Abstract

AquaBlok is generally marketed as a non-specific capping material that could encapsulate any class or type of contaminant and any range of contaminant concentration. Although the manufacturer claims there is no practicable limit to the depth at which the material would function, AquaBlok is typically formulated to function in relatively shallow, freshwater to brackish, near-shore environments. It is commonly comprised of bentonite clay with polymer additives covering a small aggregate core. Other specific formulations of AquaBlok are available:

• Varieties that can function in saline environments
• Advanced formulations that incorporate treatment reagents to actively treat or sequester sediment contaminants or plant seeds to promote the establishment or re-growth of vegetated habitat

Under EPA’s Superfund Innovative Technology Evaluation (SITE) Program, the effectiveness of AquaBlok as an innovative contaminated sediment capping technology was evaluated in the Anacostia River in Washington, DC. Sediments in the Anacostia River are contaminated with polycyclic aromatic hydrocarbons, polychlorinated biphenyls, heavy metals, and other chemicals at levels that have hindered commercial, industrial, and recreational uses. The performance of AquaBlok was assessed by monitoring an AquaBlok cap over about three years using a multitude of invasive or noninvasive sampling and monitoring tools. The performance of AquaBlok was compared to the performance of a traditional sand cap relative to three fundamental study objectives. Control sediments were also monitored to provide critical context to the data evaluations.

The study objectives were to determine, relative to the traditional sand cap material, the:

• Physical stability of AquaBlok
• Ability of AquaBlok to prevent hydraulic seepage
• Impact of AquaBlok on benthic habitat, ecology, and conditions in the native river system

There were field data collection issues and inherent data uncertainties within the SITE demonstration that limit the usefulness of certain data and minimized the power of certain evaluations and interpretations. The conclusions of the demonstration must be reviewed in this context. However, the overall results of the AquaBlok SITE demonstration indicate that the AquaBlok material is highly stable and likely more stable than traditional sand capping material, even under very high bottom shear stresses.

The AquaBlok material is also characteristically more impermeable and the weight of evidence gathered suggests it is potentially more effective at controlling contaminant flux than traditional sand capping material. AquaBlok also appears to be characterized by impacts to benthos and benthic habitat generally similar to traditional sand capping material.

Contact

Ed Barth

See Also

Superfund Innovative Technology Evaluation

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