GEOTECHNICAL & ENVIRONMENTAL CONSULTING GEOTECHNICAL ENVIRONMENTAL WYG ENVIRONMENTAL LTD. MAYTON WOOD QUARRY ENVIRONMENTAL PERMIT APPLICATION Stability Risk Assessment Report GEC NO: GE200243006 Geotechnical and Environmental Ltd 10 Seven Acres Road, Weymouth, Dorset. DT36DG Tel: +44 (0)800 0407051 www.geosure.co.uk GEOTECHNICAL & ENVIRONMENTAL CONSULTING WYG ENVIRONMENTAL LTD. MAYTON WOOD QUARRY ENVIRONMENTAL PERMIT APPLICATION Stability Risk Assessment GEC NO: GE200240610 Document History: Reference: GE20024/SRA/V1 Date of Issue Document Description Prepared 30/11/2020 Stability Risk Assessment Dr David Fall CGEOL FGS GEOTECHNICAL AND ENVIRONMENTAL CONSULTING LTD., 10 Seven Acres Road, Weymouth, Dorset. DT3 6DG. Telephone: +44 (0)800 0407051 www.geosure.co.uk GE200240610 i Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd GEOTECHNICAL & ENVIRONMENTAL CONSULTING CONTENTS 1.0 INTRODUCTION 1 2.0 STABILITY RISK ASSESSMENT 9 3.0 MONITORING 18 LIST OF TABLES Table SRA1 Local Stratigraphy of the Application Area 3 Table SRA2 Groundwater Strikes during the Construction of the Boreholes 3 Table SRA3 Groundwater Monitoring Data 4 Bibliography of Published Sources used in the Determination of the Table SRA4 7 Characteristic Geotechnical Parameters of the Inert Waste Table SRA5 Side Slope Subgrade Stability – Summary of Characteristic Geotechnical Data 11 Table SRA6 Side Slopes Liner Stability – Summary of Characteristic Geotechnical Data 11 Table SRA7 Waste Mass Stability - Summary of Characteristic Geotechnical Data 11 Table SRA8 Partial Factors used in Design in Accordance with the UK National Annex to 12 EC7 Table SRA9 Side Slope Subgrade Stability – Summary of Results 13 Table SRA10 Side Slope Liner Stability – Summary of Results 14 Table SRA11 Waste Mass Stability – Summary of Results 15 LIST OF FIGURES Figure SRA1 Cross-Sections Through Side Slope Subgrade 6 LIST OF APPENDICES Appendix 1 SlopeW Worksheets Side Slope Subgrade Appendix 2 SlopeW Worksheets Side Slope Liner Appendix 3 SlopeW Worksheets Waste Mass GE200460610 - ii - Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd GEOTECHNICAL & ENVIRONMENTAL CONSULTING 1.0 INTRODUCTION Report Context 1.1 The operator of the installation is Mick George Ltd. (MGL). 1.2 WYG Environmental Ltd. (WYG) have instructed Geotechnical & Environmental Consulting Ltd. (GEC) to undertake a Stability Risk Assessment (SRA) to form part of an Environmental Permit Variation Application for Mayton Wood Quarry. 1.3 This environmental permit application is for the permanent placement of inert material within the void formed by the extraction of minerals. 1.4 The following documents and drawings have been supplied by the Client and referred to in the compilation of this Report:- • Mayton Wood Quarry, Environmental Permit Application, Environmental Setting and Site Design – WYG Report No A116126 dated November 2020. • Mayton Wood Quarry Extension Groundwater Protection and Hydrogeological Impacts – TerraConsult Report No. 10152-RO5 dated June 2019. • Mayton Wood Quarry, Environmental Permit Application – Operating Techniques - WYG Report No. A116126 dated November 2020. • Mayton Wood Quarry Extension Geotechnical Design Report – TerraConsult Report No. 10152-RO6 dated November 2020. 1.5 This Report has been completed in conjunction with the Environmental Setting and Site Design Report (ESSD) (June 2018). It is not a standalone document and factual data related to the site, its setting and receiving environment are located in the ESSD and referred to in this document. All drawings referred to in this SRA are to be found in the ESSD unless otherwise stated. 1.6 This document has been prepared in accordance with the Stability Risk Assessment Report Template (Version 1 – March 2010). Conceptual Stability Site Model Location 1.7 This Stability Risk Assessment refers to the area that is included within the Environmental Permit Application boundary shown on Drawing No MGL/A116126/PER/01 of the Environmental Setting and Site Design Report and covers the area known as Mayton Wood Quarry Extension. GE200240610 1 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd GEOTECHNICAL & ENVIRONMENTAL CONSULTING 1.8 The application site is located approximately 700m to the west of the hamlet of Little Hautbois in Norfolk and approximately 12.6km NNE of the centre of Norwich. The centre of the site is located at NGR 624200,320969. 1.9 The application site comprises three fields to the south of the existing Mayton Wood Quarry site which are currently in agricultural use and are separated by hedgerows. The proposed facility will cover an area of approximately 32.2ha and is on gently north easterly sloping terrain (17mAOD to 15mAOD) towards the River Bure. Regional Geology Solid Geology 1.10 With reference to British Geological Survey Sheet 147 Alysham1:50000 Sold & Drift, the Application site is underlain by the Wroxham Crag Formation overlying units of the White Chalk Group which are up to 300m thick. 1.11 The BGS Lexicon of Named Rock Units describes the Wroxham Crag Formation a sheet of interbedded gravels, sands, silts and clays. The gravels are dominated by flint (up to c.80%) and by quartz and quartzite (up to c.60%), with far-travelled minor lithologies. The deposits are interpreted as being of estuarine and near-shore marine origin, Superficial Geology 1.12 The geological map records superficial deposits across the site comprise the Happisburgh Glaciogenic Formation. 1.13 The Happisburgh Glaciogenic Formation consists of a range of diamictons, sands and gravels, sands and laminated silts and clays. The diamictons (Happisburgh Till, Corton Till and California Till members) are typically sandy matrix-supported diamictons that contain a high abundance of flint and quartzose lithologies Structural Geology 1.14 No structural features are shown within the area of the permit application boundary. Local Geology 1.15 14No. boreholes have been undertaken within the site area and reported in the Hydrogeological Risk Assessment. A precis of the stratigraphy encountered in these boreholes is presented as Table SRA1. Table SRA1 Local Stratigraphy of the Application Area Stratigraphy Topsoil Sand & Gravels * Whi te Chalk Grou p Borehole No. From Thickness From Thickness From Thickness (mbgl) (m) (mbgl) (m) (mbgl) (m) GE200240610 2 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd GEOTECHNICAL & ENVIRONMENTAL CONSULTING TerraConsult Borehole s 2016 BH1 GL 0.25 0.25 8.55 8.80 >6.70 BH2 GL 0.25 0.25 6.25 6.50 >7.50 BH3 GL 0.30 0.30 4.50 4.80 >5.70 BH4 GL 0.30 0.30 8.20 8.50 >2.50 BH5 GL 0.50 0.50 8.50 9.00 >3.00 BH6 GL 0.50 0.50 7.00 7.50 >4.50 BH7 GL 0.90 0.90 7.80 8.70 >3.30 BH8 GL 0.90 0.90 7.10 8.00 >5.00 MGL 2018 BH9 GL 3.70** 3.70 7.80 11.50 >7.00 BH10 GL 0.40 0.40 6.50 6.90 >14.10 MGL 2014 BHA Not Recorded (in GL 7.60 7.60 >7.40 quarry area) BHB Not Recorded (in GL 4.60 4.60 >11.40 quarry area) BHC GL 0.60 0.60 4.60 5.20 >10.30 BHD Not Recorded (in GL 5.70 5.70 9.30 quarry area) *Insufficient detail on borehole logs to allow discrimination between the Happisburgh Glaciogenic Formation and the Wroxham Crag Formation **Probable Made Ground 1.16 The borehole logs indicate the local ground conditions comprise up to 0.90m of Topsoil over 4.50 TO 8.55m of sands and gravels with units of the White Chalk Group forming the basal unit of the ground investigation. In BH9 3.70m of probable Made Ground was reported. 1.17 The major diagnostic feature used to discriminate between the Happisburgh Glaciogenic and Wroxham Crag Formations is the presence of exotic lithologies in the Wroxham Crag Formation. The level of description in the TerraConsult engineering logs is insufficient to make this differentiation; therefore, the two strata will be combined for the purposes of this SRA. There is sufficient similarity between the two materials to have no noticeable effect on the results of the side slope subgrade assessment. Hydrogeology 1.18 Groundwater was encountered during the installation of the 8No. boreholes (Table SRA 2) overleaf Table SRA2: Groundwater Strikes during the Construction of the Boreholes Borehole Water Strike Strata Description ID mbgl BH1 13.50 Structureless light brown /cream Chalk BH2 12.00 Structureless light brown yellowish gravelly Chalk GE200240610 3 Mayton Wood Quarry Stability Risk Assessment WYG Environmental Ltd GEOTECHNICAL & ENVIRONMENTAL CONSULTING Borehole Water Strike Strata Description ID mbgl BH3 6.70 Structureless light brown / dark cream slightly gravelly Chalk BH4 9.00 Structureless light brown / cream Chalk BH5 9.00 Structureless light brown / yellowish cream Chalk BH6 8.50 Structureless light brown / yellowish cream slightly gravelly Chalk BH7 8.55 Structureless light brown / yellowish cream Chalk BH8 9.70 Structureless very light brown / creamy yellow Chalk BH9 15.30 Structureless white putty Chalk BH10 15.80 Chalk with Flints BHA 10.70 White flinty Chalk BHB 10.70 White flinty Chalk BHC 12.00 White flinty Chalk BHD 10.80 White flinty Chalk 1.19 Groundwater strikes occurred at all locations and were consistently located within the White Chalk Group thus ensuring that dry working conditions will be maintained, as these boreholes were drilled during October and January when groundwater elevations are close to being at their maximum. 1.20 Groundwater monitoring has been undertaken in all boreholes since their construction. The range of groundwater depths recorded are presented in Table SRA 3. Table SRA 3: Groundwater Monitoring Data BH ID BH1 BH2 BH3 BH4 BH5 BH6 BH7 Minimum Depth (mbgl) 11.54 11.20 6.36 7.46 7.46 10.14 11.85 Maxim um Depth ( mbgl) 13.04 13.53 8.95 9.20 8.69 10.55 12.74 Mean Depth (mbgl) 12.29 12.45 7.66 8.33 8.08 10.35 12.30 BH ID BH8 BH9 BH10 BHA BHB BHC BHD Minimum Depth (mbgl) 10.36 12.47 11.94 9.80 9.37 10.94 10.54 Maximum Depth (mbgl) 12.17 11.88 11.28 8.09 8.19 7.97 8.73 Mean Depth (mbgl) 11.27 12.08 11.56 9.21 9.14 9.24 9.70 1.21 According to the MAGIC website the application site is underlain by both a Secondary B and Principal Aquifers (the Chalk).