Background
What is the Canyon Tunnel Project?
SSJID and its partner Oakdale Irrigation District (OID) are constructing a bypass tunnel for its Joint Supply Canal (JSC). Referred to as the “Canyon Tunnel Project,” it will bypass a risk-prone portion of the JSC downstream of the Goodwin Dam, extending around 12,000 feet downstream to a point where the JSC departs from the Stanislaus River canyon.
The project area is near an unstable rock slope that occasionally drops rock onto the JSC. The Canyon Tunnel Project both provides a safer work environment for District personnel and secures the District’s water supply, including for the cities of Manteca, Lathrop, and Tracy, which all rely on treated drinking water for their communities.
Landslides have previously blocked the JSC, including one in 2013 that removed the canal from operation just before the irrigation season. If this had occurred at the height of the irrigation season, it may have triggered severe water cutbacks. Without the Canyon Tunnel, the region’s water supply is threatened by these events. This includes the cities of Manteca, Lathrop, and Tracy; 50,000 acres in SSJID’s service area; and 26,305 acres in OID’s service area.
The project is expected to total $84 million. SSJID will cover 72 percent of the cost, while OID covers 28 percent based on historical water use.
Benefits
How will the Canyon Tunnel Project impact water quality for communities and agricultural areas?
The tunnel’s enclosed design helps protect water quality by reducing the risk of contamination from rockfall, sediment, and debris that might otherwise enter the canal.
This design also provides a more reliable water source, especially during peak demand periods. SSJID is compliant with all required federal and state laws to protect local water quality. We have acquired a 401 Water Quality Certification, adhering to state water quality standards. We have also entered a Lake or Streambed Alteration (LSA) Agreement with the California Department of Fish and Wildlife (CDFW) to address fish and wildlife resources. We have also acquired a 404 Clean Water Act Permit, which ensures compliance with water quality standards for waters of the United States through the Army Corp of Engineers.
In addition to securing water supply for local agriculture, the project will help protect against costly water disruptions that can impact crop yields and agricultural revenue. Additionally, the project may support local employment opportunities during the construction phase.
The tunnel is designed for a 100-year lifespan, offering a long-term solution that reduces ongoing maintenance costs, enhances the safety of District personnel, and provides resilience against natural hazards. This future-focused approach helps protect the community’s water security and reduces reliance on emergency repairs.
Construction Process
What is the timeline for the Canyon Tunnel Project’s construction?
SSJID pre-qualified six contractors for project construction in November 2024. The project will adhere to the following approximate construction timeline:
Will the Joint Supply Canal remain in operation during construction?
Yes.
Where will the tunnel spoils go?
Tunnel and outlet excavation spoils will be deposited on the two sites shown. They will not leave the project area. A relatively small amount of spoils from the Goodwin Dam tunnel intake will be deposited at the existing Tulloch Dam spoils area.
SSJID will make every effort to minimize disruption to the community.
The project may produce minimal blasting noise. Blasting noise may result from a common tunneling technique only required at or near portals with hard rock. Blasts are unlikely to be heard in the community but may produce a dull thud. Residents can expect the following based on the contractor’s baseline schedule (subject to vary):
- For outlet and intake portal construction, blasting the first week of October and the first two weeks in November 2025
- For tunneling, 1 blast per day inside the tunnel, from January to March 2026
Tunnel drilling noise will occur over a mile from residential communities, primarily 300 feet below ground, and will not be audible to the public or residents.
Intake and outlet excavation and shoring noise will occur during daylight hours for a period of several weeks each.
The contractor will carefully manage the minimal dust on the private access roads. The contractor will mitigate the dust produced during tunnel and portal construction with water trucks, pumps, and misters.
The contractor has coordinated with Cal Fire and developed a Fire Safety Plan. Part of this plan requires water trucks to always be on-site, in addition to several additional preventative measures.
Mitigation measures have been adopted through the California Environmental Quality Act (CEQA) to adequately survey and identify listed species that may be encountered and ensure they are protected.
The construction timeline is determined by the contractor. We anticipate working hours to include five to six days per week, with 24-hour shifts during the tunneling phase. Shift changes will generally take place around 6 a.m. and 6 p.m. Workers will alternate between drilling and shotcrete application.
SSJID is committed to working with the contractor to accommodate high-volume residential traffic periods, such as school drop-off and commuting travel.
California Environmental Quality Act (CEQA) Impacts
What is CEQA?
According to CEQA, public agencies are required to disclose and evaluate the potential environmental impacts of their project. There are three types of CEQA documents:
- Notice of Exemption – A document that indicates a project is exempt from CEQA review
- Negative Declaration or Mitigated Negative Declaration – A document that indicates a project has less than significant impacts on the environment, or less than significant with mitigation incorporation
- Environmental Impact Report (EIR) – A document that indicates a project has potentially significant impacts on the environment
The CEQA compliance document was prepared and submitted to the State Clearinghouse for distribution and public comment in January 2023 for 30 days. Following the public input period, the Initial Study/Mitigated Negative Declaration and Mitigation Monitoring and Reporting Program was adopted on March 14, 2023, by the SSJID Governing Board.
The documents are available at ceqanet.opr.ca.gov/Project/2023010504 or canyontunnelproject.org/documents.
There are a few updates to the project since the CEQA documentation was filed, including:
- Location of spoils disposal
- Tunnel length increased by 106 feet (from 12,000 to 12,106 lineal feet)
- Construction of new boat landings at the south and north shores of Goodwin Dam reservoir
- Minor intake adjustments at the upstream portal and the tunnel outlet
Canyon Tunnel Outreach
How will the community be kept informed about project progress and potential disruptions?
SSJID will hold regular community meetings, distribute newsletters and fliers, and post updates on their website and local social media. A dedicated project webpage will provide timely information about key milestones and any impacts on the community at canyontunnelproject.org.
How can residents voice concerns or ask questions about the project?
SSJID and OID welcome community input and feedback throughout the project. Residents can attend future community meetings, contact representatives through email, or submit questions to info@canyontunnel.com.
