Despite sand’s attributes as a sediment capping material, results of this comparative study also indicate that AquaBlok could offer several advantages over sand in capping contaminated deep water or wetland sediments in select circumstances. As opposed to more permeable sand material, AquaBlok application does not appear to result in significant compaction-related movement of sediment pore waters into capping material, thus maximizing the effective, contaminant-free thickness of an AquaBlok cap. AquaBlok displays significantly higher resistance to unidirectional current flow than sand, which could give more flexibility in cap design (perhaps no armor needed) as well as the range of hydrologic environments into which AquaBlok caps could be applied.
By virtue of its lower permeability and amenability to organic additions, AquaBlok should act as a more effective barrier to long-term contaminant transport of dissolved, sediment-borne contaminants into the bioturbation zone. AquaBlok is physically similar to fine-grained contaminated sediments and could therefore be a more effective substrate than sands for colonization by local invertebrate communities. By virtue of its higher resistance to erosive forces and effectiveness as a chemical barrier, a relatively thin AquaBlok cap (one foot or less) could be deployed to collectively meet all functional objectives at a given site. Such a relatively thin, yet effective cap could minimize restrictions on waterway uses and navigation – as opposed to sand caps, which may need to be applied at thicknesses significantly greater than one foot in order to meet functional objectives.
In summary, a one-foot AquaBlok cap would appear to be at least as effective as a one-foot sand cap in biologically, physically, and chemically isolating sediment-borne contaminants in deep water and wetland ecosystems. Both capping materials can be viable substrate for macro invertebrate colonization. Both capping materials can physically stabilize contaminated sediments, either with or without additional capping components (e.g. stone armor). Finally, transport simulations indicate that both sand and AquaBlok caps can effectively limit upward migration of hydrophobic contaminants into bioturbation zones for a period of many decades. Both cap types should also be relatively easy to deploy, monitor, and maintain over time. Cost comparisons for sand versus AquaBlok sediment capping can be readily determined on a sitespecific basis. Costs for implementing an in situ capping approach can be significantly less than costs associated with sediment removal,treatment,and disposal in many applications.
302 Proceedings of the 1999 Conference on Hazardous Waste Research