Los Vaqueros Dam Toe Drain Rehabilitation Project

Los Vaqueros Dam Toe Drain Rehabilitation Project

CCWD proposes to rehabilitate the Los Vaqueros Dam’s toe drain outfall that discharges seepage water into Kellogg Creek. The existing 24-inch diameter toe drain outfall is located on the western bank of Kellogg Creek as shown in Figure 2 and was installed in the late 1990’s as part of the original Los Vaqueros Reservoir construction project. Over time, vegetation growth and sedimentation into Kellogg Creek has raised the elevation of the creekbed, leading to the submergence of the toe drain outlet. Currently, there remains positive flow through the toe drain, but the outlet remains at risk of complete blockage due to ongoing sedimentation and vegetative growth. Rehabilitation of the toe drain outfall to remove this obstruction is a requirement of the California Division of Safety of Dams (DSOD). At the project site, the existing toe drain outfall is nearly completely submerged in sediment within Kellogg Creek. CCWD proposes to redirect the alignment of the toe drain outfall into an underground pump package system/vault that would pump seepage water out of a new 10-inch pipeline alignment that outfalls into Kellogg Creek. The new outfall pipeline would exit the creek’s embankment at a higher elevation than the existing outfall and curve downwards, eliminating the sedimentation issue. The new pump package system will consist of 3 concrete structures (valve vault, manhole, and sump) extending a maximum of 15 feet underground. The structures will be constructed using a combination of pouring concrete in place and using pre-cast vaults. The exposed surface area of the concrete pump station vault is expected to be 10 ft by 10 ft, the vault will have a 6 ft diameter, and the valve vault will be 4 ft by 6 ft. In addition, an aboveground pump control panel adjacent to the pump system will be installed that will have a 6 ft by 8 ft concrete base. The new 10-inch outfall discharge pipe will be trenched underground at a depth of 3 ft. CCWD will install a concrete base pad underneath where the new discharge pipeline to prevent erosion issues. Before installing the concrete pad, vegetation within the top of bank and within Kellogg Creek will need to be removed using weed whackers and other hand tools. The use of excavators or backhoes may be needed to remove vegetation from the channel, but this equipment will only be operated from the bank of Kellogg Creek. Once vegetation is removed and the work area is dewatered, the area will be excavated to a depth of 1.5 feet. Afterwards, approximately 30 ft by 30 ft of concrete will be poured in place at a depth of 6 inches over a layer of aggregate base consisting of small rocks and gravel. The total volume of both aggregate base and concrete is approximately 50 cubic yards (17 cubic yards of concrete and 33 cubic yards of aggregate base). Once the project is completed, the existing 24-inch outfall pipeline will be disconnected from other drainage facilities, plugged, and remain in place.

Contra Costa

Unincorporated

Contra Costa