R-11-10 Bedrock Hydrogeology – Groundwater flow modelling Site investigation SFR Johan Öhman, Geosigma AB Sven Follin, SF GeoLogic AB Magnus Odén, SKB May 2013 Svensk Kärnbränslehantering AB Swedish Nuclear Fuel and Waste Management Co Box 250, SE-101 24 Stockholm Phone +46 8 459 84 00 ISSN 1402-3091 Tänd ett lager: SKB R-11-10 P, R eller TR. ID 1288394 Bedrock Hydrogeology – Groundwater flow modelling Site investigation SFR Johan Öhman, Geosigma AB Sven Follin, SF GeoLogic AB Magnus Odén, SKB May 2013 Keywords: Kravdatabas SFR-utbyggnad (N2-273). A pdf version of this document can be downloaded from www.skb.se. Abstract The hydrogeological model developed for the SFR extension project (PSU) consists of 40 geologically modelled deformation zones (DZ) and 8 sub-horizontal structural-hydraulic features, called SBA- structures, not defined in the geological model. However, some of the SBA-structures coincide with what is defined as unresolved possible deformation zones (Unresolved PDZ) in the geological model- ling. In addition, the hydrogeological model consists of a stochastic discrete fracture network (DFN) model intended for the less fractured rock mass volumes (fracture domains) between the zones and the SBA-structures, and a stochastic fracture model intended to handle remaining Unresolved PDZs in the geological modelling not modelled as SBA-structures in the hydrogeological modelling. The four structural components of the bedrock in the hydrogeological model, i.e. DZ, SBA, Unresolved PDZ and DFN, are assigned hydraulic properties in the hydrogeological model based on the transmissivities interpreted from single-hole hydraulic tests. The main objective of the present work is to present the characteristics of the hydrogeological model with regard to the needs of the forthcoming safety assessment SR-PSU. In concrete words, simulated data are compared with measured data, i.e. hydraulic heads in boreholes and tunnel inflow to the existing repository (SFR). The calculations suggest that the available data for flow model calibration cannot be used to motivate a substantial adjustment of the initial hydraulic parameterisation (assignment of hydraulic properties) of the hydrogeological model. It is suggested that uncertainties in the hydrogeological model are studied in the safety assessment SR-PSU by means of a large number of calculation cases. These should address hydraulic heterogeneity of deterministic structures (DZ and SBA) and realisations of stochastic fractures/fracture networks (Unresolved PDZ and DFN) within the entire SFR Regional model domain. SKB R-11-10 3 Sammanfattning En hydrogeologisk modell har tagits fram inom Projektet SFR Utbyggnad (PSU). Modellen består av 40 geologiskt modellerade deformationszoner (DZ), samt 8 subhorisontella strukturer, så kallade SBA-strukturer (Eng. Shallow Bedrock Aquifer structures), vilka inte ingår i den geologiska modellen. Några av SBA strukturerna sammanfaller emellertid med det som kallas för PDZ-intervall i den geologiska modellen (Eng. Unresolved Possible Deformation Zones). Vidare består den hydro- geologiska modellen av en stokastisk spricknätverksmodell (Eng. Discrete Fracture Network model; DFN), som är avsedd för att beskriva/modellera grundvattenflödet i berg massan mellan deformation- szoner och SBA-strukturer, samt en stokastisk sprickmodell för att hantera de PDZ-intervall som inte modelleras som SBA-strukturer. De fyra byggstenarna för att beskriva/modellera bergets egenskaper, dvs DZ, SBA, Unresolved PDZ och DFN, har i den hydro geologiska modellen tilldelats hydrauliska egenskaper baserat på de transmissivitetsdata som tolkats från hydrotester. Huvudsyftet med föreliggande rapport är att redovisa den hydrogeologiska modellens egenskaper med tanke på behoven i den kommande säkerhetsredovisningen SR-PSU. Resultat från olika flödesmodellberäkningar jämförs i denna rapport med uppmätta grundvattennivåer i borrhål och tunnelinflöden till befintligt förvar (SFR). Beräkningarna visar att befintliga mätdata för modellkalibrering inte kan åberopas för en justering av den hydrogeologiska modellens initiala parameterisering (tilldelning av hydrauliska egenskaper). För att hantera osäkerheter av strukturell-hydraulisk karaktär i den kommande säkerhetsanalysen SR-PSU föreslås därför att ett stort antal beräkningsfall studeras i syfte att identifiera tänkbara ytterlighetsfall. Beräkningsfallen bör studera hydraulisk heterogenitet hos determiniskt modellerade strukturer (DZ och SBA) samt realiseringar av stokastiska sprickor/spricknätverk (Unresolved PDZ och DFN) inom SFR:s regionaldomän. 4 SKB R-11-10 Contents 1 Introduction 7 1.1 Context 7 1.2 Scope of SDM-PSU and role the hydrogeological model 8 1.3 Objectives and strategy 8 1.4 Scales and volumes 8 1.5 Data used 10 1.6 Modelling tools 11 1.6.1 FracMan 11 1.6.2 DarcyTools 12 1.7 This report 12 1.7.1 Nomenclature 12 2 Methodology and assumptions made 15 2.1 Geology 15 2.2 Systems approach 15 2.3 Approach 16 2.3.1 Model Exercises investigating model performance 17 2.3.2 Transient simulation of interference tests 17 2.4 Alternative parameterisation methods 18 2.4.1 Tunnel inflow calibration 18 2.4.2 Borehole data parameterisation 18 2.5 Skin factor 19 2.6 Groundwater levels, heads and uniform-density flow 20 2.7 Overview of constraining head and inflow data 20 2.7.1 Measured head and evolution over time 21 2.7.2 Measured inflow over time 21 2.8 Hypotheses on transient coupled decreasing inflow and head 23 2.8.1 Estimation of initial inflow 24 3 Parameterisation of hydraulic model domains 25 3.1 Hydraulic Soil Domain (HSD) 25 3.1.1 HSD implementation in DarcyTools 26 3.2 Hydraulic Conductor Domain (HCD) 28 3.2.1 Merging the geological models for Forsmark-Lens and Forsmark-SFR 28 3.2.2 Data-based HCD parameterisation 28 3.2.3 HCD depth trend 29 3.2.4 Depth trend in ZFM871 32 3.2.5 Local borehole conditioning 32 3.3 Hydraulic Rock mass Domain (HRD) 34 3.3.1 Average HRD conductivity, KCPM 34 3.3.2 Upscaled HRD conductivity, KECPM 35 3.3.3 Hydro-DFN inside the SFR Regional domain 35 3.3.4 Hydro-DFN outside the SFR Regional domain 37 3.4 Specifically modelled structures 38 3.4.1 Sheet joints in the Forsmark lens 39 3.4.2 Truncation of the sheet joint structures 39 3.4.3 SBA (Shallow Bedrock Aquifer) structures in the SFR Regional domain 40 3.4.4 Unresolved Possible Deformation Zones 41 4 Numerical model setup in DarcyTools 45 4.1 Boundary conditions of the flow model domain 45 4.1.1 Vertical boundaries 45 4.1.2 Bottom boundary 45 4.1.3 Tunnels 45 4.2 Discretisation in DarcyTools 46 SKB R-11-10 5 4.3 Orientation of computational mesh in DarcyTools 46 4.4 Implementation of constraining data in DarcyTools 47 4.4.1 Spatial differentiation of tunnel inflow 48 4.4.2 Evaluation of simulated head 49 5 Model Exercises 51 5.1 M0: Average HRD conductivity (no HCD, HSD, or skin) 54 5.1.1 Observations 55 5.2 M1: HRD anisotropy (no HCD or skin) 56 5.2.1 Observations 57 5.3 M2: Anisotropy with HCD (no skin) 57 5.3.1 Observations 58 5.4 M3: Conditioning HCD and introducing skin 58 5.5 M4: Significance of SBAs for existing SFR 60 5.5.1 Observations 60 5.6 M5: Various modifications of M4b 60 5.6.1 Observations 60 5.7 M6: Optimisation of main flow paths 61 5.7.1 Outcome 63 5.8 M7: Stochastic SBA-structures in areas outside borehole coverage 64 5.9 Simulating initial tunnel inflow 64 6 Interference tests 67 6.1 Context and objectives 67 6.1.1 Hydraulic response measures 68 6.2 Presentation of data 68 6.2.1 Initial state 69 6.2.2 The HFR101 interference test 69 6.2.3 The KFR105 interference test 73 6.2.4 Data noise filtering 77 6.2.5 Structural inference 77 6.3 Model setup in FracMan 80 6.3.1 Modelled structures 81 6.3.2 Boundary conditions and parameterisation 83 6.3.3 Modifications to structure parameterisation 84 6.3.4 Simulated transient head decrease 85 6.4 Simulations 86 6.4.1 Initial state 86 6.4.2 The HFR101 test 87 6.4.3 The KFR105 test 89 6.5 Results 91 6.5.1 The HFR101 test 92 6.5.2 The KFR105 test 94 7 Flow for two different flow regimes 97 7.1 Model setup 98 7.2 Unsaturated conditions 98 7.3 Saturated conditions 103 8 Summary and conclusions 107 8.1 Model Exercises M0 to M7 107 8.2 Interference-test simulations 109 8.3 Recharge and discharge areas for two different flow regimes 109 8.4 Concluding remarks 110 References 111 Appendix A Revised transmissivity evaluation of HCD intercepts 113 Appendix B Stochastic representation of SBA-structures 123 Appendix C Presentation of Model Exercise results, M0 to M7 133 Appendix D Geometric input for DarcyTools model setups 163 6 SKB R-11-10 1 Introduction 1.1 Context The first stage of the underground facility SFR (final repository for low and intermediate level radioactive operational waste) was constructed and taken into operation in 1987. During 2008, SKB (the Swedish Nuclear Fuel and Waste Management Company) initiated an investigation programme for a future exten- sion of the existing SFR. The project managing the activities associated with extension of SFR is referred to as PSU. The extension of SFR is necessitated by the pending decommissioning of the closed nuclear reactors Barsebäck, Studsvik, and Ågesta, the additional amounts of operational waste associated with the extended operating time of the remaining nuclear power plants, as well as the future decommission of running nuclear power plants Oskarshamn, Forsmark, and Ringhals (SKB 2008). The overall purpose of the recent site investigation is to develop a Site Descriptive Model (SDM-PSU) for the bedrock volume hosting both the existing SFR as well as the planned extension (Figure 1-1).