Contract change order approved for erosion control project

The San Diego County Water Authority approved a change order for their Moosa Canyon Erosion Control project.

The CWA board approval Oct. 25, adds $351,000 to the contract amount and is the third change order associated with the dewatering system needed to address groundwater, which was encountered at a higher level than expected. The newest change order increases the total contract amount with Granite Construction from $1,445,889 to $1,806,889, while changing the contract end date from Oct. 31 to Dec. 31.

The Moosa Canyon erosion control project will protect the CWA’s Second Aqueduct by preventing stream bank erosion, preventing head cuts from moving upstream and installing half-ton riprap. The construction will place engineered grouted and non-grouted riprap in the creek channel.

The CWA’s Second Aqueduct includes Pipelines 3, 4 and 5. The pipelines transport water through steep terrain and cross under Camino Del Rey in Bonsall. Moosa Creek is a riparian environment with dense vegetation, and in 2013, CWA staff observed that a portion of Pipeline 4 was exposed in Moosa Creek due to creek bed erosion. The location coincides with a horizontal bend in the pipeline where the pipeline crown is visible.

The exposed bend in Pipeline 4 is subject to internal water force, or thrust, as water changes direction. A structural analysis of the internal water forces conducted in 2015 indicated that those forces were not a concern at the time, but the CWA was concerned that future storms could cause additional erosion and threaten the suitability of the pipelines at the creek crossing.

During 2016, CWA staff installed interim erosion control measures to restore cover over the pipeline and stabilize the area before the next wet season. In June 2016, the CWA board authorized a $279,620 professional services contract with Michael Baker International for the design of pipeline protection and for construction phase design support services. The design incorporates the interim repair improvements into a long-term erosion control solution. The CWA board approved the project, along with the environmental Mitigated Negative Declaration and the Mitigation Monitoring and Reporting Program, in April 2017.

Temporary right of way agreements, a U.S. Army Corps of Engineers letter allowing the project, and a streambed alteration agreement with the California Department of Fish and Wildlife were prerequisites to advertising the project for bids. On Feb. 14, 2018, the project was advertised for bids. Six firms responded by the March 13 bid deadline, and the Granite Construction bid of $1,235,889.40 was the lowest.

The Granite Construction proposal included all work specified in the bid package, but the geotechnical borings conducted during the design phase showed groundwater at a depth of 9 feet below the surface and when Granite Construction began excavation activities in June, groundwater was encountered approximately 1 foot below the surface. A dewatering system became necessary to maintain the water level below the bottom of the excavation.

On July 26, the CWA approved a change order covering the additional scope of work along with an additional $200,000 funding authorization. The dewatering system which consisted of four dewatering wells to maintain the water below the bottom of the excavation was installed in August, but water quality samples indicated that some items were above the allowable limits to obtain an industrial waste permit for the discharge of construction and nuisance water.

CWA, Regional Water Quality Control Board and Valley Center Municipal Water District staff worked on a solution which allows the groundwater to blend with VCMWD effluent which is discharged into that district’s percolation ponds adjacent to the project site.

The groundwater stabilized at approximately 2 feet below the surface after the dewatering system had been operating for five days, but the contract documents stipulated excavation approximately 9 feet below the ground surface. A modified design is being evaluated, and the dewatering system will need to remain in operation.

A change order adding $20,000 to the contract and extending the contract end date from Oct. 12 to Oct. 31 was small enough that CWA board approval was not needed, and that extension allowed the CWA board to approve the larger change order.