Establishing the location of the Source Area BioREmediation (SABRE)
research cell was a primary objective of the site characterisation
programme. This bulletin describes the development of a two-stage site
characterisation methodology that combined qualitative and
quantitative data to guide and inform an assessment of dense nonaqueous
phase liquid (DNAPL) distribution at the site.
DNAPL site characterisation has traditionally involved multiple phases of
site investigation, characterised by rigid sampling and analysis
programmes, expensive mobilisations and long decision-making
timeframes (Crumbling, 2001a) , resulting in site investigations that are
costly and long in duration. Here we follow the principles of an
innovative framework, termed Triad (Crumbling, 2001a, 2001b;
Crumbling et al., 2001, Crumbling et al. 2003), which describes a
systematic approach for the characterisation and remediation of
contaminated sites. The Triad approach to site characterisation focuses
on three main components: a) systematic planning which is
implemented with a preliminary conceptual site model from existing
data. The desired outcomes are planned and decision uncertainties are
evaluated; b) dynamic work strategies that focus on the need for
flexibility as site characterisation progresses so that new information can
guide the investigation in real-time and c) real-time measurement
technologies that are critical in making dynamic work strategies
possible.
Key to this approach is the selection of suitable measurement
technologies, of which there are two main categories (Crumbling et al.,
2003). The first category provides qualitative, dense spatial data, often
with detection limits over a preset value. These methods are generally of
lower cost, produce real-time data and are primarily used to identify site
areas that require further investigation. Examples of such "decisionquality"
methods are laser induced fluorescence (Kram et al., 2001),
membrane interface probing (McAndrews et al., 2003) and cone
penetrometer testing (Robertson, 1990), all of which produce data in
continuous vertical profiles. Because these methods are rapid, many
profiles can be generated and hence the subsurface data density is
greatly improved. These qualitative results are used to guide the
sampling strategy for the application of the second category of
technologies that generate quantitative, precise data that have low
detection limits and are analyte-specific. These methods tend to be high
cost with long turnaround times that preclude on-site decision making,
hence applying them to quantify rather than produce a conceptual
model facilitates a key cost saving. Examples include instrumental
laboratory analyses such as soil solvent extractions (Parker et al., 2004)and water analyses (USEPA, 1996). Where these two categories of
measurement technologies are used in tandem, a more complete and
accurate dataset is achieved without additional site mobilisations.
The aim of the site characterisation programme at the SABRE site was to
delineate the DNAPL source zone rapidly and identify a location for the
in situ research cell. The site characterisation objectives were to; a) test
whether semi-quantitative measurement techniques could reliably
determine geological interfaces, contaminant mass distribution and
inform the initial site conceptual model; and b) quantitatively determine
DNAPL source zone distribution, guided by the qualitative site
conceptual model
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