O'Neill Forebay Dam Weir Box Modifications and Drain Pipe Replacement


SCH Number
Public Agency
California Department of Water Resources (DWR)
Document Title
O'Neill Forebay Dam Weir Box Modifications and Drain Pipe Replacement
Document Type
NOE - Notice of Exemption
Document Description
Five toe drains and five associated weir boxes located at the O'Neill Forebay Dam will be modified, and the pipes will be replaced. The toe drains scheduled for maintenance are identified as 132.45, 132.7, 132.8, 134.75, and 40.80. Each toe drain consists of up to two, 24-inch corrugated metal pipes that lead from the interior of the Dam to a cement weir box. These weir boxes are currently too large to accurately measure the amount of water seeping from the Dam and the metal pipes are rusting. To prevent further degradation of the pipes, and to regain the ability to measure water that, by design, seeps from the Dam, the Department of Water Resources’ (DWR) San Luis Field Division (SLFD) will pothole using a vacuum trailer to locate the corrugated metal pipes. SLFD will then use hand tools to remove the wood lids on the existing weir boxes and a backhoe to lower a fiberglass weir box into each of the cement weir boxes. Hand tools will be used to secure the fiberglass weir boxes to the cement weir boxes. SLFD will then use a backhoe to dig up to ten trenches with maximum dimensions of 5 feet wide by 10 feet deep by 50 feet long to expose the rusting pipes. The pipes will be removed, new 12-inch or 15-inch diameter plastic pipes will be installed, and the trenches will be backfilled. Hand tools will be used to attach the new pipes to the weir boxes. This work is necessary to preserve the physical integrity of the O’Neill Forebay Dam and to accurately measure seepage.

Contact Information

Eleuterio Diaz
Agency Name
Department of Water Resources
Job Title
Planner/Scheduler and Utility Craftsworker Supervisor
Contact Types
Lead/Public Agency


Southern California
Cross Streets
O'Neill Dam is approximately 1.6 miles southwest of Santa Nella.
State Highways
Interstate 5, SR 152, SR 33
O'Neill Forebay, San Luis Reservoir, San Luis Canal
Other Location Info
O'Neill Dam (Dam) is in Reach 3A of the portion of the California Aqueduct known as the San Luis Canal, approximately 1.6 miles southwest of the unincorporated community of Santa Nella in Merced County. The work site is on the east side of the Dam.

Notice of Exemption

Exempt Status
Categorical Exemption
Type, Section or Code
Reasons for Exemption
DWR will replace pipes and modify five weir boxes associated with O'Neill Forebay Dam. This work will not result in an increase in the use of these structures. Categorical Exemption 15301 (m): Minor repairs and alterations to existing dams and appurtenant structures under the supervision of the Department of Water Resources applies to this work.


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