ESTCP Project #1011, Rhizosphere
Final Report
5.2 Cost Analysis
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 obtaining more
meaningful data and reducing variability include composite samples, fraction specific
hydrocarbon analysis (FSH), biomarker normalization, and temperature normalization.
Monitoring using these tools and for a longer time but with greater intervals between sampling
times emerged as a reasonable monitoring plan.
6. Implementation Issues
6.1 Environmental Checklist
An up to date list of guidance documents and permits for oil-contaminated soil in Alaska is
provided by the Alaska Department of Environmental Conservations (ADEC) at:
http://www.state.ak.us/dec/landhome.htm
6.2 Other Regulatory Issues
To gain acceptance by the regulatory community, field data must demonstrate the effectiveness
of phytoremediation under conditions that can be applied to potential full-scale treatment sites
(Rock and Sayre, 1999). A primary purpose of these ESTCP demonstrations was to collect and
evaluate data that is relevant to many cold-region cleanup sites. During the early phase of the
demonstration, interactions with regulatory officials and RTDF members highlighted the
challenges in monitoring these sites. In Alaska, regulations regarding use of low-cost
remediation strategies are evolving and are, to a degree, subject to the interpretation of the front-
line regulator. Earlier regulations concerning sampling frequency and protocols were developed
to address more aggressive treatment technologies, such as incineration or biotreatment in a
mixed bioreactor. Sampling requirements, which have typically been one grab (non-composited)
sample for each 50 cubic yards (cy) of treated soil, are being modified to better describe surface
soils and less aggressive treatment techniques. For more passive systems, such as rhizosphere-
enhanced treatment, where the soil is not mixed during treatment, grab samples are not as
appropriate as they are for well-mixed systems. Our sampling plan addressed this issue by taking
both grab and composite samples, as well as soil-sock samples, at described intervals. Recently,
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