Gardiner – CSO Retention Basin

Gardiner, Maine

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City of Gardiner
6 Church Street
Gardiner, ME 04345

Project Type

CSO Retention Basin


Hoyle, Tanner & Associates
2 Pegasus Street, Suite 1, Unit 200
Brunswick, ME 04011

Start / Finish

December 2015 - October 2016

Description / Significance

Sargent crews constructed a 410,000-gallon CSO (combined sewer overflow) retention basin for the City of Gardiner, Maine, to minimize overflow discharges into the Kennebec River.  The new CSO basin was part of a $3.8 million upgrade to the Maine Avenue Pump Station.  The project also included screening upgrades at the pump station.  This project was located in a very confined area, with the Kennebec River 50 feet to the east, Cobbosseecontee Stream 40 feet to the north, and an old railroad line 30 feet to the west.

Crews excavated 7,000 cubic yards of dirt, rocks, and artifacts to construct the basin, a cast-in-place underground storage structure 100 feet long, 32 feet wide, and 20 feet deep, with an additional 7 feet deep sump at one end.  Excavation for the project required construction of a very large coffer dam with steel sheets on three sides.