Environmental Engineering Reference
In-Depth Information
A consequence of phytoremediation is the production of
biomass, the raw material similar to that produced by the
short rotation wood culture industry. The ability to recover
some of the initial costs of plant installation at a
contaminated site makes phytoremediation an attractive
remedial option compared to a more engineered solution.
The revised interest in using biomass to produce fuels or as a
source of carbon sequestration also makes phytoremediation
more attractive as an exit strategy for when the goals of a
phytoremediation system have been accomplished.
areas. If removal is warranted, where materials are to be
transferred to offsite areas for disposal, the procedure must
follow Superfund regulations. During onsite corrective
actions, Applicable or Relevant and Appropriate
Requirements (ARAR) are determined to meet site-specific
goals. Contaminated media is determined to be hazardous if
it meets the criterion specified under RCRA legislation
enacted in 1976. Once a material is deemed to be hazardous,
it must be tracked from removal to disposal to limit the
possibility of release to other areas of the environment.
Specific information on various other regulations such as
the Clean Air Act, Clean Water Act, Safe Drinking Water
Act, and the Toxic Substances Control Act is beyond the
scope of this topic.
10.1.5 Laboratory and Greenhouse Studies
Due to the wide variety of terrain and soils across the United
States, the question is raised about the transferability of
results of poplar tree growth at one site relative to applica-
tion at another site. The same tree may have a wide tolerance
for changes in soil salinity but be very sensitive to air
temperature changes. Before considerable expense is
encountered, it is reasonable to examine the effect of such
variables on plant growth and water use using controlled
experiments in the laboratory or greenhouse.
10.2.1 Time Required to Reach Hydrologic
Control
The hybrid poplars widely used at sites characterized by
contaminated groundwater are fast-growing phreatophytes,
but they require time for roots to reach the water table and
for the
LAI
to increase transpiration to affect groundwater
uptake under closed-canopy conditions. Similarly, at most
sites groundwater flow is slow, and flow rates are usually
100 ft/year (30 m/year) or less. In fact, it may take a few
years to achieve demonstrable results in relation to the
interaction of plants with groundwater. In general, this can
take from 3 years (Eberts et al. 1999) to 4 years (Landmeyer
2001). Because the goal of groundwater cleanup or control is
to reach the remedial goals in as short a time as possible, the
use of phytoremediation may not be the first choice for all
sites when viewed from the perspective of the regulatory
community.
Computationally simple models exist to determine the
time necessary for contaminants in groundwater to be
remediated using phytoremediation, as outlined in Burken
and Schnoor (1998) and Schnoor (1997). The benefit of the
computational ease of these models, however, is at the cost
of the simplifying assumptions that need to be made, such as
constant groundwater contaminant concentrations, steady-
state plume distribution, and lack of microbial biodegrada-
tion. To summarize, the uptake of organic contaminants
dissolved in water by plants can be described by:
10.2
Regulatory Factors That Affect
Implementation of Phytoremediation
Contaminated sites require cleanup to maintain compli-
ance with state or Federal laws and regulations. Although
responsible parties and remediation professionals can pro-
pose a wide range of remedial activities for the restoration
of a particular site, the remedial strategies used must be
approved by state and Federal agencies. These guidelines
for appropriate (legal) actions affect all aspects of site
remediation, from cradle to grave, or from site characteri-
zation to treatment installation to waste disposal. Each
component of site remediation is regulated under a sepa-
rate law.
Most wastes released to the environment deemed to have
the potential to cause harm to humans or wildlife are
regulated under CERCLA or RCRA. CERCLA, enacted in
1980, is more commonly known as Superfund because of the
magnitude of time and money that must be spent at many
sites under its enforcement. The power of CERCLA was
extended under amendments made in 1986 through the
Superfund Amendments and Reauthorization Act (SARA).
In sum, these regulations are designed to ensure that the
most appropriate remedial activity (corrective action or
removal) is performed at a site listed under Superfund
oversite and that it will not endanger human health or the
environment nor lead to the spread of contaminants to other
U
¼ð
TSCF
Þð
T
Þð
C
Þ
(10.1)
where
U
is the uptake rate of the contaminant (M/T);
TSCF
is the transpiration stream concentration factor, an expres-
sion that accounts for the variable uptake efficiency by
plants for different contaminant compounds (dimensionless)
(Burken and Schnoor 1997) that is described in Chap. 12;
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