GEOTECHNICAL AND ENVIRONMENTAL ENGINEERS Head Offi ce The Old Dairy Swanborough Farm Swanborough Lewes East Sussex BN7 3PF Telephone 0870 777 1574 SEAFORD HEAD SIXTH FORM STEYNE ROAD Fascimile SEAFORD 0870 777 1577 EAST SUSSEX Website GEOTECHNICAL AND www.AshdownSI.co.uk CONTAMINATION STATUS ASSESSMENT REPORT Email [email protected] Report No. LW24146 July 2013 Regional Offi ce Hertfordshire (Contact via Head Offi ce) Report prepared for the benefit of: Managing Director Kier Construction J.E.Bewick Longley House BSc MSc CEnv CEng MICE International Drive Southgate Avenue Company Secretary Crawley V.Bewick West Sussex BSc MSc FRSS RH10 6AQ Company Registration Number 242 6786 SEAFORD HEAD SIXTH FORM STEYNE ROAD SEAFORD EAST SUSSEX GEOTECHNICAL AND CONTAMINATION STATUS ASSESSMENT REPORT Report No. LW24146 July 2013 FACTUAL REPORT Prepared By: Approved By: Rebecca Jones John Bewick BSc FGS BSc MSc CEng CEnv MICE GEOTECHNICAL ASSESSMENT Prepared By: Approved By: Rebecca Jones John Bewick BSc FGS BSc MSc CEng CEnv MICE CONTAMINATION STATUS Prepared By: Approved By: Rebecca Jones John Bewick BSc FGS BSc MSc CEng CEnv MICE Report No: LW24146/contents SEAFORD HEAD SIXTH FORM STEYNE ROAD SEAFORD EAST SUSSEX GEOTECHNICAL AND CONTAMINATION (PHASE II) ASSESSMENT REPORT TABLE OF CONTENTS Page 1. INTRODUCTION 1 2. SITE DETAILS 2 2.1 Site Description 2 2.2 Expected Geology 2 2.3 Radon 3 2.4 Aquifer Status and Groundwater Source Protection Zones 3 2.5 Hydrology 4 3. GROUND INVESTIGATION 5 3.1 Introduction 5 3.2 Exploratory Holes 5 3.3 Sampling 5 3.4 In Situ Testing 5 3.5 Installations 6 3.6 Laboratory Testing 6 4. GROUND CONDITIONS 8 4.1 Stratigraphy 8 4.2 Stability 8 4.3 Groundwater Conditions 8 4.4 Existing Foundations 9 5. GEOTECHNICAL ASSESSMENT 10 5.1 Foundations 10 5.2 Groundwater 11 5.3 Stability of Excavations 11 5.4 Aggressivity to Concrete 11 5.5 Ground Floors 12 5.6 Drainage 12 6. CONTAMINATION STATUS SUMMARY 13 6.1 Historical Map and Environmental Data 13 6.2 Preliminary Contamination Test Results 14 6.3 Gas Monitoring Results 14 6.4 Recommendations 15 7. CONCLUSIONS 16 Page i of ii Report No: LW24146/contents SEAFORD HEAD SIXTH FORM STEYNE ROAD SEAFORD EAST SUSSEX GEOTECHNICAL AND CONTAMINATION (PHASE II) ASSESSMENT REPORT TABLE OF CONTENTS TABLES Table 1. Expected Geological Strata 2 Table 2. Geotechnical Testing 7 Table 3. Chemical Testing 7 Table 4. Summary of Geo-Environmental Data and Historical Maps 13 FIGURES Figure 1 Site Location Plan Figure 2 Site Plan Figure 3 Foundation Details APPENDICES APPENDIX A Exploratory Hole Notes In Situ Testing Notes Exploratory Hole Records Dynamic Probe Records Summary of Borehole Falling Head Soakage Test Results Summary of Gas Analyses and Water Depths APPENDIX B Geotechnical Laboratory Testing Notes Laboratory Test Results i) Geotechnical Testing ii) Contamination Testing Page ii of ii Report No: LW24146 1. INTRODUCTION The development proposals are understood to comprise the refurbishment of the Seaford Head Sixth Form buildings at Steyne Road, Seaford, East Sussex. Ashdown Site Investigation Limited was commissioned to carry out a combined geotechnical and contamination assessment of the site by Mr D Harwood of: Kier Construction Longley House International Drive Southgate Avenue Crawley West Sussex RH10 6AQ The instruction to proceed was received from the client, in an email dated 7th June 2013. The purpose of the works was to: i. assess shallow ground and groundwater conditions prevailing at the site; ii. undertake a brief review of EnviroCheck data provided by the client for the site; iii. undertake preliminary contamination testing; iv. investigate the form of foundations to existing structures; and v. provide information to assist others in undertaking design of spread foundations, ground floors and soakaways. The analysis and discussions contained in this report are based on the ground conditions encountered during the site work together with the findings from a programme of laboratory analyses. The possibility of a variation in ground and groundwater conditions away from the positions investigated should not be overlooked. Groundwater conditions can vary both seasonally and due to other effects. Reference has been made in this report to EnviroCheck data pertaining to the site which was provided by the client (reference 45334891_1_1, dated April 2013). It is noted that the investigation was undertaken and the report was prepared specifically for the Client’s project and the recommendations given may not be appropriate to alternative schemes. The copyright for the report and licence for its use shall remain vested in Ashdown Site Investigation Limited (the Company) who disclaim all responsibility or liability (whether at common law or under the express or implied terms of the Contract between the Company and the Client) for any loss or damage of whatever nature in the event that this report is relied on by a third party, or is issued in circumstances or for projects for which it was not originally commissioned, or where the exploratory hole records and test results contained therein are interpreted by anyone other than the Company. Seaford Head Sixth Form, Steyne Road, Page 1 of 17 Seaford, East Sussex Report No: LW24146 2. SITE DETAILS 2.1 Site Description The site comprises a rectangular shaped plot of land located at Steyne Road, Seaford, West Sussex, and is centred on the approximate Ordnance Survey national grid reference TV 4862 9881. A site location plan and site plan are presented as Figure 1 and Figure 2 respectively. The site lies to the north of Steyne Road and is bound to the west and north by residential houses and blocks of flats and to the east by a yard used for the storage and supply of timber. At the time of the intrusive works a one to two storey building occupied the majority of the southern part of the site. The existing main building was partly of a flint and mortar and partly of a brickwork and render construction. A mixture of brick and flint walls enclosed the northern part of the site. Several small outbuildings were present to the north east of the main building. Over the northern and central part of the site the topography was relatively level but the southernmost part sloped moderately downwards to the south with a small retaining wall present along the southern boundary between the site and the road. 2.2 Expected Geology The stratigraphic succession expected to underlie the site is presented in the following table. In preparing the table reference has been made to the EnviroCheck information provided by the client, the British Geological Survey 1:50,000 series scale map and the British Geological Survey lexicon of named rock units. Table 1. Expected Geological Strata Type Stratum Age Superficial Deposits None Recorded N/A Lambeth Group Eocene Bedrock Geology Culver Chalk Formation Campanian The geological map shows the northern part of the site is underlain by the Lambeth Group deposits and the southernmost part of the site may be expected to be underlain by the White chalk Subgroup (Culver Chalk Formation). 2.2.1 Lambeth Group The Lambeth Group comprises a complex and laterally variable sequence of sedimentary deposits including clay, silt, sand and gravel. Inter-laminated clay Seaford Head Sixth Form, Steyne Road, Page 2 of 17 Seaford, East Sussex Report No: LW24146 and sand deposits are common in the lower part of the succession. The component formations are the Upnor Formation, Reading Formation and Woolwich Formation. 2.2.2 White Chalk Subgroup (Culver Chalk Formation) The White Chalk Subgroup (Culver Chalk Formation) comprises a weak, white chalk locally with flint bands together with scattered nodular flints. It may be expected to have a deeply convoluted upper surface as a result of solution weathering. The presence of cavities in the chalk is very rare and solution features, if present, can be expected to be infilled with Quaternary deposits such as the Head. The infill material may be significantly weaker than the surrounding chalk. Solution features can comprise pipes extending to several metres deep into the chalk or conical depressions and basin shaped structures. 2.3 Radon The Health Protection Agency (HPA) and its predecessor the National Radiological Protection Board (NRPB) have recommended to government that excessive exposures to radon should be reduced. The HPA advise that the Action Level for radon in homes should be 200 Bq/m3, averaged over a year. Radon affected areas are defined as those areas with 1% or more of homes above this action level. The information provided in the EnviroCheck report indicates the site is in an area where between 5% and 10% of houses are above the action level. Radon protective measures will be required in the construction of new buildings. The exact nature of the radon protective measures should be determined in discussion with the local authority. 2.4 Aquifer Status and Groundwater Source Protection Zones The Environment Agency designates aquifers in accordance with the Water Framework Directive. These designations not only reflect the importance of aquifers in terms of groundwater as a resource (drinking water supply) but also their role in supporting surface water flows and wetland ecosystems. The aquifer designation data is based on geological mapping provided by the British Geological Survey. The Lambeth Group expected beneath the northern part of the site is classified as a Secondary A Aquifer. Secondary A Aquifers are characterised by permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers. The White Chalk Subgroup expected to outcrop beneath the southernmost part of the site is classified as a Principal Aquifer. Principal Aquifers comprise deposits that have high intergranular and/or fracture permeability, usually providing a high Seaford Head Sixth Form, Steyne Road, Page 3 of 17 Seaford, East Sussex Report No: LW24146 level of water storage.