Fast Facts

The U.S. Section of the International Boundary and Water Commission manages two wastewater treatment plants along the U.S.-Mexico border that treat raw sewage, mostly from Mexico. But population growth and aging plant infrastructure allow stormwater to bring bacteria, trash, and sediment from Mexico into the U.S.—affecting public health and the environment in Arizona and California.

The Commission has not taken comprehensive steps to resolve the problem, so we recommended that Congress consider directing the Commission to identify alternatives—including cost estimates and funding sources—to help resolve continuing water quality problems.

Corrosion of the International Outfall Interceptor (IOI) Pipe in Arizona

 Corroded pipe

Corroded pipe

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What GAO Found

A 1944 treaty designated the International Boundary and Water Commission (IBWC) and authorized it to resolve water and boundary issues along the U.S.-Mexico border, including providing wastewater treatment. IBWC's two sections—the U.S. Section (USIBWC) and the Mexican Section, negotiated agreements to construct, manage, and operate two wastewater plants in Nogales, Arizona, and San Ysidro (South Bay), California, to resolve ongoing water quality problems stemming from sewage flowing downhill from Mexico into the United States (see figure). Several of these agreements describe each country's roles, such as sharing costs for the operation and maintenance of each plant.

International Wastewater Plants in Arizona and California

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Several factors can affect the plants' operations, including deteriorating infrastructure in Mexico and the United States that results in raw sewage spills around the plants. USIBWC has taken steps to resolve some of these factors. For example, USIBWC proposed a binational rapid response team to address broken pipes and failing pumps that can send sewage from Mexico into the United States; however, the team has not been formalized to ensure its long-term operation. By taking steps to formalize the team, USIBWC would have assurance it can more effectively address recurring infrastructure failures contributing to sewage spills.

USIBWC and others have taken some actions to address stormwater problems, such as studying stormwater flows in the Tijuana River Valley watershed and building some retention basins. However, USIBWC has not taken action, in coordination with federal, state, and local partners, to identify alternatives, cost estimates, funding sources, and time frames for implementing solutions in either watershed. USIBWC officials said without direction from Congress, it does not have specific authorization for stormwater management in the watersheds because the 1944 treaty and accompanying legislation did not authorize it to carry out such projects. The long-standing stormwater quality problems and their associated environmental and health effects suggest congressional direction is needed to authorize USIBWC to take action. Such action would include identifying alternatives, cost estimates, funding sources, and time frames.

Why GAO Did This Study

Ongoing sewage spills and stormwater runoff carrying trash, sediment, and other pollutants in the Santa Cruz River Basin and Tijuana River Valley watersheds along the U.S.-Mexico border have affected public health, the environment, and local economies. Under the 1944 treaty, the United States and Mexico agreed to work together through IBWC to address these water quality problems. As part of this effort, USIBWC manages two wastewater treatment plants in Arizona and California. In 2018, the plants treated more than 14 billion gallons of sewage from Mexico.

This report (1) describes the authorities and roles for developing and managing the plants and sharing their costs; (2) examines factors affecting the operation of each plant and steps taken to address them; and (3) examines the extent to which USIBWC has taken actions to address water quality problems in the watersheds. GAO reviewed U.S-Mexico treaties, IBWC minutes and permits, and planning and budget data for USIBWC. GAO also interviewed officials from IBWC and other federal agencies, local and state governments, and non-governmental groups.

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GAO believes that Congress should consider providing direction and specific authorization to USIBWC to take action to resolve stormwater quality problems in the Santa Cruz River Basin and Tijuana River Valley watersheds. GAO is also making two recommendations to USIBWC, including that it formalize the rapid response team. USIBWC concurred with that recommendation and partly concurred with the other.

Recommendations for Executive Action

Agency Affected Recommendation Status
International Boundary and Water Commission, United States and Mexico The U.S. Commissioner of the IBWC should work with the Mexican Commissioner to formalize a binational rapid response team to address sewage infrastructure failures along the U.S.-Mexico border, including the Nogales and South Bay wastewater treatment plants. (Recommendation 1)
In June 2021, USIBWC stated that the IBWC continues to take actions to formalize the binational rapid response teams. We will review the final documents for each team when they are completed and available. In July 2020, IBWC established two teams with binational members, one in the Nogales, Arizona and Nogales, Sonora region and one in the San Diego and Tijuana region.
International Boundary and Water Commission, United States and Mexico The U.S. Commissioner of the IBWC should direct USIBWC staff to conduct long-term capital planning for the Santa Cruz River Basin and Tijuana River Valley watersheds, following the principles in OMB Circular A-11. (Recommendation 2)
In June 2021, USIBWC provided copies of the most recent capital plans for the Nogales and South Bay plants; however, the plans do not include the long-term capital-planning elements we outlined in our report and recommendation. In June 2021, the agency stated it continues to partially disagree with GAO's recommendation to conduct long-term capital planning for (1) nonfederal infrastructure; (2) infrastructure that does not yet exist; and/or (3) infrastructure that the USIBWC is not yet authorized to construct or maintain. The agency is a key player in managing water quality on the border and has the infrastructure and organization that will be part of the solution. Without the information that USIBWC would generate by comprehensively assessing its long-term needs, such as through long-term capital planning efforts, Congress cannot authorize specific work that needs to be done. We recommended that the agency conduct long-term planning, including for infrastructure that does not exist and for infrastructure that is not yet authorized specifically to address this problem. We continue to believe that USIBWC should recognize its role along the border and start planning for it, including by undertaking long-term capital planning for existing and potential future infrastructure and identifying alternatives to address the long-standing water quality problems. We will update this recommendation when we receive further information.

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