Crews used a tunnel boring machine with a 10-ft-dia cutter. Dubbed "Miss Betty," the TBM was rented for six months from Herrenknecht in Schwanau, Germany, at roughly $480,000 per month. Trailing behind the TBM were a couple hundred feet of tunnel equipment and earthmoving carts.

Completed on Sept. 12, the tunnel runs at a depth of between 20 ft and 200 ft. The TBM began with a relatively easy journey through "fairly confident rock" and ended with an "abrupt" transition into alluvium soil, which is lower in bearing quality than rock.

"We knew [the alluvium] was coming but it was a very drastic change, so we ended up having three sinkholes," says DWP's Reyman. "The sinkholes were where we knew they would be, very close to the rock and alluvium interface."

Because of its size, the reservoir is an exception to the rule of DWP managing its own projects. Construction management at-risk delivery allows a general contractor on site to objectively oversee the work, Quinones says.

"When an owner pushes a project, sometimes it gets a little subjective; they are the owner and they see things from an owner's point of view," he says. "But bring in a contractor and they are going to push the job; they take into account all the owner's interests and all the contractor's interests on site, and that is a big benefit."

WOL also had to take into account the interests of minority business enterprises and women business enterprises, which were mandated to be 22% of the project's construction cost, or about $30 million worth of the work.

"What makes this challenging is that because it's a public project, we have to take the low bidder," says Quinones. "So if we don't control who we contract with, we have no idea what their capabilities to meet their requirements are." A post-award evaluation of all low bidders gave WOL the assurance that they could perform the work.

With the first phase nearly ready for operation, WOL is preparing to test for water leaks in the structure. Backfilling around the basin will begin in December. WOL is also providing preconstruction services for the second phase of the project, which includes the 55-million-gallon West Reservoir. Quinones says that some time within the next 18 months, WOL will receive construction documents for the powerplant.