Environmental Applications for Sub-Surface Dredging (Ssd)
Type:
Presented during:
WODCON XVIII - 2007 Orlando, Florida, USA
Authors:
Pennekamp
Abstract: Capping, as a major remediation alternative, is sometimes precluded during feasibility studies because it reduces water depth. Reduction of water depth is often not allowed in Federal Channels, floodways, or in shallow water bodies due to possible adverse impacts. Acquisition and transport of capping material is expensive, amounting to a large fraction of the total remediation cost. Where clean, cohesionless sediment underlies the bed, Sub- Surface Dredging (SSD) can be the answer.
Recently several successful pilot projects using Sub-Surface Dredging were conducted in the Netherlands. Two major dredging contractors individually optimized and innovated the SSD-concept. The pilot projects were accompanied with extensive environmental monitoring program of which this paper gives a record. The monitoring program had high ambition levels and revealed only minute environmental impacts. SSD-technology involves penetrating with lances through surficial sediment to underlying cohesionless (sandy) sediment. Deeper sand is carefully dredged and transported to the surface. The SSD-techniques yield free sand, and a subsided bed.
This paper describes how this technology can be used for remediation, habitat mitigation and natural resources restoration with a variety of examples including:
- Using the dredged sand as a cap over the newly-subsided contaminated surficial sediments while maintaining pre-remediation water depths.
- Capping flood plain contaminants without breaking the artesian seal of the surficial fine-grained sediments, and without reducing the floodway.
- Diversifying habitat in riverine or estuarine conditions. Where no contamination is involved, a mud flat environment can be diversified by dredging underlying sand and placing it nearby, deepening part of the habitat while building a base for an adjacent island.
- Deepening a wetland, thereby changing its role in nutrient processing and creating more diverse wetlands.
Keywords: Sub-Surface Dredging, SSD, remediation, capping technique, environmental dredging