BY Neil H. Dempsey
---- — SALEM — Documents recently filed with the federal government illuminate Algonquin Gas’ plan to build a natural gas pipeline from Beverly Harbor to the Salem Harbor Station site.
The 16-inch, 1.4-mile long pipeline will eventually bring up to 115,000 dekatherms of natural gas per day to the proposed Footprint Power plant on Fort Avenue. Algonquin anticipates having the pipeline operational by late 2015; the plant is slated to open the following June.
Known as the Salem Lateral, the proposed pipeline will begin at an underwater connection with Algonquin’s HubLine Pipeline in Beverly Harbor, then run southwest until it makes landfall near the facility that stores liquefied natural gas on Pierce Avenue in Salem.
The pipeline will then head along the edge of the facility’s property adjacent to Waite Street before crossing Collins Cove. After it makes landfall again, the line will head through David J. Beattie Park, cross Fort Avenue and Derby Street, and then enter power plant property, where it will terminate at a metering station that will also be built as part of the project.
Total construction time is estimated to be seven months, beginning next May, with working hours from 7 a.m. to 6 p.m. six days a week, according to a recent report filed with the Federal Energy Regulatory Commission by Spectra Energy, Algonquin’s parent company.
Some of the most technically demanding parts of the pipe installation will be crossing two bodies of water: Beverly Harbor and Collins Cove. In both locations, Algonquin will use a technology known as a horizontal directional drill, or HDD.
“The HDD method is a trenchless installation process by which the pipeline is installed beneath obstacles or sensitive areas utilizing equipment and techniques derived from oil well drilling technology,” Algonquin wrote in the report.
“The process commences with the boring of a pilot hole beneath the water body to the opposite bank and then enlarging the hole with one or more passes of a reamer until the hole is the necessary diameter to facilitate the pull-back (installation) of the pipeline.”
In Beverly Harbor and Collins Cove, workers will drill from both sides at the same time, with the two sides meeting somewhere underneath the middle.
“This method is preferred, as it is less time-consuming, and the exact entry and exit locations can be predetermined,” wrote Algonquin.
At its deepest, the line will run roughly 80 feet below the Collins Cove seafloor. Once the reaming process is complete, sections of pipe will then be pushed into the hole, each welded to the next. Later, the pipe will flushed for dirt and debris.
It will be a similar process for Beverly Harbor, except that the beginning point for one side of the HDD hole will be underwater, 85 feet from where it will tie in with the HubLine.
To access to that site, workers will set up an at least 85-feet-by-55-feet cofferdam, an enclosure that will be constructed with steel support beams and sheet piles driven into the seabed. Suction pumps eventually will be used to excavate materials around the connecting points, and the resulting water and soil slurry will be pumped into barges.
Work to link the pipelines is expected to take between four and five months and is scheduled for next summer. Numerous support vessels and material barges will likely be employed throughout the process.
As for the horizontal directional drilling, the Beverly Harbor portion is expected to take 45 days, and the Collins Cove portion about 75 days.
On land, the pipe will generally be laid about 5 feet underground, though deeper burial might be necessary in certain areas. The pipe will be coated with an epoxy to protect it from corrosion, and certain pieces might have to be bent on site to fit curves in the route. Algonquin will install a 2-feet-wide yellow warning tape above the pipe and below the grade of the land to warn anybody digging that the pipe is below.
Some vegetation might have to be cleared from areas before the trench for the pipe can be dug. Algonquin said that construction will temporarily impact a total of 1.65 acres of “emergent and scrub-shrub wetlands” and 0.29 acres of “forested wetlands” but noted that all but 0.16 acres of the latter will eventually “return to a pre-construction state.”
That remaining 0.16 acres will be become permanently non-forested.
Algonquin has looked into whether its digging is liable to uncover anything historic and has put together a plan to address “unanticipated discoveries of cultural resources and human remains.” The company has also sought to consult with at least two Native American organizations, though it was still waiting to hear back from them when the report was filed.
The Salem Lateral isn’t currently slated to cross any residential properties, but portions of the temporary workspace Algonquin will require do come within 50 feet of residences on Waite Street, Planters Street, Lee Fort Terrace, Fort Avenue, Webb Street and Derby Street.
Also, Algonquin says that city tax maps indicate a small area of one residential property on Webb Street — about 0.03 of an acre — extends into the temporary workspace.
On Footprint property, the metering station will consist of a 12-feet-by-8-feet single-story prefabricated building. Algonquin says 10 workers will be needed to erect the station, and 61 will be employed to see through the rest of the project.
Algonquin originally said the pipeline would only be 1.2 miles long. Updated maps indicate it will take a slightly different path through the Footprint property than was first proposed, apparently accounting for at least the majority of the additional 0.2 miles.
Neil H. Dempsey can be reached at firstname.lastname@example.org.