Superior Contaminated Sediment Capping Properties Demonstrated in Newly Released U.S. EPA SITE Evaluation Report

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Report shows AquaBlok's® clay-based capping material for contaminated sediment has superior properties compared to a traditional sand capping approach in physical stability and reduced permeability or seepage through the capping material.

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Overall, benthic habitats and faunal communities in the AquaBlok® and sand cells were more similar to each other than to those in the control cell, but retained differences that clearly separated them from each other. In particular, the AquaBlok stations had relatively equal or greater abundances of individuals in the major taxonomic groups found to occur in the sand cell.

AquaBlok, Ltd., a manufacturer of innovative clay-based composite materials, is pleased to announce its capping technology for contaminated sediment has been found to demonstrate superior properties compared to the traditional sand capping approach, as documented in the long awaited release of the final report authored by the U.S. EPA's National Risk Management Research Laboratory, Office of Research and Development. The full report can be accessed on the web at: http://www.epa.gov/ORD/SITE/reports.html .

A program of the U.S. Environmental Protection Agency (EPA), referred to as the Superfund Innovative Technology Evaluation (SITE) Program, evaluated the effectiveness of AquaBlok® as an innovative contaminated sediment capping technology in the Anacostia River in Washington, DC. Contaminants in the sediment of the Anacostia River include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), heavy metals, and other chemicals to levels that generally exceed regulatory standards. Performance of an AquaBlok® cap was monitored over an approximately three year period using a range of invasive and non-invasive methods.

A comparison of AquaBlok® to a traditional sand cap was made relative to the following three basic objectives:
1. Assess the physical stability of AquaBlok® relative to a traditional sand cap,
2. Determine the ability of AquaBlok® to prevent hydraulic seepage compared to traditional sand cap material,
3. Evaluate the impact of AquaBlok® on benthic habitat and ecology relative to traditional sand cap material and conditions in the native river system.
The conclusion of the evaluation, from the abstract of the report is as follows:

"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."

A range of unique and important measurement methods were employed during the evaluation to support the conclusions of the report. Two such measurements related to stability of the capping material against flow or sheer stresses and seepage through the cap.

To evaluate the stability of the material a novel "SedFlume" approach, specifically designed for testing of core samples of sediments, was performed by an independent source. The conclusions of these tests from the report are as follows:
"In the actual AquaBlok® material, erosion rates were exceedingly low and required very high shear energy to produce erosion. The shear stresses required to erode the AquaBlok® material were between 3.2 and 10 N/m2, a range that is indicative of very high surface water energy at the sediment/water interface. In addition, this range is at least an order of magnitude higher than was required to erode the native sediment interval and significantly higher than energy required to erode the sand capping material."

Since AquaBlok is considered a low-permeability capping alternative to traditional sand caps, both hydraulic conductivity (K) measurements and seepage information collected from the field were considered to be key measurements for the evaluation. While the hydraulic conductivity is a standard measure, the seepage data was collected from the river with specialized ground-water seepage meters adapted to provide continuous measurement of aqueous flux through the sediment cap at high resolution over an extended period of time.

The conclusions of the report in regard to hydraulic conductivity is as follows:
"Hydraulic conductivity of the AquaBlok® material during both events (i.e., 10-7 to 10-8 cm/s) was very similar to the range of values determined for the native sediment and consistent with the documented range for this capping material. Hydraulic conductivities in the range determined for AquaBlok® (and native sediment in the demonstration area) are indicative of a highly impermeable material. Alternatively, the calculated hydraulic conductivity for the sand capping material from the sand cell (i.e., 10-3 to 10-4 cm/s), while it did demonstrate some decrease between the 18-month and 30-month post-capping events, was several orders of magnitude greater than AquaBlok®."

The conclusions of the report in regard to seepage are as follows:
"For each sampling event, the mean, minimum, and maximum calculated discharge rates over the representative 24-hour tidal period were generally lowest for the seepage meters deployed in the AquaBlok® cell. Calculated discharge rates in the sand cell were generally higher than in the AquaBlok® cell and the control cell, suggesting the most significant vertical movement of fluid from sediment to surface water in this cell."

Recovery of benthic habitat and ecology in the capped area is also of primary interest in the evaluation and application of sediment remediation management options. The report provides significant detail at the 30 month interval on recovery and the comparison of the AquaBlok Cell to the Sand Cap:

"Overall, benthic habitats and faunal communities in the AquaBlok® and sand cells were more similar to each other than to those in the control cell, but retained differences that clearly separated them from each other. In particular, the AquaBlok stations had relatively equal or greater abundances of individuals in the major taxonomic groups found to occur in the sand cell."

The report also provides a detailed framework for estimating and evaluating the economics of AquaBlok as a contaminated sediment remediation management approach. It is believed that this report will be invaluable to regulators and engineering firms that are charged with implementation of the EPA Sediment Management Guidelines, released in December of 2005.

For additional information on AquaBlok's® sediment capping technology or to evaluate AquaBlok as a sediment remediation alternative, please click here.

For more information on the AquaBlok® SITE demonstration project, please contact:

Edwin Barth, Ph.D., P.E., C.I.H.
U.S. Environmental Protection Agency
Office of Research and Development
26 West Martin Luther King Drive
Cincinnati, OH 45268
Telephone: (513) 569-7669
Fax: (513) 569-7158
barth.ed(at)epa.gov

Andrew Bullard, M.E.M.
Principal Research Scientist
Environmental Restoration
Battelle Memorial Institute
125 Pheasant Run, Suite 115
Newtown, PA 18940
Telephone: (215) 504-5312
Fax: (614) 458-6622
bullarda(at)battelle.org

About AquaBlok, Ltd.
AquaBlok, Ltd. is a manufacturer of composite (clay-based) materials utilizing its patented coating and amendment approach. The company has a long history in the environmental industry and a range of products utilized in contaminated sediment remediation technologies. AquaBlok also can deliver a wide range of treatment materials to the sediment, including organoclay, activated carbon, zero valent iron, sulfur and other proprietary materials such as EHC-M (an Adventus Group product). Adventus Group (http://www.AdventusGroup.com) is AquaBlok's exclusive seller of these AquaBlok+ treatment products. AquaBlok also utilizes its delivery system in a range of other products including, pond and industrial impoundment sealing, as seep collars on piping, to construct cut-off walls in porous soil conditions, flood control applications (i.e. levee and dam protection), and to deliver organoclay-based materials. In addition, AquaBlok is a licensee of Halliburton's Bariod Division for the Baraclear® algae treatment product. For more information, please visit http://www.aquablokinfo.com.

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