NORTHUMBERLAND — Construction crews are at the tail end of a $700,000 project to install a new waterline under the Susquehanna River.

Employees of Gabe’s Construction, of Sheboygan, Wis., began drilling about 1,000 feet across the river in late October, first boring a nearly 10-inch hole and then widening it to 20 inches, a task completed Tuesday.

Wednesday morning began the relatively quick process of pulling a 10-inch, high-density polyethylene pipe across the Susquehanna.

Project manager Joel Mitchell, of Pennsylvania American Water, said the underground drilling technique, used recently to install more than 1,300 feet of waterline across the same river in Luzerne County, is more economical and environmentally friendly.

“Working under the river bed allows us to avoid the significant costs and other issues associated with damming the river,” Mitchell said. “We can complete the project in a more timely and cost-efficient manner.”

Damming the river would have cost “substantially more” than the method currently under way, Mitchell said, and as Pennsylvania American spokeswoman Susan Turcmanovich pointed out, would have caused significant disruption to the Susquehanna’s flow.

“We’re not disturbing the river when we’re going underneath it,” she said, and in fact, passersby crossing the bridge between Packer’s Island and Northumberland would be unable to detect the work simply by watching the waters of the Susquehanna, which remained unchanged.

On-site project superintendent Roy Graff said work has been going smoothly as his company’s drill, capable of pulling or pushing up to 330,000 pounds, bores through a mixture of sandstone and granite 40 feet beneath the river.

“Everything varies,” Graff said. “It depends on what part of the country you’re in. The Northeast typically is rock. Rock is a slower process. You never know how long it’s going to take. There’s harder rocks and softer rocks, just like there’s harder clays and softer sands.”

The work was necessary, Mitchell said, after the existing waterline sprang a leak in July 2008 about 10 feet from the banks of the river, disrupting water service to the water company’s 130 customers on the island. That leak was temporarily repaired by divers.

The new pipe was installed parallel to the existing one. After the new pipe is tied into the water system on both sides and disinfected, the existing pipe will be disabled.

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