Proposed mixed-use development at Tennison Road, South

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Proposed mixed-use development at Tennison Road, South
Fairview New Homes
Proposed
mixed-use
development at
Tennison Road,
South Norwood,
London SE25
Site appraisal report –
Revision 1
September, 2011
Card Geotechnics Limited,
No.1 Pickford Street, Pickford Street, Aldershot, Hampshire, GU11 1TY
Telephone: 01252 310364 Facsimile: 01252 331660
Email: [email protected]
Web: www.cardgeotechnics.co.uk
PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
Site appraisal report
Copyright: Card Geotechnics Limited
Card Geotechnics Limited ("CGL") has prepared this report in accordance with the
instructions of Fairview New Homes Limited ("the Client") under the terms of its
appointment for consulting engineering services by the Client dated October 2009.
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
Richard Ball, Engineer
MSc BSc FGS
Checked
Ian Marychurch, Director
MSc BSc CEng MICE CGeol FGS
Approved
Ian Marychurch, Director
MSc BSc CEng MICE CGeol FGS
Reference
CG/4742A
Revision
0
1
Issue Date
October 2009
September 2011
PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
Site appraisal report
Contents
1.
INTRODUCTION
5
2.
DESK STUDY AND SITE VISIT
6
2.1
Site location
6
2.2
Site layout
6
2.3
Proposed development
7
2.4
Site history
7
2.5
Published geology
9
2.6
Hydrogeology
9
2.7
Surface water
10
2.8
Envirocheck® report
10
2.9
Radon
11
3.
PRESENT GROUND INVESTIGATION
12
3.1
Site works
12
3.2
Contamination testing – soils
13
3.3
Contamination testing – groundwater
14
3.4
Geotechnical testing
15
4.
GROUND AND GROUNDWATER CONDITIONS
16
4.1
Ground conditions
16
4.2
Made Ground
17
4.3
Reworked London Clay/Head deposits
17
4.4
London Clay
18
4.5
Harwich Formation
19
4.6
Lambeth Group – Upper Shelly Clay
19
4.7
Groundwater
19
4.8
Soil borne gas
20
4.9
Radioactivity survey
21
5.
CONTAMINATION
22
5.1
Risks to human health (long-term chronic risks)
22
5.2
Leachates
27
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5.3
Groundwater contamination
29
5.4
Asbestos screening
31
5.5
Fly tipping
31
6.
RISK ASSESSMENT
32
6.1
General
32
6.2
Assessed risks
32
7.
6.2.1 Construction workers
33
6.2.2 Future occupiers
33
6.2.3 Plants
33
6.2.4 Groundwater
33
RECOMMENDATIONS
34
7.1
Foundations
34
7.2
Ground floor slab
35
7.3
Pavements
35
7.4
Drainage
35
7.5
Excavations
35
7.6
Remediation
36
7.6.1 Capping layer
36
7.6.2 Services
39
7.7
Gas protection measures
39
7.8
Buried concrete
39
7.9
Waste disposal
39
7.10
Health and safety
40
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FIGURES
1 Site location plan
2 Site layout and borehole location plan
3 Master Plan showing proposed site layout
4 SPT vs. depth
5 Cu vs. depth
6 Conceptual site model
APPENDICES
A Photosheets
B Historical maps
C Envirocheck® report
D Window sample records
E Cable percussion borehole log
F Contamination test results – soil, leachate and groundwater
G Geotechnical test results
H Gas/groundwater monitoring records
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1. INTRODUCTION
Fairview New Homes Limited is putting forward a site in South Norwood, London
SE25 for a mixed-use re-development scheme. The proposed development is to
comprise eighty flats and ten houses, along with five commercial units and six
live/work units.
Card Geotechnics Limited (CGL) has been commissioned to undertake a desk
study and intrusive investigation to determine the concentrations of any potential
contamination on site, and to assess ground conditions to provide
recommendations for geotechnical design. The objectives of the investigation were
as follows:
•
To determine the ground conditions at the site.
•
To determine the nature and extent of any contamination present and to
assess its impact on development design and cost.
•
To determine appropriate types of foundations to support the structures.
The investigation comprised the excavation of window sample holes and a cable
percussion borehole to undertake in-situ testing and to obtain samples for
contamination and geotechnical testing.
This report presents the findings of both the desk study and the intrusive
investigation. The results of chemical testing on samples obtained from the
intrusive investigation are reported and assessed against their relevant guidance
values, and geotechnical design recommendations are provided on the basis of a
series of in-situ and laboratory tests. The results of gas and groundwater
monitoring results from standpipes installed during the intrusive investigation are
reported.
This report represents a development-specific version of the reports issued in 2007,
and includes updated contamination assessment frameworks. The report combines
and replaces the Site Appraisal Report and the Addendum Site Appraisal Report
relating to this site, both issued in August 2007.
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2. DESK STUDY AND SITE VISIT
2.1 Site location
The site is located off Tennison Road, South Norwood, London SE25. The
Ordnance Survey grid reference for the approximate centre of the site is
533715,167712 and the site location is presented in Figure 1.
2.2 Site layout
The site is roughly rectangular in shape, approximately 200m long by 50m wide
running northeast – southwest, and occupies an area of approximately 1ha. The
site is bounded by Tennison Road to the northeast, and by open land formerly
occupied by railway lines to the southwest of the site. The site is bounded to the
west by ‘Heaver’s Meadow’, a public open space, and to the east by railway lines
servicing rail maintenance depots to the southwest. The site falls approximately
1.6m to the southwest across its length from the high point in the northeast.
At the time of the investigation the site was occupied by the following businesses:
•
Champion Scaffolding,
•
Stop Scaffolding Services,
•
Woodside Containers Skip Hire,
•
O’Rourke Construction,
The site had been subdivided with corrugated iron sheeting and fencing to provide
individual compounds for each business. A plan showing the site layout at the time
of investigation is presented as Figure 2.
At the time of the investigation it was not possible to access the Stop Scaffolding
Services Compound, although the compound was observed to contain a large
number of scaffolding racks containing scaffolding poles and equipment. The
Champion Scaffolding compound was occupied by a series of corrugated iron
construction sheds and scaffolding racks of varying sizes. The central south-
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western area of the site was unoccupied and comprised concrete hard-standing. In
the southwest corner of the site, the Woodside Containers Skip Hire compound was
occupied by skips containing a large variety of household, garden, and construction
waste. The O’Rourke compound contained a stockpile of tarmac and was being
used as a depot for road works machinery and equipment.
Fly-tipped material was encountered across the site in various locations comprising
variously white goods, gas bottles, mattresses, car tyres and wheels, roofing
panels, and various household and light industrial waste materials. A number of
wrecked and burned cars were observed towards the eastern side of the Champion
Scaffolding compound.
Photographs of the site at the time of investigation are presented in Appendix A.
2.3 Proposed development
The proposed mixed-use development is to comprise eighty flats and ten Houses,
five commercial units and six live/work units spread across the site within two ‘U’
shaped blocks and courtyard of houses with private gardens. Parking areas, roads
and soft landscaping form the remaining parts of the development scheme.
The proposed development layout is included as Figure 3 to the report.
2.4 Site history
The historical usage of the site has been traced from old Ordnance Survey maps
dating from 1872. Selected extracts from the historical maps are contained in
Appendix B and the site’s historical development is summarised below:

The site is shown to be undeveloped in the map dating 1872 – 1874 with the
London, Brighton, and South Coast Railway (LBSCR) running immediately
to the east.

The site remains undeveloped and Tennison Road is shown to have been
constructed crossing over the LBSCR to the immediate northwest of the site
in the map dated 1896. The LBSCR is shown to have been significantly
expanded with five additional lines to the immediate east of the site. A
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expanded with five additional lines to the immediate east of the site. A
shunting yard is shown to have been constructed approximately 300m to the
southwest of the site. ‘Norbury Brook’ is shown approximately 200m to the
southwest of the site.
•
The site and its immediate surroundings are shown to remain largely
unchanged until 1914. The map dated 1914 indicates three railway lines to
have been constructed running from the southwest of the site and
terminating in the north-eastern area of the site. The site is labelled as
being a ‘coal depot’ at this time.
•
A row of terraced houses is shown to have been constructed to the
immediate northwest of the site in the map dated 1938. The site itself is
shown to be unchanged as a coal depot with three railway lines terminating
at its north-eastern end.
•
The map dated 1949 shows the site to remain largely unchanged. Further
terraced houses are shown to have been constructed along Tennison Road,
and the number of railway lines to the southwest of the site is shown to have
greatly increased. A ‘Cleaning Shed’ and a ‘Repair Shed’ are shown to
have been constructed to the southwest of the site, both of which relate to
train servicing. An isolated structure is shown to the immediate northeast of
the site.
•
The map dated 1968 shows a number of buildings to have been constructed
on site adjacent to one of the railway lines, the site is still labelled as being a
‘coal depot’ and an additional building has been constructed to the
immediate northwest of the site.
•
The map dated 1983 – 1993 shows one of the railway lines to have been
removed from the site. An excavation is shown to the southwest of the site,
in the area of ‘Norbury Brook’, extending north-east to the south-western
border of the site and is labelled as a ‘flood relief zone’.
•
The map dated 1999 shows the site to have been sub-divided into its
present usage.
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2.5 Published geology
The 1:50,000 scale geological map for the area (BGS Sheet 270 – South London 1)
suggests the site to be underlain by London Clay, with the Palaeocene Harwich
Formation, Lambeth Group, and Thanet Sands present at depth over Cretaceous
Upper Chalk. Surface outcrops of the Lambeth Group and Harwich Formation are
shown 200m to the west of the site, suggesting that the London Clay may be a
relatively thin stratum in this area.
2.6 Hydrogeology
The Environment Agency groundwater vulnerability maps provide a generalised
classification of two factors that influence the vulnerability of groundwater to
contamination from sources such as contaminated land and landfills. These are:
1. Aquifer type of the underlying geological strata
2. Leaching potential of surface soils, i.e. the ability of soils to attenuate pollutants
and the potential for non-attenuated pollutants to move into underlying strata or
groundwater.
The classification is stated to be generalised, individual sites and circumstances will
always require further and more detailed assessments to determine the specific
impact on groundwater resources. In particular mineral extraction may have
changed the vulnerability class and there will be a need to determine groundwater
vulnerability using site specific data.
The groundwater vulnerability map Sheet 40 2 for the area indicates the site to be
underlain by a non-aquifer (the London Clay) of negligible permeability.
The site does not lie within a groundwater Source Protection Zone (SPZ).
1
British Geological Survey, 1:50,000 Series, South London, England and Wales Sheet 270, Solid and Drift
Edition, 1998.
2
Environment Agency. Groundwater Vulnerability of the Thames Estuary, Sheet 40. 1:100,000 Map Series,
1995.
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2.7 Surface water
The nearest surface water features to the site are the Norbury Brook, approximately
230m to the southwest, and a pond in Woodside, approximately 300m to the east of
the site.
2.8 Envirocheck® report
An Envirocheck report was commissioned for the site and is included as Appendix
C. A summary of the findings is presented below:
•
There are no Local Authority Pollution Prevention and Controls within 500m
of the site.
•
Two Category 2 – ‘Significant’ – Pollution Incidents to Controlled Waters are
recorded within 400m of the site. The closest of these is described as ‘Oils
– Unknown’ and occurred approximately 241m from the site. The second
incident is also described as ‘Oils – Unknown’ and occurred at the Selhurst
Rail Depot, approximately 340m from the site.
•
Three Category 2 – ‘Significant’ – Substantiated Pollution Incident Register
incidents are shown to have occurred within 400m of the site, all of which
relate to construction or demolition material.
•
There are no water abstractions within 900m of the site.
•
There is a single BGS Recorded Landfill Site approximately 260m to the
east of the site.
•
There are no currently Registered Landfill Sites or Waste Treatment or
Disposal sites within 400m of the site.
•
There are 97 Contemporary Trade Directory Entries within 1000m of the
site. The closest entry is the ‘Surrey Auto Salvage’ listed as being 38m from
the site. This business was located on the now vacant compound in the
south western area of the site (see Figure 2).
•
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There are no Fuel Station Entries within 700m of the site.
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•
The site does not lie in an area of flood risk.
2.9 Radon
Reference to the Building Research Establishment guidance on Radon 3 and the
National Radiological Protection Board 4 indicates that the site lies within an area
where radon protection measures are considered unnecessary.
3
BRE, 1999 Radon: Guidance on protective measures for new dwellings. Building Research Establishment,
Report BR211, 1999.
4
Health Protection Agency, 2005, www.hpa.org.uk/radiation/radon/index
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3. PRESENT GROUND INVESTIGATION
3.1 Site works
The intrusive investigation was designed to assess the ground conditions on site
and to obtain samples for contamination testing. The site works were undertaken in
accordance with current guidance 5,6.
The site works comprised the excavation of 14 window sample holes to depths of
up to 5mbgl. It was not possible to construct the originally intended 15 no. window
sample holes due to access difficulties at the location of window sample hole
WS08. Two of the window sample holes were installed with gas/groundwater
monitoring standpipes to allow for later monitoring visits. Soil samples were
selected from each window sample hole for a suite of chemical testing. Equivalent
Standard Penetration Testing (SPT) was undertaken in window sample holes WS03
and WS07 to determine the relative densities of the near surface materials in these
locations. The energy imparted by the test is equivalent to that imparted by a
Standard Penetration Test (SPT) as described in BS1377:1999 7. The locations of
the window sample holes are presented in Figure 2, and detailed records of the
window sample holes are contained in Appendix D.
A single cable percussion borehole was excavated to 25mbgl in the location of the
proposed apartment block. SPT testing was undertaken at regular intervals for the
depth of the borehole, and undisturbed ‘U100’ samples were obtained for
geotechnical laboratory testing where cohesive soils were present. A 50mm
diameter piezometer was installed to monitor groundwater within the Harwich
Formation encountered at depth. The installation was sealed with bentonite
through the Made Ground at the surface and within the London Clay for 1m above
the Harwich Formation with slotted pipe only within the deep Harwich Formation
material. The location of the borehole is presented in Figure 2, and a detailed
borehole log is provided in Appendix E.
5
6
7
BS 10175: 2001 – Investigation of potentially contaminated sites – Code of practice
BS 5930:1999 – Code of practice for site investigations
BS1377:1990 – Parts 1-9, Methods of test for soils for civil engineering purposes.
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3.2 Contamination testing – soils
Selected soil samples from each of the window sample holes were sent to the
laboratories of ALcontrol Technichem Ltd. for the following suite of chemical
analysis:
•
Organic content,
•
Fraction of Organic Carbon (FOC),
•
Metals, including: arsenic, cadmium, chromium, lead, mercury, selenium,
copper, nickel, zinc, vanadium, beryllium, and barium.
•
Water soluble boron,
•
Total cyanide,
•
pH,
•
Total (acid soluble) sulphate,
•
Sulphide,
•
Phenols (monohydric),
•
TPH CWG, carbon banded including BTEX/MTBE,
•
Speciated Polycyclic Aromatic Hydrocarbons (PAH),
Representative soil samples were further screened for possible radioactive
contamination.
Selected samples were sent for a series of ‘leachability’ tests to determine the
potential mobility of any contaminants within the soils on site. Leachability samples
were tested for the following:
•
Metals, including: arsenic, cadmium, chromium, lead, mercury, selenium,
copper, nickel, zinc vanadium, beryllium, and barium.
•
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pH,
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PROPOSED MIXED-USE DEVELOPMENT AT
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•
Total cyanide,
•
Sulphate,
•
Sulphide,
•
Phenols (monohydric),
•
BTEX,
•
Speciated Extractable Petroleum Hydrocarbons (EPH),
•
Speciated Polycyclic Aromatic Hydrocarbons (PAH).
Full results of both the soils testing and the leachability testing are contained in
Appendix F.
3.3 Contamination testing – groundwater
Groundwater samples were obtained during a monitoring visit to the site on the 3rd
August 2007. The samples were tested for a suite of contaminants as detailed
below:
•
Metals, including: arsenic, cadmium, chromium, lead, mercury, selenium,
copper, nickel, zinc vanadium, beryllium, and barium.
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•
pH,
•
Total cyanide,
•
Sulphate,
•
Sulphide,
•
Phenols (monohydric),
•
BTEX,
•
Speciated Extractable Petroleum Hydrocarbons (EPH),
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•
Speciated Polycyclic Aromatic Hydrocarbons (PAH).
Groundwater results are also presented within Appendix F of this report.
3.4 Geotechnical testing
Undisturbed ‘U100’ samples obtained during the excavation of the cable percussion
borehole were scheduled for quick undrained triaxial testing to provide an estimate
of the undrained shear strength of the soils. Geotechnical classification testing was
undertaken on selected samples to determine liquid and plastic limits, and the
plasticity index. Sulphate testing was scheduled in accordance with requirements
of the Building Research Establishment (BRE) Special Digest 1 8 to determine levels
of sulphate with regard to the specification of buried concrete. Full results of the
geotechnical testing, which was undertaken by Southern Testing Limited, are
presented in Appendix G.
8
BRE Special Digest 1 (2005) – Concrete in aggressive ground Parts 1 – 4.
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4. GROUND AND GROUNDWATER CONDITIONS
4.1 Ground conditions
Ground conditions on site were found to broadly confirm those expected from the
desk study although some reworked/head deposits were also determined. The
strata encountered are summarised in Table 1 below:
Table 1 – Summary of ground conditions
Stratum
MADE GROUND – Generally comprising loose to medium
dense black/dark brown gravelly ash with occasional
concrete and brick rubble overlying dense white chalk fill
and very soft grey/green mottled black sandy clay
containing organic material.
Depth to top of
stratum (mbgl)
Thickness of
stratum (m)
0.0
1.1 to 2.0
1.1 to 2.0
0.7 to 1.6
Soft to firm grey/orange sandy CLAY with rare medium sub
angular flint gravel.
Occasional lenses of medium dense grey/brown SAND.
[REWORKED LONDON CLAY/HEAD]
Stiff closely to very closely fissured light brown, with light
grey veining, silty CLAY with orange stained sand pockets.
Becomes stiff to very stiff closely to very closely fissured
with selenite crystals and dustings of fine silt at 5.8m.
2.2 to 3.2
Proven to
16.3mbgl
16.3
4.2
20.5
Proven to
25mbgl
[LONDON CLAY]
Stiff grey sandy to very sandy CLAY with many medium
black rounded flint gravels over very dense dark grey silty
and clayey fine SAND.
[HARWICH FORMATION]
Stiff pale grey and green silty sandy CLAY with many
shells and shell fragments and some fine to medium angular
mudstone gravels.
[LAMBETH GROUP – Upper Shelly Clay]
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The strata are described in more detail below and for specific detail, reference
should be made to the relevant window sample and borehole logs contained in
Appendices D & E.
4.2 Made Ground
The Made Ground on site was found to generally comprise loose to medium dense
black/dark brown gravel and ash with concrete and brick rubble to a typical depth of
between 0.5m and 1.0 across the entire site.
Dense white chalk fill was encountered beneath the gravel/ash layer in all
exploratory holes with the exception of window sample hole WS12 in the northeastern corner of the site. The thickness of the chalk fill was generally uniform
across the site with a thickness of 0.5m.
A very soft dark green/grey mottled black sandy clay with an organic odour was
encountered beneath the chalk fill to a maximum depth of 2.0m in places. It is
considered that this may represent former topsoil which was covered by the chalk
and ash fill to raise site levels during the construction of the coal depot.
Equivalent and actual SPT ‘N’ values within the Made Ground record values of
between 0 and 4 corresponding to a classification of ‘very loose’. A plot of SPT ‘N’
vs. depth is presented as Figure 4.
4.3 Reworked London Clay/Head deposits
Soft to firm orange brown sandy to very sandy clay with occasional flint gravel was
encountered to a maximum depth of 3.2m across the site. It is considered that this
material represents reworked London Clay or Head deposits based on the high
proportion of sand observed and the presence of flint gravels.
In window sample holes WS10, WS11, WS12 and WS14, across the northern area
of the site, this material was found to include horizons of medium dense grey/brown
sand at depths of between 1.8 to 1.9m below ground level. The sand was typically
0.5m to 0.9m thick and was found to contain groundwater in window sample hole
WS12.
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SPT ‘N’ values of 5 and 6 were recorded within this material, corresponding to an
undrained shear strength (Cu) within the clay horizons of approximately 30kPa or
‘soft’ according to the correlation proposed by Stroud 9. A Quick Undrained (QU)
triaxial test was performed on a single undisturbed sample of this material and was
found to have a Cu of 42kPa at 2m depth. A plot of SPT ‘N’ vs. depth is presented
as Figure 3 and a plot of Cu vs. depth is presented as Figure 5.
A plasticity index of 18% was determined by laboratory testing, and the material can
be classified as clay of low plasticity (CL).
4.4 London Clay
The London Clay was encountered in all boreholes at depths of between 2.2m and
3.2m depth and was found to generally comprise firm becoming stiff very closely
fissured orange/brown becoming dark grey silty clay with occasional pockets of
sand, and common selenite crystals recorded between 3m and 6m depth.
SPT and equivalent SPT ‘N’ values within the London Clay were found to generally
increase with depth from between 6 and 9 at 3m depth to 34 at 14.5mbgl.
According to the Stroud9 correlation, these values correspond to an undrained
shear strength (Cu) of the order of 40kPa (firm) at 3mbgl increasing to 150kPa (very
stiff) at 14.5mbgl. A plot of SPT ‘N’ vs. depth is presented as Figure 4.
The results of Quick Undrained (QU) triaxial tests confirm the Cu values to be of the
order of 54kPa at 4mbgl, increasing to 140kPa at 14m depth, which is consistent
with the SPT data.
The undisturbed sample from 16m depth recorded a Cu value of 250kPa and is
described as a black/brown silty clay with occasional medium gravel. It is
considered that this sample represents the boundary between the London Clay and
the Harwich Formation and is not generally representative of the strength of the
London Clay beneath the site. A plot of Cu vs. depth is presented as Figure 5.
The plasticity index of the London Clay was found to range between 45% and 54%,
corresponding to a classification of high to very high plasticity (CH to CV).
9
Stroud, M. A., The standard penetration test in insensitive clays and soft rocks, Proceedings of the European
Symposium on Penetration Testing, 2, 367-375 (1975).
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4.5 Harwich Formation
The Harwich Formation was encountered at the base of the London Clay between
16.3m and 20.5mbgl and was found to comprise dark grey very sandy clay with
common rounded flint gravels over very dense dark grey silty and clayey fine sand.
Two SPTs were performed within the Harwich Formation material, both of which
met refusal at greater than 50 blows for penetrations of 150mm and 160mm.
Scaling the ‘N’ values according to current guidance 10 gives an equivalent ‘N’ value
of 150 or ‘very dense’.
4.6 Lambeth Group – Upper Shelly Clay
The Lambeth Group Upper Shelly Clay (USC) was encountered at 20.5mbgl and
found to extend to 25mbgl. The USC comprised generally stiff dark grey to pale
green silty sandy clay with many shells and shell fragments, and some fine to
medium angular mudstone gravels.
SPTs within this material recorded ‘N’ values of 48 at 22mbgl and of 50 for 105mm
penetration equating to an ‘N’ value of 21410 at a depth of 24mbgl. Based on the
Stroud9 correlation, an undrained shear strength of the order of 215kPa is obtained
for the Lambeth Group material at 22mbgl. Sample recovery was poor within the
Lambeth Group and it was not possible to undertake laboratory triaxial testing. A
plot of SPT ‘N’ vs. depth is presented as Figure 4.
The results of classification testing within the Lambeth Group suggest a plasticity
index of 32%, corresponding to a classification of ‘intermediate’ to ‘high’ plasticity
(CI to CH).
4.7 Groundwater
Groundwater was encountered in a number of exploratory holes during window
sampling and boring and has since been monitored on one return visit. During the
site works, groundwater was typically encountered at depths of between 0.8mbgl
and 1.5mbgl at the contact between the Made Ground and the underlying
Reworked London Clay. In window sample hole WS12, groundwater was
10
CIRIA Report 143 (1995), The Standard Penetration Test (SPT): Methods and Use.
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encountered at 2.0mbgl within a sandier horizon of the Reworked London Clay. In
window sample hole WS03, groundwater was encountered at 4.9mbgl within a silty
parting of the London Clay.
Within the cable percussion borehole, groundwater was encountered at 4.0mbgl
and at 16.5mbgl. Groundwater was observed to rise from 16.5mbgl to 6.0mbgl over
a 15 minute period.
Groundwater levels have since been monitored on a single occasion. Within
window sample holes WS03 and WS12, groundwater was recorded at depths of
0.94mbgl and 0.96mbgl respectively, within the Made Ground. Within the cable
percussion borehole, the groundwater was recorded at a depth of 3.6mbgl,
suggesting a significant head of water within the confined Harwich Formation.
4.8 Soil borne gas
Gas monitoring installations were installed in window sample holes WS03 and
WS12 in the southeast and northwest corners of the site respectively. Monitoring
was undertaken on 6 occasions after completion of the fieldwork. Detailed
monitoring records are included as Appendix H and the maximum concentrations
recorded are presented in Table 2 below.
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Table 2 – Summary of soil borne gas monitoring
Maximum Recorded Value from All Boreholes
Date
CO2 (% Vol.)
CH4 (% Vol.)
H2S (% Vol.)
Flow (l/hr)
0.7
0.2
0.0
- 0.2
th
1.2
0.0
0.0
4.0
st
0.7
0.0
0.0
0.1
th
5.4
0.3
0.0
0.0
5.1
0.1
0.0
>60
1.3
0
0.0
0.0
rd
3 August 2007
12 August 2007
21 August 2007
12 September 2007
rd
3 October 2007
th
19 October 2007
1
Note:
1. Flow reading considered to be faulty.
The results indicate that some low to moderate concentrations of carbon dioxide
are present, together with traces of methane. These are associated with relatively
low flow rates.
4.9 Radioactivity survey
Samples were scanned for possible radioactivity with a Gamma-Scout Radiation
meter calibrated for radiation levels between 0.1 and 1,000 µSv/h. No significantly
elevated levels of radiation were detected in any of the soil samples selected for
testing.
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5. CONTAMINATION
5.1 Risks to human health (long-term chronic risks)
The laboratory test results have been compared against the published Soil
Guideline Values (SGVs) for the “Residential (with home-grown produce)” land-use
category to assess the risk to human health from chemical contamination in the
soils. Currently, SGVs have only been issued by the Environment Agency for a
limited number of contaminants, namely selenium, mercury, arsenic, nickel and the
BTEX compounds. The SGVs have all been issued for a sandy loam soil with a
Soil Organic Matter of 6% as standard.
Where SGVs are not available, the soil results have been compared to Generic
Assessment Criteria (GACs) that have been derived in-house by CGL using the
Contaminated Land Exposure Assessment (CLEA) model 11 and version 1.04 of the
CLEA software. The GACs represent conservative screening criteria and have
been calculated using the default parameters for the standard land use scenario set
out in the CLEA technical report and toxicological inputs in line with the
requirements of Science Report SC050021/SR2 12 and, in the case of petroleum
hydrocarbons, Science Report P5-080/TR3 13. The GACs have been generated
assuming a sandy loam soil type and a Soil Organic Matter of 6%, which are
suitable assumptions for the site in question. More detailed information on the
derivation of the CGL GACs can be provided upon request.
The results of the assessment are set out below in Tables 3a and 3b. Assessment
against the SGVs and GACs is carried out at the 95th percentile on the sample
mean (designated US95), which is considered to represent a reasonable worst-case
scenario. Statistical assessment of the results has been completed in accordance
with the recommendations set out in the recently published CL:AIRE guidance 14. In
this regard, an assessment of the normality of the data has been undertaken.
11
Environment Agency. (January 2009). Updated technical background to the CLEA model. Science Report
SC050021/SR3.
12
Environment Agency. (January 2009). Human health toxicological assessment of contaminants in soil.
Science Report SC050021/SR2.
13
Environment Agency. (February 2005). The UK Approach for Evaluating Human Health Risks from
Petroleum Hydrocarbons in Soils. Science Report P5-080/TR3.
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Where datasets are normally distributed the one sample t-test has been applied to
calculate the US95.
In the case of non-parametric datasets, the Chebychev
Theorem has been applied.
The Grubbs Test has also been used to identify
potential outliers within datasets. Copies of the relevant statistical analysis are
available on request.
14
J. Lowe et al. (May 2008). Guidance on comparing soil contamination data with a critical concentration.
CL:AIRE, CIEH & SAGTA.
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Table 3a Summary of soil contamination (risks to human health)
Contaminant
SGV or GAC
@ 6% SOM
for Residential
(with home-grown
produce) land-use
Notes on
soil
saturation
limits
(SSL)1
US95
US95 >
Assessment
Criteria?
(Y/N)
#- fails max
value test
(mg/kg)
SOM (%)
Measured range
(mg/kg)
2
0.28 – 57.0*
(mg/kg)
*
*
<3.0 – 43.0
13
N
-
<0.5 – 0.9
0.5
N
-
<10.0 – 55.0
37
N
<10.0 – 270
44
N
Arsenic
32
3
-
Cadmium
14
Chromium
37
Lead
290
Mercury (inorganic)
170
3
-
<0.6 – 1.0
0.7
N
Selenium
3503
-
<2.5
2.5
N
<0.5 – 5.7
1.4
N
-
<5.0 – 3300
289
N
-
<4.0 – 54
31
N
-
<10.0 – 430.0
115
N
<10.0 – 490.0
110
N
Boron
*
Copper
3,700
Nickel
130
Zinc
3
18,000
Barium
*
Beryllium
23
-
<0.5 – 3.5
1.4
N
Vanadium
130
-
4.1 – 95.0
60
N
Phenols4
1900
-
<0.1
0.1
N
Cyanide
*
<1.0
1
N
0.01
N
BTEX compounds
Benzene
0.333
-
<0.01
Toluene
6103
-
<0.01 – 0.038
0.01
N
N
Ethyl benzene
350
3
-
<0.01
0.01
m-xylene5
2403
-
<0.01
0.01
N
N
N
o-xylene
250
3
-
<0.01 – 0.013
0.01
p-xylene5
2303
-
<0.01 – 0.015
0.01
5
Notes:
1. - = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL
exceeded & considered to affect interpretation. GAC limited to SSL.
2. * = no value currently defined
3. Published Soil Guideline Value (Environment Agency, 2009)
4. GAC relates to Phenol (C6H5OH) only.
5. Concentrations for total xylenes should be compared to the value for m-xylene for fresh spills and to o-xylene
for all other cases.
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Table 3b Summary of soil contamination (risks to human health) cont.
Contaminant
SGV or GAC
@ 6% SOM
for Residential
(with home-grown
produce) land-use
Notes on
soil
saturation
limits
(SSL)1
(mg/kg)
Measured range
US95
(mg/kg)
(mg/kg)
US95 >
Assessment
Criteria?
(Y/N)
Total Petroleum Hydrocarbons (TPH)
TPH aliphatic EC5-6
79
-
<0.01 – 0.23
0.04
N
TPH aliphatic EC>6-8
230
-
<0.01 – 0.42
0.05
N
TPH aliphatic EC>8-10
59
-
<0.01 – 0.5
0.08
N
TPH aliphatic EC>10-12
300
(b)
<0.01 – 0.37
0.05
N
TPH aliphatic EC>12-16
130
(b)
<5 - 150
19
N
TPH aliphatic EC>16-35
88,000 [51]
(a)
<5 - 2010
95
N
TPH aromatic EC6-7
0.33
-
<0.01
0.01
N
TPH aromatic EC>7-8
610
-
<0.01 – 0.04
0.01
N
TPH aromatic EC>8-10
88
-
<0.01 – 0.77
0.12
N
TPH aromatic EC>10-12
300
-
<0.01 – 0.56
0.08
N
TPH aromatic EC>12-16
560
-
<5 - 91
14
N
TPH aromatic EC>16-21
800 [360]
(a)
<5 - 660
65
N
TPH aromatic EC>21-35
1,200 [29]
(a)
<5 - 2600
243
N
940
(b)
<0.1 – 7.6
0.72
N
18,000 [46]
(a)
<0.1 – 15
1.59
N
18 [10]
(a)
<0.1 – 45
4.4
N
2.4
-
<0.1 – 59.0
5.3
N2
Benzo(b)fluoranthene
24 [7.3]
(a)
<0.4 – 69
6.21
N
Benzo(g,h,i)perylene
250 [0.1]
(a)
<0.1 – 30.0
2.78
N
Benzo(k)fluoranthene
24 [4.1]
(a)
<0.1 – 22.0
2.27
N
Chrysene
230 [2.6]
(a)
<0.1 – 41
4.06
N
Dibenzo(a,h)anthracene
2.4 [0.02]
(a)
<0.1 – 7.5
0.73
N
Fluoranthene
2,200 [113]
(a)
<0.1 – 100.0
3.34
N
Fluorene
1,800 [913]
(a)
<0.1 – 5.7
0.6
N
24 [0.4]
(a)
<0.1 – 28
2.6
N
8.7
-
<0.1 – 1.3
0.34
N
1,600 [13]
(a)
<0.1 – 100.0
9.43
N
Polycyclic Aromatic Hydrocarbons (PAH)
Acenaphthene
Anthracene
Benzo(a)anthracene
Benzo(a)pyrene
Indeno(1,2,3-cd)pyrene
Naphthalene
Pyrene
Notes:
1. - = green; (a) = amber i.e. GAC set to model output, [SSL provided in square brackets] ; (b) = red i.e. SSL
exceeded & considered to affect interpretation. GAC limited to SSL.
2. If outlier in WS 14 is removed US95 is 1.6 and less than GAC.
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A single high concentration of copper (3300mg/kg) was recorded at 0.4m depth
within window sample hole WS09 and is shown by statistical analysis to be an
outlier, however the sample population including this value does not exceed the
Generic Acceptance Criterion for this contaminant.
Locally elevated ‘hotspots’ of metals contamination were recorded and are
summarised in Table 4 below:
Table 4 – Summary of metals hotspots
Hotspot Contamination
Location
Arsenic
WS05
Boron
WS01
Barium
WS04, WS13
The US95 value for benzo(a)pyrene (BaP) exceeds the Generic Acceptance
Criterion for this contaminant, however this appears to be attributable to an
elevated concentration of BaP of 59mg/kg in the sample taken from window sample
WS14. If this is removed from the statistical assessment the sample population
falls within the GAC. Therefore, it is considered that this location represent a
‘hotspot’ of BaP contamination.
Preliminary Total Petroleum Hydrocarbon (TPH) screening was undertaken and the
results indicated that the US95 value for TPH exceeds the CAG. However, elevated
concentrations of TPH were detected only within the ashy Made Ground from the
top 0.5m from ground level and it is considered that TPH concentrations are
elevated only within this material. Removing the ash material from the statistical
analysis reduces the US95 for TPH to well below the minimum screening value of
150mg/kg.
Samples of the ashy Made Ground have been further selected for speciated TPHCWG testing to determine the potential risks posed to human health according to
current best practice 15. No evidence of free product was noted during the
15
Environment Agency (2005), Science Report P5-080/TR3, The UK approach for evaluating human health
risks from petroleum hydrocarbons in soils.
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investigation and hence the Generic Acceptance Criteria are relevant to the
assessment rather than the more onerous Soil Saturation Limits. The results
indicate that none of the specific carbon bands have elevated concentrations of
TPH when compared to the Generic Acceptance Criteria. On this basis it is
considered that hydrocarbon contamination is not a significant concern in respect of
human health at this site.
5.2 Leachates
Leachability testing was undertaken on selected samples to determine the mobility
of contaminants within the ground on site. The results of this testing are
summarised in Table 5 below and full results are included in Appendix F.
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Table 5 – Summary of leachability testing results
Contaminant
Freshwater
EQS1
(µg/l)
EC Drinking
Water Value
(µg/l)
Measured
range
(µg/l)
No. of samples
exceeding EQS
No. of samples
exceeding Drinking
Water Value
Arsenic
50
10
<7.0
0 of 4
0 of 4
Cadmium
5
5
<1.0
0 of 4
0 of 4
Chromium
5 – 250
50
<5.0
0 of 4
0 of 4
Lead
4 – 250
10
<5.0
0 of 4
0 of 4
1
1
<0.05
0 of 4
0 of 4
*
10
<5.0
*
0 of 4
2000
1000
<5.0 – 20.0
0 of 4
0 of 4
Copper
1 – 28
2000
<5.0
0 of 4
0 of 4
Nickel
50 – 200
20
<5.0
0 of 4
0 of 4
3
<5.0
0 of 4
0 of 4
3
(1000)
<5.0 – 8.0
*
0 of 4
<1.0
0 of 4
*
<5.0 – 29.0
1 of 4
*
Mercury
Selenium
Boron
Zinc
Barium
2
8 – 500
*
4
(5000)
Beryllium
(15)
*
Vanadium
20 - 60
*
3
Phenols
30
(0.5)
<10.0
0 of 4
#
Cyanide
55
50
<20
0 of 4
0 of 4
250
<10.0 – 26
0 of 4
0 of 4
*
<50.0
#
*
Sulphate (mg/l)
Sulphide
TPH
400
0.25
6
3
*
(10)
10 – 120
*
4 of 4
PAH
*
0.1
7
<0.1 – 1.3
*
#
Benzo(a)pyrene
*
0.01
<0.1 – 0.4
*
#
Naphthalene
10
*
<0.1
0 of 4
*
Benzene
30
1
<5.0
0 of 4
#
Toluene
50
*
<5.0
0 of 4
#
Ethylbenzene
*
*
<5.0
#
#
Xylenes
30
*
<5.0
0 of 4
*
6.0 - 9.0
6.5 - 10.0
8.0 – 9.0
0 of 4
0 of 4
pH
Notes:
1.
Evaluated against lower EQS where range given
2.
* = No values defined or given
3.
Concentration formerly prescribed within the Water Supply (Water Quality) Regulations 1989
4.
Dutch Indication Level of Serious Contamination
5.
Free cyanide.
6.
Undissociated hydrogen sulphide
7.
Sum concentration of benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene, indeno(1,2,3cd)pyrene.
#
Denotes limit of detection (LOD) greater than guidance criteria.
Inspection of the leachability results indicates generally low contaminant mobility for
the samples tested, with the exception of Total Petroleum Hydrocarbons (TPH),
Polycyclic Aromatic Hydrocarbons (PAH), and Benzo(a)pyrene; all of which were
recorded in concentrations greater than stringent EC Drinking Water values. TPH
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concentrations do not, however, exceed the Dutch Intervention Values, which may
be used as a comparator in the absence of relevant UK guidance.
It is noted that the samples selected for screening represent only the ashy Made
Ground from within the top 0.5m of ground surface, in which elevated
concentrations of PAH and TPH were recorded. It is therefore considered that the
recorded contaminant mobilities represent ‘worst case’ values and are not generally
representative of contaminant mobility across the site. No significantly elevated
concentrations of contamination were recorded from either the chalk Made Ground,
Reworked London Clay, or London Clay and it is therefore considered that
leachability within these materials will be negligible.
Furthermore the leachability tests have been assessed against very stringent
standards considering that there is no potential for use of the water or for baseflow
to water courses.
5.3 Groundwater contamination
Groundwater samples were obtained during a monitoring visit on the 3rd August,
2007. Samples of the shallow ‘perched’ groundwater within the Made Ground were
obtained from window sample holes WS03 and WS12 and deep groundwater from
within the Harwich Formation was sampled from borehole BH1.
Samples were tested for a suite of contaminants as detailed in Section 3.3 of the
Site Appraisal Report1 and the results are summarised in Table 6 below. The full
set of results is presented in Appendix F.
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Table 6 – Summary of groundwater results
Contaminant
Freshwater
EQS1
(µg/l)
EC Drinking
Water Value
(µg/l)
Measured
range
(µg/l)
No. of samples
exceeding EQS
No. of samples
exceeding Drinking
Water Value
Arsenic
50
10
<5.0
0 of 3
0 of 3
Cadmium
5
5
<1.0
0 of 3
0 of 3
Chromium
5 – 250
50
6.0 – 12.0
0 of 3
0 of 3
Lead
4 – 250
10
<5.0
0 of 3
0 of 3
1
1
<0.005
0 of 3
0 of 3
*
10
<5.0
*
0 of 3
2000
1000
42.0 – 150.0
0 of 3
0 of 3
Copper
1 – 28
2000
<5.0
0 of 3
0 of 3
Nickel
50 – 200
20
5.0 – 8.0
0 of 3
0 of 3
3
<5.0 – 20.0
2 of 3
0 of 3
3
(1000)
40.0 – 56.0
*
0 of 3
<1.0
0 of 3
*
<5.0
0 of 3
*
Mercury
Selenium
Boron
Zinc
Barium
2
8 – 500
*
4
(5000)
Beryllium
(15)
*
Vanadium
20 - 60
*
Phenols
30
(0.5)
<10.0
0 of 3
3 of 3#
Cyanide
55
50
<20.0
3 of 3#
0 of 3
250
130 – 1100
1 of 3
2 of 3
#
Sulphate (mg/l)
Sulphide
TPH
3
400
0.25
6
*
3
<50.0
3 of 3
0 of 3
2 of 3
*
(10)
<1.0 – 310
*
PAH
*
0.1
7
<0.1
*
0 of 3
Benzo(a)pyrene
*
0.01
<0.1
*
3 of 3#
Naphthalene
10
*
<0.1
0 of 3
*
Benzene
30
1
<1.0
0 of 3
0 of 3
Toluene
50
*
<1.0
0 of 3
*
Ethylbenzene
*
*
*
*
*
Xylenes
30
*
<1.0 – 1.0
0 of 3
*
6.0 - 9.0
6.5 - 10.0
7.2
0 of 3
0 of 3
pH
Notes:
1. Evaluated against lower EQS where range given
2. * = No values defined or given
3. Concentration formerly prescribed within the Water Supply (Water Quality) Regulations 1989
4. Dutch Indication Level of Serious Contamination
5. Free cyanide.
6. Undissociated hydrogen sulphide
7. Sum concentration of benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(ghi)perylene, indeno(1,2,3cd)pyrene.
#.
Denotes Limit of Detection greater than guidance value.
Generally low concentrations of contaminants were recorded in the groundwater
samples. Elevated concentrations of TPH were recorded in the two shallow
samples from WS03 and WS12 and elevated concentrations of zinc and sulphates
were recorded in both the deep and shallow groundwater. However, it is
considered that the assessment criteria against which groundwater results have
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been assessed are excessively stringent as the site is underlain by a non-aquifer;
the London Clay acts as an effective barrier between the shallow groundwater and
the water bearing Harwich Formation at depth, and the groundwater is unlikely to
be used or encountered by future occupiers.
The potential risks to construction workers are low, provided that appropriate PPE
and site inductions are made available.
5.4 Asbestos screening
No asbestos was detected in any of the samples selected for screening.
5.5 Fly tipping
Fly tipped asbestos was not observed during a walkover of the site which was
undertaken with a representative of Fairview New Homes Ltd.
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6. RISK ASSESSMENT
6.1 General
In accordance with current UK guidance, a simple source – pathway – target model
has been developed for compounds that were encountered during the
investigations at concentrations above guidance levels in order to evaluate the
possible environmental risks. This model is summarised in Table 7 and is
presented graphically in Figure 6. The risk assessment model may be subject to
change once groundwater contamination results have been received.
Table 7 – Summary of risk assessment
Sources
Pathways
Targets
Risk
Rating
TPH in Made
Ground and
shallow
groundwater
Ingestion and/or
Inhalation/ vertical
migration
Construction
workers
Low
Metals
Hotspots (As,
B, Ba)
Indirect
ingestion/Root
uptake
Future
Occupiers
Low
B(a)P hotspot
Vertica/lateral
migration
Plants
Low
Groundwater
Low
6.2 Assessed risks
Based on the proposed form of development, the generally low levels of
contamination recorded at the site are likely to present a low risk to potential
receptors. A number of elevated concentrations of metals, TPH, and B(a)P were
recorded in hotspot locations on the site however it is considered that these present
a low risk to potential targets provided appropriate measures are adopted.
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6.2.1 Construction workers
Risks to construction workers are considered to be low provided appropriate
Personal Protective Equipment is provided.
6.2.2 Future occupiers
Risks to future occupiers are considered low provided remedial measures
recommended in Section 7 of this report are adopted.
6.2.3 Plants
The risk of plant uptake is considered low provided remedial measures
recommended in Section 7 of this report are adopted.
6.2.4 Groundwater
Risks posed to groundwater quality by the proposed development are considered
low as the site is underlain by a non-aquifer.
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7. RECOMMENDATIONS
7.1 Foundations
It is understood that the proposed development is to comprise a number of
commercial units and residential apartment buildings across the central area of the
site with a number of houses with private gardens to the south.
Based on the results of this investigation, the Made Ground and the Reworked
London Clay/Head Deposits are not considered suitable founding materials due to
their general weakness and variability. Furthermore, groundwater has been
recorded at approximately 1m below ground level across the site and it is
considered that this may present difficulties in the construction of shallow
foundations. It is therefore recommended that piled foundations be adopted
throughout the proposed development.
Continuous Flight Auger (CFA) piling is recommended, taken to an appropriate
depth within the London Clay or Lambeth Group material. CFA piling is considered
appropriate as the piling methodology eliminates potential problems arising from the
high groundwater levels recorded. Furthermore the site lies adjacent to a
residential area and park and it is considered that CFA piling would minimise
disturbance to the residents.
Indicative pile calculations have been undertaken to provide an estimate of required
pile dimensions. The results of the calculation are summarised in Table 8 below:
Table 8 – Specimen pile calculation
Safe Working Load F.O.S = 3
(kN)
Pile Diameter
15m
20m
450
540
1500
600
770
2500
900
1250
5000
(mm)
Adhesion factor α = 0.60, Bearing capacity factor Nc = 9
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PROPOSED MIXED-USE DEVELOPMENT AT
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Site appraisal report
It should be noted that the pile loads are indicative only. Pile design parameters
are influenced by pile equipment and installation methodologies and, accordingly, it
is recommended that the contractor responsible for installing the piles undertakes
the final working pile design.
7.2 Ground floor slab
Suspended ground floors are recommended throughout to prevent potential
differential settlement issues where ground conditions vary beneath a building.
These should be constructed to current NHBC standards 16.
7.3 Pavements
The Made Ground at the site is seen to be variable and low SPT ‘N’ values have
been recorded. Accordingly a California Bearing Ratio of 2% should be adopted for
the design of roads, pavements, and car parks.
7.4 Drainage
Soakaway drainage is not recommended for this site, and drainage should be
directed to existing sewers.
7.5 Excavations
Generally high water levels have been recorded across the site and may
necessitate de-watering or localised close sheeting to prevent ingress of water into
excavations. Potential instabilities in excavation may exist in the north eastern area
of the site where water bearing sands were encountered, particularly in the location
of window sample hole WS12.
Prior to commencement of construction, it is recommended that trial pits be
excavated adjacent to the location of window sample hole WS12 to investigate the
behaviour of the ground in excavation.
16
NHBC Standards, Chapter 5.2 ‘Suspended ground floors’, NHBC September 2006
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PROPOSED MIXED-USE DEVELOPMENT AT
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Site appraisal report
7.6 Remediation
Although there are generally low concentrations of contaminants present within the
soils at the site, there are locally elevated concentrations of some heavy metals,
BaP and TPH (unspeciated) within the top 0.5m of the Made Ground. Some limited
TPH contamination is also present within the shallow groundwater. This is thought
to be caused by the presence of ash within the Made Ground, and limited leakage
of fuels from vehicles. Some remedial measures will therefore be required to
reduce the risk to the future occupiers to an acceptable level.
No remedial measures are recommended beneath areas of proposed buildings and
hard-standing as the building footprint and pavement construction will act to break
the source pathway target linkage.
In areas of soft landscaping, a 400mm capping layer of clean subsoil/topsoil is
recommended to provide a barrier between any contamination and potential
receptors. In areas of private gardens, a 600mm capping layer is recommended to
provide a barrier and a growth medium of sufficient depth.
Details of the capping layer thicknesses and import specifications are provided in
Section 7.6.1. below.
7.6.1 Capping layer
A capping layer of clean topsoil/subsoil, as detailed in Table 9, should be provided
in areas of open landscaping to provide a nominal barrier and act as a growth
medium for vegetation. In areas of private gardens, a capping layer of clean
topsoil/subsoil should be provided as detailed in Table 10. A geotextile separator
(e.g. Terram® or similar) must be provided at the base of the capping layer in both
situations, to prevent mixing with the underlying soils.
CG/4742A
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PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
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Table 9 – Capping layer construction (open landscaping)
Layer
Minimum thickness
(mm)
Topsoil
150
Cohesive subsoil
250
Geotextile (Terram 1000 or similar)
1
Table 10 – Capping layer construction (private gardens)
Layer
Minimum thickness
(mm)
Topsoil
150
Cohesive subsoil
450
Geotextile (Terram 1000 or similar)
1
The subsoil/topsoil placed to form the capping layer must be clean, inert soil
imported from a known and reputable source. A greenfield source should be
utilised where possible. Chemical test results and details of source must be
provided by the Contractor prior to the material being brought to site. The material
must not exceed the Maximum Permissible Concentrations (MPCs) set out in Table
11.
Once on site, the imported material should be subject to validation testing. At least
one chemical test will be undertaken for every 50m3 of imported material.
In addition, topsoil should meet the requirements of BS 3882:1994 Classification –
General Purpose Grade or better and should be free from propagules of aggressive
weeds.
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PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
Site appraisal report
Table 11 – Import specification- topsoil/subsoil
Determinant
Maximum permissible concentration (mg/kg)#
Residential gardens
Public open spaces
Arsenic
20
20
Cadmium
1-8
30
Chromium (total)
130
200
Lead
450
450
Mercury
8
15
Selenium
35
260
Copper
135
2080
Nickel
50
75
Zinc
300
8250
Boron
5
5
Barium
300
300
Beryllium
30
84.9
Vanadium
135
170
1-1.2
1.3
Benzo(a)anthracene
12.4-12.5
13.5
Benzo(b)fluoranthene
9.2-11.7
13.5
Benzo(k)fluoranthene
10.3-12
13.5
Chrysene
8.7-11.5
13.5
Dibenzo (ah) anthracene
1.0-1.2
13.5
Indeno (123cd) pyrene
10.1-12
13.5
Napthalene
6.3-30.8
7.2-34.8
C12-C16†
31
53
C16-C21†
110
731
C21-C35†
198
731
pH
5-10
5-10
5
5
Benzo(a)pyrene
Phenols
*
0.5
*
17
Water soluble sulphate
as SO4
0.5
Total Cyanide
17
Asbestos
*
*
No visible fibres
Notes:
# In mg/kg dry soil except sulphate and pH.
* Indicates if failure occurs further assessment can be made.
†
Sum of aliphatic & aromatic fractions
CG/4742A
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PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
Site appraisal report
7.6.2 Services
Where services are to pass through Made Ground it is recommended that they are
placed in oversized trenches backfilled with suitable inert fill. In view of the
presence of some locally elevated TPH concentrations in the upper horizons of
Made Ground it is considered that the use of hydrocarbon resistant water supply
pipes should be adopted in the development.
7.7 Gas protection measures
Based on the results of the 6 gas monitoring visits, the site may be characterised as
predominantly ‘Characteristic Situation 1’ with regard to soil borne gases and no
specific gas protection measures are recommended. However, during some
monitoring visits the concentration of carbon dioxide marginally exceeded 5%, and
accordingly it is recommended that a minimum 1200 gauge Damp Proof
Membrane, sealed to cavity trays and around services, is included in the floor slab
construction for all properties to prevent potential ingress by carbon dioxide and
local petroleum vapours.
7.8 Buried concrete
Buried concrete should be designed to according to current guidance 17 with regard
to sulphates. The results of the testing, which are included in Appendix G, indicate
relatively high water soluble sulphate concentrations between 2000mg/l and
3400mg/l and as such it is recommended that buried concrete be designed to
Design Sulphate Class DS – 4 with an ACEC Class of AC-4 according to current
guidance3. It is noted that this is based on a limited number of samples and that
further testing may be undertaken to rationalise the concrete class requirements
across the site.
7.9 Waste disposal
Based on the current soil contamination test results, the ashy Made Ground on site
may be classified as mainly ‘hazardous’ for disposal due to the presence of
elevated TPH concentrations. All other soils are likely to be classified as ‘non17
th
st
Canada-wide standards for petroleum (PHC)in soil, CCME April 30 to May 1 , 2001.
CG/4742A
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PROPOSED MIXED-USE DEVELOPMENT AT
TENNISON ROAD, SOUTH NORWOOD, LONDON SE25
Site appraisal report
hazardous’. These classifications are subject to confirmation by Waste Acceptance
Criteria (WAC) testing and it is recommended that a programme of more detailed
testing is undertaken once the scheme design is frozen in order that a waste
classification zoning can be developed to ensure the correct disposal route for
arisings.
7.10 Health and safety
All site works should be undertaken in accordance with the guidelines prepared by
the Health and Safety Executive (HSE, 1991) 18. In this context, the risks should be
low to moderate and nominal safety precautions should be acceptable (the adoption
of good hygiene practices and the use of overalls, gloves and dust masks if
necessary).
During the redevelopment, precautions should be taken to minimise exposure of
workers and the general public to potentially harmful substances. Attention should
also be paid to restricting possible off-site nuisance such as dust and odour
emissions. Such precautions should include, but not be limited to:
1. Personal hygiene, washing and changing procedures.
2. Personal protective equipment, including disposable overalls, gloves etc.
3. Measures to avoid surface water ponding and positive collection and
disposal of all on-site run-off.
4. Regular cleaning of all site roads, access roads and the public highway
including dust suppressions methods (e.g. water spraying), if necessary.
Excavations should be planned and inspected regularly by a competent person. No
operatives should enter unshored or otherwise protected excavations identified as
unstable by a competent person, however shallow they are.
18
HSE (1991). Protection of Workers and the General Public During the Development of Contaminated Land.
Guidance Note HS(G)66, Health and Safety Executive, HMSO, 1991.
CG/4742A
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FIGURES
SITE
Reproduced from the Ordnance Survey 1:50,000 map with permission of the Controller of Her
Majesty’s Stationary Office, Crown Copyright.
Licence No. 100012585
Client
Project
Fairview New
Homes Limited
Job No
Tennison Road, South
Norwood, London SE25
CG/4742
Site location plan
Figure 1
Title
Client
Project
Fairview New Homes
Limited
Job No
Tennison Road, South Norwood, London, SE25
CG/4742A
Site layout plan – Mixed use development
Figure 3
Title
SPT 'N'
0
10
20
30
40
50
0
MADE GROUND
REWORKED LONDON CLAY
LONDON CLAY
5
Depth (m)
10
15
HARWICH FORMATION
50/150mm
50/160mm
20
LAMBETH GROUP
SPT 'N' - CP Rig
Eq. SPT 'N' WS Rig
50/105mm
25
Client
Project
Fairview New
Homes Limited
Job No
Tennison Road, South
Norwood, London SE25
CG/4742
SPT ‘N’ vs. Depth
Figure 4
Title
Cu (kPa)
0
50
100
150
200
250
300
0
MADE GROUND
REWORKED LONDON CLAY
LONDON CLAY
5
Depth (m)
10
15
HARWICH FORMATION
(sand - Cu not applicable)
20
LAMBETH GROUP
Cu - Derived from SPT correlation
Cu - Laboratory QU testing
25
Client
Project
Fairview New
Homes Limited
Job No
Tennison Road, South
Norwood, London SE25
CG/4742
Cu vs. Depth
Figure 5
Title
Human health routes:
N
1. Soil/dust ingress and ingestion/skin contact
2. Outdoor ingestion/skin contact/inhalation of soil, dust and/or vapours
3a. Plant uptake and 3b. Subsequent ingestion of vegetables/fruit
4. Sulphate attack on buried concrete.
5. Potential contaminant leaching into groundwater.
PAH ‘Hotspot’
WS14
5
MADE GROUND
LONDON CLAY
4
1
3a
GROUNDWATER
– typically 1m
below grond level
Client
4
3b
1
2
4
Project
Fairview New Homes
Limited
Job No
Tennison Road, South Norwood, London SE25
CG/4742
Conceptual site model
Figure 6
Title