You are here

Bolton Reservoir Facts and Background

Building the Bolton Reservoir

Bolton Reservoir Facts and Background

Built: 1915

Current Size: 2.5 million gallons (500,000 gallons of which are unusable)

New Size: 4 million gallons (increase to address overall system storage deficiencies)

Location: Skyline Drive and Skyline Circle

Estimated cost to replace: $9 million

Identified revenue sources: $5 million – Lake Oswego-Tigard Water Partnership

                                                $2 million – water fund balance

                                                $2 million – water system development charges funds

Part of the current (2008) Water System Master Plan previously identified for replacement in 1999 and 2004 water plans.

More than 100 years of service

The city of West Linn is proposing to replace its existing 2.5 million gallon Bolton Reservoir with a new 4 million gallon reservoir.

The existing reservoir is located on Skyline Drive, just up the road from West Linn High School, near the intersection of Skyline Drive and Skyline Circle. It is a concrete structure built in 1915. An interior liner was installed in 1992 and a synthetic cover was placed over the reservoir in 1996.

The city has determined the reservoir is seismically deficient and is undersized. Previous inspection of the reservoir found some flaking/pitting concrete and some cracking. The floating cover is also at the end of its life, having undergone extensive repairs in 2008 and in 2012.

Although the reservoir can hold 2.5 million gallons of water, 500,000 gallons are unusable based on the level of the reservoir floor and the outlet piping.

The condition of the Bolton Reservoir is not a new issue. Its replacement was identified in previous water system master plans, including the current 2008 plan, in which replacement was labeled a high priority.

In 2012, a site analysis was completed of the site, which included the demolition of the existing reservoir and construction of the new and larger reservoir on the same site. Though other sites in the proper elevation range in West Linn were considered, the city determined repurposing the same site as the best option.

Two different reservoir shapes were analyzed for the site – circular and rectangular – to determine the most economical configuration. To reduce the risk of landslide, the site analysis recommended the new reservoir be set back from the slope.

During construction, the city will need to rely on the use of Lake Oswego’s emergency water intertie or water restrictions would be required during peak usage times. Thus, the rebuild of the Lake Oswego-Tigard water treatment plant must be completed before construction of the new reservoir can take place.

When a final design plan is reviewed and approved, construction can start in 2016 and finish in 2017.

Site access                                   

The Bolton Reservoir site has two vehicle access points: one from Skyline Drive to the south and Skyline Circle to the east. It is expected that temporary construction access will be through Skyline Drive with waterline reconstruction along Skyline Circle.


Portions of the water lines running from the reservoir to the Horton pressure zone, the Bolton Pump Station as well as the transmission main line will be replaced, with the old lines being properly decommissioned and abandoned.


In 2013, the council approved a franchise agreement that provided West Linn with $5 million from LOT. The council designated those funds for the Bolton Reservoir project, which will result in the city having secured approximately more than 50 percent of the funds necessary to complete this significant, important project for West Linn’s water supply.

Click any thumbnail image to view a slideshow