petroleum almost certainly simply volatilized. Users of products need to know the test conditions
in addition to the marketing data and presentations. Because we usually are not able to identify
the sequence of limiting nutrients at a site without a series of treatability studies, and the cost of
conducting these studies is usually greater than the benefit gained from them, applying an
appropriate level of fertilizer may be as important as using a proprietary fertilizer. Our
demonstrations were successful with the use of standard agricultural fertilizer.
Monitoring is a challenge. Although implementation costs are low, large areas can be treated,
and minimal infrastructure is needed, rhizosphere-enhanced remediation relies on a series of
relatively complex biological processes. Spatial variability of contaminants in surface soils is
inherent, and using monitoring techniques that are appropriate for more aggressive technologies
will probably provide little useful data.
Although there can be a rhizosphere benefit for essentially all petroleum compounds, the benefits
of rhizosphere-enhancement are most observable for recalcitrant compounds, such as PAHs. We
have seen this in our laboratory studies, in the field in Alaska, and also at demonstration trials
Korea.
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. Useful
tools for reducing variability and obtaining more meaningful data include composite samples,
fraction specific hydrocarbon analysis (FSH), biomarker normalization, and temperature
normalization. Using these tools for a longer time but with greater intervals between sampling
times emerged as a reasonable monitoring plan.
6.6 End-User Issues
End users at each site participated largely by agreeing to allow a technology demonstration to be
conducted at their site. Due to more knowledgeable staff, changed attitudes, more experience,
and resource constraints, regulators in some areas, including Alaska, have become more open to
low-cost approaches in recent years.
Although we have shown that this technology is more effective than the controls or than adding
only fertilizer, we are still unable to predict the time necessary for a site to reach target
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