Alyeska plans upgrades to Ballast Water Plan

Tankers arrive each week at the Valdez Marine Terminal (VMT) to transport crude oil from Prince William Sound to refineries on the West Coast. Upon arrival, a small number of tankers offload ballast water which is used to control buoyancy. The newest generation of tankers generally keeps the seawater ballast segregated from the oil tanks. Some of the older style tankers do not have the ability to segregate ballast. In those cases, the ballast becomes contaminated with remnants of oil previously carried in the tanks and must be processed at the terminal’s Ballast Water Treatment (BWT) facility.

The BWT process involves a three-part treatment that plays off the natural tendency of oil and water to separate. The first step is at the 90s “settling” tanks where most of the oil is skimmed off the top. In the second step, air bubbles are pushed through the water to carry most of the remaining oil to the surface. Clarified water is charged from the 90s tanks to the Dissolved Air Floatation (DAF) system. Recovered oil is then skimmed for transfer to the 80s tanks. Finally, microbes are released to eat the water soluble hydrocarbons. The treated water is then discharged into the port.

The double-hulled tanker configuration required by the Oil Pollution Act of 1990 results in dramatically less ballast needing treatment . Therefore, the existing BWT system is now over-sized for the current and forecasted needs. Alyeska has already started to implement its major plan to completely renovate the BWT system due to less ballast water needing treatment and other needed improvements for health, safety, environmental and operability purposes.

The proposed modifications include managing the physical assets at the BWT by removing part of the facilities from service, which will help reduce the environmental impact of the operations, especially the air emissions from the plant. Starting in 2006, final design engineering has been proceeding at a high pace and implementation is already occurring in some cases: new skimmers have been installed in the 90’s tanks, The effluent channels in the DAF cells have been modified by adding a weir that helps to control the water flow and reduce air emissions and the splitter box in the BTT’s has been covered also reducing air emissions. In 2007, vapor controls are planned for the 90’s tanks, with a pilot piping system installed in 2006.. In addition, the pilot plants and studies for the DAF system and Ballast Treatment Tanks (BTT) replacement are being utilized to move into final engineering. These changes to the DAF and the BTT are lifecycle and flow-based changes, which will dramatically decrease air emissions. Alyeska also placed vapor controls on two tanker loading berths that played a major role in reducing terminal air emissions by over 90%.