To:
From:
Re:
F. Motion:
Discussion:
City of Nashua, Public Works Division
Board of Public Works Meeting Date: February 25, 2021
Daniel Hudson, P.E., City Engineer
Engineering Department
2021 Sewer Rehabilitation — Siphon Design
To approve the engineering services contract for design of sewer siphons
rehabilitation with Hazen and Sawyer, PC of Manchester, MA in an amount of
$194,533. Funding will be through Department: 169 Wastewater; Fund: Bond;
Activity: Sewer Infrastructure Improvements.
During Phase 1 of the Capacity, Management, Operation and Maintenance
(CMOM) program, eight locations where inverted sewer siphons convey
wastewater from one side of a waterway to the other side were cleaned and
inspected using closed circuit television (CCTV). Inverted siphons are prone to
siltation and blockages and are difficult to inspect and repair because they operate
full of wastewater, under pressure, and are located beneath waterways. The siphons
are comprised of 22 sewer sections totaling 4,700 feet in length, are made of various
materials, and range in diameter from 6 inches to 60 inches. The siphons were
originally constructed between 1965 and 1982.
CCTV inspection has identified deficiencies in the siphons that include cracks,
erosion of cement lining, corrosion, holes, and exposed rebar. Different methods of
pipe lining will be used to rehabilitate the pipes. Strategies to temporarily redirect
wastewater flow through different barrels are required to make the repairs. Access
to these sites with lining equipment will also be a challenge. Hazen has the
necessary expertise to complete the design, and is knowledgeable about the city’s
wastewater system through their previous CMOM Phase 1 work.
