Formatted Title

Intertidal Sediment Remediation in Lower Columbia River: Challenges, Challenges and More Challenges (Location, Location, Poor Location)

Background/Objectives

Sediment remediation of light non-aqueous phase liquid (LNAPL) seeps at this former manufactured gas plant (MGP) and petroleum storage/distribution terminal has been complicated due to the site location and physical setting.

The project is located on the Columbia River in Astoria, Oregon.  The owners are performing the work under the State of Oregon’s Voluntary Cleanup Program (VCP).

The in-water portion of the site, the subject of this talk, consists of a 3,000 square foot sediment management area (SMA) in the intertidal zone with localized LNAPL seeps containing weathered crude oil and underlying constituents.  Historical uses of the upland property included a manufactured gas plant (MGP) from 1888 to 1921 and a petroleum storage/distribution terminal from 1905 to 1977.

Objectives of the sediment remediation are to remediate sediment posing toxicity to aquatic organisms and remediate LNAPL hot spots of contamination to the extent feasible.

Approach/Activities

The intertidal areas size and readily viewed location create the illusion of a simple, easily accessed project that can be efficiently performed using conventional methods for excavation and remediation as well as for accessing the area requiring the remediation.

However, multiple challenges and complications at this small site show how property ownership, adjacent land uses and fragile infrastructure can have huge impacts on technical and administrative feasibility.  Existing site conditions including an adjacent pile-supported condominium over the inter-tidal area, and its water and sewer service, an unstable and eroding shoreline, railroad tracks and associated active trolley service, public waterfront trail, overhead power lines and adjacent development create a range of issues affecting the implementability of the remedy that must be addressed in the project design and agency approval process.  The site is on state-owned land and only accessible from City property.  After a Record of Decision was issued by ODEQ, detailed design level site investigation and analysis revealed significant challenges that created the need to reevaluate the remedy and consider various alternatives to complete the required remediation.

Results/Lessons Learned

The location of required remediation and specific local factors can combine to create projects of much greater complexity than initially envisioned during a remedy selection process.   These site factors can require the initial remedial concept be modified such that it is implementable and able to achieve the remedial objectives. 

The remedy has been redesigned due to site access issues and restrictions imposed by the ODEQ and the City of Astoria.  The approved remedy consists of limited gravel-cobble sediment removal, placement of three layers of an organophilic clay barrier (OCB), replacement of gravel-cobble sediment layer to withstand wind and wave action, and long-term monitoring and maintenance.