system. We believe that carbon additions, and most likely analog enrichment, are a major part of
the success of rhizosphere treatments in well-drained soils. In wet, generally anaerobic soils,
carbon accumulates rather than being respired as carbon dioxide (CO2), and soil carbon is
probably not limiting. Therefore, root additions of carbon may not result in increased
biotreatment rates.
The ultimate application is to be able to add appropriate nutrients and seed to a contaminated site
and have reasonable assurance, based on defensible data, of the treatment rates and endpoints.
For sites in cold regions, implementing rhizosphere-enhanced treatment may significantly
increase treatment rates, thereby reducing treatment times. The degree of improvement likely
depends on the growing season length and the recalcitrance of the compound. Although we have
demonstrated relatively short treatment times of one to three summers in some situations, in
other situations the benefit may be that significant treatment is accomplished in five to ten years
rather than not at all.
2.5 Available Treatability Guidance
Key limitations to using rhizosphere-enhanced remediation include lack of scientifically
defensible data and uncertainty in predicting treatment times. Although efforts to provide
treatability guidance have been developed and are being updated, there are few examples of
well-documented field studies published. Below are some documents that provide overviews of
phytoremediation.
Brownfields Technology Primer: Selecting and Using Phytoremediation for Site Cleanup.
Published: 2001. http://www.clu-in.org/download/remed/phytoremprimer.pdf.
This primer explains the phytoremediation process, discusses the potential advantages and
considerations in selecting phytoremediation to clean up brownfield sites, and provides
information on additional resources about phytoremediation. This document is not limited to
rhizosphere remediation of petroleum in surface soils. Although treatability studies are
suggested, specific information on treatability studies is not provided. A general overview of the
many mechanisms potentially involved in phytoremediation is included and useful information
on plant selection based on rooting depth.
Phytoremediation Decision Tree, Published: 1999.
http://www.clu-in.org/download/partner/phytotree.pdf.
This document was produced by the Interstate Technology Regulatory Cooperation (ITRC)
workgroup. The intent of this document is to provide a tool that can be used to determine if
phytoremediation has the ability to be effective at a given site. It is designed to compliment
existing phytoremediation documents. It allows the user to take basic information from a specific
site and, through a flow chart layout, decide if phytoremediation is feasible at that site. In its
discussion of phytoremediation of organics, rather than specifically petroleum, the ITRC
Phytoremediation Decision Tree document recommends first using the decision tree to assess if
phytoremediation is a viable option, and then conducting treatability studies. These studies are
described as growing a variety of plants proposed for use in a range of concentrations, to assess
the fate of the contaminant, especially for transpiration losses, and to evaluate if desired results
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