To:
From:
Re:
B. Motion:
Discussion:
City of Nashua, Public Works Division
Board of Public Works Meeting Date: September 26, 2019
David L. Boucher, Superintendent
Wastewater Department
Gas Tank Diaphragm Upgrade
To approve the contract for the digester gas holding tank upgrade project with Methuen
Construction Company of Plaistow, NH in an amount not to exceed $311,507. Funding
will be through: Department: 169- Wastewater; Fund: Wastewater; Activity: Digester
Gas Holding Tank Upgrade Project.
Digester gas from anaerobic digester is stored in 35-foot high, 25-foot diameter gas tank.
The anaerobic digester, gas tank and related facilities were constructed in 2000. The gas
tank has had no upgrades since being installed. The gas tank is an entire steel structure
with an inner flexible diaphragm where the gas is stored. The internal diaphragm had
failed with a visible split in a seam. Due to age of diaphragm and other upgrades needed,
anew project for replacing the diaphragm is needed.
In addition to replacing the diaphragm, the upper attachment ring will be reworked such
that the diaphragm can be detached from the air side of the tank. Currently the piston has
to be raised to detach the diaphragm from the gas side of the tank making that task
difficult. The wire cables that attach the piston to external counter weight plates are
rusted and will be replaced.
The project was out to bid on August 15, 2019 with a bid opening on September 6, 2019,
Two bids were received:
NEESCO - $399,750
Methuen Construction - $311,507
Methuen Construction has done several major projects at the NWTF including the Wet
Weather Facility, Primary Tanks Upgrade and the Energy Recovery Upgrade projects.
Their projects were done satisfactorily and have the manpower and experience for this
project.
