East Eagle Harbor Bainbridge, WA: 17 Years of Cap and Natural Recovery Monitoring

摘要

Overview. The Wyckoff/Eagle Harbor Superfund Site, East Harbor Operable Unit(EHOU) is a former wood pole-treating facility located on Bainbridge Island, Washington.This paper presents the findings of the Year 17 monitoring of implemented remedieswithin the in-water operable unit. The remedies include over 60 acres of in-water subtidalisolation capping, two distinct intertidal isolation cap designs, and monitored natural recoveryof intertidal areas that also contain ecologically critical eelgrass habitat. Overallthe subtidal and intertidal caps are operating as intended; the caps are physically stableand the underlying PAH contaminants remain isolated. However, one area of the cap thatis proximal to the Washington State Ferry Terminal has been eroded away, exposing thenative NAPL-contaminated sediments. The monitored natural recovery has shown ordersof-magnitude decreases in PAH levels in the 10 years since the last monitoring.Background/Objectives. The former Wyckoff treatment plant was heavily contaminatedprincipally with creosote and pentachlorophenol, which permeated the soil, groundwater,and extensive areas of the subtidal and intertidal sediments. The site was added to theNPL in 1987 and the ROD signed in 1994. The subtidal cap was first placed in 1993-1994, with subsequent additional placements and remedial actions up through 2008. Theobjectives of this monitoring were to determine whether the caps are physically stableand effective at contaminant isolation, whether the monitoring natural recovery targetshad been achieved, and as a secondary question whether the installed caps served as habitatfor forage fish and if bivalves recovered at the site pose a human health consumptionrisk.Approach/Activities. One of the oldest sediment capping projects in the U.S., the EHOUhas been monitored since the original placement in 1993. The physical tools to evaluatesite stability were primarily elevation surveys using bathymetry and photogrammetry.Through-cap coring was used to confirm cap thickness measures estimated by the elevationmodeling. Changes in elevation indicated both erosion and accretion occurred overthe site. In 2011 hydrodynamic modeling was added to assess the effects of wind andtidal-generated waves, and propeller wash from the Washington State Ferries that traversethe cap site. The tools used to assess chemical isolation included surface andsubsurface sediment chemistry, and over a portion of the site in situ sediment (SPME)samplers. Monitored natural recovery was assessed through surface and subsurface sedimentsampling, as well checking for hydrocarbon seeps that were prevalent in theprevious monitoring in 2002. Biological monitoring included collecting clams for tissue