SOIL INVESTIGATION REPORT [PDF]

SOIL RESOURCE SURVEY AND SOIL RESOURCE PLAN CARDIFF PARTNERING HOUSING PROJECT TY NEWYDD

Prepared on behalf of: WATES CONSTRUCTION LTD

TOHA Document Ref:

TOHA/16/5232/4/LHJ

Document Revision:

00

Document Status

Draft

Document Issue Date:

Prepared by:

2nd August 2016

Tim O’Hare Associates LLP Howbery Park, Wallingford Oxfordshire, OX10 8BA Tel: 01491 822653 Email: [email protected] www.toha.co.uk

Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

Tim O’Hare Associates

CONTENTS

Section

Page

1

INTRODUCTION .................................................................. 1

2

DESK STUDY REVIEW ....................................................... 2

3

SITE INVESTIGATION......................................................... 5

4

LABORATORY ANALYSIS ................................................. 8

5

DISCUSSION ..................................................................... 11

6

SOIL RESOURCE PLAN ................................................... 15

Appendix 1 – Site Plan Showing Trial Hole Locations Appendix 2 – Laboratory Analysis Results Appendix 3 – Example Imported Topsoil Specification

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Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

1.0

INTRODUCTION

Tim O’Hare Associates LLP was commissioned by Wates Construction Ltd to undertake a Soil Resource Survey and Soil Resource Plan for the Ty Newydd development, Cardiff. Permission to carry out the work is provided by the Consultant’s Commissioning Agreement, Additional Services referenced jjc160622/Cardiff 531100 and completed on 22/06/2016. 1.1

Purpose

It is proposed to redevelop this site for residential use, including 16 units comprising flats and bungalows. The development will also include soft landscape areas (public realm), back gardens and communal gardens for the flats. The site is classified as ‘brownfield’ where previous buildings have been demolished and removed. The intention is to strip and store the existing site-won soils for landscape construction purposes. However, there is currently no information on the horticultural quality of these soil resources or their suitability for landscape purposes. Therefore, the purpose of the Soil Resource Survey is to gain a detailed understanding of the quality of the existing topsoil and subsoil on the site in order to enable more accurate decisions to be taken with regard to soil stripping and re-use. The report also takes into consideration the proposed planting types and provides soil management advice, e.g. soil stripping, stockpiling, potential soil amelioration and cultivation, together with any other potential soil related problems. This will form the basis of the Soil Resource Plan chapter within this report in accordance with the DEFRA Construction Code of Practice for the Sustainable Use of Soils on Construction Sites (2009). 1.2

Actions

Tim O’Hare Associates LLP has evaluated the quality and suitability of the soils for landscape construction by desk study review in conjunction with assessing a number of key chemical and physical soil properties by on-site investigation and laboratory analysis. This report issues the findings of the soil investigation, including our site observations and soil descriptions, results and interpretation of all analyses, discussion on soil quality and suitability for the proposed landscape purposes and recommendations for handling, treating and re-using the soils for landscape construction.

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Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

2.0

DESK STUDY REVIEW

2.1

Documents Reviewed

The following documents were reviewed prior to commencing the site investigation work: 

Soil Map of England and Wales

Sheet 5 – South West England (1:250,000).



Terrafirma

Geotechnical

and

Geoenvironmental

Report:

Proposed Residential Development at Ty Newydd and Heol Trenewydd Caerau, Cardiff. March 2016 ref 13493 

Wates Pentan Architects

Drawing No. 3403-(05)-004 – Rev. A – Ty Newydd Site Layout.

2.2

Geology and Soils

The British Geological Survey 1:50,000 Solid and Drift map indicates that the majority of the site is underlain by Mercia Mudstone Formation, predominantly red, less commonly green-grey, mudstones and subordinate siltstones with thick halite bearing units in some basal areas with thin beds of gypsum/anhydrite sandstone also present. Superficial deposits of Till – Glacial Till were recorded across the site. The Soil Map of England and Wales classifies the soils within the survey area as: Unsurveyed (Urban). Soils within urban and industrial areas are potentially subject to a wide range of natural and anthropologic influences and impacts, and can include building materials and soils which have been imported from outside of the subject site. In horticultural terms, this can result in variable soil conditions with regards to soil chemistry, fertility status and physical condition, including compaction and the presence of foreign matter within the soil matrix. The adjacent area to the site is dominated by the following soil classification: Major Group Brown soils Group

Argillic brown earth

Subgroup

Stagnogleyic argillic brown earth

Stagnogleyic argillic brown earths are loamy or loamy over clayey soils with the subsurface horizon showing significant clay enrichment with no prominent mottling or greyish colours (gleying) above 40 cm depth. Further definition places the site within an area of the SALWICK Soil Association, which is described as ‘Deep reddish fine loamy soils with slowly permeable subsoils and slight seasonal waterlogging. Some fine loamy soils affected by ground water.’

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2.3

Existing Ground Conditions

The Terrafirma Report indicates that the site ground conditions comprised Made Ground, described as ‘soft to firm, dark brown, gravelly CLAY with occasional brick/ weathered asphalt over medium dense brown clayey sandy GRAVEL. Contains brick, concrete (occasionally very large), orange plastic fencing, clay pipe fragments, cable off-cuts, metal pipe, girders and sheeting.’ The depth of Made Ground is variable across the site from 0.1 – 2.0m. There is also variable natural ground which is described as ‘firm, reddish brown, slightly sandy gravelly CLAY to very clayey GRAVEL with common cobbles and boulders.’ The depths are variable across the site. 2.4

Potential Soil Contaminants

The Terrafirma Report tested 7 no. samples. The depths from which these were taken varied from 0. 5 m to 1.0 m. These samples were tested for range of metals, inorganics and organic chemicals including petroleum hydrocarbons and polyaromatic hydrocarbons. Of the potential contaminants tested, most did not exceed the Terrafirma assessment guideline values for human health. Asbestos containing materials (chrysotile fragments and crocidolite fibres in a cement sheet) were observed at 1 no. trial hole. Terrafirma have recommended further investigation to determine the significance of this result. Of the phytotoxic (toxic to plants) contaminants determined (copper, nickel and zinc), none was found at levels that exceeded the maximum permissible levels specified in BS3882:2015 – Table 1. 2.5

Proposed Landscape Scheme

Planting Types The landscape design is currently at an early stage, however, with reference to the supplied General Site Plan drawing, the anticipated planting types at this stage are:   

Tree planting; Shrub and herbaceous perennial planting; Amenity grass.

In addition, a number of existing trees are to be felled. The soil requirements of the anticipated landscape types are considered below. Tree Planting Trees that are supplied either with a rootball or in an air pot are usually the most demanding planting type. Good, aeration and drainage around the rootball, as well as moderate to high fertility status are critical at planting and during the establishment period. Without these properties, trees will very quickly suffer and possibly die during their first few growing seasons after planting. Given their demanding nature, all rootballed trees should be planted with wellTOHA/16/5232/4/LHJ/Aug

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aerated and free-draining soils to the full rooting depth (normally considered to be 1.0m). Containerised Shrubs Container grown shrubs are normally planted with shallower depths of soil than trees and the plants themselves can be variable in their specific soil requirements. Container grown shrubs in particular are not typically tolerant of adverse soils conditions and would normally require soils which are fertile, well drained and aerated. Amenity Grass The soil requirements for amenity grass areas depend on the level of anticipated usage, as discussed below. Grass in low use areas is a robust planting type that does not require a specialist soil type. Grass in high use areas requires soil that is resistant to wear and compaction. The topsoil and subsoil should possess adequate structures to allow sufficient drainage and aeration to sustain healthy grass growth. Retained Trees Existing trees are well established and will therefore have an extensive root network. The protection of roots (including correct pruning and management of soils surrounding them) will be paramount to their health and longevity. Minimising disturbance to the root system is vital.

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Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

3.0 3.1

SITE INVESTIGATION Site Visit

The site was visited on the 14th July 2016 during a period of dry and bright weather. The development site is located south of Heol Trelai. The site is irregular in shape and occupies an area of approximately 0.37 hectares. It is centred on National Grid Reference 313010 175290. At the time of the survey, the previous buildings had been demolished and the site open access. The area was generally level in topography and vegetated with grass and mature trees around the perimeter of the site. Deleterious material and evidence of fly tipping were observed. The area to the west (Heol Trenewydd) was not surveyed due to the presence of asbestos noted in the Terrafirma report.

Plate 1 : View across the site showing site boundary and mature vegetation

Plate 2 : Deleterious material

Plate 3 : Vehicle rutting and soil disturbance

Plate 4 : Heol Trenewydd not surveyed due to the presence of asbestos

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3.2

Soil Conditions

The soils were examined by constructing a series of 7 No. hand-dug trial holes (TH) at representative locations within the survey area. Trial holes were excavated to a maximum depth of 520mm due to the very compacted and stony nature of the ground. The sample locations are shown in site plan in Appendix 1. At each trial hole the soils were examined with reference to the Soil Survey Field Handbook. Important physical soil properties were recorded, including texture, structure, Munsell colour, compaction, drainage and aeration characteristics, stoniness, topsoil depths and the presence of deleterious materials. At the same time, representative soil samples were taken for laboratory analysis. Where the soils were consistent in visual appearance, the samples were combined to form representative composite samples for laboratory analysis. Two soil profiles were observed across the two sites and were typically described as: Profile A This soil profile appears to comprise ‘natural’ soils but it has been ‘reworked’ at some stage as glass fragments were regularly found within the topsoil matrix. This soil profile was observed at TH1, TH4, and TH6. Reworked Topsoil GL-200/280mm bgl (Average depth – 225mm)

Subsoil 200/280 – 420/520mm bgl

Reddish brown (Munsell colour – 5YR 5/4), slightly moist, friable, noncalcareous SANDY CLAY LOAM and CLAY LOAM. The soil was compacted yet typically broke down into a weakly-developed fine granular structure upon disturbance. The topsoil was moderately stony, with occasional rounded and subrounded stones up to 80mm. Glass fragments were recorded in the topsoil in most trial holes. Diffuse boundary (up to 100mm thick) into: Reddish yellow (Munsell colour – 7.5YR 6/6), moist, plastic to firm, HEAVY CLAY LOAM. Typically slightly stony with frequent small fragments of deleterious materials including, tarmac, concrete. No further progress at 420/520 mm due to compaction and frequent deleterious material.

Profile B This soil profile comprised ‘Made Ground’ and was found within TH2, TH3, TH5, and TH7 in the demolition footprint in. Made Ground GL-200/430mm bgl (Average depth – 285mm)

Brown (Munsell colour – 10YR 4/3) to dark greyish brown (Munsell colour – 10YR 4/2), slightly moist to moist, friable to slightly plastic, SANDY CLAY LOAM, typically with a weakly-developed fine to coarse granular structure with occasional subrounded blocky structures. The made ground was very stony, with frequent deleterious materials noted, including part and whole bricks, tarmac, concrete, glass fragments. Please note that the ground was very compacted and hence excavation depth was shallow (restricted to 430mm)..

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Plate 5 : Profile A arisings – (subsoil to left and reworked topsoil to right)

Plate 6 : Profile B topsoil arisings

Plate 7: Profile A

Plate 8 : Profile B

Recorded topsoil Depths The following topsoil depths were recorded during the site visit. Trial Hole Ref.

Profile Reference

Topsoil Depth (mm)

TH1

A

200

TH2

B

300

TH3

B

200

TH4

A

200

TH5

B

430

TH6

A

280

TH7

B

390

Average

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225mm (Profile A) 285mm (Profile B)

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4.0

LABORATORY ANALYSIS

4.1

Analytical Schedule

Representative samples of topsoil, made ground and subsoil were submitted to the laboratory for analysis. The samples were analysed in accordance with the following schedule:        

particle size analysis (% sand, silt, clay) (subsoil only); stone content (2-20mm, 20-50mm, >50mm); pH value; electrical conductivity values; exchangeable sodium percentage (topsoil and made ground only); major plant nutrients - N, P, K, Mg (topsoil and made ground only); organic matter content; C:N ratio (topsoil and made ground only).

The results are presented on the Certificates of Analyses in Appendix 2 and an interpretation of the results is given below. 4.2

Results of Analysis – Reworked Topsoil and Made Ground

Particle Size Analysis Hand texture analysis was used to determine the texture of the Reworked Topsoil and Made Ground samples. These samples fell into the sandy clay loam and clay loam texture classes, which are usually considered suitable for general landscape applications provided the soil’s physical condition is satisfactory. Such soils usually have good water and nutrient retention capacities, but they are also prone to structural degradation and compaction during handling, and especially when plastic in consistency. Any damage to the structural condition of these soils are likely to reduce their drainage and aeration properties. pH and Electrical Conductivity The Topsoil sample was slightly alkaline in reaction (pH 7.1), with a pH value that would be considered suitable for a range of species typically used for landscape purposes. The Made Ground sample was strongly alkaline in reaction (pH 8.4). The alkalinity in this instance may be related to presence of lime-rich material (including concrete and mortar fragments for example) within the soil profile at these locations. This pH value would be considered suitable for landscape purposes, provided species with a broad pH tolerance or those known to prefer alkaline calcareous soils are selected. The electrical conductivity (salinity) values for all samples were low, indicating that soluble salts were not present at levels that would be harmful to plants. TOHA/16/5232/4/LHJ/Aug

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Organic Matter The samples contained adequate reserves of organic matter, total nitrogen and extractable magnesium. The levels of extractable potassium and phosphorus were low. The samples would benefit from a suitable application of compost or fertiliser. The C:N ratio results of the samples are considered acceptable for landscape purposes. 4.3

Results of Analysis – Subsoil

Particle Size Analysis The Subsoil sample fell into the heavy clay loam texture class and would be described as heavy in texture. Such soils usually have good water retention capacities, but they tend to be slowdraining and can suffer from seasonal waterlogging following periods of prolonged or heavy rainfall. They are also prone to structural degradation and compaction during handling, and especially when plastic in consistency. Any damage to the structural condition of this soil is likely to further reduce its drainage and aeration properties. This texture class may be considered suitable for more robust landscape applications, including hardy trees and shrubs and amenity grass, provided the physical condition of the soil is maintained and provided species tolerant of moisture retentive, heavy soil are selected. The soil would not be ideally suited to more demanding planting environments or plant species that require or prefer light or free-draining subsoil. Stone Content The stone content of the Subsoil sample was low and as such, stones are unlikely to constitute a limitation for use as landscape subsoil. pH and Electrical Conductivity The sample was strongly alkaline in reaction (pH 8.5). This pH value would be considered suitable as subsoil for general landscape purposes providing species with a wide pH tolerance or those known to prefer alkaline soils are selected for planting, turfing and seeding. The electrical conductivity (salinity) value of the subsoil samples was low, indicating that soluble salts were not present at levels that would be considered harmful to plants. Organic Matter Content The Subsoil sample contained reasonably low level of organic matter, which is considered acceptable for subsoil material.

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5.0

DISCUSSION

It is proposed to redevelop this site for residential use, including 16 units comprising flats and bungalows. The development will also include soft landscape areas (public realm), back gardens and communal gardens for the flats. The site is classified as ‘brownfield’ where previous buildings have been demolished and removed. The intention is to strip and store the existing site won soils for landscape construction purposes. However, there is currently no information on the horticultural quality of these soil resources or their suitability for landscape purposes. 5.1

Summary of Findings

Based on the visual examination and subsequent laboratory analysis, two soil profiles were encountered across the site differentiated by their content of foreign matter. These are described as summarised in the table below. Profile A This soil profile was encountered at TH1, TH4 and TH6. Topsoil

Subsoil



Average depth 225mm (range 200-290mm)



Heavy clay loam texture class



Clay loam to sandy clay loam texture classes (medium texture)



Low stone content





Strongly alkaline

Low to moderate stone content





Non-saline

Slightly alkaline





Low organic matter content

Non-saline



Adequate reserves of organic matter, total nitrogen and extractable magnesium



Slight potassium and phosphorus deficiencies



Frequent glass fragments

Profile B This soil profile was encountered at TH2, TH3, TH5 and TH7. Made Ground 

Average depth 285mm (range 200-430mm)



Sandy clay loam texture class



High stone content



Strongly alkaline



Non-saline



Adequate reserves of organic matter, total nitrogen and extractable magnesium



Slight potassium and phosphorus deficiencies



Frequent foreign matter, including brick, tarmac, concrete and glass fragments

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5.2

Considerations for Landscape Construction

Please note that asbestos was found during the Terrafirma Ground Investigation. This Soil Resource Survey report comments on the re-use of the site soils from a horticultural perspective only. Any further issues regarding the suitability of the soils from a human health perspective should be addressed to the project Environmental Consultant to confirm the site’s remediation strategy. Reworked Topsoil The Reworked Topsoil would be considered suitable for some of the proposed landscape types, provided the physical condition of the topsoil is fully restored following the required earthworks operations and any nutrient deficiencies are remedied. The presence of ‘sharps’ such as glass, would be considered a potential health and safety risk to both site operatives during the course of the earthworks and landscape construction, and end users. The risk posed to end users is lower if the topsoil is only re-used in public open space planting areas, rather than grass lawn areas (communal and private areas), as they are less likely to be accessed by the public. Therefore, the site-won Reworked Topsoil would not be suitable for re-use in back gardens and can therefore only be considered for peripheral areas. The structural condition of the Topsoil will need to be maintained by careful handling and sensitive soil management to ensure it is fit for planting. Handling the soil when it is wet will severely damage the soil structure and greatly reduce its potential for re-use. Made Ground The Made Ground samples would not be considered suitable as topsoil for landscape purposes due to the high stone content and presence of sharps. The stone contents of the Made Ground samples were moderate to high, comprising mainly small to medium stones (2 – 50mm). Stony soils of this kind have a reduced proportion of fine earth (material less than 2mm) from which water and nutrients can be obtained and so can cause patchy establishment (particularly of seeded grass) and hinder some maintenance operations, such as close mowing. Physical contaminants in the form of brick and concrete together with occasional glass were noted across the site surface and throughout the soil matrix. These materials ranged in size from small fragments (2mm to 20mm) to large cobble size pieces, including part bricks. Subsoil It will be important to ensure that the subsoil’s physical condition is fully restored prior to topsoiling or any planting, turfing or seeding. This will involve deep ripping all subsoil prior to topsoil spreading. TOHA/16/5232/4/LHJ/Aug

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Provided its physical condition is satisfactory, the subsoil has potential for re-use in most planting environments and species tolerant of moisture retentive soils are selected. The subsoil should be overlain by an appropriate depth of suitable, well-structured topsoil. The subsoil may be prone to self-compaction if placed below the weight of a large tree root ball (extra heavy standard and larger). An appropriate free-draining sand or sandy subsoil should be used to backfill the lower portion of large tree pits (heavy standard and larger). Soil Depth Topsoil (including ‘Made Ground’ topsoil) should not be placed to excessive depth because the organic component of topsoil needs to maintain a sufficient level of gaseous exchange with the atmosphere (aeration) in order to provide an adequate supply of oxygen for soil microbes and plant roots, and to release exchanged gasses. Placement of topsoil to greater depths increases the risk that the topsoil will be insufficiently aerated, which could lead to the generation of oxygen depleted or ‘anaerobic’ soil conditions, which are inhospitable to plant growth. To reduce the risk of self-compaction and anaerobism (oxygen depletion), the reworked topsoil and Made Ground (where used) should not be placed deeper than 300mm. The lower part of the soil profile should be constructed with suitable subsoil. Drainage Considerations The Ground Investigation report found clay found beneath the Made Ground, and as such the drainage performance of the soil profile is likely to be restricted. Therefore, there is a risk of tree pits acting as sumps for surface draining water. To avoid this, appropriate modifications should be incorporated into their design. This may including mounding around trees or groups of trees, or installing soakage layers / positive drainage as necessary / feasible. Drainage assistance (e.g. French drains or slot drains) may also be required in areas where surface draining water may collect, e.g. at the toe of slopes or alongside pathways or patio/lawn edges. It should be noted that positive drainage will require a suitable outfall. 5.3

Re-use of the Site Soils

The following section considers the potential to re-use the available soils for soft landscape construction. It is important to note that for all planting and seeding, the soils must have an adequate structural condition. The suitability of the site soils for the range of landscape types that may be selected is summarised on the Table 1 and Table 2 below.

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Table 1: Topsoil Suitability Reworked Topsoil

Made Ground

Amelioration / Notes

Rootballed trees





Stone reduction Fertiliser application

Shrub Planting





Stone reduction Fertiliser application

Amenity grass

X

X

Planting Environment



=

Reworked Topsoil or Made Ground suited to this landscape type provided the topsoil and subsoil are adequately structured, aerated and drained, suitable species are selected and any nutrient deficiencies are remedied through application of an appropriate fertiliser where necessary and the proportion of larger stones are reduced.

X

=

Reworked Topsoil or Made Ground not suited to this landscape type.

Table 2: Subsoil Suitability Planting Environment



Reworked Subsoil

Rootballed trees

O

Shrub Planting



Amenity grass (back gardens)



Amelioration / Notes Layer of washed sand directly below the rootball Mounding to help shed water

=

Subsoil suited to this landscape type provided the soil is adequately structured, aerated and species with a wide pH tolerance are selected.

O

=

Subsoil may be suitable for this landscape type, provided consideration is given to improving the drainage potential.

X

=

Subsoil not suited to this landscape type.

5.4

Imported Soils

Imported topsoils will be required for certain landscape types because the site-won soils are not suitable, on account of their high stone content and presence of sharps (see Section 5.3 above). In addition, an imported subsoil layer may be needed for larger rootballed trees (tree pits). The specified requirements for the imported soils should be included within the project soft landscape specification. It is recommended that the imported soils are predominantly sandy in texture to enable them to have good drainage characteristics together with high workability and resistance to compaction during the landscape works. Furthermore, their chemical characteristics, including pH and salinity should be suited to the requirements of the selected species. It is recommended that any imported topsoil contains sufficient reserves of organic matter and nutrients to reduce reliance on additional ameliorants (e.g. compost and fertiliser). Imported soils would usually also need to be compliant with the site’s environmental requirements, with regard to potential contaminants. As such, the specification should also include any site-specific assessment criteria, or if these are not available, suitable generic assessment criteria for potential contaminants (e.g. heavy metals, hydrocarbons, asbestos etc.) An example specification is provided in Appendix 3.

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6.0

SOIL RESOURCE PLAN

The following provides clear guidance on the methods of recovering, storing and re-using the soils whilst minimising a loss in quality and function as recommended in the DEFRA Code of Practice Sustainable Use of Soils on Construction Sites (2009). 6.1

Soil Handling

For the duration of the soiling works, the following soil handling recommendations should be followed. It is important to avoid physical degradation during all phases of soil handling (e.g. stripping, storage, respreading, cultivating, planting and seeding). As a consequence, soil handling operations should be carried out when soil is reasonably dry and non-plastic (friable) in consistency (at least 5% below the Lower Plastic Limit). In particular, it is important to ensure that the soil (topsoil and subsoil) is not unnecessarily compacted by trampling or trafficking by site machinery. In addition, soil handling should be stopped during and after heavy rainfall, and not continue until the soil is again non-plastic in consistency. If, during the course of the earthworks, the soil is structurally damaged, it will be important to ensure that it is suitably cultivated to relieve the compaction and restore the structure prior to any planting or seeding. Despite

the

inevitable

degradation

caused

by

stockpiling,

provided

the

soils

are

stripped/excavated, stored and respread correctly and cultivated to break up any compacted lumps, the soils should return to a healthy, aerobic state in a matter of days. If the soils are to be re-used successfully, structural degradation must be kept to a minimum. In order to achieve this, it is best practice for soil to only be handled when it is reasonably dry and non-plastic in consistency. 6.2

Topsoil Stripping

Vegetation Removal Before the topsoil is stripped, it is important to take action to minimise the amount of organic material that is incorporated with the topsoil and, this will involve removing as much of the existing vegetation as is practical. In this instance, the current grass sward should be removed by close mowing prior to the topsoil strip. If any trees are to be removed, they should be felled and their trunks disposed of. The tree stumps should be taken out using suitable equipment (e.g. tracked excavator with landscape rake or grab) and removed from site. All woody materials should be taken off-site to a green-waste recycling facility.

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To minimise anaerobism during storage and preserve the quality of the topsoil as a growing medium, woody materials should not be incorporated with the soils during stripping. This includes any chippings left on the surface after clearance of trees. Soil Stripping The loose tip method, using dump trucks and hydraulic excavators, should be used to strip, transport and respread the soils. It is the most appropriate method to use particularly for moderately heavy to medium textured soils such as these, which are prone to structural degradation and compaction. The loose-tipping method involves the use of a tracked hydraulic excavator, fitted with a flat edged grading bucket to strip the soil and load it into a dump truck. The dump truck, running along a pre-designated route, then transports the soil to the desired stockpile location. The topsoil, made ground and subsoil should be stored in separate stockpiles from one another. This operation should be closely monitored to ensure that the correct soil type is recovered without the inclusion of other soils or wastes. Cross contamination with other soil could significantly degrade the quality of the soils. Depth of Strip Where topsoil is to be stripped, the depth of strip should be set at 225mm (0.22m) - Topsoil or 285mm (0.285m) Made Ground to enable the majority of the topsoil layer to be recovered without the inclusion of significant quantities of subsoil. However, using an excavator to strip the soils, the colour differences between the topsoil layer and underlying subsoil can be seen by the machine operator carrying out the soil strip so that some discretion can be made. The topsoil layer depths at the locations inspected are indicated in the table above in Section 3.2. 6.3

Soil Stockpiling

Method Outline Once stripped/excavated, the topsoil should be stored temporarily, prior to re-spreading into the appropriate landscape areas. The soil materials should be stored in an area of the site where they will not interfere with other site operations so that it can be left undisturbed during other construction activities. The area that is to be used for storing the soils should be cleared of vegetation, in-situ topsoil and any waste arising from the development e.g. building rubble and fill materials. Stockpiling Method The diagram below (Figure 1) illustrates the sequence of operations to form a stockpile of dry/friable soil using dump trucks and a tracked dozer. It is preferable that the stockpile is created in a roughly square shape with a large ‘core’ and a minimum surface area. TOHA/16/5232/4/LHJ/Aug

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Tim O’Hare Associates

Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

The topsoil, having been transported to the storage area in a dump truck, should be ‘loose tipped’ in a series of heaps, starting at the furthest point and working back towards the storage area access point (a). Once the heaps cover the storage area, a suitable tracked dozer (e.g. D6 Caterpillar) should level the heaps to form a level, stable platform for dump trucks to travel across to tip a second layer of soil (b and c). This sequence should be repeated until the maximum stockpile height is achieved (d). Assuming that the soil is reasonably dry and friable during the stripping and storage operation, the soil should be heaped to a maximum of 5.0 metres (health and safety permitting). To protect from wet weather once the final height is achieved, the tracked dozer should regrade the sides and top of the stockpile to encourage water to runoff. It should then compact down the stockpile surface by tracking across it to seal in the dry topsoil and reduce rainfall infiltration (e). Figure 1. Stockpiling Method

If the soil is to be stored for more than 6 months, a quick germinating fescue/clover seed mix should be sown over the sides and top of the stockpile to stabilise the surface and reduce the risk of erosion. Once the stockpile has been completed, the area should be cordoned off with secure fencing to prevent any disturbance or contamination by other construction activities. 6.4

Grading Subsoil

In areas where additional subsoil is required, the material should be placed and graded in accordance with the Engineer’s requirements. Grade to smooth flowing contours to achieve the desired formation levels and falls and the specified finished levels of topsoil. Any large stones and other debris larger than 75mm brought to the surface during subsoil spreading should be stone picked or raked and removed. 6.5

Subsoil Thickness

Subsoil thickness (site-won or imported as appropriate) (after settlement) should be determined in line with the expected rooting depth of the plants selected. Typical recommended subsoil thickness (below topsoil layer) for the anticipated planting types would be:

TOHA/16/5232/4/LHJ/Aug

Draft

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Tim O’Hare Associates

Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

 Trees

400-600mm+ (depending on depth of rootball)

 Shrubs / Herbaceous Perennials

300mm

 Seeded areas (amenity grass) 150mm 6.6

Subsoil Decompaction

Following the soil recovery and construction stages, the subsoil is likely to have been compacted to some degree. Therefore, prior to spreading any topsoil (or additional subsoil), the subsoil/formation level should be loosened to a depth of at least 300mm in grass areas and 500mm in planting areas to break up any panning. The ‘rips’ should be made at 600mm centres. On this site, the landscape areas are generally reasonably small in size. As such, the appropriate equipment in this instance would be a tracked excavator, fitted with a single tine ripper attachment (ripper tooth) (see Plates 9 and 10 below). A toothed bucket is not suitable for this task. To be fully effective, all decompaction operations should be carried out when the soils are reasonably dry and friable to the full depth of working. Repeated passes may be needed to break up the subsoil sufficiently. This will be largely dependent on the strength of the soil and its resistance to cultivation at the time of the operation. Any large stones and other debris larger than 75mm brought to the surface by this cultivation should be stone picked or raked and removed. The stones should either be re-used on site or removed off-site to a suitably licensed waste facility.

Plate 9: Single Rigid Tine Attachment

TOHA/16/5232/4/LHJ/Aug

Plate 10: Single Rigid Tine working

Draft

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Tim O’Hare Associates

Cardiff Partnering Housing Project Ty Newydd Soil Resource Survey and Soil Resource Plan

6.7

Topsoil Spreading

A hydraulic excavator, fitted with a toothed-bucket to avoid excessive smearing, should be used to load the topsoil from the stockpile into a dump truck. The dump truck should transport the topsoil to the desired location and tip it in a line of heaps. It should then be spread by either a tracked dozer or second tracked excavator.

a) loosening the subsoil of the receiving ground b) loading of topsoil from stockpile c) backtipping topsoil onto loosened subsoil d) levelling topsoil

Figure 2: The loose-tipping method

6.8

Topsoil Depths

Topsoil depths should be determined in line with the expected rooting depth of the plants selected, and the quality of the topsoil. The recommended topsoil depths (site won or imported topsoil as appropriate) for the anticipated planting types would be:  Trees

300mm

 Shrubs / Herbaceous Perennials

300mm

 Seeded areas (amenity grass) 150mm 6.9 Tree Pit Construction Tree pits should be constructed to the dimensions specified and installed according to the project landscape specification. 6.10

Topsoil Cultivation

After respreading topsoil, any large, compacted lumps should be broken down using suitable tillage equipment (e.g. excavator with landscape rake attachment) to break down larger clods and produce a fine tilth suitable for planting (50mm) 8. Organic Matter (%) 9. Saturated Hydraulic Conductivity (ASTM Method F1815-11 - modified) 10. Potential Contaminants – See parameters in Clause 500 Additional samples and/or additional testing may be required if the initial results are not satisfactory or conclusive.

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Wates Construction Ltd Imported Soil Specification

410 IMPORTED SUBSOIL COMPOSITION • Quantity: Provide as necessary to complete the work. Make due allowance for settlement after laying. • The subsoil shall comply with the following lower and upper limits: Parameter Clay (50mm) Saturated Hydraulic Conductivity pH Value Electrical Conductivity (1:2.5 water extract) Electrical Conductivity (CaSO4 extract) Exchangeable Sodium Percentage Organic Matter

Unit % % % %DW %DW %DW mm/hr Unit µS/cm µS/cm % %

Lower Limit 0 0

Upper Limit 10 20

75

95

---20 5.0 -----

35 15 0 -8.5 1500 2800 15 1.5

420 PEA GRAVEL • Gravel to be used in the base of the tree pit shall be a quarried, washed, non-calcareous, subrounded to rounded gravel with particle size 6-10mm. - Product reference: pea gravel or pea shingle 500 ENVIRONMENTAL REQUIREMENTS • The following Generic Assessment Criteria (GAC) shall be used as Tier 1 screening values for the assessment of soil(s) to be used, unless Site-Specific Assessment Criteria (SSAC) are provided for this project. • In circumstances where any of these values are exceeded, further risk assessment and/or testing should be undertaken to confirm the significance of the non-compliance. Parameter Inorganic Arsenic Boron (soluble) Cadmium Chromium (III) Chromium (IV) Copper Lead Mercury Nickel Selenium Zinc Phenol Benzene Toluene Ethylbenzene Xylene - m Xylene - o Xylene - p

Unit mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg

Generic Assessment Criteria 37 290 11 910 6 100 200 1.2 60 250 200 280 0.087 130 47 59 60 56 Page 3

Ref: TOHA/16/52332/4/LHJ/Aug

Wates Construction Ltd Imported Soil Specification Continued… Parameter Aliphatics C5-C6 Aliphatics C6-C8 Aliphatics C8-C10 Aliphatics C10-C12 Aliphatics C12-C26 Aliphatics C16-C35 Aromatics C5-C7 Aromatics C7-C8 Aromatics C8-C10 Aromatics C10-C12 Aromatics C12-C16 Aromatics C16-C21 Aromatics C21-C35 Acenaphthene Acenaphthylene Anthracene Benzo(a)anthracene Benzo[a]pyrene Benzo(b)fluoranthene Benzo(g,h,i)perylene Benzo(k)fluoranthene Chrysene Dibenzo[a,h]anthracene Fluoranthene Fluorene Indeno(1,2,3-cd)pyrene Naphthalene Phenanthrene Pyrene Asbestos screen

Unit mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg Detected/ Not Detected

Generic Assessment Criteria 42 100 27 130 1100 65,000 70 130 34 74 140 260 1100 210 170 2400 7.2 2.2 2.6 320 77 15 0.24 280 170 27 2.3 95 620 Not Detected

GAC values derived from LQM CIEH S4ULs (2015) and BS3882:2015

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Wates Construction Ltd Imported Soil Specification

SPECIFICATION QUALIFICATIONS This document considers the proposal to use imported topsoil, subsoil and drainage media for soft landscape areas within Ty Newydd, Cardiff. This document should not therefore be relied on for alternative end-uses or for other schemes. This report has been prepared solely for the benefit of our client Wates Construction Limited. No warranty is provided to any third party and no responsibility or liability will be accepted for any loss or damage in the event that this document is relied upon by a third party or is used in circumstances for which it was not originally intended.

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