EXHIBIT B
Sequence of Operation
The sequence of operation stated below is based on information from the past digester cleaning
and plant knowledge on it. The goal is to dewater the sludge in the digesters and incoming
sludge in the shortest time possible while meeting all permit requirements. Should a contractor
have a better method to conduct the dewatering it should be discussed with NWTF plant
management and a new procedure may be developed. In addition, the sequence stated below is a
guideline and is subject to change if a better method or any obstacle, such as pump failure,
prohibits or changes how a step is to be conducted.
One week prior to starting the NWTF will dewater the secondary digester to the
extent possible.
At start the sludge holding tanks will be lowered as much as possible to allow for
incoming sludge.
Contractor shall setup dewatering equipment to dewater incoming sludge from the
sludge holding tanks.
Contractor shall setup dewatering equipment for dewater sludge in the primary and
secondary digesters.
Prior to start of dewatering the primary digester the remaining contents in the
secondary digester shall be screened and dewater. A much of the material possible in
the bottom of the secondary digester shall be removed. This will involve opening the
manway and hosing/diluting heavy material as the base so it can be pumped to
dewatering equipment.
Following cleanout of secondary digester, the NWTF will open valves and fill the
secondary digester. The cleanout of the primary digester will occur by transporting
sludge from the primary tank to the secondary tank.
The primary digester will be pumped out as much as possible. Once all the sludge
that can gravity feed to the secondary digester is complete the remaining sludge in the
bottom of the digester will be drained back to the sludge holding tanks or an influent
sewer manhole per direction by the NWTF. The final cleanout of the primary tanks
may require flushing water from the plant water system following proper aeration of
the vessel from the top man entry opening as described in step 8.
Gas flow valves from the primary digester will be closed and the manway hatch at top
opened. Contractor shall monitor levels of carbon dioxide and methane in the tank,
follow all OSHA regulations pertinent to ventilation needed for an explosive gas, and
ensure continuous gas monitoring throughout the inspection. Once determined it is
safe to enter, the contractor will inspect the inside of the structure using a camera.
The contractor shall have his own camera equipment or subcontract it to a sewer
video company. Camera shall have sufficient cable to be lowered to carefully inspect
the base area of the tank, about 100 feet deep from top to the bottom of the conical
section below grade. Pictures taken or videos shall be clear so that plant personnel
can review it and decide if any correction action is needed.
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