Evaluation of Cooling Water Intake Technology Alternatives with Consideration of Engineering, Costs, and Biological Efficacy on a Narrow, Sediment-Laden, and Barge-Heavy River

Compliance with the Clean Water Act Section 316(b) Phase II Rule and also meeting the fully-permitted cooling intake capacity at a riverside power plant in Minnesota has presented unique challenges. The existing traveling screens (3/8" slot size) at the screenhouse are several decades old and are not adequate for meeting the Phase II Rule requirements, while the size of the eight existing bays within the screenhouse limit the number and size of wedgewire screens that could be placed within each bay. There are also space limitations in the area outside the screenhouse, which is located on a 300 to 500 feet wide river bend that experiences barge traffic during the open water season. Barges have been noted to come within several feet of the screenhouse sheet piling, and tugboat motors generate a large amount of turbulence (and hence sediment) when driving the barge around the river bend near the screenhouse when heading upstream. Given these conditions, HDR conducted a study to determine the feasibility of locating wedgewire screen units at the existing screenhouse. Options considered included 1) placement of all screen units inside of the screen house, 2) placement of all screen units outside of the screen house in the area between the log boom and the screen house wall, and 3) a hybrid in which screen units were placed both inside and outside of the screen house. Considerations also included 2.0 vs. 0.5 mm slot sizes, debris removal, and fish recovery.