Development and Evaluation of Reactive Capping Mat for Sequestration of Contaminants in Sediments
The presence of hydrophobic organic contaminants in sediment of rivers and estuaries poses a risk to human health and ecosystems and continue to degrade the quality of estuarine and riverine environments. The two classes of chemicals that are most widespread and contribute the most risk to sediments are polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The primary reason for their continued persistence is the lack of effective means of remediation. Dredging is contentious due to sediment and contaminant dispersion, and sand caps are merely a short term solution as it neither degrades nor sequester the contaminant to make them less available. A recent idea of using a reactive cap for in-situ remediation has been developed with conceptual acceptance of regulatory agencies and with much more attractive economics as compared to dredging and disposal.
Reactive Core Mat Deployment of mat in Anacostia River
A combination of laboratory and field experiments will be conducted to evaluate the efficiencies of a composite active capping system, that is capable of sequestering both heavy metals and organic contaminants by combining the apatite minerals, which sequester heavy metals effectively, with other sorbent materials, which sequester hydrophobic organic contaminants, within an engineered geotextile mat. Composite material testing is being conducted to identify the mixture of amendment materials that most effectively sequesters contaminants by collecting data on adsorption, sequestration and chemical breakthrough.
Adsorbents that can be used as reactive cap material.
Batch experiments have been conducted for initial characterization of the sorption properties of the selected sorbents for a range of chemical properties and to test contaminant mixtures and mixtures of sorbents. These experiments were conducted using naphthalene as a representative PAH because it is the most soluble and least sorptive. The concentration of naphthalene and amount of sorbent were selected on the basis of loading rates (mg of naphthalene added per gram of the sorbent).
Sorbents being evaluated for the sequestration of PCBs and PAHs are a number of different organoclays and activated carbon, and apatite will be used in conjunction for sequestration of metals. Column experiments with small mats comprised of sorbent mixtures and discrete sorbent layers will be conducted to evaluate kinetic limitations and the influence of tidal pumping on the mat efficacy.
Dr. Kevin Gardner
Center for Contaminated Sediments Research
336 Environmental Technology Building
University of New Hampshire
Durham, NH 03824