Conceptual Site Modelling, Hydraulic and Water Balance … Site Modelling, Hydraulic and Water...
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Transcript of Conceptual Site Modelling, Hydraulic and Water Balance … Site Modelling, Hydraulic and Water...
Conceptual Site Modelling, Hydraulic and Water Balance Modelling as basis for the development of a remediation concept I Chemnitz, 04.12.2012
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Presentation outline
I Motivation
I From conceptual site understanding to modelling Conceptual model Water and load balance modelling Conceptual Site Models
I WISMUT case studies
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Motivation for a conceptual model
I Remediation of Uranium mining and milling legacy sites focusses on prevention of immediate and long-term hazards
Pre-exitisting situation, abandoned site Ensure safe closure of operation
I How will contaminant releases develop for various remediation options; what are potential long-term impacts?
I Reliable basis for decision on remediation measures needed: Information on contaminant potential Identification of driving processes for release and spreading Emission pathways, potential receptors Predictions for future conditions at the source, emissions and of
immisions
I Available information/ data vs. data needs Geology, Geochemistry, Geotechnics etc.
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Remediation Concepts for contaminated sites - Essentials I Identification and balancing of contamination source terms
Status quo and future development Evaluation of impacts (environmental, social ..)
I Optimisation of remediation solutions Definition of priorities technical and financial effort Highest possible effects by appropriate financial means Identification of technical and infrastructural needs
Remediation Solution (Environmental)
Impacts
Costs
Technology/ Infrastructure
„BATNEC“ Which reduction is reasonably achievable?
What technologies are available?
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Reoccurring Questions in Conceptual and Remedial Planning, Permitting, Project Implementation I Environmental Assessment
What are the dominating environmental impacts? What is the contribution of contaminant sources to the overall environmental impact? What are the processes and parameters controlling the loads of contaminants? Which uncertainties have the largest impact on the performance of remediation measures?
I Monitoring What measurements are most significant and at which points? How to proof effectiveness of measures (parameters, location)?
I Remedial Planning / Optimisation / Project Execution What level of remedial costs is justified compared to the impacts? How do specific remedial measures affect the contaminants release processes and environmental impact?
Reliable predictions require appropriate tools!
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Define purpose
Conceptual model
Mathematical model
Model design
Calibration *
Verification
Data base
• Geology
• Hydrogeology
• Hydrochemistry
• Topography
• Hydrology
• ...
Modelapplication/ Prediction *
Presentation of results
Postaudit
* Includes sensitivity analyses
Compilation and Interpretation of
Field data
Code selection
General Sequence of Modelling
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Conceptual Model
I Pictoral representation of
an environmental system including physical, chemical and biological processes and data that determine release and spreading (groundwater flow and transport)
I Abstraction and schematisation of influential parameters I Documentation of main system characteristics and
behaviour, including summary of available information and data for the site
• Structure and parameters • boundary conditions • Migration pathways, Receptors
historical site information, present status
I Determines prediction method, dimensions of (numerical) model and grid design – Top-Down-Approach
precipitation infiltration
Waste rock pile Tailings pile Water
treatment seepage
aquifer
Recieving stream
Well field
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Conceptual model - chart of development Scope of the task,
area of investigation
Assessment, collection and compilation of data
Evaluation of data, regionalisation
Development of the conceptual model
Validation of the conceptual model
Sufficient representation
To much simplified ?
purpose, time, costs
topography, hydrology, geology, hydraulics,
hydrochemistry
Field measurements, estimations
balance area, model area, hydrostratigraphic formations, parameters
boundary conditions
yes
no
yes
no (numerical) Model
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Modelling software for water- and contaminant transport, Geotechnics (used at WISMUT) I Groundwater hydraulic (FEFLOW, MODFLOW, SPRING)
Saturated/ Unsaturated (Hydrus 2d) I Water balance of cover layers (HELP, BOWAM)
Waste rock pile and tailings ponds covers I Contaminant release and transport
Tracer transport or use of reaction isotherms (FEFLOW, MT3D) reactive transport (PhreeqC)
I Specific codes for prediction of contaminant release (source term)
Problem and site specific solutions (FLOODING, TEN3D): • Box models with approximation of hydraulic conditions and
geochemical processes Analytical approaches
I Consolidation models (CONSOL2D, PLAXIS, FSConsol) Porewater release (combined with settlement predictions)
I Site Models (GoldSim), integration of site specific information and detailed model results
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Water and load balances – object specific focus
I precondition for technical planning e.g. cover design
I Optimisation of the infiltration rate
I Determination of surface runoff
I Evaluation of Contaminant release from pile
Mass balances Estimation of Mass fluxes
aquifer
P ETR
RO
RH
seepage
RU
∆S
P=ETR+RO +RH +RU +∆S
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Water and load balances – site specific focus
Water collection system Gessental
Upstream load
e-423 well 2
Pore water wells Culmitzsch A
Surface and seepage waters
Consolidation pore water
Wipse
Culmitzsch
Wei
ße E
lste
r
Diffuse discharge (via Aquifer)
Surface and seepage waters
Ronneburg mining site
Seelinstädt tailings deposition site e-423
Salt-concentration and hardness in Weiße Elster river
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CaO
9891 15
735
1634
0
1654
9
1700
0
2000
0
1800
0
1700
0
1600
0
1600
0
1600
0
1600
0
1700
03966
3621
3431
3206 42
00
4100
8200
8200
7200
7200
6200
5200
4000
0
5000
10000
15000
20000
25000
30000
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
annu
al lo
ad [t
]
Seelingstädt
Ronneburg
Load Balances as basis for management decision on catchment scale
Qmin(Greiz)=3,5 m/s [time series 2008]
0
10
20
30
2010 2012 2014 2016 2018
hardness Limit 19 °dH
1. Estimation of load balances 2. Hydraulic scenario of stream discharges 3. Analysis of critical scenarios Management Decision
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Purpose of site modelling – Conceptual Site Models
I Integration of knowledge about a remediation site with Complex hydraulic, geochemical, geotechnical conditions various contaminant sources
• e.g. tailings ponds, waste rock piles, mine workings variety of relevant processes
• contaminant mobilisation and release • Hydraulic and geochemical conditions along flow path
Different modelling results • Variety of models (numerical, analytical, simple estimations) • Different aspects (geotechnical, geochemical, hydraulic..)
I Modelling tool (e.g. GoldSim)
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Remediation Oriented Use of Conceptual Site Models (CSM) I Conceptual Site Model Approach (CSM) used for
Remediation oriented Performance Assessment • Evaluation of particular remedial measures • Predictions in a complex system with various influencing factors
(hydrogeology, geochemistry, operational issues) Environmental and Risk Assessment
• Proof of future compliance with dose and release limits • Optimisation based on variable parameters
Support of Strategic Project Decision Making • Scenario calculations to compare various remediation options
concerning relevant effort and impacts • Multi-Attribute Analysis • Cost-Benefit-Analysis
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CSM approach Data collection and site characterisation
(Data base)
Quantification in detailed models
(parameterisation, interfacing, boundary conditions, initial conditions / history matching)
Integration in Conceptual Site Model (CSM)
(mass balance, interfacing with / import of results from detailed models, time integration)
Performance / Risk assessment
Uncertainty/sensitivity analysis varying assumptions
Conceptualisation
Risks (radiological, stability,..), pathways (transport mechanism), socio-economic aspects, costs (short and
long term)
Ope
rativ
e fe
edba
ck
To a
nd fr
om m
onito
ring
and
rem
edia
l pla
nnin
g,
Des
ign
of p
oten
tial s
ite s
peci
fic re
med
ial m
easu
res
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Conceptual Site Model
Regional Hydraulic Model
DetailedModels
Process model (mine flooding)
Transport Model
Regional flow field
Boundary conditions
Dominating processes
Concentrations, loads
Conceptual Site Model
Regional Hydraulic Model
DetailedModels
Process model (mine flooding)
Transport Model
Regional flow field
Boundary conditions
Dominating processes
Concentrations, loads
Examples for the implementation of the CSM-approach
I Remediation of mill tailings piles at the Seelingstädt site
Integration in one model application
I Deep mine Flooding at the Königstein site
Combination of various modelling tools with clearly defined interfaces
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Advantages of CSM Approach I Top-Down approach:
Consequent quantification • processes driving the overall system performance (esp. mass
balances) Consistency among the various types of data
• very different time and spatial scales Focus on questions to be answered
• processes and parameters dominating the task to be resolved I Open Model Structure:
Combination of completely different types of process models (different levels of detail) Model development in phases Well defined interfaces with detail models Site discretisation into smart compartments
• provides spatial flexibility without compromising on essential details I Meaningful results obtained for complex sites
Based on limited data available Reasonable effort, time and cost saving