R2 PM Evaluating Short- and Long- Term Effectiveness In Sediment Remediation
Thursday, 17 November 2005: 1:50 PM - 5:30 PM in Ballroom 2

(STE-1117-852688) Evaluation and management of dredging residuals to meet sediment remediation and risk reduction goals.

Stern, J¹, Patmont, C², ¹ King County Dept. of Natural Resources and Parks, Seattle, WA, USA² Anchor Environmental, L.L.C., Seattle, WA, USA

ABSTRACT- A variety of recently completed remedial dredging projects show that residuals have been spread both within dredged areas and offsite. Site conditions, dredging equipment, and best management practices may all effect residual levels. A survey of recent projects demonstrates that residuals can be expected in all dredging projects to differing degrees, and can result in significant contaminant exposure within and immediately beyond the dredge prism. Residuals can potentially result in post remediation exposures up to one half the pre-remediation levels. The effective reduction in site exposures often does not meet site cleanup goals or reduce ecological or human health risks to acceptable levels. Using a mass balance-based measure of residuals from a series of well-documented dredging projects, realistic expectations of residuals can be used to plan how to anticipate and respond to residuals. We look at several recent projects with relatively moderate levels of contamination (typically 10 to 50 times the cleanup goals) and discuss how lessons learned can be incorporated into other project designs. A combination of focused re-dredging, capping, and enhanced natural recovery was implemented to effectively control exposure and achieve final cleanup goals at many of the sites. Results suggest that residuals both within and immediately adjacent to at any dredge site will need proactive planning to meet cleanup goals including risk reduction objectives. We discuss limitations with available options to address residuals and outline methods to incorporate residuals abatement into the approved project before dredging begins.

Key words: dredging, residuals, remediation, exposure