ANCHORAGE, Alaska (AP) - The engineering feat that is the trans-Alaska pipeline is celebrating a milestone.
On Wednesday, the 800-mile pipeline marked 35 years of production with more than 16.5 billion barrels of oil loaded at the North Slope's Prudhoe Bay oil field for delivery to Valdez at the line's southern end. There, tankers leave Prince William Sound and head for West Coast refineries.
It was June 20, 1977, when oil was loaded for the first time into the pipeline, also known as TAPS. It arrived in Valdez - the country's northernmost ice-free port - 38 days later.
"The pipeline is an engineering marvel, but it's the TAPS workforce who has kept oil moving for 35 years," Alyeska Pipeline Service Co. President Tom Barrett said in a statement.
The pipeline now accounts for 11 percent of U.S. domestic oil supply.
The company has more than 2,000 employees and contractors whose job is to keep the oil safely flowing through the pipeline. Twenty-nine employees have been on the job since the start, Barrett said.
Two oil companies, Atlantic Richfield Co. and Humble Oil and Refining Co., announced oil in a discovery well at Prudhoe Bay on March 13, 1968. Almost a decade later, after building a pipeline that crosses three mountain ranges, 34 major rivers and numerous earthquake fault lines - and spending $8 billion in what was the world's largest privately funded construction project - the oil began flowing and kept flowing with the discovery of more oil in more fields on Alaska's North Slope.
Engineering work and construction of the pipeline moved at an astonishing pace. The pipeline was finished in just three years and two months. It began in April 1974 and finished in June 1977, with more than 70,000 people working on it. Thirty-two people died during construction.
About 75 percent of the pipeline passes through permafrost, land that is perpetually frozen. That posed engineering challenges for the designers of the pipeline. While permafrost in some areas was just a few inches deep, it was more than 2,000 feet in another.
The 800-mile pipeline route required that the pipeline be placed above ground on an elevated support system to avoid melting the permafrost. In areas where the land was unfrozen, the pipeline was buried. Some permafrost areas required the construction of special below-ground sites for highway, animal crossings, or to avoid rockslides and avalanches.
When the oil flowed, so did the money, creating heady times for many Alaskans. Some were new arrivals, lured by the promise of good-paying jobs.
Alyeska Pipeline Service Co. employee Mel Jessee was 20 when he began working for the company. He remembers piles of pipe stored in a large yard in Fairbanks in 1974 and hotels being built as fast as crews could put them up.
Fairbanks was just a small frontier town then, but it quickly filled with people there to build the pipeline. Welders came from Louisiana and oilmen from Texas, Jessee said.
"It was hard enough to understand them but they were folks who knew what they were doing," he said.
Jessee still marvels at the engineering solutions for complex problems, such as using a zigzag design to allow the pipeline to expand in the summer and contract in the winter.
"It didn't seem possible, but somehow they got it done," he said.
Alaska remains heavily dependent on the pipeline and the money it generates from transporting North Slope oil. It has no state income tax.
The pipeline is owned by a consortium of companies. It was designed to withstand powerful earthquakes, and did just that on Nov. 3, 2002, when a 7.9-magnitude earthquake centered about 50 miles west of the pipeline shook near Denali National Park.
The ground along the fault moved an estimated 18 feet horizontally and nearly 2.5 feet vertically. The quake was so strong that it opened cracks 6 feet wide in roads and rocked boats on lakes as far away as Louisiana.
Yet, the 48-inch diameter pipe did not rupture.
There have been hundreds of oil spills since the pipeline started up in 1977, especially in the first two decades of operation. The number of gallons spilled since the mid-1990s has been greatly reduced, with no spills recorded in 2004 and 2005.
The worst year was in 1989, when the Exxon Valdez oil tanker ran aground on Bligh Reef in Prince William Sound and spilled nearly 11 million gallons of crude. It was the nation's worst offshore oil spill until the 2010 blowout of a BP well in the Gulf of Mexico.
Another bad spill year for the Alaska pipeline was in 2001, when a man shot the pipeline, spilling 258,000 gallons of oil onto the tundra.
The pipeline is aging, along with the Prudhoe Bay oil fields. That means the amount of oil flowing through the pipeline is declining as oil reserves on the North Slope are drawn down. Oil through-put peaked at 2.1 million barrels a day in 1988. It averaged about 590,000 barrels a day last year.