Predicting and Validating the Performance of Novel Sorbent-amended Sediment Caps
Funding Agency
Cooperative Institute for Coastal and
Estuarine Environmental Technology
(CICEET)
Collaborators
David Dzombak, CMU
Jeanne VanBriesen, CMU
Publications
McDonough, K., Fairey, J., Lowry, G. (2007). Adsorption of polychlorinated
biphenyls to activated carbon: equilibrium isotherms and a preliminary
assessment of the effect of dissolved organic matter and biofilm
loadings. Water Research (in press).
McDonough, K., Murphy, P. J., Olsta, J., Zhu,
Y., Reible, D., Lowry, G. V., Development and
Placement of a Sorbent-amended Thin Layer Sediment
Cap in the Anacostia River. (2007). Journal of Soil and Sediment Contamination,
an International Journal 16 (3) 313-322.
Murphy, P., Marquette, A., Reible, D., Lowry,
G. V. (2006). “Predicting the Performance of Sediment Caps Amended with Sorbing Media”, Journal
of Environmental Engineering, 132
787-794.
Abstract
The proper
management of PCB- and PAH-contaminated sediment has proven to be a
wide-spread, complex, and costly issue, and there are few viable cost-effective
technologies to manage contaminated sediments. There are many potential
disadvantages of dredging including high costs, the generation of wastewater,
residual contamination, and loss of habitat.
In situ capping (ISC) is a potentially effective technology that can
overcome many of the problems associated with dredging. Regulatory and public
acceptance of ISC with sand, the most common approach considered, has sometimes
been difficult because contaminants are not removed or destroyed, and because
the ability of a sand cap to isolate contaminants for long time periods depends
upon site hydrogeology (e.g. groundwater seepage) and is uncertain.
Adding a sorbent layer such as
activated carbon into a sediment cap provides the ability to contain
contaminants for very long times. Model
simulations indicate that incorporating a thin activated carbon layer creates
sediment caps that can isolate PCBs and PAHs in the
underlying sediment for hundreds to thousands of years, even in the presence of
moderate groundwater seepage. These simulations are based on sorption isotherms
parameters measured in clean water and assume no effect of competitive
sorption. Equilibrium sorption was also assumed. The length of time that a cap
can isolate contaminants depends highly on the sorption strength and on the
ability to reach sorption equilibrium in the cap. Competitive sorption by
dissolved organic matter (DOM) or the growth of a biofilm
on the activated carbon incorporated into the cap may decrease the sorption
strength and capacity, and may significantly slow sorption kinetics.
The objectives of the proposed study are to i) determine the primary mechanisms affecting the
performance of novel activated carbon-amended sediment caps under field
conditions, ii) develop the system understanding needed to interpret the
performance data collected for caps placed in the field, and iii) develop
design criteria for caps based on site hydrology and geochemistry. Batch
isotherm experiments will be used to evaluate the effect of DOM and biofilm growth on sorption strength and capacity. Column
experiments will be used to evaluate the effect of groundwater seepage and the
ability to achieve equilibrium sorption in the cap sorbent
layer. The effect of sorbent particle size, colloid
transport, and the potential for contaminant degradation within the cap will be
assessed. The performance data collected in the laboratory will be used to
predict and interpret performance data collected on pilot caps placed in the
field, and allow for the robust engineering design of sorbent-amended
sediment caps at all sediment sites.
The long isolation time provided by these caps suggests
that the contaminants in the underlying sediment may degrade naturally or
through engineered strategies to enhanced degradation. Sorbent-amended
sediment caps may therefore lead to effective cap-and-treat technologies.
Placing the appropriate granular media over the thin sorbent
layer would promote habitat restoration with select benthic fauna so this
technology has the potential to isolate and treat contaminants in place, while
simultaneously promoting habitat restoration.
Greg Lowry Home | Dept. Civil & Env.
Engr.