Environmental Engineering Reference
In-Depth Information
the U.S. Coast Guard, and Tennessee Valley Authority.
The RTDF includes members from government, academia,
and industry. In their review, costs of pump-and-treat were
considered averaged annual costs, and because they were
ongoing projects, the NPV was not calculated. Rather, the
authors chose to compare costs as costs per year or costs per
1,000 gal of pumped groundwater (U.S. Environmental Pro-
tection Agency 2001).
As stated previously throughout this chapter, costs vary
and the remedial designs are often site specific. Of the 32
pump-and-treat sites evaluated, the total cost ranged from
$1,700,000 to $5,900,000 (in 2001 U.S. dollars). Annual
operating costs ranged from $180,000 to $770,000.
Although the USEPA looked at treatment costs of the
pumped water the life-cycle costs of each of the sites
evaluated as part of the USEPA report were not calculated
due to the need for site-specific information.
In some of the cases where pump-and-treat is occurring
but inefficiently, phytoremediation may not be the appropri-
ate substitute. A Superfund site at Fort Lewis, WA, provides
such an example. The remediation is near the Fort Lewis
Logistics Center. Extensive groundwater contamination by
chlorinated solvents was found in the shallow aquifer
beneath the property as well as in the shallow and deeper
aquifers offsite about 1 mi (1.6 km) downgradient, beneath a
town on the shores of American Lake (U.S. Geological
Survey 1998). In 1995, a pump-and-treat system was
completed in two areas of the site, and treated groundwater
is added back to the shallow aquifer. One well field was
installed in the source area, and one well field was installed
near the property boundary downgradient of the source area.
Because estimates of the amount of solvent spilled are near
110,000 lbs, groundwater pumpage is about 5 Mgal/day (204
million L/day). The contaminants removed from groundwa-
ter amounted to about 1,400 lbs, so it was estimated that
at least 78 years would be needed to remediate the plumes
(U.S. Geological Survey 1998).
In order to accelerate the remediation timeframe, alterna-
tive clean up technologies were offered, including
phytoremediation. This would be an impracticable alterna-
tive to pump-and-treat at this site for many reasons, and
these limitations are acknowledged (U.S. Geological Survey
1998). For example, up to 790 acres (3.1
Table 10.2
Life-cycle costs for pump-and-treat compared to
phytoremediation using a Net Present Value (NPV) cost comparison.
Horizontal
Plant-based
Extraction
Hydrologic barrier
Item
Cost
Item
Cost
R&D
$0
R&D
$110,000
Installation
$1,000,000
Installation
$200,000
$750,000
a
Operation and
Maintenance
Monitoring
Operation and
Maintenance
Monitoring
$45,000 year 1
$25,000 year 2
$80,000 year
3 to year 8
Total NPV
Cost
$1,603,000
$416,000
Cost Savings
(
$416,000)
$1,187,000
a
@$150,000/year for 5 year
Even when the NPV is used instead of the life-cycle
approach, the final answer as to whether or not
phytoremediation will be cost effective is not always clear.
As pointed out by Linacre et al. (2005), the uncertainties
inherent to a phytoremediation project can increase the
projected costs. A phytoremediation planting in similar to
an agricultural crop, subject to the whims of the weather.
Some of this uncertainty is common to most groundwater
remediation issues, due to the subsurface nature of these
types of projects. Given the additional fact that
phytoremediation systems are exposed at land surface,
increased uncertainty may occur as a result of threats from
storms, fire, and other forms of catastrophe.
One of the uncertainties of phytoremediation examined
by Linacre et al. (2005) was the future property value of
the land being remediated by either phytoremediation or by
an alternative technology. In relatively non-urban areas,
where the price of land is stable, the assumed lower price
of such land (as opposed to the price of urban land) relates
to a lower profit if the remediated land is sold, so the length
of time to clean up is of little relevance. In urban areas,
where the price of land may increase rapidly, the longer
period of time attributable to phytoremediation may render
it second choice relative to a more aggressive technology,
even if preliminary NPV calculations indicate that the
NPV would be positive with phytoremediation as the reme-
dial strategy.
The USEPA, members of the Federal Remediation
Technologies Roundtable (FRTR), and the Remediation
Technologies Development Forum (RTDF) analyzed the
costs for 32 pump-and-treat technologies at Superfund and
RCRA sites (U.S. Environmental Protection Agency 2001).
The FRTR includes members from the U.S. Departments
of Defense, Energy, and Interior, as well as the U.S. Envi-
ronmental Protection Agency, the Nuclear Regulatory Com-
mission, National Aeronautics and Space Administration,
10
6
m
2
)of
poplar trees would need to be planted if the goal was to
replace the mechanical pump-and-treat system. Although in
certain areas of the plume, especially in the shallow aquifer
near the source area (where the water table is between 4 and
12 ft below land surface), installation of a phytoremediation
system would not be detrimental to the pump-and-treat sys-
tem. In fact, phytoremediation could assist in the removal of
contaminated groundwater without the associated cost of
pumping, after the installation costs were recovered. The
Search WWH ::
Custom Search