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A marine terminal containment headache Damage to the membrane for containing oil from a storage tank spill at the Valdez Marine Terminal raises concerns and questions ALAN BAILEY Petroleum News
The 14 large crude oil storage tanks in the east tank farm at the Valdez Marine Terminal sit in basin-like enclosures lined with impervious material, designed as secondary oil containment, should a tank develop a leak. The idea is to hold any spilled oil for a sufficient time to enable responders to remove the oil without the oil contaminating the groundwater under the farm.
But evidence has emerged that the liner along the base of the secondary containment area is damaged, thus raising questions over whether the secondary containment can any longer meet the required specifications for holding back spilled oil.
The marine terminal accepts oil from the trans-Alaska oil pipeline and loads the oil onto tankers in Port Valdez. The oil tanks provide buffer storage, to enable the efficient loading of oil into the tankers.
Austin Love, a project manager with the Prince William Sound Regional Citizens’ Advisory Council, talked about the issue during a Jan. 19 meeting of the PWSRCAC board. Love explained that the membrane, composed of a material called catalytically blown asphalt, or CBA, had originally been installed at the terminal in 1977.
Importance of liner integrity The integrity of the liner matters, not just because of the protection it provides to the environment, but also because of the economics of oil spill contingency arrangements at the marine terminal, Love explained. State and federal regulations spell out the permeability requirements for the liner. And the state allows Alyeska Pipeline Service Co., the terminal operator, to reduce the oil volume specified in the terminal’s spill response requirements by more than half, on the assumption that the tank secondary containment meets the regulatory standards and would, therefore, be effective. Any increase to the response requirement as a consequence of the secondary containment being inadequate would require a corresponding increase to the equipment and people that would need to be available to respond to an oil spill, Love said.
The issues relating to the liner came to light in the course of carrying out a successful project to refurbish the system of pipe work used to drain rainwater and snow melt from the secondary containment enclosures. Normally, the CBA liner is invisible, being covered by several feet of gravel designed to protect the liner from damage from any heavy equipment operating around the tanks. But renovating the drainage system involved removing some of the gravel, thus exposing some sections of the liner, Love said.
And the uncovering of the liner revealed a couple of problems: a network of cracks permeating one section of the liner, and holes in the liner that appeared more widespread.
Liner cracking The problem with cracks, some of which were superficial but some of which went right through the liner, impacted an area of 5,000 to 6,000 square feet. Beyond that area, no cracking was evident, and Alyeska remedied the problem by installing a sheet of modern impermeable material over the damaged area of the liner. But, although the cracking appears to only impact that one area and no evidence for cracking has been found elsewhere, the reason for the cracking remains an enigma. Scott Hicks, Valdez Marine Terminal manager, told the PWSRCAC board that there must be something particular to the liner in the region of the cracking, perhaps a spill of diesel fuel at some time in the past, or perhaps a bad batch of the CBA material. Alyeska is still conducting rigorous testing of the damaged material and anticipates results from the testing in March, Hicks said.
Liner holes The problem of holes in the liner was found at each place where the liner was exposed for the pipe work repair work, Love said. The holes range from 5 inches in diameter to an opening as big as 20 inches by 60 inches. In one example, a rock had pushed up through a hole, although a permeability test indicated that the rock had, in fact, retained the permeability of the liner to within regulatory requirements. In one area some holes had become filled with bentonite clay and it was not clear whether those holes would leak oil, Love said.
The pipe work renovation project continues and, with it, more examinations and tests of the CBA liner. Test results from 2016 have yet to appear.
The CBA material is an obsolete technology, now replaced by more advanced materials. However, having found the liner problem, Alyeska tested some undamaged CPA material, finding that the material still comes within the regulatory standards for permeability and durability, Love said.
A challenge to fix Finding a way of fixing the liner presents something of a headache for Alyeska, given the huge area that the liner covers and the fact that it is buried under several feet of gravel. Each cell of the containment system is 4.5 to 5 acres in extent, and each storage tank has a footprint of about an acre, Hicks said.
Amanda Bauer, PWSRCAC president, commented that it was necessary to be reasonable in figuring out what to do and that people want the terminal to remain viable in years to come. Perhaps there is some interim fix, such as shortening the tank internal inspection intervals, she suggested. However, the secondary containment system does not appear to meet regulatory requirements and there needs to be some recognition that there probably is a problem, she said.
Donna Schantz, executive director of PWSRCAC, commented that the secondary containment issue is a top priority in PWSRCAC’s long term plan.
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