Eagle Harbor, a shallow marine embayment of Bainbridge Island, WA approximately 10
miles west of Seattle, WA), was formerly the site of the Wyckoff wood-treatment facility.
The facility used large quantities of creosote in its wood-treating processes from
the early 1900s to 1988. Historical creosote seepage into the harbor resulted in substantial
accumulation of polycyclic aromatic hydrocarbon (PAH) contamination in the harbor
sediments over time. This investigation focused on the distribution and fate of the
PAH-contaminated harbor sediments. Analyses of 10 sediment cores using total petroleum
hydrocarbon (TPH) fingerprinting, the distribution of 50 PAH analytes, and sediment
age dating revealed the contributions of three distinct sources of PAHs to sediment
contamination in the harbor during various periods over the past 100 years; namely,
creosote, urban runoff, and natural background. Surface sediments (upper 20-30 cm)
in the cores closestto the Wyckoff wood-treatment facility and southeast of an existing
cap were dominated by urban runoff and weathered creosote; the deeper sediments (>
30 cm) were heavily contaminated with relatively unweathered creosote and some pure-phase
creosote. Cores located the furthest from the area of contamination, in the center
of the harbor, were dominated by urban runoff, showed no signs of creosote contamination,
and had much lower PAH and TPH concentrations than those adjacent to the facility.
In the four cores in the center of the Harbor, farthest from the former Wyckoff facility,
PAH concentrations increased significantly (p < 0.01) with proximity to the northern
shore of the harbor, which is more heavily developed than the southern shore and is
where all automobile traffic enters and exits the island through the Bainbridge Island
ferry terminal. Deeper portions of these cores were contaminated primarily with natural
background PAHs, likely representing preurbanization sediments. Sedimentation rates
ranged from 0.54 to 1.10 gm/ cm2 in the four cores located in the middle of the harbor,
and for the single nearshore core that could be used to calculate sedimentation rates.
Recognition that urban runoff has been a fairly consistent and ongoing source of PAHs
to the harbor's sediments for the past 50-70 years may influence future sediment management
decisions for this site with respect to long-term monitoring of surface sediments
to assess cap performance. The results provided information on the ability of Eagle
Harbor sediments to recover under natural conditions, identified the occurrence of
creosote-derived PAH weathering in off-cap surface sediments, and distinguished between
these distinct PAH sources in the harbor (creosote, urban runoff, and natural background).