20 - 22 Bridge Street, Staines Land Contamination Assessment

20 - 22 Bridge Street, Staines Land Contamination Assessment

CDP Staines Limited 20 - 22 Bridge Street, Staines Land Contamination Assessment June, 2018 Card Geotechnics Limited 4 Godalming Business Centre Woolsack Way, Godalming GU7 1XW Telephone: 01483 310600 www.cgl-uk.com 20 – 22 BRIDGE STREET, STAINES Land Contamination Assessment Copyright: Card Geotechnics Limited Card Geotechnics Limited ("CGL") has prepared this report in accordance with the instructions of CDP Staines Limited ("the Client") under the terms of its appointment for consulting engineering services by the Client dated 28 November 2017. The report is for the sole and specific use of the Client, and CGL shall not be responsible for any use of the report or its contents for any purpose other than that for which it was prepared and provided. Should the Client require to pass copies of the report to other parties for information, the whole of the report should be so copied, but no professional liability or warranty shall be extended to other parties by CGL in this connection without the explicit written agreement thereto by CGL. Author Gwennan Thomas, Graduate Engineer BEng (Hons) Checked Sarah Key, Principal Engineer MSc BSc CEnv FGS MIEnvSc Approved Dan Matthews, Director BEng CSci CEnv MIEnvSc MCMI Reference CG/28425 Revision 0 Issue Date December 2017 Revision 1 June 2018 Card Geotechnics Limited, 4 Godalming Business Centre, Woolsack Way, Godalming, Surrey GU7 1XW Telephone: 01483 310600 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment Contents EXECUTIVE SUMMARY 4 1. INTRODUCTION 5 2. SITE LOCATION AND DESCRIPTION 6 2.1 Site Location 6 2.2 Site Description 6 2.3 Site Walkover 6 2.4 Proposed Development 7 3. HISTORICAL DEVELOPMENT 8 3.1 Sources of Information 8 3.2 Summary of Development 8 4. ANTICIPATED GROUND CONDITIONS 11 4.1 Published Geology 11 4.2 Unpublished Geology 11 4.3 Hydrogeology and Hydrology 12 4.4 Ground Hazards and Mining 12 5. ENVIRONMENTAL SETTING 14 5.1 Environmental Disclosure 14 5.2 Radon 15 5.3 Regulatory Enquires 15 6. PRELIMINARY RISK ASSESSMENT 19 6.1 Introduction 19 6.2 Preliminary Conceptual Model 19 6.3 Preliminary Qualitative Risk Assessment 22 7. CONCLUSIONS AND RECOMMENDATIONS 24 7.1 Conclusions 24 7.2 Recommendations 24 CG/28425 2 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment FIGURES Figure 1 Site Location Plan Figure 2 Site Layout Plan Figure 3 Conceptual Site Model Glossary of Abbreviations APPENDICES Appendix A Site Walkover Photographs Appendix B Existing Plan Appendix C Proposed Development Plans Appendix D Historical Maps Appendix E GeoInsight Report Appendix F Historical BGS Borehole Data Appendix G EnviroInsight Report Appendix H Correspondence with Pollution Control Officer CG/28425 3 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment EXECUTIVE SUMMARY Card Geotechnics Limited (CGL) was commissioned by CDP Staines Limited to undertake a Land Contamination Assessment for 20 – 22 Bridge Street, Staines TW18 4TW. This report is to support the planning application for demolition and redevelopment of the site. The site is currently occupied by a two-storey building fronting onto Bridge Street. Historical maps indicate that northern part of the site had been developed prior to 1865 with the construction of the southern part of the building by the time of the map dated 1896. A one-storey extension was constructed to the rear by 1973. Historically the surround area was indicated to comprise a number of industrial uses including a Linoleum and Engineering Works, Mills, and a Brewery. The surrounding area comprise of predominately commercial and residential properties, the adjoining property to the south, 41 Clarence Street, is known to be listed. Published geology indicated that the site is underlain by Alluvium with the Shepperton Gravel Member (Secondary A Aquifer) overlaying the London Clay Formation (Unproductive Strata). The site is located within a groundwater Source Protection Zone 3 (SPZ), with groundwater assumed to be towards the base of the Shepperton Gravel Member flowing south-south east towards the River Thames. The preliminary qualitative risk assessment (which includes information provided by Spelthorne Council regarding the findings of previous investigation at the site) indicates that the potential risks to human health and controlled waters associated with the proposed development of the site are generally considered to be low to medium. The potential risk to construction workers is also considered to be low to medium but it is considered that this can be mitigated by the implementation of appropriate health and safety measures during construction. Should perched groundwater be present on site, potential risks to controlled waters is likely to be low to medium. Potential geotechnical risks at the site include the variable/unknown nature of Made Ground and Alluvium, which is considered unlikely to be a suitable bearing stratum. The Shepperton Gravel Member is likely to be medium dense sands and gravel and potentially water-bearing. Due to the presence of perched groundwater excavations are likely to be unstable. The underlying London Clay formation is known to have a high shrink-swell potential and can by pyritic. It is recommended that an intrusive investigation is undertaken prior to development to inform the redevelopment design and further quantify and refine the identified potential risks. Based on the findings of the previous investigation, it is anticipated that remediation will be required to mitigate potential risks, which can be undertaken under conditioned planning. CG/28425 4 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment 1. INTRODUCTION CGL was commissioned by CDP Staines Limited to undertake a desk based Land Contamination Assessment for the proposed redevelopment of 20 – 22 Bridge Street, Staines TW18 4TW to support the planning application for the redevelopment of the site. This report provides a preliminary assessment of ground conditions, environmental issues and potential for contamination to be present at the site by evaluating the environmental setting of the site and the surroundings. The report presents the following information: Information obtained from a site walkover, a review of available historical maps and an environmental disclosure report for the site; A summary of the ground conditions and associated geotechnical and geoenvironmental constraints based on review of the available published and unpublished sources; A preliminary source-pathway-receptor risk assessment based on the available desk study information; and; Recommendations for additional investigation and assessment, should this be required. CG/28425 5 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment 2. SITE LOCATION AND DESCRIPTION 2.1 Site Location The site is located along Bridge Street, Staines-Upon-Thames near the intersection of Bridge Street and Clarence Street. The postcode for the site is TW18 4TW and the approximate national grid reference for the centre of the site is 503278N, 171617E. A site location plan is presented as Figure 1. 2.2 Site Description The site fronts onto Bridge Street to the west and is bounded by Provident House to the north, a private car park to the east and by 41 Clarence Street to the south. It is understood that 41 Clarence Street is a listed building and the Old Courage building to the north west of the site is currently being redeveloped. The River Thames is located approximately 90m to the south west of the site and the River Colne is located 45m to the east. A site layout plan is presented Figure 2. 2.3 Site Walkover A walkover of the accessible external areas of the site was undertaken by a CGL engineer on 6 December 2017. Photographs from the site walkover are included in Appendix A. The site forms an irregular shape and is approximately 0.02 hectares in size. The site is currently vacant, although temporarily occupied by Live-In Guardians for site security. The site levels are approximately 16.6 metres above Ordnance Datum (mAOD) at the front of the property along Bridge Street, with a step down to approximately 15mAOD at the rear in the private car parking area. Bridge Street was noted to slope towards the north. Access to the site was off Bridge Street and through the private car park to the rear of the building. The walkover noted that no significant vegetation was located on the site, however, some weeds including stinging nettles were located along a boundary chain link fence at the rear. On the opposite side of Bridge Street two semi-mature trees were noted. A plan of the existing structure of the site shows the building to comprise a two-storey building fronting Bridge Street. The building includes a basement, which due to the local topography is at ground level at the rear of the site. The basement is noted to extend below the front of the property beneath the entrance from Bridge Street. The plan is included in Appendix B. CG/28425 6 20 - 22 BRIDGE STREET, STAINES Land Contamination Assessment There was no visual or olfactory evidence of gross contamination across the site. However, due to the age of the building it is assumed Asbestos Containing Materials (ACMs) may be presented within the building itself. While CGL were unable to view the inside of the existing building at the time of the walkover, we were provided with photographs from the Architect, Kirkwood, to assess the condition of the ground floor and basement with regards to potential contamination. The photos showed both the ground floor and the basement to be underlain by a concrete slab which showed no visual evidence of gross contamination. A topography and service location plan provided by Kirkwood1 details the locations of underground services around the site. Along Bridge Street the drawing indicates a drainage channel, electricity cables, traffic control cables, telephones cables and a gas pipe. Towards the rear of the site in the small courtyard surface water and fowl drains are indicated.

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