BANGOR — Three feet below ground near the banks of the Penobscot River, the city’s new 1.2 million-gallon waste-water holding tank is ready to go. One day this week, officials expect to shut off a 42-inch interceptor pipe and bring on-line a 2,350-foot concrete container that will help prevent sewer overflows in the area during heavy rains.

Call it a sewer pipe, or call it a holding tank — it’s both. Under normal conditions, the container that stretches along the waterfront between Railroad Street and Barrett Paving will act as a pipe, with sewage flowing along the bottom toward the city’s waste-water treatment plant on the Hampden end of Main Street.

But during flood conditions, when spring rains combine with snow melt to create what officials call “wet weather events,” the city will be glad for every cubic inch of space available in the tank, which is 8 feet wide and 9 feet in height.

Acting as a holding tank, it will hold the sewage and storm water, and, in most instances, will prevent the overflows which can occur when the regular system can’t handle them.

A reporter and photographer took a walking tour of part of the tank recently with Assistant City Engineer John Murphy, construction inspector Will Eisworth and Tim Ford from the waste-water treatment plant.

After entering the tank by climbing down a ladder, the group headed toward the Railroad Street end of the pipe, where sewage will flow into the tank through a square hole, rimmed by concrete, looking not unlike a fireplace.

At the other end, sewage will exit the tank and flow into a 48-inch round pipe for transport to the waste-water treatment plant.

The tour took place on a rainy day, but the tank was dry inside except for condensation along the bottom. Connecting each 5-foot section of pre-cast concrete to the next were four joints, a few with orange markings where Eisworth had noted the need for extra patching to prevent leaks. Each section also showed a penciled-in date and time of installation.

The original plan called for the installation of a traditional rectangular tank, 80 feet by 120 feet by 24 feet. Such a project would have required the use of expensive pumps to clear it out, pumps that also would have been expensive to operate.

The major concern, however, was the price tag outlined by the U.S. Army Corps of Engineers — an estimated $6.9 million.

City Manager Edward Barrett didn’t like the price tag, Murphy recalled.

“He basically said, find a better, cheaper way to do it,” he said.

Murphy came up with the concept of building a longer, narrower tank that wouldn’t interfere with planned development for the city-owned land, and that could clear the tank without expensive pumps.

The solution was to build a linear tank with a V-shaped bottom that would use gravity to move the waste water. Jim Seiler, a civil engineer with the department, designed the project.

American Concrete Industries of Veazie built the pre-cast concrete sections, and Lou Silver Construction Co. of Veazie is installing the tank, piece by piece.

The finished product is expected to come in at a price of $1.2 million, saving $5.7 million over the original estimate. That’s $5.7 million that the city’s sewer ratepayers won’t have to cover in quarterly fees.

The project wasn’t supposed to be done until a few years from now, according to City Engineer James Ring, but it only made sense to do it now before the city completes plans for development of the waterfront.

When the tank is on-line, nobody will be taking tours of the snake-shaped facility. But just in case workers need access to it at some point, two of the 470 sections have removable tops.

Murphy, who is a member of a national Environmental Protection Agency committee, said that smaller tanks have been used to store water for fire protection in some communities. He doesn’t know of anything like this being used for a sewer system, however.