Trees help cleanse landfill

Friday, December 26, 2008 | 1:00 p.m. CST; updated 6:35 p.m. CST, Sunday, January 4, 2009
A bulldozer moves trash at the Columbia landfill. Trees were planted at the facility in an effort to soak up toxic groundwater before it reaches nearby Hinkson Creek. Dirty groundwater can lead to many problems, including unwelcome smells, mosquitoes and structural damage.

COLUMBIA — Some newly planted trees may someday ensure cleaner water for Columbia’s Hinkson Creek.

Last year, 1,800 cottonwood and sycamore trees were planted at the Columbia Solid Waste Division landfill. These trees are not yet fully grown but are designed to soak up and cleanse any toxic groundwater that could flow from the landfill into nearby Hinkson Creek, which is on a Federal Government list of impaired waters.


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This cleansing process is called phytoremediation. Phyto means "plant", and remediation means "to correct an evil." It’s a big word for a simple process.

How it works

Think of three stairs. The top stair is the landfill. The middle stair is where the trees are planted, and the bottom stair is Hinkson Creek. Garbage is dumped on the top stair and could possibly contaminate a water table under the landfill. This water flows down to Hinkson Creek – unless the tree's roots can intercept the contaminated groundwater.

The landfill's elevation is 78 feet upslope of the seven-acre tree site. In turn, the trees sit at an elevation six feet higher than the creek.

The trees were donated by The Missouri Department of Conservation, and planted at 13 inches tall, said Scott Hamilton, an urban conversationalist with the Hinkson Creek Watershed Restoration Project.

Chung-Ho Lin, a phytoremediation researcher for the MU Agroforestry Department, says he knows why cottonwood trees were used.

“The cottonwood has been widely used in the strategy,” Lin said. “They are tolerant to heavy metals.”

According to the Environmental Protection Agency, trees, such as cottonwood, have been shown to take in as much as 200 gallons of water per day, preventing the spread of contaminated groundwater.

Lin says phytoremidation became popular in the 1990s and the process has been successful in cleaning soil at waste sights in the past.

In 1998, the Ford Motor Company in Michigan, planted 7,500 cottonwoods over 4.7 acres that were used as a landfill for the company. According to a case study published by the company, the project has been a success as levels of toxins at the landfill have decreased.

 Richard Wieman, a solid waste utility manager at the landfill, says the most important benefit of the process is keeping toxins and heavy metals out of the groundwater, which eventually ends up as drinking water. He says the importance of clean drinking water cannot be overstated.

“It’s been documented that lead in young children reduced the IQ of an individual,” Wieman said.

Hamilton says that dirty groundwater can lead to all sorts of problems for home and business owners — including unwelcome smells, mosquitoes, eroding yards and damages to the structure itself.

He also noted the other benefits of a cleaner Hinkson Creek, including prettier water and more opportunities for fishermen.

“It’s a combination of aesthetics and recreational qualities,” Hamilton said.

Preventative measures

Neither Federal government nor Missouri government forced the landfill to plant the trees.

Michael Symmonds, landfill superintendent, says he is trying to be proactive about protecting Hinkson Creek.

“We’re trying to put up a fence in case there ever is a situation or problem," Symmonds said. "This will be the first start in assessing any damages or taking care of any problems.”

The Missouri Department of Natural Resources requires the Columbia Solid Waste Division to take groundwater and soil samples, testing for man-made constituents and volatile organic compounds.

The landfill is divided into cells that are lined with compacted clay and plastic to keep pollutants from percolating into the groundwater.

Wieman says there are no harmful contaminants present and says this project “will kind of buy insurance in the future for this site, if it should be contaminated.”

Inexpensive, but not complete

Taking care of the trees is inexpensive and that is why phytoremidation is popular among both government and private sectors, Lin says.

“It is very cost-effective compared to the traditional, conventional treatment and cleanup process,” Lin said.

The primary energy source for these trees is the sun. Just a few basic farm tools are required to plant the sycamores and cottonwoods.

This project was funded with a portion of a $400,000 grant from the EPA to improve Hinkson Creek. The Missouri Department of Conservation donated the trees, which were planted by volunteers. The landfill has vowed to maintain the trees, including watering.

Some of the trees had to be replanted early this year, Hamilton said. Still, he calls the project a success.

“They had pretty good survival on the cottonwood stakes we planted,” Hamilton said.

Both Hamilton and the EPA acknowledge that instant gratification is not the reason for planting these trees. It takes several years before they grow enough to make a big impact.

“We’re not going to see a lot of benefits until those trees get bigger,” Hamilton said. “In a couple more years, we will see some real benefits.”

“This is the first phase of the project.”

Lin says it’s imperative that the landfill or other sites wanting to try phytoremedation choose the right tree or plant for their area.

“The species selection is important,” Lin said. “You have to make sure those plants are tolerant to the pollutant.”

Lin views phytoremediation as a viable option to improve water and soil quality.

“It uses Mother Nature to take care of human problems.”

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