After flooding, work continues to re-bury TAPS
Flooding of the Dalton Highway last spring caught a lot of attention, mainly because the vital road link to the North Slope oil fields was cut off for days. Hundreds of trucks delivering supplies and equipment were backed up and delayed.
What got very little, if any, attention was that washed-out areas nearby exposed buried parts of the Trans-Alaska Pipeline System to the open air and moving water.
There was never any danger to the integrity of the pipeline, Alyeska spokeswoman Michelle Egan said. However, it was something Alyeska had to respond to right away. In places, the gravel overburden and pipe insulation were washed away along with a gravel workpad that runs nearby.
“The waters started to recede in June, and our baseline (contractor) folks started work immediately on moving ice, repairing access roads and cleaning up debris,” said Shaune O’Neil, Alyeska’s manager on the project. “Before work could start in August, we had to have survey crews locate and identify and map the damaged areas, and do some engineering work to facilitate the more complex repairs.”
After the initial steps, work was started on the long-term fix but that has turned out to be a big challenge for Alyeska and its contractors, and it still isn’t finished.
Flood repair operations had to be shut down in early December because a continuing flow of water proved difficult to manage. Work is scheduled to resume in February when the winter freeze sets in, which should diminish the water flow, O’Neil said.
The problem area, which also affected the Dalton Highway, was in the areas south of Deadhorse, the industry-service center for Prudhoe Bay and other oilfields, and there were two separate flooding events.
An earlier flooding, in March, pushed large ice sheets, six to twelve feet thick, out of the Sagavanirktok River onto the road and blocked traffic. The ice created dams for the water, which compounded the early spring flooding.
The ice was cleared away but the normal spring “breakup” a few weeks later brought more flooding, closing the road again and covering about 600 square miles of tundra lands mainly south of Deadhorse, O’Neill said.
In the second flooding, in May, five feet of ground cover over the pipeline was washed out, exposing the pipe in six locations, with the longest stretches exposing 23 feet and 40 feet of pipe.
Alyeska had to respond quickly but also in a measured way, O’Neil said.
“We can’t just throw gravel on top of the pipeline. We must do a careful assessment, checking to make sure the pipe coating and the pipe weren’t damaged, along with the pipeline’s cathodic protection,” she said.
That meant excavating around sections of pipe to a level below the pipeline, with the longest section being 80 feet.
“We had to go two feet below the pipeline and to build side slopes, and since the pipeline was buried at five feet below the surface at these points it meant we had to excavate a trench to the 11-foot level,” before the pipe inspections could be done, O’Neil said.
Most of the work was scheduled to be done in the fall through September, October and November, but the continued rush of groundwater complicated and slowed the project even with the 24-hour operation of two 10-inch pumps that were dewatering the trench.
“The conditions were very challenging,” O’Neil said. “We had to do the excavation, check the tape wrap (around the pipe) and if the pipe was exposed we had to sand-blast down to bare pipe, do an ultra-sound inspection to ensure the pipe integrity, and then recoat the pipe.”
It wasn’t just the main pipeline, either. Work had to be done on the small fuel gas line that runs parallel to the oil pipeline from Prudhoe Bay to Galbraith Lake, in the southern foothills of the Slope.
The origin of the water was only partly the river. There was also unexpectedly high groundwater seeping in.
“There are a lot of small tundra lakes in this area and we believe that damage and surface erosion from the flooding changed the hydrology,” O’Neil said.
If the excavations and inspections were challenging, cleaning up all the broken pieces of insulation left scattered across the tundra by the flood was a labor-intensive nuisance, but it had to be done.
Gravel also had to be back-filled around three vertical support members, or VSMs, that hold nearby above-ground sections of pipeline, but there was no damage, O’Neil said.
Alyeska mustered four contractors to deal with the problem, with Athna Construction, subsidiary of Ahtna Inc., an Alaska regional Native corporation, handling some of the most difficult work, O’Neil said.
Other firms mobilized were Houston Contracting, which is owned by Arctic Slope Regional Corp.; Price Gregory and Hamilton Oilfield Services, she said.
Ahtna Construction, Houston Contracting and Price Gregory are under long-term service contracts with Alyeska, and Hamilton was added to the mix.
They also needed a lot of material (gravel and rock) so Brice Construction, which was also working for the state on the Dalton Highway repair, was able to open a new gravel pit for both gravel and sand, and also to bring larger rock from a source near Atigun Pass, in the mountains south of the Slope.
Hamilton’s part of the project was in mining and moving gravel and rock.
O’Neill said the project required extraordinary coordination and cooperation among contractors who are also competitors for work on TAPS. The companies do specialize, however.
Ahtna has been doing main-line inspections and repairs for TAPS for several years and has a lot of experience in that area, O’Neill said, and Houston and Price Gregory also do pipeline integrity work but Price Gregory also had to take on civil work, which it ordinary does not do, O’Neil said.
There easily could have been resentment within these companies because they may not have gotten as much of the work as desired, but there was none on this job, she said.
“People really stepped up to the plate,” she said.
Through early December Alyeska and its contractors expended 48,000 man-hours of work, moved about 50,000 cubic yards of gravel; 10,000 cubic yards of large rock and 350 cubic yards of sand.
Ahtna mobilized Aug. 29 and demobilized Dec. 9. Price Gregory mobilized Aug. 26 and demobilized Oct. 30. Houston is under a continuing maintenance agreement for the pipeline, so its crews were already mobilized.
However, it isn’t yet complete.
Tim Bradner can be reached at [email protected].