Station Rd. Bethesda Preliminary Geo-Environmental Report RBA Ltd
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Station Rd. Bethesda Preliminary Geo-Environmental Report RBA Ltd. Report Date – October 2016 Report Revision - 01 CONTENTS 1.0 INTRODUCTION 1 2.0 THE SITE 2 3.0 ENVIRONMENTAL SEARCHES 6 4.0 PROPOSED DEVELOPMENT 7 5.0 GROUND INVESTIGATION 8 6.0 GROUND CONDITIONS 10 7.0 RESULTS OF CHEMICAL TESTING 13 8.0 CONCEPTUAL GROUND MODEL & RISK ASSESSMENT 18 9.0 GEOTECHNICAL RECOMMENDATIONS 23 REFERENCES FIGURES Figure 1 Site Location Figure 2 Site Layout Figure 3 Site History (3a - 3e) APPENDICES Appendix A Site Photographs Appendix B Envirocheck Report Appendix C Radon Report Appendix D Trial Pit Logs & Photos Appendix E Physical Test Results (Celtest) Appendix F Chemical Test Results – (DETS) GeoEnvironmental Report Rev. 01 October 2016 Client: RBA Ltd. Station Rd. Bethesda 1.0 INTRODUCTION RBA Ltd. (RBA) has been appointed by Grwp Cynefin (Cynefin) to carry out engineering services in relation to their proposed purchase of land currently occupied by the Rugby and Football club on Station Rd. in Bethesda. Daear GeoConsulting (Daear) has been appointed by RBA to carry out a desk study and site investigation to inform the planning process and preliminary design stages. This report presents the findings of the desk study and investigation and provides preliminary geotechnical and geo-environmental recommendations for the proposed development. Preliminary Geo-Environmental Report; Rev. 01 October 2016 1 Client: RBA Ltd. Station Rd. Bethesda 2.0 THE SITE 2.1 Site Location and Description The site is located on the western fringe of the village of Bethesda, off Station Road and centered at approximate grid reference SH61868 66856, see Figure 1. The site occupies the former mainline train station, which ran from Bethesda to Bangor, and is accessed from grade off Station Road. A topographical survey has been carried out by RBA (Drawing ref. 101), an extract of which is included on Figure 2. All elevations and gradients quoted below are based on the topographical survey information. The site is relatively flat and level, and is constructed on a fill platform at an elevation of approximately 131mAD. The land to the north and north east is typically at grade, with a medical centre to the east and a scaffold yard to the north Along the southern boundary, which is defined by Station Road, ground levels fall to between 130m and 129.5m in the SE, where the boundary comprises a masonry retaining wall, see Photo 1 and decrease to 128.5m in the SW; where the boundary comprises a 1.2m high random rubble wall, which is in poor conditions, at the toe of a sloping embankment, at a gradient of approximately 23 to 26o, see photo 2. There is a narrow strip of land to the south of the station road, which is occupied by residential housing in the east, a vacant plot and an electricity substation in the west; ground levels then fall at a relatively steep gradient to the River Ogwen. The western boundary comprises an unsurfaced track leading to the rugby pitches, which separates the site from the GL Jones fabrication plant. Ground levels on the track fall from 128.5m in the SW to approximately 123.5m in the NW; the elevation of the rugby pitch and the G L Jones site have not been picked up by the topographical survey, however are estimated to be at approximately 121m to 122mAD, and represent the general elevation of the River Ogwen floodplain. The western boundary comprises a 1m to 1.2m high random rubble wall, which is in poor condition, at the toe of a sloping embankment, which is at a gradient of approximately 26o in the southwest corner, but increases to approximately 330 along the majority pf the boundary, see photo 3. A footpath traverses the boundary slope in the NW leading up to the site, see photo 4; the slope between the footpath and the site is at a shallower gradient of approximately 22o, see Photo 5. Japanese knotweed growth is present adjacent to the footpath and was also noted in other locations along the western boundary, see Photo 6. The River Ogwen flows in a generally northerly direction, towards Bangor. It’s course meanders to the south and east of the site; It is positioned approximately 25 - 35m south of Preliminary Geo-Environmental Report; Rev. 01 October 2016 2 Client: RBA Ltd. Station Rd. Bethesda the site, situated to the rear of the residential properties along the southern side of Station Road. The photographs listed above, as well as general photographs of the site are presented in Appendix A. 2.2 Geological and Hydrogeological Geology The geology of the site has been studied on the BGS geoindex online database using the 1:50,000 scale coverage, Ref. 1. A prominent area of artificial ground is shown beneath, and to the north and east of the site, representing the made ground placed to create the elevated development platform for the train station and tracks. Superficial deposits are shown to be absent beneath the artificial ground, with alluvial deposits shown to the east and glacial deposits to the west. The bedrock is shown to comprise the Llanberis Slate Formation. A number of faults are shown trending NE-SW and NW-SE in close proximity to the site, although none appear to be present on the site itself. Hydrogeology The bedrock aquifer beneath the sites is classed as a Secondary B aquifer. The superficial deposits beneath the site are un-classified. Hydrology Groundwater flow is likely to be to the southwest, towards the River Ogwen. 2.3 History The history of the site has been researched from the tithe map for the area and Ordnance Survey maps dating from 1889, obtained from the Envirocheck report of the site; see Appendix B for full copies and Figures 3a to 3e for selected map extracts. Reference has also been made to the website www.disused-stations.org. The tithe map, dated approximately 1830’s, shows the land of the train station to be undeveloped, with the River Ogwen following a similar course as present. It is understood from online sources that the station first opened in 1884. Preliminary Geo-Environmental Report; Rev. 01 October 2016 3 Client: RBA Ltd. Station Rd. Bethesda 1889 (1:2,500 OS map), see Figure 3a - By the time of the first OS map in 1889, the station was shown to occupy the entire site footprint, with the station and access road positioned in the south eastern part of the site, the mainline tracks and associated embankment running along the western site boundary and the remainder of the site underlain by associated sidings, which extended to the north and east of the site. Station road was shown to the south of the site, which was also constructed on a raised embankment adjacent to the River Ogwen. The land to the south and west were undeveloped, however there was a small track shown adjacent to the western boundary, on an embankment with a shallow gradient providing access from station road down to the fields to the west of the site, which appear to be in agricultural use. To the north and east was the town of Bethesda and associated quarries and infrastructure. The closest quarry was approximately 200m north east of the site, and a small gasworks was positioned approximately 100m north of the site. A Goods shed, associated with the sidings was present approximately 50m north of the site. 1900 (1:2,500 OS map), see Figure 3b - No significant changes were shown. 1914 (1:2,500 OS map); see Figure 3c - No significant changes were shown. 1938 (1:10,560 OS map) - No significant changes were shown 1953 (1:10,560 OS map) - No significant changes to site. Large building to the west of the station, on the floodplain (in area of present day GL Jones site). 1963 (1:10,560 OS map) - No significant changes to site or boundaries. 1970/71 (1:2,500 OS map); see Figure 3d – Railway tracks and siding had been dismantled. Although the station building and goods shed remained. The building to the west identified as an engineering works. 1995(1:2,500 OS map); see Figure 3e – all infrastructure and buildings associated with the station have been removed and the current football and social club building had been constructed on the site, occupying a similar footprint to today. A recent aerial photo and site visit suggests that no subsequent development has occurred on the site since the 1995 OS map. 2.4 Radon A radon report has been obtained for the site, which has confirmed that the site is in a Radon Affected Area. The estimated probability of the property being above the Action Level for radon is 3-5%. Preliminary Geo-Environmental Report; Rev. 01 October 2016 4 Client: RBA Ltd. Station Rd. Bethesda Basic Protection measures are required under Building Regulations for radon protection in new buildings and extensions at the site location. A copy of the Radon report is presented in Appendix C. 2.5 Potential Contamination A planning application has not been made for the development. Based on the site history it is reasonable to assume that a planning condition relating to potential contamination will be applied to any development on the site. The historical review shows that the site has previously been used as a mainline train station, with ground raising carried out to form a suitable development platform. The site is therefore considered as brownfield, with the following potential contamination sources: Potentially contaminated materials used to raise ground levels; Potential contamination associated with the former railway; Potential fuel leaks during recent use as a car park.