Land Revitalization Summer '07 Newsletter – The Hearty Fern – Tough Survivor and Humble Servant
Ferns are among the toughest plants on Earth. While they may look graceful and delicate – fronds waving in the breeze next to shady streams – their look belies their true vigor. In fact, ferns will invariably be the first plants to sprout on a new lava flow.
And so, it is not surprising that ferns are being used to clean up soil contamination at hazardous waste sites. Right now, in the Blue Ridge Mountains of Virginia, 20,000 fern plants are busily sucking up arsenic from the soil at a former apple orchard site.
The site is the Crozet Arsenic Site in Crozet, where during the 1970s, a variety of chemicals, including DDT and lead arsenates, were routinely sprayed on apple trees to control weeds and insects. These chemicals were legal until their ban in the early 1970s. Today, there are still areas of the site contaminated with arsenic that poses an unacceptable risk to public health.
While traditional "dig and haul" removal techniques are being used at several of the properties in the area, a technique called phytoremediation is being used at one of the residential properties. Phytoremediation is the use of plants to extract a contaminant, in this case arsenic, out of soil.
The entire property covers about 20 acres on a densely forested hillside, however only small sections of it are actually contaminated. There are 24 separate plots that total about one acre, mainly along a creek that runs through the property. It was common to mix the chemicals near water prior to spraying. Phytoremediation was chosen at this site due to several factors, lack of physical access, potential erosion, and dense forest.
The Chinese Brake Fern, also known as Pteris Vittata, is the fern of choice for this job, shown to readily accumulate arsenic from the soil. The 20,000 plants are being watered with a drip irrigation system which uses two separate springs. The first spring, at the top of the hill, uses gravity to feed a 4,000-gallon holding tank. This tank again uses gravity, to feed 17 of the plots.; The second spring is located at the bottom of the hill and uses a solar-powered pump to get the water uphill to an 1,800-gallon holding tank. This tank feeds the remaining seven plots of ferns. Each plot is on a programmable timer that waters at specific times.
Depending on weather and soil conditions, and the length of the growing season, each fern can extract up to 40-50 mg/kg arsenic from a square foot of soil. The arsenic is absorbed through the roots and concentrated in the fern leaves. At the end of the growing season, the ferns will be mowed, tested, and disposed of according to RCRA regulations. The result is significantly less waste, perhaps one or two truckloads of waste, rather than 60 or 70 of soil. This technology has been used at several sites around the country but is still considered as an "alternative" when it is compared to traditional techniques.
A company called Edenspace has the exclusive license to utilize Pteris Vittata ferns for phytoremediation. EPA used several contractors to aid in the development and implementation of this project. Among them are Edenspace, who supplied the ferns through a direct contract with EPA, Tetra Tech who provided sampling and technical consultation, and Kemron Environmental Services who provided the workforce to implement the plan. EPA Environmental Response Team was also instrumental in making this project happen.
Article contributed by
EPA On-Scene Coordinator
and Ruth Wuenschel
EPA Land Revitalization Update