Environmental Engineering Reference
In-Depth Information
The ability to remove large masses of contaminant in a relatively short
time is attractive to both regulators and stakeholders, who might be reluctant
to support an extremely long natural attenuation option for the duration of
natural DNAPL dissolution (assuming that natural attenuation processes are
functioning in a sufficiently protective manner). It is also attractive to respon-
sible or potentially responsible parties who might otherwise have no options
other than expensive long-term and energy-intensive pumping-and-treating
operations for containment. The in situ treatment train approach improves
on either natural attenuation or enhanced bioremediation in the DNAPL
scenario by both removing large masses of DNAPL and reducing toxicity
for long-term biological processes to operate on the dissolved contaminants.
There are also disadvantages to the SERB technology, as there are for
any remediation scheme:
The technique is innovative and remains to be proven at sites having
a variety of characteristics.
Both cosolvent and surfactant in situ floods have the potential and
are implemented to mobilize or dissolve the contaminants. If hydro-
dynamic control is inadequate, the potential exists for contaminating
larger volumes of the aquifer and the groundwater.
The cosolvent flood itself will probably not reduce contaminant con-
centrations to the needed regulatory requirements; hence, a success-
ful residual biotreatment phase is very important.
The choice of cosolvent is critical for both the solvent extraction and
residual biotreatment phases of the technique, and success or failure
can depend upon this choice. Laboratory studies must be considered
before going to field scale.
There is considerable regulatory resistance to the injection of foreign
materials (e.g., cosolvents) into the groundwater, which may require
a significant effort and large amounts of documentation and persua-
sion to overcome.
The residual biotreatment phase of SERB might still take a very long
time to come to completion following the cosolvent flooding phase,
depending upon the conditions created and the mass of contaminant
remaining.
Recommendations for transitional research include:
Additional pilot-scale and full-scale demonstrations
Further characterization of shifts in microbial ecology in response to
SERB
Evaluation of mixtures of optimal cosolvent/electron donor solutions
Modeling of impact of source removal on long-term economics for
site-remediation costs
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