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Comparison of Dredge/Cap Production Rates and Construction Times: Are They Realistic?

Additional Info

  • Practice Areas: Contaminated Sites Publications
  • Event or Publication: Battelle Contaminated Sediments Conference
  • Title: Comparison of Dredge/Cap Production Rates and Construction Times: Are They Realistic?
  • All Authors: Anne Fitzpatrick, Reid Carscadden
  • Geosyntec Authors: Anne Fitzpatrick
  • Date: January 11, 2017
  • Location: New Orleans, Louisiana
  • Type: Presentation

Background/Objectives: The need for realistic construction duration estimates is critical to the development and evaluation of remedial alternatives for complex and large scale sediment remediation projects. Poorly developed duration estimates can lead to unrealistic projections of cleanup timeframes, costs, and impacts to supporting transportation infrastructure and surrounding communities. 

However, a review of several recent feasibility studies and decision documents for major sediment sties indicates that these factors are often overlooked or grossly underestimated. For example, it is estimated that the construction durations presented in two recent feasibility estimates (Lower Passaic River and Portland Harbor) may be substantially underestimated, equating to several years increased project duration. Construction times should be realistic and consider actual dredge production rates realized at other projects, seasonal efficiencies, storage capacity for dredge material, ability to move material in/out of urban corridors, water quality monitoring, vessel traffic, and work restrictions near residential communities. The solution to "just add another dredging operation and reduce the construction duration" is not always implementable and should consider many local factors.

Approach:  This presentation will compare production rates and construction timeframes for several different sediment remediation projects. This is an important variable when evaluating the cost-benefits of a remedial alternative and how long the project will realistically take to implement. This assessment also looked at unit cost assumptions, seasonal efficiency, equipment use, debris, residuals management, cleanup passes, confirmation sampling, and transloading/transport logistics that all factor into construction duration estimates for complex sediment remediation projects. Aspects of this metric will be presented, including assumptions, challenges, comparisons, and effects that should be considered when selecting a remedial alternative and communicating the selected remedy to the public. 

Results/Lessons Learned: Why are these project details important at the feasibility phase of a cleanup?  A key consideration is that shorter construction timeframes equate to more rapid achievement of remedial action objectives, fewer short-term impacts to local communities and the environment, and thus more favorable CERCLA rankings when comparing remedial alternatives. Unrealistic construction durations estimates at the feasibility stage can introduce unintended bias and undermine the remedy selection process. Results show a variety of different production rate assumptions among projects.

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