(2 THE CITY OF NASHUA “the Gate Cy
Division of Public Works
Wastewater Department
DATE: July 24, 2019
Lisa Fauteux, Director of Public Works
TO:
Carolyn O’Connor, Finance Manager
FROM: David Boucher, Wastewater Superintendent
RE: Headworks Bar Rack
The Wastewater Facility had logs and damaging debris
enter into the wet well of the Facility on May 13, 2019.
This debris caused significant torque on the equipment,
bending the scraper arms and rakes on both bar racks. We
replaced the scraper arms and straightened the rakes,
thinking this was the extent of the damage.
On July 6, 2019, the Facility experienced a failure of
the short channel bar rack. We called the manufacturer
who sent a technician out to inspect the equipment and
determine what had happened. The tech reported that the
chain appeared to have come free of the sprockets at the
bottom of the channel when the equipment had reversed
itself. Once the chain was free of the sprockets, the bar
rack continued to run, with no indication on our SCADA
computer system of any alarms. This caused the chains to
kink, the rakes to bend, and damage to the sprockets and
other components.
When discussing why this happened, the technician did ask
if we had anything abnormal come up the bar rack. We told
him about the logs from May and he said that could
absolutely have had an effect on the stretching of the
chains.
This equipment is pivotal to the operation of the
Wastewater Facility. We currently have a redundant
screen; however, if the second screen were to fail, the
Wastewater Facility would not be able to take flow into
it. The Facility currently takes an average of 11 million
gallons of sanitary sewer waste each day. This waste
would not be able to get to the Facility for treatment.
During a rain event, the Facility can take 50 million
2 Sawmill Road « Nashua, New Hampshire 03060 e Phone (603) 589-3560 e Fax (603) 589-3474
