6. Implementation Issues
6.1 Cost Observations
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 may not be
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 established themselves. This is usually beneficial
and, in our experience, the vegetation will shift with time to resemble the local vegetation.
Typical sampling and monitoring techniques used for tracking more aggressive treatments are of
little use for monitoring rhizosphere-enhanced remediation of contaminated surface soils. Data
are too heterogeneous for firm conclusions to be made. 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.
6.2 Performance Observations
Vegetative cover and sustained plant growth were obtained for the rhizosphere-treated plots.
Acceptance criteria for the demonstration were met as significant plant effects were observed.
Reasonably sophisticated analyses techniques are needed to show that treatments are having an
effect.
This technology was developed for use on surface soils at remote sites, where conditions limited
alternatives. There are no provisions for contaminant breakthrough, although the
evapotranspiration of the crop will reduce water available for leaching. In most situations, water-
soluble petroleum compounds, such as BTEX, will have already moved into lower horizons or
volatilized.
6.3 Scale-up
There are no engineering limitations involved in the move from demonstration-scale to full-scale
implementation of this technology. Full-scale use of the technology should be relatively easy to
initiate. Seeding and fertilization of larger areas will bring increased costs for materials and
labor, but the per-unit cost should go down due to economies of scale, and the techniques remain
the same as for the ESTCP demonstrations. The main cost issues involve the number of
monitoring samples to be taken and the types of analyses to be performed.
6.4 Other Significant Observations
This guidance is relatively complete for implementing this technology. Site-specific factors
include location, size, and available seed and fertilizer sources. Monitoring, including sample
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