Biomedical Engineering Reference
In-Depth Information
how well RMD data represent the natural microbial populations. Ultimately, the selection of
sample collection procedure is dependent on site-specific data objectives.
Traditional “well volume” groundwater sampling methods involve bailers or high speed
pumps (
500 mL/min) to purge 3-5 well casing volumes prior to collecting groundwater
samples. Alternatively, low-flow purging methods (100-500 mL/min) with a peristaltic or
submersible bladder pump are generally recommended to collect groundwater samples for
volatile organic compounds (VOCs) and/or geochemical analysis (Puls and Barcelona,
1996
).
Whether using traditional “well volume” methods or “low-flow” methods, it is imperative that
the same protocol be applied for every sampling event and for each sampling location in an
event. These approaches also apply to microbial (e.g.,
Dhc
) sampling, which should occur after
geochemical parameters have stabilized.
Surging the monitoring well with a surge block or disposable bailer can increase particulate
matter in the sample and recovery of associated (i.e., attached) biomass. However, if field
filtration is used for on-site biomass collection, excess sediment in the filter material can impact
the DNA extraction process in the laboratory and inhibit subsequent analytical techniques.
Additionally, the presence of excess sediment can restrict the flow of groundwater through the
filter and may clog a filter prior to collection of adequate sample volume.
Low-flow purging and sampling methods typically can be completed in 1-2 h per well, and
field filtration using Sterivex
™
cartridges will add approximately 30 min per well. Volume
requirements for MBT analysis of a single sample are generally about 1 liter (L) for laboratory
filtration and 1-3 L for field filtration.
Since the stability of microbial biomarkers is of concern, it is important to maintain sample
integrity through all of the sample handling and shipping procedures. Aseptic techniques should
be employed to the extent possible when handling groundwater samples destined for biological
analysis. Preservation of samples through use of chemical additives can help minimize chemical
and biological changes within a sample; however, current laboratory-recommended procedures
typically specify no chemical preservative additions. Collected samples (i.e., bottles filled with
groundwater and/or Sterivex
™
cartridges) should be maintained at 4 degrees Celsius (
C) and
shipped, with appropriate packaging to prevent breakage, for overnight delivery to the analyti-
cal laboratory.
Innovative sampling techniques are being developed, such as cryogenic collection of
“complete” subsurface core samples (i.e., water plus aquifer solids). By collecting a complete
core with direct push technology, this technique promises to improve the accuracy of MBT data
for planktonic and attached microbes and provide an opportunity to evaluate small scale
features in subsurface samples (Johnson,
2007
).
Microbial surrogates have been developed and tested for use as quality control methods.
Such surrogates could be added to samples at the time of sampling, or prior to nucleic acid
extraction in the field or laboratory (Lebr
´
n et al.,
2008
). Adding appropriate surrogates can
allow for quantitative assessments of potential biases throughout the process from sampling,
shipping, storage and analysis. Such biases may include microbial growth due to prolonged
storage at warm temperatures prior to analysis.
>
6.4.2 Groundwater Sampling Protocol
The following protocol provides a step-by-step approach that can be used for groundwater
sampling during bioaugmentation monitoring (also see Figure
6.4
). Methods may vary accord-
ing to site-specific conditions; however, it is crucial that the sampling protocol for a given well
(or site) be defined and maintained for the duration of the monitoring efforts. Changes to the
protocol during monitoring will complicate data interpretation and should be avoided.
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