It has been almost a decade since the City of Redmond began planning for the South Detention Vault in Overlake Village and it is now scheduled to be completed this summer.

Joe O’Leary, a senior engineer for the city and the project manager for the vault, said plans for the vault began in 2007, with design starting in 2011 and construction beginning in 2013, adding that they are looking at a completion date of sometime in July — August at the latest.

Construction for the vault has been broken into two phases. The first phase, which began two years ago, consisted of rerouting the area’s utilities around the construction site.

“We moved everything out of the way,” O’Leary said.

The second and current phase of the project began in 2014 and will finish out the project in a few months, he said.

The vault — which will be 533 feet long and 123 feet wide — will address stormwater drainage for about 322 acres and will be able to hold up to 6.5 million gallons of water.

“It’s big,” O’Leary said, adding that it will likely be the largest stormwater vault in the state.

This will be a regional facility, he said, meaning large developments such as the 28-acre future urban center at the old Group Health Cooperative site nearby won’t need to have vaults on their own sites. They just need to lay a pipe in the ground and connect it to the vault, O’Leary said.

Now that developers won’t need to install a vault themselves, he said that will trigger redevelopment in Overlake as they will be saving money.

In addition to the economical benefits, the vault will also help the environment.

O’Leary said the vault will help with flood control downstream.

The detention vault will collect the stormwater runoff from the pavement and release the water back downstream gradually.

“(The vault) detains it,” O’Leary said. “This holds the water.”

As a result there will be less erosion, he said, which will help the fish in the streams.

“It’s a win-win situation,” O’Leary said.

The total cost of the Overlake detention vault is estimated at $21.5 million. Roughly $3.9 million was for the preliminary work and final design and about $17.6 million is for the final construction costs. To help fund the project, the City of Redmond received a $1 million grant from the Department of Ecology.