Lake Oswego is one of the most affluent suburbs of Portland, Oregon and encircles the banks of the 415-acre Oswego Lake. The city of Lake Oswego’s existing interceptor sewer pipeline, located beneath the surface of the lake, began deteriorating from corrosion and was seismically vulnerable, making water quality a concern. An award-winning design of the new Lake Oswego Interceptor Sewer (“LOIS”) replaced the existing sewer line with an innovative buoyant gravity sewer, the first known pipeline of this type in the world. The City of Lake Oswego (“City”) awarded the LOIS project in two phases – Lake Full and Lake Down.
The Lake Down Contract involved the installation of over 7,300 feet of 22- to 42-inch high-density polyethylene pipe (HDPE) at grade tolerances of 0.02 inches to connect the buoyant interceptor to the existing sewer system. Pile supports and caps and pipe cradles were welded to steel piles to support the new pipeline and a cathodic protection system was installed for protection. Lateral sewer pipes were connected to the lake-front residents and new manholes were installed along the pipeline. The City also took advantage of the
lake draw-down conditions and JWF’s management skills to add significant rehabilitation and replacement pipelines within the near-shore sewer system including individual residential laterals. This $4 million of additional work was designed “on the fly” jointly between the engineer and JWF.
The quiet, narrow residential streets leading to the lake were unaccustomed to heavy construction equipment. A small 11-foot boat ramp and two public lake access sites of less than a half acre were the only points of access to the lake. In total, approximately 7,000 truckloads of materials and equipment traveled the neighborhood streets. The City and JWF worked diligently with residents, under the “good neighbor guidelines” developed by the project team to keep them informed of the project progress and minimize the impacts of
the project as much as possible. Social media, videos, project websites, email communication and flyers all were utilized for status updates on the project.
Another unique challenge of the project involved keeping the residential sewer system operational during construction. By installing over 30 individual temporary bypass pumping stations, JWF was able to successfully divert flows around the work area without any impacts to the residents. The bypass pumping system required 24-hour monitoring to ensure continued operations throughout construction. Special sound buffering was installed on the pumps which were carefully positioned to minimize noise intrusion to local homeowners.
Oswego Lake is private and used year-round for recreational pursuits by the lake-front homeowners. A critical component of the project involved limiting the duration of time the lake would be inaccessible by the owners. The lake was closed to users after Labor Day 2010 to begin the draw down process with full use to be restored by Memorial Day 2011. The refilling process began in February 2011, which required certain lower elevation tasks to be complete in order to meet the tight deadline. JWF was able to carefully sequence the work in over 15 different areas around the lake to meet the contract’s condensed 8 month time frame – typically this work would be spread out over 18 months.
The unique and exclusive lake setting, coupled with complex scope requirements and high expectations for community involvement put the project teams under a considerable amount of pressure to construct the uniquely designed project. Through a true partnership environment, the City, designer and JWF were able to complete the project in time for the prime recreational and tourist season and under the project budget.
