Seattle City Light, which was established in 1910 by the City of Seattle, is managed by Seattle’s Mayor and overseen by the nine-person Seattle City Council. It is the seventh largest publicly owned utility in the United States in terms of customers served. It owns significant hydroelectric resources and its 131 square mile service area includes Seattle and several surrounding cities. City Light serves over 345,000 customers and has annual revenues in excess of $700 million.
The Boundary Hydroelectric Project is owned and operated by City Light under a license administered by the Federal Energy Regulatory Commission (FERC). The current license was issued on March 20, 2013 for a term of 42 years. On the same timeline, Pend Oreille County Public Utility District (PUD) received a Surrender Order for its Sullivan Creek Hydroelectric Project (FERC No. 2225). As part of Settlement Agreements for both the Relicensing of Boundary and the License Surrender of the Sullivan Creek Project, the parties to the Agreements have agreed that City Light will act on the PUD’s behalf in removing Mill Pond Dam and restoring the Affected Area of Sullivan Creek to a more natural riverine condition. Additionally, City Light and PUD have signed an Interlocal Agreement that establishes their respective obligations in completing the project. The documents that comprise the above referenced agreements can be found at the Seattle City Light website.
Mill Pond is located at RM 3.5 on Sullivan Creek. While it is part of the Sullivan Creek Hydroelectric Project, Mill Pond Dam does not perform hydroelectric functions or provide flood protection. Mill Pond was originally formed when a log crib dam was constructed in 1909 by the Inland Portland Cement Company. A gated concrete dam, built in 1921 and retrofitted several times since then, is located just downstream of the log crib dam. The concrete dam is 134 feet long and about 55 feet high and historically maintained the water surface elevation of Mill Pond at approximately 2,520 feet NAVD 88. In 1973, the gates were removed from the top of the dam creating an open spillway and establishing the current elevation of approximately 2,012 feet NAVD 88. The current area of the impoundment is approximately 64 acres. Both the concrete and log crib dams will be removed as part of this scope of work. In addition to removing Mill Pond dam the project includes habitat restoration of the Affected Area (Sullivan Creek from immediately downstream of the dam to Outlet Creek; approximately 1.7 miles upstream). The Affected Area includes two unstable slope sites upstream of the dam, habitat improvements within Sullivan Creek, and restoration of the channel and uplands currently inundated by Mill Pond.
Following the guidelines established in the project goals and objectives, the expected benefits of Mill Pond Dam removal and associated site restoration will include restoring the suite of riverine ecosystems processes to its pre-dam condition to the extent possible. These include restoration of downstream transport of coarse sediment and large woody debris, riparian and floodplain environments, and benefits to water quality in the form of reduced summer water temperatures due to reductions in water surface area and increases in water velocity in the area of Mill Pond.