ENVIRONET
Conceptual Site Model
Exercise
Peter Booth
Senior Technical Director
05/04/2011
Definition
The conceptual site model (CSM) can be seen as;
“A representation which sets out the critical pollutant linkages of concern for a
particular land contamination problem”
The CSM provides an understanding of what needs to be undertaken to
achieve risk management, and from this point appropriate remediation
techniques for any set risk management goals can be chosen.
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Source – pathway – receptor
• Source
The cause or source of the contamination is identified. For example, the
source might be a leaking tank or contaminated ground or water. The
location of the contamination is identified, such as in soils, ground or
surface waters.
• Pathway
The pathway is the route the source takes to reach a given receptor.
Pathways include, for example, air, water, soil, animals, vegetables and
eco-systems.
• Receptor
If contamination is to cause harm, it must reach a receptor. A receptor is a
person, animal, plant, eco-system, property or a controlled water. Each
receptor must be identified and their sensitivity to the contaminant must be
established.
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Source – pathway – receptor
• From the information above, a conceptual model is created displaying all
the sources, pathways and receptors. Conclusions are drawn about the
potential risks caused by the source of contamination. Conceptual models
are used to inform and drive site investigations and to assist with remedial
strategies.
• A pollutant linkage occurs when a source, pathway and receptor exist
together.
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The Conceptual Site Model (CSM)
•
The CSM is one of the primary planning tools that can be used to support the
decision making process in the management of contaminated land and groundwater.
•
The CSM organises available information about a site in a clear and transparent
structure and facilitates the identification of data and information gaps.
•
Once the CSM is established, additionally needed data can be gathered and
integrated within it. The CSM can then be revised and the decision goals can be
refined if necessary.
•
The CSM therefore matures and enables an improved understanding of the site
characteristics such as contaminant status and receptor profiles and the readjustment of the decision criteria.
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Where does CSM fit into the site investigation process?
• Site investigation work is expensive
• Before any expensive work is undertaken you need to collate all available
information through;
•
Desk studies.
•
Walk over surveys.
•
Interviews with previous site personnel.
• CSM produced
• Qualitative risk assessment undertaken
• If significant pollutant linkages occur there will generally be a requirement
for an intrusive site investigation.
• The CSM therefore helps drive the site investigation programme.
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Once the CSM is established it can be used to:
• Support the development of a framework for conducting and scoping a site
investigation of the site or the clean up action that takes into account any
future land use.
• Provide a detailed description of the site and its setting which can then be
used to form an understanding about the release and ultimate fate of
contamination at the site.
• Identify sources of contamination at the site, potential chemicals of concern,
and the media (soil, groundwater, surface water, structures) affected.
• Quantify how contaminants may be migrating from the sources and the
media and pathways through which migration and exposure of potential
human or environmental receptors could occur (including possible air
releases).
• Evaluate potential or preferred clean up options.
• Develop site specific sampling designs and procedures for sample
collection and analysis.
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Once the CSM is established it can be used to (cont’d) :
• Estimate site conditions that may lead to unacceptable risks and warrant
further study.
• By integrating permanently data and information to a CSM in a step wise
manner it achieves an increasing level of complexity.
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CSM Data Requirements
• Archaeological and historical use of the site area.
• Climatic data – precipitation rates, air temperature, prevailing wind speeds
and direction.
• Geology – sediment types, structural features, geomorphology.
• Hydrogeology
•
Aquifer characteristics
•
Hydrologic budget
•
•
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•
Recharge rates – precipitation, artificial recharge.
•
Discharge rates – evaporation, transpiration, groundwater pumping.
Groundwater flow
•
Hydraulic gradient – groundwater elevations, flow direction.
•
Flow velocity (travel time).
An example of a CSM
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An example of a CSM
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CSM exercise based on a fictitious site
• The aim of the exercise is to draw a conceptual site model similar to the
examples provided, but based on the information of a fictitious site
highlighted in the subsequent three slides.
• The conceptual site model should depict the site setting and show some
sources, pathways and receptors.
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The site and its setting
• The site measures approximately 5km2 and is located about 600m from a
coastline in the south.
• Two small villages lie within1km from the site, one to the east and one to
the west.
• A rail line runs through the side in an east-west direction adjacent to the
site’s southern boundary with a loading point on the site.
• The beach adjacent to the site is used for recreational purposes (including
people walking dogs, swimming, children playing.
• The site has up to 5000 workers on it at any time predominantly supporting
the site’s activities but additionally working on a number of construction
projects.
• The site lies in a region exhibiting above average rainfall levels.
• The coastal area adjacent to the site is well known for a number of
protected plants and animals.
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Site setting – geology and hydrogeology
• The site has a river crossing through it from north to south which flows into
the sea. This river contains a variety of fish.
• A slightly smaller river flows between the southern site boundary and the
coast from the west and flows into the first river before the latter itself flows
into the sea.
• The regional groundwater is being driven in a coastal direction from a range
of northerly lying hills.
• There are clear groundwater discharge points in the form of springs on the
beach. Contamination has been detected in water samples here.
• The site geology consists of sandstone bedrock overlain by a complex
sequence of glacial sediments consisting predominantly of a mixture of
sands, clays, and gravels. An easterly trending channel feature filled mostly
with gravels is thought to act as a preferential groundwater flowpath across
the site.
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Site setting – potential contaminant sources
• The site is authorised to discharge low levels of radioactive material into the
sea through a pipeline. This pipeline has a discharge point located about
500m out from the beach so discharges are always into the water rather
than on the beach or sands at low tide.
• The site has a number of ageing facilities which are known to be leaking.
• A number of old disposal trenches across the site have the potential to be
leaking.
• Waste materials are loaded and transported offsite via the rail link.
• Groundwater monitoring boreholes situated onsite, and outside the site
boundary towards the beach have detected some radionuclides.
• Some of the older groundwater monitoring boreholes may be acting as
preferential groundwater flowpaths and leading to cross contamination of
the geological aquifers.
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Additional Questions
• What are the primary contaminant sources on the site?
• Are there potential pathways for contamination to leave the site boundary?
• What are the key receptors for any residual or migrating contamination?
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Thank you for Listening - Any Questions?
Peter Michael Booth
Staff
Photo Here
Senior Technical Director
T. +44 (0) 161 886 2641
E. [email protected]
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