SITE INVESTIGATION 53 DUNCAN TERRACE ISLINGTON, LONDON
Prepared for: Olivier and Neary Pollak
ASL Report No. 346-15-088-09
March 2016
ASL Holly Farm Business Park Honiley Warwickshire CV8 1NP
T: +44(0)1926485508 F: +44(0)1926485507 E: [email protected] W: www.aslenvironmental.co.uk
SITE INVESTIGATION 53 DUNCAN TERRACE ISLINGTON, LONDON
1 INTRODUCTION ...... 4
2 THE SITE...... 5
3 GEOLOGY ...... 6
4 HYDROGEOLOGY ...... 6
5 HYDROLOGY ...... 7
6 SITE HISTORY ...... 8
7 ENVIRONMENTAL DATABASE SEARCH ...... 10 7.1 Database Search Results ...... 10 7.2 Environmental Database Search Results ...... 10 7.3 Geological Hazards ...... 10 7.4 Contemporary Trade References ...... 11
8 ASSESSMENT OF POTENTIAL CONTAMINATION RISKS ...... 12 8.1 General ...... 12 8.2 On-Site Sources of Contamination ...... 12 8.3 Off-Site Sources of Contamination ...... 12 8.4 Receptors ...... 12 8.5 Pathways ...... 13 8.6 Conceptual Site Model ...... 13 8.7 Summary ...... 14
9 GROUND INVESTIGATION AND TESTING ...... 15 9.1 Ground Investigation ...... 15 9.2 Gas and Groundwater Monitoring Programme ...... 15 9.3 Laboratory Testing ...... 15 9.4 Geotechnical Laboratory Testing ...... 16
10 GROUND, GROUNDWATER AND GAS CONDITIONS ...... 17 10.1 Materials Encountered ...... 17 10.2 Groundwater ...... 18 10.3 Gas ...... 18
11 GEOTECHNICAL ASSESSMENT ...... 19 11.1 General ...... 19 11.2 Basement Construction ...... 19 11.3 Floor Slabs ...... 20 11.4 Excavations ...... 20 11.5 Dewatering ...... 20 11.6 Buried Concrete Classification ...... 21 11.7 Gas Protection Measures ...... 21 11.8 Existing Foundations ...... 21
12 CONTAMINATION ASSESSMENT – HUMAN HEALTH ...... 22 12.1 Introduction ...... 22
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12.2 Chemical Test Results - Soils ...... 22 12.3 Discussion ...... 23
13 CONTAMINATION ASSESSMENT – CONTROLLED WATERS ...... 25 13.1 Introduction ...... 25 13.2 Summary of Results - Soils ...... 25 13.3 Discussion ...... 25
14 WASTE DISPOSAL ...... 27
15 DISCOVERY STRATEGY ...... 28
16 CONCLUSIONS AND RECOMMENDATIONS ...... 29
REFERENCES ...... 31
GENERAL NOTES ...... 32
TABLES 1 Summary of Site History 2 Summary of Pollutant Linkages 3 Summary of Strata Encountered 4 Summary of Data with Respect to Human Health (Tier 1) 5 Summary of Soils Data with Respect to Controlled Waters (Tier 1)
FIGURES 1 Site Location Plan 2 Site Layout Plan 3 Conceptual Model
APPENDICES I Proposed Development Plan II Environmental Database Search Results III Historical Map Extracts IV Field Records V Chemical Laboratory Test Results VI Geotechnical Laboratory Test Data VII Qualitative Risk Assessment
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SITE INVESTIGATION 53 DUNCAN TERRACE ISLINGTON, LONDON
1 INTRODUCTION
In January 2016, ASL were instructed by Engineers HRW Limited on the behalf of the clients Olivier and Neary Pollak to undertake the necessary site investigation and consultancy services associated with the site known as 53 Duncan Terrace, Islington, London.
A site investigation is required in order to determine the ground conditions at the site ahead of its proposed development. It is understood that the proposed development comprises the construction of a new basement within the rear garden of the existing residential dwelling. A proposed development layout is presented as Appendix I.
The scope of works for this project was set out in ASL’s proposal references 346-15- 088.elo.1692 dated 22nd December 2015. The proposal was formerly accepted by Engineers HRW Limited acting on the behalf of the clients Olivier and Neary Pollak their email dated 27th January 2016.
This report presents a desk study, the development of a conceptual site model, the factual results from an intrusive investigation and subsequent laboratory analyses and interpretative comment in terms of the geotechnical properties of the ground conditions encountered at the site in relation to the proposed development together with an assessment of the contaminative status of the site.
This report has been prepared for the sole benefit of the Clients, Olivier and Neary Pollak and their representatives and agents. The report has been written based on the results of data searches and ground conditions encountered at the time of the investigation and the results of subsequent analyses. Future changes in legislation and advances in current best practises or provision of more detailed design proposals will result in this report requiring review and possible further assessment after the date of issue. The general notes section within this report should be noted in relation to the limitations of this investigation and assessment.
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2 THE SITE
The site is located to the north-west of Duncan Terrace and Colebrooke Row roadway and the north-east of Charlton Place roadway approximately 3.5km north-east of London city centre and can be located approximately by National Grid Reference TQ 317 834 shown on Figure 1.
The site comprises an approximately rectangular shaped piece of land with the long axis aligned approximately north-west to south-east with maximum dimensions of approximately 22m by 6m.
The site is occupied by the residential property 53 Duncan Terrace, a four and half story brick built residential dwelling with a sloping tiled roof. The site fronts on to Duncan Terrace. The frontage of the site comprises paving slabs with an area of managed soft landscaping and three mature trees beyond.
A managed garden area is located to the rear of the property and comprises a lawned area centrally, raised flower beds in the north-west and a patio comprising paving slabs in the south-east. The garden area is bound to the south-west, north-west and north-east by a brick walls approximately 2m in height. The patio area is topographically lower than the lawn area with a change in elevation of approximately 0.9m. The lawned area and patio area are separated by a brick built retaining wall. The raised flower bed is topographically higher than the lawn with a change in elevation of approximately 0.4m.
The site is bound to the north-west, south-west and north-east by residential dwellings and to the south-east by Duncan Terrace with Colebrooke Row roadway and residential dwellings beyond.
It is understood that the proposed development comprises the construction of a new basement within the rear garden of the existing residential dwelling. A proposed development layout is presented as Appendix I.
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3 GEOLOGY
The British Geological Survey (BGS) Sheet No. 256 - North London and the BGS Geoindex indicate the site to be devoid of drift deposits and to be directly underlain by solid geology comprising the London Clay Formation. The London Clay Formation is generally described as ‘bioturbated or poorly laminated, blue-grey or grey-brown, slightly calcareous, silty to very silty clay, clayey silt and sometimes silt, with some layers of sandy clay’ by the BGS. The London Clay Formation is indicated to be between 90m and 110m thick in the vicinity of the site.
Drift geology comprising Boyn Hill Gravel is indicated to be present at the surface to the west of the site. The Boyn Hill Gravel is generally described as ‘post diversionary Thames River Terrace Deposits; gravel, sandy and clayey in part’ by the BGS. The thickness of the Boyn Hill Gravel is indicated to be between 1m and 9m thick and on average 5m thick in the vicinity of the site.
Drift deposits comprising Langley Silt is indicated to be present at the surface to the east of the site. The Langley Silt is generally described as ‘varies from silt to clay, commonly yellow-brown and massively bedded’ by the BGS. The Langley Silt is indicated to be between 1m and 5m thick and on average 3m thick in the vicinity of the site.
Further to the east and to the south-east, drift deposits comprising Hackney Gravel Member is indicated to be present at the surface. The Hackney Gravel Member is generally described as ‘post diversionary Thames River Terrace Deposits; gravel, sandy and clayey in part’ by the BGS. The Hackney Gravel Member is indicated to be on average 6m thick and up to 10m thick in the vicinity of the site.
In addition to the published geology, it is anticipated that Topsoil and/or Made Ground materials will be present at surface or beneath hardstandings across the site given its current use.
The site is indicated to be located in an area that may not be affect by coal mining.
The site is indicated to be located in an area at no hazard from non coal mining.
The environmental database search indicates the site to be in an area where new homes or extensions do not require radon protection measures.
Further details are presented in Appendix II.
4 HYDROGEOLOGY
The London Clay Formation and the Langley Silt are classified by the Environment Agency (EA) as an Unproductive Strata defined as ‘these are rock layers or drift deposits with low permeability that have negligible significance for water supply or river base flow’.
The Boyn Hill Gravel and Hackney Gravel Member are classified by the EA as Secondary Aquifers - A defined as ‘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. These are generally aquifers formerly classified as minor aquifers’.
There are thirteen abstractions from groundwater located within 1km of the site. The first listing relates to the abstraction of groundwater from the chalk aquifer for ‘staff welfare’
ASL Report No. 054-15-055-09 Page 6 of 32 March 2016 located approximately 555m to the south-east. The next seven listings relate to the abstraction of groundwater for potable supply, cooking, sanitation and washing located approximately 620m to the south-west. The ninth listing relates to the abstraction of groundwater for potable supply located approximately 630m to the south-west. The tenth and eleventh listings relate to the abstraction of groundwater for potable supply located approximately 705m to the west. The final two listings relate to the abstraction of groundwater for potable supply located approximately 830m to the south-west.
There are no discharge consents to groundwater located within 1km of the site.
The site is indicated to be located in a Source Protection Zone (SPZ) II (outer protection zone). A boundary with a SPZ I (inner protection zone) is located approximately 405m to the west and south. Groundwater Source protection zones associated with abstraction boreholes are located approximately 620m and 705m to the south-west and west respectively. It is considered that the SPZ’s are associated with the chalk aquifer at depth.
The site is not indicated to be located in a nitrate vulnerable zone.
Further details are presented in Appendix II.
5 HYDROLOGY
The nearest watercourse is identified as an un-named stream located within a culvert approximately 25m to the north-west. This watercourse is not classified chemically or biologically by the EA in the vicinity of the site.
The nearest surface water feature is identified as the Grand Union Canal located approximately 155m to the south. This surface water feature is classified as a category C – ‘fairly good’ quality watercourse by the EA in the vicinity of the site.
There are three abstractions from surface water located within 1.0km of the site. The first two listings relate to the abstraction of surface water for spray irrigation located approximately 605m to the south-east. The final listing relates to the abstraction of surface water for industrial cooling water located approximately 605m to the south-east.
There is one discharge consent to surface water located within 0.5km of the site. The listing relates to the discharge of cooling water located approximately 395m to the south- east.
The site is not indicated to be located in an area susceptible to flooding from rivers and seas.
The site is not indicated to be located in a nitrate vulnerable zone.
The site is indicated to be located in an area susceptible from flooding from surface water.
Further details are presented in Appendix II.
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6 SITE HISTORY
The history of the site has been derived from historical OS maps dating back to 1877. The map extracts are presented in Appendix III. Table 1 below presents a summary of the key developments in and around the site shown on the historical map extracts.
Table 1 Summary of Site History Date of Map On site and surrounding Land-use Extract The site is occupied by a residential dwelling in the south-east in the general layout seen today. The roadway directly to the south-east is named New Terrace. Residential development has occurred surrounding the site. A graveyard is located to the north. 1877 A water works is located to the north. (1:2500) An agricultural hall and a hospital are located to the north-west. A school, a canal, a dairy and stables are located to the south. Churches are located surrounding the site. A wharf is located to the south-east associated with the canal. The site remains generally unchanged. 1896 The roadway directly to the south-east is now known as Duncan Terrace. (1:2500) Residential development has occurred directly to the north-west. Some of the structures associated with the hospital have been cleared to the north-west. The site remains generally unchanged. 1916 Residential dwellings to the south-east have been replaced with a new school. (1:2500) The hospital to the north-west has been extended. 1920 The site remains generally unchanged. (1:10560) Residential development has occurred directly to the north-west. The site and immediate surrounding area remains generally unchanged. 1938 Structures have been cleared further to the west, south and south-east that may be associated (1:10560) with bomb damage. The site remains generally unchanged. 1940 Further clearance of structures has occurred surrounding the site including directly to the west (1:10000) that may be associated with bomb damage. 1946 The site remains generally unchanged. (1:1250) The residential dwelling directly to the north-west. 1954 The site remains generally unchanged. (1:1250) The property located directly to the north-west has undergone development. The site remains generally unchanged. A number of residential dwelling located to the north have been replaced with new larger undefined structure. 1966-71 A large area of structures to the north have been cleared. (1:1250) A new school is located to the north-east. A large area of structures to the south-west has been cleared and now comprises a car park. A large area of structures to the south-east has been cleared. 1974-76 The site remains generally unchanged. (1:1250) Residential development has occurred to the north at the areas of cleared structures. The site remains generally unchanged. 1982-90 Residential development has occurred surrounding the site including directly to the north-west. (1:1250) The car park to the south-west has been developed with a number of undefined commercial buildings. 1991 The site and surrounding area remains generally unchanged. (1:1250) 1995 The site and immediate surrounding area remains generally unchanged. (1:10000) 2006 The site and the immediate surrounding area remains generally unchanged. (1:10000) Significant residential and commercial development has occurred further from the site. 2016 The site and immediate surrounding area remains generally unchanged. (1:10000) Minor commercial development has occurred further from the site.
The site’s history dating back to 1877 has comprised a residential dwelling in the general layout seen today. The site is situated in a mixed residential and commercial land-use area. There is little evidence of significant industrial land-uses in the vicinity of the site.
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Significant possible bomb damage is noted in the surrounding area including directly to the north-west. No damage is noted at the site during this period. However, it may be considered appropriate to complete an unexploded ordnance (UXO) risk assessment for the site as part of the development to determine whether there is a potential risk from UXO at the site.
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7 ENVIRONMENTAL DATABASE SEARCH
This section details any relevant information from registers maintained by the EA. Information provided by the BGS, The Coal Authority, Health Protection Agency and the National Environment Research Council (NERC) is also considered. The information held by the various bodies is summarised below and presented in detail in Appendix II.
It should be noted that the information provided in the desk study is obtained from independent third party sources. It is provided in good faith, but no guarantee can be provided as to its accuracy. Independent enquiries should be made relating to information provided in the desk study information that may impact on the proposed development. The desk study information is not necessarily exhaustive and further information relevant to the site may be available from other sources.
7.1 Database Search Results
There are no registrations listed within 0.5km of the site under the following: