Interceptor work begins
- Sam Bennett
- Lake Oswego Review - News
First phase of project studies
Beginning today, subcontractors for the city's interceptor sewer design team will begin exploring geologic conditions in Oswego Lake and its bays and canals.
The work will uncover information about bedrock and sediments on the lake bottom that are important to the design of the tether and pile supports for the buoyant pipeline, as well as the type of materials that will be required.
This work is part of the design phase of the Oswego Lake interceptor sewer replacement project.
The design phase began in earnest after the city council chose the in-lake buoyant gravity alternative as the preferred option to replace the lake pipeline.
In the first two weeks of this phase, Earth Dynamics of Portland, a geophysical consulting firm, will launch a 20-foot long boat from the boat ramp on McVey Avenue, and will map the bottom of the lake using electronic sensors lowered from the boat to obtain information on the depth and location of bedrock.
The city council recently approved $12 million in revenue bonds to fund the design phase of the interceptor project. In total, its cost will be about $100 million.
When completed in December, the exploration program will have determined the depth, strength and quality of the bedrock in the lake and the corrosive properties of the lake bed sediments.
These results will provide information about the types of ground anchors that will be needed for the floating pipe tethers, and the best location for pile supports for the new pipeline.
Early next week, Advanced American Construction of Portland will launch and assemble three barges on the lake from the Lake Corp boat ramp. Once assembled, the barges will be towed to the Lake Corp's Maple Circle easement. Haztech Drilling will then load two drill rigs and other equipment onto the barges.
The initial loading process is expected to be completed by Oct. 1. There will be periodic transfers of equipment, workers and materials to and from the barges in support of offshore drilling operations at the Lake Corp boat ramp. Those operations will take place through mid-December.
The drilling and sampling operations will create some noise, primarily from a small diesel engine that provides power to the rock drill.
Shannon and Wilson, a geotechnical consulting firm, is managing the drilling and anticipates that work in the main canal will take about a week to complete. The bulk of the effort focuses on the main lake.
No work will be done beyond the hours of 7 a.m. to 6 p.m. Monday through Friday, or 8 a.m. to 6 p.m. on Saturday. No work will be done on Sunday.