The Wrexham (Gas Fired Power Station) Order

Planning Act 2008 The Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009

Revision: Date: Description:

0 March 2016 Submission version

PINS Reference Number: EN010055Document Reference Number: 6.4.8Regulation Number: 5(2) (a)Lead Author: Atkins (Halcrow)

6.4.8 Volume 4: Environmental Statement Appendix 13.4: SKM Enviros Acorn Power Development LtdPhase 1 Desk Study 2010

The Wrexham(Gas Fired Power Station) Order

SEC6.4-ES Appendix TABS.indd 50 10/03/2016 09:48

Acorn Power Developments Ltd

PROPOSED GAS FIRED COMBINED CYCLE GAS TURBINE PLANT AT WREXHAM INDUSTRIAL PARK - PHASE I DESK STUDY

V1

26 October 2010

The SKM logo trade mark is a registered trade mark of Sinclair Knight Merz Pty Ltd.

Acorn Power Developments Ltd

PROPOSED GAS FIRED COMBINED CYCLE GAS TURBINE PLANT AT WREXHAM INDUSTRIAL PARK

V1

26 October 2010

SKM Enviros Hetton Court, The Oval Hunslett LS10 2AU Tel: +44 (0)113 385 6185 Fax: +44 (0)113 385 6175 Web: www.skmenviros.com

COPYRIGHT: The concepts and information contained in this document are the property of Sinclair Knight Merz (Europe) Ltd. Use or copying of this document in whole or in part without the written permission of Sinclair Knight Merz (Europe) Ltd constitutes an infringement of copyright.

LIMITATION: This report has been prepared on behalf of and for the exclusive use of Sinclair Knight Merz (Europe) Ltd’s Client, and is subject to and issued in connection with the provisions of the agreement between Sinclair Knight Merz (Europe) Ltd and its Client. Sinclair Knight Merz (Europe) Ltd accepts no liability or responsibility whatsoever for or in respect of any use of or reliance upon this report by any third party.


SKM Enviros

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INC-WRX-RPT-00019 Wrexham Geo-env desk study\Wrexham_Phase_1_gad_v2_reviewed_cs.docx PAGE i

Contents

1. Introduction 1

2. Site Profile 2

2.1. Site Location 2

2.2. Site Description 3

2.3. Proposed Development 3

2.4. Adjacent Site Use 4

2.5. Site Drainage 4

2.6. Site Regulatory and Environmental Data 4

2.7. Site History 5

2.8. Summary of Previous Investigations 6

2.9. Potential Contamination Sources 6

3. Environmental Setting 8

3.1. Geology 8

3.2. Coal Mining 8

3.3. Hydrogeology 8

3.4. Hydrology 9

3.5. Ecology 9

3.6. Summary of Site Sensitivity 9

4. Conceptual Model and Risk Assessment 11

4.1. Introduction 11

4.2. Conceptual Model 11

4.3. Qualitative Risk Assessment 12

5. Summary of Risks 16

5.1. Environmental Risk Assessment 16

6. Conclusions and Recommendations 17

6.1. Conclusions 17

6.2. Recommendations 18

7. References 19

Appendix A Landmark report 20

Appendix B Figures 21

Appendix C Site Photographs 22


SKM Enviros


INC-WRX-RPT-00019 Wrexham Geo-env desk study\Wrexham_Phase_1_gad_v2_reviewed_cs.docx PAGE iii

Document history and status

Revision Date issued Reviewed by Approved by Date approved Revision type

1 26/10/2010 Chris Stewart

Distribution of copies

Revision Copy no Quantity Issued to

Printed: 7 May 2015

Last saved: 7 May 2015 04:08 PM

File name: Document1

Author: Graham Duffield

Project manager: Larraine Wilde

Name of organisation: SKM Enviros

Name of project: Wrexham CCGT

Name of document: Phase 1 Desk Study

Document version: V1

Project number: JS30101


SKM Enviros


INC-WRX-RPT-00019 Wrexham Geo-env desk study\Wrexham_Phase_1_gad_v2_reviewed_cs.docx PAGE 1

1. Introduction

In September 2010, Enviros was commissioned by Acorn Power Developments Ltd

(APDL) to undertake a Phase 1 Desk Study at a portion of land adjacent to Wrexham

Industrial Park to the east of Wrexham. The study has been undertaken to support a

planning application which will be submitted to Wrexham County Borough Council for

construction of a gas-fired Combined Cycle Gas Turbine (CCGT) electricity generating

station.

The proposed scope of works was outlined in our proposal to Acorn Power Developments

Ltd, dated 23rd July 2010. The scope of works included the preparation of a Phase 1 Desk

Study and the design and implementation of a Phase 2 Geo-Environmental site

investigation as detailed below:

Undertake a Phase 1 Desk Study and review / finalise the scope of works for a Phase 2

intrusive site investigation;

Tender the Phase 2 site investigation works to three site investigation contractors;

Undertake a Phase 2 investigation;

Prepare a Phase 2 Geo-Environmental risk assessment, geotechnical interpretation,

conclusions and recommendations for further works associated with land

contamination (if necessary).

The scope of the desk study investigation comprised a review of relevant information

sources to characterise the environmental setting and historical use of the site. The

structure and outline of the geo-environmental desk study report can be summarised as

follows:

Section 2 provides a description of the site and its setting and details of the proposed

development;

Section 3 provides a summary of the environmental setting of the site;

Section 4 provides a qualitative risk assessment; and

Section 5 provides a summary of key findings of the desk study and recommendations

with respect to further work.

The conceptual model for the site and environmental risk assessment has been undertaken

in accordance with current UK guidance relating to the assessment of contaminated land,

including CLR11 (Ref. 6).

The findings and opinions in this report are based upon information obtained from a

variety of sources as detailed within the report. SKM Enviros believes the information

obtained from third parties is reliable but does not guarantee its authenticity.




2. Site Profile

2.1. Site Location

The proposed power plant will be located on a portion of land adjacent to Wrexham

Industrial Park to the east of Wrexham. The site is currently unoccupied and comprises

open ‘green field’ land. A site location plan is presented in Figure 1 of Appendix 2, as

below:

Figure 1 Site Location

Grid Squares = 200m x 200m

Table 1 Summary of Site Details

Site Address Wrexham Industrial Park, Wrexham

Grid Reference 339200, 350760

Site Area Approximately 17 Ha

Local Authority Wrexham County Borough Council




2.2. Site Description

A site walkover was conducted by an Enviros representative on 27th October 2010 and

photographs are provided in Appendix 3. The site comprises open fields intersected by

two drainage ditches running north / south and a pond is located in the centre of the site. A

road cuts through the western portion of the site, originating from Bryn Lane, and the

southern boundary and a portion of the western boundary are bordered by trees.

Access to the site is gained from the east via Bryn Lane, although vehicular access to the

site is yet to be established.

2.3. Proposed Development

The proposed development will consist of up to 1,550 MW combined cycle power plant

arranged in three generation trains. The power trains may be configured in 'single shaft' i.e.

as two completely separate generation lines or as 'multi-shaft', sharing a common steam

cycle. There is no significant difference between the options in environmental terms.

The development will include a 150 MW peaking power generation plant which will be an

open cycle gas turbine (OCGT) configuration operating only during periods of peak

demand for electricity. In addition, a 25 MW generator will be provided to generate

electricity to start the power plant in the event that the grid is de-energized.

The generating plant will normally be fired using natural gas which will be supplied to the

power station site by means of a new pipeline teeing into the local NTS gas system,

terminating at an Above Ground Installation on site. No natural gas will be stored on site.

Ancillary plant will include an auxiliary boiler, water demineralization plant, transformers

and switchgear, control building, office and personnel building. Fire detection systems will

be provided for major equipment and plant areas.

In the gas turbine, fuel is mixed with compressed air supplied from the gas turbine

compressor and the combustion gases flow through the gas turbine producing power to

rotate the compressor and generator. The exhaust gas passes through a heat recovery steam

generator raising steam, which is introduced into the steam turbine. The resulting power

produced by the steam turbine augments that supplied by the gas turbine to drive a

generator. Gases (mostly carbon dioxide, water vapour and air) exit the steam generator

and are emitted through the stack. Pollutants such as nitrogen oxide, sulphur dioxide

(distillate oil firing only) and carbon monoxide are emitted at relatively low

concentrations.

Buildings will be constructed to house the gas turbines, steam turbines and associated

plant.




2.4. Adjacent Site Use

The site is surrounded by agricultural fields to the north and east. The western boundary is

bordered by Bryn Lane beyond which lies Wrexham Industrial Park. The southern

boundary of the site is bordered by a ditch / stream beyond which lies open fields. The

nearest residential properties are located approximately 100m east of the site (Park

Cottage).

2.5. Site Drainage

As the site is currently undeveloped, no dedicated drainage is present. A ditch / stream is

situated along the southern boundary of the site flowing west to east.

2.6. Site Regulatory and Environmental Data

Information regarding potential hazards associated with environmental regulatory controls

is summarised in Table 2. This information is taken from the data provided by Landmark,

a copy of which is provided in Appendix 1.

Table 2 Regulatory Data

Data Source On/off site? Details Potential for Impact on-site?

On Site

Landfill Sites, Waste Management Facilities & Waste Transfer Sites

On site None listed at the study site. No

IPC authorisations and IPPC permits


Trade directory entries On site None listed at the study site. No

LAPPC On site None listed at the study site. No

Discharge consents On site None listed at the study site. No

Recorded pollution incidents to controlled waters


Off Site

Landfill Sites, Waste Management Facilities & Waste Transfer Sites

Off site Two licensed waste management facilities are located within 500m of the site. They are both licensed to Waste Recycling Group Ltd for material recycling and treatment located 350 to 400m south west of the site. However, no further details are available regarding waste types, tonnages etc.

Unlikely given distance from site




Data Source On/off site? Details Potential for Impact on-site?

IPC authorisations and IPPC permits

Off site Five IPC authorisations are listed within 500m of the site relating to Owens Corning Fibreglass Ltd located 145m south west although all authorisations are all now listed as inactive.

Two IPPC permits are licensed within 500m of the site. The first relates to Kellogg’s for treatment of animals, vegetables and foods, and the combustion of fuel >50Mw. The second relates to glass fibre manufacture at Owens Corning Fibreglass Ltd. Both sites are listed as being located 148m south west of the study site.

Possibly, although management and environmental controls in place for site operations as part of permitting regime.

Trade directory entries Off site 92 trade directory entries are listed within 1km of the site – see Appendix 1 for details.

Possibly

LAPPC Off site No active licenses within 500m. No

Discharge consents Off site Fifteen licensed consents listed within 1km, the closest relates to sewage discharges into a tributary of the River Dee located 335m east of the site.

No

Recorded pollution incidents to controlled waters

Off site Nine incidents listed within 1km of the site, all listed a Category 3 (Minor).

No

IPC = Integrated Pollution Control; IPPC = Integrated Pollution Prevention & Control; LAPPC = Local Authority Pollution Prevention & Controls; APC = Air Pollution Control

2.7. Site History

The site history has been determined from a review of OS historical maps. The text below

describes significant historical activities on the site and surrounding area. The on-site

history focuses on the 1:2,500 scale maps, with the off-site history concentrating on the

1:10,560 scale maps. Both scale maps have been used in some instances to describe

relevant features. Table 3 indicates potential contaminative uses of the site and surrounding

land. The maps are included in Appendix 1.

2.7.1. On-site history

The earliest map dated 1873 showed the site as agricultural / open fields with a number of

small ponds in central areas and a footpath cutting through its eastern flank. A road was

observed to cut through the western portion of the site. No significant changes occur on

site from this time until the present day, although there is only now one pond on site.

2.7.2. Off-site history

The 1873 map shows the site was located to the north of Ridley with a number of small

farms and surface water ponds in the surrounding areas. No significant changes occur in




surrounding areas until the mid 1900s when development commenced to the south and

west of the site comprising a number of industrial works which later form Wrexham

Industrial Park.

The 1938-54 historical maps show a number of buildings located to the west of the site

which resemble historic munitions sheds which may possibly be associated with a former

WWII munitions factory based at the former Wrexham Industrial Park. However, military

buildings of this type are not usually labelled on historical OS maps. An unexploded

ordnance (UXO) report from Landmark (Ref. 9) has been reviewed which indicates the

presence of Wrexham Royal Ordnance Factory located 250m west of the site. The report

also assesses the probability of UXO discovery beneath the site as moderately high.

By the 1970 a large factory is shown to the south of the site and a telephone exchange

emerges adjacent to the site’s western boundary. A number of industrial and commercial

works, tanks, road links and associated infrastructure formed part of Wrexham Industrial

Park and this area dominates the surrounding land to the south and west of the study site.

Development of Wrexham Industrial Park continues through the latter part of the 1900s

and the site as seen today comprises large numbers of factories, works, depots, tanks and

interconnecting roads. No further significant developments are observed in surrounding

areas.

2.8. Summary of Previous Investigations

No previous desk based or intrusive investigations have been completed at the study site

for environmental purposes.

2.9. Potential Contamination Sources

Based on our review of information and our understanding of site activities the following

potential contamination sources have been identified.




Table 3 Summary of Site History & Potential Sources of Contamination

Dates Feature Distance/ Direction from site

Potential Contaminants Potential for Impact on-site?

Mid to late 1900s

Ponds (possibly backfilled)

On site Various Yes

Mid 1900s Wrexham Royal Ordnance factory

250m west Explosives, pyrotechnics, munitions Yes

1980s to early 2000

Owens Corning Fibreglass (part of Wrexham Industrial Park)

100m west Hydrocarbons, solvents, oils Yes

Early 200 to present

Kellogg’s Co Ltd (part of Wrexham Industrial Park)

100m west Oils, hydrocarbons, COD, alkalis, Yes

1960s to present

Wrexham Industrial Park

100m to 1km south and west

Various contaminants including heavy metals, hydrocarbons, acids, alkalis, asbestos, oils,

Yes




3. Environmental Setting

The environmental setting of the site has been determined through a review of publicly

available British Geological Survey (BGS) maps for the area.

3.1. Geology

The geological map for the area (Ref. 1) indicates that the site is underlain by Boulder

Clay, comprising red brown sandy, stony clay. A number of BGS borehole logs (Ref. 8)

were obtained for boreholes in the immediate surrounding areas to the south and west of

the site, including one borehole within the site boundary. The logs indicate the thickness

of Boulder Clay to be in the region of 40-60m, comprising medium to stiff occasionally

sandy clay.

BGS maps indicate the solid geology beneath the site to be Lower Mottled Sandstone (of

the Sherwood Sandstone Group) comprising red sandstone and breccia. BGS logs to the

south and west of the site encountered bedrock at approximately 40-60m bgl comprising

red sandstone. BGS borehole logs did not confirm thickness of the Lower Mottled

Sandstone, although BGS maps for the area indicate this unit to be in the order of 250 to

300m thick.

3.2. Coal Mining

A Coal Mining Report was obtained from the Coal Authority which states that the property

is not within the zone of likely physical influence on the surface from past underground

workings.

The property is not in an area for which the Coal Authority is determining whether to grant

a licence to remove coal using underground methods. The property is not in an area for

which a licence has been granted to remove coal using underground methods.

The property is not in an area that is likely to be affected at the surface from any planned

future workings. However reserves of coal exist in the local area which could be worked

at some time in the future. No notice of the risk of the land being affected by subsidence

has been given under section 46 of the Coal Mining Subsidence Act 1991.

3.3. Hydrogeology

The groundwater vulnerability map of the area (Ref. 2) classifies the Sherwood Sandstone

Group underlying the site as a Principal Aquifer, which may be highly productive and able

to support large abstractions for public supply and other purposes. Soils are classified as

having a high leaching potential.

Groundwater data is only available from one BGS borehole logs which initially recorded

groundwater levels at 47.4m bgl. Rest groundwater levels recorded between 13.0 to 13.5m

bgl suggesting that the overlying Boulder Clay is confining groundwater within the




sandstone aquifer. Sufficient data was not available to interpret the direction of

groundwater flow.

There are two licensed groundwater abstractions within 1km of the site; the closest is

located 893m east of the site for general farming and domestic use. The site does not lie

within a Groundwater Protection Zone as designated by the EA (Ref. 3).

The site geology and hydrogeology are summarised in Table 4.

Table 4 Summary of Site Geology & Hydrogeology

Unit Composition Thickness (m) Information Source

Aquifer Status

Boulder Clay Red, brown, stony clay 40-60m BGS map, BGS logs

Non Aquifer

Lower Mottled Sandstone

Red sandstone and breccia

250-300m BGS map, BGS logs

Principal Aquifer

3.4. Hydrology

The nearest surface water course is a ditch/stream running west to east adjacent to the

southern boundary of the site which eventually flows into the River Dee located 2.5km

east. The quality of the River Dee at this stretch is classified as Grade A (very good) for

chemistry under the EA’s General Quality Assessment Scheme. The River Clywedog

flows west to east approximately 2km south of the site.

A large number of surface water bodies are located in surrounding areas which mainly

comprise small to medium sized ponds. A small pond is located in the centre of the study

site.

There are fifteen active discharge consents to surface water within 1km of the site relating

to treated effluent, five of which are listed within 500m from domestic and industrial

premises. There are no licensed surface water abstractions within 1km of the site.

The EA indicate that the site does not lie within a tidal or fluvial floodplain.

3.5. Ecology

There are no designated ecologically sensitive sites (e.g. Ramsar sites, SSSIs or nature

reserves) within 1km of site.

3.6. Summary of Site Sensitivity

The sensitivity of each of the identified receptors in the vicinity of the site to

contamination along with pathways from the site are summarised in Table 5.




Table 5 Sensitivity of Environmental Receptors in the Vicinity of the Site

Receptor Type Receptor(s) Sensitivity Reasoning

Groundwater Principal Aquifer (Sherwood Sandstone Group)

Moderate Site underlain by a Principal Aquifer with protection afforded from overlying low permeability boulder clay. Two abstractions from groundwater within 1km for farming and domestic use. Site not located within a groundwater protection zone.

Surface water Ditch / stream

Low

Ditch/stream running west to east adjacent to the southern boundary of the site which flows into the River Dee 2.5km east of the site. No abstractions from surface water within 1km of the site.

Ecological None identified

Very Low

No ecologically sensitive areas designated within 1km of the site.




4. Conceptual Model and Risk Assessment

4.1. Introduction

Environmental Risk has been addressed by adopting a site-specific qualitative approach to

identify the risk of environmental harm. The guiding principle of this approach is an

attempt to establish connecting links between a hazardous source via an exposure pathway

to a potential receptor. This is in accordance with the Department of Environment,

Transport and Regions (DETR) Statutory Guidance on Contaminated Land (Ref. 4) and the

Construction Industry Research and Information Association (Ref. 5).

By considering where a viable pathway exists, which connects a source with a receptor,

this assessment will identify where pollutant linkages may exist. A pollutant linkage is the

term used by the DETR in their standard procedure on risk assessment. If there is no

pollutant linkage, then there is no risk. Our risk assessment is based on the redevelopment

of the site with a commercial/industrial land use.

4.2. Conceptual Model

Contaminated land risk assessment is based on development of a conceptual model for the

site. This is representation of the relationship between contaminant sources, pathways and

receptors developed on the basis of hazard identification.

4.2.1. Identified Sources

The following sources of contamination have been identified from historic and current uses

of the site and surrounding area. These are summarised below:

4.2.1.1. On Site Sources

Backfilled ponds.

4.2.1.2. Off Site Sources

Potential current sources of contamination in the immediate site surroundings include:

Wrexham Industrial Park including, but not limited to, the following activities:

engineers, food manufacturers, powder coatings, printers, cable and wire

manufacturers, dry cleaners, road haulage services, oil fuel distributors, waste disposal

services, recycling centres, plastic product manufacturers, coating specialists, garage

services, petrol stations.

Wrexham Royal Ordnance Factory.




4.2.2. Receptors

The following receptors have been identified:

Future site users;

Construction workers during redevelopment works;

Controlled waters –Groundwater (Sherwood Sandstone classed as a Principal Aquifer);

Controlled waters – Surface water (ditch / stream);

Future buildings/services.

The following pathways link the potential contaminants with the sensitive receptors:

Direct contact, ingestion and inhalation of contaminants by humans;

Infiltration/leaching of contaminants through permeable strata to underlying

groundwater associated with the Sherwood Sandstone Principal Aquifer;

Direct contact of underground services (particularly potable water supply pipes) with

contaminated soils.

4.3. Qualitative Risk Assessment

A qualitative risk assessment has been undertaken for these potential source-pathway-

receptor linkages. This is based on consideration of both:

The likelihood of an event (probability – takes into account both the presence of the

hazard and receptor and the integrity of the pathway);

The severity of the potential consequence (takes into account both the potential

severity of the hazard and the sensitivity of the receptor).

The risk assessment has been based on redevelopment of the site with a proposed industrial

land use (Table 6).

It has been assumed that appropriate measures will be implemented during redevelopment

to address the risks identified and new buildings will be appropriately designed for the

extant ground conditions.


SKM Enviros

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Table 6 Environmental Risk Assessment – Proposed Industrial/Commercial Land Use

Source Pollutant / Hazard

Receptors Pathways to Receptor

Associated Hazard [Potential severity]

Likelihood of Occurrence Potential Risk

Historic ponds (possibly backfilled)

[On site]

Various contaminants

Future Site Users

Direct contact, ingestion, inhalation

Effect on human health

[Medium]

Unlikely: No evidence of contamination observed during site walkover, and no historic evidence of backfilling of ponds. Majority of site will be covered with buildings and hardstanding mitigating the risk of exposure by human receptors to potential underlying contamination.

Low

Construction Workers



[Medium]

Unlikely: No evidence of contamination observed during the site walkover, and no historic evidence of backfilling of ponds. Any risk posed to site workers through potential exposure to contaminated materials would be mitigated through the adoption of health and safety measures and wearing appropriate Personal Protective Equipment (PPE).

Low

Future buildings and services

Accumulation of gases in sub-floor voids and confined spaces

Effect on buildings and services

[Medium]

Unlikely: Backfilling of ponds not confirmed, and any migration of gases beneath building footprints will be impeded by the presence of low permeability Boulder Clay. The development will comprise buildings designed in accordance with current good practice including where appropriate, vapour/gas membranes and clean covers/ hardstanding.

Low

Wrexham Industrial Park

[100m to 1km south and west]

Various contaminants including heavy metals, hydrocarbons, acids, alkalis, asbestos, oils, solvents

Future Site Users



[Medium]

Unlikely: No evidence of contamination observed during site walkover. Majority of site will be covered with buildings and hardstanding mitigating the risk of exposure by human receptors to potential underlying contamination.

Low




[Medium]

Unlikely: No evidence of contamination observed during the site walkover. Any risk posed to site workers through potential exposure to contaminated materials would be mitigated through the adoption of health and safety measures and wearing appropriate Personal Protective Equipment (PPE).

Low








Controlled Waters (Principal Aquifer)

Downwards migration of contaminants via leaching into shallow groundwater

Pollution of groundwater

[Mild]

Unlikely: The sensitivity of groundwater has been assessed as low as the site is directly underlain by a Principal Aquifer but protection is afforded by ~50m of overlying Boulder Clay (indicated by data from BGS logs from boreholes in surrounding areas). The clay will significantly impede the vertical migration of potential contaminants into the underlying aquifer. Presence of contamination at the site not proven. The proposed development will predominantly comprise buildings and hardstanding, thus significantly reducing the infiltration of surface water into soils and subsequent leaching of contaminants.

Very Low

Controlled Waters (Ditch / stream)

Lateral migration of leachable contaminants in soils and contaminants in shallow groundwater

Pollution of surface water [Mild]

Low: Presence of contamination at site not proven. The proposed development will predominantly comprise buildings and hardstanding, thus significantly reducing the infiltration of surface water into soils and subsequent leaching of contaminants. Any potential contaminants entering the stream via direct site drainage or shallow groundwater flow will undergo significant natural attenuation before flowing into the River Dee (2km distant).

Very Low

Future Buildings and services

Direct contact Contamination of potable water supply pipes

[Medium]

Unlikely: Presence of contamination at site not proven. Presence of ~50m of Boulder Clay (indicated by data from BGS logs from surrounding areas) will impede the lateral migration of potential contaminants beneath the site. Any risks could be mitigated by the use of clean, inert backfill material in service corridors and the adoption of contaminant resistant pipe compounds in accordance with current good practice.

Low

Wrexham Royal Ordnance Factory

Explosives, pyrotechnics, munitions

Future Site Users



[Medium]

Unlikely: No evidence of contamination observed during site walkover. Majority of site will be covered with buildings and hardstanding mitigating the risk of exposure by human receptors to potential underlying contamination.

Low




[Medium]

Unlikely: No evidence of contamination observed during the site walkover. Any risk posed to site workers through potential exposure to contaminated materials would be mitigated through the adoption of health and safety measures and wearing appropriate Personal Protective Equipment (PPE).

Low








Controlled Waters (Principal Aquifer)

Downwards migration of contaminants via leaching into shallow groundwater

Pollution of groundwater

[Mild]

Unlikely: The sensitivity of groundwater has been assessed as low as the site is directly underlain by a Principal Aquifer but protection is afforded by ~50m of overlying Boulder Clay (indicated by data from BGS logs from boreholes in surrounding areas). The clay will significantly impede the vertical migration of potential contaminants into the underlying aquifer. Presence of contamination at the site not proven. The proposed development will predominantly comprise buildings and hardstanding, thus significantly reducing the infiltration of surface water into soils and subsequent leaching of contaminants.

Very Low

Controlled Waters (Ditch / stream)

Lateral migration of leachable contaminants in soils and contaminants in shallow groundwater

Pollution of surface water [Mild]

Low: Presence of contamination at site not proven. The proposed development will predominantly comprise buildings and hardstanding, thus significantly reducing the infiltration of surface water into soils and subsequent leaching of contaminants. Any potential contaminants entering the stream via direct site drainage or shallow groundwater flow will undergo significant natural attenuation before flowing into the River Dee (2km distant).

Very Low

Future Buildings and services

Direct contact Contamination of potable water supply pipes

[Medium]

Unlikely: Presence of contamination at site not proven. Presence of ~50m of Boulder Clay (indicated by data from BGS logs from surrounding areas) will impede the lateral migration of potential contaminants beneath the site. Any risks could be mitigated by the use of clean, inert backfill material in service corridors and the adoption of contaminant resistant pipe compounds in accordance with current good practice.

Low


SKM Enviros



5. Summary of Risks

5.1. Environmental Risk Assessment

The preliminary risk assessment undertaken for the site based on existing desk study data

has identified the following:

5.1.1. Risks to Human Health

Risks to future site users are assessed as Low. No evidence of contamination has been

identified at the site, and any risks will be mitigated by the presence of buildings and

hardstanding covering the proposed industrial development.

Risks to site workers from historic contaminants are assessed as Low. The presence of

contamination on site is not proven and any risks can be mitigated by the adoption of

health and safety measures and wearing of appropriate personal protective equipment

during groundworks.

5.1.2. Risks to Groundwater and Surface Water

Risks to groundwater from historic sources have been assessed as Very Low. The

presence of contamination at the site is not proven, and the proposed development will be

covered with buildings and hardstanding, significantly reducing the potential for

infiltration of contaminants into soils and subsequent leaching. The significant thickness

of Boulder Clay (~50m from BGS logs from boreholes in surrounding areas) will impede

the downward migration of potential contaminants into the underlying sandstone aquifer.

Risks to surface waters from current and historic sources have also been assessed as Very

Low. A stream / ditch runs adjacent to the southern site boundary which eventually flows

into the River Dee located 2km distant. The presence of contamination beneath the site is

not proven.

5.1.3. Risks to Buildings and Services

Risks to buildings and services from historic contamination are assessed as Low. The

presence of contamination beneath the site is not proven, and any risks will be mitigated by

the use of clean, inert backfill material in service corridors and the adoption of contaminant

resistant pipe compounds in accordance with current good practice.

The potential for migration of historic contaminants beneath the site will also be limited by

the presence of significant thicknesses of Boulder Clay, anticipated to be ~50m from BGS

logs from boreholes in surrounding areas.




6. Conclusions and Recommendations

6.1. Conclusions

6.1.1. Site History

Historical OS map data shows that the site has remained as open ‘green field’ land and has

not been developed.

6.1.2. Environmental Setting

The site is directly underlain by Boulder Clay, and BGS logs from areas to the south and

west of the site indicate deposits to be ~50m thick comprising medium to stiff occasionally

sandy clay.

The solid geology is the Lower Mottled Sandstone of the Sherwood Sandstone Group

which classified as a Principal A Aquifer by the EA. BGS logs from areas to the south and

west of the site indicate rest groundwater levels to be 13.0-13.5m bgl.

A ditch / stream runs adjacent to the southern boundary of the site which eventually flows

into the River Dee located approximately 2km distant.

6.1.3. Risk Assessment Summary

The potential risks to site users and development workers from potential on and off-

site historic contaminant sources are assessed to be low. This assessment reflects the

absence of evidence of historical contamination1 and the proposed development

comprising buildings and hardstanding limiting the potential for exposure by human

receptors. Risks to development workers will also be mitigated by the adoption of

appropriate PPE.

Risks to groundwater (Sandstone Principal Aquifer) are assessed as very low. This

reflects the absence of evidence of historic contamination within soils, the presence of

buildings and concrete hardstanding over the site following the proposed development,

and the presence of a substantial thickness (~50m) of Boulder Clay protecting

migration into the underlying aquifer.

Risks to surface waters from current and historic sources have also been assessed as

very low. A stream / ditch runs adjacent to the southern site boundary which

eventually flows into the River Dee located approximately 2km distant. The presence

of contamination beneath the site is not proven.

1 A number of ponds were present at the site in the late 1800s that are now shown to be no longer present. It

is possible these have been backfilled but there is no historical evidence to substantiate this.




Risks to buildings and services from historic contamination are assessed as low. Any

risks will be mitigated by the use of clean, inert backfill material in service corridors

and the adoption of contaminant resistant pipe compounds in accordance with current

good practice. The potential for migration of historic contaminants beneath the site

will also be limited by the presence of significant thicknesses of Boulder Clay,

anticipated to be ~50m from BGS logs from boreholes in surrounding areas.

6.2. Recommendations

6.2.1. Potential Impacts for Redevelopment

The possible presence of contamination beneath a site has potential to generate a number

of impacts following redevelopment of the site for industrial end use.

With respect to historic land contamination, Planning Policy Guidance: Planning and

Pollution Control (PPS 23) establishes ground contamination is a material planning

consideration for the local planning authority (LPA). The LPA may require further works

to investigate, assess or remediate any known or suspected contamination to be present,

unless suitable mitigation measures are adopted.

6.2.2. Recommendations

Based on our understanding of the proposed redevelopment and general requirements of

the local planning authority when considering planning submissions, our opinion is that the

risks posed to the future development are acceptably low.

However, give that a site investigation is to be completed in order to obtain geotechnical

information as part of the design and build process, we propose to complete a limited

environmental investigation in conjunction with this work. Such an investigation will

allow an environmental ‘baseline’ to be established for the site prior to its redevelopment

and the data collected will be used to support the planning application.

The investigation will include targeting locations of the former historical on-site ponds in

order to establish whether these were backfilled as part of historical operations.

During site preparation and redevelopment works there is the potential for unforeseen

contamination “hotspots” to be encountered. These potential risks could be mitigated by

undertaking a ‘watching brief’ by an environmental specialist during closure works to deal

with any contamination related issues if they arise. Laboratory testing of materials that are

suspected to be contaminated should also be undertaken to confirm levels.




7. References

1) British Geological Survey, Sheet 122, Nantwich, Solid and Drift Edition, 1:50,000,

1967.

2) National Rivers Authority, Sheet 16: West Cheshire, Groundwater Vulnerability Map

1:100,000, 1997.

3) Information from the Environment Agency website: www.environment-agency.gov.uk

4) Department of the Environment, Transport and the Regions, Environment Agency and

Institute of Environmental Health. Guidelines for Environmental Risk Assessment and

Management. HMSO July 2000.

5) Construction Industry Research and Information Association (CIRIA). Contaminated

Land Risk Assessment. A Guide to Good Practice. CIRIA C552 2001.

6) Department of the Environment, Transport and the Regions and Environment Agency,

Model Procedures for the Management of Land Contamination. Contaminated Land

Report 11.

7) Coal and Brine Report, Site at Ridley Wood Close, Wrexham, Clwyd – The Coal

Authority.

8) British Geological Society Borehole Logs – SJ35SE50, SJ35SE53A, SJ35SE53B,

SJ35SE53C.

9) Landmark Information Group, Preliminary Unexploded Ordnance (UXO) Risk

Assessment, November 2010.




Appendix A Landmark report




Appendix B Figures




Appendix C Site Photographs

The Wrexham (Gas Fired Power Station) Order

Documents

Transcript of The Wrexham (Gas Fired Power Station) Order