewed its Memorandum Of Understanding (MOU) with Nogales, Sonora. The MOU outlines the roles and responsibilities relating to the technical and information exchange that pertains to bi-national wastewater quality in Ambos Nogales. Since IBWC is the responsible party in associated matters, the MOU is exercised only when necessary.

OBEP and EPA have a history of working on wastewater quality issues in Nogales. With some assistance from a grant through the Border 2020 Program's predecessor, Nogales, Sonora built a water quality laboratory to analyze wastewater samples collected in Sonora. The OBEP encourages Mexican authorities to support laboratory certification for metal analyses. This laboratory would be the first in the Arizona-Sonora border region, and may serve the needs of other border communities in Sonora. Laboratory certification is an outstanding recommendation of the IBWC’s Nogales Bi-national Technical Committee.

OBEP has acted as a contact between the City of Phoenix's pretreatment program and the Nogales, Sonora wastewater utility. The goal is to aid the donation of monitoring equipment that is being replaced or upgraded for the purpose of identifying water quality in the Nogales wastewater collection system. OBEP's bilingual staff trained in using the equipment. During the last decade, the Nogales, Sonora pretreatment program has increased its interaction with the regulated community it serves.

Nogales Wash Sanitary Sewer Overflows
During heavy rain, the sanitary sewer in Nogales may overflow.

Nogales Wash Sanitary Sewer Overflows

The Nogales Wash is the main drainage avenue for the Ambos Nogales watershed. During heavy rain, surface runoff may bring sand, oil, grease, and/or garbage into the wastewater infrastructure of Nogales, Sonora. These obstructions cause sanitary-sewer overflows (SSO's) that may create sewage problems in Nogales Wash, which flows north into Arizona.

OBEP notes these events and makes recommendations at Nogales BTC meetings hosted by IBWC. Concerns are also raised through informal meetings with the Nogales, Sonora Water and Wastewater Utility (OOMAPAS-NS). Communication leads to rapid bypass of sewage to the International Outfall Interceptor (IOI), which is the pipe that carries wastewater from Ambos Nogales to the Nogales International Wastewater Treatment Plant when SSO's take place.

In response to SSO's and when need arises and funding is available, water quality samples are analyzed at a state-certified laboratory. Data is then shared at bi-national venues such as Nogales Bi-national Technical Committee meetings to find long-term strategies for SSO solutions in Nogales, Sonora.

In support of ongoing pollution prevention, OBEP worked with ADEQ’s Water Quality Division and EPA’s Border 2020 Program to host a Stormwater Workshop in the border region. The workshop summarized stormwater regulations and best-management practices for preventing non-point source pollution resulting from monsoon rains along the border. Federal, state and municipal representatives from Sonora attended the workshop. They received translated information to consider within Mexico’s environmental policies pertaining to bi-national watersheds.

Santa Cruz River Monitoring

santa cruz river monitoring by ADEQ
An ADEQ employee takes samples from the Santa Cruz River.

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. Given funding shortages, ADEQ frequently relies on data collection activities of volunteer monitoring organizations. One such organization has been 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 has worked closely with FOSCR volunteers on data collection activities for integration into the ADEQ water quality database. Formal water quality monitoring responsibilities for sites located downstream of the NIWTP has now shifted to the IBWC under its new Arizona Pollution Discharge Elimination System (AZPDES) permit for the NIWTP (March, 2014).

Technical Assistance to Sonoran Wastewater Utilities

The border region is unique in that bi-national watersheds share 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 shared water basins as well as investments in shared wastewater infrastructure.

A wastewater monitoring system
A wastewater monitoring system, in Nogales, Sonora.


The Nogales, Sonora Wastewater Utility (OOMAPAS-NS) is running 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 Committee. Given the significance of Sonoran wastewater quality on Arizona, ADEQ is encouraging the U.S. International Boundary and Water Commission to support OOMAPAS-NS in this work.

OBEP will remain active in Nogales Bi-national Technical Committee meetings hosted by the IBWC, the U.S.-Mexico Border 2020 Environmental Program, and the Environment and Water Committee of the Arizona-Mexico Commission. Their involvement will ensure bi-national stakeholders are engaged and informed regarding the unique environmental challenges faced on the border, and state and federal resources are efficiently used for mitigation.

Increasing Awareness of Arizona Water Quality Issues in a Bi-national Context

OBEP staff delivered a presentation entitled “The Case of Ambos Nogales: Two Countries Sharing One Watershed” for the session on Joint International Topics at the Arizona Water Association 87th Annual Conference & Exhibition in Glendale in 2014.

The U.S. and Mexican cities that make up Nogales, Arizona and Nogales, Sonora (Ambos Nogales) are located 65 miles south of Tucson in the upper Santa Cruz River watershed. Nogales, Arizona is an example of a U.S. border city that hosts infrastructure shared with a neighboring country. A bi-national agreement known as Minute 276 allows Mexico to deliver up to 9.9 million gallons (mgd) of its wastewater per day to the Nogales International Wastewater Treatment Plant (NIWTP) in Rio Rico, Arizona. An additional 4.75 mgd of plant capacity is allocated to communities in Arizona. The International Outfall Interceptor (IOI) is the main vehicle that transfers this bi-national sewage to the NIWTP in Rio Rico. The plant has both an Aquifer Protection Permit (APP) and an Arizona Pollution Discharge Elimination System (AZPDES) permit for discharge of treated bi-national effluent to the Santa Cruz River.

Nogales, Sonora is home to a vibrant industrial and manufacturing sector. It hosts ten times the population of Nogales, Arizona. Although Sonora shares storm and wastewater infrastructure with Arizona, it adheres to different regulatory standards for stormwater management, industrial discharge, and operation and maintenance of wastewater-conveyance infrastructure.

Rapid population growth in Nogales, Sonora has contributed Mexican wastewater discharges above treaty limits by up to three mgd. Although Sonoran wastewater is important in maintaining the flow of the Santa Cruz River, constant excesses may impact the operational efficiency of the NIWTP and the water quality of the downstream environment. In response, the U.S. Environmental Protection Agency (EPA) has supported construction of the Los Alisos Wastewater Treatment Plant (LAWTP) south of the watershed divide in Mexico. Wastewater diverted to the LAWTP protects the operational efficiency of the NIWTP, but comes at the cost of pumping wastewater uphill over an elevation change of 340 feet. LAWTP diversions may shorten the perennial segment of the Santa Cruz River. The river hosts rare aquatic and cottonwood-willow habitat, supports groundwater recharge, and sustains real-estate values in Arizona.

The U.S. International Boundary and Water Commission (IBWC) is responsible for working with its sister agency in Mexico (CILA) on water-quality and quantity issues in bi-national watersheds. This presents unique regulatory and environmental challenges for Arizona. In response, ADEQ coordinates with Arizona’s Department of Water Resources, EPA’s U.S.-Mexico Border 2020 Environmental Program, the Arizona-Mexico Commission, public utilities, professional organizations and non-profits on activities that yield positive environmental metrics for the border region..

Environmental Infrastructure Needs Support

Since the late 1990s, ADEQ has sought improvements to environmental infrastructure in Arizona border communities. Well functioning wastewater systems, drinking water services, and waste management infrastructure support environmentally responsible economic growth. The Office of Border Environmental Protection performed engineering evaluations, provided technical assistance, and guidance about available funding options to facilitate the design and construction. They coordinated with ADEQ and EPA to ensure that proposed infrastructure designs will conform to applicable regulations. Additionally, direct communications with Mexican agencies at the local, state, and federal levels provided opportunities to address trans-boundary environmental contamination of shared natural resources along the Arizona border with Mexico.

Nogales International Wastewater Treatment Plant
The Nogales International Wastewater
Treatment Plant completed in 2009.

Collaboration with bi-national organizations such as the Border Environmental Cooperation Commission and the North American Development Bank, as well as U.S. and other state agencies, has secured significant investments in environmental improvement projects that are protective of Arizona’s environment and public health. A few of these include:

  • Was technical leader on the project to upgrade the Nogales International Wastewater Treatment Plant. Construction began in 2006 and was completed in 2009.
  • Worked with North American Development Bank staff to expedite funding for the Patagonia Wastewater Treatment Facility. This was the first Arizona BEIF project, as it had been held up for over three years due to financing problems.
  • Work with Yuma County staff to find conceptual plans for the Colonia B and C projects.
  • Provide technical assistance to Douglas for the BEIF water and wastewater treatment plant by working with the city engineer to leverage BEIF funding with WIFA loans.
  • Helped BECC staff in Huachuca City so the city could define its BEIF projects.
  • Continued working with Nogales on the Nogales International Wastewater Treatment Plant. The OBEP engineer was the technical leader for the design. The focus was on creative procurement efforts to accelerate development of the project.
  • Assisting Nogales, Arizona with Congressional line-item funds for municipal wastewater collection system improvements.
  • Consult with Bisbee project staff to find cost-cutting measures in the construction of the municipal wastewater collection system and wastewater treatment plant.

Assistance to Binational Border Environment Infrastructure Fund (BEIF) Projects

NACO Sanitary District treatment plant
Naco Sanitary District treatment plant.
  • ADEQ continued their involvement with the Nogales, Sonora, wastewater and water projects. The focus has been on questions of engineering controls for wastewater spillage during construction, specification of materials resistant to destructive wastewater environments and workplace safety.

Assistance to General Water/Wastewater Issues Along the Arizona Border

  • Assessed the San Luis poor quality potable water issues. Sought a hardship grant from WIFA for remediation study. Served as technical project manager. Water treatment facilities are being installed.
  • Worked with the Naco Sanitary District for improvements to its treatment plant under a WIFA hardship grant. The project received "2003 project of the year" from the Arizona Water Pollution Control Association.
  • Collaborated with Cochise County and International Boundary and Water Commission to react to fugitive transboundary wastewater flows entering Arizona from Naco, Sonora.
  • Integrated with WIFA to provide enhanced service along the border.
  • Developed geographic information system covers of critical wastewater infrastructure to support emergency planning and incident response efforts related to the flooding of Nogales Wash.

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