Brightwater Tunnel Inches Through Toughest Stretch Toward Finish

On a good day, 100 feet below ground, you can see progress as a 3,000-ton machine slowly bores the tunnel for King County's Brightwater sewage-treatment plant.

Not so on one recent day, as the behemoth churned away in rigid clay and its propulsive hydraulic jacks seemed to stand still.

Machine operator Mike Allen grumbled about the rock-hard earth as he held back the machine to one-tenth the speed it can go in soft soil. "If you put too much pressure on it," he said, "you'll bust the bearings like anything."

During two working shifts, the machine mined 20 feet of the 13-mile tunnel that will connect the plant north of Woodinville to Puget Sound.

If tunneling is completed by September, as now scheduled, the tunnel could begin carrying treated wastewater to Puget Sound in July 2012 — a year and a half past the original target date.

Earthworming its way under Ballinger Way Northeast in Shoreline, the tunnel-boring machine rounded the curve onto Northeast 195th Street in Lake Forest Park last week. It now is approaching the last, most difficult segment of the entire $1.8 billion Brightwater project