20180544 Ver 1_Project Narrative_20180418

Site 5 – CCUC Sewer Crossing Stabilization
Project Narrative

Site 5 of the CCUC project is located on a tributary to Leak Fork Creek, which is a perennial tributary to Mill
Creek. The tributary flow is generally from east to west, with the confluence with Leak Fork Creek just
downstream of the project area. The drainage area is approximately 0.017 square miles of mostly
industrial/commercial land use. The sanitary sewer crossing is exposed above the channel bottom and
causing erosion. The existing stream banks are very steep and the stream bed is actively down-cutting. The
current drop is unpassable for most aquatic life until flows from Leak Fork Creek back up over the structure.
Without intervention, the bed will erode below the sewer crossing, creating an aerial crossing and risk of failure
of this sewer pipe.

The proposed project will utilize natural channel design techniques to restore the grade and protect the sewer
crossing. The channel elevation at the utility crossing will be raised approximately 6 inches above the sewer
pipe with a constructed riffle. A downstream control drop structure of boulder steps will be built to prevent future
erosion and to meet existing channel grade before the stream converges with Leak Fork Creek. The placement
and design of the drop structure was chosen to prevent the need for extensive bank damage during installation.
The sanitary sewer pipe under the stream bed will remain in place, but a portion of the pipe in the stream bank
will be replaced with ductile iron pipe.