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Re:
B. Motion:
Attachments:
Discussion:
City of Nashua, Public Works Division
Board of Public Works Meeting Date: February 23, 2017
Noelle Osborne, Piant Operations Supervisor
Wastewater Department
Primary Clarifier Upgrades — Study and Evaluation Phase
To approve the contract to Wright Pierce for professional services for a
preliminary study and report on needed upgrades to the NWTF primary
clarifier in an amount not to exceed $95,500. Funding will be through:
Department: 169 - Wastewater; Fund: SRF Loan; Activity: Primary Tank
Upgrades.
Wright Pierce Work Scope and Cost Proposal
The primary clarifiers are located at the wastewater treatment facility and
consist of 5 large rectangular tanks which were last upgraded in 2006. Over
the years, the primary solids collection mechanism, one for each tank, became
unreliable with frequent mechanical problems. The mechanism consists of
plastic chains that rotate fiberglass flights that push the settled solids to a
hopper at the beginning of each primary tank. The plastic chains were found to
stretch and dislodge off its track causing a tank to become inoperable. A more
durable and robust system is needed. Other issues include sludge hoppers that
do not concentrate the sludge to the extent needed, a grease removal method at
the inlet channel that failed and an odor removal system that failed. Other
upgrades needed include renovations to the primary thickeners to increase the
thickening of the primary solids collected from the primary clarifiers.
A request for qualifications was sent to 6 consultants. Three of the consultants
expressed an interest in the project and were interviewed. A committee picked
Wright Pierce based on their better experience and familiarity with the NWTF.
The design project will have various phases beginning with this request to fund
a preliminary evaluation and study of the primary clarifiers. Following this
phase Wright Piece will move onto the design phase. They estimate it will
take § months to complete the preliminary design report.
Wright Piece has completed several recent successful upgrade projects at the
wastewater treatment plant. They have also completed numerous primary tank
upgrades similar to those at Nashua at other wastewater treatment plants.
