San Luis Rio Colorado, Sonora, Mexico
Expansion of Wastewater Collection and Treatment Systems (PIMAS III)

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Project Location and Description
Purpose and Need for the Proposed Action
Environmental Assessment and Finding of No Significant Assessment
(Public comment period closes October 13, 2008)
Contact Information

Project Location and Description

EPA is considering authorizing the award of a Border Environment Infrastructure Fund (BEIF) grant to the City of San Luis Rio Colorado, for construction of wastewater collection and conveyance lines to serve existing residents that lack adequate wastewater treatment and disposal. San Luis Rio Colorado, a municipality comprised of more than 150,000 people, is located in the northwestern part of the State of Sonora, Mexico, on the U.S./Mexico border, adjacent to the town of San Luis, Arizona.

Purpose and Need for the Proposed Action

The purpose of the proposed action is to address the environmental and public health risks associated with inadequate collection, treatment and disposal of wastewater. The proposed action will protect public health by providing appropriate wastewater collection and treatment to approximately 50,000 residents that now rely on cesspools or open ditches for wastewater disposal. The proposed action consists of the installation of approximately 90,000 linear meters of laterals and subcollectors, plus expansion of lift station and force capacity of 200 liters per second (lps). The expansion of services will result in the collection and treatment of around 160 lps (nearly 4 million gallons per day) of raw wastewater that would otherwise be discharged untreated to the environment. The wastewater treatment plant expansion will consist of the addition of a third lagoon system module to the facility. All collected wateswater flows will be treated at the recently completed facultative lagoon facility. The treatment plant’s effluent will be directed to infiltration basins for aquifer recharge. The proposed action will significantly reduce the use of inadequate wastewater disposal practices in San Luis Rio Colorado by expanding collection, conveyance and treatment services from to approximately 95% of the community, resulting in improved environmental and sanitation conditions

EPA's involvement in the San Luis Rio Colorado, Sonora project is part of a national commitment to improve environmental conditions along the U.S.-Mexico border. EPA participates in the development and implementation of water supply and wastewater infrastructure projects in coordination with the Border Environment Cooperation Commission (BECC) and the North American Development Bank (NADBank) . BECC is responsible for certifying projects so that they comply with sound technical, environmental, financial, and public participation principles. NADBank administers the BEIF grants for projects that have been certified by BECC and approved by EPA.

Environmental Assessment and Finding of No Significant Impact

In compliance with the National Environmental Policy Act (NEPA), EPA has prepared a Supplemental Environmental Assessment (SEA) that supplements the Environmental Assessment of the Effect on San Luis, Arizona by the Proposed Construction of a Wastewater Treatment Plant and Improvements to the Wastewater Collection System for San Luis Rio Colorado (EA), which was prepared by EPA in January, 2000. The purpose and scope of the SEA is limited to cataloging the changes that have been made in the project’s design since the original assessment was written and detailing the potential impacts that may occur as a result of those changes. After considering a wide range of regulatory, environmental (both natural and human) and socio-economic factors, the SEA did not identify any significant impacts to the environment that would result from the implementation of the modified wastewater collection system and treatment plant improvements.

The SEA and Finding of No Significant Impact (FNSI) are being made available for public review for a 30-day comment period that ends on October 13, 2008. Interested persons, including those who disagree with this proposal, may submit written comments to EPA Region 9.

To view the EA or FNSI, please click on the links below.

Supplementary Environmental Assessment (PDF) (59 pp, 1.2M, About PDF)
Finding of No Significant Impact (PDF) (2 pp, 24K, About PDF)

Contact Information

For further information about these documents, contact:

Thomas Konner (konner.thomas@epa.gov)
U.S. EPA Region 9 (WTR-4)
75 Hawthorne Street
San Francisco, CA 94105
Phone: (415) 972-3408
Fax: (415) 947-3537

San Luis Rio Colorado, Sonora, Mexico Expansion of Wastewater Collection and Treatment Systems (PIMAS III)