BLACKSBURG, Jan. 31, 1997 -- Virginia Tech
environmental engineers, working with the railroad, an Iowa tree
company, and a consulting firm, are attempting to use Mother Nature
to restore a site contaminated by a leaking creosote holding pond.
More importantly, they hope the knowledge gained from this project
will enhance the use of natural biological means to correct environmental
problems.
For railroads, the use of creosote to preserve
ties has been common practice since the 1800s. An easy method
to treat a railroad tie with the preservative was to dip it in
a creosote holding pond. One of these ponds is in Oneida, Tenn.,
where the lagoon was in use until 1973.
Seventeen years later, when the U.S. Army
Corps of Engineers rechanneled a nearby creek, areas of contamination
were then exposed and free to enter the newly constructed channel.
Despite measures that eventually eliminated the flow of the contaminated
groundwater to the channel, the site itself remains polluted.
The solution may be in the planting of the
stately poplar tree. The use of these fast growing, deciduous
plants was proposed by a consulting firm, Geraghty and Miller
Inc. Recent data indicate poplar trees can remediate a contaminated
water area due to their ability to draw the polluted groundwater
to their roots. Although the process is not yet well understood,
it appears that the contaminants are rendered harmless as they
interact in the area of the trees' roots. Plants, in general,
create a microbial environment near their roots that result in
the more rapid demise of pollutants.
"Engineers try to fight nature,"
says Simone Grace, an environmental engineer with Ecolotree, the
Iowa firm promoting the use of poplar trees. She adds, "Now,
the engineers are using nature."
One reason Ecolotree selected the poplar
is because they can capitalize on the volumes of research already
conducted by paper companies and logging concerns that use the
poplar as a primary resource. "A lot of research has been
performed on the poplar to make them disease resistant...There
more than 250 natural species of poplar trees,...but there are
approximately 2500 hybrids that have been genetically engineered,"
Grace says.
However, as John Novak and Mark Widdowson
of Virginia Tech's environmental engineering program,
note, a number of questions remain regarding this natural restoration
approach that is called phytoremediation. In a proposal submitted
to Norfolk Southern Corporation and subsequently funded for almost
$400,000, the two suggest that "specific mechanisms for phytoremediation
will vary with the type of contaminant and the plant species.
It is also probable that the dominant mechanisms will vary from
site to site, depending on site characteristics such as the depth
to groundwater, moisture content of the soil, type of soil, organic
matter of the soil, and other local features."
For regulatory bodies such as the Environmental
Protection Agency (EPA) to accept a proposal from a company that
plans to use phytoremediation, these questions need to be answered.
N&W's commitment of $400,000 in funding to identify solutions
represents a strong commitment for investing in the future and
for protecting the environment.
Novak, an expert in water and wastewater
treatment as well as soil and groundwater remediation, explains
that poplar trees can "generally withstand a lot of pollution."
Some of his knowledge about the tree is based on a project conducted
in Virginia by Ecolotree. It planted poplar trees on top of a
Virginia landfill to control the moisture on the surface of the
sites. "Within three years, the deep root systems of the
trees were accomplishing a lot," says Novak.
At the Oneida Tie Yard Site, Novak and Widdowson
have also added a grass study. They are excavating the contaminated
soil and spreading it around the site, and then planting different
types of grasses such as clover and fescue to determine which,
if any, restore the site to a healthy state.
"If we needed a quick clean up, this
is obviously not the way to go," Novak says, "but if
there is time, using the plant system may be optimal."
Widdowson compares this remediation process
to some procedures in the medical practice. "Oftentimes,
you will have a patient who is subjected to different treatments
and the results are monitored. Well, we are dealing with a natural
system too, and we are poking holes in the ground, and we have
limited access to knowledge about what is going on down there."
He adds that "poplar trees have proven
to be efficient in agricultural areas. For example, chemical fertilizers
on a field will percolate down and eventually flow with the groundwater
towards a stream. When the right systems (i.e. poplar roots) start
absorbing the groundwater, they can practically eliminate the
nitrate getting to the stream."
Grace reports that Ecolotree had a project
in River Bend, Oregon where the poplar trees were planted on top
of a landfill site, and they have proof that the vegetation is
taking all of the nitrate out of the leachate, "and the trees
are growing like wild fire."
She adds that they have also been successful
in using the trees as part of a wastewater treatment process.
A last step was added to the process that took the wastewater
and used the liquid as a irrigation source for the trees. "The
trees sucked up the nitrogen, and the plant was left with cleaner
wastewater," Grace says.
Widdowson's main role in the Oneida study
is to develop a predictive model for how one can assess a site,
as well as evaluate a process in terms of its ability to clean
up a contaminated area. The model would have to account for such
variables as groundwater flow, the long term fate of the contaminant
and the long term fate of the soils contaminant.
In the process, Novak and Widdowson will
also be measuring the rate of biodegradation of highly toxic polyaromatic
hydrocarbons in the soil and the groundwater using the poplar
trees versus that which occurs through natural or intrinsic processes.
"The key to proving that enhanced remediation is occurring
in the planted areas at the Oneida site is to compare the planted
areas with the unplanted regions with similar levels and types
of contamination," the environmental engineers report.
Widdowson and Novak's project should take
a little less than three years to complete.