Board of Directors

Interlake Tunnel

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photo of Interlake Tunnel
Proposed approximate tunnel alignment

The Interlake Tunnel Project (Interlake Tunnel) was included in the July 1991 Water Facilities Capital Plan (Volume I, Volume II), prepared by Boyle Engineering Corporation for the Monterey County Water Resources Agency (MCWRA). Operationally, the Interlake Tunnel would divert water from Nacimiento Reservoir to San Antonio Reservoir that would have otherwise been spilled at Nacimiento Dam. The Nacimiento River basin produces nearly three times the average annual flow of the San Antonio River basin, therefore, capturing high Nacimiento River flows and diverting those flows to San Antonio Reservoir increases the overall storage capacity of the system.

Subsequent to 1991, MCWRA efforts were focused on completion of the Salinas Valley Water Project (Salinas River Diversion Facility and modification to the Nacimiento Dam Spillway). The current drought has created a renewed interest in the Interlake Tunnel concept.

The Interlake Tunnel requires a detailed engineering analysis; but is generally planned to consist of an 11,000 foot gravity flow tunnel with an intake structure in Nacimiento Reservoir and an exit structure in San Antonio. Total project cost is estimated at $48 million, including $3.4 million in contingency. Depending upon the degree of environmental documentation required the Interlake Tunnel could be completed in two to three years.

The Interlake Tunnel has been divided into three phases: project feasibility, including preliminary engineering and water rights requirements analysis; pre-construction tasks, including environmental review, permit applications, geotechnical and final design, right-of-way acquisition and financing arrangements; and construction.

The MCWRA, with approval of the Board of Supervisors of the MCWRA, proceeded to contract with a Program Manager to begin project feasibility and pre-construction tasks. However, the MCWRA will not proceed beyond the preliminary engineering and water rights requirements analysis until environmental review is completed and authorization to proceed is received from the Board of Supervisors of the MCWRA. The estimate of Pre-construction Phase costs is as follows:

Timeline of Events:

On June 3, 2014, the Board of Supervisors of the MCWRA authorized negotiation and execution of a funding agreement between Monterey County and the MCWRA for an amount not to exceed $500,000 for program management, engineering and environmental review of the Interlake Tunnel, said funds to be reimbursed to Monterey County if the Interlake Tunnel is approved and financed; and directed staff to return to the Board of Supervisors in July 2014 with a project status report and information on financial impact to the County in regards to funding the agreement. The Board of the MCWRA also authorized the MCWRA General Manager to enter into the necessary agreements to prepare for and commence environmental review of the Interlake Tunnel in an initial amount not to exceed $500,000 provided funding is approved by Monterey County. Presentation slides for this meeting are found here.

On July 1, 2014, the Monterey County Board of Supervisors approved a funding Agreement and approved the use of County funds for the Agreement. The MCWRA has contracted EPC Consultants as the Program Manager and Construction Manager, a legal firm to perform the water rights analysis, and will solicit a qualified environmental firm.

On August 25, 2014, the Board of the MCWRA held a public workshop to provide background information about the Interlake Tunnel and to provide an update of current project activities and accomplishments. The agenda and presentation slides for this workshop are found here.

On November 19, 2014, the Board of the MCWRA held a public workshop to provide current feasibility status on the Interlake Tunnel. The agenda, including technical memoradum, and presentation slides for this workshop are found here.

On January 15, 2015, MCWRA published an Informational Notice of pending RFP’s for engineering design.

On February 26, 2015, MCWRA held a public meeting on the proposed Interlake Tunnel and San Antonio Spillway Modification project. The meeting was held in the Heritage Ranch Conference Room, Paso Robles, CA. Updated slides are found here.

On March 13, 2015, MCWRA published an UPDATED Informational Notice of pending RFP’s for engineering design. This notice contains the RFP schedule.

On April 16, 2015, a RFP pre-proposal meeting was held. The presentation can be found here.

On April 28, 2016, a Notice of Preparation/Initial Study (NOP/IS) was circulated, initiating a 45-day scoping period for the Environmental Impact Report. The scoping period concluded on June 13, 2016. The NOP/IS can be found here.

On May 16 and 17, 2016, scoping meetings were held. The presentation can be found here.

EIR Development

Scoping Comments
Scoping Presentation

Contract Documents

Water Resources Agency Agreement for Services
Water Resources Agency Professional Services Agreement with Surveyors, Architects, Engineers or Design Professionals


June 3, 2014
August 25, 2014
November 19, 2014
February 26, 2015
April 16, 2015
July 14, 2016
September 15, 2017
September 15, 2017 Q&A

May 10, 2018
July 6, 2018


Interlake Tunnel LIDAR Salinas River San Antonio River 100-Yr Floodplain
Lake Naciniento Lidar San Antonio Inundation Area at 790 ft.
Nacimiento River San Antonio Lidar


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Monterey County Water Resources Agency
1441 Schilling Pl., North Bldg., Salinas, CA 93901

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