Removal of Creosote Piles to Restore Estuarine Shoreline Habitat

Removal of three large derelict piers and their creosote treated piles was conducted to restore shoreline habitat at the former ASARCO Smelter site on Commencement Bay, southern Puget Sound, Washington.  This restoration removed the physical and chemical alterations to the site that had been present for about 80 years.  Habitat restoration by removal of these structures and their toxic creosote is a major priority for many resource agencies.  This is an example of issues encountered with removal of harbor structures that are present in many of our estuarine-ports.  Various assessments were conducted to evaluate the release of creosote from piles and metals contaminated sediment during habitat restoration.  Creosote is a complex mix of many toxic polycyclic aromatic compounds (PAHs) that are potentially released during demolition.  This paper presents the results of several investigations conducted to identify the nature of creosote released during removal, by shearing near the bottom, of more than 2,300 piles formerly supporting three large docks in Commencement Bay.  Because the docks were remnants of a large copper smelter, there was concern both for the release of creosote from piles and metals in disturbed sediment.  Monitoring involved pre- and post-demolition sediment analysis (metals and PAHs) to evaluate before and after conditions, and creosote (PAH) bioaccumulation within in-situ mussel populations.  Considerable demolition debris, including creosote treated wood, was found to sink to the bottom under the docks and adjacent previously capped areas.  Several PAHs indicating creosote contamination were found to exceed sediment management standards adjacent to the docks in areas previously capped with clean material, requiring remedial capping.  Concentrations of PAHs in mussels were found to increase dramatically during the early stage of dock demolition and remain high through the period of pile removal.  A laboratory leaching evaluation of freshly cut samples from the creosote saturated portion of piles demonstrated the release of substantial amounts of PAHs occurs from freshly exposed creosote surfaces of aged piles.  Fresh creosote surfaces are exposed both by piles breaking and being cut during demolition.    Although the release of some creosote chemicals decreases rapidly within 96 hours, the release of others remains high through at least three weeks.