Document Author: Morgan L. Bender

From the abstract:

Hydrocarbon concentrations were monitored in sediments, in intertidal Pacific blue mussels, and in the water via passive sampling devices. This work helps the Council understand the environmental impact, fate, and source of hydrocarbons related to the operations of Alyeska Pipeline Service Company’s Valdez Marine Terminal.

In the 2022 and 2023 results, we see low levels of petroleum (petrogenic) hydrocarbons in sediments at the terminal that can be attributed to terminal operations. Passive water sampling devices and Pacific blue mussels from all sampled locations had low levels of toxic hydrocarbons. Sediment and mussels sampled from sites away from the terminal in Port Valdez contained more combustion (pyrogenic) related compounds than detected at the terminal. In 2022, mussels from the Valdez Small Boat Harbor had the highest levels of hydrocarbons, likely due to frequent small spills and heavy human activity not forensically attributed to terminal operations. In 2023, higher polycyclic aromatic hydrocarbons (PAH) levels were found in some mussel samples at Knowles Head in northeastern Prince William Sound than those in the harbor. Other mussel sites sampled in 2023 as part of the expanded sampling regime included Disk Island, Zaikof Bay, a new site in outer Zaikof Bay, Sleepy Bay, and Sheep Bay. Generally, the expanded sampling sites had comparable PAH levels to annual sampling sites (e.g., Gold Creek and sites near the terminal) with low potential hydrocarbon ecotoxicity for organisms.

In 2022 and 2023, the hydrocarbons detected by the Long-Term Environmental Monitoring Program sampling, and determined to be from the terminal and tankers, posed low potential ecotoxicological risk. Since 1993, hydrocarbon concentrations are generally low with localized spikes corresponding with spill events like the April 2020 oil spill at the terminal. Following an all-time low in the mid-2010s, hydrocarbon concentrations detected in sediments and mussels have slowly increased across all sites but are still below any threshold for adverse effects on aquatic life. Prince William Sound-wide trends in these hydrocarbon concentrations may be influenced by environmental factors such as increased freshwater input, glacial melt, and warming ocean temperatures. We recommend that future monitoring efforts maintain the current three-matrix design and attempt to preserve, economize, and modernize aspects of Prince William Sound Regional Citizens’ Advisory Council’s Long-Term Environmental Monitoring Program.

See also: LTEMP 2022‒2023 Technical Supplement