Preliminary Risk Assessment for Contaminated Land

Croxley Rail Link Scheme Desk Study - Preliminary Risk Assessment for Contaminated Land

5th March 2010

Produced for Hertfordshire County Council

Knights House 2 Parade Sutton Coldfield West Midlands B72 1PH

T 0121 355 8949 F 0121 355 8901

Croxley Rail Link Scheme Desk Study - Preliminary Risk Assessment for Contaminated Land

Document Control Sheet

Project Title Croxley Rail Link Scheme

Report Title Desk Study - Preliminary Risk Assessment for Contaminated Land

Revision 1020783/RPT/ENV/GEO/001

Status C

Control Date 05 March 2010

Record of Issue

Issue Status Author Date Check Date Authorised Date

A Draft 11/09 11/09 11/09

K Spruth S Layton J Nelson

Internal B issue for 11/09 11/09 11/09 comment K Spruth S Layton J Nelson

Internal C comments 03/10 03/10 03/10 included S Layton J Nelson J Nelson

Distribution

Organisation Contact Format Copies Mouchel – Sutton Coldfield Office Copy Electronic 1 Mouchel - Manchester Thomas Smeeton Electronic 1

Contents

Document Control Sheet...... ii

Contents...... iii

List of Figures...... vi

List of Tables ...... vii

1 Introduction...... 6

1.1 Terms of Reference...... 6

1.2 Development Proposals/Legislative Context...... 6

1.3 Previous Studies...... 7

1.4 Objectives and Scope...... 7

1.5 Report Structure ...... 8

2 Desk Study Research ...... 10

2.1 Site Location...... 10

2.2 Site Setting and Description...... 10

2.3 Adjacent Land Use ...... 12

2.3.1 Disused Site Section 12

2.3.2 Live Rail Section 14

2.4 Environmental Designations and Ecology...... 15

2.5 Site History ...... 15

2.5.1 Disused Site Section 15

2.5.2 Live Rail Section 17

2.6 Geology...... 18

2.7 Hydrology ...... 20

2.8 Hydrogeology ...... 22

2.9 Soil and Groundwater Chemistry ...... 23

2.10 Ground Gas...... 24

2.11 Services Information...... 25

3 Preliminary Risk Assessment...... 26

3.1 Ground Model...... 26

3.2 Potential Pollutant Linkages...... 27

3.2.1 Sources 27

3.2.2 Receptors 29

3.2.3 Pathways Creating Pollutant Linkages 30

3.3 Risk Evaluation...... 30

3.3.1 Risks to Human Health 31

3.3.2 Risks to Controlled Waters 33

3.3.3 Risks to Ecology 35

3.4 Consideration of the Risks to the Proposed Development ...... 36

4 Conclusions...... 38

4.1 Key Findings...... 38

5 Recommendations...... 40

5.1 Other Considerations...... 41

6 References ...... 42

Appendices

Appendix A - Envirocheck Report

Appendix B - Photographs

Appendix C - Preliminary Risk Assessment Tables

Appendix D - Envirocheck 1:10 000 scale Site Sensitivity Maps Slices

Drawings

736700/001/000/007 - Route Plan

787413/006/001 - Site Walkover and Waste Locations

List of Figures

Figure 2.1: Geology Underlying The Croxley Rail Link Scheme...... 18

List of Tables

Table 2.1: Potentially contaminative Active Trade Directory Businesses -Disused site section...... 12 Table 2.2: Potentially contaminative Active Trade Directory Businesses (Live rail section)...... 14 Table 2.3:Discharge Consents...... 20 Table 2.4: Pollution Incidents to Controlled Waters...... 21 Table 3.1:Sources of Contamination...... 27 Table 3.2:Receptors ...... 29 Table 3.3: Pathways ...... 30 Table 3.4:Summary of potential Pollutant Linkages which have the greatest risk rating 31 Table 3.5:Summary of Pollutant Linkages which have been identified as having the greatest risk rating for Human Health ...... 32 Table 3.6: Summary of Pollutant Linkages which have been identified as having the greatest risk rating to Controlled Waters...... 33

Disclaimer This report is presented to Hertfordshire County Council in respect of the Croxley Rail Link scheme and may not be used or relied on by any other person or by the client in relation to any other matters not covered specifically by the scope of this report.

Notwithstanding anything to the contrary contained in the report, Mouchel Limited is obliged to exercise reasonable skill, care and diligence in the performance of the services required by Hertfordshire County Council and Mouchel Limited shall not be liable except to the extent that it has failed to exercise reasonable skill, care and diligence, and this report shall be read and construed accordingly.

This report has been prepared by Mouchel Limited. No individual is personally liable in connection with the preparation of this report. By receiving this report and acting on it, the client or any other person accepts that no individual is personally liable whether in contract, tort, for breach of statutory duty or otherwise.

Executive Summary The proposed Croxley Rail Link scheme is located within the administrative boundaries of Watford Borough Council (WBC) and Three Rivers District Council (TRDC) Watford, both in south west Hertfordshire. The scheme occupies approximately 30ha and stretches between approximate National Grid References (509380, 195730), (511140, 196010) and (511010, 197390).

The scheme involves the joining of the Watford Branch of the London Underground Limited (LUL) Metropolitan Line and the currently disused Croxley Green Branch Line (part of the National Rail Network) in Watford. This will involve the addition of approximately 4.5km of new railway to the Metropolitan Line and the construction of approximately 0.2km of viaduct and embankment structures to connect the Metropolitan Line to the currently disused Croxley Green Branch Line. The viaduct will cross over the A412 Watford to Rickmansworth Road, the Grand Union Canal, and Ascot Road.

The scheme is located in a predominantly residential area, with light industry near the centre of Watford. Since 1899, the eastern portion of the scheme has been the site of a live railway; the London and North West Railway (L&NWR) with associated rail infrastructure such as stations, engine and carriage sheds. The western portion of the scheme was undeveloped until approximately 1920 when a single track railway line, the Croxley Green Branch Line, was built. The Croxley Green Branch Line functioned until approximately 1993. Following this, the area was left undeveloped and became overgrown.

The geology underlying the scheme is comprised of made ground overlying the Upper Chalk Formation of the Upper Cretaceous Period. Quaternary Drift Deposits of glacial sand and gravels exist at the site and overlie the chalk in a number of areas. Alluvium associated with the Rivers Colne and Gade. Peat is also present, noted in a borehole drilled by Costain, close to the proposed new Ascot Road Station. Shallow groundwater may exist beneath the site as the stratum below is classified as a major aquifer. Groundwater may be present within the drift deposits as well as the Upper Chalk Formation. The site is situated within Zone 1 and Zone 2 of a Source Protection Zone (SPZ).

Three surface water courses pass under the proposed Rail Link scheme and comprise the River Colne, the River Gade and the Grand Union Canal. These are considered to have Environment Agency (EA) General Quality Assessment (GQA) River Quality Grades of B (good), C (fairly good) and C (fairly good), respectively.

A nature reserve known as ‘Lairage land’ is situated south of the eastern end of the disused site section, sharing a boundary with the site, for approximately 200m.

Potentially contaminative land uses were identified close to the scheme. These included a chemical works, a printing works, an abattoir, a sewage farm, a number of

works of undesignated industrial use and waste facilities – inclusive of transfer, storage and treatment facilities.

Two historic landfills may partially underlie parts of the site. These are at Riverside Road to on the eastern side of the disused rail section and Waterfields Recreation Ground, to the east of the live rail section. Due to the age of the landfills it is likely that they were unlined and operated under a dilute and disperse regime. Therefore, any leachable contaminants are likely to have already been diluted and dispersed through the aquifer.

During a site walkover, areas of fly-tipping, which included potential ACMs, were identified. Made ground is likely to be present at the scheme, associated with both the active railway line and the now disused Croxley Green Branch Line.

Ground gas may be present at the scheme due to the former landfills close to the scheme (Riverside Road-disused rail section and Waterfields Recreation Ground – live rail section) and alluvium strata beneath the site, including peat. Gas data obtained from a report written by STATS indicated that there was sufficient ground gas observed to warrant gas protection measures in any proposed buildings.

The preliminary risk assessment indicated that the risks to human health and groundwater are greatest where there will be and as a result of ground disturbance during construction works.

There is a HIGH to MODERATE/LOW risk of potential contamination to controlled waters. The activities associated with the greatest risk are piling into the aquifer (proposed as part of the construction of the viaduct) and the movement of material associated with making the disused line, live again (areas of proposed cutting and possibly embankment enhancement) and new station construction (Ascot Road and Watford West Stations).

The risk to human health posed by the scheme ranges from MODERATE to VERY LOW . The greatest risk is associated with suspected ACMs on site contained with the fly-tipped material and elevated concentrations of contaminants in soil identified during the STATS site investigation on Ascot Road. However, the Riverside Road former landfill still represents a potential source of contamination for human health as ground excavation and disturbance is expected in this area as part of the scheme construction. Yet, as it is assumed ground workers will be wearing appropriate PPE the risk is only MODERTAE/LOW to LOW . The human group considered most at risk are ground workers during the construction phase of the development.

There is a LOW to VERY LOW risk to the Lairage Land nature reserve from potential contamination from the scheme.

It is recommended that a ground investigation is undertaken which is targetted to investigate only those areas where there will be ground disturbance. Based on the conceptual model, the only potential moderate and high risk ratings are directly

attributable to the construction phase of the works. It is recommended that the targetted areas will be in areas of proposed cuttings and potential embankment enhancement, the viaduct piling areas and where the new stations will be built. Within these areas, the areas of fly-tipping and the area thought to be underlain by former landfill (Riverside Road) should certainly be investigated. Ground gas may be present at the scheme and the new stations will have buildings and lift shafts, therefore, gas installations are recommended to be included in boreholes or window samples specified within the proposed station locations. Finally, as the earthworks will include movement of material and potential waste generation and removal, the ground investigation should include waste classification testing and Waste Acceptance Criteria (WAC) analysis.

Consent from the Environment Agency (EA) may be required to drill boreholes into the aquifer during the ground investigation and a piling risk assessment may be required prior to the construction phase of the works.

It is recommended that prior to any intrusive investigation is commissioned that information regarding buried services is obtained.

An asbestos survey could be undertaken to determine the nature and extent of asbestos containing materials on site.

In order to minimise the cost it is recommended that the contaminated land intrusive investigation should be undertaken jointly with an initial geotechnical design investigation.

Dependent on the findings of a ground investigation, the risks to human health, controlled waters and ecology from potential contamination can be mitigated using appropriate health and safety and environmental management during the construction of the scheme. Should correct health and safety procedures be followed, the overall risk rating will be reduced to LOW-VERY LOW.

Movement of material from one place to another within the scheme boundary will need to be considered as well as that designated for off site disposal. An appropriate waste management plan may be required to address the implications of waste movement, re-use and removal. If identified, Japanese Knotweed or other similar invasive species should be included within the waste assessment.

Any cut and fill operations within the scheme which may include the import of fill and disposal of surplus or unsuitable arisings will come under the waste management regulations. An appropriate waste management plan will be required to address the implications of waste movement, re-use and removal. Invasive species such as Japanese Knotweed should be included.

Overall, the main constraint to the scheme determined from this study is the major aquifer beneath the site and the fact that the scheme is located within a SPZ1 and

SPZ2. The potentially contaminated land constraints are associated with the former/live railway, former landfills, fly-tipping and suspected ACMs.

1 Introduction

1.1 Terms of Reference Mouchel was commissioned by Hertfordshire County Council (HCC) to carry out a preliminary risk assessment (PRA) for contaminated land in relation to a short section of proposed rail link; the Croxley Rail Link scheme in Watford, south west Hertfordshire.

It is understood that this study will form part of a submission to the Secretary of State for a consent order under the Transport and Works Act, 1992.

Henceforth, for clarity, the Croxley Rail Link scheme has been discussed as two separate site sections.

• The eastern portion of the scheme which traces the currently active portion of railway running north west – south east between Watford Junction Station and south west of Watford High Street Station is referred to as the live rail section.

• The remaining portion of the scheme running east-west along an existing disused portion of railway known as the Croxley Green Branch Line is referred to as the disused site section. When referring to the site in its entirety, the terms Croxley Rail Link scheme or scheme are used.

1.2 Development Proposals/Legislative Context The proposed scheme lies within the administrative boundaries of Watford Borough Council (WBC) and Three Rivers District Council (TRDC) in the County of Hertfordshire.

The Croxley Rail Link scheme was initially proposed by London Underground Limited (LUL) over 30 years ago. The scheme is currently being promoted by HCC and involves the joining of the Watford Branch of the LUL Metropolitan Line and the Croxley Green Branch Line (part of the National Rail Network) in Watford. Metropolitan Line trains will therefore terminate in central Watford, at Watford Junction Station, which currently services main line trains only.

The scheme will involve the addition of approximately 4.5km of new railway to the Metropolitan Line and the construction of approximately 0.2km of viaduct and embankment structures to connect the Metropolitan Line to the currently disused Croxley Green Branch Line. The viaduct will cross over the A412 Watford to Rickmansworth Road, the Grand Union Canal, and Ascot Road.

In addition, in order to ensure LUL rail functionality the Croxley Green Branch Line, which is currently a single track line, will be converted to a dual track with new signalling installed.

The scheme will also involve the construction of two new stations. One situated at Ascot Road which will provide a park and ride facility into the Watford Town Centre and the second being a new Watford West Station. The disused stations at, Croxley Green, Watford Stadium and the old Watford West Station will be closed permanently. It is likely that Watford Stadium and the old Watford West Station will be dismantled.

It is the intention that this study will form part of an Environmental Statement (ES) designed to assess potential environmental impacts related to the construction and future operation of the Croxley Rail Link scheme. Where possible, any potentially adverse impacts arising from the scheme should be avoided and, where this is not possible, mitigation measures should be proposed to reduce the residual effects.

1.3 Previous Studies Several previous studies and site investigations relating to the site have been undertaken by various third parties. These are listed below

• Aspinwall & Company Ltd: Croxley Rail Link Environmental Statement, June 1995 1

• Mouchel Parkman: Croxley Rail Link Environmental Impact Statement, June 2001 (updated March 2004) 2.

• Costain Geotechnical Services Ltd: Ground Investigation – The Croxley Rail Link Stage 1, 16 July 2003 3.

• STATS Ltd: Supplementary Contaminated Land Investigation – Ascot Road, Croxley, Watford, September 2008 4 The content of these reports, where appropriate and relevant, has been used and referenced as additional information to supplement the desk study.

1.4 Objectives and Scope The study was carried out in order to identify key areas of potentially contaminated land and its effects on the proposed scheme. In addition, the study assessed the potential contamination risks posed by and to the Croxley Rail Link scheme in terms of human health and controlled waters and as a result identifying the potential risk drivers for the development.

The aims of this study were to identify and assess whether contaminated land was likely to be present within the vicinity of the Croxley Rail Link scheme and the possible constraints to the associated development. Ecology has been briefly discussed in relation to waste issues associated with invasive species and the impact of potential contamination mobility on any sensitive ecological areas. A thorough ecological survey has been undertaken separately from this Desk Study. Archaeological considerations do not form part of this assessment.

It is intended that the findings of the study will form part of an ES which will be used within a Transport and Work Act application to the Secretary of State.

The following data sources were used to assess the whether contamination might be present at the proposed rail link.

• A Landmark Envirocheck Report (28792620_1_1) 5 for the study area. The report is reproduced in Appendix A and includes maps showing the subject site area;

• A walkover survey undertaken by Mouchel staff on 15th October 2009. Photographs taken during the survey are presented in Appendix B.

• The Environment Agency (EA) ‘What’s In Your Back Yard?’ database (www.environment-agency.gov.uk) 6. Search conducted on 3 rd October 2009;

• Ordnance Survey Landranger Map Sheet 176 West London, Rickmansworth & Staines (1:50,000 scale) 7

• British Geological Survey (BGS) (1:50,000 scale, solid and drift) Geological map of Beaconsfield (Sheet 255) 8

• British Geological Survey (BGS) (1 inch:1 mile scale, solid and drift) Geological map of North London (Sheet 256) 9

• Groundwater Vulnerability Map West London Area (Sheet 39) 10 • Environmental Impact Statement (Mouchel Parkman Limited, June 2001 (updated 2004) 2; and

• Previous reports – as detailed in Section 1.3. This information was used to develop a Conceptual Site Model (CSM) of the site based on identifying potential contamination issues which have a realistic likelihood of impacting the proposed Croxley Rail Link scheme. This model was based on the requirements of CLR11 Model Procedures for the Management of Land Contamination, 2006 11 and identified potential sources, receptors and pathways of contamination based on the proposed end use.

The Department of the Environment (DoE) industry profiles 12 were consulted to identify what contamination was likely to be present as a result of previous and current contaminative land use on and around the site.

Each source-pathway-receptor pollutant linkage was assessed in terms of the risk that each poses to the receptor/project. This was undertaken in general accordance with CIRIA guidance document CIRIA/DETR C552, 2001 Contaminated Land Risk Assessment, A Guide to Good Practice 13 .

1.5 Report Structure • Section 1 – Introduction. This section provides the background to the project and details the scope and objectives required of the desk study;

• Section 2 - Desk study research. This section provides factual, relevant information regarding the site and surrounding area which was used to undertake the preliminary assessment;

• Section 3: Preliminary Risk Assessment: This section uses and interprets the information detailed within Section 2 to provide an assessment of the contamination risks posed to and by the proposed Croxley Rail Link;

• Section 4: Conclusions: This section presents the key findings of the desk study and preliminary risk assessment;

• Section 5: Recommendations. This section details appropriate recommendations that should or could be incorporated into the Croxley Rail Link project programme. These recommendations are based on the findings of the preliminary risk assessment.

2 Desk Study Research

2.1 Site Location The proposed Croxley Rail Link scheme covers an area of approximately 30ha in Watford, south west Hertfordshire. The proposed scheme corridor comprises two main site sections being:

• A section of live rail line trending north west – south east between Watford Junction Station and Watford High Street station (live rail section); and

• A section of disused railway line formerly known as the Croxley Green Branch Line trending east-north east (disused site section). The scheme is located between National Grid References (511010, 197390), (511140, 196010) and (509380, 195730). The site location is shown on drawing 736700/001/000/007.

2.2 Site Setting and Description A site walkover was undertaken by Mouchel on 15 th October 2009. The description of the site which follows is based on the site conditions encountered at the time of the walkover. Relevant photographs are presented in Appendix B.

The walkover comprised the majority of the disused site section. The route of the walkover is shown on drawing 787413/006/001. The live rail section was not accessed as part of the site walkover as there will be no change in land use or ground disturbance in this area. Therefore, access was not required. The land immediately adjacent to the proposed scheme corridor was not accessible at the time of the walkover .However, observations of adjacent site use from the disused site section were made where possible. These observations were adequate for this initial phase works.

Access to the portion of disused railway was obtained from National Rail and was provided under their direct supervision. Due to the overgrown nature of the railway land, a corridor approximately 1.5m wide generally following the course of the single track was stripped using a brush-cutter prior to arrival on site to allow access and to allow observations of site conditions to be made (Plate 1). Direct observation of the ground within the disused railway cutting was therefore, only possible within the 1.5m corridor. Inspection of the areas outside the 1.5m corridor was restricted due to the thick vegetation.

The disused site section comprised a narrow corridor of land formerly utilised as railway land – the site of the former Croxley Green Branch Line. Although largely overgrown along the entire course of the route with a combination of brambles, thick shrubs and trees (Plate 1), a single track was still visible in places (Plate 2).

Both Watford Stadium (Plate 3) and Watford West Station (Plate 4) were still present. Although no buildings remained at either location, the station platforms themselves were still present.

Suspected asbestos roof tiling was identified on site immediately adjacent to the southern boundary (Plate 5). Due to the location of this tile and the absence of any structures within the disused site section from which it could have originated it is likely that the tile has been fly-tipped rather than being a remnant of a former building. Suspected asbestos-containing materials (ACMs) was also identified at the eastern end of the site section (Plate 6) – forming a structure (possibly from cabling ducts) parallel to the former railway line. The locations of these suspected ACMs are shown on drawing 787413/006/001.

Waste items were identified scattered randomly along the disused site section indicating the area has been used for fly-tipping (Plate 7). Items included iron kettles, plastic bags, tyres, wooden pallets an old TV and a mattress. In addition, a high volume of fly tipped waste material was evident adjacent and beneath the two road bridges that crossed over the disused site section. These bridges were situated to the east of the disused site section. These were the Vicarage Road Bridge, and immediately to the west of Watford West Station the A4145 road bridge respectively. Miscellaneous waste including broken glass bottles, plastic bags, cans, a mattress and an iron framed bench were all identified (Plate 8).The main locations of fly tipped waste are shown on drawing 787413/006/001.

The site was bound with a combination of 2m high wire fencing with concrete bollards, steel fencing (Plate 9) and wooden palisade fencing. The boundaries of the site, however, are not secure. In a number of places fencing was absent altogether, holes were present in the wooden fencing. Anecdotal evidence from Network Rail staff indicated that the site has been accessed by drug users on a number of occasions and ‘sharps’ had been identified beneath the A4145 road bridge.

In addition, ‘encroachment’ of the neighbouring residential development was identified at the eastern end of the section where National Rail boundaries were not secure and had thus allowed residents to extend their gardens into an unauthorised area. Generally, this appeared to involve residents using National Rail land as an additional storage area rather than for a recreational purpose. Evidence of this included wooden garden furniture being stored immediately adjacent to the residential property boundary on National Rail property.

Visible adjacent land uses included residential housing, a retirement home, a film studio, car parks and a school playground.. An active electricity substation was present to the south of Watford Stadium Station (Plate 11).

The site walkover was terminated at the A412 (Plate 12), where it is proposed to build a viaduct over the road and canal joining the disused site section to the Metropolitan Line.

2.3 Adjacent Land Use The Croxley Rail Link scheme is located in a predominantly residential area near the centre of Watford. Several small industrial estates are present in the area, along with schools, recreation grounds, hospital complex and a business park. An electricity substation is situated immediately to the south of the disused site section adjacent to the now disused, Watford Stadium Station.

A more detailed description of the land uses immediately adjacent to the scheme is provided in the following sections. For clarity, these land uses have been divided into two groups, those close to the disused site section in the west, and those close to the live rail section in the east.

2.3.1 Disused Site Section The closest active business with a current trade directory entry was located 7m south west of the disused site section. The business was classified as a ‘Car dealers-used’ 5 and could represent a potential source of contamination.

A further 24 trade directory businesses were located within 50m of the disused site section. Of these, 12 were active of which 8 are considered to represent potentially contaminative land uses. Details of these active trade directory entries, which may also be potentially contaminative land uses are listed in the table below. The types of potential contamination associated with these industries are discussed in Section 3.

Table 2.1: Potentially contaminative Active Trade Directory Businesses -Disused site section

Potentially contaminative Active Trade Directory Businesses (Disused site section)

Name Classification Distance Description of location from disused site section (m)

Croxley Car Centre Car dealers - used 7 South of western tip

Tolpits Motors Garage services 19 North, on Tolpits Lane

Watford Refrigeration & Air conditioning & 24 East, on Wiggenhall Road Air Conditioning Ltd refrigeration contractors

Ralco Tubings Ltd Hose, tubing & fittings 31 East, on Wiggenhall Road

WDS Marico Engineers- general 34 North, on Hagden Lane

Three Rivers Display Ltd Print finishers 36 North, on Sydney Road

Fine Cut Finishing Ltd Print finishers 37 North, on Sydney Road

Piper Toughened Glass Safety glazing 37 North, on Sydney Road Ltd

Solo Services Garage services 38 North, on Sydney Road

A single active fuel station operated under the name of HKS Colne for British Petroleum Ltd (BP) was identified 160m east of the disused site section 5.

Two historic landfill sites were also identified within 200m of the disused site section. The closest, located at Riverside Road, Oxhey shares a boundary with the eastern edge of the disused site section,5,6 on the opposite side of railway line from the hospital complex. It is unclear if the boundaries of the landfill are accurately defined and therefore waste might underlie the disused site section, or encroach into the railway cutting. The second historic landfill site was located approximately 175m north west of the disused site section, located on Rousebarn Lane. The licence was held by H G Sanson and Sons and was authorised for the deposit of inert and special waste. The last recorded input date to the landfill was 1 st June 1958 5.

Two licensed waste management facilities were located within 100m of the disused site section. The closest was located approximately 50m north of the disused site section within the Cardiff Road Industrial Estate and was operated by DMC Recycling Limited. The site was categorised as a metal recycling site (vehicle dismantlers). The licence is currently active 5. A second licensed waste management facility was located 80m north west of the disused site section on Ascot Road, operated by Holywell Haulage Limited. The site was categorised as a transfer station taking non-biodegradable wastes.

A licensed waste transfer site was located approximately 215m south east of the disused site section and was licensed to Hertfordshire County Council Waste Management Unit. The transfer site was categorised as a civil amenity site and was authorised to operate with a very small input rate – less than 10,000 tonnes per year 5. Waste accepted by the site included civic amenity waste. The licence status is operational.

Two registered waste treatment or disposal sites were located within 50m of the disused site section. The closest, defined as a transfer site, was located less than 10m to the north west of the site section. The licence is held by Wilsons (Cricklewood) Ltd and was licensed to operate with a very small input rate – less than 10,000 tonnes per year 5. Waste authorised at the site included paint residues and paint thinners. The licence has lapsed or has been cancelled.

The second site, defined as a waste storage site, was licensed to Oldhams-Sun Printers Ltd, Whippenhall Road, and is located less than 10m south west of the site section. No input rate was defined for this site. Authorised waste included chromic acid, oil/water mixtures, other inorganic compounds, sawdust/bark and waste solvents. The licence has lapsed or has been cancelled 5.

A single prosecution incident relating to authorised processes was recorded for a location 65m to the south west of the disused site section on Ascot Road. This incident involved the unauthorised storage of waste on site. The perpetrator was found guilty at a hearing which was held on 7th August 2001 and was prosecuted under the Environmental Protection Act, Sections 33 and 34 5.

2.3.2 Live Rail Section The closest active businesses with current trade directory entries were located less than 10m south east of the live rail section. These businesses were classified as ‘commercial vehicle dealers’, ‘commercial vehicle manufacturers and telecommunications equipment & systems 5.

A further 23 trade directory businesses were located within 50m of the live rail section. Of these 9 were active and 8 of these considered to represent potentially contaminative land uses. The location of these potentially contaminative active trade directory entries are listed in the table below. The types of contamination originating from these industries are discussed in Section 3.

Table 2.2: Potentially contaminative Active Trade Directory Businesses (Live rail section)

Potentially contaminative Active Trade Directory Businesses (Live rail section) Name Classification Distance from live Description of rail section (m) location Iveco Ltd Commercial vehicle <10 West, on Station road dealers Iribus UK Ltd Commercial vehicle <10 West, on Station road manufacturers Telecom Resource Telecommunications <10 West, on Orphanage Equipment & Systems Road Brookdene Motors Car dealers 11 East, on New Road Throughway Motors Ltd Garage services 12 West, on Bridle Path Mazway Car body repairs 24 West, on Bridle Path Fluke Networks Testing, inspection and 31 West, on St Albans calibration equipment Road manufactures Printing.Com Printers 41 North west, on St Albans Road Colour Separations Ltd Lithographic plate 41 West on Woodford makers Road Axle Garage services 41 West, on Queens Road C&C Glass Glass engravers & 47 West, on Queens Road decorators

In addition, a single active fuel station operated under the name of TCS Watford for TOTAL was identified approximately 200m to the north of the live rail section 5. A single local authority pollution prevention and control permit had been issued for this business with regard to air pollution and was currently in effect.

Two historic landfill sites were located within 50m of the live rail section. The closest, known as Waterfields Recreation Ground runs parallel to the eastern boundary of the live rail section and may underlie it in places. No further details on the landfill were idenitifed 5. The second historic landfill site was located approximately 80m to the

south east of the live rail section, located on Radlett Road. The licence was held by the Borough of Watford and authorised for the deposit of inert, commercial and household wastes between 1 st January 1984 and 18 th December 1985 5

A registered waste transfer site was located approximately 50m north west of the live rail section and was licensed to R.J & H Haulage Ltd .The transfer site was authorised to operate with a medium input rate, which is equal to or greater than 25,000 tonnes per year and less than 75,000 tonnes per year. Waste accepted by the site included ferrous metal, hardcore and rubble, metals, paper/cardboard waste and spoil. The licence has lapsed or has been cancelled 5.

A registered waste treatment/disposal site was located approximately 60m north of the live rail section, licensed to BASF Coatings and Inks Limited. The site was authorised to operate with a maximum input rate of less than 10,000 tonnes per year (which is classified as a very small input rate). Waste accepted by the site included heavy sludge/semi solids, non-usual waste awaiting analysis, oil ink filters and solvent processed washes. The licence has lapsed or has been cancelled 5

A single local authority pollution prevention and control permit had been issued for a business within 50m of the live rail section with regard to air pollution. This permit was issued to London Concrete Ltd located approximately 40m south west of the live rail section, within Orphanage Road Yard, and was issued with regard to air pollution arising from the blending, packing loading and use of bulk cement. This control was currently authorised 5.

2.4 Environmental Designations and Ecology The following information relating to environmental designations and ecology, details only those areas which could be impacted by potential contamination from the site. A full ecological survey in relation to the scheme is being undertaken separately from this desk study.

The Croxley Rail Link scheme is located within a Nitrate Vulnerable Zone as designated by Department for Environment, Food and Rural Affairs (DEFRA) 5.

There is a small area of nature reserve known as Lairage land present immediately to the south of the eastern end of the disused site section 5. The nature reserve shares a boundary with the site section for approximately 200m.

2.5 Site History 2.5.1 Disused Site Section

Map Extracts dated 1899 5. 1:10,560, 1:10,000 scale

The earliest map extract available showing the western portion of the scheme is dated as 1899 and showed the current disused site section to be undeveloped agricultural land. The surrounding area comprised undeveloped agricultural land to

the west and the residential development to the east. Two sewage works were shown at the eastern end (at the southern most bend of the scheme) of the disused site section, to the north and the south of the railway line. These were named as Watford Sewage Pumping Station and Bushey Sewage Outfall Works respectively. Watford Steam and Dye works was also noted in this area, to the south of the railway line.

Map Extracts dated from 1920 to 1921 inclusive5. 1:10,560 scale.

The Croxley Green Branch Line, running from the north west to the south east, and associated rail infrastructure was present on map extracts dated 1920/1921. Two railway stations, the Croxley Green Station situated at the sections western edge and the Watford West Station located in the centre of the section, were shown. Towards the east, two new portions of railway: the Croxley Green Curve and the Bushey Curve were also shown linking the Croxley Green Branch line to the north- south trending North Western railway line in the east representing significant development of transport links in the area during this period. Where the Croxley Green Curve and the Croxley Green Branch Line join, this point was called Croxley Green Junction. This junction is located at the most southerly point of the overall scheme.

A number of potentially contaminative land uses were evident within 250m of the disused site section at this time. These included a printing works, chemical laboratory and speedometer works. These potentially contaminative uses are no longer shown on map extracts from 1938 onwards. In addition by 1920/21 the Watford Sewage Pumping Station sewage works had been renamed to an electricity works (named as Watford UDC (Urban District Council)).

Map Extracts dated 1938 5. 1:10,560 scale.

By 1938 a lorry works is shown to have been constructed approximately 50m south of Watford West station. 450m south of Watford West Station, there was also a sewage farm. A large amount of residential development in the area surrounding the disused site section to the west, northwest and north was shown to have taken place by this time.

Map Extracts dated from 1961 to 1978 inclusive 5. 1:10,560, 1:10,000, 1:2500, 1:1250 scales.

Between 1961 and 1978 further widespread industrial and residential development was shown to have taken place within the area. A number of works of unidentified use appear to have been built within 250m of the disused site section and residential development continued within areas immediately surrounding the site section. Shrodells hospital was marked on the 1961 map extracts, at Vicarage Road, north of the railway line. A large carriage shed, located adjacent to the railway line, near to Croxley Green Junction was also shown. By 1975, the Bushey Sewage Outfall

Works was no longer shown. It had been replaced by a caravan park and later, housing.

Map Extracts dated from 1978 to 2009 inclusive 5. 1: 25,000, 1:10,560, 1:10,000, 1:1250 scales.

By 1978, several more works are located within the scheme area. Residential development in surrounding areas continued throughout this period and an abattoir was present 100m to the south of the site section at Holywell. The Croxley Green Curve is shown to have been dismantled. On the 1991 map extract an electricity transmission station was shown within 250m to the south of the Croxley Green Junction. The works between the hospital and the railway line were shown to consist of a sewage works, depots and a power station. The carriage shed first noted on the 1961 map extract was no longer shown.

From 1999 onwards the Croxley Green Branch Line and station was labelled as ‘disused’. With the exception of the power station building no longer being shown on map extracts from 2006 onwards, no further significant changes were shown to have occurred on or in the immediate vicinity of the site between 1999 and 2009 (present day).

2.5.2 Live Rail Section

Map Extracts dated from 1873 to 1898 inclusive 5. 1:10,560, 1:2500 scales.

The earliest map extracts show that the railway had been constructed. Between 1873 and 1898 a number of additional railway lines had been constructed parallel to the existing track.

Map Extracts dated 1899-1914 5 1:10,560, 1:10,000 scale.

Throughout this period the live rail section was shown to be undergoing development. The 1899 map extract shows the London and North Western Railway Line and associated railway infrastructure including the Watford Junction Station, a goods shed and an engine shed within the live rail section. Three breweries (80m south, 200m south east and 250m north), a saw mill (80m north east) and plate works (200m north) were also apparent at this time. Undeveloped agricultural land was indicated to the north east and east, and residential housing along with small industries shown to the west and southwest.

Map Extracts dated from 1925 to 1961 inclusive 5 1:10,560, 1:10,000, 1:2500, 1:1250 scales.

Between 1925 and 1961 the area to the west, north, north east and east of the live rail section is shown to be greatly developed. A large amount of residential housing

with associated infrastructure was shown to have been constructed in the areas surrounding the live rail section and from 1961 is labelled on map extracts as North Watford. A number of Works between 100m and 800m distance were also recorded to the north east of the live rail area from 1961. However, their industrial uses are not shown.

Map Extracts dated from 1961 to 1975 inclusive 5. 1:10,000, 1:1250 scales.

Between 1961 and 1975 a number of additional sidings were shown at Watford Junction Station and further residential development shown to the far north of the site section.

Map Extracts dated from 1975 to 2009 inclusive 5 1:25,000,1:10,000, 1:1250 scales.

No further significant changes are recorded on the map extracts between 1975 and 2009 (present day).

2.6 Geology The Croxley Rail Link scheme is underlain by Quaternary Drift Deposits inclusive of alluvium and glacial sands and gravels.8, 9 These deposits overlie the Upper Chalk formation of Cretaceous age, which also outcrops directly at the surface in a number of locations.

Approximate areas of Quaternary Drift Deposits and their position in relation to the chalk are presented in Figure 2.1 below.

KEY Watford Junction Station Alluvium

Glacial sands & Watford Station Gravels

Watford High St Upper Chalk Station

New Ascot Road Station & Croxley Rail Link Scheme – Car Park Proposed New disused and live rail sections Station (location TBC) Watford Live OLD Watford West Rail Line (not within Scheme) Station Railway Station

NOT TO SCALE

Figure 2.1: Geology Underlying The Croxley Rail Link Scheme (Summarised from BGS Geological map sheets 8,9 ).

Alluvium associated with the Rivers Colne and Gade overlie the Cretaceous Upper Chalk at both the eastern and western ends of the disused site area. In addition, glacial sand and gravel overlie the Upper Chalk Formation in the centre of the disused section and the northern portion of the active rail section. In all other locations along the scheme, the Upper Chalk Formation outcrops directly at the surface.

The Cretaceous Upper Chalk comprises very fine-grained limestone, characterised by flint nodules and fossils of brachiopods, echinoderms, sponges and some bivalves. It reaches a maximum thickness of approximately 100m beneath the site 8,9 .

Ground conditions at the western end of the disused site section were confirmed during a ground investigation undertaken adjacent to the existing railway track, to the immediate south of the A412 in Croxley Green, by Costain Geotechnical Services in July 2003.3.

All exploratory holes encountered granular made ground between 0.4 to 1.10m below ground level (bgl). This was underlain by flint gravels in most exploratory locations, which extended to between 5.6 to 8.0m bgl. Pseudofibrous peat was identified in one exploratory location directly underlying the made ground to a depth of 2.5m bgl. This was in turn underlain by flint gravels to a depth of 4.7m bgl 3.

In all cases, the flint gravels were immediately underlain by chalk containing nodules and cobbles of flint. All boreholes were terminated within this stratum 3.

Findings of this investigation are considered to confirm the geology as stated within geological maps of the region.

The scheme and surrounding area were not considered to be in an area affected by coal mining or in an area where shallow mining was a hazard 5.

As the scheme is underlain by chalk, the scheme is located in an area where underground cavities could be present. Solution pipes (natural cavities formed by surface water entering a cave system) have been identified approximately 200m to the south west of the disused site section 5 at approximate grid references (508450,195800) and (508500,195750) respectively. Solution pipes are also located 60m north west (NGR 511380,196300) and approximately 220m south west ( NGR 511200,196500) of the live rail area 5.

The scheme is located in an area where ground stability hazards were generally moderate-low 5. Collapsible stability hazards were absent from ground conditions underlying the scheme and compressible stability hazards ranged from moderate to absent 5. The risk from ground dissolution stability hazards ranged from moderate to very low and the risk from landslide stability hazards from low to absent 5. In addition, the potential for running sand and shrinking or swelling clay hazards was considered low to absent 5.

2.7 Hydrology The scheme passes over two main rivers and the Grand Union Canal. According to the 1:10,000 scale map extract dated 2009 5, the River Colne flows parallel to the Watford mainline towards the south before turning to the east where it intersects the active section of the site to the south west of Colne Bridge. The River Colne also intersects the eastern end of the disused site section at Croxley Green Junction. The River Colne was considered to have an overall River Quality Grade of B (good). The flow direction was to the south-south west 5.

The River Gade intersects and crosses the disused site section at its western edge. The River was considered to have a GQA River Quality Grade of C (fairly good).. The flow direction was to the south 5.

A canal also crosses beneath the railway at the western end of the disused site section. The ‘GUC’ (Cassiobury Reach) part of the Grand Union Canal system runs parallel to the River Gade north to south. The canal was considered to have a River Quality Grade of C (fairly good).5.

The disused site area is located downstream of the Rivers Colne and Gade thus both western and eastern portions of the disused site section are considered to be at risk from fluvial flooding. The central portion of the live rail section is also considered to be at risk 5.

Two surface water abstraction locations were identified between 250 to 500m of the scheme. Both abstraction locations were situated at the western end of the disused site section, south of Sydney Road. The permits for the two abstractions were for taking water from the River Gade for agricultural purposes 5.

A total of eleven discharge consents were noted for discharges within 250m of the scheme. Of these, five were located within 50m of the scheme and six between 50 to 250m of the scheme. Information on the type, location and status of these discharge consents is provided in Table 2.3 below.

Table 2.3:Discharge Consents

Discharge Consents Site Section Distance Operator Discharge Type Receiving Consent from site Water status section (m) Live Rail 2 Thames Water Other matter- River Colne Revoked Section Utilities Ltd surface water 109 Thames Water Public sewage – Hilfield brook Temporary Utilities Ltd storm sewage consent overflow 109 Thames Water Sewage Tributary of Transferred. Utilities Ltd discharges – storm River Colne overflow/storm

Discharge Consents Site Section Distance Operator Discharge Type Receiving Consent from site Water status section (m) tank 167 Tesco Stores Ltd Other matter- River Colne Transferred surface water <10 Thames Water Other matter- River Colne Revoked Authority surface water <10 Unit Moulders Ltd Trade discharges Gravel Strata Revoked – cooling water <10 Thames Water Trade Tributary of Revoked Utilities Ltd Effluent/unknown River.Gade 43 Hertfordshire Ice & Trade discharges Into Land Revoked Disused Site Cold storage – cooling water Section company Ltd 75 Powergen Ltd Trade discharge – Not supplied Not supplied site drainage 151 Scottish provident Other Matter- Tributary of Lapsed Institution Surface Water River Gade 167 National Grid Trade effluent River Colne New consent Transco Plc discharge – site drainage

Of the five discharge locations noted within 50 m of the site, four were located near the disused rail section and one near the live rail section. Two were noted south of Cardiff Road, on the northern side of the disused rail line, near to the hospital and football ground. The other two locations in the vicinity of the disused rail line were noted on the southern side of the rail line, to the west of Wiggenhall Road and north of Riverside Park former landfill and, on Ascot Road, close to the proposed New Ascot Road Station at the western end of the disused rail section. The discharge consent by the live rail section was located at the site of the former Waterfields Recreation Ground landfill. All five discharge consents have been revoked. For further details on the location of these discharge consents see Envirocheck Site Sensitivity Maps Slices A-C, Appendix D.

Thirty nine pollution incidents to controlled waters were recorded within 250m of the scheme. These are summarised in Table 2.4 below:

Table 2.4: Pollution Incidents to Controlled Waters

Pollution Incidents to Controlled Waters Distance from site section Pollutant Description Site Section Incident Category <50m 50-250m >250m Live Rail Category 3 - Minor 1 4 None Miscellaneous- unknown, Section Incident unknown sewage,

Pollution Incidents to Controlled Waters Distance from site section Pollutant Description Site Section Incident Category <50m 50-250m >250m unknown oils, unknown chemicals. Category 2 – None 1 None Miscellaneous – natural Significant Incident pollutants Eastern Category 3 - Minor 1 15 None Miscellaneous unknown, Disused Site Incident unknown sewage, Section unknown oils, unknown chemicals Category 2 – None 3 None Unknown oils, unknown Significant Incident sewage. Western Category 3 - Minor 5 9 None Miscellaneous –fire Disused site Incident water/foam, unknown section sewage, unknown oils, unknown chemicals

Seven pollution incidents to controlled waters were recorded within 50m of the scheme. All were designated as category 3 - minor incidents and involved the discharge of various pollutants (see Table 2.4) into an unspecified water course. The pollution incident recorded as having occurred within 50m of the live rail section was located adjacent to the site within the former Waterfields Recreation Ground Landfill boundary. The receiving water course was likely to be the River Colne. In terms of the disused rail section, of the six locations recorded within 50 m of the site, five were recorded within in the vicinity of Cassie Bridge at the western end of the disused rail section. The pollution incidents occurred to the north of the railway line, north of the proposed new Ascot Road Station. All are likely to have been associated with the River Gade. The sixth pollution incident was in the area of the hospital complex, at the southern most point of the disused railway line. The receiving water here was likely to have been the River Colne.

A further 32 incidents were recorded within 50-250m of the scheme. Of these 28 incidents were designated as category 3 – minor incidents involving the discharge of a variety of pollutants (see Table 2.4) into local water courses. The remaining 4 incidents were designated category 2 – significant incidents and involved the discharge of miscellaneous natural pollutants, unknown oils and unknown sewage into an unspecified water course 5.

For further detail on the location of these pollution incidents see Envirocheck Site Sensitivity Maps Slices A-C, Appendix D.

2.8 Hydrogeology The superficial deposits of alluvium and glacial sands and gravels and the Upper Chalk Formation of Cretaceous age are considered to represent, what was formerly classified as, a major aquifer. These are described as highly permeable formations usually with a known or a probable presence of significant fracturing. They may be

highly productive and able to support large abstractions for public water supply and other purposes 10 . Under the EAs new, recently published hydrogeological classification system/guidance, the Upper Chalk Formation would likely be reclassified as a ‘principal aquifer stratum’. The ‘principal aquifer’ classification is considered directly comparable to the former EA ‘major aquifer’ classification. However, as the new EA classification system has not yet been published for geological strata across the UK, (as only the terminology has been published) the ‘major aquifer’ definition has been used within this desk study to describe the aquifer properties of the Upper Chalk Formation.

The major aquifer strata identified are in turn overlain by soils of high leaching potential. These are considered to be soils which can transmit non-absorbed pollutants and liquids, but may attenuate adsorbed pollutants due to high clay/organic matter content 5,10 .

The Croxley Rail Link scheme is located within a groundwater Source Protection Zone (SPZ). The disused site section and the south of the live rail section are located within an inner source protection zone (Zone 1) defined by a travel time of 50 days or less for a pollutant to reach an abstraction point 5.

The northern portion of the live rail section is located within an outer SPZ (Zone 2) defined by a travel time of 400 days to an abstraction point or by a journey of 25% of the source catchment area, whichever is larger 5.

Two groundwater abstraction locations were identified <10m from the scheme, situated to the north west of the western and eastern ends of the disused site section respectively. A further four were located between 250-500m of the scheme and were used for the abstraction of potable water supplies. The abstraction locations within 10m of the scheme were operated by A A Fishers Property Ltd and Watford Launderers and Cleaners Ltd 5. The abstraction licence granted to AA Fishers Property Ltd was issued in 1992 and was for extracting water from two boreholes located at Wiggenhall Road, Watford for industrial/commercial/public services: non evaporative cooling 5. The abstraction permit granted to Watford Launderers and Cleaners was issued in 1989 and was a permit to abstract water from a single point for industrial/commercial/public services: laundry use 5. No information on expiry dates for these permits was provided, therefore it is assumed abstraction from these locations is still authorised.

For further detail on the location of these abstractions, see Envirocheck Site Sensitivity Maps Slices A-C, Appendix D.

2.9 Soil and Groundwater Chemistry An investigation was undertaken by STATS which was reported in September 2008 for a site on Ascot Road. The information summarised below relates to a small area south of the disused site section on Ascot Road which is intended to be the site of a new car park of the new Ascot Road Station. Therefore, the following information is relevant and representative of the ground conditions likely to be present in the area

of the new Ascot Road Station but the information contained therein cannot be considered representative of the chemical characteristics of the soil underlying the entire scheme.

The site was formerly used as a Waste Transfer Station. 36 soil samples were obtained from both the made ground and natural strata to a maximum depth of 2m bgl for chemical analysis 4. All soils were inspected at the time of sampling for asbestos/ACMs and a total of 12 samples of the made ground were screened in the chemical laboratory for asbestos fibres 4. The chemical results were then subjected to an initial screening exercise by STATS using Contaminated Land Exposure Assessment (CLEA) Soil Guideline Values (SGVs) 14 for a commercial end use (car park). Where no CLEA SGV had been published, STATS used Generic Assessment Criteria (GAC) published by the Chartered institute of Environmental Health (CIEH) and Land Quality Management Ltd (LQM) 14 . Where neither a SGV or a GAC was available, Site Specific Assessment Criteria (SSAC) were derived by STATS using CLEA UK methodology 4,14 .

According to STATS, the results indicated the presence of diffuse contamination within the soils. Elevated concentrations of copper and zinc were identified within both the made ground and the alluvium. Elevated concentrations of benzo(a)pyrene and petroleum hydrocarbons were identified within the made ground. STATS also identified two “hotspots” of lead contamination - one in made ground and one in alluvium 4.

In addition STATS stated that 5-15%v/v of chrysotile (white) asbestos fibres were found within a single sample during the 2005 site investigation 4.

No information was obtained with regard to groundwater chemistry on or around the site. STATS previous quantitative groundwater risk assessment concluded that the site represented no significant risk to controlled waters. Therefore no further assessment was undertaken during their Supplementary Contaminated Land Investigation Study.

2.10 Ground Gas The site investigation undertaken by STATS included gas monitoring in September 2008. The results contained therein are summarised below.

During May 2005, six standpipe monitoring installations were monitored by STATS. Three site visits were undertaken on a weekly basis during which atmospheric pressure varied between 1007 and 1015mb. Results indicated maximum concentrations of 6.9%v/v and 4.9%v/v of carbon dioxide and methane respectively with a maximum flow rate recorded of 4 litres per hour 4.

The ground gas results were assessed by STATS in accordance with the CIRIA Guidance Document C659 “Assessing Risks Posed by Hazardous Ground Gases to Buildings” (CIRIA 2006) 15 .

Based on the results obtained during the investigation, the site was characterised by STATS as Characteristic Situation 2 in line with the method proposed by Wilson and Card, (1999) 4. Recommended protective measures for the proposed commercial development for Characteristic Situation 2 included a 2000 gauge reinforced gas proof membrane, possibly in conjunction with underfloor venting depending on the end use. The STATS report did not recommend passive or active venting.

STATS did conclude however, that although the gas monitoring undertaken provided an indication of a low risk gas regime typically associated with made ground or the underlying alluvium, it was likely that the investigation had not established the “worst case scenario” and therefore further gas monitoring would be required prior to any development to adequately characterise the gas regime 4.

The STATS gas assessment was confined to the small area to the south of the disused site section on Ascot Road (which is intended to be the site of a small car park associated with the new Ascot Road Station). Therefore, the assessment does not directly relate to the whole scheme. As such further monitoring, or in the absence of further monitoring, more stringent gas protection measures should be considered. However, as the scheme is unlikely to have dwellings or other buildings constructed other than at stations it is considered that any future monitoring or protection should focus, only on these areas. Appropriate gas protection measures, if required will need to be incorporated into buildings and lift shafts built as part of any railway station construction. Monitoring in these areas will help to determine the appropriate measures required.

2.11 Services Information The project brief did not contain provision for Mouchel to obtain relevant information from service providers therefore no information on services present at or underlying the site has been obtained at this preliminary assessment stage. Service information will be provided should further investigation be required.

3 Preliminary Risk Assessment

3.1 Ground Model The site is directly underlain by the Upper Chalk Formation of the Upper Cretaceous Period, although in places this is obscured from outcropping at the surface by Quaternary drift deposits (Glacial sand and gravel) and alluvium associated with the Rivers Colne and Gade. These strata are classified as major aquifer strata. A number of groundwater abstraction wells were situated in close proximity to the scheme for industrial/commercial/public services. It is likely therefore that groundwater will be present at a shallow depth beneath the site.

The site lies within a combination of Zone 1 (Inner) and Zone 2 (Outer) SPZs for groundwater, indicating the underlying aquifer and potable water supplies are considered especially vulnerable to surface contamination. As these strata are in turn overlain by soils of high leaching potential, it is likely that any contamination could leach from the soils and contaminate the groundwater and/or surface water.

Groundwater flow direction is considered to be towards the south to south west towards the Rivers Colne and Gade and the Grand Union Canal. It is therefore possible that potential contamination within the soils beneath the site could migrate toward these surface water courses. As the strata underlying the site are considered to be highly permeable, the potential for migration in the subsurface is high.

As the River Gade has an overall River Quality Grade of B (good), the sensitivity of this water course to potential contamination is considered high. The River Colne and the Grand Union Canal section that pass under the scheme have an overall River Quality Grade of C (fairly good) and are therefore considered to have moderate sensitivity to potential contamination.

There have been 39 known pollution incidents to controlled waters within 250m of the scheme. Of these, seven have occurred within 50m of the scheme boundary. The majority of the incidents are considered to be upstream of the scheme, which therefore may have impacted the scheme in terms of migration of contaminants beneath the site.

Surface cover at the site is a combination of railway tracks and buildings with associated hardstanding/made ground in the active portion of the scheme particularly in the vicinity of Watford Junction Station. A surface cover of made ground with extensive vegetation cover is evident in the disused site section.

Since 1899, a small portion of the L&NWR has been situated within the live rail section at the eastern end of the scheme.

From 1920 the currently disused portion of the scheme was previously used as the Croxley Green Railway Line, connecting to the L&NWR Line to the east. Rail tracks, sidings and associated rail infrastructure including railway stations, carriage and

engine sheds were identified representing potential sources of contamination. The site section continued to be used as a railway line until approximately 1991.

The site walkover of 15 th October 2009 identified areas of fly-tipped waste concentrated beneath two road bridges, (These bridges were situated to the east of the disused site section, being the Vicarage Road Bridge, and immediately to the west of Watford West Station the A4145 road bridge). Waste was also scattered randomly along the disused site section. Although the fly-tipped items may not represent a direct source of contamination, the act of fly-tipping in these areas and thus the disposal of unknown items and materials in these areas is considered to represent a potential source of contamination.

Present and past land uses immediately adjacent to the scheme include undeveloped agricultural land, residential housing with gardens, landfill sites, waste management facilities, and unknown works sites. In addition a sewage farm, chemical works, former power station and electricity substation were identified on historic map extracts and were considered to pose a potential contamination risk to the scheme. A number of potentially contaminative trade directory businesses were also evident within 50m of the site (see section 2.1) which could represent a contamination risk to the scheme. The site walkover of 15 th October 2009 also identified an active electricity substation immediately to the south of the disused site section. From historic maps, this substation has been present since approximately 1975.

3.2 Potential Pollutant Linkages 3.2.1 Sources Table 3.1 presents the potential sources of contamination, the likely contaminants related to each source and their likely distribution. The likely contaminants have been identified using DoE Industry Profiles 12 .

Table 3.1:Sources of Contamination

Sources of Contamination Ref Primary Location of Expected distribution Likely contaminants source source S1 Made Ground Onsite Widespread Hydrocarbons, inorganic chemicals, metals, Polycyclic aromatic Hydrocarbons (PAHs) S2 Area of former Onsite Disused site section Asbestos, hydrocarbons, inorganic railway (Disused (formerly Croxley chemicals , metals, PAHs, PCBs, Croxley Green Green Branch Line) sulphate Branch Line) S3 Active railway Onsite Live rail section Asbestos, hydrocarbons, inorganic chemicals, metals, PAHs, polychlorinated bi phenols (PCBs), sulphate S4 Fly-tipped Onsite Concentrated beneath Asbestos, metals, organic waste/suspected Vicarage Road Bridge, chemicals asbestos and the A4145 road

Sources of Contamination Ref Primary Location of Expected distribution Likely contaminants source source bridge. Also scattered randomly along section. S5 Historic landfill On & Offsite Eastern end of disused Arsenic, asbestos, hydrocarbons, site(s) site section, central live inorganic chemicals, metals, (Riverside Road rail section. PAHs, PCBs, sulphur and Waterfields Recreation Ground )

S6 STATS Onsite South of disused site Arsenic, hydrocarbons, metals investigated (possible car section, Ascot Road. (“hotspots” of lead according to area (Ascot park for STATS investigation, 2003), PAHs, Road) former proposed sulphur waste transfer Ascot Road station. Station) S7 Waste Offsite North east and north Arsenic, asbestos, hydrocarbons, management west edges of disused inorganic chemicals, metals, facilities site section. PAHs, PCBs, phenols, sulphur S8 Abattoir, landfill Offsite Entire scheme Arsenic, cyanide, hydrocarbons, sites, electricity (widespread) inorganic chemicals, nitrate, substation, metals, organic chemicals, PAHs, former power PCBs, sulphate, sulphur station, sewage works, works, garages, used car dealerships.

There is the potential for made ground may be present at the scheme associated with the L&NWR Railway in the active section of the site and the disused site section where the Croxley Green Branch Line was situated. Unless evidence to the contrary can be obtained, such as evidence of the origins of the soil and analysis confirming an absence of potential contaminants, made ground may be considered as a potential source of soil contamination, ground gas and vapours.

The scheme encompasses an area of active railway land and an area that in the past was used as a railway. Railway and associated structures are considered to represent a potentially contaminative land use. In addition, a small amount of suspected ACMs was identified during the site walkover of 15 th October 2009 and this could represent a risk to human health to trespassers and to future construction and maintenance workers.

The central part of the live rail section and the eastern section of the disused section could be partially underlain by former landfills. (See Appendix D) It is unclear how accurately these boundaries have been defined and it is not known the extent, if any of remediation of either of these landfills.. Therefore, these former landfills are considered as a potential source of soil contamination, ground gas and vapours. The

landfill adjacent to the disused section (Riverside Road) is considered to present a more significant risk to receptors as ground disturbance associated with the scheme construction is more likely in this area compared with the other former landfill adjacent to the live rail section.

The closest active businesses to the scheme include a commercial vehicle dealer (close to the live rail section), and a used car dealer (close to the disused site section). These are considered to represent potential sources of contamination.

Previous offsite sources of contamination include a number of waste facilities located within 50m of the scheme licensed to deal with a variety of waste types, inclusive of (but not limited to) – chromic acid, non-biodegradable wastes, paint residues/thinner and ferrous metals, an electricity substation, power station, sewage farm and multiple works of unknown industrial use.

Based on the relevant DoE Industry Profiles 12 , potential contaminants that may be associated with these offsite industries include; metals, aliphatic and aromatic hydrocarbons, polycyclic aromatic hydrocarbons (PAHs), polychlorinated bi-phenyls (PCBs), cyanide, nitrate, sulphate and sulphide.

3.2.2 Receptors Based on the information provided in Sections 2 and 3.1, the following receptors have been identified in relation to the site.

Table 3.2:Receptors

Receptors Ref Receptor Description R1 Humans R1 (a) Ground workers associated with the construction of Croxley Rail Link. R1 (b) future site users (i.e., passengers at stations) R1 (c) users of adjacent sites. R2 Groundwater (major The stratum underlying the site is considered as a major aquifer) aquifer therefore controlled waters within this body are likely to be at risk. R3 SPZ Zone 1 and 2 The scheme is located within an SPZ (zones 1 and 2) with a potable water supply within 280m of the scheme. R4 Surface waters R4(a) River Colne, River Gade R4(b) Grand Union Canal R5 Ecology R5 (a) Fauna & Flora living in the currently disused section of the Rail Link scheme. R5 (b) Fauna and Flora living within the Lairage Land nature reserve. R6 Potential future Building foundations and structures and underground construction materials services associated with the rail-link.

3.2.3 Pathways Creating Pollutant Linkages Contamination can only pose a risk to receptors if a pathway is present between the source and the receptor. As pathways can only be assessed in association with sources and receptors, the table below identifies the potential pollutant linkages for this site

Table 3.3: Pathways

Pathways Ref Pathway Description P1 Direct contact with contaminated Humans on site may come into direct contact with soils, liquids (Ingestion) contaminated materials and vapours. P2 Direct contact with hazardous Humans on site may come into direct contact with gases and vapours. (Inhalation) contaminated materials and vapours. P3 Mobile contamination from the site Contaminants on site may be mobilised during the contained in leachates, water and construction of the Rail Link and associated gas. infrastructure and be transmitted through permeable strata via infiltration, leaching and subsurface migration. Vapours may be transmitted through lateral migration through the unsaturated zone. This may impact on groundwater, surface water and humans. P4 Current and future construction Building foundations and underground services can materials act as pathways for the migration of contamination. P5 Piling activities associated with Dependent on the type of piling used, there is the viaduct construction creating potential that a preferential pathway may be created preferential infiltration pathway along the side of the piles enabling contaminants from the shallow soils to enter the major aquifer P6 Piling activities associated with Dependent on the type of piling used, contaminated viaduct construction creating a soils could be pushed into the aquifer during piling, pathway by pushing contaminated thus contaminating the aquifer soils into the aquifer

3.3 Risk Evaluation Potential pollutant linkages assigned risk ratings of moderate and above are summarised in Table 3.4. The full evaluation of the risk that each pollutant linkage (as identified in section 3.2 above) poses to the project has been undertaken, in general accordance with CIRIA Guidance document C552, 2001,13 and is presented in Table C-5, Appendix C.

The risk ratings in Table C-5 in Appendix C have been determined using the information and rationale provided in Tables C1, C2, C3 and C4, also in Appendix C which have been reproduced from the CIRIA Guidance C552, 2001 13 . Table 3.4 presents a summary of the greatest risk ratings and associated pollutant linkages.

Table 3.4:Summary of potential Pollutant Linkages which have the greatest risk rating

Summary of potential Pollutant Linkages Pollutant Linkage Contaminant Pathway Receptor Risk Classification Source L25 S4 P2 R1(a) MODERATE L47 S1 P5 R2 MODERATE

L48 S2 P5 R2 MODERATE

L49 S1 P6 R2 MODERATE

L50 S2 P6 R2 MODERATE

L51 S1 P3 R3 MODERATE

L52 S2 P3 R3 MODERATE

L53 S3 P3 R3 MODERATE

L54 S4 P3 R3 MODERATE

L55 S1 P5 R3 HIGH

L56 S2 P5 R3 HIGH

L57 S1 P6 R3 HIGH

L58 S2 P6 R3 HIGH

3.3.1 Risks to Human Health The pollutant linkages which pose the greatest risk (moderate) to human health are those associated with source S4. S4 is the fly-tipped waste which contains suspected ACMs identified on the disused site section during the site walkover of 15 th October 2009.

The main/highest risk pollutant linkages described above are summarised in Table 3.5 below.

Table 3.5:Summary of Pollutant Linkages which have been identified as having the greatest risk rating for Human Health

Summary of Pollutant Linkages which have been Identified as having the greatest risk rating for Human Health Pollutant Contaminant Source Pathway Receptor Risk Linkage Classification L25 Fly tipped Waste containing Direct contact with Future Ground ACMs (S4) hazardous gases or workers (R1(a)) MODERATE vapours. Inhalation.

Using the CIRIA Guidance C552, 2001 13 (Appendix C), the rating of moderate has been assigned to the risk from the fly-tipped waste which includes asbestos due to the discovery of suspected ACMs on site during the walkover of 15 th October 2009. Using Tables C1 to C4 (Appendix C), although the consequences of asbestos inhalation are considered to be severe (Table C1), there is considered to be a low likelihood (Table C2) of this risk being realised. The appropriate removal of the asbestos will reduce the risk to moderate-low. It should be noted that a lower risk rating of moderate/low was assigned to the risk of ingestion of asbestos, as the consequence of dermal contact with asbestos as opposed to the inhalation pathway is less. In assigning these risk ratings it has been assumed that appropriate PPE would be worn during all removal operations and by ground workers during construction works.

The overall risk to future site users is low to very low. This is primarily based on the principle that hardstanding at station platforms and restrictive access to the railway will sufficiently mitigate any exposure pathways. In addition, with respect to passengers, the limited exposure time to any potential contamination would be minimal, further reducing the risk. Therefore, although the potential consequences of the risk being realised is medium (Table C1) the likelihood of the risk being realised is unlikely (Table C2).

Two further pollutant linkage related to human health were assigned a rating of moderate/low. These risk ratings were associated with S5- former landfills and S6 – contaminated soils associated with the STATS investigated area. These ratings were assigned as, although the consequences were considered to be medium (Table C1), there was considered a low likelihood (Table C2) of contamination from these sources affecting human health. The soils associated with the STATS investigation Ascot Road contained contamination at a concentration which would pose a risk to human health. However, during construction of the proposed car park facility exposure of ground workers to contaminated soils would be reduced through the use of appropriate PPE. In terms of the future site users, the pathway from source to receptor should be broken by hardstanding.

Based on the gas assessment undertaken by STATS, Mouchel recommend that the buildings and associated lift construction proposed as part of the Ascot Road Station

development will require appropriate gas protection measures to be incorporated into their design. This should mitigate any risk posed to future site users and the structures themselves. As buildings and lift areas are proposed for the new Watford West Station, these should also incorporate appropriate gas protection measures.

As well as the ground gas observed as part of the STATS ground investigation, there may be ground gas within the soils beneath other sections of the scheme. The former landfills, any residual contamination associated with the railway line and the alluvium soils (which include peat) all have the potential to be a source of ground gas. A gas monitoring programme along the proposed scheme would aid in identifying any protective measures which may be required.

3.3.2 Risks to Controlled Waters The construction of the scheme and its future operation are considered to be potentially polluting activities which could result in the accidental release of contaminants into the sensitive groundwater. Contaminants could also be mobilised during construction and/or operation and thus infiltrate the major aquifer underlying the scheme. Similarly it is considered that mobilisation of contaminants could result in the deterioration of nearby surface water quality. The Rivers Colne, Gade and the Grand Union Canal have been assigned GQA grades of B (Good) and C (fairly good), respectively, and are thus considered sensitive to pollution.

The main/highest risk pollutant linkages described above are summarised in Table 3.6.

Table 3.6: Summary of Pollutant Linkages which have been identified as having the greatest risk rating to Controlled Waters

Summary of Pollutant Linkages which have been Identified as having the greatest risk rating to Controlled Waters Pollutant Contaminant Source Pathway Receptor Risk Classification Linkage L47 Made ground (S1) Piling activities MODERATE associated with Groundwater L48 Disused site section viaduct construction (major aquifer) (former Croxley Green creating preferential (R2) MODERATE Branch Line) (S2) infiltration pathway (P5) L49 Made ground (S1) Piling activities MODERATE associated with L50 Disused site section viaduct construction Groundwater (former Croxley Green creating a pathway (major aquifer) Branch Line) (S2) by pushing (R2) MODERATE contaminated soils into the aquifer (P6) L51 Made ground (S1) Mobile SPZ 1 – MODERATE contamination Potable water L52 Disused site section contained in supply (R3) (former Croxley Green leachates, water MODERATE Branch Line) (S2) and gas. (P3) L53 Live rail section (S3) MODERATE

Summary of Pollutant Linkages which have been Identified as having the greatest risk rating to Controlled Waters Pollutant Contaminant Source Pathway Receptor Risk Classification Linkage L54 Historic Landfill (S4) MODERATE L55 Made ground (S1) Piling activities HIGH associated with SPZ 1 – L56 Disused site section viaduct construction Potable water (former Croxley Green creating preferential supply (R3) HIGH Branch Line) (S2) infiltration pathway (P5) L57 Made ground (S1) Piling activities HIGH associated with viaduct construction SPZ 1 – creating a pathway Potable water L58 Disused site section by pushing supply (former Croxley Green contaminated soils Branch Line) (S2) into the aquifer (P6) HIGH

The risk to the SPZ-potable water supply has been assigned ratings of high and moderate. The high risk rating is associated with the piling activities which will be part of the viaduct construction works. The moderate rating is associated with the mobilisation of contaminants during the construction works of the disused railway line and new stations and during the future site operation. Dependent on the piling techniques used, there is the potential for contamination to enter the groundwater within the SPZ1 area via two pathways. These pathways are infiltration, as the piles and surrounding material could act as a preferential pathway and by contaminated soils being directly pushed into the aquifer as the pile is put into the ground. As the piles are likely to be placed within the chalk aquifer (major aquifer) and in an area which is a SPZ 1 the consequence of risk could be severe (Table C1, Appendix C) in terms of the impact on the potable water supply and because the piles are being placed within the chalk, the likelihood of the risk occurring is considered as likely (Table C2, Appendix C). The potential sources associated with the piling activity are made ground and the disused railway.

The moderate risk to the SPZ-potable water supply has been assigned to the pollutant linkages (L51, L52, L53 and L54). These pollutant linkages are for potential contaminants from made ground, the disused and live rail sections and/or former landfills being mobilised during construction works and during operational use of the scheme entering the SPZ. The consequence of the risk is likely to be severe but there is a low likelihood (Table C2, Appendix C2) of the risk being realised. This is because the potential sources associated with the disused railway line and made ground are not thought to be a continuing source and thus any contamination is likely to have already leached in to the aquifer over previous years. In terms of potential contaminants from the former landfills, based on the ages of the landfill sites identified it is likely they were unlined and operated under a dilute and disperse

regime. As such any leachable contaminants are likely to have already been diluted and dispersed by the underlying aquifer thus there is considered to be a low likelihood of contaminants from the historic landfill continuing to affect controlled waters. In addition, the nearest public/potable water supply is approximately 270m to the east of the active site section, located at Watford Field Pumping Station. This location appears to be upstream of the scheme. However, as mobilisation of contaminants would occur primarily during construction works, which would accentuate the mobility of contamination and, due to the high sensitivity of the SPZ, the consequence of any contamination entering the SPZ would be severe (Table C1, Appendix C) as there is the possibility of contaminating potable water supplies.

The major aquifer body has been deemed to be at moderate risk from potential contamination from piling activities associated with the construction of the proposed viaduct. This is because, although the piling activities described above could mean that the probability of risk being realised is likely (Table C2, Appendix C), the impact on the aquifer would only be medium (Table C2, Appendix C). This impact is less than that given to the SPZ1 as the sensitivity of the aquifer as a whole, is less than the specific SPZ1 as the impact rating also considers the aquifer outside the specific SPZ, and therefore is less sensitive.

Appropriate construction methods and management would mitigate and reduce the above risks significantly, to low. As the scheme lies within a SPZ1 and a SPZ2 the sensitivity of the aquifer is high and it is considered likely that the EA would require a piling risk assessment to ensure that the aquifer if protected during and after the scheme’s construction.

A further eight pollutant linkages relating to controlled waters (L43, L44, L45, L46, (major aquifer)) L59, L60, L61 and L61 (surface waters – River Colne and River Gade)) were assigned a rating of moderate/low. These were associated with S1 – made ground, S2 the disused site section, S3 the active railway and S5 – historic landfill sites. The rating moderate/low was assigned in these instances although the consequence of the risks being realised would likely be medium (Table C1, Appendix C) in all cases, there was considered to be a low likelihood (Table C2, Appendix C) of mobile contamination from these sources affecting controlled waters.

For full details of all the pollutant linkages associated with controlled water, see Table C4, Appendix C.

3.3.3 Risks to Ecology A detailed ecological study of the scheme is currently being undertaken to identify these potential risks in detail. The findings of this report will be available in a separate Mouchel Report.

There is considered to be a low-very low risk to the Lairage Land nature reserve from potential contamination from the scheme. This risk rating has been assigned as contaminants associated with the disused railway, where the majority of earthworks movement would be, are likely to have already leached into the subsurface. As there

has been no railway activity any sources of contamination would be declining. An appropriate Environmental Management Plan (EMP) would be required if construction activities take place adjacent to this area to mitigate against any migration of contaminants.

3.4 Consideration of the Risks to the Proposed Development Desk study research has indicated that there is a potential, due to the past land uses and current activities on site and in the surrounding area, that the scheme will contain land affected by contamination. If contamination is encountered during development, additional costs may be incurred for removal and/or treatment of the affected materials.

Future site workers and the groundwater (major aquifer, specifically the SPZ) are the two main sensitive receptors to the scheme. Material disturbed (in areas of proposed cutting, possible embankment enhancement, station areas and the proposed piling areas associated with the proposed viaduct), may contain contamination which might come into contact with ground workers. The ground disturbance in these areas may mobilise contaminants into the aquifer beneath the site and/or the nearby surface waters of the Rivers Gade and Colne. Therefore, it is likely that the EA will require a piling risk assessment and that a preliminary ground investigation will be required to identify any contaminants within the ground disturbance areas.

Movement of material from one place to another within the scheme boundary will also need to be considered as well as that designated for off site disposal. Dependent on the contaminants identified within the proposed ground disturbance areas, some material may be suitable for re-use, other material may not. An appropriate waste management plan may be required to address the implications of waste movement, re-use and removal.

Should Japanese Knotweed or other similar invasive species be encountered on site, these species, which are classified as ‘controlled waste’ under the Environment Protection Act (EPA) 1990 16 treatment of the area will be required prior to disposal to landfill.

In terms of the risk to human health, appropriate removal of ACMs will reduce the risk to low. Therefore, an asbestos survey should be undertaken. Appropriate PPE should be worn during all removal operations and during any groundwork activities to reduce the likelihood of exposure to any contaminated material. A Health and safety plan highlighting any risks should be incorporated into any ground investigation and construction works associated with the scheme.

Based on the historic landfills within the vicinity of the scheme, any potential residual contamination associated with the railway line and the alluvium soils (which includes peat) may generate ground gases within the soils at the site. Any buildings and associated lift construction proposed as part of the new station developments would require a gas assessment in order to identify the appropriate gas protection

measures which should be incorporated into their design. A gas monitoring programme would aid in identifying any protective measures which may be required.

4 Conclusions

4.1 Key Findings

• Made ground is likely to be present at the scheme, associated with both the active railway line and the now disused Croxley Green Branch Line. Therefore, there is the potential that contamination may be present which may pose a risk to human health and controlled waters.

• Potentially contaminative land uses have been identified within 100m of the scheme inclusive of former landfill sites, waste management facilities, garages, an electricity substation, former power station and a number of ‘works’ of unidentified industrial use.

• Ground gas may be present at the scheme due to the former landfills close to the scheme (Riverside Road-disused rail section and Waterfields Recreation Ground – live rail section). Ground gases could also be being generated in the alluvium strata beneath the site, including from the peat. Interpretation by STATS of the gas data obtained as part of their ground investigation also indicated that there was sufficient ground gas observed to warrant gas protection measures in any proposed buildings. Therefore, structures will have to be equipped with gas protection measures as part of their design.

• Due to the age of the landfills it is likely that they were unlined and operated under a dilute and disperse regime. Therefore, as such any leachable contaminants are likely to have already been diluted and dispersed by the aquifer. Therefore, there is a low likelihood that contamination of controlled waters or significant harm to human health will occur. However, as the consequence of polluting the aquifer is severe, these landfills cannot be discounted as a source. The Riverside Road former landfill represents a potential source of contamination for human health as ground excavation and disturbance is expected in this area as part of the scheme construction.

• The preliminary risk assessment indicated that the risks to human health and groundwater are greatest where there will be and as a result of ground disturbance during construction works. • There is a HIGH to MODERATE/LOW risk of contamination of controlled waters. The scheme is located within a SPZ1 and the Upper Cretaceous Chalk Formation underlying the scheme is a major aquifer. As the scheme is within a SPZ1, the groundwater beneath the site is particularly sensitive as any contamination within this zone has the potential to contaminate potable water supplies. The nearest potable water supply is 270m east of the live rail section. The activities associated with the greatest risk are piling into the aquifer (proposed as part of the construction of the viaduct) and the movement of material associated with making the disused line, live again

(areas of proposed cutting) and new station construction (Ascot Road and Watford West Stations). • The risk to human health posed by the scheme ranges from MODERATE to VERY LOW . The greatest risk is associated with suspected ACMs on site associated with fly-tipped materials observed during the site walkover and elevated concentrations of contaminants in soil identified during the STATS site investigation on Ascot Road. The human group considered most at risk are ground workers during the construction phase of the development. Providing that correct health and safety procedures are followed, all ground workers wear appropriate PPE during construction works and appropriate management and disposal measures for asbestos are undertaken during development of the scheme then the overall risk rating will be reduced to LOW-VERY LOW.

• The risk to human health posed by the scheme is considered to be LOW to VERY LOW for future users on the site due to the proposed future end use as a railway. Hardstanding forming train platforms would limit human exposure to potential contaminants, and break the pathways from source to receptor. • There is considered to be a LOW to VERY LOW risk to the Lairage Land nature reserve from potential contamination from the scheme.

• These risks outlined above could be mitigated through an intrusive ground investigation to identify, delineate and assess potential areas of contaminated land.

5 Recommendations

It is recommended that a targetted, intrusive ground investigation should be undertaken prior to any development to identify and assess the presence of contamination in the soils at the scheme.

The contaminated land aspect of the ground investigation will only target those areas where there will be ground disturbance or areas where contamination has been identified, such as fly-tipped areas, dormer landfills etc. Based on the conceptual model, the only potential moderate and high risk ratings are related to the construction phase of the works. Access, currently, or in the future is and will be restricted/denied to members of the public and any future maintenance of the tracks or embankments will be done in accordance with appropriate health and safety measures in place. Therefore, the only interaction with potential contaminated soils for humans and potential accentuated mobility of contaminants or actively creating a pathway for controlled waters will be from construction and associated earthworks. Ground gas might be present at the scheme and the proposed stations will include buildings and other structures such as lifts/shafts. Hence, gas installations should be included in boreholes or window samples specified within the proposed station areas. Finally, as the earthworks will include movement of material and potential waste generation, the ground investigation should consider waste classification testing and Waste Acceptance Criteria (WAC) analysis.

The targetted areas will be in areas of proposed cuttings and potential embankment enhancement, the viaduct piling areas and where new stations will be built. Within these areas, particular emphasis should be on the areas of fly tipping and the area thought to be underlain by former landfill (Riverside Road).. This may include, but not be limited to hand dug pits, window samples, boreholes, soil, leachate, water and gas sampling and analysis.

Chemical testing of the soils together with leachate analysis should be undertaken from locations across the scheme. These locations will be positioned to provide adequate information on the ground conditions underlying areas where new railway stations are to be constructed, where piling will be required as part of the viaduct construction, in areas where it is possible historic landfill underlies the scheme and general coverage of areas where ground disturbance will occur. Chemical analysis of the soils within the viaduct piling areas would help identify if there is the potential for the piling to cause contamination form the soils above to enter the groundwater. The leachate analysis would identify if any potential contaminants in the soils at the scheme are mobile. Groundwater standpipes installed within the window sample or borehole locations across the scheme, as well as provided information on groundwater levels, would provide sufficient information as to whether the groundwater beneath the scheme has been affected by contamination and whether the Croxley Rail Link scheme would have a detrimental affect on the groundwater beneath the site.

Any materials deemed to be physically unsuitable for reuse on the scheme may require disposal off site. These materials would be subject to waste Acceptance Criteria (WAC) testing and assessment in order to determine its classification for landfill disposal.

In order to minimise the cost it is recommended that the contaminated land intrusive investigation is undertaken jointly with an initial geotechnical design investigation. This would be beneficial by reducing time and capital costs in terms of mobilisation and the number of exploratory holes. In addition this would limit the amount of time required for site clearance, limit problems imposed by access restrictions and the coordination of a single intrusive investigation rather than two intrusive investigations.

It is recommended that prior to any intrusive investigation is commissioned that information regarding buried services is obtained.

An asbestos survey should be considered to determine the nature and extent of ACMs at the scheme.

5.1 Other Considerations As part of the ground investigation and as part of the construction phase of the scheme, boreholes and piles will be drilled in to the major aquifer. Consent from the EA maybe required to drill boreholes into the aquifer during the ground investigation and a piling risk assessment maybe required prior to the construction phase of the works.

Dependent of the findings of the ground investigation, during the construction phase of the works, the risks to human health, controlled waters and ecology from potential contamination can be mitigated using appropriate health and safety and environmental management during the construction of the scheme. An EMP and health and safety plan which covers the potential risk issues associated with contaminated soil and water should be incorporated into the overall construction phase documentation provided by the contactor of the works.

Any cut and fill operations within the scheme which may include the import of fill and disposal of surplus or unsuitable arisings will come under the waste management regulations. The proposed operations may not require a waste management permit and might be registered as being exempt from the requirement for a permit (formerly described as a Waste Management Licence Exemption). An appropriate waste management plan will be required to address the implications of waste movement, re-use and removal. Invasive species such as Japanese Knotweed should be included 16 .

A Materials Management Plan developed in accordance with CL:AIRE Definition of Waste Development Industry Code of Practice, 2009 17 , although not a regulatory requirement may be useful in order to aid with identifying potential waste materials.

6 References

1 Aspinwall & Company Ltd: Croxley Rail Link Environmental Statement, June 1995

2 Mouchel Parkman: Croxley Rail Link Environmental Impact Statement, June 2001 (updated March 2004)

3 Costain Geotechnical Services Ltd: Ground Investigation – The Croxley Rail Link Stage 1, 16 July 2003

4 STATS Ltd: Supplementary Contaminated Land Investigation – Ascot Road, Croxley, Watford, September 2008

5 Landmark Envirocheck Report (28792620_1_1), Landmark Information Group Service 2009.

6 The Environment Agency (EA) ‘What’s In Your Back Yard? ’ database www.environment-agency.gov.uk. Search conducted on 03/10/2009

7 Ordnance Survey Landranger Map Sheet 176 West London, Rickmansworth & Staines (1:50,000 scale)

8 British Geological Survey (BGS) (1:50,000 scale, solid and drift) Geological map of Beaconsfield (Sheet 255)

9 British Geological Survey (BGS) (1 inch:1 mile scale, solid and drift) Geological map of North London (Sheet 256)

10 Groundwater Vulnerability Map West London Area (Sheet 39)

11 Department for Environment, Food and Rural Affairs and the Environment Agency, 2004. Model Procedures for the Management of Land Contamination. Contaminated Land Report 11 (CLR 11).

12 Department of Environment, Industrial Profiles, 1995

Railway Land

Road vehicle fuelling, service and repair – garages and filling stations.

Sewage works and sewage farms

Waste recycling, treatment and disposal sites – landfills and other waste treatment or waste disposal sites

13 CIRIA/DETR C552 Contaminated Land Risk Assessment, A Guide to Good Practice.2001

14 STATS Ltd: Supplementary Contaminated Land Investigation – Ascot Road, Croxley, Watford: Ground Contamination section p20-23, September 2008

15 CIRIA, C659, Assessing risks posed by hazardous gases to buildings, 2006

16 HMSO, Environmental Protection Act, 1990.

17 CL:AIRE, Definition of Waste Development Industry Code of Practice, 2009