USMCA Tijuana River Watershed
And Adjacent Coastal Transboundary Wastewater Flows
In the Tijuana River Valley and neighboring coastal areas, contaminated flows from Mexico enter the U.S. and create significant negative impacts to water quality, public health, and the environment. In 2020, the U.S. government, through the U.S. Environmental Protection Agency, committed $300 million in the United States-Mexico-Canada Agreement (USMCA) Trade Agreement to identify infrastructure solutions to mitigate this decades-old problem. The USMCA requires EPA, in coordination with eligible public entities to carry out the planning, design, and construction of high priority treatment works in the Tijuana River watershed to address transboundary flow pollution.
- Transboundary Flow
- Pollutants in this Flow
- Negative Impacts of these Pollutants
- Next Steps: Evaluate Potential Solutions
- Some Key Considerations for Projects
- Impact Comparison: Tijuana River vs. SAB Creek
Transboundary flow refers to the movement of water across an international boundary—in this case, from Mexico into the U.S. These flows contain a combination of treated wastewater, untreated wastewater, groundwater, and stormwater. There are three major points of entry for these transboundary flows:
- Tijuana River, conveys flows from the City of Tijuana, through the Tijuana River Valley in Southern California, and discharges into the Pacific Ocean. Although there are no transboundary flows for an average of 212 days of the year (2015-2019), wet-weather events cause an average of 109 million gallons per day of transboundary flows.
- San Antonio de los Buenos (SAB) Creek, releases 50 million gallons of flow, of which a significant percent is raw sewage, into the Pacific Ocean each day. Northward currents carry the discharge up the coast to the U.S. causing marine transboundary flows.
- Cross-border Canyon tributaries at the U.S.-Mexico border act as entry points for transboundary flow. Flows from these canyons enter the Tijuana River.
- Untreated wastewater, often referred to as sewage, enters the flow due to spills from wastewater pipeline breaks, aging wastewater treatment systems, poorly maintained manholes and canyon collectors, lack of stormwater drainage systems, and homes without plumbing.
- Trash from Tijuana’s urban area, when not properly disposed, enters the flow with an increased volume during wet-weather events.
- Sediment, usually eroded soil from the canyons and upstream of the Tijuana River, increases in the flow during wet-weather events.
Pollutants negatively impact water quality in the Tijuana River Valley and the Pacific Ocean.
- Public Health and Beach Water Quality: Untreated wastewater contains harmful pathogens that pose risks to human health. To minimize human contact with untreated wastewater during transboundary flow events, local governments mandate beach closures, reducing access to fishing, swimming, surfing, other recreational activities, and tourism. Sediment and trash contribute to flooding, which pose public safety and property loss concerns.
- Wildlife and Habitat: Sediment, trash and polluted wastewater can also negatively impact aquatic and terrestrial wildlife and degrade the riparian, marine, and estuarian habitats that wildlife relies on to thrive.
- Government Activities: U.S. Navy and Customs and Border Protection personnel are sometimes exposed to untreated wastewater while performing their job duties. The presence of trash and sediment also poses challenges to U.S. Navy and Customs and Border Protection personnel in carrying out their mission support operations.
EPA evaluated twelve different alternatives and their ability to reduce environmental and human health impacts from transboundary flows using the Augmented Alternatives Analysis (AAA), an EPA-developed analysis tool. The evaluation considered each alternative’s feasibility, cost of construction, and operations and maintenance costs to inform EPA’s decision. The AAA method also takes into account the social, environmental, and economic benefits.
Broadly, projects focused on three types of interventions:
- Conveyance projects evaluate the construction or repair of the infrastructure (e.g., pipes, pumps) that convey wastewater to treatment and disposal facilities.
- Treatment projects increase facility capacity to treat wastewater, remove pollutants, and put clean water back into waterways and waterbodies.
- Source Control projects intervene at the source of contamination to stop or reduce pollutants before reaching a waterbody or treatment facility.
|Project Title*||Conveyance||Treatment||Source Control|
*ITP: South Bay International Wastewater Treatment Plant; SAB: San Antonio de los Buenos Wastewater Treatment Plant; SBWRP: City of San Diego South Bay Water Reclamation Plant
- Ownership and sustainable funding for operation of projects.
- Sediment/sludge disposal options for applicable projects are unknown.
- Presidential Permit required for transboundary pipelines.
Scripps Institution of Oceanography developed an estuary and ocean model to evaluate impacts of “infrastructure solutions to improve shoreline water quality and reductions on regional beach closures.” Their work, which analyzed all flows during 2017, concluded that:
- “Eliminating or dramatically reducing [wastewater flows to SAB Creek] has the strongest benefit to the City of Imperial Beach, Silver Strand State Beach, and City of Coronado.”
- In wet season the Tijuana River causes two-thirds of closures and SAB Creek one-third of closures.
- SAB Creek “is the dominant source that leads to regional beach closures” year round, and especially during the dry season (109 days during the year).
- Beach closure estimates are made based on wastewater bacteria concentrations and may not correlate with actual beach closures due to additional factors.
Graph is generated using Scripps Institution of Oceanography findings. Graph shows annual impacts to Imperial Beach. Similar conclusions are drawn at Playas Tijuana, Silver Strand State Beach, and Hotel del Coronado.
Source: Feddersen, F., X. Wu, and S. N. Giddings, Modeling impacts of various wastewater and stormwater flow scenarios on San Diego South Bay and Tijuana beaches, Tech. Report for the North American Development Bank, November 2020.