Biomedical Engineering Reference
In-Depth Information
regarding the phase distribution of bacterial populations of interest, sampling of aquifer solids
is optional.
Groundwater samples for
Dhc
analysis should be collected from the source area(s)
and downgradient plume locations where biodegradation products may have been observed
or are anticipated, and where geochemical conditions are favorable for anaerobic bioremedia-
tion. Wells should produce sufficient water for adequate purging and appropriate sample
quantities. Well screen depths and lengths should be considered when selecting a sampling
location. Utilize wells installed for establishing vertical profiles of contaminant (i.e., chlorinated
ethenes) concentrations to establish a similar profile for
Dhc
distribution. Discrete sampling
zones in intervals with dechlorination daughter products (i.e., DCEs, VC) are preferred for
Dhc
analysis. However, sampling in zones without dechlorination daughter products can be useful
to establish baseline conditions prior to bioaugmentation. Wells with extended screens used for
injection of substrates (e.g., electron donor) or bioaugmentation culture may be considered for
sampling immediately following bioaugmentation to confirm the presence and abundance of
the injected culture, but should not be used for monitoring performance of the bioremediation
system because there may be artificially elevated concentrations of
Dhc
surrounding these
injection points.
6.4 MBT SAMPLING METHODS
6.4.1 General Sampling Considerations
Groundwater sampling methods for microbial analysis typically are the same as those
established for evaluating groundwater chemistry. Selecting a sampling method for MBT
analyses depends on a number of site-specific conditions including sampling depth, well
construction, and aquifer permeability, as well as historic site data and regulatory require-
ments. Groundwater sampling for subsequent biological analysis can be done using a variety of
purging and sampling devices, and applicable procedures have been described (reviewed in
Yeskis and Zavala,
2002
). The ultimate goal of these procedures, as with sampling approaches
for chemical analyses, is to generate a sample representative of the formation groundwater in
the vicinity of the well.
Geochemical and contaminant stratification within a screened interval is affected by
seasonal changes (e.g., rain events, temperature changes) and can lead to variations in bio-
marker abundance, which in turn may confound data interpretation (Stroo et al.,
2006
).
Such environmental influences on sample quality should be considered when developing a
sampling strategy and when evaluating MBT data. Appropriate cover is recommended
to protect sample equipment, samples and field personnel from influences such as direct
sunlight or rain.
This section describes two different procedures for sample collection following well
preparation (e.g., purging and surging). The first procedure relies on collecting groundwater
for off-site laboratory filtration and biomass collection, whereas the second involves on-site
collection of biomass by field filtration or retrievable media devices (RMDs). For analyzing
DNA biomarkers, each of these approaches provide valuable information (Ritalahti et al.,
2010
); however, on-site filtration using Sterivex
™
cartridges has several advantages. The
cartridges (Figure
6.2
) are easy to ship, it is easy to add nucleic acid preservatives to stabilize
biomarkers, and depending on the aquifer characteristics, larger volumes of groundwater can
be collected and filtered. In addition, bottle breakage and disposal of contaminated groundwa-
ter in the analytical laboratory are avoided. The primary advantage of laboratory filtration is the
reduced effort in the field.
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