Phytoremediation of Volatile Organic Compounds in ... - CLU-IN

Phytoremediation of Volatile Organic Compounds in Groundwater
benzene (TMB, up to 2,000 ppb), and xylenes (up to 2,700 ppb). Depth to the aquifer at this site
is about 9 feet, and most of the contamination is located between 5 and 18 feet below the surface.
The soil at this site is a loamy sand and is slightly acidic.
In December of 1996, 118 hybrid poplar trees (P. charkoweiiensis x incrassata, NE 308) were
planted on about 0.33 acres as part of a pilot-scale phytoremediation project implemented by the
EPA’s Environmental Response Team. Using a deep-rooting planting process to maximize
groundwater uptake, 12-foot trees were planted 9 feet under the ground, with only 2 to 3 feet
remaining above the surface. Trees were planted about 10 feet apart.
Fertilizer has been applied to trees annually at rates based on soil fertility results in order to
promote tree growth. Pesticides were also used to prevent various problems that have been
encountered in the past such as caterpillars that defoliate trees.
PERFORMANCE TO DATE
During the 1998 growing season, large reductions in dichloromethane and trimethylbenzene were
reported. The reductions were sustained through 2001, with the highest TCE concentration of 87
µg/L found in well WP12 in August 2001. This reflects a decrease of over 80 percent from the
initial concentration of 500 µg/L in 1995. The highest DCM and TMB concentrations found in the
2001 sampling were 2 µg/L and 500 µg/L, respectively. Methylene chloride, which was once
present at concentrations greater than 5,000 µg/L, is now virtually non-detectable. The only two
contaminants that have not shown much reduction are xylene (at a maximum concentration of
3,000 µg/L in 2001) and PCE (Figure 8).
Figure 8. PCE concentrations in groundwater at Edward Sears Property, September 2001 (Gussman, 2002)
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