Title
Receive an update on the Castroville & Eastside Canals and Alternatives Preliminary Feasibility Study. (Staff: Shaunna Murray)
Report
RECOMMENDATION:
It is recommended that the Monterey County Water Resources Agency Board of Directors:
Receive an update on the Castroville & Eastside Canals and Alternatives Preliminary Feasibility Study.
SUMMARY/DISCUSSION:
Background
In 2025, Salinas Valley Basin Groundwater Sustainability Agency (SVBGSA) initiated the Castroville & Eastside Canals and Alternatives Preliminary Feasibility Study (C&E Study) to evaluate surface water diversion opportunities from the Salinas River that could support Sustainable Groundwater Management Act (SGMA) implementation. The work is funded through the Department of Water Resources Sustainable Groundwater Management (SGM) Implementation Grant and is being conducted collaboratively with the Monterey County Water Resources Agency (MCWRA).
The C&E Study builds upon longstanding concepts-dating back to the 1940s-for diverting excess flows from the Salinas River to raise groundwater levels. The feasibility study team includes Montgomery & Associates (M&A), MBK Engineers, Wallace Group, and Denise Duffy & Associates. The first phase focused on evaluating water rights options, reviewing historical documents, analyzing surface water flows and identifying viable project components for potential diversion and conveyance systems. Information from the first phase was applied to develop four project scenarios to address four different groundwater goals:
1. Raise Groundwater Levels in Central Eastside Subbasin
2. Raise Groundwater Levels in Northern Eastside Subbasin
3. Stop Seawater Intrusion in 400-Foot Aquifer
4. Provide In-Lieu Supply to Reduce Pumping from Seawater Intruded Areas and Deep Aquifers.
If any of the project concepts are ultimately constructed, they could partially contribute to the solution to one or more of the groundwater goals.
Discussion
Building on Phase 1 findings, the potential project scenarios were developed using MCWRA’s existing water right permit 11043 (Permit 11043) with a modification to add storage, and potentially other modifications. The first phase of the C&E Study also looked at new water rights as potential sources of surface water. A new water right would be last in priority, limiting surface water availability to large and infrequent events. In addition, the timeline and uncertainty around acquiring a new water right does not align with the SGMA deadlines.
Flood exemptions may also be a potential source of surface water available under strict conditions, but exemptions are usually pursued with existing infrastructure. A different feasibility study is analyzing the use of detention basins to capture flood flows. This approach requires dispersed basins along the river and generally a large footprint of land to recharge.
Potential project scenarios with storage - either above ground or in the aquifer - would most likely contribute to meeting groundwater goals. Without storage, project benefits are limited by timing of available flow in December through April, and the timing is not aligned with peak water demand. The existing Permit 11043 prohibits storage. Modification of Permit 11043 to add storage requires a defined project and will be subject to CEQA, public protest, and regulatory review.
The existing Permit 11043 limits diversion to 400 cfs and 135,000 AFY at designated locations for irrigation and municipal use. It limits diversion to a portion of excess natural flows, not reservoir releases intended to meet downstream flow requirements. A potential project scenario cannot interfere with existing operations. Therefore, project scenarios were not considered that would impact the stored water that is already committed to existing projects. For example, a diversion using shallow well fields would have to be pumped after downstream flow requirements are met which limits the applicability of that concept.
Diversion opportunities typically occur December-April, averaging less than 15% of days per year. Diversion potential depends on diversion facility size and ranges from 1,100 to 31,700 AF/year. A diversion facility comparable to the Salinas River Diversion Facility would have resulted in an average of 3,800 AF/year at the diversion point near Chualar. The largest facility, 400 cfs, has an average diversion potential of 31,700 AF/year.
Key technical considerations of the potential project components were identified and further analyzed for inclusion in the potential project scenarios. A full explanation of the potential and constraints of the components will be included in the final report.
Potential Project Scenarios
1. Raise Groundwater Levels in Central Eastside Subbasin
• Divert water at Castroville Canal Intake
• Convey to recharge basins in the Central Eastside Subbasin
• Beneficial use consistent with existing Permit 11043 for irrigation and municipal use.
2. Raise Groundwater Levels in Northern Eastside Subbasin
• Divert water at Castroville Canal Intake
• Convey to surface storage in the Northern Eastside (2 versions)
• Treat at new water treatment plant (2 versions)
• Convey and inject into Eastside Subbasin
• Beneficial use consistent with existing Permit 11043 for irrigation and municipal use.
3. Stop Seawater Intrusion in 400-Foot Aquifer
• Divert water at new location downstream of the Castroville Canal Intake
• Convey to surface storage in northern 180/400 Subbasin
• Treat at new water treatment plant
• Convey and inject into 400-Foot Aquifer
• There is uncertainty about consistency with existing beneficial uses associated with Permit 11043 and the ability to modify those to address seawater intrusion.
4. Provide In-Lieu Supply to Reduce Pumping from Seawater Intruded Areas and Deep Aquifers
• Divert water at new location downstream of the Castroville Canal Intake
• Convey to surface storage in northern 180/400 Subbasin
• Treat at new water treatment plant
• Convey to “New Seawater Intrusion Project” (NSIP) for irrigation (infrastructure layout and cost of NSIP distribution being conducted under the NSIP feasibility study)
• Beneficial use consistent with existing Permit 11043 for irrigation
The next steps underway are conducting high-level engineering feasibility, cost analysis, and modeling of the impacts on groundwater conditions relative to the Sustainable Management Criteria. Project scenarios will be evaluated at a high level for regulatory and environmental requirements.
Results will inform SVBGSA’s long-term project portfolio for achieving SGMA sustainability targets and will support preparation of CEQA and permitting documentation for subsequent implementation.
OTHER AGENCY INVOLVEMENT:
Salinas Valley Basin Groundwater Sustainability Agency
FINANCING:
The feasibility study work, including consultants and staff participation, is funded by the Sustainable Groundwater Management Round 2 grant between DWR and SVBGSA. The MCWRA staffing and consultant appropriations are funded through a subgrant agreement with the SVBGSA and are included in the FY2025-26 Adopted Budget and will not require any additional funding needs.
Prepared by: Shaunna Murray, Deputy General Manager, (831) 755-4860
Approved by: _________________________________________________
Ara Azhderian, General Manager, (831) 755-4860