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
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
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