WAPA » Regions » SN » Environmental review--NEPA

Colusa-Sutter (CoSu) Transmission Line Project, DOE/EIS-0514

​About the Project:

The Colusa-Sutter Transmission Line, or CoSu Line Project, is a proposed 500-kilovolt (kV) transmission line project currently being studied by the Western Area Power Administration (WAPA) and Sacramento Municipal Utility District (SMUD). The CoSu Line Project would provide a new link between the California-Oregon Transmission Project (COTP) and SMUD and WAPA's facilities on the east side of the Sacramento Valley. The proposed project would enhance the reliability of the electrical grid in Northern California and increase SMUD's ability to import power from the Pacific Northwest and export power from the Sacramento area.

This new link between the COTP and the Sacramento Valley would: 

  • improve local and regional energy reliability;
  • help the region meet required reductions in greenhouse gas emissions
  • help the region meet required renewable energy content goals
  • ensure the continued safe and reliable operation of the regional transmission system to deliver clean power to homes and businesses in the region;
  • assist SMUD in planning for anticipated growth and energy demand; and​
  • improve the transmission infrastructure network and the Sacramento area's import/export capabilities

Project Features:

WAPA and SMUD will examine three different study corridors and two segment alternatives as part of the environmental review process. The project features would include new transmission lines and two new substations. WAPA and SMUD initially considered two study corridors and a segment alternative for the CoSu Line in Colusa and Sutter counties. Based on comments received during the public scoping period held from December 2015 to April 2016, the two agencies determined that an additional study area and segment alternative further south of the O'Banion Substation in Sutter County should be considered.

The updated proposed corridor study area maps can be viewed within the PROJECT DOCUMENTS section below.

Current Status:

January 2018:  WAPA and SMUD Eliminate Three of the Five Areas under Consideration

During public scoping, which closed in March 2017, WAPA and SMUD shared five study areas under consideration for potential transmission line routes. With development of the Draft Environmental Impact Statement/Environmental Impact Report (EIS/EIR) underway, the agencies have decided to eliminate three of the five study areas. This decision evolved due to comments received during the scoping period and further evaluations that determined their infeasibility to build and/or maintain. The Southern Corridor Study Area was found to be infeasible due to hazards, public safety, and reliability risks posed by the density of agricultural aircraft travel and agricultural airstrips, and the lack of meaningful options to mitigate that risk. The County Road 16 Corridor Study Area and Segment 2 Alternative were found to be infeasible due to technical restrictions on tower heights of the river crossings in proximity to the Sacramento International Airport.

Eliminated Study Areas

  • Southern Corridor Study Area: A 27-mile long area that runs west to east from west of Arbuckle to the O'Banion Substation.
  • County Road 16 Corridor Study Area: A 27-mile long area that runs west to east from the COTP near Dufour in Yolo County to the existing Elverta Substation in Sacramento County.
  • Segment 2 Alternative Study Area: A 9-mile long line that runs 6 miles northwest of the existing Elverta Substation.

Study Areas Remaining under Consideration​

  • Northern Corridor Study Area: A 44-mile long area that runs west to east from the COTP near Maxwell in Colusa County to the O'Banion Substation in Sutter County. This study area generally follows an existing 230-kV transmission line corridor.
  • Segment 1 Alternative: A 9-mile long area that provides a different north-to-south route of the Northern Corridor Study Area to bypass the Sutter Wildlife Refuge.

Next Steps

WAPA and SMUD will continue to study the areas under consideration as they develop the Draft EIS/EIR, which is anticipated for public release in mid-2019. The Draft EIS/EIR will include an analysis of the impacts on environmental resources in the study areas. It will also include a "No Action" alternative that addresses impacts if the CoSu Line is not built. No decisions will be made about selecting a final project alternative or moving forward with construction of the CoSu Line until the Final EIS/EIR is completed, which is anticipated in 2020.

Please visit the Frequently Asked Questions page    for further information about the Draft EIS/EIR and corridor study areas.​

​​​Contact Information and How to Comment:

The scoping period is now closed. However, if you need any additional information regarding the proposed CoSu Line Project, you can contact us though the following methods:

  • Email:

  • Mail:
    Mr. Andrew M. Montaño
    National Environmental Policy Act (NEPA) Document Manager
    Western Area Power Administration, Headquarters
    P.O. Box 281213
    Lakewood, Colorado 80228-8213​

Project Documents:


Project Update
Project Update


​News Release: ​​​WAPA, SMUD release Scoping Report for Proposed Colusa-Sutter Transmission Line Project​
Public Scoping Report        
Public Scoping Meeting Photos​
News Release:  ​​CoSu Public Meetings Help Scope Environmental Review​
News Release:  WAPA, SMUD ​accepting comments on CoSu through March 21​
News Release:  WAPA, SMUD extend Scoping Period of California Transmission Project​
Updated proposed corridor study areas map
Updated Scoping notice newsletter
WAPA's Notice of Additional Public Scoping Meetings​​
News Release:  ​​Colusa, Sutter County communities share insights and concerns on transmission line​
Scoping period extension postcard​
News Release:  Scoping period extended for CoSu Line Environmental Impact Statement​​​​
WAPA's Notice of Scoping Extension
Scoping meetings informational display boards​
CoSu Line Project fact sheet
Scoping comment card
Proposed study areas aerial overview map
Scoping meetings postcard
Scoping notice newsletter
News Release: WAPA, SMUD begin environmental review of California transmission project
WAPA’s Notice of Intent


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Page Last Updated: 1/25/2018 12:06 PM