IMPORTANT FACTORS IN SPECIFYING AND CONTRACTING ENVIRONMENTAL DREDGING PROJECTS AND PROJECT EXAMPLES

摘要

Environmental dredging projects, when compared to navigational (maintenance) dredging projects, are often times more complex due to additional work elements and factors that must be considered in achieving project success. For example, navigational dredging can be as simple as moving sediment from Point A (a defined area and cut depth) to Point B (an aquatic or upland deposit area), where project success is determined by post-dredge survey verification. The dredging contractor's financial success hinges on meeting or beating his solids production goal. On the other hand, working fast on an environmental dredging project, although desired, is not the primary goal. Further, environmental dredging frequently requires that the dredged sediments be dewatered or solidified so they can be transported and disposed as solid waste in a secure facility, and the dredge water frequently requires treatment for more than solids removal prior to permitted discharge. Dredge operational controls are often specified to minimize contaminant losses from sediment re-suspension. Beyond post-dredge survey verification that the dredge prism has been removed, frequently project success is determined by post-dredge sampling and comparison to an established clean-up limit (CUL) and/or to an overall mass removal goal (MRG) for the contaminant(s) of concern (COCs). Uncertainties in establishing the dredge prism, and residual contamination even following best method practices in dredging, can be factors causing an exceedance of the CUL/MRG, through no fault of the dredging contractor. Contingency plans must balance the cost effectiveness, for example, of additional dredging or alternative placement of a thin sand cover to improve exposure conditions. This paper describes important factors that must be considered in developing fair and reasonable specifications and contract payment strategies for environmental dredging projects. Several project examples are also discussed.