MWD awards Howard Ridley Company contract to reline Rainbow Tunnel

Joe Naiman

Village News Reporter

The Metropolitan Water District of Southern California awarded Howard Ridley Company Inc. the contract to reline MWD’s Rainbow Tunnel.

The MWD board vote Tuesday, Nov. 8, approved a $1,228,607.10 contract with Howard Ridley Company, which is based in Chino, for the rehabilitation of the concrete liner at 10 locations within the Rainbow Tunnel segment of the San Diego Aqueduct’s Pipeline 1. The relining will reduce the risk of water quality impacts or an unplanned shutdown in the future.

Currently five CWA pipelines carry water along the San Diego Aqueduct from MWD's Robert A. Skinner Water Treatment Plant in Temecula. The First Aqueduct consists of Pipelines 1 and 2, and the Second Aqueduct has Pipelines 3, 4 and 5. Pipelines 1, 2 and 4 convey treated water while Pipelines 3 and 5 deliver untreated supply. The aqueduct system has a treated water capacity of 650 cubic feet per second and an untreated water capacity of 780 cubic feet per second.

The First Aqueduct pipelines are the oldest in the CWA’s system. Construction on Pipeline 1 began in 1945, and water was first delivered in 1947. Pipeline 2 was constructed between 1952 and 1954 and brought on-line in 1954. Both are primarily reinforced concrete pipes with welded steel pipe being utilized in high-pressure siphons.

The First Aqueduct also includes 10 flow control facilities which were built between 1954 and 1987; some of those flow control facilities connect to both pipelines while others connect to only one. The First Aqueduct pipelines range in diameter from 48 inches to 72 inches and are comprised of multiple materials including steel, precast concrete and tunnel segments.

The parallel pipelines merge twice, and one of those merges in a horseshoe-shaped tunnel segment known as Rainbow Tunnel. The tunnel segment is approximately 4,700 feet long and has a height of six feet.

Recent inspections of the Rainbow Tunnel have identified areas of cracking and spalling of the existing concrete liner, which creates the potential for water intrusion. A structural integrity investigation of the tunnel using ground penetrating radar was performed to study areas of concern further.

The testing revealed that the tunnel was in good condition from a structural standpoint but that voids in the soil behind the liner which is seven inches thick were observed in 10 locations. The repair method for the ten locations will involve the injection of grout behind the tunnel liner to stabilize the soil and prevent water intrusion before removing and replacing the distressed concrete liner.

The final design for the liner rehabilitation has been completed. The project was advertised for bid Aug. 31. Two bids were received by the Oct. 4 deadline. Harrison Western had the low bid of $799,490, but the Lakewood, Colorado, company does not have a California contractor’s license so the bid was deemed non-responsive.

The Howard Ridley Company bid of $1,228,607.10 complies with the requirements of the specifications and is also below the engineer’s estimate of $1,340,000. Howard Ridley Company will use Slater Waterproofing of Montclair as a subcontractor.

The Howard Ridley Company scope of work includes complete replacement of concrete liner at 10 locations, grout curtain injection, temporary ventilation and surface preparation at the tunnel access. MWD staff will handle shutdown support and continuing inspections, grading and preparation of the staging area, submittal review, construction inspection and project management.

MWD had considered a complete tunnel relining, but it would have required a shutdown of four to six months and would have cost between $10 million and $15 million. Two planned 10-day shutdowns for inspection and maintenance are scheduled to occur in winter 2023, so the work will be performed during those shutdown periods.

The construction phase budgets a total of $2,300,000. In addition to the contract amount, the estimates anticipate $335,000 for MWD labor force shutdown activities; $202,000 for construction management and inspection; $155,000 for submittals review, responding to requests for information and preparation of record drawings; $125,000 for contract administration, environmental monitoring support and project management and $254,392.90 for contingency.

Because the work will involve the reconstruction of an existing structure on the same site with the same purpose and capacity, the rehabilitation was found to be categorically exempt from California Environmental Quality Act review.

Joe Naiman can be reached by email at [email protected].