On August 9, 2021, a leak in the concrete liner of the California Aqueduct was discovered on the left side (L) of milepost (MP) 54.9. Initial flow out of the leak was
approximately 700 gallons per minute. A sandbag ring with a PVC pipe was established to direct the flow from the leak away from the right-of-way (ROW) and into an existing concrete-lined ditch, then into an un-named drainage adjacent to and east of the ROW. A short-term repair of the leak was conducted by divers injecting grout and a concrete/cement mix into the concrete liner.
To fully repair the leak, two rockfill cofferdams, composed of approximately 6,000 cubic yard (cy) of material, will be installed in the Aqueduct to dewater it. Material for the cofferdam will be borrowed from an existing stockpile located at the intersection of McCabe Avenue and the Aqueduct and Basalt Road at the toe of Sisk Dam. An approximately 670 cy layer of sand and visqueen will be placed on the rock slopes on the water side to reduce seepage. The Aqueduct will be fully dewatered between the cofferdams and the existing concrete liner panels will be pressure washed in the work area.
Geological exploration will be done by sawcutting or coring approximately twelve 3-inch diameter cores through the concrete liner panels between MP 54.8 and MP 55.0 on both the primary and secondary embankments. The core holes will be backfilled to match existing liner surface when complete. Additional cores will be added as necessary.
An estimated 30 Aqueduct liner panels will be removed and replaced or repaired as necessary. This effort includes removing the damaged panels, excavating unsuitable material from behind the panels, and backfilling the excavated area and voids with either imported material or concrete. Approximately 1,000cy of embankment will be excavated with additional excavation as required. Formwork will be placed over the finished grade and the removed panels will be replaced with new 4-inch cast-in-place concrete liner.
Panel repair will include cleaning cracks and applying joint sealant, filling voids behind panels with stable cementitious grout, and filling larger cracks or holes in the concrete with shotcrete, mortar, hydraulic cement, or conventional concrete. Once the new panels are in place and panel repair has been completed, a geosynthetic geomembrane liner (asphalt mat) will be placed on top of the concrete panels over an approximate total of 600 feet length of Aqueduct. Joint sealant will be applied in the finished joints and will be allowed to cure a minimum of 3 days.
Three staging areas will be established at MP 55.1 L, MP 54.9 R, and MP 55.2 R. Water trucks will be continuously traveling both sides of the Aqueduct for the entire length of Pool 10 to keep the existing exposed concrete panels wet and to prevent damage. This will occur for the duration of the project; approximately 6 weeks. The site will be cleaned up, equipment demobilized, and Pool 10 will be carefully refilled.