Sediment Recovery Analysis Through the Application of 3-D Models, 1999 Environmental Conference Proceedings

Tarang Khangaonkar, Stephen Breithaupt, R. Dreas Nielsen, John A. (Andy) Maloy--A predictive numerical model of long-term sediment concentrations is a highly desirable tool in the decision-making process in support of remedial alternatives selection and design. A methodology to support sediment remediation analysis has been developed and implemented with the help of 3-D hydrodynamic and toxics models. The models used were EFDC, a hydrodynamic model, and WASP/TOXI5, a toxics fate and transport model. In the analysis of contaminated sediments and data, the use of these sophisticated models allows better characterization of impacted regions and resolution of “hot-spots” which may be targeted for clean up, and delineates regions which show potential for quick natural recovery and may be left alone.

The methodology was implemented for Ward Cove, the receiving water body for Ketchikan Pulp Mill’s discharge in Ketchikan, Alaska. The toxics fate and transport model was calibrated and applied to simulate the 43-year discharge of pulp mill effluents. Natural recovery of sediments was simulated with the help of processes such as: 1) burial by new clean sediments, 2) chemical biodegradation, and 3) diffusion and tidal flushing and the implementation of zero discharge. Model results showed sediment recovery of TOC in the top 10 cm of sediment within 15 years. Results for 4-methylphenol and ammonia also showed recovery with the exception of some hot spots.