If it’s spring, it’s time to tear up downtown streets and replace the underground waterlines.

This year is no exception – construction is planned to run between May and October – and Massachusetts Street merchants are bracing for the fallout.

“I think I can probably speak for most of the 700 block merchants when I say that we’re a little dismayed at the length of time that’s being appropriated for the project,” said Geri Riekhof, owner of The Bay Leaf, 725 Mass.

But Chris Stewart, the city’s acting utilities director, said the pain is unavoidable.

The project “provides reliability of service for our customers, additional fire protection for our customers,” he said. “And you know, you can’t have waterlines that are over a hundred years old. They break down or have a main break.”

The Lawrence City Commission on Tuesday is scheduled to get the ball rolling on the project by setting a date of April 11 for bids from contractors.

Plans call for waterline replacement this summer along Massachusetts, between Seventh and Ninth streets, and along Ninth Street, between Vermont and Kentucky streets. Only one side of a street will be closed at any time.

The total cost is projected to be $1.2 million.

This summer’s project is part of a three-year effort to replace century-old waterlines in and around downtown.

Riekhof said merchants would plan special promotions to lure customers past the construction.

“We don’t want people to be discouraged, so we’re emphasizing that the community support the downtown retailers,” she said.

And Stewart said City Hall would try to be supportive of merchants, as well.

“We’ve kind of continuously been in contact with the downtown business association to let them know what’s going on,” he said, “and we’ll do the same thing right before construction starts to let them know what’s happening.”

Stewart added: “Our goal has always been to do the best job we can to make sure that the inconvenience is minimal, but there’s going to be some inconveniences, and I think they realize that.”

The commission meets at 5:30 p.m. Tuesday at City Hall, Sixth and Massachusetts streets.