Lower Monumental Dam Transformer Oil/Water Separator

Snake River near Kahlotus, WA

Client: US Army Corps of Engineers
Date Completed: 2019

The Lower Monumental Dam is a Concrete Gravity Dam on the Snake River in Washington State. The powerhouse was constructed with six (6) main transformers on the top deck within concrete containment basins. The concrete containment basins were drained directly to the river, making collection and handling of rainwater necessary to prevent inadvertant discharge of contaminated water from the containment basins.

Twelve embedded drains (2 per containment basin) were to be intercepted and re-routed into the breaker gallery, where they would be connected to a new oil/water separator. 

Emagineered Solutions, Inc. (ESI) conducted an extensive GPR survey to locate the embedded drains and rebar. Core-drilled holes were painstakingly located to intercept each embedded drain and avoid existing rebar in the 3′-thick deck concrete. After core-drilling, the existing drains to the river were plugged and abandoned. 3″ GSP pipe drops were tied-in to the existing drain piping and routed down through the deck into the drainage gallery. The core-drilled penetrations were then grouted flush with the deck.  Finally, a new flexible joint seal was installed under the transformers to seal monolith joints within the containment basins.

Within the breaker gallery, a new 3″ galvanized steel drainage header was designed and installed to convey drainage 600′ through the powerhouse to a new oil/water separator. Each of the 12 new drops were connected to the header. ESI successfully installed and commissioned the system in two phases in 2018 and 2019 to minimize impacts to operations at the Dam.