Search Result from the May 2008 Issue
| Return to Search |
LONG-TERM MONITORING (1993-2007) OF THE EFFECT OF HYBRID POPLAR TREES ON A PETROLEUM- HYDROCARBON CONTAMINATED GROUND-WATER SYSTEMLandmeyer, J.E. (USGS); A.R. Contrael (MTR); T.N. Effinger (SCE&G). Fourth International Phytotechnologies Conference, 24-26 September 2007, Denver, Colorado: Abstracts, p 39, 2007
Changes in ground-water levels and contaminant geochemistry were observed in
a shallow aquifer contaminated with coal-tar near Charleston, South Carolina,
before and after the installation of a hybrid poplar tree grove. The grove was
planted in the fall of 1998 as part of site remediation activities and
consisted of about 600 6-ft rooted hybrid poplar cuttings. Monitoring of
ground water, tree tissue samples, and sap flow was performed to evaluate
performance. Ground-water levels decreased about 3.5 ft across the planted and
unplanted areas of the site between 1998 and late 2000 due to regional drought
conditions in the Southeast. After 2001, decreases in ground-water levels in
the planted area were about 1 ft deeper than measured in unplanted areas.
Estimates of water flow through the 7-year old trees using sap-flow
instruments indicate that the poplar trees are transpiring nearly 5 gallons of
water per day per tree. Long-term monitoring activities show that the hybrid
poplars also have decreased ground-water contaminant concentrations in planted
areas to a larger extent than observed in unplanted areas. The magnitude of
the observed decrease in ground-water contaminant concentrations in the
planted area is dependent upon the presence or absence of pockets of coal-tar
as a dense nonaqueous-phase liquid (DNAPL) beneath the trees. In the planted
areas not characterized by DNAPL, milligram per liter concentrations of
benzene, toluene, and naphthalene in monitoring wells have decreased since
2000 by an average of 85, 83, and 82%, respectively. These areas exhibited a
seasonal variation in dissolved-phase contaminant concentrations, with the
lowest concentrations observed during spring and summer, when transpiration
rates and ground-water uptake by the hybrid poplar trees were measured to be
at maximum. Benzene, toluene, and naphthalene, as well as other coal-tar
related polycyclic aromatic hydrocarbons, such as styrene, were detected in
various tree tissues sampled during the summers, when the concentrations in
ground water were lowest. In areas where DNAPL existed beneath the trees,
concentrations of benzene, toluene, and naphthalene have decreased only an
average of 32, 55, and 49%, respectively. A long-term trend is noted in
decreasing dissolved-phase contaminant concentrations in ground water beneath
the trees in areas with no DNAPL present.
The Technology Innovation News Survey welcomes your comments and
suggestions, as well as information about errors for correction. Please
contact Michael Adam of the U.S. EPA Office of Superfund Remediation
and Technology Innovation at adam.michael@epa.gov or (703) 603-9915
with any comments, suggestions, or corrections.
Mention of non-EPA documents, presentations, or papers does not constitute a U.S. EPA endorsement of their contents, only an acknowledgment that they exist and may be relevant to the Technology Innovation News Survey audience.