Environmental Engineering Reference
In-Depth Information
such parties have to show limited site access or contaminant
containment.
In these regards, phytoremediation can be used to achieve
both of these requirements for the TI waiver, although con-
trol to the planted area, which could be considered an
“attractive nuisance” may need to be implemented. If
sources of contamination cannot be removed, for example
due to site restrictions, then plants can be added to decrease
the potential of leachate formation or extensive plume
development. This has been accomplished at coal-tar
contaminated sites in Tennessee (Widdowson et al. 2005a)
and South Carolina (see Chap. 13).
produced in such abundant quantities on account of fertilizer
application that any not taken up by the food crop unfortu-
nately ended up in the surface and groundwater.
An example of plants and sustainability is given by the
situation of groundwater use by humans and plants in the
western United States as introduced in Chap. 1. Discharge of
groundwater by phreatophytes in riparian corridors before it
reaches streams is considered consumptive use in such areas
and, therefore, had negative economic impacts on residents.
In a paper that compares sustainability to safe yield, Alley
and Leake (2004) describe a report by C.V. Theis that
indicated that the capture of groundwater by wells rather
than by phreatophytes would be an economic benefit. This
was especially true for areas that wanted to attract new
residents and growth. An equally valid stance once the
growth has been achieved, however, is that natural
greenspace or vegetated waterways have strong positive
economic attributes for recreation, quality of life, ecological
habitat, and current or future waste assimilation.
Alley and Leake (2004) also present an example of an
approach to determine the sustainability of groundwater use
in a basin in Nevada: drainage through Paradise Valley. In
this arid area, the basin-fill aquifer prior to development
received most of its recharge by surface-water leakage,
which was balanced by natural discharge by evapotranspira-
tion. A numerical model for the basin simulated the removal
of half the natural recharge (44 out of 91 cubic hecta meters
(hm
3
/year)) for up to 300 years. As could be expected, a
majority of this demand was met by a significant (72%)
reduction in evapotranspiration. The resultant effect on the
riparian vegetation was not simulated, but potential
consequences could be lower humidity and more turbid
surface water as the size of the riparian areas decreased.
At least 50% of the population of the United States relies
on groundwater to meet its daily water needs. Because most
people in the developed world need not fret about the quan-
tity of water they can access, issues of the water quality are
debated. The availability of water is a concern in arid areas
where aquifers are being mined and coastal areas where
saltwater contamination can render even productive aquifers
unusable. These scenarios all go back to the central issue
of sustainability; can we re-use water that becomes
contaminated as long as it is restored by a natural or
engineered process? Examples exist all over the United
States at Brownfield sites, where previously industrialized
sites are being remediated and developed. Groundwater can
be used to decontaminate wastes, much like rivers and
streams are allowed to while needing to meet, at the same
time, recreational and aquatic criteria. In most cases, how-
ever, the time for such assimilation to take place in ground-
water will be measured in years, rather than days.
Other aspects will affect the sustainability of phyto-
remediation over time relative to the costs associated with
16.5
Sustainability of Phytoremediation
and When to Stop
Generation of wastes is a consequence of all biological
systems. It also is common to all human cultures. The
removal of wastes at rates that do not allow accumulation
is unique to most civilized societies and often results in the
re-use of once-contaminated lands. The full potential,
in both non-economic and economic factors, of the
contaminated subsurface may be actualized. The restoration
of contaminated groundwater and its potential for re-use
comprise
part
of
the
larger
concept
of
resource
sustainability.
In general, sustainability consists of two major parts: use
of the resource while permitting no net degradation of the
resource, over time. The concept of no-net degradation can
apply to coastal aquifers under the threat of saltwater con-
tamination as population centers grow, to contaminated
groundwater in areas that may be developed, and for plant
use of water to sustain ecological niches in arid areas with
little surface water for drinking water or waste treatment. In
many early studies of such interactions, the term safe yield
was used, which is similar to the concept of sustainability.
It is interesting to note the general mindset that existed
prior to the onset of environmental restoration, and how it
fits in with recent conceptualizations of sustainability. For
most of even recent history, the most pressing problems that
humans had to solve were to acquire adequate water, food,
shelter, and resources. When waste did accumulate, it was
either burned or people moved to virgin land, as it was
readily available. As population centers increased in density
and space became a premium by the middle of the twentieth
century, technology provided some solutions to the
problems of food and shelter. This gave people the luxury
of being able to become concerned about the quality of the
water and food and shelter. The idea of moving to another
place to use those less contaminated resources became less
of an option as those areas had become inhabited by others
perhaps wanting to do the same thing. Food was being
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