Environmental Engineering Reference
In-Depth Information
Table 13.4 Relation between plant type and potential for interaction
with particular groundwater contaminants. Where site conditions indi-
cate a period of high water table such that the root zone would be
saturated for more than 1 week, willows can be used instead of poplars.
Reduced organics
Petroleum hydrocarbons
Aromatics
Alfalfa ( Medicago sativa L.)
Willow ( Salix spp .)
Poplar ( Populus spp .)
Pine ( Pinus sylvestris L.)
Polycyclic aromatics
Poplar
Alfalfa
Buffalo grass
Oxidized organics (Kassel et al. 2002)
Chlorinated solvents
Populus spp .
Alfalfa (Narayanan et al. 1999)
Oxidized/reduced organics
TNT, HMX, RDX
Hybrid poplar
Willows (Shoenmuth and Pestemer 2004a, b)
Birch ( Betula pendula )
Pine
Fig. 13.21 Number of new phytoremediation sites and type of con-
taminant started per year (Modified from U.S. Environmental Protec-
tion Agency 2005c).
13.9 Historical Trends in the Initiation and
Continuation of Phytoremediation at
Groundwater Contamination Sites
Although the use of plants to restore contaminated water has
been around for some time (see Chap. 11), the application of
vegetation to remediate subsurface contamination such as
groundwater was suggested only in the early 1990s
(Cunningham and Berti 1993). The early 1990s had very
few new projects, no more than five per year, where plants
were specifically being used to remediate the subsurface
contaminated by xenobiotics such as chlorinated solvents,
pesticides, explosives, and metals (U.S. Environmental Pro-
tection Agency 2005b; Fig. 13.21 ). From 1996 on, however,
there was a three-fold increase in the number of sites where
plants were being applied as part of or were the sole remedial
activity to address contaminated groundwater (Fig. 13.21 ).
The highest number of sites (14) of phytoremediation appli-
cation occurred in 1999 (U.S. Environmental Protection
Agency 2005b).
The expansion of government-funded sites for innovative
projects of high risk such as phytoremediation is typical of
other such efforts that include government venture capital
funding of the Interstate Highway System and national mail
service. Of the 79 sites evaluated as part of the report
(U.S. Environmental Protection Agency 2005b), they ranged
Fig. 13.22 Generalized distribution of phytoremediation sites in the
United States (Modified from U.S. Environmental Protection Agency
2005b).
across the United States in 31 States from the East Coast,
Central Plains, and West Coast. The sites were located in
areas that had cool seasonal temperatures and warm sum-
mers, and little to large amounts of precipitation, with great
variations in climate and ET P characteristics (Fig. 13.22 ).
Although Cunningham and Ow (1996) stated that phyto-
remediation was still in its initial stages of research and
development, this probably is a valid statement even today.
Not just the number of sites but the type of contaminant
changed at phytoremediation sites since the 1990s
(Fig. 13.23 ). Of the few sites where plants were being used
prior to 1996, most were characterized by pesticide or metal
contamination. This reflects the historical natural progres-
sion from the early studies of pesticide bioaccumulation and
early experiments into metal-accumulating plants that was
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