British Pipeline Agency (BPA) Land off Fishers Green Lane, Cheshunt, EN9 2ED
Geo-environmental Site Assessment
Project no. 1921133 R01 (00)
MARCH 2020
RSK GENERAL NOTES
Project No: 1921133 R01 (00)
Title: Geo-environmental Site Assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED
Client: British Pipeline Agency, 5-7 Alexandra Road, Hemel Hempstead, Hertfordshire, HP2 5BS
Date: March 2020
Office: RSK Environment Ltd, 18 Frogmore Road, Hemel Hempstead, Herts, HP3 9RT. Tel.: 01442 437500, contact: Alena Landers
Status: Final
Author Alena Landers Technical reviewer David Anchor
Signature Signature Date: March 2020 Date: March 2020
Project manager Alena Landers Quality reviewer Samantha Gower
Signature Signature Date: March 2020 Date: March 2020
RSK Environment Limited (RSK) has prepared this report for the sole use of the client, showing reasonable skill and care, for the intended purposes as stated in the agreement under which this work was completed. The report may not be relied upon by any other party without the express agreement of the client and RSK. No other warranty, expressed or implied, is made as to the professional advice included in this report. Where any data supplied by the client or from other sources have been used, it has been assumed that the information is correct. No responsibility can be accepted by RSK for inaccuracies in the data supplied by any other party. The conclusions and recommendations in this report are based on the assumption that all relevant information has been supplied by those bodies from whom it was requested. No part of this report may be copied or duplicated without the express permission of RSK and the party for whom it was prepared. Where field investigations have been carried out, these have been restricted to a level of detail required to achieve the stated objectives of the work. This work has been undertaken in accordance with the quality management system of RSK Environment Ltd.
CONTENTS
1 INTRODUCTION ...... 1 1.1 Background ...... 1 1.2 Objective ...... 1 1.3 Planning ...... 1 1.4 Scope ...... 2 1.5 Existing reports ...... 2 1.6 Limitations ...... 3 2 THE SITE ...... 4 2.1 Site location and description ...... 4 2.2 Proposed development ...... 4 3 PRELIMINARY RISK ASSESSMENT (PRA) ...... 5 3.1 Site walkovers ...... 5 3.2 Ground conditions ...... 5 3.2.1 Geology ...... 5 3.2.2 Mining and quarrying ...... 6 3.2.3 Landfilling and land reclamation ...... 6 3.3 Hydrogeology ...... 7 3.3.1 Aquifer characteristics ...... 7 3.3.2 Vulnerability of groundwater resources ...... 7 3.3.3 Licensed groundwater abstraction ...... 8 3.4 Hydrology ...... 9 3.4.1 Surface watercourses ...... 9 3.4.2 Surface water abstractions ...... 10 3.4.3 Site drainage ...... 10 3.4.4 Preliminary flood risk assessment ...... 10 3.5 History of site and surrounding area ...... 10 3.6 Sensitive land uses ...... 12 3.7 Local authority environmental health department information ...... 13 3.8 Initial conceptual model ...... 13 3.8.1 Summary of potential contaminant sources ...... 13 3.8.2 Sensitive receptors ...... 14 3.8.3 Summary of plausible pathways ...... 14 3.8.4 Potentially complete pollutant linkages ...... 15 4 PROPOSED REROUTE OF THE PIPELINE ...... 18 4.1 The proposed pipeline design ...... 18 4.2 Corrosion protection ...... 18 4.3 Design improved parameters of the proposed section ...... 18 4.4 Leak/spills avoidance and mitigation ...... 19 4.5 Leak/spills detection ...... 19 4.6 Pipeline Construction Details ...... 19 4.7 Pipeline Construction Phase ...... 19
British Pipeline Agency i Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
5 SITE INVESTIGATION METHODOLOGY ...... 21 5.1 Sampling strategy and methodology ...... 21 5.1.1 Investigation locations ...... 21 5.1.2 Groundwater monitoring and levelling ...... 22 5.1.3 Groundwater sampling and analysis ...... 22 6 INVESTIGATION RESULTS ...... 24 6.1 Soil ...... 24 6.2 Groundwater ...... 26 6.3 Geophysical survey ...... 28 6.4 Hydrogeological cross-section ...... 28 7 BASELINE DATA ...... 29 7.1 Soil sampling and testing ...... 29 7.2 Groundwater sampling and testing ...... 29 8 PROPOSED PIPELINE AND MITIGATION MEASURES ...... 31 8.1 Proposed and existing pipeline construction details ...... 31 8.2 Mitigation measures ...... 32 9 CONCLUSIONS AND RECOMMENDATIONS ...... 33 9.1 Conclusions...... 33 9.2 Recommendations ...... 34 10 BIBLIOGRAPHY ...... 36
TABLES Table 1: Site setting ...... 4 Table 2: Geology at the site ...... 5 Table 3: Groundwater abstractions ...... 8 Table 4: Surface water abstractions ...... 10 Table 5: Summary of historical development ...... 11 Table 6: Potential sources and types of contamination ...... 14 Table 7: Risk estimation for potentially complete pollutant linkages ...... 16 Table 8: Proposed design parameters ...... 18 Table 9: Exploratory hole location rationale ...... 22 Table 10: Scheduled analysis – groundwater ...... 23 Table 11: General succession of strata encountered ...... 24 Table 12: Groundwater results during investigation ...... 27 Table 13: Groundwater monitoring data ...... 27
FIGURES Figure 1 Site location plan
Figure 2 Existing and proposed pipeline routes and investigation borehole locations
Figure 3 Geological cross section
Figure 4 Geological cross section and proposed pipeline
British Pipeline Agency ii Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
APPENDICES Appendix A Service constraints Appendix B Summary of legislation and policy relating to contaminated land
Appendix C Site photographs
Appendix D BGS borehole records Appendix E Environmental database report
Appendix F Other historical information sources
Appendix G Risk assessment methodology Appendix H Exploratory hole records
Appendix I Groundwater monitoring records
Appendix J Geophysical survey report
Appendix K Chemical test results (groundwater)
Appendix L Chemical test results (soil)
Appendix M Certificates of geotechnical analysis
Appendix N Response letter from Epping Forest District Council
British Pipeline Agency iii Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
1 INTRODUCTION
RSK Environment Limited (RSK) was commissioned by the British Pipeline Agency (BPA) to carry out a Geo-environmental Assessment of the land off Fishers Green Lane in Cheshunt, EN9 2ED.
The infrastructure comprises an existing petroleum pipeline, which is situated above ground as a bridge over the River Lea. It is proposed that this pipeline will be re-routed beneath a canal basin and the River Lea flood relief channel.
This report is subject to the RSK service constraints given in Appendix A.
1.1 Background
The pipeline comprises a single 350 mm diameter pipe transporting jet fuel between Epping Booster Station and Hemel Junction.
The proposal to re-route the existing above-ground section of the pipeline to below the canal basin and Lee Valley Flood relief would eliminate the following hazards:
• Deliberate and malicious acts of sabotage; and
• Accidental damage by a third party.
There is no boat traffic on the stretch of the River Lee in the site area, and therefore the risk from pipeline damage caused by boat traffic is considered low.
1.2 Objective
The main objective of the work is to support the planning application for the replacement of the above-ground section of pipeline with a buried section, and to obtain information about the ground conditions through site investigation.
1.3 Planning
A full planning permission was previously granted for the works by Epping Forest District Council (ref: PL/EPF/0857/17) with several conditions that needed to be satisfied. The planning permission granted in 2017 has now lapsed, and this report is prepared to support a new planning application.
British Pipeline Agency 1 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
1.4 Scope
The scope of the investigation and layout of this report has been designed with consideration of CLR11 (Environment Agency, 2014) and BS 10175: 2013 (BSI, 2013) and guidance on land contamination reports issued by the Environment Agency (EA) (2010a).
The project was carried out to an agreed brief as set out in RSK’s proposals (ref. 28841- 01T01(00), dated 10th October 2016 and ref. 1921133 T02(01) dated 22nd January 2020).
The scope of works for the assessment included:
• a Preliminary Risk Assessment (PRA) using Envirocheck database a commercially available environmental database to review existing geological, hydrogeological and hydrological information, and historical plans as well as correspondence with regulatory authorities;
• a site walkover to develop an initial conceptual site model to consider any potentially complete pollutant linkages;
• an intrusive investigation consisting of 3 No. boreholes to a depth of 20mbgl to assess the ground conditions and geotechnical parameters to assist a tunnelling engineer;
• Laboratory analysis of samples to determine any possible contamination along with subsequent groundwater and gas monitoring;
• A discussion of the ground conditions encountered along the proposed route of the pipeline, including their likely strength and condition, the presence of any particularly weak or strong soils and the presence of groundwater;
• a geophysical survey to confirm the depth of the sheet pile walls;
• Construction of a geological cross section;
• A review of construction details for the pipeline and Incident Action Plan prepared by BPA; and
• Conceptual Site Model with mitigation measures in place.
1.5 Existing reports
RSK reports 28841 R01(00) and 28841 R02(00) were previously issued in reference to the planning conditions attached to the previous planning approval (ref: PL/EPF/0857/17).
RSK is unaware of any other existing reports pertaining to the site.
Information from the previous RSK reports is used in this document.
British Pipeline Agency 2 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
1.6 Limitations
The comments given in this report and the opinions expressed are based on the ground conditions encountered during the site work and on the results of tests made in the field and in the laboratory.
However, there may be conditions pertaining to the site that have not been disclosed by the investigation and therefore could not be taken into account. In particular, it should be noted that there may be areas of made ground not detected due to the limited nature of the investigation or the thickness and quality of made ground across the site may be variable. In addition, groundwater levels and ground gas concentrations and flows may vary from those reported due to seasonal, or other, effects.
British Pipeline Agency 3 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
2 THE SITE
2.1 Site location and description
The site comprises of an above-ground section of pipeline located north of the confluence of the Horsemill and Cornmill Flood relief channels at Fishers Green Lane, Lee Valley Park, Cheshunt, EN9 2ED, approximately centred at National Grid reference 537907, 202656 as shown on Figure 1.
The pipeline bridge comprises one 350 mm diameter pipe, which emerges from below the ground on the eastern side of the River Lea, forms a bridge over to the river and returns underground by Hooks Marsh Car Park.
The area surrounding the existing and proposed pipeline routes comprises Fishers Green Lane, which serves two residential properties (Fishers Green Cottage and Fishers Green Farm) and two small car parks. A system of lakes/marshes as part of Lee Valley Park is located beyond the car park to the west of the river channel.
The area to the east of the channel currently comprises open agricultural land. The area between the two channels is densely overgrown with trees and shrubs.
Table 1: Site setting
To the east of Two residential properties, grazing fields, a small car park the channels: Lee Valley Farm comprising a large complex of greenhouses situated 300 m To the north: to the north
To the west of Hooks Marsh and Cheshunt Lakes are situated to the west of the site with a the channel: large industrial estate beyond, approximately 1000 m to the west Historical remnants of a cast iron Victorian aqueduct and nitro-glycerine hills To the south: (remnants of a Royal Gunpowder Mill)
The site elevation remains fairly constant throughout with some variation from 19.5 m Ordnance Datum (AOD) at Hooks Marsh Car park on the west side of the site to an elevation of 22 m Ordnance Datum (AOD) by Holyfield Fishery on the east side of the site. The elevation along the River Lea is approximately 21.4 m Ordnance Datum (AOD), with most of the land in the surrounding area remaining relatively flat.
2.2 Proposed development
The site in question comprises a pipeline bridge over the River Lee. It is proposed to replace the existing above-ground section of pipeline with a buried section. The location of the existing pipeline bridge and the proposed below-ground section is shown on Figure 2.
British Pipeline Agency 4 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
3 PRELIMINARY RISK ASSESSMENT (PRA)
3.1 Site walkovers
The site was visited on 13th December 2016 and in February 2020 to undertake a site walkover. Photographs are provided in Appendix C.
No potentially significant ground contamination issues were identified during the site reconnaissance survey. The fuel pipeline was identified as a potential source of contamination, however, the pipeline system is operated and maintained to a high standard and the occurrence of an incident or release of hydrocarbons associated with the pipeline under normal operation is highly unlikely.
No changes were noticed between the observations made in 2016 and the observations during the recent site visit in 2020.
3.2 Ground conditions
3.2.1 Geology
Published records (British Geological Survey, map sheet 239, Hertford, 1978, scale 1:50,000) for the area indicated the geology of the site to be characterised by the succession recorded in Table 2.
Table 2: Geology at the site
Estimated thickness Geological unit Description (m) Silt, sand, clay with layers of peat and organic Alluvium ~3 m material. River Terrace Sand and gravel, locally with lenses of silt, clay ~5 m Deposits or peat. Mottled blue-grey or grey-brown, slightly calcareous, silty to very silty clay, clayey silt, with some layers of sandy clay. Carbonate concretions and pyrite. Beds of shells and fine London Clay ~8 m sand partings or pockets of sand are also present. Flint gravel occurs in places. Glauconite is present in some of the sands and in some clay beds, and white mica occurs at some levels. Vertically and laterally variable sequences Lambeth Group mainly of clay, some silty or sandy, with some ~15 m Formation sands and gravels, minor limestones and lignites and occasional sandstone and conglomerate.
British Pipeline Agency 5 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Estimated thickness Geological unit Description (m) Glauconitic with nodular flints, overlain by pale Thanet Sand yellowish clay rich and glauconitic fine-grained ~7 m Formation sand with some calcareous/siliceous sandstones.
Chalk, with or without flint and discrete limestone, Could be variable White Chalk Sub- marl (calcareous mudstone), sponge, calcarenite, group 350 m to 470 m (BGS phosphatic, hardground and fossil-rich beds. lexicon) Source: BGS maps and website
The geological maps suggest that the superficial geology is represented by Alluvium and River Terrace Deposits. The solid geology beneath the site comprises the London Clay and Lambeth Group Formations over Thanet Sand with the White Chalk at depth.
Several borehole records were downloaded from the British Geological Survey website to provide further information regarding ground conditions in the vicinity of the site. Copies of these are included in Appendix D. These borehole records suggest that the site is underlain by Alluvium, described as clayey peat/brown green clay along with the River Terrace Deposits, described as black and brown ballast. Underlying these superficial lithologies is the London Clay, Lambeth Group and Thanet Sand Formations with the White Chalk at depth.
The borehole logs also suggests that in addition to these natural strata, there is the possibility of made ground beneath Fishers Green Lane.
3.2.2 Mining and quarrying
Evidence has been sought to identify any mining and quarrying operations, past and present, which have taken place within the vicinity of the site. The sources of information referenced in this element of the desk study include:
• an environmental database report;
• records held by local authority/EA; and • geological maps (see Section 4.1).
With reference to the above data, the area to the southeast of the site was identified as a BGS Recorded Mineral site. The minerals comprise sands and gravels of the River Lea Deposits.
3.2.3 Landfilling and land reclamation
Evidence has been sought to identify any landfilling or land reclamation operations, past and present, which have taken place in the vicinity of the site. The sources of information referenced in this element of the desk study include:
• environmental database report.
British Pipeline Agency 6 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
• records held by local authority/EA.
• geological maps (see Section 4.1).
A historic landfill is situated on the site. There are three records related to this landfill. Two of the records confirmed that commercial/industrial waste types were deposited on the eastern side of the site between the late 1950s and the late 1970s. The third record refers to the site as ‘Thorogoods’ landfill, Fishers Green, Waltham Abbey, Essex, which was operated from 31st December 1961 until 31st December 1970 and at the time of its operation accepted inert waste.
There are a further fifteen records of historic landfill sites within 1 km of the site, two of which were situated within a 250 m radius of the site. The closest off-site landfill is located at The Cheshunt Sand and Gravel Company Limited, Hertfordshire, 54 m to the north. This landfill, which accepted inert and industrial waste, operated from 31st October 1944 till 12th October 1977.
Another historic inert waste landfill, situated 249 m to the west of the site, operated between 19th October 1955 and 31st December 1963 by the British Waterways Board.
3.3 Hydrogeology
3.3.1 Aquifer characteristics
Based on the published geological map referred to above, the hydrogeology of the site is likely to be characterised by the presence of a Secondary undifferentiated aquifer comprising the Alluvium due to the variable amounts of Clay. The River Terrace Deposits beneath this are likely to be the Secondary A aquifer, which overlies the unproductive low permeability London Clay Formation. The Thanet Sand and Chalk aquifers define the base of this sequence.
3.3.2 Vulnerability of groundwater resources
The site has been classified by the EA website to overlie a:
• Principal aquifer associated with the White Chalk: layers of rock or drift deposit that have high intergranular and/or fracture permeability (usually providing a high level of water storage). They may support water supply and/or river base flow on a strategic scale; • Secondary A aquifer associated with the River Terrace Deposits and the Thanet Sands: permeable layers capable of supporting water supplies at a local rather than strategic scale, and in some cases forming an important source of base flow to rivers; • Secondary undifferentiated aquifer associated with the Alluvium: it has not been possible to attribute either a category A or B to a rock type. In most cases this means that it was previously designated as both minor and non-aquifer in different locations owing to the variable characteristics; and
British Pipeline Agency 7 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
• ‘unproductive’ strata associated with the London Clay Formation: low permeability with negligible significance for water supply or river base flow.
The River Terrace Deposits are classified to have a HIGH URBAN leaching potential. The cohesive Alluvium deposits are defined as having a LOW leaching potential.
HU- soils of high leaching urban potential are restored mineral workings and urban areas is based on fewer observations than elsewhere, so a worst-case vulnerability classification is assumed until proven otherwise.
L- soils where pollutants are unlikely to penetrate the soil layer either as a result of largely horizontal water movement or because the soil has the ability to attenuate diffuse pollutants. Lateral flow in these soils may contribute to groundwater recharge elsewhere in the catchment and generally have a high clay content.
3.3.3 Licensed groundwater abstraction
The environmental database (Envirocheck report, 8th November 2016) report indicates that there are five current licensed groundwater abstractions within a 2 km radius of the site summarised in Table 3. The nearest is located approximately 59 m to the southeast of the site and is operated by Holyfield Farm, Fishers Green, Waltham Abbey for spray irrigation purposes.
Table 3: Groundwater abstractions
Distance and orientation Reference Comment from site General agriculture: Spray Irrigation Mr N D Chapman, 59 m southeast Holyfield Farm, Fishers Green, Holyfield Farm (537800, 202500) Waltham Abbey, Essex Direct Source - groundwater General farming and domestic Lee Valley Regional 1406 m northeast Holyfield Hall Farm, Waltham Abbey Park Authority (538300, 204000) Single point source - groundwater Non-remedial River/Wetland Support Lee Valley Regional 1523 m northeast Holyfield Lake, Fishers Green, Waltham Park Authority (537980, 204210) Abbey Single point source - groundwater Sports Grounds/Facilities: Make-up or Lee Valley Regional 1688 m south top up water Park Authority (537101, 200895) Cheshunt Marsh, Eleanor Cross Road, Waltham Cross
British Pipeline Agency 8 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Distance and orientation Reference Comment from site Drinking, cooking, sanitary and washing British Pipeline 1711 m east Booster Pumping Station, Galley Hill Agency Limited (539500, 202300) Road, Waltham Abbey Single point source- groundwater
In terms of aquifer protection, the EA generally adopts a three-fold classification of source protection zones (SPZ) for public supply abstraction wells:
• zone 1 or ‘inner protection zone’ is located immediately adjacent to the groundwater source and is based on a 50-day travel time from any point below the water table to the source. It is designed to protect against the effects of human activity and biological/chemical contaminants that may have an immediate effect on the source • zone 2 or ‘outer protection zone’ is defined by a 400-day travel time from a point below the water table to the source. The travel time is designed to provide delay and attenuation of slowly degrading pollutants.
• zone 3 or ‘total catchment’ is the area around the source within which all groundwater recharge is presumed to be discharged at the source.
Information available on the EA website indicates that the site does not lie within a currently designated groundwater Source Protection Zone. However, an outer zone (zone 2) associated with potable abstraction boreholes in Waltham Abbey, is located within 183m south of the site.
3.4 Hydrology
3.4.1 Surface watercourses
The river meanders through the landscape in a southerly direction, with man-made flood relief channels to the north and south of the site. The stretch of River Lee to the north of the site ranges in width between 20 m and 35 m. At the Fishers Green Lane, the river divides into Horsemill Stream (to the west) and Cornmill Stream (to the east). Hooks Marsh is situated directly west of the site.
The water quality along the River Lee ranges from grade A to grade D (Envirocheck report, 8th November 2016).
The classification of the water quality in the vicinity of the site is considered to be grade D (fair quality). The classification of the water quality in the stretch of the River Lee at Kings Weir Tottenham Lock 569 m west of the site is considered to be a grade A (very good).
There are seventeen discharge consents within 960 m of the site. The nearest to the site is located at Holyfield Nursery, Fishers Green Lane, Holyfield, Waltham Abbey. This discharge consent is associated with the sewage treatment plant.
British Pipeline Agency 9 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Sixteen pollution incidents were identified within 800 m of the site, the majority of which was identified as a category one and one was identified as a category 2. The nearest pollution incident (category 3-minor incident) occurred on the 4th December 1995 at Waltham Abbey, 99 m north of the site. The pollutant was identified as unknown.
3.4.2 Surface water abstractions
One surface water abstraction was identified, using the environmental database (Envirocheck report, 8th November 2016), within a 2km radius of the site, which is detailed in Table 4.
Table 4: Surface water abstractions
Distance and orientation from Reference Comment site General Agriculture: Spray Irrigation Mr D A 310m south Chapman, Direct source- surface water Holyfield Farm (537600, 202200) Holyfield Farm, Waltham Abbey, Essex
3.4.3 Site drainage
The majority of the site is unsurfaced, comprising either an arable field or a grazing field with Fishers Green Lane, Hooks Marsh Path and car park. It is therefore assumed that much of the rainwater infiltrates into the ground with some surface runoff possibly draining into Hooks Marsh. No drains were observed on the site during the site walkovers.
3.4.4 Preliminary flood risk assessment
The indicative floodplain map for the area, published by the EA, shows that the site lies within the designated floodplain of the River Lee. The site area lies within both Zones 2 and 3 for flood risk.
A flood defence system has been put in place within the vicinity of the site, which involved construction of a wall/embankment along the western bank of Horsemill Stream. The area to the east of the wall/embankment, located between two river channels, benefits from the defence.
This report is not intended to replace a full hydrological study and it is recommended that additional specialist studies be conducted to confirm flood risks at the site.
3.5 History of site and surrounding area
The history of the land-use and development of the site and surrounding area has been assessed based on the following sources:
• historical maps within the environmental database from 1888 to 2016;
British Pipeline Agency 10 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
• internet search;
• aerial photography; and • Dangerous Energy publication ‘The archaeology of gunpowder and military explosives manufacture’, published by English Heritage in 2000.
Copies of OS and County Series maps are included in the environmental database report in Appendix E. Reference to historical maps provides invaluable information regarding the land use history of the site, but historical evidence may be incomplete for the period pre-dating the first edition and between successive maps.
The development history of the site and surrounding area from the above sources is detailed in Table 5 and summarised below.
Table 5: Summary of historical development
Land use/features in vicinity of site Date Land use/features on site (of relevance to the assessment) Fishers Green Farm is located 50 m to the east of the site and comprises of a The River Lea runs directly residential farm house and outbuildings through the middle of the site. surrounded by fields. Cornmill and Horsemill Stream Woodland is present 50 m to the south flow around Paynes Island. west of the site where Watch and Barrel Hooksmarsh Bridge crosses the Houses are located. These structures 1884-1897 River Lea to the Boat House on are associated with a Royal Gunpowder the west side of the site. Factory situated 700 m to the south of the site. Fishers Green Farm is situated on the east side of the site as open An embankment is present along the land. River Lea 120 m south west of the site. The River Lea meanders 100 m north of the site. Two buildings were identified at 110 m and 240 m south west of the site on the floodplain between the River Lea and A boat house is identified on the Cornmill Stream. The Dining Room 1897-1898 southwest corner of the site on building is also located 60 m south west the River Lea. of the site along Cornmill Stream. The River Lea and Fishers Green are now covered by less forests. 1898-1970’s No historical maps are available in these dates.
A pipeline has now been identified Two drains are located on the floodplain across the River Lea, north of between Horsemill and Cornmill 1972-1987 Hooksmarsh Bridge. Streams, 200 m and 20 m southwest of the site. The land on this flood plain A drain is situated to the north of 200m south of the site (formerly the Fishers Green Lane. occupied by Royal Gunpowder Factory
British Pipeline Agency 11 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Land use/features in vicinity of site Date Land use/features on site (of relevance to the assessment) Two ponds are located in the field facilities) has now been identified as a near Fisher Green Farm on the Government Research Establishment. east side of the site. A number of nitro-glycerine hills (the A path, separating Horsemill remnants of gunpowder making history) Stream and Hooksmarch, with are present to the south east of the site, embankments on either side with the closest structure 120 m to the extends west of the site. south east. Horsemill Stream has been A few large surface water features such straightened and widened. as ponds and lakes are located 120 m and 10 m north of the site. Hooksmarsh is located northwest of the site. A nursery with a complex of greenhouses is located 240 m to the north east. The River Lea was subject to straightening 100 m north of the site. A A car park is situated in the lake was separated into two smaller 1987-1992 middle of the site to the west of lakes. Hooksmarsh Bridge The ponds to the east of Cornmill Stream are no longer present. 1992- present No changes to the site and the surrounding area
The above summarised history indicates that the site formed the northern tip of the Royal Gunpowder Factory. The previous sections of this report indicate that a landfill is located on the eastern side of the site. However, the historical map series is limited, and no historical maps of the site are available in dates between the end of 19th Century and the 1970’s, which could potentially confirm the timing and extent of gravel extraction and subsequent infilling.
3.6 Sensitive land uses
Three special scientific sites of interest (SSSI) were identified in the vicinity of the site. The following ecological receptors were identified in the vicinity of the site:
• Waltham Abbey located directly southwest of the site - Site of Special Scientific Interest (SSSI), designated by Natural England in October 1986;
• Turnford and Cheshunt Pits directly north of the site - Site of Special Scientific Interest (SSSI), designated by Natural England in April 1995; and
• Cornmill Stream and Old River Lea 817m south of the site - Site of Special Scientific interest (SSSI), designated by Natural England in May 1986.
British Pipeline Agency 12 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
A comprehensive evaluation of ecological receptors is outside the scope of this report.
3.7 Local authority environmental health department information
RSK sent an enquiry to the environmental health department (EHD) of Epping Forest District Council in 2016 in relation to information about contaminated land within the vicinity of the site.
The council’s response is included in Appendix N and indicates that there have been no pollution or contamination incidents on or in the vicinity of the site. The searches conducted by the Environmental Health Officer (EHO) also confirmed that the southeast section of the site is highlighted as having been subject to a former land-use as a landfill (industrial) filled 1974-1976. The area to the southwest is highlighted as being used as a gunpowder works historically as well as areas of filled canal. The area to the northwest is highlighted as filled landfill. Therefore, although there have not been any specific incidents, the EHO concluded that the area can be considered higher risk of contamination due to significant infilled waste materials in the area.
Furthermore, the EHO’s search confirmed that there are several historical closed landfills in the vicinity of the site. Fill materials are mostly unknown unless otherwise stated. There is a previous industrial landfill located on the southeast section of the site - landfill (industrial) filled 1974-1976 located at: TL 37747 02523. There is a previous landfill located on the northeast section of the search site located at: TL 37804 02732. There is a historical landfill located on the northwest section of the search site located at: TL 37561 02736. The Council has not completed any gas monitoring on these locations and is not aware of any gassing issues.
The response letter also indicates that there are no known private water supplies that are subject to the Private Water Supplies (England) Regulations 2016 highlighted on the Council’s electronic database within 500 metres of the requested site.
3.8 Initial conceptual model
The information presented in Sections 2 and 3.1 to 3.7 has been used to compile an initial conceptual model. The identified potential sources of contamination, associated contaminants and receptors have been considered with plausible pathways that may link them. The resulting potential pollutant linkages are considered in Section 3.8.4. The risk classification has been estimated in accordance with information in Appendix G.
3.8.1 Summary of potential contaminant sources
Potential sources and contaminants of concern are summarised in Table 6.
British Pipeline Agency 13 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Table 6: Potential sources and types of contamination
Potential sources Contaminants of concern On-site historical Petroleum pipeline (from the late Jet fuel (petroleum hydrocarbons, polycyclic aromatic 1960’s till present day) hydrocarbons (PAHs), methyl tertiary butyl ether (MTBE)) Gunpowder production Nitro-glycerine, metals (potassium nitrate), solvents, cyanides, petroleum hydrocarbons and PAHs. Unknown fill material on the Unknown fill material (but could potentially include heavy eastern area of the site metals, ash, clinker, sulphates, polycyclic aromatic hydrocarbons (PAHs), asbestos) Carbon dioxide and methane could also be present.
The main potential contamination source is the petroleum pipeline, which was constructed in the late 1960’s. Other historical contamination sources include the former gunpowder factory and the landfill located on the eastern side of the site. However, it should be noted that the gunpowder production was historically carried out to the south of the site. The gunpowder factory is located hydro-geologically down gradient of the site and therefore it is unlikely that any contamination migrated to the site from gunpowder making activities.
3.8.2 Sensitive receptors
Sensitive receptors at this site include:
• Occupiers of adjacent residential land users in Fishers Green;
• vegetation and crops on fields along with farm animals;
• Sites of Special Scientific Interest including Waltham Abbey directly southwest of the site as well as Turnford and Cheshunt Pits directly north of the site;
• Secondary A aquifer associated with the River Terrace Gravels and the Thanet sands;
• The River Lea, which flows through the middle of the site along with Cornmill and Horsemill Stream. Hooks Marsh situated north west of the site.
Please note that construction workers have not been identified in the conceptual model as receptors because risks are considered to be managed through health and safety procedures including CDM regulations.
3.8.3 Summary of plausible pathways
The plausible pathways are summarised below:
• direct contact (soil, dust and vegetable ingestion, dermal contact, dust and fibre inhalation) and ground gas / soil gas inhalation; • vertical and lateral migration including leaching into the soils and impacting the Secondary A aquifer comprising River Terrace Deposits; and
British Pipeline Agency 14 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
• hydrocarbon contamination migration into and within the River Lea (Cornmill and Horsemill Streams).
3.8.4 Potentially complete pollutant linkages
The outline conceptual model is presented in Table 7. The risk classification has been undertaken in accordance with CIRIA C552 (Rudland et al., 2001), a summary of which is included in Appendix G.
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Table 7: Risk estimation for potentially complete pollutant linkages
Potential Contaminant Potential receptor Possible pathway Likelihood Severity Risk and justification Leak directly into the ground Shallow Secondary A beneath Fishers Unlikely Severe Moderate/low Leak on the underground aquifer Green and section of the pipeline – migration within hydrocarbons the aquifer On-site, linear source Migration into the Surface water drainage/River Cornmill and Unlikely Severe Moderate/low Lea system and Horsemill Streams Hooks Marsh Residents of Fishers Green Farm/Cottage, farmers using fields Direct contact with High and their animals hydrocarbon spills Likely Severe The ‘likely’ rating is adopted due to the grazing in them; and the inhalation of vapours potential for the pipe bridge being Leak on the above SSSI area of Hooks damaged by deliberate act/sabotage. ground section of the Marsh pipeline – hydrocarbons It was confirmed by BPA that deliberate Spill/leak directly drilling into the pipeline bridge occurred 5 On-site, linear source into the River Lee years ago. The attempt was noticed in the River Lee, Horsemill and oil migration pipeline operation centre and damage to Stream and Cornmill downstream into Likely Severe the pipeline was avoided by a prompt Stream the River Lee, emergency response. Cornmill and Horsemill Stream
Notes: The principal source of contamination considered in the Conceptual Site Model is the pipeline transporting petroleum hydrocarbons. The presence of the existing landfill in the eastern area of the site should be considered as a risk to the ground-workers/neighbouring residents during the construction phase of the proposed pipeline section.
British Pipeline Agency 16 Geoenvironmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
The conceptual site model (CSM) presented in the above table indicates that the risk associated with the existing pipeline bridge is High. The likelihood of the potential spill/leak is considered ‘likely’, as the above ground pipeline section is exposed it is therefore susceptible to deliberate sabotage and attempts to abstract petroleum fuel.
Even though this risk is considered to be high, the presence of Alluvial clays and sheet pile walls of the River Lea streams toed into the London Clay beneath the site will impede lateral migration of contaminants to surface water bodies and Hooks Marsh.
The likelihood of spills/leaks from the below ground pipeline was categorised as unlikely, based on the fact that there was not any below-ground spill/leak since the 1960’s when the pipeline was constructed. The risk associated with the below-ground pipeline section is Moderate to Low.
In conclusion, the initial CSM indicates that the risk of hydrocarbon spills/leaks from the above-ground section of the pipeline would be reduced if the pipeline was re-routed below the River Lea. The proposed works to re-route the pipeline are discussed in the following sections.
Furthermore, the presence of the landfill on the eastern side of the site should be considered during the construction phase of the works in order to protect groundworkers and residents of the Fishers Green Farm/cottage.
British Pipeline Agency 17 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
4 PROPOSED REROUTE OF THE PIPELINE
The existing pipeline comprises a single 350mm diameter pipe constructed from API 5L X52 carbon steel line pipe and bends. The following information was provided by BPA.
4.1 The proposed pipeline design
The new section of pipeline will be a fully welded construction. Welds will be carried out by qualified welders in accordance with BS 4515 Part 1, and the completed welds will be inspected using phased array ultrasonic technique.
4.2 Corrosion protection
Primary corrosion protection is provided by applying a 700 micron thick fusion bonded epoxy (FBE) coating. The coating will be applied to the pipe under factory conditions with only the weld areas and bends requiring coating on the site. The coating will be inspected on the site prior to installation in the ground. The pipeline will be placed into selected fill material free from sharp stones to prevent damage to the coating during backfill operations.
Secondary corrosion protection is provided by an impressed current cathodic protection system. Test posts will be installed on either side of the canal to enable the effectiveness of the corrosion protection systems to be regularly monitored.
4.3 Design improved parameters of the proposed section
Improved design features will be used for the proposed stretch of the pipeline, including thicker walls and improved pressure residence, as detailed in Table 8 below.
Table 8: Proposed design parameters
Pipe Pressure Diameter Wall thickness (mm) (bar) Existing Proposed Maximum Allowable Integrity Testing pipeline pipeline Operating pressure Pressure 350mm 7.1 7.9 82.8 124.2
The design parameters indicate that the new pipeline section will include thicker walls and withstand higher hydrostatic pressure than the existing pipeline.
British Pipeline Agency 18 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
4.4 Leak/spills avoidance and mitigation
An internal assessment of the pipeline is carried out periodically utilising an in-line inspection tool. The pipeline is examined for defects, damage or corrosion. The results of the inspections are processed and if any defects detected these would trigger mitigation of the damage/defect.
4.5 Leak/spills detection
The pipeline operates under a pressure sensitive monitoring system combined with a flow balancing statistical system.
The existing emergency procedure for the Fisher Green (Lean Valley Regional Park) section includes upstream and downstream isolation valves. The valves are located at Epping Booster Station (grid reference TL 007-985) and BV3 Broxbourne (TL 363-047). The oil volume between the valves is 3,623m3. The booming points may vary, depending on the preference of the Park Warden.
In addition, in the event of spill from the existing pipeline section, a canal sluice gate would be used to prohibit product migration in the Cornmill Stream.
4.6 Pipeline Construction Details
The proposed below-ground pipeline section will include for one bored crossing beneath the Cornmill and Horsemill Streams. The tunnelling machine will commence from a piled pit on the eastern side of the Cornmill Stream and terminate in a concrete reception shaft in the Hooks Marsh Car park, to the west of the Horsemill Stream.
A concrete base will be placed in the bottom of the pits. The micro-tunnel will be ~1m diameter, constructed from concrete jacking pipes. Once completed the pipeline will be installed centrally in the tunnel and the annulus filled with grout. The elevation of the auger bores will be a minimum of 2m below the base of the canal construction/sheet pile walls. The base of the sheet pile walls will be confirmed by a geophysical survey.
4.7 Pipeline Construction Phase
The excavation works will be dewatered by a well-point dewatering system or similar. The groundwater will be discharged back into the ground via soakaway or into surface water, although this is subject to further discussion pending the award of the construction contract. The construction contractor will obtain groundwater abstraction and discharge licences and all works will be subject to having approved risk assessment and method statements.
Prior to tie-in works commencing the pipeline will be cleared of product by purging it with nitrogen. Once it is confirmed that the pipe is free of product the top of the pipeline will be
British Pipeline Agency 19 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
drilled and physically dipped to check for the presence of any residual product. Appropriate equipment (spill kits, drip trays, gulley sucker etc.) will be on site to prevent the escape of any product.
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5 SITE INVESTIGATION METHODOLOGY
RSK carried out intrusive investigation works between 11th and 18th January 2017 to confirm the geological sequence beneath the site.
Groundwater monitoring was carried out on 1st February 2017 to confirm the depth of the groundwater table beneath the site and obtain groundwater samples for chemical testing. In addition, a geophysical survey was completed on the site on 1st February 2017. The objective of the geophysical survey was to confirm depths of the sheet pile walls along the Horsemill and Cornmill Streams.
5.1 Sampling strategy and methodology
The techniques adopted for the investigation were chosen considering the anticipated ground conditions, existing land use and the proposed construction works.
Three boreholes were drilled on the site, one of which was situated in the Hooks Marsh car park and the other two boreholes were drilled in the field to the east of the Cornmill Stream. No boreholes were drilled between two streams on Paynes Island, as this area was in 2017 densely overgrown with trees and shrubs. The boreholes were drilled utilising a 200mm diameter casing in order to accommodate two installation pipes. One of the installation pipes was a shallow 19mm diameter groundwater monitoring pipe and the other was a deep 80mm diameter pipe required for a geophysical survey.
5.1.1 Investigation locations
The following site work was carried out between 11th January and 1st February 2017:
• Drilling and installation of three cable-percussive boreholes (BH01, BH02 and BH03);
• Groundwater monitoring (BH01, BH02 and BH03);
• Groundwater monitoring (BH01, BH02 and BH03);
• GPS survey to obtain National Grid co-ordinate and mAOD levels at all borehole locations; and • Geophysical survey utilising boreholes BH01 and BH02.
The investigation and the soil descriptions were carried out in general accordance with ‘BS 5930:1999. Code of Practice for Site Investigations’ (BSI, 1999). The exploratory hole records are presented in Appendix H.
The locations of the intrusive investigations are shown in Figure 2. The rationale for these locations is given in Table 9. The investigation was designed to confirm the geological sequence and characterise baseline condition for the proposed rerouted pipeline. In addition, the aim of the works was to confirm the depth of the sheet pile walls and a depth of the shallow groundwater beneath the site.
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Table 9: Exploratory hole location rationale
Drilled by Exploratory hole Location Rationale ID Easting Northing Geological information, groundwater BH01 537631 202634 level/condition, geophysical survey Geological information, groundwater RSK BH02 537682 202608 level/condition, geophysical survey Geological information, groundwater BH03 537711 202596 level/condition
The investigation points were located approximately by reference to physical features present on the site at the time of investigation. The boreholes were later surveyed utilising a Leica GPS tool. The results of the survey are presented in Table 9 above.
5.1.2 Groundwater monitoring and levelling
Depths to groundwater were recorded using an electronic dip meter on 1st February 2017. The monitoring results are discussed in Section 5.2.2.
The ground levels and the highest point of the top of casing of the monitoring wells were established in relation relative to an Ordnance Datum using a Leica GPS to enable the calculation of groundwater elevations. However, a groundwater flow direction was not calculated, as it is anticipated that the shallow groundwater to the east of Cornmill Stream is not in hydraulic continuity with the shallow groundwater to the west of Horsemill Stream due to the steel sheet-pile walls effectively forming a barrier.
The groundwater monitoring data are provided in Appendix I.
5.1.3 Groundwater sampling and analysis
In order to characterise the baseline conditions, four groundwater samples were retrieved using a United States Environment Protection Agency (USEPA) approved low-flow purging and sampling methodology. The low-flow method relies on moving groundwater through the well screen at approximately the same rate as it flows through the geological formation. This results in a significant reduction in the volume of water extracted before sampling and significantly reduces the amount of disturbance of the water in the monitoring well during purging and sampling. Drawdown levels in the monitoring well and water quality indicator parameters (pH, temperature, electrical conductivity, redox potential and dissolved oxygen) are monitored during low-flow purging and sampling, with stabilisation indicating that purging is complete and sampling can begin. As the flow rate used for purging, in most cases, is the same or only slightly higher than the flow rate used for sampling, and because purging and sampling are conducted as one continuous operation in the field, the process is referred to as low-flow purging and sampling.
In-situ water quality measurements undertaken during the low-flow sampling process are provided in Appendix I. British Pipeline Agency 22 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
The groundwater samples were collected in containers appropriate to the anticipated testing suite required. The containers were filled to capacity and placed in a cool box to minimise volatilisation. Samples were transported directly to the testing laboratory under chain of custody documentation. The rationale for groundwater analysis is presented in Table 10.
Table 10: Scheduled analysis – groundwater
Exploratory hole no. Analyte Rationale BH01 speciated TPH, BTEX and BH02 Baseline data MTBE BH03
British Pipeline Agency 23 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
6 INVESTIGATION RESULTS
The results of the intrusive investigation and subsequent laboratory analysis undertaken are detailed below. The descriptions of the strata encountered, list of samples taken, field observations of soil and groundwater, in-situ testing and details of monitoring well installations are included on the exploratory hole records presented in Appendix H.
6.1 Soil
The exploratory holes revealed that the site is underlain by a variable thickness of made ground over Alluvium and River Terrace Deposits with the London Clay Formation over Lambeth Group encountered at depth. In addition, Harwich Formation comprising a thin layer of sand was encountered at the base of London Clay Formation.
The made ground encountered in the most eastern borehole (BH03) comprises the fill materials deposited on the site during the landfilling operations between the 1950’s and 1970’s.
The exploratory boreholes further revealed that the maximum thickness of the River Terrace Deposits of 6.3 m was encountered in borehole BH02, situated next to Cornmill Stream. The thickness of the River Terrace Deposits in borehole BH03, situated approximately 20 m to the east of borehole BH02, was only 2.0 m. The reduced thickness of the gravel deposits in borehole BH03 is likely due to gravel extraction and subsequent infilling in this area of the site.
For the purpose of discussion, the ground conditions are summarised in Table 11 and the strata discussed in subsequent subsections.
Table 11: General succession of strata encountered
Exploratory holes Depth to top of Strata Thickness (m) encountered stratum m bgl
BH01, BH02 GL 1.2-1.8 Made ground BH03 (capping layer and Capping layer - GL Capping layer - 1.1 fill material) Fill material – 1.1 Fill material – 4.4
BH01 and 1.8 (BH01) and 5.5 0.7 (BH01) and 1.0 Alluvium (BH03) (reworked in (BH03) (reworked BH03 (reworked) BH3) in BH3) 1.2 (BH02) - 6.5 6.3 (BH02) – 2.0 River Terrace Deposits BH01, BH02, BH03 (BH03) (BH03) London Clay BH01, BH02, BH03 7.3-8.5 4.5 -7.0 Harwich Formation BH01 12.0 1.5
British Pipeline Agency 24 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Exploratory holes Depth to top of Strata Thickness (m) encountered stratum m bgl Lower Mottled BH01, BH02, BH03 13.5-15.0 2.0-3.5 Beds Lambeth (cohesive) Group Upnor Formation BH01, BH02, BH03 17.0-17.5 2.5-3.0 (granular)
Made ground
The shallow made ground within the Hooks Marsh car park is described as brown / reddish brown silty sandy GRAVEL. The gravel predominantly comprises fine to coarse, angular to sub-rounded flint and some brick fragments.
The shallow made ground in the field located to the east of the Cornmill Stream is described as dark brown silty sandy gravelly CLAY with rootlets. This material forms a capping layer to the fill placed in this area of the site between 1950s and 1970s. The fill material comprises either slightly clayey gravelly SAND or very soft dark brown black sandy, gravely, silty CLAY with brick, tiles and chipwood fragments. A slight hydrocarbon odour was also encountered at a depth of 5.5 mbgl. However, the screening for Volatile Organic Compounds (VOC) utilising a PID monitor indicated concentrations below the instrument’s level of detection of 0.1ppm. The results of screening are included on the borehole records in Appendix H.
Alluvium
This stratum was encountered in borehole BH01 and typically comprised soft to very soft, very low strength, brownish, grey, black slightly sandy, slightly gravelly organic CLAY. No alluvial deposits were encountered in boreholes BH02 or BH03 located to the east of Cornmill Stream. It is, however, possible that the Alluvium could have been removed at BH03 by the former quarry activities and placed at a greater depth (5.5 mbgl) to form a cohesive base for the landfill.
River Terrace Deposits
This stratum was encountered at a depth of between 1.2 m and 6.5 m below ground level and varies between 2.0 m and 6.3 m in thickness. However, it should be noted that the gravel deposits within the field to the east of the Cornmill Stream were extracted and replaced with the fill material. It is assumed that the original thickness of the gravels in this area of the site (prior to extraction) was around 6.0 m.
Based on the site descriptions and laboratory and in-situ tests, this layer can be described as predominantly medium dense to dense silty sandy GRAVEL.
British Pipeline Agency 25 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
London Clay
London Clay was encountered at depths between 7.3 m and 8.5 m below ground level. The borehole records further indicate that the thickness of London Clay ranges between 6.2 m and 7.0 m.
Based on the site descriptions and in-situ and laboratory testing carried out, this stratum can be described as a firm to stiff dark grey, silty slightly sandy CLAY.
Harwich Formation
The Harwich Formation was found in one (BH01) of three boreholes and it was described as medium dense brown to yellow silty fine to coarse SAND.
Lambeth Group
The site work records indicate the absence of Upper Woolwich and Reading Formations from the Lambeth Group sequence encountered beneath the site. Furthermore, no Lower Shelly or Laminated Beds of the Woolwich Formation were encountered beneath the site. The Lambeth Group beneath the site is represented by the Lower Mottled Beds of the Reading Formation and the base layer of the Group known as Upnor Formation.
Lambeth Group (Lower Mottled Beds)
The Lower Mottled Beds were described as stiff to very stiff light brownish, grey, yellow, orange, occasionally reddish mottled CLAY with subvertical fissures filled with orange/brown sand and silt.
Lambeth Group (Upnor Formation)
The base layers of the Lambeth Group are described as dense to very dense light greenish, grey, orange, brown slightly clayey SAND with black pebbles.
6.2 Groundwater
Groundwater was encountered during the investigation as detailed in Table 12.
British Pipeline Agency 26 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Table 12: Groundwater results during investigation
BH Stratum Strike (m bgl) Rise (m) BH01 RTD (groundwater) 3.5 3.2 (in 0.5hour)
BH02 RTD (groundwater) 2.0 1.8 (in 0.5hour) Made Ground (fill) BH03 1.8 1.6 (in 0.5hour) (perched water)
Note: RTD = River Terrace Deposits
The results of the subsequent groundwater monitoring and well surveying exercise are summarised in Table 13.
Table 13: Groundwater monitoring data
Groundwater depth Groundwater /perched (mbgl) measured Elevation of the pipe Monitoring well water elevation from the tops of (mAOD) (mAOD) the installation pipe BH01 1.83 21.13 19.30 BH02 1.66 21.17 19.51 BH03 1.50 21.19 19.69 Notes: m AOD metres above Ordnance datum
The findings reflect the general groundwater table in the River Terrace Deposits, which is at an elevation of around 19.4 m AOD. In addition, the groundwater monitoring data indicates that the shallow perched water table in the eastern area of the site (in the landfill) may be in hydraulic continuity with the groundwater in the River Terrace Deposits in the wider area.
It should be noted that steel sheet piles were used to construct the walls of flood relief channels (Cornmill and Horsemill Streams) of the River Lea. The results of a geophysical survey, conducted on site by RSK and discussed in Section 6.3, indicate the maximum depth of the sheet pile walls between 10.27 mAOD and 11.31mAOD, and therefore the walls are toed into the London Clay.
It is therefore assumed that there is not hydraulic continuity between the flood relief channels and the shallow groundwater. In addition, the shallow groundwater encountered in the Hooks Marsh car park is likely in the continuity with Hooks Marsh, but it is not considered likely to be in continuity with the perched water in the landfill to the east of the Cornmill Stream.
A piezometric surface was not calculated, as the groundwater encountered on both sides of the channels is not thought to be in hydraulic continuity. However, it is considered that
British Pipeline Agency 27 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
the shallow groundwater is likely to flow in a southerly direction, i.e. in the direction of the River Lea flow.
It should be noted that groundwater levels might fluctuate for a number of reasons including seasonal variations. Ongoing monitoring would be required to establish both the full range of conditions and any trends in groundwater levels.
6.3 Geophysical survey
The objective of the survey was to determine the depth to the base of the steel sheet piling along this section of the Lea River flood relief channels. To enable the testing, two boreholes (BH01 and BH02) were installed to depths of approximately 20 m in the vicinity of Horsemill and Cornmill channels. The boreholes were located 2.60 and 3.07 m lateral distance away from the river wall for BH01 and BH02, respectively.
The geophysical techniques employed were down-hole parallel seismic and down-hole magnetometry.
The results of the survey indicate a depth of the sheet pile wall on the Horsemill Stream side of 9.86 mbgl +/-0.5 m and a depth of the sheet pile wall on the Cornmill Stream side of 9.36 mbgl +/-0.5 m.
The full survey report is included in Appendix J. The results of the survey are utilised in hydrogeological cross-section presented in Figure 3 and discussed below.
6.4 Hydrogeological cross-section
The hydrogeological cross-section, including the groundwater table, construction details of the flood relief channels and the proposed pipeline, is presented in Figure 4.
The cross-section shows that the proposed pipeline will cross beneath the channels within the London Clay, at a depth of 9.3 mAOD. The tunnelling depth includes for a 2 m clearance from the maximum depth of the sheet pile walls.
It should be noted that the existing pipeline is located beneath the shallow groundwater table and that the proposed works will require dewatering of both the entry and receiving pits.
Dewatering may also be needed at depth if the sands in BH1 are water-bearing.
British Pipeline Agency 28 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
7 BASELINE DATA
Soil and groundwater samples were tested to characterise the baseline conditions in relation to the proposed pipeline construction works on the site.
7.1 Soil sampling and testing
The site work records presented in Appendix H indicate that a slight organic/hydrocarbon odour was encountered in the fill material at borehole BH03 at a depth of 5.5mbgl. However, in-situ screening for volatile hydrocarbons confirmed the PID results below 0.1ppm. In addition, a fragment of possible asbestos cement was encountered in the fill material at a depth between 2.1 mbgl and 3.8 mbgl.
In total, six selected soil samples were tested for speciated petroleum hydrocarbons (TPH CWG), benzene, toluene, ethyl benzene, xylenes (BTEX) and Methyl Tertiary Butyl Ether (MTBE).
In addition, a sample obtained from the fill material in the eastern area of the site was tested for the presence of asbestos. The results of testing indicate the absence of asbestos in the sample however, it should be noted that only one sample was tested and that asbestos may be present in the wider body of the landfill.
The testing for petroleum hydrocarbons indicates the absence of hydrocarbon contamination in the River Terrace Deposits and London Clay in the vicinity of the flood relief channels (BH01 and BH02). However, the sample obtained from the fill at borehole BH03 (depth between 3 mbgl and 3.5 mbgl), contains slightly elevated total petroleum hydrocarbon concentrations of 350 mg/kg. The detected total concentration of petroleum hydrocarbons in the fill is predominantly attributed to the heavy end hydrocarbons with carbon numbers between C12 and C35.
The chemical test results are included in Appendix K.
7.2 Groundwater sampling and testing
Groundwater samples were collected from boreholes BH01 and BH02. In addition, a sample of perched water was obtained from borehole BH03 in February 2017. The samples were obtained using a low-flow method (a peristaltic pump in line with flow cells measuring aquifer stabilisation parameters). The site work records are presented in Appendix I.
The samples were tested in laboratory for speciated petroleum hydrocarbons (TPH CWG), benzene, toluene, ethyl benzene, xylenes (BTEX) and Methyl Tertiary Butyl Ether (MTBE). The chemical test results are included in Appendix K.
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The results indicate an absence of detectable petroleum hydrocarbons within the groundwater. However, detectable concentrations of petroleum hydrocarbons were encountered in the perched water within the landfill in the eastern area of the site. The detected concentration of total petroleum hydrocarbons was 6µg/l.
British Pipeline Agency 30 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
8 PROPOSED PIPELINE AND MITIGATION MEASURES
8.1 Proposed and existing pipeline construction details
The existing pipeline runs to the east of the River Lea at an elevation of around 18mAOD (approximately 1.5 m below the ground). The site investigation results indicate that the existing pipeline is located within the made ground / Alluvium / River Terrace Deposits.
It is understood that a guided augerbore machine will be utilised to construct the proposed below-ground pipeline crossing. A thrust pit will be constructed on the eastern side of the channels with approximate plan dimensions of 15.0 m by 5.0 m. The crown of the tunnel will be at 9.32 m AOD and therefore the base of the pit will be constructed at an elevation of approximately 8 m AOD, in the London Clay / Harwich Formation / cohesive layers of Lambeth Group. Temporary steel sheet-pile walls will be installed to keep the pit sides open and form an effective cut-off wall. The pit will be dewatered to control residual groundwater ingress.
A reception pit will be constructed to the west of the Horsemill Channel, in the Hooksmarsh Car Park. The reception pit will be a circular shape, smaller (approximately 4 m in diameter) than the rectangular thrust pit. The base of the reception pit will also be at an elevation of around 8 mAOD.
The proposed below-ground pipeline crossing is at an elevation of around 8.5 mAOD, which is approximately 12.5 m below the existing ground level in the vicinity of the channels. The site investigation results indicate the majority of the crossing is likely to be constructed within the London Clay Formation, but it could possibly encounter the surface of the Lambeth Group within western section of the bore towards BH01, as shown on the cross-section presented in Figure 4. Furthermore, the Harwich Formation beneath the London Clay comprised a 1.5 m thick layer of medium dense silty fine to coarse sand between elevations of 9.13 m and 7.63 mAOD in BH01 (i.e. within the proposed alignment). The variable geology could potentially pose problems during tunnelling works, however, the proposed guided augerbore technique is considered suitable to mitigate against the risk.
In addition to the tunnelling works, an open trenching method will be employed to expose the existing pipeline and construct a connection between the new and existing sections. The base of an open trench will be at an elevation of around 19 mAOD.
The cross-section presented in Figure 4 indicates a minimum of 2 m clearance from the toes of sheet pile walls located along the channels. In addition, the section indicates the presence of approximately 5 m thick clay layers of London Clay and Lambeth Group, which are protecting deep groundwater resources in the Thanet Sand and Chalk aquifers.
British Pipeline Agency 31 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
8.2 Mitigation measures
The existing pipeline currently runs within the made ground, Alluvium and River Terrace Deposits. In addition, it is likely that some sections of the existing pipeline are located below the shallow water table.
The majority of the proposed pipeline section would be rerouted from the groundwater- bearing River Terrace Deposits and placed in the London Clay and Harwich Formations. The deep groundwater resources in the Thanet Sand and White Chalk aquifers will be protected by the cohesive layers of Lambeth Group. Low permeability clays at depths between 13.5 mbgl and 17.0 mbgl would significantly retard the downward movement of any accidental release of fuel.
British Pipeline Agency 32 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
9 CONCLUSIONS AND RECOMMENDATIONS
9.1 Conclusions
The results of the assessment indicate a HIGH potential risk associated with the existing above-ground pipeline bridge located on the site. The high risk-rating is based on the likelihood of the pipeline bridge section being damaged by sabotage or by an accident. It was confirmed by BPA that deliberate drilling into the pipeline bridge previously occurred on the eastern side of the existing crossing. Damage to the pipeline bridge could potentially cause a hydrocarbon product spill into the ground/groundwater and River Lea.
In order to reduce the high risk-rating it is proposed to replace the pipeline bridge with a new below-ground section. The likelihood of spill/leaks from the below-ground pipeline is categorised as unlikely, because there has not been any known below-ground spill/leak since the 1960’s when the pipeline was constructed. The operational risk associated with the below-ground pipeline section is therefore considered to be MODERATE to LOW.
The site investigation results indicate that the site is underlain by a variable thickness of made ground over Alluvium and River Terrace Deposits with the London Clay and Harwich Formations over Lambeth Group encountered at depth. A landfill is located in the field to the east of the Cornmill Channel.
The Alluvium and River Terrace Deposits are classified as Undifferentiated and Secondary A Aquifers, respectively. The groundwater table is located at depths between 19.3 mAOD and 19.5 mAOD. The groundwater below the site is likely to flow in a southerly direction. Perched water was encountered in the fill material at a depth of 19.7 mAOD.
The baseline monitoring data confirmed the absence of hydrocarbons in the groundwater, indicating no leaks/spills associated with the existing pipeline. However, slightly elevated concentrations of petroleum hydrocarbons were detected in the fill material and perched water in the landfill in the eastern area of the site.
The existing pipeline currently runs within the made ground, Alluvium and River Terrace Deposits. In addition, it is likely that some sections of the existing pipeline are located below the groundwater table.
Along the majority of the proposed section the pipeline will be rerouted from the groundwater-bearing Alluvium/River Terrace Deposits into the low permeability London Clay and Harwich Formation, approximately 2 m below the toe of sheet pile walls of the River Lea flood relief channels. The tunnelling depth will be at an elevation of around 8.5mAOD. However, the alignment could possibly encounter the surface of the Harwich Formation and water bearing sands within western section of the bore towards BH01.
British Pipeline Agency 33 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
A small section of the rerouted pipeline, connecting the existing pipe and the reception pit to the east of the river, will be below the groundwater/perched water table, and the vertical section of the rerouted pipeline will also pass through the shallow aquifer.
The mitigation of the leaks/spills includes the following:
• The proposed pipeline section will have an improved construction design including thicker walls withstanding higher pressures than the existing pipeline;
• Where the new pipeline section runs through the London Clay any leak or spills will be contained by the low permeability clay, however, the pipeline will also pass through more permeable layers of Harwich Formation;
• The deep groundwater resources in the Thanet Sand and White Chalk will be protected by cohesive layers of the Lambeth Group, ranging between 2.0m and 3.5m in thickness; and
• The proposed rerouting of the pipeline would remove entirely the potential risk of a discharge of fuel directly into the River Lea.
The tunnel alignment could possibly encounter water bearing sand layers within Harwich Formation within western section of the bore towards BH01. The proposed guided augerbore method is considered suitable technique to mitigate variable ground conditions beneath the site. These conditions would also prove problematic for the construction of the reception shaft. However, the current proposal is to construct the base of the shaft at an elevated of 8.0 mAOD, which indicates that the shaft will be toed into more stable/less permeable clays.
9.2 Recommendations
A precautionary approach to health and safety should be adopted when trenching through the landfill area. The risk rises from the potential presence of asbestos, volatile hydrocarbons, ground gases and other potential contaminants.
The majority of the works will be carried out below the groundwater/perched water table. Sealing of the excavations or/and dewatering procedures should be undertaken to keep tunnelling pits safe and free of groundwater. A discharge permit is likely to be required in connection with dewatering operations.
This report should be submitted to the Local Authority and Environment Agency in order to support a planning application for the proposed pipeline works.
In addition, a monitoring and maintenance plan is likely to be required to outline monitoring of the proposed construction works in reference to risks to Controlled Waters.
An existing environmental permit for the works issued by the Environment Agency in 2017 (ref EPR/DB3697QG) would need to be extended.
British Pipeline Agency 34 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Specialist contractors should be consulted in respect to the most suitable methods/techniques for construction of the shaft for the reception pit and boring/tunnelling in light of the risks posed by encountering water bearing sands of the Lambeth Group at the level of the proposed alignment in the western section of the crossing.
British Pipeline Agency 35 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
10 BIBLIOGRAPHY
British Geological Survey (1978), Sheet Number 239 Drift 1:50 000.
British Standards Institution (2015), ‘BS 5930:2015. Code of practice for ground investigations’.
British Standards Institution (2013), ‘BS 10175:2013. Investigation of potentially contaminated sites: Code of practice’.
Environment Agency (2014), Model Procedures for the Management of Contaminated Land. Contaminated Land Report Number 11 (CLR11), September (Bristol: Environment Agency).
Environment Agency (2004b), ‘Policy Number 199_04, dated 9 March 2004, Part IIA – Detailed Quantitative Assessment of Chronic Risks to Human Health from Contaminated Soils’.
Environment Agency (2006a), ‘Remedial Targets Methodology: Hydrogeological Risk Assessment for Land Contamination’.
Environment Agency www.environment-agency.gov.uk/.
Landmark Information Group (2016), ‘Envirocheck report reference 103889342_1_1”, dated 8th November 2016.
Rudland, D. J., Lancefield, R. M. and Mayell, P. N. (2001), CIRIA C552. Contaminated Land Risk Assessment: A Guide to Good Practice (London: CIRIA).
The Surface Waters (Abstraction for Drinking Water) (Classification) Regulations 1996 (London: HMSO).
The Surface Waters (Dangerous Substances) (Classification) Regulations 1998 (London: HMSO).
British Pipeline Agency 36 Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
FIGURES
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00) Site Location
Contains Ordnance Survey data © Crown copyright and database right 2013
Client BRITISH PIPELINE AGENCY (BPA)
Project Title LAND OFF FISHERS GREEN LANE
18 Frogmore Road Tel: +44 (0) 1442 437500 Hemel Hempstead Fax: +44 (0) 1442 437550 Drawing Title Hertfordshire Email: [email protected] HP3 9RT Web: www.rsk.co.uk United Kingdom SITE LOCATION MAP
Rev Drawn Date Checked Date Approved Date Project Number Drawing File Drawing Number 00AP 13.02.17 SJ 13.02.17 SJ 13.02.17 Dimensions Scale Original Size 1921133-R01 (00) 1921133 - SLP.dwg FIGURE 1 m 1:50,000 A4 LEGEND
Borehole Location
Proposed pipeline route
Existing pipeline route
Rev. Date Amendment Drawn Chkd. Appd.
18 Frogmore Road Tel: +44 (0) 1442 437500 Hemel Hempstead Fax: +44 (0) 1442 437550 Hertfordshire Email: [email protected] HP3 9RT Web: www.rsk.co.uk United Kingdom BH01 Client BRITISH PIPELINE AGENCY (BPA)
BH02 Project Title BH03 LAND OFF FISHER GREEN LANE
Drawing Title EXISTING & PROPOSED PIPELINE ROUTES & INVESTERGATION BOREHOLE LOCATIONS
Drawn Date Checked Date Approved Date AP 13.02.17 SJ 13.02.17 SJ 13.02.17
Scale Orig Size Dimensions 1:1500 A3 m
Project No. Drawing File 1921133 (R01-00) 1921133-R01-00) Figure 2
Drawing No. Rev. FIGURE 2 P1
Scale 1 : 500 0 5 10 15 20 25m Hook Marsh LEGEND
Borehole Location Receiving pit Entry pit Made ground/Fill 0 10 BH01 20 30 40 50 60 70 BH02 80 90 100 BH03 110 120 130 22 22 Alluvium (21.13mAOD) (21.17mAOD) (21.19mAOD) Horsemill Cornmill River Ternace Deposits (stream) (stream) 20 20 London Clay GW GW GW Harwich Formation
Lambeth Group (cohesive) 18 18 MADE GROUND Lambeth Group (Granular) (LANDFILL)
16 16 9.86±0.5m 9.86±0.5m Sheet pile wall Sheet pile wall REWORKED ALLUVIUM/FILL ? ? ? 14 14
Rev. Date Amendment Drawn Chkd. Appd.
12 12 11.81mAOD±0.5m 11.27mAOD±0.5m Elevation (m)
10 10
18 Frogmore Road Tel: +44 (0) 1442 437500 ? Hemel Hempstead Fax: +44 (0) 1442 437550 ? Hertfordshire Email: [email protected] 8 8 HP3 9RT Web: www.rsk.co.uk United Kingdom ? ? HARWICH FORMATION Client
6 6 BRITISH PIPEINE AGENCY (BPA)
Project Title 4 4 LAND OFF FISHERS 2 2 GREEN LANE
Drawing Title
0 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 GEOLOGICAL CROSS SECTION Distance along the baseline (m)
Drawn Date Checked Date Approved Date AP 02.03.17 AL 02.03.17 AL 02.03.17
SITEMAP AND SECTION BASELINE MATERIAL LEGENDS Scale Orig Size Dimensions As shown A3 M
Clayey SAND MADE GROUND Sandy CLAY Sandy silty CLAY Project No. Drawing File 1921133 R01(00) 1921133 (R01-00) Figure 3 Sandy gravelly Sandy gravelly Silty sandy CLAY Topsoil Drawing No. Rev. CLAY silty CLAY FIGURE 3 P1 Silty sandy Silty SAND GRAVEL Horizontal scale 1:500 Vertical scale 1:62.5 Hook Marsh LEGEND
Borehole Location Receiving pit Entry pit Proposed Pipeline 0 10 BH01 20 30 40 50 60 70 BH02 80 90 100 BH03 110 120 130 22 22 Entry/Recieving Pits (21.13mAOD) (21.17mAOD) (21.19mAOD) Horsemill Cornmill Made ground/Fill (stream) (stream) 20 20 Alluvium GW GW GW River Ternace Deposits
London Clay 18 18 MADE GROUND Harwich Formation (LANDFILL) Lambeth Group (cohesive) 16 16 9.86±0.5m 9.86±0.5m Lambeth Group (Granular) Sheet pile wall Sheet pile wall REWORKED ALLUVIUM/FILL ? ? ? 14 14
Rev. Date Amendment Drawn Chkd. Appd.
12 12 11.81mAOD±0.5m 11.27mAOD±0.5m Elevation (m)
10 10
9.3mAOD 18 Frogmore Road Tel: +44 (0) 1442 437500 ? Hemel Hempstead Fax: +44 (0) 1442 437550 ? Hertfordshire Email: [email protected] 8 8 HP3 9RT Web: www.rsk.co.uk United Kingdom ? ? HARWICH FORMATION Client
6 6 BRITISH PIPEINE AGENCY (BPA)
Project Title 4 4 LAND OFF FISHERS 2 2 GREEN LANE
Drawing Title
0 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 GEOLOGICAL CROSS SECTION Distance along the baseline (m) AND PROPOSED PIPELINE
Drawn Date Checked Date Approved Date AP 02.03.17 AL 02.03.17 AL 02.03.17
SITEMAP AND SECTION BASELINE MATERIAL LEGENDS Scale Orig Size Dimensions As shown A3 M
Clayey SAND MADE GROUND Sandy CLAY Sandy silty CLAY Project No. Drawing File 1921133 R01(00) 1921133 (R01-00) Figure 3 Sandy gravelly Sandy gravelly Silty sandy CLAY Topsoil Drawing No. Rev. CLAY silty CLAY FIGURE 4 P1 Silty sandy Silty SAND GRAVEL Horizontal scale 1:500 Vertical scale 1:62.5 APPENDIX A SERVICE CONSTRAINTS
1. This report and the site investigation carried out in connection with the report (together the "Services") were compiled and carried out by RSK Environment Limited (RSK) for the British Pipeline Agency (the "client") in accordance with the terms of a contract between RSK and the "client", dated March 2020. The Services were performed by RSK with the skill and care ordinarily exercised by a reasonable environmental consultant at the time the Services were performed. Further, and in particular, the Services were performed by RSK taking into account the limits of the scope of works required by the client, the time scale involved and the resources, including financial and manpower resources, agreed between RSK and the client.
2. Other than that expressly contained in paragraph 1 above, RSK provides no other representation or warranty whether express or implied, in relation to the Services.
3. Unless otherwise agreed in writing the Services were performed by RSK exclusively for the purposes of the client. RSK is not aware of any interest of or reliance by any party other than the client in or on the Services. Unless expressly provided in writing, RSK does not authorise, consent or condone any party other than the client relying upon the Services. Should this report or any part of this report, or otherwise details of the Services or any part of the Services be made known to any such party, and such party relies thereon that party does so wholly at its own and sole risk and RSK disclaims any liability to such parties. Any such party would be well advised to seek independent advice from a competent environmental consultant and/or lawyer.
4. It is RSK's understanding that this report is to be used for the purpose described in the introduction to the report. That purpose was a significant factor in determining the scope and level of the Services. Should the purpose for which the report is used, or the proposed use of the site change, this report may no longer be valid and any further use of or reliance upon the report in those circumstances by the client without RSK 's review and advice shall be at the client's sole and own risk. Should RSK be requested to review the report after the date of this report, RSK shall be entitled to additional payment at the then existing rates or such other terms as agreed between RSK and the client.
5. The passage of time may result in changes in site conditions, regulatory or other legal provisions, technology or economic conditions which could render the report inaccurate or unreliable. The information and conclusions contained in this report should not be relied upon in the future without the written advice of RSK. In the absence of such written advice of RSK, reliance on the report in the future shall be at the client's own and sole risk. Should RSK be requested to review the report in the future, RSK shall be entitled to additional payment at the then existing rate or such other terms as may be agreed between RSK and the client.
6. The observations and conclusions described in this report are based solely upon the Services which were provided pursuant to the agreement between the client and RSK. RSK has not performed any observations, investigations, studies or testing not specifically set out or required by the contract between the client and RSK. RSK is not liable for the existence of any condition, the discovery of which would require performance of services not otherwise contained in the Services. For the avoidance of doubt, unless otherwise expressly referred to in the introduction to this report, RSK did not seek to evaluate the presence on or off the site of asbestos, electromagnetic fields, lead paint, heavy metals, radon gas or other radioactive or hazardous materials.
7. The Services are based upon RSK's observations of existing physical conditions at the Site gained from a walk-over survey of the site together with RSK's interpretation of information including documentation, obtained from third parties and from the client on the history and usage of the site. The Services are also based on information and/or analysis provided by independent testing and information services or laboratories upon which RSK was reasonably entitled to rely. The Services clearly are limited by the accuracy of the information, including documentation, reviewed by RSK and the observations possible at the time of the walk-over survey. Further RSK was not authorised and did not attempt to independently verify the accuracy or completeness of information, documentation or materials received from the client or third parties, including laboratories and information services, during the performance of the Services. RSK is not liable for any inaccurate information or conclusions, the discovery of which inaccuracies required the doing of any act including the gathering of any information which was not reasonably available to RSK and including the doing of any independent investigation of the information provided to RSK save as otherwise provided in the terms of the contract between the client and RSK.
8. The intrusive environmental site investigation aspects of the Services is a limited sampling of the site at pre-determined borehole and soil vapour locations based on the operational configuration of the site. The conclusions given in this report are based on information gathered at the specific test locations and can only be extrapolated to an undefined limited area around those locations. The extent of the limited area depends on the soil and groundwater conditions, together with the position of any current structures and underground facilities and natural and other activities on site. In addition chemical analysis was carried out for a limited number of parameters [as stipulated in the contract between the client and RSK] [based on an understanding of the available operational and historical information,] and it should not be inferred that other chemical species are not present.
9. Any site drawing(s) provided in this report is (are) not meant to be an accurate base plan, but is (are) used to present the general relative locations of features on, and surrounding, the site. Features (boreholes, trial pits etc) annotated on site plans are not drawn to scale but are centred over the approximate location. Such features should not be used for setting out and should be considered indicative only.
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
APPENDIX B SUMMARY OF LEGISLATION AND POLICY RELATING TO CONTAMINATED LAND
Part IIA of the Environmental Protection Act 1990 (EPA) and its associated Contaminated Land Regulations 2000 (SI 2000/227), which came into force in England on 1 April 2000, formed the basis for the current regulatory framework and the statutory regime for the identification and remediation of contaminated land. Part IIA of the EPA 1990 defines contaminated land as ‘any land which appears to the Local Authority in whose area it is situated to be in such a condition by reason of substances in, on or under the land, that significant harm is being caused, or that there is significant possibility of significant harm being caused, or that pollution of controlled waters is being or is likely to be caused’. Controlled waters are considered to include all groundwater, inland waters and estuaries.
In August 2006, the Contaminated Land (England) Regulations 2006 (SI 2006/1380) were implemented, which extended the statutory regime to include Part IIA of the EPA as originally introduced on 1st April 2000, together with changes intended chiefly to address land that is contaminated by virtue of radioactivity. These have been replaced subsequently by the Contaminated Land (England) (Amendment) Regulations 2012, which now exclude land that is contaminated by virtue of radioactivity.
The intention of Part IIA of the EPA is to deal with contaminated land issues that are considered to cause significant harm on land that is not undergoing development (see Environmental Protection Act 1990: Part 2A Contaminated Land Statutory Guidance, April 2012). This document replaces Annex III of Defra Circular 01/2006, published in September 2006 (the remainder of this document is now obsolete).
Water Framework Directive (WFD)
The Water Framework Directive 2000/60/EC is designed to:
• enhance the status and prevent further deterioration of aquatic ecosystems and associated wetlands that depend on the aquatic ecosystems • promote the sustainable use of water
• reduce pollution of water, especially by ‘priority’ and ‘priority hazardous’ substances
• ensure progressive reduction of groundwater pollution.
The WFD requires a management plan for each river basin be developed every six years.
Groundwater Directive (GWD)
The 1980 Groundwater Directive 80/68/EEC and the 2006 Groundwater Daughter Directive 2006/118/EC of the WFD are the main European legislation in place to protect groundwater. The 1980 Directive is due to be repealed in December 2013. The European legislation has been transposed into national legislation by regulations and directions to the Environment Agency.
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Environmental Permitting Regulations (EPR)
The Environmental Permitting (England and Wales) Regulations 2010 provide a single regulatory framework that streamlines and integrates waste management licensing, pollution prevention and control, water discharge consenting, groundwater authorisations, and radioactive substances regulation. Schedule 22, paragraph 6 of EPR 2010 states: ‘the regulator must, in exercising its relevant functions, take all necessary measures - (a) to prevent the input of any hazardous substance to groundwater; and (b) to limit the input of non-hazardous pollutants to groundwater so as to ensure that such inputs do not cause pollution of groundwater.’
Water Resources Act (WRA)
The Water Resources Act 1991 (Amendment) (England and Wales) Regulations 2009 updated the Water Resources Act 1991, which introduced the offence of causing or knowingly permitting pollution of controlled waters. The Act provides the Environment Agency with powers to implement remediation necessary to protect controlled waters and recover all reasonable costs of doing so.
Priority Substances Directive (PSD)
The Priority Substances Directive 2008/105/EC is a ‘Daughter’ Directive of the WFD, which sets out a priority list of substances posing a threat to or via the aquatic environment. The PSD establishes environmental quality standards for priority substances, which have been set at concentrations that are safe for the aquatic environment and for human health. In addition, there is a further aim of reducing (or eliminating) pollution of surface water (rivers, lakes, estuaries and coastal waters) by pollutants on the list. The WFD requires that countries establish a list of dangerous substances that are being discharged and EQS for them. In England and Wales, this list is provided in the River Basin Districts Typology, Standards and Groundwater threshold values (Water Framework Directive) (England and Wales) Directions 2010. In order to achieve the objectives of the WFD, classification schemes are used to describe where the water environment is of good quality and where it may require improvement.
Planning Policy
Contaminated land is often dealt with through planning because of land redevelopment. This approach was documented in Planning Policy Statement: Planning and Pollution Control PPS23, which states that it remains the responsibility of the landowner and developer to identify land affected by contamination and carry out sufficient remediation to render the land suitable for use. PPS23 was withdrawn early in 2012 and has been replaced by much reduced guidance within the National Planning Policy Framework (NPPF).
The new framework has only limited guidance on contaminated land, as follows:
• “planning policies and decisions should also ensure that:
o the site is suitable for its new use taking account of ground conditions and land instability, including from natural hazards or former activities such as mining,
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
pollution arising from previous uses and any proposals for mitigation including land remediation or impacts on the natural environment arising from that remediation;
o after remediation, as a minimum, land should not be capable of being determined as contaminated land under Part IIA of the Environmental Protection Act 1990; and
o adequate site investigation information, prepared by a competent person, is presented”.
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
APPENDIX C SITE PHOTOGRAPHS AND WALKOVER CHECKLIST
PHOTOGRAPHIC LOG
Photo no. Date:
12/01/2017 1
Direction photo taken:
Hooks Marsh Car Park
Description:
BH01
Photo No. Date:
2 16/01/2017
Direction photo taken: Field next to Cornmill Stream
Description: BH02
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Photo No. Date:
3 11/01/2017
Direction Photo Taken: Field next to Cornmill Stream
Description: BH03
PHOTOGRAPHIC LOG
Photo no. Date:
25/01/2020 4
Direction photo taken:
Hooks Marsh Car Park and riverbank
Description:
As above
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
Photo No. Date:
5 25/02/2020
Direction photo taken: Field next to Cornmill Stream
Description: BH03
Photo No. Date:
6 25/02/2020
Direction Photo Taken: Field next to Cornmill Stream
Description: BH02
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00)
APPENDIX D BGS BOREHOLE RECORDS
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00) Page 1 | Borehole TL30SE307 | Borehole Logs Page 1 of 2
BGS ID: 13967076 : BGS Reference: TL30SE307 British National Grid (27700) : 537715,202642 Report an issue with this borehole
<< < Prev Page 1 of 1 Next > >>
http://scans.bgs.ac.uk/sobi_scans/boreholes/13967076/images/18703520.html 24/02/2017 Page 1 | Borehole TL30SE307 | Borehole Logs Page 2 of 2
http://scans.bgs.ac.uk/sobi_scans/boreholes/13967076/images/18703520.html 24/02/2017 Page 1 | Borehole TL30SE306 | Borehole Logs Page 1 of 2
BGS ID: 13967075 : BGS Reference: TL30SE306 British National Grid (27700) : 537715,202642 Report an issue with this borehole
<< < Prev Page 1 of 1 Next > >>
http://scans.bgs.ac.uk/sobi_scans/boreholes/13967075/images/18703531.html 24/02/2017 Page 1 | Borehole TL30SE306 | Borehole Logs Page 2 of 2
http://scans.bgs.ac.uk/sobi_scans/boreholes/13967075/images/18703531.html 24/02/2017 Page 1 | Borehole TL30SE217 | Borehole Logs Page 1 of 2
BGS ID: 537340 : BGS Reference: TL30SE217 British National Grid (27700) : 537710,202552 Report an issue with this borehole
<< < Prev Page 1 of 1 Next > >>
http://scans.bgs.ac.uk/sobi_scans/boreholes/537340/images/12142001.html 24/02/2017 Page 1 | Borehole TL30SE217 | Borehole Logs Page 2 of 2
http://scans.bgs.ac.uk/sobi_scans/boreholes/537340/images/12142001.html 24/02/2017
APPENDIX E ENVIRONMENTAL DATABASE REPORT
British Pipeline Agency Geo-environmental site assessment: Land off Fishers Green Lane, Cheshunt, EN9 2ED Project no: 1921133 R01 (00) Historical Mapping Legends
Ordnance Survey County Series 1:10,560 Ordnance Survey Plan 1:10,000 1:10,000 Raster Mapping
Historical Mapping & Photography included:
Mapping Type Scale Date Pg Middlesex 1:10,560 1868 2 Essex 1:10,560 1881 3 Middlesex 1:10,560 1882 4 Middlesex 1:10,560 1897 - 1899 5 Essex 1:10,560 1897 - 1899 6 Hertfordshire 1:10,560 1899 7 Hertfordshire 1:10,560 1920 - 1921 8 Essex 1:10,560 1920 - 1923 9 Essex 1:10,560 1923 10 Essex 1:10,560 1923 11 Hertfordshire 1:10,560 1935 12 Essex 1:10,560 1935 13 Hertfordshire 1:10,560 1938 14 Essex 1:10,560 1938 15 Historical Aerial Photography 1:10,560 1947 16 Ordnance Survey Plan 1:10,000 1960 17 Ordnance Survey Plan 1:10,000 1962 18 Ordnance Survey Plan 1:10,000 1975 19 Ordnance Survey Plan 1:10,000 1987 20 10K Raster Mapping 1:10,000 1999 21 10K Raster Mapping 1:10,000 2006 22 VectorMap Local 1:10,000 2016 23
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 1 of 23 Middlesex Published 1868 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 2 of 23 Essex Published 1881 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 3 of 23 Middlesex Published 1882 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 4 of 23 Middlesex Published 1897 - 1899 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 5 of 23 Essex Published 1897 - 1899 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 6 of 23 Hertfordshire Published 1899 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 7 of 23 Hertfordshire Published 1920 - 1921 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 8 of 23 Essex Published 1920 - 1923 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 9 of 23 Essex Published 1923 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 10 of 23 Essex Published 1923 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 11 of 23 Hertfordshire Published 1935 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 12 of 23 Essex Published 1935 Source map scale - 1:10,560 The historical maps shown were reproduced from maps predominantly held at the scale adopted for England, Wales and Scotland in the 1840`s. In 1854 the 1:2,500 scale was adopted for mapping urban areas; these maps were used to update the 1:10,560 maps. The published date given therefore is often some years later than the surveyed date. Before 1938, all OS maps were based on the Cassini Projection, with independent surveys of a single county or group of counties, giving rise to significant inaccuracies in outlying areas. In the late 1940`s, a Provisional Edition was produced, which updated the 1:10,560 mapping from a number of sources. The maps appear unfinished - with all military camps and other strategic sites removed. These maps were initially overprinted with the National Grid. In 1970, the first 1:10,000 maps were produced using the Transverse Mercator Projection. The revision process continued until recently, with new editions appearing every 10 years or so for urban areas.
Map Name(s) and Date(s)
Historical Map - Slice A
Order Details Order Number: 103889342_1_1 Customer Ref: 28841 National Grid Reference: 537660, 202610 Slice: A Site Area (Ha): 5.27 Search Buffer (m): 1000 Site Details Site at 537910, 202660
Tel: 0844 844 9952 Fax: 0844 844 9951 Web: www.envirocheck.co.uk
A Landmark Information Group Service v50.0 08-Nov-2016 Page 13 of 23