Kennebec River Sewer Siphon Crossing

Summit Geoengineering Services provided geotechnical consulting for a replacement sewer siphon crossing beneath the Kennebec River in Augusta, Maine.

The sewer siphon extends from the wastewater treatment plant by the west riverbank through the east riverbank to Arsenal Street. The length of the river crossing is approximately 700 feet with tidal water, has a channel depth ranging from 2 to 15 feet, and has a tall, steep east bank. Horizontal directional drilling (HDD) construction and/or trench excavations were planned for the installation of the replacement sewer siphons. New sewer mains will connect the treatment plant to the Kennebec River siphon crossing and underground structures are anticipated at each end of the siphon crossing. Summit performed subsurface explorations (test borings) for the proposed siphon alignment and structures on both riverbanks, as well as several test borings in the river channel (through ice in the winter) to determine subsurface conditions. SGS provided recommendations for horizontal directional drilling (HDD) construction and trench excavation construction options for the sewer siphon; conducted slope stability analysis for the east bank (exit pit structure); and provided groundwater control and construction monitoring recommendations for all project components.