Site Assessment and Characterization - Introduction to Phytoremediation of Contaminated Groundwater - page 131

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Site Assessment and Characterization

The applied use of plant and groundwater interactions (as
described in Part I) to achieve remediation goals at sites
characterized by contaminated groundwater is a direct
extension of these long-observed natural interactions. The
specific application of plants to achieve remedial goals is,
however, relatively new. The installation of plants at sites to
affect the flow of contaminated groundwater in response to
regulatory-driven site-restoration mandates was initiated in
the late 1980s and early 1990s. Relative to the total number
of sites in the United States that have documented ground-
water contamination and require some type of corrective
action, the number of published case studies of phytore-
mediation that specifically addresses groundwater flow
issues is few. In most cases at sites characterized by
contaminated groundwater, the chosen corrective action
involves conventional pump-and-treat of contaminated
groundwater or groundwater flow interception by trenching.
This is despite the efforts made by various state and federal
regulatory agencies, such as the U.S. Environmental Protec-
tion Agency (USEPA), as well as other federal agencies,
to promote phytoremediation as an alternative corrective
action.
Since the 1990s, the amount of information about phyto-
remediation of contaminated groundwater has increased
with the release of numerous reports, journal articles, and
the formation of the PhytoSociety, which publishes an inter-
national journal devoted to all aspects of phytoremediation.
Many of these publications focus on the use of plants to
remediate sites where soil contamination is the regulatory
concern, however, rather than contaminated groundwater.
As a result, the scientific and regulatory communities often
are not in the position to unequivocally state how best
to determine when phytoremediation will work at sites
characterized by contaminated groundwater, how to imple-
ment phytoremediation correctly, and how to determine
if the outcome is beneficial for site-remedial goals in a
reasonable amount of time and in a cost-effective manner.
A goal of Part II, therefore, is to present useful information
that addresses concerns that surround the assessment,

implementation, and verification of the effect of

phytoremediation on the hydrology of contaminated

groundwater.
In general, at most sites characterized by contaminated
groundwater, phytoremediation can be used to achieve three
main hydrologic goals:

• Prevention of contaminated-groundwater flow to cleaner
offsite areas;
• Prevention of contaminated-groundwater flow from
reaching regulated receptors, such as surface-water
bodies, that may be located on or off site, and;
• Reduction in leachate formation and subsequent ground-
water contamination near source areas.

Although each hydrologic goal is different, each is based
on the successful interaction of plants and groundwater.
Throughout Part II, the assumption is made that for a site
where phytoremediation is being evaluated, the groundwa-
ter is either contaminated and the first two hydrologic goals
are important or groundwater contamination is to be
avoided and, therefore, the third goal is important. Also,
the terms hydrologic and hydraulic will often be used
interchangeably in Part II to emphasize the importance of
the wide range of environmental factors that control
groundwater flow.
The development of rigorous assessment and characteri-
zation approaches in order to successfully apply phytore-
mediation to achieve the three hydrologic goals is important
for many reasons. First, site characterization activities may
indicate that phytoremediation will not successfully affect
the flow of contaminated groundwater, such as for
conditions where the water table is too deep to promote
groundwater and root interaction. Implementation of
phytoremediation at such sites will lead only to the impres-
sion that phytoremediation, as a whole, is not a defensible
technology. Second, inappropriate site-assessment activities
may lead to the installation of a remedial technology that
not only is more expensive but also may be less effective
than phytoremediation. Third, if site-assessment activities