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

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1600

0

1600

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1600

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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)

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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

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Thomas Metschies Department of Engineering and Radioprotection, Wismut GmbH

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