Conceptual Site Modelling, Hydraulic and Water Balance Modelling as basis for the development of a remediation concept. Chemnitz,

Transcription

1 Conceptual Site Modelling, Hydraulic and Water Balance Modelling as basis for the development of a remediation concept I Chemnitz,

2 2 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

3 3 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.

4 4 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 Costs BATNEC Technology/ Infrastructure Remediation Solution (Environmental) Impacts What technologies are available? Which reduction is reasonably achievable?

5 5 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!

6 6 General Sequence of Modelling Compilation and Interpretation of Field data Define purpose Conceptual model Mathematical model Data base Geology Hydrogeology Hydrochemistry Topography Hydrology... Code selection Model design Calibration * Verification Modelapplication/ Prediction * Presentation of results Postaudit * Includes sensitivity analyses

7 Conceptual Model precipitation infiltration Well Waste field rock pile Tailings pile Water treatment seepage Recieving stream 7 aquifer 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

8 8 Conceptual model - chart of development Scope of the task, area of investigation purpose, time, costs no Assessment, collection and compilation of data Evaluation of data, regionalisation topography, hydrology, geology, hydraulics, hydrochemistry balance area, model area, hydrostratigraphic formations, parameters boundary conditions To much simplified? yes Development of the conceptual model Validation of the conceptual model Field measurements, estimations no Sufficient representation yes (numerical) Model

9 9 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

10 10 Water and load balances object specific focus I precondition for technical planning e.g. cover design P S ETR R O R H I Optimisation of the infiltration rate I Determination of surface runoff seepage R U I Evaluation of Contaminant release from pile Mass balances Estimation of Mass fluxes P=ETR+R O +R H +R U + S aquifer

11 11 Water and load balances site specific focus Salt-concentration and hardness in Weiße Elster river Ronneburg mining site e-423 Water collection system Gessental well 2 Surface and seepage waters e-423 Weiße Elster Wipse Seelinstädt tailings deposition site Diffuse discharge (via Aquifer) Surface and seepage waters Pore water wells Culmitzsch A Consolidation pore water Culmitzsch Upstream load

12 12 Load Balances as basis for management decision on catchment scale 1. Estimation of load balances 2. Hydraulic scenario of stream discharges 3. Analysis of critical scenarios Management Decision annual load [t] CaO Seelingstädt Ronneburg Limit 19 dh hardness Q min (Greiz)=3,5 m/s [time series 2008]

13 13 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)

14 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 14

15 15 CSM approach Data collection and site characterisation (Data base) Conceptualisation Risks (radiological, stability,..), pathways (transport mechanism), socio-economic aspects, costs (short and long term) 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 Operative feedback To and from monitoring and remedial planning, Design of potential site specific remedial measures

16 16 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 Conceptual Site Model Detailed Regional Models Hydraulic Model Dominating Boundary processes conditions Process model (mine flooding) Concentrations, loads Regional flow field Transport Model

17 17 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

18 22 Thank you for your attention! Glückauf Thomas Metschies Department of Engineering and Radioprotection, Wismut GmbH