Located in the state of Washington, this is the second largest dam to be decommissioned in the United States. Completed in 1913, the 471-foot-long, 125-foot-high gravity dam provided electrical power for local industry. As owner’s engineer, Kleinfelder led a multi-disciplinary effort to complete this high-profile dam removal project on schedule in December 2012.
The project’s tight schedule was driven by stringent regulatory requirements from various agencies. Pre-breach work included blasting a 90-foot long drain tunnel through the dam, replacing a city waterline, and replacing foundations of a bridge. Post-breach work included managing former reservoir sediments, removing the dam and related facilities, disposing of 30,000 cubic yards of concrete debris, and restoring and revegetating the stream corridor.
Initial work included reservoir sediment characterization and preparing decommissioning plans and specifications, permit submittals, and post-decommissioning management plans. Kleinfelder provided preliminary design of a replacement waterline and protection measures for a bridge foundation. Kleinfelder also prepared the Environmental Monitoring Plan to provide guidance for water and sediment quality monitoring during post-decommissioning recovery of the nearby river. Kleinfelder proposed innovative solutions, including a flowline to dispose concrete demolition rubble and a soil nail wall to stabilize an exposed bridge abutment.
Stringent project and construction management strategies kept this project on schedule. Kleinfelder’s responsiveness and technical diversity enabled the utility to respond effectively to unanticipated events and maintain compliance with permit requirements. Use of the flowline saved money, and the soil nail wall enabled the utility to keep the bridge open, satisfying needs of surrounding communities.