ESTCP Project #1011, Rhizosphere
Final Report
For comparing rhizosphere-enhanced remediation to other treatments it is important to look at
both the decrease in total petroleum hydrocarbons (TPH) and how the different components in
the petroleum are changing--i.e., the composition of the contaminant. Using a biomarker
approach, we have demonstrated the benefits of the rhizosphere system, and the results agree
with laboratory findings
For potential DoD use in low-cost treatment, the goal may be to show that the treatment is
working, but not really to compare it to other treatments. The biomarker approach is very
beneficial for monitoring changes because it helps to vitiate the oddities of wildly varying
contaminant concentrations caused by uneven or heterogeneous contaminant distribution. The
biomarker approach looks at changes in contaminant composition rather than concentration.
Depending on installation arrangements with the chemical laboratory that you are working with,
one can obtain concentration data as well as composition data.
Again, monitoring depends on site needs, but composition or biomarker data are very
informative and will better characterize the processes than the standard TPH analysis.
6.4.6 Costs
The greatest cost for rhizosphere-enhanced bioremediation typically is in sampling and
monitoring, and that is specific to the frequency of sampling, the type of analysis done, and cost
of analysis per sample. The transport, spreading, seeding, and fertilizing are essentially one-time
costs, although some re-seeding may be needed annually, and even some watering may be
beneficial during seedling establishment. Annual fertilizer can be added but is probably not
necessary. Again, this is specific to the site and the goals. We have found that in year two (and
even the first season); many volunteer plants tend to establish themselves. This is usually
beneficial and, in our experience, the vegetation will shift with time to resemble the local
vegetation.
7. References Cited in this Report
Donnelly, P.K., and J.S. Fletcher. 1994. Potential use of mycorrhizal fungi as bioremediation
agents. pp. 93-99. In T.A. Anderson and J.R. Coats (ed.) Bioremediation through
rhizosphere technology. Am. Chem. Soc., Chicago, IL.
Leigh MB, Fletcher JS, Fu X, Schmitz FJ. 2002. Root turnover: an important source of microbial
substrates in rhizosphere remediation of recalcitrant contaminants. Environ Sci Technol.
36(7):1579-83.
Pivetz, B. E. 2001. Phytoremediation of Contaminated Soil and Ground Water at Hazardous
Waste Sites. EPA Ground Water Issue. EPA/540/S-01/500, US Environmental Protection
Agency. (available at http://www.epa.gov/ada/download/issue/epa_540_s01_500.pdf)
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