Current is shipped only a short distance to the transmission lines of the Bonneville Power Administration. Through a "wheeling" arrangement (the transmission of electricity produced by one utility through facilities owned by another for a fee), the Bonneville Power Administration transmits an equivalent amount of power to Seattle, 300 miles away.
The power house was built completely underground because there was no room in the narrow canyon for conventional construction. Room was left for more units and in 1985, two more generators were completed. By 1999, Boundary supplied one-half of the hydro-electricity for Seattle, 23 percent of the city's total.
When City Light planned a $143 million, 12-year rehabilitation of the dam and power house, City Light employees bid on the project. Their proposal was 25 percent below the estimate and they got the job.