BIOAUGMENTATION WITH DEHALOCOCCOIDES: A DECISION GUIDE - Bioaugmentation for Groundwater Remediation - page 121

reducing environment. Highly aerobic sites are defined as sites with DO > 2 mg/L throughout,
low levels of reduced metals (particularly dissolved iron and manganese), and no evidence of
significant anaerobic zones within the target treatment volume that can serve as reservoirs of
competent Dhc .

4.7 WILL BIOSTIMULATION WORK?
The testing used to evaluate biostimulation includes both laboratory diagnostic tests and
field testing methods. The available laboratory analyses and tests are summarized in Table 4.1
and in the following section. Field testing techniques are discussed in Section 4.7.2 .

Table 4.1 Key Diagnostic Analyses Available to Assess the Need for Bioaugmentation
Analysis Advantages Limitations Interpretations

> 10 6 Dhc/L -
Bioaugmentation likely
not needed

Dhc 16S rRNA Specific for Dhc

Rapid results
Relatively low cost

Some Dhc are not capable of
complete dechlorination
Possible sample bias or
inhibitory materials

> 10 5 vcrA or bvcA/L -
Bioaugmentation likely
not needed

VC reductase
genes

Specific for key
detoxifying step in
reductive
dechlorination
Rapid results
Relatively low costs

Not all VC reductive
dehalogenase genes
(RDases) have been
identified

Ethene/ethane Proof of complete

dechlorination

Can be degraded
anaerobically or aerobically
Low levels may be generated
by inefficient cometabolism

10% of original VOCs -
Bioaugmentation likely
not needed

>

Compound
specific isotope
analysis (CSIA)

Can provide conclusive
proof that
biodegradation is
occurring in situ

Limited availability
May require added cost, time
and significant volumes
of water for analysis

Fractionation changes in VC
prove complete
biodegradation
Biodegradation rates
estimated from changes
in fractionation along a
plume

Laboratory
microcosms

Very strong evidence
for or against the
need to bioaugment
in the field

Requires additional cost and
time (6-12 months)
May require aquifer solids and
groundwater for accuracy

Ethene production within
12 months -
Bioaugmentation likely
not needed
Lack of ethene and Dhc
< 10 5 /L - Bioaugmentation
likely necessary

In situ
microcosms

Very strong evidence
for or against the
need to bioaugment
in the field

Requires additional cost and
time (usually
1-2 months)
Well microenvironment may
not reflect in situ
conditions

Ethene production within
2 months -
Bioaugmentation likely
not needed
Lack of ethene and Dhc
< 10 5 /L - Bioaugmentation
likely necessary

Note: rRNA-ribosomal ribonucleic acid