Austin water utility officials have decided not to use a small property in a northwest Austin neighborhood to excavate a large tunnel for a planned water treatment plant, partially satisfying residents who said the work would disrupt their neighborhood and threaten local creeks.

"My take is that, if the city is going to do this project, this (change) is at least better than what they had been planning," said Eric Deal, president of the Mountain Neighborhood Association.

The city plans to dig the six-mile tunnel to pipe water from the $500-million-plus water treatment plant near Lake Travis to a reservoir near U.S. 183 and McNeil Road. City plans had called for digging a 100-foot-deep shaft on a one-third-acre lot in the Spicewood Springs neighborhood, along the path of the tunnel. That would have required approximately 11,500 heavy truck trips down a two-lane residential road over three years.

Instead, the city will pull the tunneling debris out of the ground at a site a few miles away, next to the reservoir, in a commercial area with few nearby homes.

"As we designed the tunnel, moving the (excavation) site just turned out to be the best solution," said Greg Meszaros, director of the Austin Water Utility.

Meszaros said there were several reasons for the change of plans. One was neighborhood objections in Spicewood Springs to the truck traffic and tunneling under an environmentally sensitive area, where a network of underground limestone caverns are home to rare species.

Digging a large shaft in a residential area posed other challenges. To minimize truck traffic during hours when children are going to and returning from school, the city had agreed not to haul material from the Spicewood Springs site before 9 a.m. or after 3 p.m.

By using the new site, Meszaros said, the city can work longer each day and potentially get the treatment plant running six months earlier.

The general path of the tunnel remains unchanged.

Changing the excavation site will not raise costs, according to a memorandum sent Friday from City Manager Marc Ott to the City Council.

The city still plans to dig a shaft up to 100 feet deep on the Spicewood Springs property. But the shaft would be somewhat smaller — up to 30 feet wide, instead of 40 feet wide — and would be used only to drop equipment into the tunnel or remove equipment from the tunnel, Meszaros said.

The project will require about 800 truck trips on Spicewood Springs Road, down from the 11,500 originally projected.

Deal said neighborhood concerns remain about whether the city should be digging such a tunnel at all, and whether the treatment plant will be worth the price tag.

Still, he said, "it's much better than having the dump trucks."