Tijuana River Watershed Technical Evaluation of Infrastructure Solutions

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Technical Evaluation of Potential Infrastructure Solutions
Beach Impact Comparison Study

Technical Evaluation of Potential Infrastructure Solutions

The technical evaluation of potential infrastructure solutions to mitigate contaminated transboundary Tijuana River and coastal flows began in August 2020. This technical evaluation included two steps, Project Feasibility Analysis and Alternatives Analysis. Click on the links for a more in-depth overview of the two-step process:

Step 1: Project Feasibility Analysis (August 2020 - May 2021)
Step 2: Alternatives Analysis (June - October 2021)

Step 1: Project Feasibility Analysis

EPA completed Step 1 of the technical evaluation in May 2021. Incorporating stakeholder input, EPA evaluated an initial ten projects with potential to address the public health and environmental concerns caused by transboundary flows into the United States from the Tijuana River and Pacific Ocean. The analysis evaluated all ten projects, subsequently narrowed to eight due to feasibility concerns, to determine their ability to reduce environmental and human health impacts from these transboundary flows. The evaluation considered each project’s feasibility, cost of construction, and operations and maintenance costs to inform next steps.

The figure below shows the location of existing infrastructure that provided the basis for defining the initial ten projects as well as the regions and areas that are affected by the transboundary flows.

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.

The Overview of Projects / Resumen del Proyectos summarizes the key issues and potential solutions, as well as provides a baseline conditions document. The baseline document is a companion to the 10 individual Feasibility Analyses Technical Memorandums which are available in the table below.

The initial ten projects covered a range of pollutants and entry points, and each focused on one or more intervention categories. Below is a list of the initial ten projects and their respective intervention focus. Each project is linked to a fact sheet and map outlining the proposed solution, as well as a feasibility analysis. Project names in the table below are consistent with the April 2020 Federal Register Notice of Intent to conduct NEPA Public Scoping and may differ from other content on the website as revisions were made to improve clarity and directness.

	Project Title*	Conveyance	Treatment	Source Control
1	New Tijuana River Diversion System in the U.S. and Treatment in the U.S. Nuevo sistema de desvío del Río Tijuana en EE. UU. y tratamiento en EE. UU.
2	Expand and Upgrade Tijuana River Diversion System in Mexico and Provide Treatment in the U.S. Ampliar y mejorar el sistema de desvío del río Tijuana en México y proporcionar tratamiento en EE. UU.
3	Treat Wastewater from the International Collector at the ITP Tratar las aguas residuales del Colector Internacional en el ITP
4	Shift Wastewater Treatment of Canyon Flows to U.S. (via Expanded ITP) to Reduce Flows to SAB (Complements Projects 3) Trasladar el tratamiento de aguas residuales de los flujos cañoneros a EE. UU. (mediante ITP ampliado) para reducir flujos a San Antonio de los Buenos
5	Enhance Mexico Wastewater Collection System to Reduce Flows into Tijuana River Mejorar el sistema de recolección de guas residuales de México para reducir los flujos al río Tijuana
6	Construct New Infrastructure to Address Trash and Sediment During Wet Weather Flows Construir nueva infraestructura para abordar basura y sedimentos
7	Divert or Reuse Treated Wastewater from Existing Wastewater Treatment Plants in Mexico to Reduce Flows into the Tijuana River Desviar o reutilizar las aguas residuales tratadas de las plantas de tratamiento de aguas residuales existentes en México para reducir los flujos al río Tijuana
8	Upgrade SAB Wastewater Treatment Plant to Reduce Untreated Wastewater to Coast Mejora de la Planta de Tratamiento de Aguas Residuales SABTP para reducir las aguas residuales no tratadas en la costa
9	Treat Wastewater from the International Collector at the SBWRP Tratar las aguas residuales del Colector Internacional en el SBWRP
10	Sediment and Trash Source Control Control de sedimentos y fuentes de basura

*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

Step 2: Alternatives Analysis

After completing Step 1: Project Feasibility Analysis, individual projects were grouped to form thirteen alternatives. These alternatives were formed based on individual project purposes, impacts, environmental benefits, capital costs, and operations and maintenance costs. Next, they were scored using a systematic, replicable, and transparent evaluation tool developed by EPA called the Augmented Alternatives Analysis (AAA). This analysis considered each alternative’s feasibility; cost of construction and operations and maintenance; and health, environmental, and economic benefits.

Overview of the Alternatives Evaluation Process (pdf) (525.78 KB)

Three of the higher scoring alternatives were chosen for further evaluation and are summarized in report below. The highest scoring alternative, while over budget, represents the most comprehensive solution to both transboundary river wastewater flows and coastal wastewater flows. The other two alternatives are within budget while making significant progress towards improving water quality. All three alternatives focus on U.S.-side infrastructure that (1) diverts and treats contaminated flows after they are already in the river and/or (2) treats contaminated flows before they reach the river and coast.

Top Three Alternatives (pdf) (564.29 KB)

The full report evaluates the ability of the three alternatives to improve water quality in the Tijuana River watershed and adjacent coastal areas. A Spanish version of the Executive Summary is also available below.

Water Infrastructure Alternatives Analysis Final Report (pdf) (3.6 MB)
Resumen Ejecutivo del Informe Final (pdf) (273.96 KB)

In November 2021, EPA announced it is moving forward with the environmental review of one of the top three alternatives or the Comprehensive Infrastructure Solution (Comprehensive Solution) to address the ongoing transboundary pollution problems, which pose significant negative impacts to water quality, public health, and the environment in the San Diego/Tijuana border region. The Comprehensive Solution is the alternative that scored the highest in the Technical Evaluation of Infrastructure Solutions – Alternatives Analysis.

Comprehensive Alternative (I-2) Fact Sheet (pdf) (1.27 MB)
News Releases for Comprehensive Infrastructure Solution:
- English
- Español

Beach Impact Comparison Study

Tijuana River vs. San Antonio de los Buenos (SAB) Creek

Of the pollutants commonly found in transboundary flows, untreated wastewater, which contains harmful pathogens, poses the greatest risk 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.

Due to public health and beach water quality concerns, Scripps Institution of Oceanography developed an estuary and ocean model to evaluate the impacts of “infrastructure solutions to improve shoreline water quality and reductions on regional beach closures.” Their work analyzed all Tijuana River and SAB Creek transboundary flows during 2017 and concluded:

“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 showing Percentage of Year Imperial Beach is Impacted by Tijuana Sewage

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.