Environmental engineers use nature for restoration efforts
By Lynn Nystrom
Spectrum Volume 20 Issue 19 - February 5, 1998
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 lie in planting poplar trees. 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," said Simone Grace, an environmental engineer with Ecolotree, the Iowa firm promoting the use of poplar trees. "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 are more than 250 natural species of poplar trees,...but there are approximately 2,500 hybrids that have been genetically engineered," Grace said.
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, said 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," Novak said.
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 cleanup, this is obviously not the way to go," Novak said, "but if there is time, using the plant system may be optimal."
Widdowson compared 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."
"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," Widdowson said.
According to Grace, 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 said 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 said.
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 said.
Widdowson and Novak's project should take a little less than three years to complete.