T 6.13.3 N E M U O C D Appendix 13.3: Hydrogeological Impact Assessment River Humber Gas Pipeline Replacement Project Under Regulation 5(2)(a) of the Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 April 2015 Application Reference: EN060004 Environmental Statement Volume 6 Environmental Statement Document 6.13.3 CONTENTS Tables ....................................................................................... iv  Figures ...................................................................................... v  DCO Documents Referenced .................................................... ix  Abbreviations ............................................................................ x  Glossary .................................................................................... x  EXECUTIVE SUMMARY .......................................................... xii  1  Introduction ....................................................................... 1  1.1  Scheme Description ................................................. 1  1.2  Scope of Works ........................................................ 2  2  The HIA Methodology ....................................................... 3  2.1  Introduction .............................................................. 3  3  Step 1: Establish the regional water resource status ........ 5  3.1  Catchment Abstraction Management Strategy (CAMS) status .......................................................... 5  3.2  Water Framework Directive status ........................... 5  3.3  Step 1 Outcome ....................................................... 6  4  Step 2: Develop a conceptual model for the abstraction and the surrounding area .................................................. 7  4.1  Regional conceptual model ...................................... 7  4.2  Site conceptual model ............................................ 10  4.3  Physical configuration of excavations ..................... 47  4.4  Reinstatement of the pits ........................................ 52  4.5  Groundwater Management ..................................... 53  4.6  Summary ................................................................ 54  4.7  Assessment of impacts from the tunnel .................. 60  4.8  Numerical model setup ........................................... 62  5  Step 3: Identify all potential water features that are susceptible to flow impacts ............................................. 65  5.1  Drive Pit .................................................................. 65  5.2  Reception pit .......................................................... 66  The River Humber Gas Pipeline Replacement Project Page i Environmental Statement Volume 6 Environmental Statement Document 6.13.3 6  Step 4: Apportion the likely flow impacts to the water features ........................................................................... 69  6.1  Groundwater abstraction flow rates ........................ 69  6.2  Baseflow impacts ................................................... 69  7  Step 5: Allow for the mitigating effects of any discharges, to arrive at net flow impacts ......................... 71  8  Step 6: Assess the significance of the net flow impacts .. 72  8.1  Drive Pit .................................................................. 72  8.2  Reception Pit .......................................................... 73  9  Step 7: Define the search area for drawdown impacts ... 75  9.1  Drive pit .................................................................. 75  9.2  Reception pit .......................................................... 76  10  Step 8: Identify all features in the search area that could be impacted by drawdown .............................................. 78  10.1 Introduction ............................................................ 78  10.2 Water features ........................................................ 78  11  Step 9: For all these features, predict the likely drawdown impacts .......................................................... 82  12  Step 10: Allow for the effects of measures taken to mitigate the drawdown impacts ....................................... 88  13  Step 11: Assess the significance of the net drawdown impacts ........................................................................... 93  13.1 Introduction ............................................................ 93  13.2 Derogation of existing abstractors .......................... 93  13.3 Environmental impacts on water bodies and wetlands ................................................................. 95  13.4 Settlement .............................................................. 97  14  Step 12: Assess the water quality impacts ................... 101  14.1 Discharge of abstracted groundwater ................... 101  14.2 Point sources ........................................................ 103  14.3 Diffuse pollution .................................................... 105  14.4 Dilution of poor quality surface water being adversely affected ................................................ 106  14.5 Saline intrusion ..................................................... 107  15  Step 13: If necessary, redesign the mitigation measures to minimise the impacts ................................................ 110  16  Step 14: Develop a monitoring strategy ........................ 111  16.1 Baseline monitoring .............................................. 111  16.2 Construction phase monitoring ............................. 111  16.3 Post-construction monitoring ................................ 111  17  Overall Summary .......................................................... 112  18  Bibliography .................................................................. 118  19  2D GROUNDWATER MODELLING ............................. 120  19.1 Introduction .......................................................... 120  19.2 Approach to 2D numerical modelling .................... 122  19.3 Scope and purpose .............................................. 122  The River Humber Gas Pipeline Replacement Project Page ii Environmental Statement Volume 6 Environmental Statement Document 6.13.3 19.4 Model setup .......................................................... 122  19.5 Distribution and properties of hydrogeological units124  19.6 Model boundaries ................................................. 124  19.7 Model calibration .................................................. 126  19.8 Results of numerical modelling............................. 127  20  Response to EA Comments.......................................... 132  20.1 HIA methodology .................................................. 132  The River Humber Gas Pipeline Replacement Project Page iii Environmental Statement Volume 6 Environmental Statement Document 6.13.3 Tables Table Title Table 3-1 Current status of Water Framework Directive parameters Table 4-2 Lithological descriptions of layers immediately above the Chalk Table 4-3 Estimates of hydraulic properties Table 4-4 Estimates of Storage Coefficient Table 4-5 Estimates of Coefficient of Compressibility (Mv) Table 4-6 Summary of groundwater level monitoring Table 4-7 Boreholes sampled for groundwater chemistry (Soil Engineering, 2014) Table 4-8 National grid references and elevations relative to ordnance datum for selected points along the tunnel based on Capita drawing ref. H160/BH/03/03/F9/101 Rev. A Table 4-9 Adopted hydraulic parameters used in the 2D model Table 6-10 Average groundwater abstraction flow rates for various scenarios Table 6-11 Modelled baseflow response to dewatering Table 6-12 Modelled baseflow response to dewatering Table 8-13 Summary of the Water Framework Directive assessment for East Halton Beck Table 8-14 Summary of the Water Framework Directive assessment for Thorngumbald Drain Table 10-15 Water features around the drive pit Table 10-16 Water features around the reception pit Table 11-17 Summary of drawdown effects around the drive pit Table 11-18 Summary of drawdown effects around the reception pit Table 12-19 Summary of mitigated drawdown effects around the drive pit Table 12-20 Summary of mitigated drawdown effects around the reception pit Table 13-21 Private water supplies and other potential abstractors around the drive pit Table 13-22 Private water supplies and other potential abstractors around the reception pit The River Humber Gas Pipeline Replacement Project Page iv Environmental Statement Volume 6 Environmental Statement Document 6.13.3 Table Title Table 13-23 Summary of mitigated drawdown effects around the drive pit Table 13-24 Summary of mitigated drawdown effects around the reception pit Table 13-25 Summary of settlement estimates Table 14-26 Summary of groundwater chemical analyses Table 19-27 Adopted hydraulic parameters used in 2D model Table 19-28 Model Setup – Boundary Conditions Table 19-29 Modelled drawdown - Drive Pit Table 19-30 Modelled Drawdown - Reception PIt Table 19-31 Average Dewatering flow rate (alternative scenarios) Figures Figure Title Tunnel long section showing vertical alignment Figure 1-1 based on Capita drawing ref. H160/BH/03/03/F9/101 Rev. A Schematic hydrogeological cross-section illustrating regional conceptual model (adapted Figure 4-2 from Entec, 2011) Location of ground investigation boreholes (Capita Figure 4-3 2014b) Geological cross section along the tunnel route Figure 4-4 (Capita 2014b) Summary borehole log descriptions around the Figure 4-5 drive pit (adapted from Capita 2014a; Soil Engineering, 2014) Particle size distribution plot for superficial Figure 4-6 sediments in boreholes L01, L02, L03 and L08 (Soil Engineering, 2014) Particle size distribution plot for superficial Figure 4-7 sediments in boreholes M12, M13, M14, M19 and M20 (Soil Engineering, 2014) Summary borehole log descriptions around the Figure 4-8 reception pit (adapted from Capita 2014a; Soil Engineering, 2014) Particle size distribution plot for borehole L15 from Figure 4-9 11.5 m to 33.5 m bgl (Soil Engineering, 2014) The River Humber Gas Pipeline Replacement Project Page v Environmental Statement Volume 6 Environmental Statement Document 6.13.3 Figure Title Summary borehole log descriptions for tidal flat Figure 4-11 deposits (adapted from Capita 2014a; Soil Engineering, 2014) Particle size distribution plot for tidal flat deposits Figure 4-12 from boreholes L04, L05 and L06 (Soil Engineering, 2014) Summary borehole log descriptions for borehole Figure 4-13 M01 to M04 (adapted from Capita 2014a; Soil Engineering, 2014) Summary borehole log descriptions for borehole Figure 4-14 M05 to M11 (adapted from Capita 2014a; Soil Engineering, 2014) Particle size distribution plot for estuarine alluvium Figure 4-15 from boreholes M01 to M04 (Soil Engineering, 2014) Particle size distribution plot for estuarine alluvium from boreholes M06 to M11 (Soil Engineering, Figure 4-16 2014) Chalk groundwater contours on the South Humber Figure 4-17 Bank (Entec, 2011) Chalk groundwater contours on the South Humber Figure 4-18 Bank (Entec, 2011) Chalk groundwater hydrograph at East Halton Figure 4-19 (data provided by EA) Chalk groundwater hydrograph at Saltend (data Figure 4-20 provided by EA) Figure 4-21 Groundwater levels near the drive pit Tidal variations in groundwater levels near the Figure 4-22 drive pit Figure 4-23 Groundwater levels near the reception pit Tidal variations in groundwater levels near the Figure 4-24 reception pit Chalk groundwater chloride concentration on the Figure 4-25 North Humber Bank (Gale and Rutter, 2006) Chalk groundwater chloride concentration on the Figure 4-26 North Humber Bank (Gale and Rutter, 2006) Piper diagram of groundwater in superficial Figure 4-27 deposits within boreholes near the drive pit Piper diagram of groundwater in superficial Figure 4-28 deposits within boreholes near the drive pit The River Humber Gas Pipeline Replacement Project Page vi Environmental Statement Volume 6 Environmental Statement Document 6.13.3 Figure Title Average chloride concentrations (mg/l) in Figure 4-29 boreholes near the drive pit (adapted from Capita 2014a, 2014b) Piper diagram of chalk groundwater in boreholes Figure 4-30 near the reception pit Piper diagram of groundwater in superficial Figure 4-31 deposits within boreholes near the reception pit Average chloride concentrations (mg/l) in Figure 4-32 boreholes near the reception pit (adapted from Capita 2014a, 2014b) Spot flows in a wet and dry period (taken from Figure 4-33 Entec 2011) Survey across drainage ditch near the drive pit Figure 4-34 (taken from Capita Drawing No. H160/BH/02/01/F9/102. Rev A) Survey across the Thorngumbald Drain and a drainage ditch near the reception pit (taken from Figure 4-35 Capita Drawing No. H160/BH/02/01/F9/101. Rev A) Figure 4-36 Proposed location of the drive pit Drive pit long section showing key features based Figure 4-37 on Capita drawing ref. H160/BH/03/03/F9/101 Rev. A Tunnel long section showing vertical alignment based on Capita drawing ref. Figure 4-38 H160/BH/03/03/F9/101 Rev. A Long section of the reception pit showing key Figure 4-39 features Long section of the reception pit showing key Figure 4-40 features Hydrogeological long section along the tunnel Figure 4-41 route Figure 4-42 Hydrogeological cross section through the drive pit Hydrogeological cross section through the Figure 4-43 reception pit Water features around the drive pit highlighting Figure 5-44 East Halton Beck Water features around the drive pit highlighting Figure 5-45 East Halton Beck The River Humber Gas Pipeline Replacement Project Page vii Environmental Statement Volume 6 Environmental Statement Document 6.13.3 Figure Title Groundwater velocity vectors during dewatering of Figure 5-46 the reception pit with the proposed groundwater control Water features around the reception pit Figure 4-47 highlighting Thorngumbald drain Modelled drawdown and radius of influence at Figure 9-48 Drive pit Drawdown response and indication of radius of Figure 9-49 influence at Reception pit (no engineering controls) Modelled drawdown and radius of influence at Figure 9-50 Reception pit Figure 10-51 Water features around the drive pit Figure 10-52 Water features around the reception pit Figure 11-53 Effect of dewatering on land drains – Drive Pit Figure 11-54 Effect of dewatering on land drains – Reception Pit Groundwater mounding response (up-hydraulic Figure 11-55 gradient) at drive pit Groundwater mounding response (up-hydraulic Figure 11-56 gradient) at reception pit Modelled drawdown with uniform lower Figure 12-57 permeability glacial deposits around the reception pit Figure 12-58 Effect of dewatering on land drains – Drive Pit Figure 12-59 Effect of dewatering on land drains – Reception Pit Figure 14-60 Landfill sites near the reception pit Figure 14-61 NVZs near the drive pit and reception pit Figure 14-62 NVZs near the drive pit and reception pit Effect of dewatering on saline interface (particle Figure 14-63 tracking) – no groundwater control Figure 19-64 Line of drive pit cross section model Figure 19-65 Line of reception pit cross section model General setup of 2D models, long section (top), Figure 19-66 drive pit cross section (middle), reception pit cross section (bottom) Figure 19-67 Calibration of groundwater levels The River Humber Gas Pipeline Replacement Project Page viii Environmental Statement Volume 6 Environmental Statement Document 6.13.3 DCO Documents Referenced DCO Title of Document Document Reference 6.8 Chapter 8: Geology and Soils 7.3 Initial Construction Environmental Management Plan The River Humber Gas Pipeline Replacement Project Page ix