The project is located on Pierce Island in Portsmouth, New Hampshire, and can only be reached by one passage.
Photo courtesy of METHUEN Construction
Efficient work on the 3.8 acre site requires careful coordination.
The project team installed a 4-foot-diameter backwash pipe in the pipe gallery of the biological aeration filter.
Photo taken by JOHANNA KNAPSCHAEFER for ENR
The city took the unusual step of setting up three small-scale processing system pilots for $1.8 million before deciding which technology to choose.
Photo courtesy of AECOM
The city took the unusual step of setting up three small-scale processing system pilots for $1.8 million before deciding which technology to choose.
Photo courtesy of AECOM
When the flow is lowest, the pipe cutting is reserved for the night shift, and the staff installs and tests the discharge saddle and the production line stop device during the day shift.
Photo courtesy of METHUEN Construction
When the flow is lowest, the pipe cutting is reserved for the night shift, and the staff installs and tests the discharge saddle and the production line stop device during the day shift.
Photo courtesy of METHUEN Construction
On the scenic Pierce Island, the earthen remains of Fort Washington can be traced back to the War of Independence and the War of 1812. The construction of the largest public works project in Portsmouth, New Hampshire requires close coordination from the first day.
The task of the staff is to upgrade the Portsmouth Sewage Treatment Plant located on the banks of the Piscataqua River. Its floor space is the same as that of the existing plant. The sewage treatment operations and public swimming pool access must be maintained. The project team, led by Methuen Construction in Plaistow, New Hampshire, must also manage the flow and delivery of traffic on a single pathway to the 27-acre rocky historic island.
"The city and we have to set a timetable for when things will happen," said Andy Brodeur, the Methuen project leader. "We must specify in every subcontract and every purchase order that the delivery must arrive at a specific time. If it exceeds a certain time, they must be escorted in and out by the police."
The four-year, $73 million design-build, one-off project-part of the city's $99.9 million package for the facility-met the budget and met the deadline for the federal consent order on time. The upgraded plant includes a biological aeration filter (BAF) system that processes an average of 6.1 million gallons per day, replacing the 1990 sand filtration system that processed an average of 4.8 mgd.
The system can treat nitrogen in sewage at a rate of 8 milligrams per liter (mg/l), and can achieve a limited 3 mg/l treatment through operational adjustments.
"This project will result in a major change in the processing level of the facility," said Portsmouth City Manager John Bohenko. "The Environmental Protection Agency's regulatory requirements have promoted the level of processing demand, not only secondary processing, but also nitrogen removal," he said.
The project involved six structural work, including the construction of a single-story, 2,700-square-foot head building completed in May last year; a three-story, 12,232-square-foot sludge treatment building; and a four-story, 11,407-square-foot BAF building ; A 40-foot diameter by 20-foot high gravity enrichment facility; and an electrical building. The staff is transforming the solid building into a two-story, 6,750 square foot administrative building. The project also includes the replacement of sand removal equipment and primary and concentrated sludge pumping systems.
Methuen project executive Greg Galbraith said that maintaining wastewater treatment operations and access to public swimming pools during construction involved “installation of temporary systems, relocation of factory operations and temporary use of new infrastructure to free up areas for demolition and reconstruction”.
Getting staff to work effectively on the 3.8-acre compact project site requires planning and careful coordination. The team transformed a public swimming pool parking lot into a construction trailer complex and rebuilt a new pool parking lot with a permeable pavement cross-section to control rainwater. It also allowed the city to move a ski resort off the island so that the space could be used as part of a staging area.
"There is a lot of activity between the different buildings under construction, so it is difficult to get everyone in different industries to move in the same direction," said Erik Meserve, a project engineer at AECOM, who used AutoCAD for 3D design of sewage systems.
The 2009 Federal Consent Order required the city to build a secondary sewage treatment facility by the March 2017 deadline. The decree settled a lawsuit accusing the city of discharging contaminated wastewater to the mouth of the Great Bay estuary, which was supplied by tidal water from the Piscataqua River. However, in 2012, the original timetable was extended, allowing electrical services to continue in the old facilities "long enough to establish new electrical services," Portsmouth engineer Terry Desmarais Say. According to the revised consent order, the construction of the BAF system must be approved before April 2020.
– Erik Meserve, AECOM project engineer
In 2011 and 2012, the city took an unusual step before choosing a high-speed, small-footprint sewage treatment system, which was to invest $1.8 million to build three small, side-by-side treatment system pilots at the site of the sewage treatment plant. The new headquarters building. The largest of these is 26 feet long, 4 feet wide, and 8 feet deep. "Finally, we were able to find a treatment technology that fits the physical constraints and provided flexibility to meet the potential future denitrification requirements that we believe to be," Desmarais said.
The BAF system of 250 feet long x 100 feet wide x 40 feet high "was selected as the other two technologies because BAF can achieve a higher level of denitrification capacity without additional capital, and only needs to increase the cost of denitrification. The amount of carbon added to BAF in the second stage," Pearson said. Bohenko added: “Any other options may have a long-term permanent impact on the recreational trails and other facilities on Pierce Island.”
Desmarais said that unlike traditional waste activated sludge systems, this high-efficiency, small-footprint facility can be treated and settled in the same basin. As a combined collection system, it has a secondary processing bypass for wet weather processing. "We are the only joint wastewater treatment plant in the estuary," he added.
If the system exceeds the maximum flow rate of 9.1 mgd in wet weather, the remaining flow rate of up to 22 mgd will be transferred to the secondary bypass around the BAF, thereby receiving only enhanced primary treatment.
One of the biggest challenges of the project involved managing traffic flow and on-site delivery on an available channel. An aging bridge connects the island to the narrow road at the historic southern end of Portsmouth. After conducting a structural evaluation of the 300-foot-long x 35-foot-wide two-lane bridge, the city hired George Cairns & Sons in a separate contract to complete the bridge deck worth $400,000 before the water treatment plant started in September 2016 replace.
– Jon Pearson, Executive Vice President of AECOM
Kyle Tenan, the head of Methuen, said the team must install the bypass system before starting construction. The staff used a hand-held pneumatic hammer and a 12,000-pound hoe hammer for several hours of gouges before the pipe was exposed.
The Nanan Pipeline installed and tested an opening saddle and pipeline stop device during the day shift in mid-May 2017, and kept the pipe cut during the night with the lowest flow rate. After closing the pre-installed valve, the staff merged and installed a nearly 400-foot-long 24-inch high-density polyethylene (HDPE) bypass pipe, and then installed the pipeline block to divert the flow through the bypass pipe. Tenan said this is "the most complicated part of the whole process."
On June 6, the staff began to "lower the water head", closing the valve, preventing the influent water from flowing through the existing pipeline, and forcing the wastewater into the temporary bypass pipeline. Shortly after 2 am, the crew witnessed the water flowing from the bypass pipe to the grit tank. Tenan recalled that this complicated procedure was proceeding "perfectly".
The construction of the head project overlaps with the relocation of all the computer control equipment of the facility, so the team can build the BAF building. “The power and electrical equipment of the existing plant is located directly in front of the proposed BAF facility,” Galbraith said. This prevented the work from starting until a new permanent power source was established and the electrical building was constructed.
In order to speed up the progress, Methuen worked with the city government, Eversource and Wayne J. Griffin Electric to establish a rerouted power supply line and temporary backup generators so that the demolition of old infrastructure and construction of new BAF facilities could begin earlier.
Desmarais recalled: "When a building with a large number of computer controls was demolished, the team found a way to integrate computer controls in the infrastructure to speed up the construction of early electrical renovations."
Desmarais said that during the permit period, archaeologists worked on site to assess the historical significance of the area. Fort Washington was established at the highest point on the island in 1775, when a British ship entered the port and mistaken it for Boston Harbor.
"There used to be ruins, but they are now gone," said Jon Pearson, executive vice president of AECOM. "The earthen remains of the fortress have been fenced off for historical protection on both sides of the site, which increases the restrictions on sites that have been restricted."
Unexpected development occurred in 2015. The sludge treatment building has a history of 50 years. The following year, it was designated as a contribution building to the National Register of Historic Districts in Portsmouth City Centre, which was proposed at that time.
“As part of our work and permits, we must complete the history of the treatment plant, including the sludge treatment building,” Desmarais recalled. The city was also asked to provide explanatory signs about the historical significance of the Pierce Island sewage treatment facility.
Soon, half of the sludge buildings will be demolished, and the remaining half will be used for new sludge treatment operations, which are scheduled to go online in December. Desmarais said the upper part will be razed to the ground and replaced by a new laboratory administration building. The old laboratory administrative building is currently being placed in the sludge operation plan to be decommissioned in June. Once the new sludge system is put into use, it will be demolished.
Desmarais is very happy that the project is about to be completed, but "in the last 25% of progress", he hopes to avoid the fatigue caused by the construction so that the team can complete it. Most importantly, he wants to make sure that his team is ready to control the factory. Although Methuen is “preparing to pack up and move on, but they can use up all their energy, but our employees must start to step up the operation of the factory.”
For more than a decade, Johanna Knapschaefer, ENR's New England Special Correspondent, has been writing articles on trends in the design and construction of buildings, bridges, tunnels, and other infrastructure. She also introduced award-winning industry leaders and delved into broader construction issues such as labor training, worker safety and health, climate change remediation, and emerging offshore wind and tidal energy development. In the past two decades, her articles have appeared in Architectural Record, BusinessWeek, Boston Globe, American Banker, Modern Metal, BusinessNH Magazine, Pittsburgh Magazine and Many other publications. Johanna is fluent in Japanese and has taught English and academic writing at the Science and Engineering Department of Ritsumeikan University, Kyoto, and has lived in Japan for eight years.
When not writing, Johanna enjoys climbing mountains, singing and playing Spanish guitar.
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