The Salt Lake County Council gave the OK Tuesday night to spend nearly a half-million dollars to plan for a massive project that could bring new homes for 500,000 people to the Salt Lake Valley in the next 75 years.

Mayor Peter Corroon on Tuesday asked the County Council to consider updating the current budget to include $350,000 to hire a consultant to manage the planning of 75,000 acres along the valley's west bench. He also wants the District Attorney's Office to hire a full-time employee to focus entirely on zoning and land-use issues for the west bench. Corroon expects that position would cost about $134,000 annually for salary and benefits.

The council approved both requests but said it would re-examine the issues in November to determine if funding for the the attorney's position and the consulting contract is to continue.

"It's a bigger project than anybody had anticipated. We can't do this half-baked," said Darrin Casper, the county's chief financial officer.

The land in question lies along the Oquirrh foothills, from the Utah County border to near the Davis County line and spilling over the mountaintops into Tooele County. The property is owned by Kennecott Land, a sister company of Kennecott Utah Copper, which for almost a century has used the land for transportation and buffers in its mining operations. It is the largest undeveloped swath of land in a U.S. metropolitan area, Salt Lake County planners say.

As Kennecott's mining operations wind down and change focus, the company plans to create a series of developments — starting with South Jordan's Daybreak, which is already under construction — that are expected to change the face of the Salt Lake Valley dramatically. Of the 75,000 acres Kennecott Land owns in the county, about 41,000 is expected to be developed. The rest will be left as open space.

"We think that's pretty significant," the county's chief administrative officer, Doug Willmore, said of the project's scope. "We realized we need to put more resources into this to make sure we do it right. If we don't, everybody will pay for a long time."

Most of the land lies in unincorporated Salt Lake County, and at least four major county documents will govern the development, county planning director Jeff Daugherty said. It is those documents that planners want the consultant to oversee.