Dredge & Cap Approach to Contaminated Sediment Remediation
According to the U.S. EPA’s 2005 guidance document for Contaminated Sediment Remediation Guidance for Hazardous Waste Sites – Dredging as a remedy provides the following primary advantages and limitations:
A dredge & cap approach is believed to address many of the above limitations, while reducing risk of remedy and costs.
The essential concept behind this approach is that dredging activity should be focused on only the highest levels of contaminant concentrations within a site and removal should not be driven by achieving a low target residual concentration level. Any remaining contaminants in the underlying sediment can be sequestered or isolated with either a low-permeability cap (AquaBlok®) or a permeable in-situ amendment layer (AquaGate®+). The graphic below illustrates the concept and shows the reduction in removal volume that can be achieved assuming different assumptions regarding cap type and cap thickness.
AquaBlok materials have been used on many occasions to implement this remedial approach. One example is shown below, where an excavation in the dry was performed in the Genesee River (Wellsville, NY) at a historic refinery site. Because it was known that soil and sediment impacts extended a significant distance, it was determined that removal of only the top 3-feet of sediment would be performed and a low-permeability isolation barrier (AquaBlok) would be used to sequester any residual – minimize the potential of impacts to the restored stream bed.
The approach provides the following key advantages:
Other examples are provided in the Library section of the web site under 'Installation Profiles'.