Invasive species in ballast water

Why do tankers use ballast water?

After offloading the crude oil cargo tanks at a refinery, empty oil tankers take on ballast water to ensure vessel trim and stability during ocean voyages. Prior to loading their cargo, the tankers must discharge the ballast water used during the voyage. Crude oil is loaded onto empty tankers at the Valdez Marine Terminal (VMT). Segregated ballast water is discharged directly into Port Valdez.

How much ballast water comes to Valdez?

Tankers can carry 150,000-400,000 barrels of ballast water per trip. As of 2006, tankers arrived in Valdez approximately 312 times each year to offload ballast water and load crude oil. Until 1998, tankers arrived about 700 times annually. The number of tanker arrivals has been slowly declining due to the decreased output of crude oil from the North Slope oil fields. Estimates for 1998 alone put the number of gallons of segregated ballast water discharged into Prince William Sound at 107 million.

What is the difference between segregated and unsegregated ballast water?

Crude oil tankers that serve the VMT either fill “empty” crude oil tanks with ballast water or fill dedicated ballast water tanks with water for the return trip to Valdez. When an empty crude oil tank is filled with ballast water, that water is typically referred to as “unsegregated” or “dirty” ballast because the ballast uses the same tanks as the crude oil rather than a separate tank. Although every effort is made at the refinery to completely unload the oil from the cargo tanks prior to loading the tanks with ballast water, some residual oil inevitably remains on the tank walls and floor and mixes with the ballast water, creating an oily water mixture that requires treatment prior to discharge into the ocean. Most new tankers are designed with segregated ballast tanks, but a few older tankers that service the Valdez terminal are only able to carry unsegregated ballast.

Studies completed on unsegregated oily ballast water at the VMT have shown that the amounts of hydrocarbons in the oily ballast water are lethal to aquatic or benthic species in the ballast tanks. Based on this research, it is unlikely that non-indigenous species in unsegregated ballast water would survive the trip. As a result, unsegregated ballast has been eliminated from the PWSRCAC NIS project scope of concern, and the project’s emphasis has concentrated on the control and treatment of segregated ballast water.

What happens to segregated ballast water when it reaches Valdez?

Ballast water is pumped out of the segregated ballast water tanks and discharged directly into Prince William Sound and Port Valdez with no treatment. Non-indigenous species may potentially survive the trip in segregated ballast tanks and pose an invasion risk to the waters of Prince William Sound.

What happens to unsegregated oily ballast water when it reaches Valdez?

Prior to loading crude oil at the VMT, unsegregated ballast water contained in the oil cargo tanks must be pumped ashore for treatment to make room for the cargo. The unsegregated ballast water typically contains 0.5-1.5% crude oil and is pumped to the Ballast Water Treatment Facility (BWTF) before being discharged into Port Valdez. Treatment of contaminated ballast water is regulated by the Environmental Protection Agency (EPA) under a National Pollutant Discharge Elimination System Permit (NPDES) and a mixing zone permit issued by the Alaska Department of Environmental Conservation (ADEC). The oil concentration is reduced to a few parts per million prior to being discharged into Port Valdez.

Where is the ballast water from?

Approximately 86% of the ballast water discharged into Port Valdez originates from the ports of Puget Sound, San Francisco, and Long Beach. The residence time of segregated ballast water shipped from those ports is typically 5-10 days. This short residence time favors the survival of transported non-indigenous aquatic organisms in ballast water. Repeat inoculation of competent organisms on a high volume basis poses a serious NIS risk for the waters of Prince William Sound. Currently, no crude oil is being shipped to foreign ports from Alaska.


Although the foreign export of Alaska North Slope crude oil is still permitted by law, since 2003 the oil tankers from the Valdez Marine Terminal have been exporting only to domestic ports. The most common trade routes for oil tankers leaving Port Valdez are to refineries in:

• Puget Sound, Washington: Anacortes, Cherry Point, Ferndale, Port Angeles, Tacoma
• San Francisco Bay, California: Benicia, Martinez, Richmond
• Southern California: El Segundo, LA/Long Beach

A limited number of shipments have also been made to refineries in Cook Inlet, Alaska (Nikiski) and Hawaii (Barber’s Point).


In May 1996, a previous ban on export of crude oil from the Valdez Marine Terminal to foreign ports was lifted by Presidential order. Shipment of oil to foreign ports increased the risk of non-indigenous aquatic species being transported back to Prince William Sound in tanker ballast water.

During 1996-2002 the majority of the crude oil (about 95%) continued to be shipped to U.S. refineries; however, some crude oil (5% or less) was shipped to Japan, China, Korea, and Taiwan.

The Presidential order requires exporting tankers to adopt a mandatory program of deep water ballast exchange in at least 2,000 meters water depth. Exceptions to this requirement can be made by the tanker captain to ensure the safety of the vessel and crew. Record keeping requirements are in place to document that deep water ballast exchange is being conducted. (15 CFR 754.2). Tankers sailing to domestic ports are not required to practice deep water ballast exchange


The Valdez Marine Terminal and the Trans-Alaska Pipeline System began operations in 1977. Between 1977 and 1996, 11 billion barrels of oil were shipped from Port Valdez to refineries in U.S. ports. (Prior 1996, U.S. law prohibited the export of crude oil from the Valdez Marine Terminal to foreign ports, with one exception to the Caribbean.)

No ballast water treatment or management plan (including ballast exchange) was required during this time period.

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