Best Management Practices 137236.docx

Mill Creek Fish Ladder Best Management Practices U.S. Army Corps of Engineers Walla Walla District Aquatics ID# 137236

September 13, 2024

This list of best management practices was prepared to comply with certain Clean Water Act requirements necessitated by the Washington Department of Ecology (Ecology). Ecology will review and approve this list prior to implementation. Ecology will also review and approve all substantive changes prior to implementation.

The U.S. Army Corps of Engineers (USACE), Walla Walla District proposes to construct a new fish ladder on the Federally owned flood risk reduction portion of Mill Creek in Walla Walla County, Washington. Work would also include construction of a new (replacement) stilling basin access ramp. Construction activities will be conducted in 2025 and 2026, spanning at least two in-water work seasons. All of the in-water work will be conducted between June 15 and October 31 of both years. After placement of the fish ladder cofferdam, work on the ladder would continue outside of the in-water work window.

Best Management Practices:

1. In-water work would be conducted during the extended in-water work window (June 15 to October 31).

2. Work areas would be dewatered. The contractor would prepare a dewatering plan for approval by USACE.

3. The contractor is required to prepare an environmental protection plan for approval by USACE.

4. The contractor is required to prepare a fish salvage plan for approval by USACE.

5. Fish salvage would be conducted prior to and during dewatering.

6. A USACE biologist would be on site for the fish salvage.

7. Concrete would be finished with smooth surfaces and no abrupt edges.

8. The contractor would be required to prepare a water quality monitoring plan for approval by USACE.

9. Water quality monitoring would be performed during in-water work activities.

10. The contractor would prepare a water quality monitoring report after completion of the work.

11. The new ladder would be designed to meet current fish passage criteria and would improve fish passage.

12. In certain instances, refueling or fuel storage near the creek may be unavoidable due to site-specific conditions or unique construction requirements (e.g., continuously operating pumps). The following precautions will be taken when refueling within 100 feet of the creek:

− Adequate amounts of absorbent materials and containment booms will be kept on hand by each construction crew to enable the rapid cleanup of any spills.

− If fuel must be stored near streams for refueling of continuously operating pumps, adequate secondary containment will be employed.

− Secondary containment structures will be lined with suitable plastic sheeting, and provide a containment volume of at least 125 percent of the storage vessel.