Glyn Rhonwy Pumped Storage Development Consent Order Appendix 8.5 Zetica (2015) UXO Desk Study Report Project No. P3300-12 Project Title SITESAFE UXO DESK STUDY Project Location Glyn Rhonwy, Llanberis, Gwynedd Client Quarry Battery Report Ref. P3300-12-R1-C Report Date 12th May 2015 Prepared by Clark Friend Checked by Stefan Lang Authorised by Mike Sainsbury CONTENTS Page Executive Summary 1 INTRODUCTION 14 1.1 Project Outline 14 1.2 Report Structure 15 2 THE SITE 16 3 SOURCES OF INFORMATION 18 3.1 Historical Information 18 3.2 Zetica Ltd Defence Related Site Records 18 3.3 Zetica Ltd Bombing Density Records and Maps 18 3.4 Ministry of Defence and Government Records 18 3.5 Other Historical Records, Maps and Drawings 19 3.6 Local Authority Records 19 3.7 Local Record Offices and Libraries 19 3.8 Local Historical and Other Groups 19 3.9 Data Confidence Level 19 4 SITE HISTORY 20 4.1 General History 20 5 SITE OPERATIONS 31 5.1 RAF Llanberis Ordnance Depot 31 5.2 Ordnance Disposal at RAF Llanberis 35 5.3 Other Sources of UXO 39 6 EXPLOSIVE ORDNANCE CLEARANCE ACTIVITIES 41 6.1 No. 71 MU EOD Operation, 1969-1975 41 6.2 Post-1975 UXO Discoveries 56 6.3 Residual UXO Hazard 57 6.4 Radioactive Contamination 57 7 ANTICIPATED ORDNANCE TYPES 58 8 UXO HAZARD ASSESSMENT 64 8.1 UXO Hazard Level 64 9 UXO RISK ASSESSMENT 69 9.1 UXO Risk Register 69 Zetica Ltd – Report No. P3300-12-R1-C 1 9.2 Risk Management Recommendations – Ground Investigation 71 9.3 Risk Management Recommendations – Future Works 72 Appendices Appendix 1 Overall Clearance Summary Appendix 2 Abbreviations Appendix 3 Glossary & Definitions Appendix 4 Bibliography Appendix 5 General Notes Figures, Plates & Tables Figure 1 Site location map Figure 2 Historical map, 1889 Figure 3 Historical map, 1914 Figure 4 Historical map, 1920 (with MoD annotations) Figure 5 Historical map showing land requisitioned for RAF Llanberis, 1938 Figure 6 Historical map, 1953 Figure 7 Historical map, 1972 Figure 8 Plan of RAF Llanberis, 1946 Figure 9 Plan of bomb stores at RAF Llanberis, post-1942 Figure 10 Plan showing ordnance disposal pits at RAF Llanberis, WWII Figure 11 Plan showing post-WWII disposal areas and pits at RAF Llanberis Figure 12 Plan of disposal pits and connecting tunnels at RAF Llanberis, 1969 Figure 13 Ordnance recovered from Disposal Area No. 1 Figure 14 Clearance Certificate for Disposal Area No. 1 Figure 15 Ordnance recovered from Disposal Area No. 4 Figure 16 Clearance Certificate for Disposal Area No. 4 Figure 17 UXO hazard zone plan of the Site Figure 18 UXO hazard zone plan of the Site (with GI locations) Figure 19 Plan of fixed EOD facility Plate 1 Recent aerial photograph of the Site Zetica Ltd – Report No. P3300-12-R1-C 2 Plate 2 Aerial photograph, 10th May 1946 Plate 3 Aerial photograph, 1954 Plate 4 Aerial photograph, 1962 Plate 5 Aerial photograph, 1973 Plate 6 Aerial photograph, 1986 Plate 7 Aerial photograph of RAF Llanberis, 10th May 1946 Plate 8 Aerial photograph of Disposal Area No. 2, 1962 Plate 9 Oblique aerial photograph showing former disposal pits at RAF Llanberis Plate 10 Photograph of ramp from Pit 2A into Pit 2C, RAF Llanberis Plate 11 Photograph of ordnance clearance Pit 2C, RAF Llanberis Plate 12 Photograph of the Bomb Pile in Pit 2C, RAF Llanberis Plate 13 Photograph of stacked 25lb IBs in Pit 2C, RAF Llanberis Plate 14 Photograph showing steaming plant at RAF Llanberis Plate 15 Photograph of typical WWII RAF SAA Plate 16 Photographs of a typical and an excavated WWII Mills No. 36 hand grenade Plate 18 Photograph of American Navy 100lb bombs at RAF Llanberis Plate 18 Illustrations of 25lb incendiary bombs Plate 19 Photograph of new and degraded 4lb incendiary bomb Plate 20 Illustrations of AAD bombs Plate 21 Photograph of an M103 fuze Table 1 EOD designation of numbered disposal pits, WWII Table 2 Bombing statistics Table 3 Live items found Pit 2C, 1st January 1973 – 31st March 1973 Table 4 Live items found Pit 3C, 1st January 1973 – 31st March 1973 Table 5 UXO hazard assessment for preliminary ground investigation Table 6 UXO risk assessment for the Site Accompanying Drawings P3300-12-DWG01-C Unexploded Ordnance Hazard Zone Plan P3300-12-DWG02-B UXO Hazard Zone Plan (with GI Locations) Zetica Ltd – Report No. P3300-12-R1-C 3 UXO DESK STUDY & RISK ASSESSMENT Glyn Rhonwy, Llanberis, Gwynedd Executive Summary Zetica Ltd was commissioned by Quarry Battery to carry out an Unexploded Ordnance (UXO) Desk Study and Risk Assessment for an approximate 27 hectare (ha) area of former Royal Air Force (RAF) land at the Glyn Rhonwy Slate Quarry, Llanberis, Gwynedd (the ‘Site’). The aim of this report is to gain a fair and representative view of the UXO hazard for the Site and its immediate surrounding area in accordance with the Construction Industry Research and Information Association (CIRIA) ‘Unexploded Ordnance (UXO), a Guide for the Construction Industry’. Initial works on the Site comprise a preliminary ground investigation, including boreholes, trial pits and sample pits. It is understood that further ground investigations will take place prior to the development of a Pumped Storage Facility. Works for the Pumped Storage Facility may include excavations, tunnelling, trenching and Horizontal Directional Drilling (HDD) associated with the development of a dam, a turbine house, a pipeline and related infrastructure. UXO Hazard Assessment Quarry Pits During and post-WWII, the quarry pits at the former Glyn Rhonwy Slate Quarry were used to dispose of large quantities of ordnance. These were divided into 4No. separate disposal areas. The entire Disposal Area No. 2 was located on the Site and comprised 3No. separate quarry pits. These were designated as Pits 2A, 2B and 2C. Additionally, Pit 1B and a small section of Pit 3A were located within the Site boundary. During the 1970s, an Explosive Ordnance Disposal (EOD) operation was undertaken at the former quarry pits and large quantities of ordnance were cleared. Despite this, areas have been identified where a potential UXO hazard may remain:- On the south-eastern side of Pit 2C, a large Bomb Pile had built up, comprising a mixture of live and inert ordnance. During the EOD operation in the 1970s, this Bomb Pile was not completely cleared. It was only partially removed until the frequency of encounter of live bombs was determined to be 0.5%. The remaining part of the Bomb Pile was buried under slate waste. Given that there is positive evidence that live ordnance remains at this location, this part of the Site is assigned a high UXO hazard level. Zetica Ltd – Report No. P3300-12-R1-C 4 The quarry floor of Pit 2C was used to dispose of thousands of tons of ordnance with items ranging from cartridges, fuzes and grenades to Incendiary Bombs (IBs), Anti-Aircraft Devices (AADs) and American High Explosive (HE) bombs. This was cleared by the EOD operation in the 1970s. However, it is known that the floor of the pit (which is currently flooded) has numerous crevices. Despite the thorough clearance efforts, it is probable that ordnance remains within the crevices on the quarry floor. As such, this part of the Site is considered to have a moderate UXO hazard level. Pit 2B was used as a dump for ordnance-related scrap arising from the EOD operation in the 1970s. Given the vast quantities of ordnance being disposed of, and the less rigorous working standards of the period, it is possible that live items of ordnance remain within the scrap. At the end of the EOD operation, Pit 2B is recorded as having been completely infilled with slate debris. This infill is recorded as being sterile and is assigned a low UXO hazard level. Beneath the infill, it is considered that the UXO hazard level is moderate to account for the possibility of live explosives being present within the designated ordnance scrap. Pits 1B and 3A are recorded as having been used for the disposal of ordnance both during and after WWII, particularly 25lb IBs and various fuzes. Many of the items discovered in the pits during the post-WWII EOD operation were disposed of in situ, with the ordnance scrap being channelled into crevices. As with Pit 2C, there is a potential for UXO to remain within the crevices in these quarry pits, either due to it being incorporated into designated ordnance scrap or missed during the clearance operation. These areas of the Site are considered to have a moderate UXO hazard level. Pit 2A is not recorded as having been used for the disposal of ordnance. However, records indicate that crevices within the pit floor were used for the disposal of ordnance scrap, some of which may contain explosive material. As such, this part of the Site is considered to have a moderate UXO hazard level. Slate Piles (within quarry pits) The slate piles within the quarry pits (including the current access paths) were all modified or moved about as part of the EOD operation in the 1970s. The clearance was progressive and, to maximise efficiency, cleared slate was used to backfill the pits after the completion of the EOD operation. Because of the large volume of ordnance disposed of within the quarry pits, and the very difficult working conditions during the EOD operation, there is a possibility that some ordnance-related items remain within the slate piles. This is proved by the discovery of 2No. items of UXO in quarry Pit 3A (part of which is on the Site) during the 1980s.