Against the backdrop of the scenic Pembina Hills in North Dakota, the Keystone Pipeline inches its way southward, construction advancing at a rate of a mile or two a day.

As of Friday, the pipeline had been extended just less than 20 miles south of the U.S.-Canadian border.

It's a massive project that progresses meticulously, heavy equipment clearing wide swaths of trees and moving tons of dirt, while at the same time, tip-toeing mechanically through environmentally sensitive wetlands, even pausing to wait for nesting hawks to fledge.

Markers and caution signs warn workers of occupational hazards all around, from moving equipment to narrow, steep grades.

"We try to build the pipeline with the safety of the workers at the top of the priority list," said Robert Jones, vice president of the Keystone Pipeline Project, as he guided an inspection tour along the pipeline construction route Friday. "We use the best practices throughout, from safety to protecting the environment."

The company employs a team of three environmental inspectors and five biologists.

Keystone also operates its own clinic at its Grafton, N.D., headquarters. Workers not only are encouraged to seek treatment for any injury, even dirt in the eyes, they're encouraged to report near-misses.

The Keystone Pipeline is being built through 218 miles of North Dakota soil, along a 2,148-mile route from Hardisty, Alta., to U.S. markets at Wood River and Patoka, Ill., and to Cushing, Okla. When it's completed in 2009, it will move about 435,000 barrels of heavy crude oil daily. By 2010, daily capacity will grow to 590,000 barrels.

The pipeline is being buried 48 inches underground. While regulation is 24 inches, most pipeline companies use 36 inches as the standard, according to Jones.

"It really reduces the probability of third-party damages, and it allows for deep tillage," he said.

The thickness of pipe is doubled in sections that cross rivers or pass through environmentally sensitive areas.

Friday's tour stopped at the Tongue River, just south of the intersections of N.D. Highways 5 and 32, south of Walhalla, where welding crews -- 30 welders and 60 welders' helpers -- were fusing together sections of pipe before using a horizontal directional drilling method to extend the pipeline under the river.

Those welders are among the nearly 450 workers who are building the pipeline across northern North Dakota, from the Canadian border to Valley City. About 20 percent of the crew is hired locally.

"Welding. It's the heartbeat of the pipeline," said Bill Laffoon, resident construction supervisor for Universal Ensco Inc., an independent contractor of TransCanada Keystone Pipeline.

The tanned, gray-goateed Oklahoma resident knows a good weld when he sees one. His grandfather and father were pipeline welders. He has a son who is a welder, and his 18-year-old grandson is about to enter the trade.

Though he knows the welding industry as well as anybody, Laffoon's not the only inspector -- and certainly not the last -- to examine the welds. Each weld goes through a series of inspections before a final stamp approval allows the pipe to be lowered into the ground.

"There's a lot of, a lot of, eyes looking at this stuff," he said.

It takes about 90 minutes to complete one entire weld. The crews normally do 60 to 70 welds a day, according to Laffoon.

"One of the things that impresses me the most is the welds themselves," said North Dakota Public Service Commissioner Kevin Cramer, who toured the site Friday. "It gives me a sense of comfort. This is safe."

"I also was impressed with the priority they place on safety," Cramer added. "It didn't surprise me, but it's something to see."

The pipeline will move part of its operations from Grafton to Emerado, N.D., by the end of August, as it continues its trek southward. Another section is being built south from Valley City, N.D.

Construction will be mostly completed through North Dakota by the end of the year.

When it's operating, the pipeline will have a pump station located every 50 miles along the route. Keystone also uses a computerized leak detection system to constantly monitor the line, Jones said. If a leak occurs, however small, the computer shuts it down.

Keystone uses a four-step approach to prevent and minimize leaks:

- Pipe design.

- Computerized leak detection system.

- Aerial surveillance.

- Relationship with the community.

"That's a real key. It's going to be a partnership for 50 years," Jones said. "You can start out on a good foot or a bad foot, and we want to start out on a good foot."

Copyright (c) 2008, Grand Forks Herald, N.D. Distributed by McClatchy-Tribune Information Services.