Jane HeislerJane Heisler

Read below for some answers to questions we have received about the Lake Oswego Interceptor Sewer. If you don't see an answer to your question, submit it using the form at the end of this page and we will get back to you!


Q: During construction, will nearby residents experience foul smells from sewage and exposed muck?

A: There should be no objectionable odors as a result of the lake drawdown. Keep in mind that the drawdown is during the winter. If it occurred during the summer, there could be some odors from more rapidly decaying organic matter. There should be no sewage odors either. The bypass pumping system that will be in place should not result in any increased odors.

Q: What precautions are in place to protect fish habitat?

A: As part of the "Nationwide Permit" issued by the Army Corps of Engineers (ACE) many agencies have reviewed the project and signed off on the permit, including the Oregon Department of Fish and Wildlife (ODFW), the State Historic Preservation Office (SHPO), the Oregon Department of Environmental Quality (ODEQ) and the National Marine Fisheries Service (NMFS). These groups are all stewards of important federal and state legislation like the Clean Water Act and the Removal-Fill Act.

The greatest danger to fish is turbidity of the water caused by construction activities. The City received a "Water Quality Certification" as part of its Nationwide Permit, that Oregon Department of Environmental Quality had to approve. This certification indicates that the methods that the City has in place, called best management practices, have been found to meet the requirements for fish habitat as part of the project's environmental permit. There are several water quality conditions that are imposed by the permit, including monitoring for turbidity. Anchor drilling and pile installation, parts of Lake Full Construction, are two of the biggest ‘culprits' for turbidity. The contractor is conducting a two-stage purification process. First, water is captured in a tank. This water may contain drilling fluids, grout, and sediments as well as lots of water. They add flocculants to the captured water, which causes the solids to sink to the bottom of the tank. They then run the clarified water through a sand filter system before it reenters the lake. This is a fairly sophisticated drilling treatment, but the advantage to the contractor is that it is faster than waiting for the sediments to settle out on their own and then having to test the water to make sure it is ready to be put back in the lake.

The other requirement that the City had to fulfill, was an Essential Fish Habitat Analysis. This was required by Oregon Department of Fish and Wildlife. It demonstrated that the project as a whole, from start to finish, is not causing any undue harm to fish habitat. There are no endangered or threatened species in the Lake. Contractors will restore the contours at the lake bottom if they are disturbed during the Lake Down phase. This should not impact habitat. During the Lake Down phase of the project, the only restriction placed on the project is that if any type of coffer dam is constructed, and fish are trapped, the project will need a fish salvage plan.

Q: Does the project consider potential impacts from invasive aquatic species?

A: Project designers invited input from world renowned experts on invasive mussel species about the susceptibility of Oswego Lake and the new interceptor sewer. They learned that the risk is low because of some important features of the lake.

In 1988 Zebra mussels were discovered in Lake St. Clair, Michigan. This invasive species, native to Russia and Eastern Europe, has since been carried to lakes in the western U.S. Since this species and its relative, the Quagga mussel, both cling to any available hard surface, LOIS team members knew it was important to investigate the impact they could have on the Interceptor sewer if they ever found their way to Oswego Lake.

The City invited six nationwide experts to a "Mussel Summit" on May 19, 2008 along with project consulting engineers and Lake Corporation representatives, to learn about the life cycle of these species, whether they could adapt to conditions in the lake and what types of prevention or mitigation could reduce their harmful effects. What the team learned was:

  • Zebra and Quagga mussels will likely reach Oswego lake during the 75 to 100-year life of the LOIS line,
  • The calcium, pH, alkalinity, dissolved oxygen and temperatures in the lake will not encourage the proliferation of these mussel species, and
  • Even a dense buildup of mussels could be accommodated by slight increases in the length of the buoyancy pipe used in the project in order to maintain the proper grade.

The project design team now has a solution to what could have been a surprising and potentially untimely arrival of these mollusks. The team also learned from the experts that these shellfish are not even good to eat!

Learn more about the environmental work related to the interceptor project.


Q: How much will it cost? How is the project being financed?

A: The total current estimate is approximately $95 million for the in-lake buoyant pipeline gravity system. This estimate may change somewhat as designs are refined and the lake down contractor is selected. Read more about the total cost of the project and what the project team has done to keep costs down.

The City Council voted in 2009 to finance the LOIS project through revenue bonds which are repaid through utility bills.

A rate increase was approved by City Council that took effect July 1, 2009. 30% rate increases are anticipated in the next two budget cycles. It is possible that the increase could be reduced to 14% in the 2012-2013 fiscal year. Starting in July 2010, a ratepayer, who currently pays about $77 per month, could see wastewater rates rise to $100 in the 2010-2011 fiscal year, $130 in 2011-2012, and $148 in 2012-2013. Increases after 2013 should mirror inflation.

Q: How do I know if my sewer bill will be affected?

A: Homes and businesses connected to public sewer within the City will pay for the interceptor replacement through increases to their sewer bills. Some homes or businesses at the western edge of the City are served by Clean Water Services and will not see their bills increase because of the LOIS Project. If you are unsure if you are inside the City's service area, call Utility Billing at (503) 635-0265.

Design & Construction

Q: How did the City assess the problem?

A: In 2002, the City retained Brown and Caldwell, Inc. a national environmental engineering firm with a local office, and commissioned a pre-design study to determine how to best correct the LOIS deficiencies. This Phase I study built upon earlier engineering evaluations of possible alternatives to replace the LOIS system. Those earlier studies suggested an in-lake gravity system would likely be the most cost efficient solution to the interceptor problems.

Updated construction cost estimates prepared as part of Phase I were substantially higher than preliminary estimates prepared in earlier studies. With the findings of the Phase I study in hand, and acknowledging the significant complexity and costs associated with any alternative to replace the current LOIS system, the City Council authorized Brown and Caldwell to begin Phase II of this study effort.

Q: Did the city consider an around the lake option?

A: The City Council directed project staff to pursue the in-lake option in July 2007 after several months of analysis and public comment. The decision was based on several factors, but the primary differences between the in lake and around the lake options were in long-term operations and maintenance costs and impacts to the community.

Unlike the gravity system proposed in the lake, the around the lake option would require the construction of six large pump stations throughout the community. Maintenance and operations for those pump stations would add $20 million to the cost of the project over the life of the system. The pump stations would have to occupy private property-many with above ground structures.

These six pump stations would be disruptive to the private property owners who would be asked to accommodate them. In addition, the around lake option would require the construction of an additional four miles of upland sewer pipes below the streets of Lake Oswego. Hundreds of Lake Oswego residents would be impacted if pipelines were constructed under busy Lake Oswego thoroughfares. Lastly, the around-the lake option would not preclude a drawdown of Oswego lake. A drawdown would be required to collect the flows from three trunk lines at the west end of the lake impacting the 700+ household with lake access.

Q: Are you sure a buoyant, tethered, gravity system will work?

A: The design is innovative, but it's not untested. All components of the buoyant system have a long track record in equal or more demanding conditions than Oswego Lake. For example, high density polyethylene (HDPE) pipe is used around the world to transport natural gas, water and sewage. In the 1960s, HDPE quickly became the pipe of choice over clay and metal pipe because of its durability, high resistance to corrosion and chemicals, and load carrying capabilities. HDPE pipe has been laid at the bottom of the ocean! The same anchors that will hold the pipe in Oswego Lake are commonly used in tunnels, dams, building and bridge foundations, and to anchor transmission towers.

The combined application of these components in a gravity sanitary sewer is new, which makes the project unique, but an extensive research and evaluation process has established its safety and reliability based on buoyancy, thermal dynamics and gravity. Learn more here.

The buoyant gravity system requires less maintenance than a more conventional, underground sewer system and therefore, has lower maintenance costs.

Q: Why are portions of the interceptor designed as a buoyant system and other portions pile-supported?

A: Some parts of the interceptor replacement pipeline are proposed to be supported on piles below the lake's surface and some are proposed to be buoyant and tethered to the bedrock beneath the lakebed. Since the buoyant portion is less expensive to build, some citizens ask why not just make the entire pipeline buoyant and tethered. This is sometimes followed with "Since one reason the existing interceptor is being replaced is that the piles won't hold up in an earthquake, why would piles be used again?"

The pile-supported sections are at the west and east ends of the main lake and at four locations on the north and south shore where on-shore trunk lines enter the lake.  At each of these locations, the pipe is either below or only slightly above the existing lake bottom. For the buoyant system to be effective, it needs at least 10 feet of water beneath the pipe to ensure the proper grade for gravity flow. Water depths in the west end of the lake are typically 3-8 feet. To make the buoyant system work in these areas the City would have to excavate and remove lake sediments. However, the City's permit from the U.S. Army Corps of Engineers requires restoring the lakebed to its existing contours. Therefore, the buoyant system is not possible in these locations.

Since the buoyant system won't work in these shallow areas, why not support the pipe directly on the lakebed without driving piles? There are two reasons. First, in many locations, the lake sediments are too soft to support the pipe system, which would have to include heavy concrete anchor blocks to keep it from floating up out of the lakebed during summertime low flow, when the pipe is the lightest. Second, in an earthquake, much of the existing lakebed in these areas will "liquefy," and would not be able to support the pipe system.

That leaves pile supports as the only feasible option in these shallow areas. The new piles will be substantially different than the existing piles. They will be designed to resist the 1000-year earthquake and they will be protected against the effects of corrosion, two of the fatal flaws in the existing system.

An added benefit of pile supports is that future drawdowns of the lake will not affect operation of the sewer system. The Lake Oswego Corporation periodically draws the lake down 10-12 feet to allow property owners to make repairs to their docks and boat houses. This level of drawdown will expose much of the upstream reaches of the pipeline, which, if buoyant, would result in sags and require sewer cleaning. With the planned pile system, the grade of the trunks and interceptor will be maintained.

Q: What's happening at Kelok Road?

A: Although initial designs called for the replacement of the pile-supported sewer line inside the main canal, project designers determined that pumping-around the main canal and building a new, underground pipeline in Kelok Road might reduce costs and cause less disruption to Main Canal property owners. Those initial designs required a drawdown of the main canal for at least a year. Unlike pumping around the entire lake, pumping around just the Main Canal provides a solution to a small, focused area that has benefits that appear to exceed costs for this feeder line to the interceptor. The in-lake gravity solution chosen for the bulk of the interceptor project still provides the most economical and efficient solution over the life time of the interceptor.

Staff initiated discussions with the Lake Corporation and with neighbors from the area. The result was almost universal support for the Kelok Pump-Around option. The City Council supported the replacement option in June. Some of the reasons for this recommendation include cost, preserving lake summer access, impacts to canal docks and seawalls and a slight improvement in dredging opportunities.

Q: How will the new Kelok/Maple pipeline relieve Cardinal overflows?

A: During sustained periods of heavy rain, after the ground is already saturated, water finds its way into the wastewater pipes and combines with the wastewater flows. The limited capacity of the current interceptor and its tributary trunk lines cannot handle the surface water and groundwater "inflow and infiltration" (I & I) which causes the sewer upsets at Cardinal.

Currently, wastewater from several hundred homes in the Westridge/Palisades area flows through the sewer line in Cardinal Drive. The Bryant Road and Kelok Road sewer project, will remove those flows from the line in Cardinal to help eliminate the overflows.

Of course, upsizing the interceptor in the lake will also provide greater capacity for the entire system, which will also help eliminate backups. In addition to increasing capacity, the City is also taking measures on an ongoing basis to reduce I & I by lining and replacing older, broken and cracked pipes within the wastewater collection system. It is an ongoing job for every city to try to keep ahead of capacity issues by making sure collection systems are more watertight.

Q: What happens on that big barge in the middle of the lake?

A: They say learning a language is something you can draw on throughout your life. Whether that applies to ‘drill-barge-speak' is arguable, since it may not be transferable beyond ‘Barge Country'. The barge has been responsible for drilling, installing and grouting the anchors that hold the buoyant wastewater pipe below the surface of the lake.

If you've seen it on the lake, you know that the island country of Barge flies four flags: two American, an orange Beavers flag and a green Duck flag, paying homage to the diversity of barge citizens.

The language spoken in Barge is also unique. While not quite a Romance language, we English speakers can catch on quickly as you'll see below.

In order to place the drills so they can reach their destination beneath the lake bottom to be securely fastened to dense gravels or bedrock, drillers need access to the water. Access is provided through a "moon pool" which is the opening in the middle of the barge where the two drills are located. This is difficult to see unless you are on the barge (the country of Barge does not grant visas so a photo is provided below.)

Keeping the country of Barge in place while the two drills and a dozen workers are creating enough movement to cause a lesser craft to pitch in the water can be a challenge. "Spuds", the long, steel pipes rising up from the bottom of the lake through the barge, hold the barge in place. For added support, several anchor lines, each attached to tons of concrete, ensure the barge does not move.

Crews must drill over 100 feet through muck, sediment and gravel before they reach a surface capable of holding an anchor. Once it reaches the right depth, gallons of water, drilling fluids and sediments it has picked up are pumped out and placed securely in a container for disposal. The anchor is then inserted and grouted into place where it dries for about three days before it is strength tested.

Attire in the country of Barge is also unusual. Since the anchor and grout travel through gravels and fractured rock, the grout must be kept contained so it is not lost in the gravels. Naturally, it wears a "grout sock". Unlike our stockings, a grout sock is about 12 feet long and forms a balloon around the grout so that it goes to the right place.

Lake Drawdown

Q: Why is a lake drawdown needed?

A: There are undersized, buried lines in the west end of the lake that need to be replaced. Doing this work in dry conditions prevents stirring up sediments into the water.

Q: What water source will be used to refill the lake?

A: A combination of sources, including the Tualatin River, local streams and creeks, rainfall runoff and the Tualatin River, will be used to refill the lake as quickly as possible.

Other Questions

Q: What area is served by the LOIS system?

A: Homes and businesses connected to public sewer within the City of Lake Oswego will pay for the interceptor replacement through increases to their sewer bills. Some homes or businesses at the western edge of the City are served by Clean Water Services and will not see their bills increase because of the LOIS Project. If you are unsure if you are inside the City's service area, call Utility Billing at (503) 635-0265.

Q: Did the Lake Corporation agree to the LOIS construction plans?

A: Yes. The Lake Corporation expressed its support for the preferred option in August 2007. Since then, the City and the Lake Corporation have negotiated the terms of two agreements: a "Drawdown Agreement" and an "Easement Agreement". Those agreements were signed in March 2008. The agreements address access locations to the Lake, bays and canals, the duration and schedule for lowering the level of Oswego Lake and roles and responsibilities of the parties prior to and during construction of the new LOIS system.

Q: Could a boat anchor damage the pipeline?

A: The HDPE material that the interceptor pipe will be made from is a very strong material that can withstand a far greater force than what would be caused by a boat anchor. HDPE is the preferred material for pipelines today because it is stronger and less susceptible to leaks than steel. In fact, HDPE sewer pipelines run along the ocean floor in the Pacific. These pipes withstand forces far stronger than anything the interceptor will be exposed to inside Oswego Lake.

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