Blandford, MA-Cobble Mountain Diversion Gates Outlets Mods

The Commission owns and operates the Cobble Mountain Reservoir, a 22.8 billion gallon reservoir that serves as the primary water supply for the City of Springfield and surrounding communities. Flow from the reservoir can be passed through the Diversion Tunnel, a low-level outlet for the Cobble Mountain Reservoir through a tunnel in the left abutment of Cobble Mountain Dam. Flows are controlled by two (2) 42-inch by 30-inch jet flow gate valves in a Gate Chamber approximately in line with the crest of the dam and 200 feet below the ground surface. Control of the valves is done from a Control Chamber approximately 22 feet above the Gate Chamber.

Airflow down a vertical 10-foot by 4-foot, 8-inch concrete lined shaft has been observed to cause icing immediately downstream of the 42-inch discharge pipes for the valves and on the access stairway to the Control Chamber for the jet flow gate valves. The icing downstream of the valves has damaged equipment and structures. Icing on the stairs makes access to the Control Chamber unsafe.

The Commission is issuing this Contract to make modifications to the discharge pipes for the Diversion Gate Valves by extending the pipes, adding new air vent pipes, and constructing a new concrete masonry unit (CMU) wall to limit air flow into the tunnel. The Work also includes replacing a damaged security gate at the downstream end of the tunnel and injecting seeping construction joints in the tunnel to address other icing issues.

The project also includes a local HVAC for control of air through the Control Chamber.

Electrical improvements include the installation of new conduit, wires and lighting in the Control Chamber access stairwell and power supply and controls to new HVAC systems