Research Brief:
Risk and Uncertainty in Environmental Evaluations of Dredged Material


Issue     

   


How confident can we be in our projections about unacceptable impacts? Uncertainty associated with environmental regulatory evaluations of dredged material can lead to delayed, costly, and unwise management decisions. The uncertainty associated with environmental assessments and projections about environmental risk can be partitioned into that which results from:

    1. a lack of knowledge about a particular parameter or process of importance
    2. variability resulting from natural heterogeneity in the environment

This distinction is important because uncertainty associated with lack of knowledge can, in some cases, be reduced by collection of additional information, whereas natural variability in most cases cannot be reduced, but can be described. Uncertainty can be ascribed to:

  • our incomplete understanding of the specific environmental setting or scenario under consideration
  • model uncertainty arising from necessary simplifications of real-world relationships
  • parameter uncertainty arising from such elements as measurement error in specific model parameters


Research/Objectives    

   

The importance of more than 40 specific sources of uncertainty in environmental assessments of dredged material was evaluated using three criteria:

  • whether the uncertainty results from a failure to consider a potential adverse impact
  • the magnitude of the uncertainty
  • how easily the uncertainty can be reduced with available or readily obtained data and information

(Continued on reverse)

 


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U.S. Army Engineer Research and Development Center

February 1999
www.erdc.usace.army.mil
www.wes.army.mil/el/dots/doer


Results/Products    

   

Following our analysis, sources of uncertainty were ranked according to the relative amount of uncertainty associated with each. Those sources of uncertainty with the greatest potential to affect dredged material management decisions include:

  • estimating fate and transport in the far field
  • interpreting chronic sublethal toxicity tests which are being scheduled for regulatory implementation in the dredging program
  • evaluating trophic transfer potential for contaminants in dredged material
  • assessing effects on fish and other upper trophic level receptors including humans
  • estimating effects caused by complex mixtures of contaminants

Information gained will assist managers to improve the regulatory decision making process.


Research Team    

   

Todd S. Bridges, Ph.D., ERDC; Susan Kane Driscoll, Donna Vorhees, and Trina von Stackelberg, contract support
U.S. Army Engineer Research and Development Center
Waterways Experiment Station
3909 Halls Ferry Road, Vicksburg, MS 39180