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Portland Water Bureau

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Uncovered Reservoirs

Washington Park Reservoir 4

Portland has a schedule to replace its open finished drinking water reservoirs with enclosed storage by December 31, 2020.

A finished drinking water reservoir contains water that has been through all the treatment steps required by the federal Safe Drinking Water Act and can be delivered to the public without further treatment. Portland had five uncovered finished drinking water reservoirs. Three located at Mount Tabor Park and two located in Washington Park.

The Long Term 2 Enhanced Surface Water Treatment Rule (LT2) affects uncovered finished drinking water reservoirs by requiring that water systems either replace, cover the reservoirs or provide treatment at the outlets of the reservoirs to remove or inactivate 99% (2 log) of the Cryptosporidium protozoa, 99.9% (3 log) Giardia bacteria and 99.99% (4 log) of viruses.

Portland developed a schedule for replacing its existing open drinking water facilities with enclosed storage by December 31, 2020.

The uncovered reservoirs at Mt Tabor were disconnected from the drinking water system on December 31, 2015. New seismically stable covered finished reservoirs at Kelly and Powell Butte replaced the storage capacity of the Mt Tabor Reservoirs. While the three open reservoirs at Mt. Tabor no longer supply drinking water, they continue to be important assets to the City of Portland. The City of Portland has committed $4 million over a four-year period (2016-2020) for maintenance, repair, and preservation work

The uncovered reservoirs at Washington Park are currently being rebuilt [link to Washington Park project page]. A new seismically stable covered finished reservoir is being constructed in the footprint of the existing Reservoir 3 (upper), while Reservoir 4 (lower) has been disconnected from the drinking water system and is being developed into a lowland wildlife habitat area, bioswale, and reflecting pool.