C
To:
From:
Re:
H. Motion:
Discussion:
City of Nashua, Public Works Division
Board of Public Works Meeting Date: December 20, 2018
David L. Boucher, Superintendent
Wastewater Department
Gas Tank Evaluation
To approve the inspection and evaluation of the gas holding tank for the anaerobic
digester with McDermott-CBI Services of Plainfield, IL in an amount of $18,280.
Funding will be through: Department: 169- Wastewater; Fund: Wastewater;
Account Category: 54 Property Services.
The Anaerobic Digester at the Wastewater Facility produces methane gas as a
byproduct of the digestion process. This gas is stored in a large gas holding tank
(35 feet high, 25 foot diameter) which is necessary to provide a constant flow and
pressure for the boilers and generators that run on digester gas.
The tank is failing to trap gas and maintain pressure. Wastewater personnel
opened the side hatch and determined the inner diaphragm appears to be sagging
on the opposite side af the vessel, however, could not enter inside the tank to
inspect further due to gas levels.
Wastewater reached out to several companies to evaluate the inside and outside of
the tank, Only McDermott and HEI were found to be qualified and submitted the
following prices:
McDermott $18,280
HEI $140,000
HEI included the additional cost to purge the methane gas, making the tank safe
for entry, McDermott did not, however the Facility has been quoted a reasonable
price through ACV Environmental and will hire them through a separate contract.
We are recommending McDermott perform the evaluation of needed repairs, in
order to have the repairs quoted and work completed by August of 2019, when the
Energy Recovery Generators are scheduled to be finished,
