RECOMMENDATION(S): (CONT'D)
DIRECT the Director of Department of Conservation and Development, or designee, to file a Notice of Exemption with the County Clerk, and
AUTHORIZE the Chief Engineer, or designee, to arrange for payment of a $25 fee to the Department of Conservation and Development for processing, and a $50 fee to the County Clerk for filing the Notice of Exemption.
FISCAL IMPACT:
Estimated Project cost: $3.3 million. 50% Central Contra Costa Sanitary District Funds, 50% Flood Control District Zone 3B Funds.
BACKGROUND:
The Contra Costa County Flood Control and Water Conservation District (District), in partnership with the Central Contra Costa Sanitary District (CCCSD) proposes this Project at the CCCSD Treatment Plant located in Martinez, CA (unincorporated Contra Costa County), to improve flood protection.
The CCCSD treatment plant is a critical piece of regional infrastructure, and due to its proximity to Grayson and Walnut Creeks, is vulnerable to flooding. The western levee between the CCCSD treatment plant and Grayson and Walnut Creeks provides flood protection against a 100-year or a 1% chance flood event but lack the necessary freeboard.
This particular levee section is a part of the United States Army Corps of Engineers Walnut Creek Levee Project. Due to the design and layout of CCCSD’s facilities as well as their critical nature, CCCSD recommends increasing its flood protection level to a 500-year or 0.2% chance with three feet of freeboard. The deficiencies for the 500-year storm plus three feet of freeboard can be satisfied in most locations by raising the levees by adding new fill. Engineering analysis indicates that the average height of fill required along the levees is approximately 3.5 feet. The project would raise the western levee along an approximately 7,500-linear feet (1.4 miles) segment adjacent to Grayson and Walnut Creeks from the State Route 4 (SR4) overpass in the south to the Burlington Northern and Santa Fe (BNSF) railroad bridge in the north.
The creek side of the levee will remain in place and the raised levee will be constructed towards the CCCSD property. Portions of the adjacent CCCSD-owned railroad tracks will need to be removed to accommodate this improvement; the fence between the levee and tracks will need to be removed and reinstalled in the new levee alignment. In addition, concrete floodwalls will be constructed on top of the levee on the north and south sides of the Imhoff Drive overcrossing above Grayson Creek.
Construction is anticipated to occur sometime between 2023 and 2025 and take approximately 104 working days. The Project will require additional property transfer from CCCSD to the District which is planned for a separate Board approval later this year. The District and CCCSD have entered into a funding agreement, approved by the Board of Supervisors on December 15, 2020, describing their respective roles and responsibilities for the Project.
CONSEQUENCE OF NEGATIVE ACTION:
Delay in approving the project may result in a delay of design, construction, and may jeopardize funding.