WATER ENVIRONMENT 9 CONTENTS INTRODUCTION ........................................................................................................................... 9-1 METHODOLOGY .......................................................................................................................... 9-1 Report Context ....................................................................................................................................... 9-1 Data Sources ........................................................................................................................................... 9-2 Assessment Methods .............................................................................................................................. 9-3 SITE SETTING AND DESCRIPTION .................................................................................................. 9-4 Location .................................................................................................................................................. 9-4 Current Quarry Workings and Proposed Extension ................................................................................ 9-4 Topography ............................................................................................................................................. 9-5 Soils… ...................................................................................................................................................... 9-5 Hydrology ............................................................................................................................................... 9-5 Geology ................................................................................................................................................... 9-7 Hydrogeology.......................................................................................................................................... 9-9 Environmental Setting .......................................................................................................................... 9-11 PROPOSED DEVELOPMENT ........................................................................................................ 9-16 Overview ............................................................................................................................................... 9-16 Mineral Extraction and Processing ....................................................................................................... 9-16 Slate Reject Tipping .............................................................................................................................. 9-17 Quarry Water Management and Drainage ........................................................................................... 9-17 Restoration ........................................................................................................................................... 9-20 HYDROGEOLOGICAL IMPACT ASSESSMENT ................................................................................ 9-20 Assessment Methodology .................................................................................................................... 9-20 Hazard Identification ............................................................................................................................ 9-21 Receptor and Pathway Identification.................................................................................................... 9-21 Risk Assessment .................................................................................................................................... 9-22 Risk Analysis and Mitigation ................................................................................................................. 9-24 FLOOD CONSEQUENCES ASSESSMENT ........................................................................................ 9-27 Flood Zones .......................................................................................................................................... 9-27 Vulnerability of Development ............................................................................................................... 9-27 WATER ENVIRONMENT 9 Existing Flood Risk ................................................................................................................................. 9-27 Summary of Potential Flood Risk .......................................................................................................... 9-29 CONCLUSIONS ........................................................................................................................... 9-29 WATER ENVIRONMENT 9 INTRODUCTION Envireau Water has been instructed by Breedon Southern Limited to prepare a Hydrogeological Risk Assessment (HRA) and Flood Consequences Assessment (FCA) as art of the EIA to support a planning application. As noted from Chapters 1 and 3 above, the planning application is for a small lateral extension to the slate workings, together with the ancillary deposit of quarried waste and overburden, at Penrhyn Quarry. 9.1 In November 1947, Penrhyn Quarry was granted permission for “proposed tipping and quarrying development” for producing slate products. In November 1994, registration of the quarrying activities was granted by Gwynedd County Council (Ref. 3/16/456 and NP 3/17/27) under the planning and Compensation Act 1991. Subsequently, planning permissions C96A/0020/16/MW and C08A/0039/16/MW were granted on 19th January 2000 and 9th June 2008, respectively, for an extension to the quarry and variations to existing conditions. Following this, a proposed realignment of quarry workings was applied for and subsequently granted on 18th December 2012 under planning permission C12/0874/16/MW. 9.2 The proposed extension is contiguous with and located at the north-western corner of the existing quarry. Notably, the extension would be wholly within the confines of the area covered by planning permission C12/0874/16/MW (dated 18 December 2012) granted for a “proposed extension and realignment of slate extraction operations with a progressive scheme of restoration”. 9.3 The proposed extension will be worked in an identical fashion to the current workings, for which a comprehensive working scheme was approved in 2017 as part of a review under the Environment Act 1995 (the ‘Review of Mineral Permissions (ROMP) review’ planning application ref. C16/1164/16/MW). The extension would form a logical progression from the previous extension to the workings (planning permission ref. C12/0874/16/MW), expanding the workings along the north-western side of the quarry. 9.4 The basis of this assessment is a hydrological and hydrogeological appraisal of the proposed extension area for the dewatering operations, giving consideration to potential impacts to water dependent environmentally sensitive features. This report also includes a flood consequence assessment relating to the proposed extension area. METHODOLOGY Report Context 9.5 The report combines published regional and local data and the results of intrusive site investigations, and comprises the following: Penrhyn Quarry – Volume 2A Page 9-1 WATER ENVIRONMENT 9 • A review of the baseline hydrology, geology and hydrogeology around the proposed extension area; • Identification of surface water and groundwater features in proximity to the proposed extension area; • The proposed development plan and proposals for water management and drainage throughout the proposed quarry extension area within the context of the quarry; • A Hydrogeological Risk Assessment (HRA) following the principals outlines in the technical framework for groundwater risk assessment set out in Groundwater protection: Principles and practice (GP3) [Ref. 1] and the risk assessment methodology set out in DEFRA’s Green Leaves III (GL III) [Ref. 2]; together with proposals to mitigate hydrogeological risk, where required; and • A Flood Consequences Assessment (FCA) prepared in accordance with the Technical Advice Note (TAN) 15: development and flood risk dated July 2004 [Ref. 3]. Data Sources 9.6 The following data sources were used in this assessment: Natural Resources Wales • Licensed and deregulated water abstractions; • TAN 15: Development and Flood Risk – Development Advice Maps; • Surface Water Flood Risk Maps; • Groundwater Source Protection Zones (SPZs); • Discharge permits; and • Landfill sites. Ordnance Survey • OS Explorer Maps 1:25,000 and 1:50,000 scale. British Geological Survey • Geological map, 1:50,000 scale, Sheet 106 (Bangor); • Onshore GeoIndex; • Borehole and water well records; and Penrhyn Quarry – Volume 2A Page 9-2 WATER ENVIRONMENT 9 • Physical properties of major and minor aquifers in England and Wales. Natural England • MAGIC Map application (Protected sites and water dependent features). Gwynedd Council • Registered Private Water Supplies (PWS). Centre for Ecology and Hydrology • Flood Estimation Handbook (FEH) Web-Service. SLR Consulting Ltd/GWP Consultants Ltd • Topographical data for Penrhyn Quarry and the proposed extension area; • Site investigation reports and development plans. Envireau Water • Review of Old Mineral Permissions at Penrhyn Quarry, Bethesda, Gwynedd: Hydrogeology, Hydrology, Water Quality, Drainage and Flood Risk [ref. P:\WS Penrhyn HIA (1736)\ROMP HIA r3.docx by Envireau Water and dated May 2015] [Ref. 4]. Assessment Methods 9.7 Current hydrological and hydrogeological conditions have