BIOAUGMENTATION WITH DEHALOCOCCOIDES: A DECISION GUIDE - Bioaugmentation for Groundwater Remediation - page 130

Stakeholder input and concerns often are important when determining whether the time
required for optimal performance will be acceptable. In the case of bioaugmentation decisions,
the fundamental point is that if adaptive management is relatively easy, biostimulation is a more
attractive alternative. If managers have an effective relationship with the regulators and public,
adaptive management can be easier to implement. For example, there may be much less need for
certainty regarding the eventual performance if there is an atmosphere of trust. Conversely, at
sites where the relationship has deteriorated, it may be more costly to wait for several months
prior to bioaugmentation because of the additional monitoring and testing that may be required.
At many sites, the lag time will be a relatively unimportant factor. Waiting 12-18 months
after the first electron donor injection before the onset of measurable complete dechlorination
may be of little concern and less expensive than an unneeded bioaugmentation treatment.
There are many long-term, relatively passive in situ bioremediation systems that will need very
infrequent reinjections, such as edible oil biobarriers injected into low-strength plumes at sites
that pose little risk or public concern. In such cases, it may be prudent to bioaugment only after
the monitoring data demonstrate a failure to attain remedial objectives despite otherwise
favorable conditions for long periods of time.
4.9 IS THE RISK OF EXPOSURE TO TOXIC
INTERMEDIATES UNACCEPTABLE?
Human health and environmental risks can play a critical role in bioaugmentation
decisions. The key question is whether the risks of a temporary or long-lasting accumulation
of more toxic byproducts - particularly VC - are acceptable. Incomplete dechlorination for
some period of time may be of little concern if the concentrations are sufficiently low, or if
there is no open exposure pathway. The exposure pathways of potential concern include public
contact with groundwater, surface water exposures, indoor air vapor intrusion and even
outdoor air exposure from shallow groundwater with little vapor attenuation.
Biostimulation, particularly when used for source zone remediation, is designed to enhance
the dissolution of chlorinated compounds. Treatment therefore can lead to an increase in the
mass discharge from the source zone and possible plume expansion (ITRC, 2005 ). It also will
alter the contaminant distribution so that the plume may pose a greater risk to receptors
exposed to the groundwater or vapors released from the groundwater.
If accumulation of partial dechlorination daughter products represents a potential risk to
human health or the environment, then bioaugmentation as a method to reduce the potential or
duration of such accumulations becomes a more attractive alternative. In some cases, tempo-
rary accumulations of daughter products may not increase the health hazards or environmental
risks, but still may be unacceptable from a regulatory or public perception perspective.
Therefore, addressing the risks of partial dechlorination will sometimes require considering
the interests of other stakeholders as well as technical factors.
4.10 ECONOMIC ASSESSMENTS OF BIOAUGMENTATION
An economic assessment of the benefits of bioaugmentation is worth doing at any site,
unless it is clear from the existing data that bioaugmentation is not necessary. As a first
approximation, the detailed cost assessments presented in Chapter 11 should be consulted.
These assessments, done for three template site scenarios, concluded that bioaugmentation
increased the capital costs for an in situ bioremediation system by roughly 10-12%, which
represented an increase of roughly 1-3% in the life cycle costs of the remedy. For example,
Krug et al. (Chapter 11) calculated an additional cost of $8,000 to bioaugment a source zone 250