Environment Glamorgan Power Co Ltd October 2014
Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales Hydrogeological and Contaminated Land Assessment Interpretative Report
Amended by: …………………………………………… . Checked by: ...... Philip Smart Murtala Bashir Technical Director (Hydrogeology) Principal Hydrogeologist
Approved by: …………………………………………… . Claire Parkinson Regional Director
Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales Hydrogeological and Contaminated Land Assessment - Interpretative Report
Rev No Comments Checked Approved Date by by 0 Final – Updated for inclusion in revised ES 22 April 2009 1 Modified final to support amended scheme mb clp 9 October 2014
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Job No 60327633 Reference 03 – Final Date Created August 2014
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Table of Contents
1 Introduction ...... 4 1.1 Instruction ...... 4 1.2 Project Objectives ...... 4 1.3 Sources ...... 4 1.4 Limitations ...... 5 2 Site Location and Background Information ...... 8 2.1 Site Location and Description ...... 8 2.2 Environment Agency Conditions ...... 8 2.3 History of the Site ...... 9 2.4 Proposed Site Works ...... 10 3 Environmental Setting ...... 12 3.1 Topography and Hydrology ...... 12 3.2 Geology ...... 12 3.3 Mining ...... 14 3.4 Hydrogeology ...... 17 3.5 Hydrology ...... 18 4 Ground Investigation Works ...... 23 4.1 Methodology ...... 23 4.2 Boreholes ...... 23 4.3 Trial Pits ...... 23 4.4 Sampling ...... 24 4.5 Groundwater Instrumentation ...... 24 5 An Interpretation of the Results of the Ground Investigation – Geology ...... 27 5.1 Geology ...... 27 5.2 Borehole BH1 ...... 27 5.3 Borehole BH2 ...... 28 5.4 Borehole BH3 ...... 28 5.5 Borehole BH4 ...... 28 5.6 Borehole BH5 ...... 29 6 6 An Interpretation of the results of the ground investigation - Hydrogeology ...... 31 6.1 Introduction ...... 31 6.2 Groundwater levels ...... 31 6.3 Summary ...... 33 6.5 Groundwater Quality ...... 35 6.6 Surface Water ...... 37 7 An Interpretation of the Results of the Ground Investigation – Ground Contamination ...... 40 7.1 Introduction ...... 40 7.2 Data Assessment...... 41 7.3 Leachate Test ...... 44 7.4 Statistical Analysis ...... 46 7.5 Summary ...... 47 8 Conceptual Site Model ...... 50 8.1 Introduction ...... 50 8.2 Conceptual Model of Hydrology and Hydrogeology ...... 50 8.3 Conceptual Model for Contaminated Land ...... 51 9 An Assessment of the Impact of the Proposed Scheme on Controlled Waters ...... 54 9.1 Hydrology and Hydrogeology ...... 54 9.2 Proposed drainage strategy ...... 57
9.3 Water treatment areas ...... 58 9.4 Drainage-related site activities ...... 59 9.5 Licensing ...... 60 9.6 Monitoring ...... 60 10 An Assessment of the Impact of the Proposed Scheme on Human Health ...... 62 10.1 Contaminated Ground ...... 62 10.2 Mitigation ...... 62 11 Conclusions and Recommendations ...... 67 11.1 Summary ...... 67 11.2 Conclusions ...... 67 11.3 Recommendations ...... 68
List of Figures
Figure 2.1 Plan showing site location Figure 2.2 Plan showing the site location Figure 3.1 Plan showing the approximate locations of shafts and adits Figure 4.1 Plan showing locations of exploratory holes and lines of section Figure 5.1 Geological cross-section through the proposed coal extraction area (north-south) Figure 5.2 Geological cross-section through the proposed coal extraction area (north west-south east) Figure 6.1 Groundwater hydrograph for borehole BH1 Figure 6.2 Groundwater hydrograph for piezometer BH2a Figure 6.3 Groundwater hydrograph for piezometer BH2a October and November 2005 Figure 6.4 Groundwater hydrograph for piezometer BH2b Figure 6.5 Groundwater hydrograph for piezometer BH4a Figure 6.6 Groundwater hydrograph for piezometer BH4b Figure 6.7 Groundwater hydrograph for borehole Bh5 Figure 6.8 Groundwater hydrographs for piezometer BH2a, Bh4a and BH5 equipped with data loggers Figure 6.9 Plan showing the groundwater contours for the Upper Sandstone (July 2006) Figure 6.10 Plan showing the groundwater contours for the Gellideg Rock (July 2006) Figure 6.11 Plan showing the water quality monitoring points Figure 7.1 Plan showing soil contamination Figure 8.1 Schematic Hydrogeological conceptual site model of the proposed extraction area Figure 9.1 Plan showing the extent of the workings where groundwater ingress is anticipated Figure 9.2 Plan showing the proposed monitoring scheme
List of Tables
Table 3.1: Regional Geology Table 4.1 Laboratory Testing Suites Table 4.2: Details of Piezometers Table 6.1 Groundwater monitoring installations Table 6.2: Groundwater levels Table 6.3 Water quality analytical suite Table 6.4 Groundwater quality 2006 Table 6.5 Surface water quality Table 7.1: Summary of the Laboratory Analysis of the Soil Samples Table 7.2: Summary of leach test results Table 7.3 Summary results of the statistical analysis Table 9.1 Catchment areas of new Water Treatment Areas. Table 10.1 Impact Assessment and Proposed Mitigation Measures
Appendices
Appendix A - Copies of EA/NRW correspondence dated 18 November 2009 and 8 July 2014 Appendix B - Plan showing the restoration proposals Appendix C - Plans showing the extent of former underground coal workings Appendix D - Borehole logs 1979 Appendix E - Rainfall and evaporation data Appendix F - Ground Investigation Appendix G - Geophysical Report Appendix H - Laboratory data sheets for the water quality analyses Appendix I - Laboratory data sheets for soil samples Appendix J - Statistical analysis of soil laboratory testing results Appendix K - Proposed environmental monitoring scheme
Introduction
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 4
1 Introduction
1.1 Instruction AECOM Limited (AECOM) is instructed by Harmers on behalf of Glamorgan Power Co Ltd, to provide an interpretative report in respect of hydrogeological and contaminated land issues associated with the proposed Varteg Hill Reclamation and Coal Recovery Scheme site, near Blaenavon. The report will support the Environmental Statement which will accompany the revised planning application for land reclamation and coal recovery at Varteg. A report on the hydrogeological and contaminated land elements of the proposed scheme initially was prepared in September 2006 by Faber Maunsell Limited (now AECOM) in support of the original Environmental Impact Assessment for the proposed development. Following the implementation of Minerals Technical Advice Note 2: Coal in 2009 and concerns raised by the Council leading up and a planning inquiry held in February 2012, it was necessary to reduce the proposed coal extraction area from 14ha to 11.6 ha. Subject to the implementation of appropriate conditions, the Planning Inspector recommended that planning permission should be granted. This was supported by the first Welsh Minister’s Decision letter dated 4th February 2013 who was minded to grant permission subject to revisions to the Section 106 Agreement. However, this decision was over-ruled by the second Welsh Minister’s Decision Letter dated 22 November 2013, principally in respect of the lack of consideration of alternatives for carrying out the land reclamation other than the extraction of coal and the adequacy of the Unilateral Undertaking in respect of the Restoration Bond.
Whilst the outcome of the Public Inquiry had no significant implications in respect of hydrogeological and contaminated land aspects of the scheme, the initial report on the contaminated land and hydrogeological conditions has been reviewed and updated to address new guidance and documents issued since 2006. The report also addresses the points raised by Natural Resources Wales (NRW) in the response to the request for an amended scoping opinion dated 8 July 2014.
1.2 Project Objectives The principal project objectives have been identified and are listed below:-
Review published and unpublished sources of information and data pertaining to the site, including historical Ordnance Survey maps;
Construct a conceptual model of the site and its environs focussed particularly on hydrogeology and contaminated land;
Present the ground investigation works, interpret and evaluate the geochemical testing of soil samples, surface water and groundwater monitoring results in order to clarify the groundwater and contaminated land conceptual models;
Undertake qualitative and quantitative risk assessments of the potential impacts of the development on controlled waters and on human health; and;
Provide proposals for water management and pollution control.
1.3 Sources The following sources of information have been consulted in the preparation of this report:-
Viponds Top and Washery Spoil Heaps: Report on the investigation into security of Tips 527 and 528. Sir William Halcrow & Partners, October 1979;
Viponds Top and Washery Tips No. 527 and 528: Report No. 2 on disused colliery spoil heaps. IMCL. Reference 527/32/3, May 1994;
Landmark Envirocheck Report reference EC11507571, June 2005;
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 5
British Geological Survey (BGS) 1:50,000 sheet 232, Abergavenny and 1:10,560 scale map SO20NE; A reserves assessment on land at Varteg, Abersychan, near Pontypool. Blandford Consulting. Reference BC/MC/05.02.02, 2002;
Cementation Co Ltd, Brace’s pit drillers’ logs, 1996, copy held at Blandford Consulting archives; NCB Opencast Executive, Eastern Area Office, Brace’s Pit borehole schedules, copy held at Blandford Consulting archives;
NCB Opencast Executive South West Region No. 7. Prospecting Site Area: Brace’s Pit, Site No. 070842, Scale 1:2500, Drawing No. 07D455. Annotated plan showing constraints and prospecting borehole locations. 29 September 1964;
NCB Opencast Executive South West Region No. 7. Prospecting Site Area: Aqueduct, Site No. 070852, Scale 1:2500. Annotated plan showing limits of previous opencast workings in the vicinity of the Varteg Hill Reclamation and Coal Recovery Scheme site. Undated;
Anon. Varteg WA/8/96. Cross-sections 1-1, 2-2 and 3-3 and vertical section, 1:500. Undated; Report on Geophysical Logging at Varteg Hill R&CR Scheme. European Geophysical Services, August 2005;
Varteg Hill Reclamation & Coal Recovery Scheme: Water Features Survey, Faber Maunsell Limited, March 2004; Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales: Phase I – Desk Study, Faber Maunsell Limited, September 2005.
Rainfall and evapotranspiration data for the area provided by the Meteorological Office; Groundwater level monitoring information for the period August 2005 and September 2006; The results of groundwater and surface water quality monitoring in February and July 2006; A site walkover in July 2014; and, Correspondence from Torfaen CBC and the Environment Agency/NRW between February 2005 and July 2014.
1.4 Limitations This report has been prepared on behalf of and for the sole use of Harmers and its client Glamorgan Power Co Ltd (the Client). Any third party relies on this report solely at its own risk unless it is the beneficiary of a warranty executed by AECOM Ltd specifically for the purposes of creating a duty to it. The interpretation of the hydrogeological and geological conditions at the site is based on an assessment of published information, ground investigation and laboratory results, and on an extrapolation of point-source information using geological experience. There is a degree of subjectivity in any interpretation. The effects of ground and water borne contamination on the environment are constantly under review and authoritative guidance values are potentially subject to change. The conclusions presented herein are based on the guidance available at the time this report was prepared. No liability can be accepted for the retrospective effects of any changes or amendments to the legislation or guidance. This report addresses the hydrogeological conditions at the site and potential land contamination arising through historical industrial use of the site. The report does not consider ground engineering aspects of the proposed development, including effects of the proposed excavations on the stability of adjacent areas of backfilled spoil.
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 6
The copyright in this document (including its electronic form) shall remain vested in AECOM Ltd but the Client shall have a licence to copy and use the document for the purpose for which it was provided by AECOM. This document shall not be reproduced in whole or in part or relied upon by third parties for any use whatsoever without the express written authority of AECOM.
Site Location and Background Information
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 8
Capabilities on project: Environment
2 Site Location and Background Information
2.1 Site Location and Description The site of the proposed coal recovery and land reclamation scheme occupies land immediately west of the village of Varteg, beside the B4246 Varteg Road, running from Blaenavon in the north to Abersychan in the south. It is centred on approximate National Grid Reference (NGR) SO26150610, as shown on Figure 2-1.
The site comprises two main land holdings joined by a narrow isthmus following the bed of a former mineral railway track, currently used as access to farms to the west (Figure 2-2). The larger eastern land holding (“Main Area”) incorporates the proposed coal extraction site and the site facilities and includes the former drift mine compound, spoil tips and relatively flat-lying poorly – drained grazing land. This part of the site covers an area of approximately 62ha of which the proposed coal extraction site is approximately 11.6ha. The proposed coal extraction area lies within the eastern slopes of Varteg Hill near the head of the Cwm Llwyd catchment, where the watershed runs north-south along the ridge of Varteg Hill and then north west to Coity Mountain. The Afon Llwyd is approximately 130m below the base of the proposed workings and 600m to the east. The river flows southerly from Blaenavon through Abersychan and Pontypool. The catchment falls steeply from 445mAOD in the west on the ridge of Varteg Hill to 365mAOD at the base of the extraction area over a distance of approximately 400m, at an average gradient of 1 in 5. The western land holding (“Second Area”) consists of rough upland grazing comprising restored former opencast workings forming a valley on the south eastern flank of Mynedd Farteg Fach. It is proposed that spoil arising from the coal extraction area is deposited in this area. This area lies within the catchment of the Cwm Ffrwd, which drains the south western slopes of Coity Mountain and flows south easterly to join the Afon Llwyd, approximately 2.2km south of the site. The land separating much of the two holdings consists of opencast backfill from the former Waun Hoskyn Extension opencast site. Two pronounced colliery spoil tips which have merged with tipping, occupy part of the southern half of the eastern land holding (Tips 528A and 528B). A planning application for the development of opencast workings and subsequent restoration firstly was submitted by Glamorgan Power Co Ltd to Torfaen County Borough Council (TCBC) in May 2004. Following statutory consultation, a number of concerns were raised by the Environment Agency with regard to contaminated land and the potential impacts on controlled waters. 2.2 Environment Agency Conditions In their letter of 22 February 2005, the EA detailed four conditions which needed to be addressed as part of any planning permission for the site:- 1. A site investigation must be undertaken that allows for appropriate background monitoring of groundwater levels and quality. This must include an adequate time period to collect baseline data (a minimum of 6 months or as otherwise agreed) prior to commencement of workings at the site. It must be ensured that sufficient monitoring points are in place to assess the extent of any impacts on groundwater should dewatering be required. 2. A robust and appropriately detailed conceptual model must be developed that includes the additional site investigation and monitoring data. It must include consideration of volumes of minewater likely to be intercepted, which will require information regarding the vertical and horizontal extent of workings with respect to the main groundwater bearing strata beneath the site. 3. An assessment of the potential impacts from the development on controlled waters in the vicinity of the site must be submitted to and agreed by the Environment Agency. This must be based on the robust hydrogeological conceptual model previously developed. It must include a quantitative assessment of the potential impacts arising from any physical dewatering on surface and groundwater features present at or close to the site. The assessment of potential impacts must include consideration of the discharge of acid mine drainage on controlled waters. 4. Proposals for mitigating measures to be implemented should any adverse impact be identified on water features must be submitted to and agreed by the Environment Agency.
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 9
Capabilities on project: Environment
Subsequently meetings were held in 2006 and 2007 with both Torfaen CBC and the Environment Agency (EA) to discuss the concerns raised. Following these meetings in March 2007, the EA indicated that subject to the inclusion of appropriate conditions, they had no objections to the proposed coal extraction operations. In their response to a re-consultation, in a letter dated 18 November 2009, the EA confirmed that ‘...planning permission should only be granted to the proposed development as submitted if the following planning conditions are imposed as set out below’. A copy of the EA letter of 18 November 2009 with the proposed planning conditions is provided at Appendix A In the response from NRW of July 2014 to the scoping opinion for the amended scheme, also provided at Appendix A, the following comments were provided:-
Agreement to up-date the previous ES report; Requirement for a Water Features Survey;
Undertake a Hydrogeological Impact Appraisal; Requirement of a Water Management Plan; and, Inclusion of Pollution Prevention Measures. This report sets out the current knowledge of the site and its surroundings, in terms of the geology, hydrogeology, hydrology and ground contamination, to facilitate an assessment of the risks to controlled waters and human health during the operational phases and following restoration. The report addresses the four conditions specified in the EA’s letter of February 2005 and the issues raised in the NRW letter of July 2014. The points raised in the two responses are not mutually exclusive and have been considered in combination.
2.3 History of the Site A review of historical Ordnance Survey (OS) maps for the site has been carried out for the period 1882 to 2002. The following account describes relevant features or changes identified from these maps. The historical Ordnance Survey plans of the site are provided in the Phase 1 desk study report of September 2005.
By 1882, Varteg Hill Colliery and Mine Slope Colliery to the north are shown, working coal and ironstone with numerous spoil heaps all around and several mine buildings present. A tramway connects the colliery to the railway, approximately 750m to the east. Numerous shafts and trial shafts are shown. To the south of the site, Brace’s Pit is shown as disused. Housing is shown to the east along Pembroke Place and Twenty Houses. By 1902, the Varteg Hill Colliery tip is expanding south eastwards from the shaft, north of the current spoil tips. A coal washery is shown immediately west of existing spoil Tip 528, south of Varteg Hill Colliery. Housing is present along Salisbury Terrace. New Slope Colliery is shown approximately 400m north west of Mine Slope Colliery. On the plan dated 1922, a well is marked at approximate NGR SO25950569 between Upper Five Houses and Spring Cottage. By 1938, Mine Slope Colliery, north of the site, is absent from OS maps and is assumed to be disused. Further north, New Slope Colliery is shown as disused. High voltage electricity pylons are shown crossing the site. By 1962, the majority of the Varteg Hill Colliery mine infrastructure no longer is shown, including much reduced mineral track railway. Only the ‘Lighthouse’ and remnant drift mine buildings remain. The spoil heaps occupy the present configuration of Tip 528. A large pond or reservoir is shown immediately north of the former drift mine entrance. On the 1964 revision, Mynedd Farteg Fach is shown largely as opencast workings to the north, south and west of the site. Spoil tipping is shown at an early stage of development at ‘Varteg Waste’ south of Varteg Hill Colliery Tip 528 and around the Spring Cottage well.
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Capabilities on project: Environment
On the 1976 map, only the ‘Lighthouse’ remains on the Varteg Hill Colliery site with remnant mineral railway tracks. The reservoir or pond is not shown. By 1977, the opencasted land in the valley of Mynedd Farteg Fach has been restored to the current topography. The reservoir or pond immediately north of the former Varteg Hill Colliery drift entrance is shown. By 1993, the ‘Lighthouse’ building and the reservoir or pond are no longer present. No significant changes are apparent on the 1999 revision. The 2002 revision, 1:25,000 scale Explorer map shows the ruins of ‘The Light House’ buildings present on the site. No other buildings are shown and extensive areas of spoil tip are indicated. The Spring Cottage well is shown.
In the Viponds Top and Washery Spoil Heaps report by Sir William Halcrow and Partners (1979), it is indicated that Varteg Hill Colliery was opened around 1860 with the sinking of the Varteg Hill Pit shaft. Earlier opencast patch working along the outcrops or subcrops of ironstones and coal seams is believed to have been largely complete by 1820. The NCB Viponds Top and Washery, History of Development Plan, dated 1979, indicates that extensive spoil tips were present both immediately north of, and on the site of, the existing tips by 1879. Some, or all, of the northern tip was removed during the 1950s by Star Brick and Tile Co. The NCB Viponds Top and Washery, Plan of Mining Prior to 1830, shows extensive ironstone workings across the area, indicating mining was well developed in this area by that time.
2.4 Proposed Site Works The re-submitted application proposes to remove colliery spoil Tips 527 and 528 from the main site, placing the spoil in the previously soil-stripped valley of Mynedd Farteg Fach. Soil stripping of the main site also will be carried out, starting at the southern end of the proposed cut and working northwards. The exposed overburden either will be stored in the valley of Mynedd Farteg Fach or used to construct screening bunds between the site and the houses of Salisbury Terrace and Pembroke Place to the east. Coal seams exposed with the removal of overburden will be recovered for transport off site by road. The opencast excavation will progress northwards, with successive backfilling of the void using freshly exposed overburden. Following completion of the coal recovery, the remnant void at the northern end of the excavation will be backfilled with spoil from the screening bunds. Re-instatement of cover will be carried out using soil retained in the stockpiles. The material formerly in spoil Tips 527 and 528, deposited in the valley of Mynedd Farteg Fach, will be restored using soils stored south of the mineral track on the western half of the site. Restoration of the spoil disposal area in the valley of Mynedd Farteg Fach will be completed within Phase 1 of the scheme.
Rainfall incident to the site, in addition to any groundwater or mine water ingress to the opencast workings, will be directed/pumped via purpose-cut channels/ditches to two water treatment areas, one to the south east of the proposed workings and one east of the proposed opencast excavation close to the B4246. Suspended solids will be removed by settlement and any significant chemical contamination will be treated to satisfy the relevant Environmental Permits to discharge. It is proposed that the area of the opencast workings will be restored to a mosaic of acid grassland and wet and dry heath. The area of spoil disposal in the valley of Mynedd Farteg Fach will be restored to a similar vegetation type with steep shale escarpments of exposed colliery spoil to mirror the sensitive ecological areas in the vicinity of the existing colliery spoil tips. The restoration proposals for the site are shown at Appendix B.
Environmental Setting
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Capabilities on project: Environment
3 Environmental Setting
3.1 Topography and Hydrology The coal extraction site lies on the upper western flanks of the Cwm Llwyd, the valley of the southerly flowing Afon Llwyd. The proposed coal extraction area falls from a level of 400mAOD to 410mAOD on the western edge to between approximately 350mAOD and 380mAOD on the eastern boundary. The northern boundary varies between approximately 380mAOD and 400mAOD and the southern boundary between approximately 350mAOD and 400mAOD. The Afon Llwyd is at a level approximately 130m below the base of the proposed site, 600m to the east and flows southwards from Blaenavon through Abersychan and Pontypool to the south. Cwm means river valley in Welsh. The name of the river is Llwyd (which means ‘brown’ and which may be an indirect reference to the former mining in the area and pollution by acid mine drainage, AMD). The land falls eastwards across the main site, draining via numerous ephemeral streams into ditches along the B4246. These feed into two culverts beneath the road. The northern culvert flows down a steep gully to the Afon Llwyd. The southern culvert crosses the B4246 at approximate NGR SO26430570, flowing south eastwards to join the Afon Llwyd. To the immediate west of the main site lies a restored colliery spoil tip comprising part of the former Waun Hoskyn Extension opencast site. Further to the west of the main site lies the valley of Mynedd Farteg Fach, shaped by the restoration of opencast workings associated with the same opencast site. A former mineral railway track bed runs across the mouth of the valley on an embankment providing access to land further west. The valley of Mynedd Farteg Fach drains southwards through a culvert beneath the embankment and across the former Brace’s Pit restored opencast site, toward the confluence with the Cwm Ffrwd. Ffrwd means “sudden torrent” in Welsh, which may provide an insight into the response of this catchment to precipitation. At the time of the site visit in July 2014, there was no flow in the watercourse through the culvert beneath the embankment. The Cwm Ffrwd flows south easterly towards its confluence with the Afon Llwyd, at NGR SO27180392 approximately 2.2km south of the Varteg Hill site, via the Golynos Watercourse, a man-made culvert between approximate NGRs SO25600486 and SO26200430.
3.2 Geology The geology of the site is interpreted from the British Geological Survey (BGS) 1:50,000 scale sheet 232, Abergavenny; the BGS 1:10,560 plan SO20NE; and, from an appraisal of reports prepared by Halcrow (1979), IMCL (1994) and Blandford Consulting (2002). Table 3.1 provides a summary of the regional geology of the area. In brief, the geology of the site comprises strata belonging to the Lower and Middle Coal Measures, Westphalian A and B, dipping gently to the west and south west at an angle of 5o-6o, forming the north eastern margin of the South Wales Coalfield. The stratigraphy of the site with relevance to the proposed opencast operations incorporates cyclotherms extending upward from the Garw seam to the Two Foot Nine seam. The basal seam for excavation is the Lower Seven Feet (Lower Meadow Vein) seam. The base of the proposed excavation falls from north to south from a level of approximately 380mAOD in the north to approximately 340mAOD in the south western corner. The main high wall of the excavation will be along the western and south western boundaries. The sequence of coal seams included within the proposed opencast extraction is (top-down): - Two Feet Nine (Elled) seam - Four Feet (Big) seam - Six Feet (Three-quarter) seam - Upper Nine Feet (Horn) seam - Lower Nine Feet (Bottom Rock) seam - Bute or Bydylog (Dirty) seam - Yard [including Standard Yard & Amman Rider seams] (Upper Meadow vein) seam - Upper Seven Feet (Middle Meadow Vein) seam - Lower Seven Feet (Lower Meadow Vein) seam
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Capabilities on project: Environment
The Coal Measures strata in this area are dominated by mudstone facies with subordinate sandstones, siltstones, seatearths and thin coal seams. Sandstones within the Coal Measures comprise both rare thick lenticular channel sandstones and thin, discontinuous interbedded sandstone dominated units. Table 3.1: Regional Geology
Formation Strata Thickness Lithology (m)
Superficial deposits Boulder clay, head, peat and Variable – largely absent from former coal 2-3 solifluction deposits extraction areas
Coal Measures Upper Coal Measures:- Pennant Measures Hughes Beds Principally sandstone with some thin mudstones Up to 265 and a few coal seams Brithdir Beds
Rhondda Beds Mudstone, siltstone, quartzite and conglomerate. Llynfi Beds Occasional coal seams.
Middle Coal Measures Mainly mudstone and siltstone with quartzitic 300 Lower Coal Measures sandstone, ironstone and coal seams
Millstone Grit 25 Quartzitic sandstone and marine mudstone
Carboniferous Limestone Dowlais Limestone Bioclastic limestone with thin shales Llanelly Formation Dolomitic Limestone Clydach Valley Group 185 Grey mudstone with thin limestone Cwmyniscoy Mudstone Oolitic sandy limestone Castell Goch Limestone
Old Red Sandstone Brownstones 140 Reddish-brown sandstone and thin red mudstone units
Senni Beds 240 Green and buff sandstone with some thick mudstone beds and conglomerates. Purple sandstone at base.
Two significant sandstone members have been identified in the locality. The Gellideg Rock, a lenticular, quartzitic channel sandstone, proved locally between 1.9m and 8.2m in thickness, is known from borehole and mining evidence to occur between the Five Feet/Gellideg seam and the underlying Garw seam. To the north of the site, the Elled Rock, comprising a hard quartzitic sandstone, forms the roof of the Two Feet Nine seam in the Waun Hoskyn opencast coal site (OCCS). However, a cautious interpretation of the stratigraphic sequence from borehole data in the vicinity of the site suggests that the Two Feet Nine seam locally has a mudstone roof and that the Elled Rock is not present at the Varteg site.
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Capabilities on project: Environment
The BGS 1:10,560 sheet SO 20 NE indicates the presence of further localised sandstone units within the sequence above the Five Feet/Gellideg coal seam and a more persistent sandstone unit forming the floor of the Garw seam. To the east of the site, on the steep western side of the Llwyd valley, the Coal Measures overlie a thin outcrop of Namurian Millstone Grit strata, which rest unconformably on the Visean, Carboniferous Limestone Group, comprising the Llanelly Formation, the Gilwen Oolite and the Clydach Valley Group strata, here dominated by the Castell Coch Limestone. The Llanelly Formation comprises an oolitic sandy limestone and crops out in the base of the Afon Llwyd valley. The ground has experienced significant disturbance throughout a long history of mining and it is likely that superficial deposits either have been removed or disturbed across much of the site. Historical plans indicate that spoil disposal occurred across much of the site during the period of working from the Varteg Hill and Mine Slope Collieries. However, the presence of numerous shafts and adits on old plans indicates that significant mining already had been attempted across the site prior to the development of Varteg Hill Colliery (Figure 3-1). Variable thicknesses of mine spoil from these workings are likely to be distributed widely across the proposed opencast site. Where not disturbed by shallow working, the superficial deposits are reported by Sir William Halcrow & Partners to comprise a 2- 3m thick layer of head and in-situ weathered rock with some slope wash and local patches of peat. The head comprises a light to dark grey occasionally orange, soft to stiff clayey or sandy silt with sandstone and siltstone gravel, cobbles and boulders. The sandstone boulders are in places weathered entirely to loose coarse grained sand. A thin coal-rich layer often occurs at the base of the superficial deposits.
3.3 Mining The area has experienced a long history of mining predating the OS maps and the keeping of records. Records are available which show that coal extraction was taking place at least before 1820. Evidence for earlier working of coal and ironstone from the outcrop is provided by numerous adits marked on plans prepared of the site for the tip reports by Sir William Halcrow and Partners of 1979 and IMCL of 1994. It is likely that unrecorded entrances, either collapsed or buried, exist along the outcrop of many of the seams present across the site. Figure 3-2 shows the approximate locations of shafts and adits on the site, based on the Halcrow and IMCL reports. Three colliery spoil tips are present on the site, within the area to be excavated - Tip 527 to the north of the former Varteg Hill Colliery and Tips 528a and 528b further south respectively. Tip 528a is understood to comprise ‘run-of-mine’ spoil, whilst Tip 528b in the south of the proposed opencast area is reported to comprise washery discard and to be partially burnt. Burning of colliery spoil commonly results in the creation of indurated red shale, but also friable red ash, dependant on the initial composition of the tip and contributory factors in terms of carbon, clay and sulphur contents. Colliery spoil also is understood to be present as a thin layer across much of the valley beneath Mynedd Farteg Fach and in the hummocky terrain to the east of Tip 528. The spoil within Mynedd Farteg Fach is understood to be derived from the former Waun Hoskyn opencast sites (OCCSs). The spoil to the east of the site is believed to be derived from coal and particularly ironstone patch workings along the outcrop and possibly later accessed from the numerous adits recorded within the project area. Recorded old workings are reported from historical mining records in most of the seams of interest to the opencast project including the following: - Four Feet seam - Six Feet seam - Lower Nine Feet seam - Yard / Standard Yard seam - (Upper/Lower) Seven Feet seam - Five Feet / Gellideg seam (not included in extraction scheme)
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However, there are no records of significant former workings present beneath the proposed coal extraction area. Evidence exists of unrecorded old workings in the majority of seams incorporated within the opencast proposal. The evidence is in the form of notes on historical mine plans, where recorded mine workings have intersected older workings. Unrecorded old workings are understood to be present in the following seams in the vicinity of the project:
- Two Feet Nine seam - Four Feet seam - Six Feet seam - Standard Yard seam - Seven Feet seam - Five Feet / Gellideg seam (not included in extraction scheme) - Garw seam and ironstone beds (not included in extraction scheme)
There are records of a number of collieries in the area. Shafts associated with Varteg Hill Colliery, referred to as Mine Pit in the Blandford Consulting report are present on the eastern edge of the proposed coal extraction area. An adit associated with Mine Slope is located immediately to the north of the proposed coal extraction area. Cwm Glo Mine adit is located in the northern part of the coal extraction area. There are a number of access adits running north westerly beneath the site, principally but not exclusively in the lower target seams. These adits provided access to and drainage from former workings located immediately west of the site (Figure 3.1).
The last recorded deep workings in the area were in the Five Feet/Gellideg and Yard seams in the early 1930s. However, there is a record of workings in the Seven Feet seam from Cwm Glo Mine in the 1980s. Plans showing the recorded extent of former workings in these seams are provided in Appendix C, taken from the Blandford Consulting report BC/MC/05.02.02 of 2002. 3.3.1 Two Feet Nine (Elled) seam The outcrop of the Elled seam crosses the south western corner of the proposed coal extraction area. There are records that the seam has been worked to the north west of the site from Mine Slope Colliery. There is no recorded evidence that the Elled seam has been worked beneath the proposed opencast extraction area. 3.3.2 Four Feet (Big) seam The outcrop of the Big seam also crosses the south western corner of the proposed coal extraction area. There are records of underground workings in the Big seam immediately west of the south western corner of the site and also to the north west of the site. Access to the workings west of the site was from an adit to the south of the site. There are records that the Big seam has been worked from both Mine Pit and Mine Slope Colliery and an adit is shown running north westerly beneath the site, from the south eastern corner, known as Stable House Watercourse. The adit connects with Mine Pit and also Mine Slope Colliery and may have provided drainage for the underground workings. There is no recorded evidence that the Big seam has been worked beneath the proposed opencast extraction area. 3.3.3 Six Feet (Three-quarter) seam The outcrop of the Three-quarter seam cuts across the south western corner of the proposed coal extraction area. The detailed stratigraphy of the seam is complex and varies significantly across the area. In borehole V1/3, the seam is represented by two leaves of coal, a lower 1.5m seam and an upper 2.8m seam, separated by a 0.5m band of seatearth. There are records of extensive underground workings in the Three-quarter seam within 100m to the west of the area with access from both New Slope and Mine Slope collieries to the north of the site and from other collieries to the south west. There is no recorded evidence that the Three-quarter seam has been worked beneath the proposed opencast extraction area. 3.3.4 Upper Nine Feet (Horn) seam The outcrop of the Horn seam runs north-south and then south westerly across the south western part of the proposed coal extraction area. The Horn seam consists typically of a band 1m thick.
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The records show that in the area, the seam only has been worked from Mine Slope Colliery to the north west of the site. There is no recorded evidence that the Horn seam has been worked beneath the proposed opencast extraction area. 3.3.5 Lower Nine Feet (Bottom Rock) seam The outcrop of the Bottom Rock seam runs across the south western part of the proposed coal extraction area. The seam is in the order of 0.7m thick. There are records that the seam has been worked beneath the south western corner of the site, possibly from the Droydeg No. 2 level to the south. The seam has been worked to the west of the site from Mine Slope Colliery and New Slope Colliery and also from drift workings accessed from the south. The Stable House Watercourse adit, which runs north westerly beneath the site, is connected to the Bottom Rock workings through Mine Pit and Mine Slope Colliery. 3.3.6 Bute (Dirty) seam The outcrop of the Dirty seam runs roughly north-south across the centre of the proposed coal extraction area. In the Hoskins opencast workings the seam was approximately 1.5m thick. Within the site a more complex sequence is present with up to four leaves of coal giving a total thickness of coal of 3.5m. The full structure and thickness of the seam was proved in borehole V1/1 at a depth of 18.6m to 23.2m. There is evidence of minor workings of the Dirty seam to the north west of the site from Mine Slope Colliery. There is no recorded evidence that the Dirty seam has been worked beneath the proposed opencast extraction area. 3.3.7 Yard (Upper Meadow Vein) seam The outcrop of the Upper Meadow Vein seam runs roughly north-south across the eastern part of the proposed coal extraction area. Often the seam is included as part of the underlying Seven Feet seam. Where the seam has been identified as a discrete seam, it is in the order of 0.8m thick. There are records of extensive underground workings in the seam immediately to the west of the site from Mine Slope Colliery and also from drift workings to the south. The Stable House Watercourse adit, which runs north westerly beneath the site, is connected to the Upper Meadow Vein seam workings through Mine Pit and the Mine Slope Colliery workings. 3.3.8 Seven Feet (Meadow Vein) seam The outcrop of the Meadow Vein seam runs in a gentle arc north-south across the eastern part of the proposed coal extraction area. South of the proposed coal extraction area, a single seam is present approximately 2.7m thick. Within the site, up to three leaves have been identified. The workings from Cwm Glo Mine proved two seams 1.06m and 0.84m thick. The Meadow Vein seam is the basal coal seam which will be worked in the proposed coal extraction scheme. Extensive workings in this seam are recorded to the west of the site. There is a suggestion, but no detailed records that the seam was worked beneath the northern part of the proposed extraction area from two adits associated with Cwm Glo Mine, located within the site. There also is a record that opencast workings of the Meadow Vein seam extend into the extreme northern part of the proposed extraction area. Three adits, including the Stable House Watercourse are shown crossing beneath the site, connected to workings in this seam. 3.3.9 Five Feet/Gellideg (Old Coal) seam The outcrop of the Old Coal seam forms the eastern boundary of the proposed coal extraction area. Workings north of the proposed coal extraction area proved a single seam approximately 1m thick. Within the site, the seam is represented by two partings each approximately 0.6m thick. There are records of workings in the seam below the western central and south western parts of the site, with more extensive workings to the west, associated mainly with Mine Slope Colliery and also from Varteg Hill Colliery. A number of adits running north westerly cross beneath the site providing access to the Old Coal seam. There is recorded evidence that the area was worked, prior to the extraction of coal, for ironstone. Details of the ironstone workings are poor. However, it is understood that the Jack and Balls and the Bottom Vein Ironstone veins, which crop out below
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the Five Feet/Gellideg seam on the lower ground to the east of the proposed coal extraction area, both were worked in the area. It is understood that the Stable House Watercourse located immediately to the south east of the extraction area is the adit which drained the ironstone workings in the area. The Stable House Watercourse is associated with the Bottom Vein Ironstone.
3.4 Hydrogeology It is likely that the sandstone units within the Coal Measures sequence have a low intergranular permeability due to the indurated nature of the units, but a moderate secondary permeability imparted by the presence of fissures and fractures, which facilitate rapid groundwater movement. It is likely that the mudstone units have a low intergranular and secondary permeability, restricting the flow of groundwater and supporting perched water tables in the overlying sandstone units. Under natural conditions it is considered that the sandstone bands within the Coal Measures provide the main pathways for groundwater flow and act as a series of discrete thin aquifers. It is likely that under these conditions groundwater would flow in a south westerly direction, consistent with the dip of the strata. However, as a result of historical mine working, it is likely that the integrity of the strata between the sandstone units has been disrupted, creating additional groundwater flow pathways within the sequence, partially controlled by the presence of goaf and former underground roadways. The Coal Measures and the Millstone Grit are classified as a Secondary A aquifer in the Environment Agency’s Groundwater Protection - Policy and Practice and confirmed in Groundwater Vulnerability Map number 36, Gwent, South & Mid Glamorgan. The ground immediately beneath the site is shown as a secondary (minor) aquifer with an unclassified soil risk, resulting from the presence on the site of made ground arising from the former mining activities in the area. The Castell Coch Limestone and other units of the Carboniferous Limestone cropping out between the Castell Coch Limestone and the Coal Measures are classified as a principal aquifer of regional significance with regard to water supplies. The ground to the east of the site forming the lower valley side of the Afon Llwyd comprises the Carboniferous Limestone overlain by thin granular soils and is shown as having a high groundwater vulnerability due to the limited capacity of these soils to adsorb contaminants. The Carboniferous Limestone outcrop and the outcrop of the overlying strata within the limestone catchment, which includes the majority of the application area is designated by NRW as Source Protection Zone (SPZ) 1. The SPZ 1 area has been designated to protect the Northern Limestone Outcrop Springs. The nearest licensed groundwater abstraction is 5km to the north east, within sandstones and conglomerates of the Devonian Senni Beds, beyond the zone of influence of activities at the proposed opencast site. A water features survey of the proposed Varteg Hill OCCS was undertaken in February 2004. The survey located a rectangular brick-built structure at or near the location of a former water well, shown on historical maps from 1922, north east of Spring Cottage at NGR SO25950567 (survey reference 125, catchment N). It is likely that the structure is a catch-pit constructed to intercept the spring flow for abstraction. All domestic properties visited during the survey were noted to be connected to the mains water supply network, including Spring Cottage. Discussions with local residents confirmed that mains water had been installed throughout the area. Under the terms of the Water Supply (Water Quality) Regulations 1991, the local authority has a statutory duty to inspect and test annually for wholesomeness, all recorded private water supplies within its jurisdiction. Torfaen CBC Environmental Health Officer confirmed that no private water supplies are recorded in the area. A lenticular well jointed quartzitic sandstone may be developed within the intra-seam measures of the Five Feet/Gellideg (Old Coal) seam and the bottom leaf of the Seven Feet (Lower Meadow) seam which may form the floor of the proposed extraction area. Cored borehole VI/3 drilled by Sir William Halcrow and Partners proved 1.9m of sandstone, 6.3m beneath the Lower Seven Feet seam. Plans contained in the IMCL report illustrate the location of two sandstone outcrops, between the conjectured outcrops of the Old Coal and Meadow Vein seams, both associated with springs. The inferred sandstone bands above the Five Feet/Gellideg seam were not proved in any of the boreholes drilled in 2005. The Halcrow report interprets the spring issues as
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groundwater from small surface catchments further north or groundwater within the superficial deposits which locally enters the sandstone uphill of its outcrop. It is likely that groundwater in the sandstone units is confined immediately beneath the proposed opencast site, with a piezometric head above the surface of the sandstone band and hence possibly above the projected floor of the excavation. Subject to the level of the water table/piezometric level, discharges may arise to the east of the site. Surface water draining from the site may permeate into the sandstone subcrop and ingress as groundwater to the excavation may occur. In addition to the groundwater monitoring programme instigated as part of the ground investigations in August 2005, groundwater level data is presented in the 1979 Halcrow report. Whilst it is accepted that data are historical, they are indicative of the presence or absence of significant groundwater within the strata breached by the respective piezometer response zones. Piezometers VI/1a, VI/3a and VI/3b were installed in measures closely associated with the Bute/Yard seams, the Bute/Yard/Amman Rider seams and the Upper/Lower Nine Feet seams respectively. The remaining piezometers (VI/1b and VI/2a/b) were installed at the tip/superficials interface. Piezometers VI/1a, VI/3a and VI/3b only recorded small heads consistent either with nuisance water from condensation; seepage from low permeability horizons; or, with piezometric heads controlled by drainage to nearby former coal workings, connected by permeable collapsed ground. None of the piezometers’ response zones include the main sandstone horizons proved in the respective boreholes. The logs of the boreholes drilled in 1979 are provided at Appendix D.
Numerous ephemeral springs and sinks have been identified to the immediate east of the colliery spoil tips on the site and on the lower ground immediately below the eastern edge of the proposed coal extraction area. It is likely that these are related to variations in the thickness of older colliery spoil deposits and the variably thin superficial deposits in these areas and to outcrops of sandstone bands present below the Five Feet/Gellideg seam. However, some may be related to intermittent water discharges from former adits, both recorded and unrecorded, intact or collapsed, accessing the coal and ironstone workings present beneath the site. Several springs and seepages have been identified immediately to the south east of the proposed coal extraction area above the Stable House Watercourse adit. The flow of the largest of the springs is assessed visually during groundwater monitoring visits. Plate 3.1 shows the spring in June 2006 with only a negligible flow. Plate 3.2 shows the condition of the Stable House Watercourse adit in 2006. During a site visit in July 2014, all of the ditches and watercourses on and surrounding the application area were dry. Small pools of water were observed at the spring close to borehole BH4 but there was no visible flow from the spring. The Afon Llwyd to the east flows on a thin bed of alluvium, the floor of which rests on the Castell Coch Formation of the Carboniferous Limestone. It is considered likely that the limestone is in hydraulic continuity with the river and that the limestone provides groundwater discharge to the river.
3.5 Hydrology The existing topography of the proposed coal workings and the surrounding area dictates that surface water run-off generally flows from west to east. The B4246 Varteg Road runs north-south through Varteg village and forms a barrier to overland drainage from the site to the Afon Llwyd valley. Information from Torfaen County Borough Council (CBC) and on-site observations shows that there are culverts crossing Varteg Road at strategic locations. The culverts vary greatly in size, capacity and condition. A road ditch collects surface water runoff from the north of the site and conveys the drainage via a 1200mm diameter culvert under Varteg Road to an ephemeral watercourse that flows easterly along the old tramway route to the Afon Llwyd cascading downstream into the valley. Torfaen CBC indicate that there are scour and surcharge problems along this steep drainage route and that any drainage proposals should not exacerbate these problems. A number of ephemeral springs rise from the colliery spoil heaps within the southern part of the coal extraction area. These support transitory watercourses flowing generally easterly towards sinks set within older low-lying hummocky spoil to the east
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and south east of the site and form localised marsh/mire areas. Denser vegetation and more evidence of wildlife are found in these areas. The small ponds formed within the hummocky spoil and former excavations create local habitats around the south eastern edge of the site. There are no positive outfalls from the ponds and flows dissipate to sinks or are collected in ditches adjacent to Varteg Road. The side ditches along the western upstream side of the road were heavily vegetated at the time of the site visit in July 2014, following an extended period of dry weather. It is considered that surface water run-off is attenuated by these ditches with low flows discharging to sinks and a tank downstream of the road through small bore culverts under Varteg Road. Anecdotal evidence identifies that the highway ditches surcharge during intense storm periods. Records held by Torfaen CBC confirm this evidence and indicate that the receiving tank on the eastern side of Varteg Road drains to a 15 inch diameter culvert running southerly through Rockvilla Close and discharges to a watercourse to the south of Balance Road at NGR SO 26090513, which forms a tributary of the Nant Ffrwd. The existing spoil tips 527, 528A and 528B are located in the southern part of the proposed coal extraction area. Surface water runoff from the slopes on Varteg Hill above the tips filters through the spoil tips. Visual inspections have identified small areas of ochrous deposits in the eroded gullies within and below the spoil tips. Disturbance of the spoil could result in the generation of acidic runoff.
Plate 3.1 Spring discharge close to borehole BH4 – June 2006
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Plate 3.2 Stable House Watercourse adit – June 2006
The proposed spoil disposal site within Mynydd Farteg Fach west of the coal extraction area currently comprises a natural valley overlain by spoil from historical opencast coal workings. A farm access track extends along an old railway embankment that ‘dams’ the valley, forming a basin. A 600mm diameter culvert runs under the embankment permitting surface water drainage to Cwm Ffrwd. At the time of the site visit in July 2014, there was no flow from the culvert (Plate 3.3). Evidence from historical maps identifies that surface water drainage from the area originally flowed directly to the south. This has now been disrupted by more recent opencast workings and flows now discharge higher up the Cwm Ffrwd catchment to the west. Discussions with Torfaen CBC identifies that scouring occurs downstream in this catchment and is therefore sensitive to flow routeing. Inspection of the Welsh Water records identifies a public foul sewerage system in the field to the north of Salisbury Terrace, which originally drained “Twenty Houses” that have since been demolished. This sewer was not located in the walkover surveys. The pipe size and level are not detailed in the available sewer records and will require inspection and survey if it is to be used in the development. A Trade Effluent Discharge Consent would be required from Welsh Water to connect to this system. As the sewer is not within the current land ownership, it is considered likely that foul sewage will be collected on site in a holding tank.
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Plate 3.3: Culvert draining Mynedd Farteg Fach. July 2014
Rainfall and evaporation data has been collected for the site from the Meteorological Office. Daily rainfall data has been provided for a rainfall station at Cwmavon Reservoir (NGR SO 269070) approximately 700m north of the proposed coal extraction area. The site is located in an area of high rainfall. The average annual rainfall for the period 1971-2000 is 1543.4mm. The annual evaporation data (1961-1990) for the MORECS square including the site is 471.7mm for a land use of rough grazing. The rainfall and evaporation data are provided at Appendix E.
Ground Investigation Works
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4 Ground Investigation Works
4.1 Methodology Following discussions with the Environment Agency (EA) and Torfaen CBC in 2005, it was agreed that further information was required to clarify the geological and hydrogeological conditions at the site and to identify the presence of any areas of contaminated land associated with previous operations on the site. A ground investigation specification was prepared and agreed with the two Regulatory Authorities. The ground investigation was carried out between 25 July and 4 August 2005. The works comprised the drilling of six boreholes, using a combination of percussive and rotary drilling techniques, and the excavation of 30 trial pits. Apex Drilling Services carried out the ground investigation. A programme of groundwater level and quality monitoring followed completion of the borehole drilling. To provide greater details of the geology of the site than normally can be interpreted from the borehole drilling returns, down-hole geophysical logging was carried out by European Geophysical Services of the five rotary boreholes using natural gamma and dual density (High Resolution Density “HRD” / Long Spaced Density “LSD”) gamma-gamma sondes. The locations of the boreholes and trial pits are shown on Figure 4-1. All of the boreholes and the majority of the trial pits are located in the proposed coal extraction area. The ground investigation report which includes the geological logs of the trial pits and boreholes and the laboratory results is presented at Appendix F.
4.2 Boreholes In order to clarify the hydrogeology of the site, six boreholes were drilled by a cable-tool percussive method to rockhead. Five boreholes (BH1, BH2, BH3, BH4 and BH5) were extended by rotary follow-on to investigate the characteristics of the underlying Coal Measures, including the presence of coal seams, old workings, broken ground and sandstone horizons. The boreholes were drilled to a maximum depth of 81.36m. With the use of geophysical logs, the lithology of the Coal Measures was defined by low density and low natural gamma response. Broken rocks or voids are defined as erratic low HRD but moderate LSD. Zones of infilled workings are identified in boreholes BH1, BH2, BH3 and BH5 in the northern half of the site. The geophysical logs of the boreholes are provided at Appendix G. Borehole BH6 was drilled through the full thickness of the colliery spoil in spoil tip 528b to characterise the tip deposits and to prove the underlying natural ground (weathered bedrock). This borehole terminated in a sandy gravelly clay at a depth of 16m below ground level.
4.3 Trial Pits The trial pits were excavated using a JCB 3CX excavator to depths of 0.3m to 4.0m. The trial pits principally were located in areas of the various mine infrastructure formerly present on the site where the greatest risk of ground contamination was anticipated. A lower density of trial pits was designed for other parts of the site, where there was no prior evidence of potentially contaminative uses. Historical Ordnance Survey maps were consulted and anecdotal information obtained from former employees of the most recent mining at the site to identify the locations, and where possible, the former uses of infrastructure on the site. A total of 18 trial pits were excavated inside the proposed coal extraction area and 10 trial pits were excavated outside the proposed extraction area but inside the “Main Area”. The remaining two trial pits were excavated inside the “Second Area” for site characterisation.
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4.4 Sampling 4.4.1 Soils 312 soil samples were recovered from the boreholes and trial pits based on the following depth sampling profile: 0.3m, 0.5m, 1.0m, and then at 1m intervals. Additional samples were taken at any significant change in soil characteristics observed between the prescribed depths. 4.4.2 Laboratory Analysis A total of 36 soil samples were scheduled for geochemical analysis by TES Bretby. The specific analysis carried out on each sample depended on the nature of the sample, the site setting and whether other samples in the same trial pit, or close by, were being submitted for testing. The testing suites are summarised in Table 4.1. Table 4.1 Laboratory Testing Suites
Analytical suites
A General pH, cyanide, sulphate, sulphide, sulphur, asbestos and soil organic matter
B Metals I arsenic, boron, cadmium, chromium, lead, mercury, selenium, copper, nickel and zinc
C Metals II sodium, aluminium and iron
D Hydrocarbons total petroleum hydrocarbons and polycyclic aromatic hydrocarbons (PAH 16)
E VOCs phenols
F Combustibility loss on ignition (LOI) and/or calorific value (CV)
G AMD Potential Acid-Base Accounting
H Leachability NRA Leachate test and analysis of eluate
I Groundwater aqueous suites A, B, D and major ions
Samples of soils recovered from areas of known or suspected ground contamination were submitted for suites A - E. Samples of soil recovered from other areas where contamination was not anticipated were scheduled for suites C, F and G. Three soil samples were scheduled for both suites G and H to provide a comparison of methods for leachability assessment. Where suite F is scheduled, both LOI and CV occasionally were assessed to provide a comparison of results. 4.4.3 Water A water sample was collected from trial pit TP16 at 1m depth to identify the water quality in the spoil tip area north east of the proposed coal extraction area. The water sample was scheduled for suite I.
4.5 Groundwater Instrumentation Single or dual piezometer standpipes were installed in the five boreholes at depths based on the findings of the geophysical survey and, where possible, to monitor the piezometric head in water-bearing horizons across the site. The piezometer depths were selected to investigate the potential for uplift of the floor of the coal extraction area as a result of confined groundwater in the underlying sandstone bands. Together with two existing piezometers, there are eight standpipes for groundwater monitoring. Apart from borehole BH3 and the 1979 borehole V1/3, all of the boreholes are located just outside the boundary of the proposed coal extraction area and hence can be utilised for long-term groundwater level monitoring. Each borehole has been surveyed and the details are summarised in Table 4.2.
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In borehole BH1, the response zone of the piezometer standpipe is a sandstone sequence between 22m and 31m depth (364.7mAOD to 355.7mAOD), below the proposed floor of the workings. In borehole BH2, the upper monitored horizon (borehole BH2b) is within a sandstone dominated sequence between 35m and 48m depth (362.6mAOD to 349.6mAOD). The lower monitored horizon is between 65m and 74m depth (332.6mAOD to 323.6mAOD), within a mudstone dominated sequence with two thin (approximately 1m thick) sandstone bands. Both monitored horizons are below the base of the proposed workings. The upper piezometer in borehole BH3 monitors a mudstone dominated sequence above the Five Feet/Gellideg seam, including potential backfilled workings in the seam, at 14m to 19m depth (364.4mAOD to 359.4mAOD). This standpipe monitors the sequence within that proposed to be extracted. The lower standpipe is between 33m and 46m depth (345.4mAOD to 332.4mAOD) within a thick sandstone sequence (the Gellideg Rock) below the proposed floor of the workings. In borehole BH4, the two standpipe piezometers are below the floor of the workings and both monitor sandstone bands. The upper monitored horizon is at a depth of 7m to 10m (352.7mAOD to 349.7mAOD) in a sandstone below the Five Feet/Gellideg coal and the lower standpipe is at 18m to 23m depth (341.7mAOD to 336.7mAOD) in the Gellideg Rock. The response zone in borehole BH5 is at a depth of 65m to 70m (334.8mAOD to 329.8mAOD) in a mudstone sequence with a thin (0.9m) thick sandstone band below the proposed floor of the workings. Table 4.2: Details of Piezometers Borehole ID Easting Northing Ground level Depth to the base Top elevation of (mAOD) of piezometers piezometers (m (m) AOD) BH1 326159.91 206432.3 386.72 31.0 364.72 BH2a 326048.36 206223.9 397.61 74.0 332.61 BH2b 326048.36 206223.9 397.61 48.0 362.61 BH3a 326143.41 206113.5 378.40 46.0 332.40 BH3b 326143.41 206113.5 378.40 19.0 359.40 BH4a 326234.36 205958.9 359.70 23.0 341.70 BH4b 326234.36 205958.9 359.70 10.0 352.74 BH5 325965.16 205890.5 399.77 70.0 334.80 V1/3a 325980.39 205878.2 398.03 52.3 350.62 V1/3b 325980.39 205878.2 398.03 38.2 366.32
To provide a detailed appraisal of the natural variations in the groundwater level, three piezometers (boreholes BH2a, BH4a and BH5) were installed with data loggers attached to pressure transducers, which recorded the groundwater level at a 10 minute frequency.
An Interpretation of the Results of the Ground Investigation – Geology
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5 An Interpretation of the Results of the Ground Investigation – Geology
5.1 Geology Made ground was proved in most of the trial pits and in all of the boreholes inside the proposed coal extraction area. The made ground materials comprise principally colliery spoil, an angular to sub-angular clayey sandy gravel of mudstone, coal, brick and occasional metal. Other superficial deposits are mostly clayey sandy gravels/cobbles of mudstone and occasional gravels of sandstone with clay. The thickness of the made ground varied between 0.2m in trial pit TP5 on the mid-western edge of the site to a maximum of more than 3.8m in trial pit TP8 on the north eastern boundary. Borehole BH6 drilled in colliery spoil tip 528b proved 16m of made ground. The Coal Measures strata within the proposed opencast excavation are dominated by mudstone facies with subordinate sandstones, siltstones and thin coal seams. The five deep boreholes proved variable sections of the Coal Measures sequence, including the sequence below the floor of the proposed excavation. The findings of the five deep boreholes drilled in the proposed coal extraction area show that the lithology of the sequence to be worked comprises almost entirely of alternating coals and mudstones. A number of sandstone units were proved, principally at lower levels below the proposed base of the workings. Infilled voids, interpreted as old coal workings, were identified from the geophysical survey in boreholes BH1, BH2 and BH3 in the northern half of the proposed extraction area. In borehole BH1 on the northern edge of the site, old workings approximately 0.9m thick were identified between 21.5m and 22.4m depth (364.3mAOD to 365.2mAOD). One level of old workings also was identified in borehole BH3 in the centre of the site, at a depth between 13.7m and 14.0m, a similar level to borehole BH1 at 364.4mAOD to 364.7mAOD. Three sets of former workings were identified in borehole BH2 on the western edge of the site. In this borehole, shallow workings, approximately 1m thick, are present at 11.1m to 12.1m depth (385.5mAOD to 386.5mAOD). Deeper workings were interpreted at 37.5m-37.8m depth (359.8mAOD to 360.1mAOD) and also possibly at 53.9m to 54.2m (343.4mAOD to 343.7mAOD). In most of the boreholes, the proposed floor of the opencast workings lies just above the first major sandstone unit. The strata underlying the floor of the workings includes several thick sandstone units.
5.2 Borehole BH1 Borehole BH1 is located immediately north of the proposed coal extraction area. The ground level at the borehole is approximately 386.7mAOD and the borehole terminated at 351.7mAOD at a depth of 35m.
The sequence proved in borehole BH1 forms the basal section of the proposed coal workings. The base of the proposed coal extraction area is at a depth of approximately 10.5m in the borehole. One of the coal seams within the proposed workings was present in the borehole. The three leaves of the Seven Feet (Meadow Vein) seam were proved between 4.0m and 7.1m depth. The seams were approximately 0.6m, 0.2m and 0.2m thick and were separated by mudstone bands. A second coal seam, approximately 0.7m thick, was proved at 8.6m depth and is interpreted as the Five Feet/Gellideg seam. The sequence within the proposed coal extraction area comprises entirely mudstones with coal seams. The section of the borehole below the base of the Five Feet/Gellideg seam consists of a mixture of mudstone and sandstone. The sandstone units become more extensive with depth. Infilled or collapsed old workings were proved between 21.5m and 22.4m depth (365.2mAOD – 364.3mAOD) and are attributed to workings in the Bottom Vein Ironstone. The Bottom Vein Ironstone is underlain by a 7.8m thick sandstone bed, the Gellideg Rock, which rests directly on the Garw Coal at approximately 30m depth. The Garw Coal is approximately 0.9m thick and includes a thin sandstone band. The strata below the Garw Coal consists of a mixture of mudstone and sandstone.
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5.3 Borehole BH2 Borehole BH2 is located on the western edge of the coal extraction area. The ground level at the borehole is approximately 397.6mAOD and the borehole terminated at 316.2mAOD at a depth of 81.2m. The borehole proved the majority of the coal seams to be worked at the site. The base of the proposed workings in the borehole is at a depth of approximately 30m. The sequence to the base of the proposed workings comprises mudstones and coal seams. In the borehole the following seams were proved: Upper Nine Feet (8.0m-8.9m depth); Lower Nine Feet (11.1m-12.2m depth); Bute (16.8m-17.1m depth); Yard (25.9m-26.8m depth); and the Seven Feet (as two leaves 27.9m-29.8m depth). The Five Feet/Gellideg seam was proved at 37.5m-37.8m depth approximately 10.5m below the floor of the proposed workings. The strata between the Seven Feet and the Five Feet/Gellideg seams consists primarily of mudstone. There was evidence of former workings in the Lower Nine Feet and the Five Feet/Gellideg seams. The sequence below the Five Feet/Gellideg seam consists of mudstone and sandstone. A 5m thick sandstone band was proved directly below the Five Feet/Gellideg coal. Former workings in the Bottom Vein Ironstone were proved at 53.9m-54.16m depth, separated from the underlying Garw Coal by a 5.3m thick sandstone (Gellideg Rock). The strata below the Garw Coal consists of mudstones and sandstones.
5.4 Borehole BH3 Borehole BH3 is located in the centre of the proposed coal extraction area. The ground level is approximately 378.4mAOD and the borehole terminated at 323.4mAOD at a depth of 55m. The borehole proved the lower coal seams to be worked at the site. The base of the proposed workings is at a depth of approximately 15m in this borehole. The sequence within the proposed workings consists of mudstones with coal seams. A series of coal seams were proved between approximately 7m and 11.4m depth. These are interpreted as the Seven Feet/Meadow Vein seam. Old workings, approximately 0.3m thick, were inferred between 13.7m and 14.0m depth. It is not possible to correlate these workings to an obvious coal seam. A zone of soft and poor ground was identified between approximately 15.1m and 18.3m near the floor of the proposed workings, but no obvious infilled workings were proved. It is considered likely that this disturbed zone includes former workings in the Five Feet/Gellideg seam. The sequence below the inferred Five Feet/Gellideg seam consists of mudstones with occasional sandstone bands to a depth of 33m (345mAOD), at which point a 8.3m thick sandstone band was proved resting on the Garw Coal at 41.4m depth. The sandstone is interpreted as the Gellideg Rock. Workings in the Bottom Vein Ironstone identified in other boreholes, immediately above the Gellideg Rock, were not evident in borehole BH3. In the geophysical log, ‘broken rock’ was inferred at a depth of 33.7m near the top of the Gellideg Rock, which may reflect workings in the Bottom Vein Ironstone. The sequence below the Garw Coal is dominated by sandstone bands with subordinate mudstone units.
5.5 Borehole BH4 Borehole BH4 is located to the east of the proposed coal extraction area. The ground level is approximately 359.7mAOD and the borehole terminated at 334.7mAOD at a depth of 25m. The sequence proved in the borehole mainly is that below the base of the proposed coal extraction, which is at the approximate ground level of borehole BH4. The borehole proved mudstone overlying the Five Feet/Gellideg seam (0.8m thick) at approximately 5m depth. The strata below the coal seam consists of sandstone and mudstone to a depth of 17.9m, where a 0.2m thick coal seam was identified. The coal is at a a similar position to the Bottom Vein Ironstone proved in the other boreholes on the site. The ‘coal’ is underlain by a 5.6m thick sandstone band, interpreted as the Gellideg Rock, which rests on
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the Garw Coal. The Garw Coal is present as two leaves, separated by a thin sandstone, between approximately 22.9m and 24.2m depth. There was no evidence of former workings in this borehole.
5.6 Borehole BH5 Borehole BH5 is located at the south western corner of the proposed coal extraction area. The ground level is approximately 399.8mAOD and the borehole terminated at approximately 324.8mAOD at a depth of 75m. The base of the proposed workings is at a depth of approximately 55m. The borehole proved all of the coal seams to be worked at the site. In the borehole the following coal seams were proved: Two Feet Nine (6.5m-8.5m depth); Four Feet (19.0m-20.2m depth); Six Feet (as three leaves between 21.8m and 24.4m depth); Upper Nine Feet (33.5m-35.1m depth); Lower Nine Feet (38.0m-38.5m depth); Bute (42.8m-43.1m depth); and the Seven Feet/Meadow Vein (as three leaves between 51.4m and 54.5m depth). The Five Feet/Gellideg was proved as a 1.3m thick seam at 62.2m-63.5m depth. There is evidence of former workings in the Four Feet, Six Feet and Seven Feet/Meadow Vein seams. Unlike many of the other boreholes, the strata beneath the floor of the proposed workings consist predominantly of mudstones, with a much lower proportion of sandstone bands.
Figures 5.1 and 5.2 show geological cross-sections through the proposed coal extraction area based on the findings of the boreholes and an interpretation of the down-hole geophysical survey.
An Interpretation of the Results of the Ground Investigation – Hydrogeology
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6 6 An Interpretation of the results of the ground investigation - Hydrogeology
6.1 Introduction Based on an interpretation of the geology proved in each of the five deep boreholes and in borehole V1/3 drilled in 1979, it is considered that the standpipe piezometers facilitate groundwater monitoring in the units detailed in Table 6.1. Table 6.1 Groundwater monitoring installations
Borehole Monitored depth Monitored horizon (mbs)
BH1 22m-31m Gellideg Rock
BH2a 65m-74m Garw Sandstone
BH2b 35m-48m Upper Sandstone below Five Feet/ Gellideg Coal
BH3a 33m-46m Gellideg Rock
BH3b 14m-19m Disturbed ground associated with Five Feet/ Gellideg Coal
BH4a 18m-23m Gellideg Rock
BH4b 7m-10m Upper Sandstone band below Five Feet/Gellideg Coal
BH5 65m-70m Mudstone and Upper Sandstone below Five Feet/Gellideg Coal
V1/3a 48m-53m Bute Coal and underlying mudstone
V1/3b 32m-38m Upper Nine Feet and Lower Nine Feet Coals and intervening mudstone
mbs – metres below surface
6.2 Groundwater levels Groundwater levels were monitored monthly between August 2005 and September 2006, apart from the period March to May 2006. The manual ‘dips’ are presented in Table 6.2. The depth to groundwater varies significantly across the site reflecting the variation in the ground level. The depth varies from approximately 5m-6m in standpipe piezometer BH4b on the eastern site boundary to approximately 65m in the lower standpipe in borehole BH2 on the western boundary. The two piezometers in borehole BH3 in the centre of the site have been dry throughout the period of monitoring with monitored depths of 19.2m (359.2mAOD) and 39.6m (336.9mAOD) respectively. The two piezometers in borehole V1/3 in the south western corner of the site both have been dry apart from November 2005, when groundwater was recorded in the upper piezometer at a level of 37.6mbgl (361.0mAOD). The deeper piezometer has been dry at a recorded base level of 52.3mbgl (346.3mAOD). The groundwater level recorded in borehole BH5, close to borehole V1/3, is lower than that recorded in borehole V1/3 in November 2005 and lower than the base of the deeper piezometer in borehole V1/3. To facilitate an assessment of the response of the groundwater level to rainfall, daily rainfall for the period of monitoring was obtained from the Meteorological Office for a rain gauge at Cwmavon Reservoir (NGR SO 269070) approximately 700m north of the site. The rainfall data is provided at Appendix E.
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6.2.1 Borehole BH1 Borehole BH1 is located adjacent to the northern limit of the proposed coal extraction area. This borehole facilitates monitoring of the Gellideg Rock, within a 9m thick zone between 22m and 31m depth. Figure 6.1 shows the groundwater hydrograph for this borehole based on the manual water level monitoring. The recorded groundwater level shows little change and varies between 356.3mAOD in August 2005 and a maximum level of 356.53mAOD in February 2006. The groundwater level is consistent with a thin saturated zone at the base of the Gellideg Rock. 6.2.2 Borehole BH2 Piezometer 2a in borehole BH2 facilitates monitoring of the Garw Sandstone below the Garw Coal. The groundwater level recorded in the piezometer showed major changes in October and November 2005. Since mid-November 2005, the groundwater showed a general trend of slightly rising levels from approximately 332.0mAOD to a maximum 332.9mAOD in May 2006. Over this period, the groundwater level shows a good relationship with rainfall. The groundwater level shows a slight rise following major rainfall events, with a few days delay (Figure 6.2).
Over the period 11 October to 1 November 2005, major changes in the groundwater level in piezometer 2a were recorded. The water level rose by approximately 10m over a period of less than three hours and over a 4-day period had risen by approximately 13.7m reaching a maximum level of 345.95mAOD on 14 October 2005. The water level remained high until 24 October, when the water level fell by approximately 13m over a 7-day period to a level of approximately 332mAOD. Figure 6.3 shows the changes in the groundwater level recorded in piezometer 2a during October and November 2005. The high groundwater level recorded during this period is attributed to a period of heavy rainfall. Between 11 October and 11 November 2005, a total of 399.7mm of rain was recorded at the Cwmavon Reservoir site. Since November 2005, no similar major fluctuations in the groundwater level have been recorded in piezometer 2a, even though periods of heavy rainfall were recorded in March and May 2006. Piezometer 2b facilitates monitoring of the sandstone unit below the Five Feet/Gellideg Coal as well as former workings in the Five Feet/Gellideg Coal present in this borehole. In October 2005, the groundwater level in piezometer 2b showed an increase of approximately 10m, rising from approximately 349.5mAOD in September to 359.5mAOD in October, a similar response to that of piezometer 2a. Unlike piezometer 2a, the water level remained high with very little fluctuations until August 2006, when a groundwater level approximately 6m lower than in July was recorded. However, in September 2006, the groundwater level had recovered to a level similar to that recorded in July 2006. Based on this apparent recovery, it is considered likely that the August data is spurious. Figure 6.4 shows the groundwater hydrograph for piezometer BH2b. The cause of the irregular and large fluctuations in the groundwater level recorded in Piezometer 2a is unclear. 6.2.3 Borehole BH4 The lower piezometer in borehole BH4 (piezometer 4a) facilitates monitoring of the Gellideg Rock. The groundwater hydrograph for piezometer 4a is shown as Figure 6.5. Over the period of monitoring, the groundwater level varied by approximately 1.2m from a minimum of approximately 348.6mAOD in October 2005 to a maximum of approximately 349.8mAOD in November 2005. The hydrograph shows a close relationship with rainfall, with a slight delay of approximately 2 days to rainfall events. The upper piezometer in borehole BH4 (piezometer 4b) facilitates monitoring of the sandstone unit present below the Five Feet/Gellideg Coal. During the monitoring period, the groundwater level varied between approximately 353.9mAOD in October 2005 and a maximum 355.7mAOD in November 2005. The fluctuation in the groundwater level is attributed to the heavy rainfall over this period. Since November 2005, the groundwater level in piezometer 4b has fallen gradually to a level of 353.9mAOD in September 2006. Figure 6.6 shows the groundwater hydrograph for piezometer 4b. 6.2.4 Borehole BH5 Borehole BH5 facilitates monitoring of a mudstone and sandstone sequence below the Five Feet/Gellideg Coal between 65m and 70m depth. The groundwater hydrograph for borehole BH5 is presented in Figure 6.7. The groundwater hydrograph shows three main features. A major rise in the groundwater level was recorded in October 2005 when the groundwater rose by approximately 8.7m over a 9 day period to a peak level of 353.8mAOD. Since November 2005 the water level has slowly receded, with a number of minor increases reflecting a response to rainfall. In May 2006, a sharp increase in the groundwater level of approximately 8m was recorded. This rise in the groundwater level coincided with a period of very wet weather. Between 17 and 25 May, a total of 144mm of rain was recorded. The groundwater level remained elevated for a period of 11 days before falling and returning to the previous trend of a gradual recession.
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6.3 Summary Figure 6.8 shows the groundwater hydrographs for the three boreholes equipped with data loggers. The hydrographs for boreholes BH2a and BH5 both showed a marked rise in levels in October 2005 in response to the heavy rainfall. The response in borehole BH5 was delayed by approximately 5 days. Subsequently the two hydrographs differ. In borehole BH2a, the groundwater level fell rapidly and then only fluctuated gradually on a slightly rising trend. In contrast, the groundwater level in borehole BH5 fell gradually over the period but also showed a more marked response to rainfall than borehole BH2a, particularly in May 2006. The hydrograph for borehole BH4a is totally different with a much more subdued response. However, when considered in detail, the water level variation does show a good correlation with rainfall (Figure 6.5). Two piezometers are present in boreholes BH2 and BH4. In both boreholes there is a significant difference in the water levels recorded in the two piezometers. In borehole BH2, the water level in the upper piezometer (BH2b) is typically 20m to 25m higher than that recorded in the deeper piezometer (Table 6.2). In borehole BH4 a similar pattern is present. The water level recorded in the upper piezometer (4b) is approximately 6m higher than that recorded in the deeper piezometer. Based on the results of the water level monitoring, it is considered that there are several water-bearing units in the Coal Measures sequence at the site, principally associated with sandstone units present in the sequence. The recorded water levels are consistent with these units not being in direct hydraulic continuity. The groundwater levels have been compared with the proposed floor of the workings in the coal extraction area. Across the northern third of the proposed extraction area, the recorded groundwater levels are below the proposed floor of the workings. In the northern part of the site, the maximum water level recorded in borehole BH1 is approximately 356.5mAOD, approximately 19m below the floor of the workings. On the mid-eastern boundary of the site, the maximum recorded groundwater level in boreholes BH4a and BH4b is approximately 355.7mAOD, similar to that of the floor of the workings. In the centre of the site, the groundwater level in the upper piezometer, which facilitates monitoring of the strata above the floor of the workings is approximately 359mAOD, similar to the floor of the workings. In the lower piezometer, the groundwater level is more than 20m below the floor of the proposed workings. On the western edge of the site, the groundwater level generally is more than 10m below the floor of the proposed workings. Based on the results of the groundwater level monitoring, it is only in the central and southern parts of the site that the groundwater level is above the proposed floor of the coal extraction area. In borehole BH5, the recorded water level varied between approximately 338.74mAOD and 352.9mAOD, above the floor level of approximately 340mAOD. Accordingly, based on the results of the groundwater level monitoring, it is considered likely that ingress of significant volumes of groundwater to the workings will be limited to the central and southern parts of the proposed workings.
6.4 Groundwater flow Based on the results of the groundwater level monitoring, it is concluded that there are a number of water-bearing units in the Coal Measures sequence below the site. These principally are related to sandstone units, which are present generally below the level of the base of the proposed coal extraction area. Two principal sandstone units have been identified as being laterally consistent beneath the proposed coal extraction area.
Figure 6.9 shows the interpreted groundwater contours for July 2006 for the measures immediately below the Five Feet/Gellideg Coal, which includes a sandstone band up to 5m thick, for the purpose of this report known as the Upper Sandstone. The plan is based on the results of groundwater level monitoring in boreholes BH2b, BH4b and BH5. Based on the groundwater level contours, it is concluded that groundwater in the measures directly below the floor of the workings, which includes the Upper Sandstone, flows in a south westerly direction at a steep hydraulic gradient of approximately 1 in 7, consistent with the dip of the strata from approximately 360mAOD in the north to approximately 339mAOD in the vicinity of borehole BH5. In the southern and central parts of the site, the groundwater level in this part of the sequence is above the floor of the proposed coal extraction. Figure 6.10 shows the interpreted groundwater contours for the deeper Gellideg Rock for July 2006. The plan is based on the results of groundwater level monitoring in boreholes BH1, BH2a, BH3a and BH4a. Based on the groundwater level contours, it is concluded that groundwater in the Gellideg Rock flows in a west south westerly direction at a gradient of approximately 1 in 15. Based on the groundwater contours, it is concluded that the piezometric level of the groundwater in the Gellideg Rock is below the floor of the proposed workings by approximately 10m. The two groundwater contour plans show no evidence of any easterly component of groundwater flow towards the Afon Llwyd.
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Table 6.2: Groundwater levels
Water Level (mbgl)
16-Aug- 14- 14-Oct- 16- 13- 13-Jan- 14- 15-Jun- 11-Jul- 11- 15- 05 Sep-05 05 Nov-05 Dec-05 06 Feb-06 06 06 Aug-06 Sep-06
BH1 30.38 30.27 30.22 30.27 30.27 30.27 30.19 30.27 30.28 30.25 30.24
BH2a 64.51 65.41 51.66 65.68 65.46 65.26 65.15 64.98 65.05 65.19 65.28
BH2b 49.52 48.16 38.07 38.07 38.07 38.06 38.05 38.09 38.09 43.95 38.67
Dry Dry Dry Dry Dry Dry Dry Dry Dry Dry BH3a Dry (41.5) (39.60) (39.60) (39.60) (39.60) (39.60) (39.60) (39.60) (39.60) (39.60) Dry Wet Dry Dry Dry Dry Dry Dry Dry BH3b 19.5 Dry (19.19) (19.07) (19.19) (19.19) (19.19) (19.19) (19.19) (19.19) (19.19)
BH4a 10.75 10.72 10.79 10.41 10.59 10.57 10.66 10.7 10.79 10.74 10.71
BH4b 4.62 5.29 5.86 4.07 4.55 4.77 5.41 5.03 5.23 5.73 5.8
BH5 53.83 54.65 54.69 46.88 50.39 54.5 57.29 59.8 60.5 61.03 61.4
Dry Dry Dry V1/3A Dry Dry Dry Dry Dry Dry Dry Dry (52.30) (51.73) (51.73) Wet Wet Wet Wet Wet Wet Wet Wet Wet Wet Wet V1/3B (37.90) (37.90) (37.77) (37.60) (37.90) (37.77) (37.79) (37.81) (37.77) (37.73) (37.77)
Water Level (mAOD)
16-Aug- 14- 14-Oct- 16- 13- 13-Jan- 14- 15-Jun- 11-Jul- 11- 15- 05 Sep-05 05 Nov-05 Dec-05 06 Feb-06 06 06 Aug-06 Sep-06
BH1 356.34 356.45 356.5 356.45 356.45 356.45 356.53 356.45 356.44 356.47 356.48
BH2a 333.10 332.20 345.95 331.93 332.15 332.35 332.46 332.63 332.56 332.42 332.33
BH2b 348.09 349.45 359.54 359.54 359.54 359.55 359.56 359.52 359.52 353.66 358.94
BH3a <336.9 <336.9 <336.9 <336.9 <336.9 <336.9 <336.9 <336.9 <336.9 <336.9 <336.9
358.91 BH3b <359.2 <359.2 <359.2 <359.2 <359.2 <359.2 <359.2 <359.2 <359.2 <359.2 (?)
BH4a 348.95 348.98 348.91 349.29 349.11 349.13 349.04 349.00 348.91 348.96 348.99
BH4b 355.12 354.45 353.88 355.67 355.19 354.97 354.33 354.71 354.51 354.01 353.94
BH5 345.94 345.12 345.08 352.89 349.38 345.27 342.48 339.97 339.27 338.74 338.37
V1/3A <346.3 <346.3 <346.3 Dry Dry Dry Dry Dry Dry Dry Dry
V1/3B <360.7 <360.7 <360.7 361 <360.7 <360.7 <360.7 <360.7 <360.7 <360.7 <360.7
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6.5 Groundwater Quality Water samples were collected in February and July 2006 from the boreholes drilled in 2005 and from surface water features in the area. In February, samples were collected from boreholes BH2b, BH4b and BH5; from the spring discharge near to borehole BH4; from the Stable House Watercourse adit; from the two watercourses which flow easterly across the site (locations A and B); and, from the Afon Llwyd downstream of the site (location C). The sampling locations are shown on Figure 6.11. In July 2006, there was no flow from the adit, the two watercourses were dry and there was negligible discharge from the spring near borehole BH4, preventing the collection of a representative sample. As a result samples only were collected from boreholes BH2b, BH4a, BH4b and BH5. The samples were submitted to an independent laboratory (ALcontrol Technichem) for analysis of the parameters listed in Table 6.3. Table 6.3 Water quality analytical suite pH, electrical conductivity, arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, zinc, iron, manganese, ammoniacal nitrogen, COD, phenols, calcium, magnesium, sodium, potassium, alkalinity, chloride, sulphate, nitrate, PAH (16) and total petroleum hydrocarbons
A summary of the results of the laboratory analyses is presented in Table 6.4 and the laboratory data sheets are provided at Appendix H. All of the groundwater samples recorded an acidic pH. Samples from both piezometers in borehole BH4 recorded the lowest values between pH 3.9 and pH 4.5. The other groundwater samples recorded values between pH 6.1 and pH 6.5. With the exception of the acidic pH in the groundwater in borehole BH4, the results of the groundwater analyses generally show a water of satisfactory quality. Slightly elevated concentrations of arsenic, copper, lead, nickel and zinc have been recorded in several of the samples, at concentrations which slightly exceed the Environmental Quality Standards (EQS) for ‘freshwater’. The highest concentrations of metals were recorded for the samples taken from the two piezometers in borehole BH4. This is consistent with the low pH recorded in the samples providing conditions conducive to the mobilisation of metals, naturally occurring in the Coal Measures rocks. Elevated concentrations of sulphate, iron and manganese frequently are associated with water draining from and generated within Coal Measure strata and zones of former underground coal workings. Sulphate concentrations were significantly below the EQS of 400mg/l, ranging from 50mg/l in borehole BH2b to a maximum 250mg/l in borehole BH5. Elevated iron and manganese levels were recorded in many of the groundwater samples. The dissolved iron values varied from less than the limit of detection of 0.02mg/l to a maximum of 0.44mg/l in a sample from borehole BH4b. No sample exceeded the UK Drinking Water Standard of 1mg/l. The recorded manganese concentration varied from 0.32mg/l to 1.2mg/l, both recorded in borehole BH2b. All of the samples exceeded the UK Drinking Water Standard of 0.05mg/l. There is no evidence of any groundwater contamination associated with the former industrial use of the area. Ammoniacal nitrogen levels were low, varying between 0.08mg/l and 0.24mg/l. Nitrate and polyaromatic hydrocarbons (PAH16) were at or below the respective limits of detection. Extractable hydrocarbons also generally were low at between 0.02mg/l and 0.82mg/l.
The analytical laboratory was unable to characterise the hydrocarbons, which eluted in the range C10 to C40. The major anions and cations generally were present at low concentrations, consistent with groundwaters with a low residence time. This is reflected in the low electrical conductivity values recorded in the samples from boreholes BH2b and BH4b. A higher electrical conductivity was recorded for the samples from borehole BH5.
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Table 6.4 Groundwater quality 2006
BH2b BH4a BH4b BH5
Strata Upper Sandstone Gellideg Rock Upper Sandstone Upper Sandstone
Date 14/02/06 11/07/06 11/07/06 14/02/06 11/07/06 14/02/06 11/07/06 pH 6.2 6.5 4.5 4.1 3.9 6.1 6.5
As 0.006 <0.005 <0.005 0.007 <0.005 0.007 <0.005
Cd <0.001 <0.001 0.001 <0.001 <0.001 <0.001 <0.001
Cr <0.01 <0.005 <0.005 <0.01 <0.005 <0.01 <0.005
Fe <0.02 5.4(T) 0.41(T) 0.44 1.7(T) <0.02 30(T)
Pb 0.06 0.021 0.05 0.07 0.019 <0.01 <0.005
Mn 1.2 0.32 0.67 0.65 0.63 0.77 0.95
Hg <0.00005 <0.00005 <0.00005 <0.00005
Ni 0.063 0.028 0.058 0.055 0.053 0.033 0.030
Se <0.01 <0.005 <0.005 <0.01 <0.005 <0.01 <0.005
Zn 0.06 0.03 0.12 0.13 0.096 0.047 0.044
EC 373 510 316 235 375 589 818
Amm-N 0.09 0.19 0.24 0.22 0.08 0.16 0.13
Ca 16 25 22 17 25 43 69
Mg 12 16 4.2 3.9 4.2 42 60
Na 3.7 4.3 4.4 4.7 4.9 5.1 6.3
K 3.9 4.7 4.3 4.2 4.5 8.6 12
B nd 0.034 0.044 nd 0.046 nd 0.078
Alk 40 65 <20 <20 110 160
SO4 50 86 81 69 99 160 250
Cl 13 <10 <10 <10 <10
NO3 <1 <0.5 <0.5 <1 <0.5 <1 <0.5
COD <10 <10 <10 49 <10
EPH 0.17 0.15 0.43 0.02 0.07 0.82 0.22
Phenol <0.01 <0.01 <0.01 <0.01
PAH(16) 0.0002 <0.0001 <0.0001 0.0002 <0.0001 0.0002 <0.0001 All data expressed as mg/l, except pH and electrical conductivity (EC) expressed as µS/cm. (T) - total iron
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6.6 Surface Water Three adits and the spring around borehole BH4 on the eastern side of the site were visited during each monthly monitoring visit. A visual assessment was made of the flow conditions at each location. Adits A and B frequently were dry and adit C had a low water level in an area of rushes. The spring by BH4 had a slow seepage and often contained very little water, although generally had a greater flow than the three adits. In February 2006, water samples were collected from adit C (Stable House Watercourse); from the spring; and, from two ephemeral streams which drain the site in an easterly direction. A sample also was collected from the Afon Llwyd downstream of the confluence with the two streams which drain the site. The samples were analysed for the suite of parameters listed in Table 6.3. The results of the analyses are presented in Table 6.5 and the laboratory data sheets are provided at Appendix H. In July 2006, the adit and the two streams were dry and the spring discharge was only a small seepage, insufficient to collect a representative sample. The water samples from the adit and the spring were both acidic, with values of pH 5.2 and pH 3, respectively. The spring sample contains elevated iron and manganese levels, at concentrations of 2.6mg/l and 1.8mg/l respectively. Slightly elevated concentrations were recorded for many of the metals - arsenic (0.019mg/l); nickel (0.15mg/l); and, zinc (0.19mg/l). The spring water had a high sulphate concentration of 710mg/l, ammoniacal nitrogen of 0.35mg/l and an electrical conductivity of 1600µS/cm. The catchment to the spring includes the colliery spoil tips on the southern part of the proposed coal extraction area. The elevated iron, manganese and sulphate and the low pH recorded at the spring are attributed to runoff from the colliery spoil tips, seepages and shallow groundwater flow to the spring. The water quality of the two streams draining the site generally was satisfactory. The pH values were close to neutral. Iron and manganese were present but at much lower concentrations than recorded in the spring sample. The water quality of the Afon Lwyld downstream of the site was satisfactory.
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Table 6.5 Surface water quality
Adit Spring Stream A Stream B Afon Llwyd Date 14/02/06 14/02/06 14/02/06 14/02/06 14/02/06
pH 5.2 3.0 6.8 7.3 7.7
As 0.007 0.019 <0.005 0.008 <0.005
Cd <0.001 <0.001 <0.001 <0.001 <0.001
Cr <0.01 <0.01 <0.01 <0.01 <0.01
Fe <0.02 2.6 0.23 0.18 0.05
Pb 0.02 0.05 <0.01 <0.01 0.01
Mn 0.71 1.8 0.015 0.064 0.03
Hg <0.00005 <0.00005 <0.00005 <0.00005 <0.00005
Ni 0.053 0.15 0.008 <0.005 <0.005
Se <0.01 <0.01 <0.01 <0.01 <0.01
Zn 0.12 0.19 0.006 0.016 <0.005
EC 379 1600 237 277 365
Amm-N 0.12 0.35 0.06 0.06 0.05
Ca 46 170 18 22 25
Mg 7.9 7.3 11 9 11
Na 4.6 5.1 3.3 10 22
K 3.2 1.8 4.5 4.3 3.9
Alk <20 <20 25 50 60
SO4 120 710 66 43 47
Cl <10 <10 <10 38 16
NO3 <1 <1 <1 <1 <1
COD <10 <10 16 10 <10
EPH 0.02 0.01 0.02 0.02 0.04
Phenol <0.01 <0.01 <0.01 <0.01 <0.01
PAH(16) 0.0002 0.0001 0.0001 0.0001 nd
All data expressed as mg/l, except pH and electrical conductivity (EC) expressed as µS/cm.
An Interpretation of the Results of the Ground Investigation – Ground Contamination
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7 An Interpretation of the Results of the Ground Investigation – Ground Contamination
7.1 Introduction The results of the laboratory analyses of the soil samples are summarised in Table 7.1 and the laboratory data sheets are presented at Appendix I. The soil samples analysed were mainly from either the made ground in the area of the former Varteg Hill Colliery in the northern part of the proposed coal extraction area or from the colliery spoil tips on the site. The samples were tested for a variety of contaminant suites in accordance with Section 4.4. The results of the soils testing initially were compared against generic soil guideline values (SGVs) issued by DEFRA as part of the Contaminated Land Exposure Assessment (CLEA) model. At the time of undertaking the laboratory analyses, nine SGVs had been published. The CLEA guidance recognised four end-uses consisting of residential use with plant uptake; allotments; residential use without plant uptake; and, commercial/industrial use. In accordance with guidance published by DEFRA and the Environment Agency, a review of the conceptual model used to derive the generic SGVs was made. At the time, there was no model published for a general ‘open space’ land-use. Accordingly, the generic conceptual model ‘commercial/industrial’ was used as an initial model. This model was considered the most appropriate for use in screening soil contaminant concentrations at the scheme site. The commercial/industrial generic SGVs were the least stringent of the SGVs published by the DEFRA. However, due to the limited exposure duration of any end users and the restoration proposals, it is considered that the commercial/industrial SGVs are conservative and it is unlikely that contaminant levels below these guidance values presented a significant risk to human health in relation to development of the site as an opencast coal site and subsequent restoration of the site to grassland and heath. The SGV were withdrawn by DEFRA in 2006. Apart from the issue in March 2014 of revised guidance (Category 4 Screening – C4SL) levels for six contaminants, the SGV have not been replaced. The C4SL includes guidance values for public open space. One of the purposes of the C4SL for potentially contaminated land is to identify those sites where contaminant levels are sufficiently low such that it is unlikely that the site poses a Significant Possibility of Significant Harm (SPOSH) in accordance with Part 2A of the Environmental Protection Act 1990. For those substances assessed under the C4SL research, comparison of the screening values for public open space (POS) Category 2, which is considered appropriate for the end use of the site, was made with the recorded contaminant levels. For other substances, not reviewed in C4SL, comparison was made against the AECOM generic assessment criteria (AGAC) derived using the CLEA version V.1.04 model approach. Comparison of the reported concentrations with the screening values is provided at Table 7.1. Both copper and zinc are considered phytotoxic contaminants, which do not pose a risk to human health unless present at very high concentrations. The significance of the copper and zinc concentrations has been assessed through comparison with MAFF guidelines for soils. The potential risks to human health have been assessed based on the current land use (public open space) which will remain largely unchanged following completion of the opencast workings and restoration of the site. The first phase of the assessment is to identify chemicals that are present at significant concentration in the soil, for example, those that exceed the generic guideline values. Where contaminant concentrations in the soils are in excess of these values, a quantitative risk assessment will be undertaken. There is no current guidance on the derivation of trigger concentrations for POS end use, other than in the recently issued C4SL guidance for a limited number (six) of potential contaminants. In the absence of published levels for the proposed end use of the site, AECOM AGAC for a standard ‘commercial/industrial’ land use was used to assess the concentrations of contaminants recorded on the site. An average soil organic matter of 2.5% was used for the surface soils and the made ground.
The AGAC have been derived using the published CLEA methodology and toxicological and physical-chemical input parameters from published SGVs and in their absence CIEH/LQM GAC (Generic Assessment Criteria for Human Health Risk Assessment, 2009). The potential chronic risks to human health have been assessed by comparing the recorded concentrations of contaminants against the AGAC or published values, as an initial screen. Suitable screening values are not available for all
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potential contaminants. All potential contaminants for which analysis was undertaken in the selected soil samples were present at concentrations below the selected trigger values.
7.2 Data Assessment 7.2.1 pH A wide range of pH values has been reported for the samples analysed, ranging from pH 5.2 to pH 11. Acidic pH values, less than pH 7, were recorded from 13 of the 18 samples tested. The maximum pH value was recorded for a sample of demolition rubble from trial pit TP13 at 1m depth. Low pH values present a risk of mobilising metals present within the soils resulting in the generation of acidic runoff containing elevated metal concentrations. 7.2.2 Metals Concentrations of metals were recorded for 20 samples from 14 trial pits and boreholes on the site. At the time of the ground investigation, nine generic SGVs had been published by DEFRA including seven metals or metalloids: arsenic (500mg/kg), chromium (5,000mg/kg), cadmium (1,400mg/kg), mercury (480mg/kg), nickel (5,000mg/kg), lead (750mg/kg) and selenium (8,000mg/kg) and two aromatic hydrocarbon compounds: ethylbenzene (48,000mg/kg) and toluene (150-680mg/kg). Where a range of concentrations is given, the SGV depends on the percentage of organic matter in the soil (fraction of organic content, FOC), with the lower guidance values corresponding to lower soil organic matter content. The recorded concentrations of metals for thirteen soil samples tested were all significantly below the respective SGVs. Comparison of the recorded contaminant concentrations with the AECOM AGAC levels also confirms that the recorded concentrations for most metals are significantly below the guideline levels. C4SL at an SOM of 6% have been published for arsenic and chromium VI for a public open space 2 end use. None of the reported concentrations exceeded the two published screening levels. Metal concentrations reported for arsenic (6.7mg/kg to 62.5mg/kg), cadmium (less than 0.1mg/kg to 0.76mg/kg); chromium (3.8mg/kg to 28.9mg/kg); mercury (less than 0.1mg/kg to 0.43mg/kg); nickel (5.1mg/kg to 85.6mg/kg); and selenium (less than 0.5mg/kg to 3.1mg/kg) are all significantly below their respective guidance levels. The maximum recorded concentration for these metals typically was less than 1% of the respective SGVs. The concentration of lead recorded did not exceed the C4SL of 1300mg/kg for a public open space end use. A sample of made ground at 0.5m depth in trial pit TP9 recorded a lead concentration of 872.6mg/kg and a sample of the colliery spoil at 5.45m depth in borehole BH6 recorded a concentration of 1075mg/kg, both of which exceed the AGAC for a commercial/industrial end use of 750mg/kg. In addition to the metals for which SGVs had been published, analysis was undertaken for zinc, copper and boron, which are regarded as phytotoxic contaminants and which normally do not pose a risk to human health. The concentrations of copper and zinc present at the site have been compared with the MAFF soil guideline values and the concentrations of boron have been compared with the former ICRCL threshold trigger level. 7.2.3 Boron The former ICRCL trigger value for boron is 3mg/kg. This value has been used as a screening value to assess the significance of the recorded levels. The recorded boron concentrations are negligible to low with a maximum concentration of 1.1mg/kg recorded for the sample of colliery spoil in borehole BH6 at 5.45m depth. Based on the results of the laboratory analyses, it is considered unlikely that boron levels pose a constraint to the proposed restoration scheme. 7.2.4 Copper Two soil samples of made ground recorded copper concentrations in excess of the MAFF guideline value of 200mg/kg. The samples exceeding the intervention value are: TP6 @ 1.0m 4630mg/kg (former lighthouse, made ground)
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TP9 @ 0.5m 3605mg/kg (former mine compound, made ground). Both elevated concentrations of copper compared with the MAFF guidelines are significantly below the AGAC for a commercial/industrial end use of 71,000mg/kg. 7.2.5 Zinc The zinc concentrations generally are below the MAFF guideline value of 300mg/kg. Only one soil sample exceeded the guideline value. The zinc concentration in trial pit TP6 at 1m depth is 742.5mg/kg. The sample is of made ground from the former lighthouse area of Varteg Hill Colliery. The AGAC trigger level for zinc for a commercial/industrial end use is 660,000mg/kg. 7.2.6 Sulphate Elevated sulphate concentrations normally do not pose a risk to human health. Elevated levels can impact on concrete foundations of new buildings. Six samples recorded sulphate concentrations in excess of the reference ICRCL concentration of 2000mg/kg. The samples are:
TP2 @ 3m 2130mg/kg (natural ground below former building) TP3 @ 0.5m 4460mg/kg (former mineral track materials) TP8 @ 0.5m 2830mg/kg (former mine compound materials)
TP8 @ 3m 2410mg/kg (former mine compound materials) TP9 @ 0.5m 3190mg/kg (former mine compound materials) TP13 @ 1m 2140mg/kg (former coal washery on made ground) Other than the sample from trial pit TP2, the elevated sulphate levels are associated with the made ground. 7.2.7 Iron and aluminium There are no published guideline values in respect of iron and aluminium. High levels of both substances frequently are associated with colliery spoil materials. High concentrations of both iron and aluminium are reported for all of the soil samples tested. The iron concentration varies between 6290mg/kg and 141,000mg/kg. The maximum concentration was recorded for a sample of colliery spoil from trial pit TP9 at 0.5m depth. The aluminium concentration varied between 2830mg/kg and 17,400mg/kg with the highest concentration being recorded for a sample of colliery spoil from trial pit TP4 at 0.3m depth. 7.2.8 Hydrocarbons The soil samples were analysed for the presence of hydrocarbons by testing for total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAH16). The TPH values recorded varied between 13mg/kg and 2010mg/kg with 16 samples exceeding the Dutch target concentration of 50mg/kg. The maximum concentration was recorded for a sample of colliery spoil from trial pit TP9 at 0.5m depth. Current guidance now relates to hydrocarbon speciation in accordance with the TPH CWG. The lowest AGAC screening value for a commercial/industrial end use is for the TPH aliphatic fraction C8-C10 at 5700mg/kg, which is more than twice the maximum reported total petroleum hydrocarbon concentration. Accordingly, it is considered that the recorded petroleum hydrocarbon levels do not pose an unacceptable risk to human health. The PAH(16) values varied from below the limit of detection of 1mg/kg to a maximum 351mg/kg for a sample of colliery spoil from trial pit TP2 at 1.0m depth. The PAH benzo(a)pyrene [B(a)P] typically is regarded as the most sensitive PAH in respect of human health. The C4SL value for B(a)P for public open space Category 2 is 21mg/kg. One of the samples reported B(a)P levels above the C4SL value of 21mg/kg at 25mg/kg. The majority of the samples reported levels below the limit of detection of 1mg/kg. The elevated hydrocarbon concentrations recorded in the made ground in trial pits TP2 and TP9 are consistent with the presence locally of hydrocarbon contamination.
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Table 7.1: Summary of the Laboratory Analysis of the Soil Samples
Determinand Range AGAC C4SL for No. of No. of No. of Values for a POSpark samples samples samples less Commercial above than limit of end use [SOM 6%] guidelines detection [SOM 2.5%] Arsenic 6.7 – 62.5 630 168 20 0 0 Boron <0.5 – 1.1 31 20 0 15 Cadmium <0.1 – 0.76 230 880 20 0 1 Chromium 3.8 – 28.9 30,000 250* 20 0 0 Copper 11.7 – 4630 71,000 20 2 0 (2003) Lead 18.1 – 1075 750 1300 20 2 0 Mercury <0.1 – 0.43 11 20 0 15 Nickel 5.1 – 85.6 22000 20 0 0 Selenium <0.5 – 3.1 13000 20 0 2 Zinc 18.5 – 742.5 660,000(300 20 1 0 3) Sodium 74 – 457 - 30 - 0 Aluminium 2830 – 17,400 - 21 - 0 Iron 6290 – 141,000 - 21 - 0 Cyanide (free) <1 1/202 20 0 20 Cyanide (total) <1 – 4 5/502 20 0 19 Sulphate (acid sol) 488 – 4460 20001 18 6 0 Sulphide <5 2501 18 0 18 Sulphur <20 – 108 50001 18 0 6 (elemental) pH (pH units) 5.2 – 11 <5 18 0 n/a SOM % (Calc) 1.4 – 72.4 - 18 n/a Asbestos Not Found - 20 n/a TPH 13 – 2010 24500+(50)2 20 0 0 Benzene <5-15 50 230 13 0 11 Toluene <5-43 1900 13 0 2 Ethylbenzene <5-9 1200 13 0 12 Phenols <0.5 – 1.9 37,000 18 0 15 PAH (16 USEPA) <1 – 351 10001 20 0 2 Benzo[a]pyrene <1-25 21 28 1 22 Calorific Value 0.34 – 6.83 75 7 0 (MJ/kg) LOI % @ 450ºC 3.5 – 20.9 - 9 n/a Acid-Base -109 – +52.8 <04 20 6 Accounting (kg/tonne) All soil parameters are measured in mg/kg on dry weight basis unless otherwise stated. 1 ICRCL 59/83 values 2 Dutch Target and Intervention Values (target value/intervention value). The comparison is using the target values and intervention values against the soil results. 3 MAFF soil guideline values 4 Negative Acid-base accounting number indicates more potentially acid producing strata in the overburden materials 5 ICRCL 61/84 + * - AGAC for speciated hydrocarbon (C8-C10) - chromium VI
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7.2.8 Other potential contaminants The soil samples also were analysed for the presence of cyanide, sulphur, sulphide and phenols. Sulphide was not recorded above the limit of detection of 5mg/kg in any of the soil samples. Concentrations of total cyanide were either below or just above the limit of detection of 1mg/kg, with a maximum recorded value of 4mg/kg, below the Dutch target level of 5mg/kg.
Low concentrations of both sulphur and phenols were recorded, with many of the samples showing concentrations below the respective limits of detection of 20mg/kg and 0.5mg/kg. The maximum concentration of sulphur of 108mg/kg, significantly below the former ICRCL trigger level of 5000mg/kg, was recorded for a sample of made ground from trial pit TP8 at 3.0m depth. The maximum phenol concentration was 1.9mg/kg from the colliery spoil in trial pit TP9 at 0.5m depth. This compares with the AGAC for phenol of 34,000mg/kg for an industrial/commercial end use. 7.2.9 Loss on Ignition and Calorific Values The percentage weight lost on ignition (LOI) gives a crude measure of the organic content of the soil providing a guide on the risk of combustion of the sample. In this situation, it is likely that the LOI relates principally to the percentage of coal in the sample. For calorific values (CV), all soil samples are below the criteria of 7MJ/kg, specified in the ICRCL document, 61/84 Notes on the fire hazards of contaminated land, 1986. However, this value should be used with caution. The samples were analysed because of the likely presence of coal derived material and coal fragments. However, alternative sources have suggested that soils are liable to combust if the recorded CVs are in the range of 0.2MJ/kg to 10.3MJ/kg. The exothermic oxidation of pyrites, frequently common in colliery spoil, can cause materials to self combust. The LOI varies between 3.5% and 20.9%, with the highest concentration recorded for a sample of demolition rubble with coal fragments from trial pit TP13 at 1m depth. 7.2.10 Acid-Base Accounting Acid-Base Accounting (ABA) is an analytical procedure that provides values to help assess the acid or alkaline producing potential of overburden rocks. ABA is designed to measure neutralisation and acidity potentials thereby indicating the likely risk of acid mine drainage. ABA is calculated by subtracting the potential acidity from the neutralisation potential. A positive number indicates potentially alkaline-producing strata in the materials and a negative number indicates potentially acid-producing strata in the materials. The unit is expressed in kg/tonnes of overburden. Negative ABA values were calculated for six of the 20 samples from three locations. The four most negative values, between -20.2kg/tonne and -109kg/tonne, were from samples of colliery spoil from borehole BH6 in spoil tip 528b. A sample of colliery spoil from trial pit TP11 recorded a value of -2.13kg/tonne and a sample of made ground from the former mine compound at a depth of 2m in trial pit TP8 recorded a value of -2.63kg/tonne. Based on the results of the analyses, it is concluded that there is potential for the generation of acidic runoff associated with the areas of exposed and weathered colliery spoil.
7.3 Leachate Test To determine the solubility of contaminants identified in the soils on the site, three samples were selected for leachate testing in accordance with the NRA R&D. Note 301 methodology:- - TP8 @ 2m – former mine compound - TP11 @ 0.5m – old spoil tip materials - TP12 @ 1m – old spoil tip materials
The laboratory data sheets are provided at Appendix I and the results are summarised in Table 7.2. The results of the leachate analysis were compared with the EQS for freshwater and the maximum admissible concentrations (MAC) specified in the UK Water Supply (Water Quality) Regulations 2000 consistent with the results of the groundwater quality analysis (Section 6.4).
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The analysis of the leachate from the leachability tests of the three soil samples shows that the majority of the parameters analysed are present at low concentrations with most below the EQS or UKDWS guidance levels. The higher concentrations generally are associated with the sample from trial pit TP8. The recorded concentrations of copper, lead, nickel and zinc slightly exceed the EQS values based on the most stringent hardness band of 0-50mg/l as CaCO3. For higher hardness values, the recorded levels of the four metals were below the respective EQS values.
Table 7.2: Summary of leach test results
Determinand Leachate Results (mg/l) Environmental No. of samples Quality above guide Minimum Maximum Standards levels (EQS/UKDWS) Arsenic <0.001 0.006 0.005* 1 Boron <0.05 0.09 2 0 Cadmium <0.0001 0.0011 0.005 0 Chromium <0.001 0.004 0.005^ 0 Copper 0.001 0.002 0.001^ 2 Lead 0.002 0.014 0.004^ 2 Mercury <0.0001 0.001 0 Nickel <0.0001 0.142 0.05^ 1 Selenium <0.001 0.009 0.01* 0 Zinc 0.019 0.135 0.008^ 3 Iron <0.01 0.83 1 0 Cyanide (free) <0.01 0.05* 0 Total sulphur as 6.65 251 400 0 SO4 Sulphide <0.2 0.00025 0+ Chloride 1 5 250 0 Ammoniacal <0.01 0.17 0.39 0 Nitrogen as N Electrical <100 543 - - conductivity (μS/cm) PAH (16 <0.18 0.1 0+ USEPA) (μg/l) Phenol <0.005 0.0033 0.3 0 * UK Drinking Water Standards + Detection limits are higher than guideline values ^ EQS for hardness band, 0-50mg/l CaCO3.
A water sample was collected from trial pit TP16 excavated in the made ground. The results were compared with Environmental Quality Standards (EQS) for ‘freshwater’ published by the Environment Agency or with the maximum admissible concentrations (MAC) specified in the UK Water Supply (Water Quality) Regulations 2000. The laboratory data sheets for the water analysis are provided in Appendix H. It is considered that the water struck in the trial pit is perched water within the made ground and is unlikely to be representative of the general water quality in the area. The results showed that recorded concentrations of most determinands were below the EQS or the MAC. The recorded values for copper and zinc were slightly above the respective EQS values. The copper concentration of 2µg/l compares with the EQS of 1µg/l and the zinc concentration of 23µg/l compares
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with the EQS of 8µg/l. For both copper and zinc, the most stringent EQS has been used, which is based on a hardness of less than 50mg/l. The total petroleum hydrocarbon concentration of 0.6mg/l is at the Dutch intervention value and above the MAC of 0.01mg/l.
7.4 Statistical Analysis Following an assessment of the analytical results, a statistical analysis of the soil geochemical data has been undertaken. This is presented in Table 7.3. The analysis uses the Mean Value Test and Maximum Value Test set out in CLR7 Assessment of Risks to Human Health from Land Contamination (Department for Environment, Food and Rural Affairs (DEFRA) 2002). Appendix J presents a brief explanation of the tests and their interpretation. Anomalously high values are subject to an outlier test to establish whether they belong to the same underlying data set as the residual values. If the test suggests that the value is an outlier, this may indicate an isolated ‘hotspot’ of contamination. Sequential removal of outliers from the data set may be used to indicate whether, on the basis of the analysis undertaken, each area as a whole should be considered as contaminated, or whether the number of hotspots appears limited.
th In the Mean Value Test, the 95 percentile upper band (US95) value is calculated for each determinand for which a guidance value is available, utilising geochemical soil data from laboratory analysis of samples representative of the site area. This US95 value is then compared with the relevant guidance value to determine whether the area as a whole should be considered contaminated with the particular determinand. A summary of the statistical analysis is provided in Table 7.3. Where analysis has proved concentrations below the limit of detection for a specific determinand, the limit of detection (LOD) has been used as a conservative estimate of the contaminant concentration. 7.4.1 Metals and Inorganic Contaminants The outlier test indicates that there are ‘hot spots’ of slightly elevated copper, zinc and boron at the site. However, all are below or only slightly exceed the screening values and are considered not to present a significant risk to human health. Copper is identified as an outlier in TP4 at 0.3mbgl (196mg/kg) and TP8 at 3.0mbgl (158mg/kg). Zinc is an outlier in TP6 at 1.0mbgl (742mg/kg). Two concentrations of boron are considered to be outliers in BH6 at 5.45mbgl (1.1mg/kg) and TP4 at 0.3mbgl (0.8mg/kg). The concentrations of lead recorded above the screening value (1075mg/kg in BH6 at 5.45mbgl and 872mg/kg in TP9 at
0.5mbgl) are considered not to be outliers based on the statistical analysis. The upper bound (US95) value (318mg/kg) of the normally distributed population is below the C4SL value (1300mg/kg). The mean values of all the metal and inorganic contaminants in a normally distributed population (i.e. excluding the outliers) are below the relevant screening values. 7.4.2 Organic Contaminants A number of organic contaminants (Total PAH, Phenols, Petroleum Hydrocarbons) have been identified at the site at concentrations significantly below the screening values. There are three outliers from the phenol data set, all of which are below the screening value. The US95 also is below the screening value. There are no outliers within the TPH data set, with the maximum, mean and US95 concentrations all below the screening value. A total of 28 samples were analysed for Benzo(a)pyrene, of which 22 were below the limit of detection of 1mg/kg. The maximum reported concentration of 25mg/kg was in TP2 at 1.0mbgl. This is slightly above the C4SL value for public open space of 21mg/kg.
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The slight exceedence of this value, and the result of the outlier test indicate that there may be a ‘hot spot’ of contamination at TP2. Two further slightly elevated concentrations of benzo(a)pyrene of 14mg/kg (TP9 at 0.5mbgl) and 5mg/kg (TP3 at 0.5mbgl) are also outliers though are below the proposed screening value. The US95 for benzo(a)pyrene is below the C4SL value of 21mg/kg.
7.5 Summary Based on the results of the soil analyses, it is considered that there is no evidence of significant or widespread ground contamination at the proposed opencast site, which would place any constraint on the proposed workings or a significant risk to human health. Locally elevated metal concentrations (lead, copper and zinc) are associated with the made ground in the vicinity of the former Varteg Hill Colliery and at depth in spoil tip 528b. A possible ‘hot spot’ of contamination has been identified at trial pit TP2, in the northern part of the proposed excavation, with the benzo(a)pyrene C4SL being slightly elevated. However, leachate tests show that most contaminants are not readily soluble. There is potential for the generation of acidic runoff from the colliery spoil tip in the southern part of the site. However, the leachate tests on other samples from the site did not show any significant contamination associated with acidic drainage. Figure 7.1 shows the locations of the elevated contaminant levels.
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Table 7.3 Summary results of the statistical analysis Upper Number of values Mean Boundary exceeding Number Critical Critical Number (mg/kg) of Guidance Maximum (US ) of Guidance guidance in Determinands of T Value Value of normally 95 (e.g. SGV, Value normally Value normally Samples (5%) (10%) outliers distributed Dutch) distributed distributed population population population Made Ground Lead 20 1075 2.01 2.36 2.53 0 204.76 318.46 C4SL 1300 0 Arsenic 20 62.5 2.85 2.36 2.53 2 15 12.72 C4SL 168 0 Cadmium 20 0.76 1.65 2.36 2.53 0 0.34 0.41 C4SL 880 0 Chromium 20 28.9 2.03 2.36 2.53 0 10 12.79 C4SL 250 0 Mercury 20 0.43 2.29 2.36 2.53 0 0.15 0.20 AGAC 4.2 0 Selenium 20 3.1 2.00 2.36 2.53 0 1.21 1.49 AGAC 13000 0 Copper 20 4630 2.74 2.36 2.53 2 73 949.05 MAFF 200 0 Nickel 20 85.6 2.07 2.36 2.53 0 27 34.31 AGAC 26000 0 Zinc 20 742.5 2.69 2.36 2.53 1 92 121.12 MAFF 300 1 Boron 20 1.1 3.55 2.36 2.53 2 0.5 0.61 MAFF 3 0 TPH 18 2010 2.17 2.30 2.47 0 305 520 Dutch 5000 0 Benzo(a)Pyrene 28 25 2.66 2.27 2.44 3 1.21 1.42 C4SL 21 1 Phenols 18 1.9 3.51 2.30 2.47 3 0.5 0.5 AGAC 34000 0
Conceptual Site Model
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8 Conceptual Site Model
8.1 Introduction Two conceptual models of the site were developed as part of the earlier Phase 1 desk study, reported in the Faber Maunsell report of September 2005. One model addressed the general and scheme-specific hydrogeological and hydrological aspects. The second model considered the potential for and impacts associated with contaminated land on the site. The purpose of the ground investigation and subsequent groundwater monitoring was to provide additional information to allow the initial conceptual models to be refined. 8.2 Conceptual Model of Hydrology and Hydrogeology The conceptual model of the hydrology and hydrogeology includes receipt, storage, flow and modification of the chemistry of groundwater and surface water by the current site and an appraisal of how these processes may be modified by the proposed scheme. It incorporates incident rainfall on the site, generating run-off and sub-surface flow through the soil or colliery spoil which ultimately discharges at the surface as springs and seepages, coalescing to form ephemeral streams converging at either the Afon Llwyd or the Nant Ffrwd. A proportion of incident rainfall percolates into the opencast colliery spoil and where present, superficial deposits, following a slower route to eventual discharge at the surface to the east of the proposed coal extraction area. Where old workings, permeable strata or goaf are present close to surface or buried beneath opencast backfill or the site spoil tips, recharge to the underlying permeable formations and old workings may occur with groundwater flowing generally to the south west.
The conceptual hydrogeological and hydrological model of the site has been prepared based on a detailed assessment of the geological conditions, interpreted from the logs of the boreholes drilled at the site in 1979 and 2005. The interpretation facilitated the preparation of detailed geological profiles through the proposed coal extraction area (Figures 5.1 and 5.2). The strata beneath the floor of the proposed coal extraction area consist of a granular dominated sequence with thick sandstone units separated by thin mudstone units and occasional coal seams. Within the sequence to be worked, sandstone bands generally are absent and where present, are thin and discontinuous. The strata consist almost entirely of mudstones and coal seams. The strata dip to the south west at an angle of 5-6 degrees. There is no evidence of extensive past workings in the site of the coal seams to be extracted. There is evidence of past workings in the Lower Nine Feet seam in the south western part of the proposed coal extraction area and possibly within the Seven Feet (Meadow Vein) seam in the northern part of the site. Adits used for accessing workings to the west and for draining these workings are present beneath the site, in particular the Stable House Watercourse. Whilst there is a possibility of unrecorded coal workings, it is considered likely that these will be limited to the outcrop of the seams across the site and did not penetrate deep underground.
The conceptual site model has been developed from the geological interpretation together with a review of the results of the groundwater level and quality monitoring. The proposed coal extraction area is situated in the recharge area for much of the strata which will be disturbed by the coal extraction operation. Previous opencast workings in the surrounding area have removed many of these units thereby reducing the potential for water to enter the workings from adjacent areas. As a result, it is considered that the volume of groundwater entering the workings will be limited principally to the infiltration of incident rainfall on the site and the immediately adjacent area. Due to the steep gradient of the site and the generally low permeability, clayey nature of the ground, it is considered that there is significant surface water run-off and that only a small proportion of incident rainfall infiltrates the strata on the site. Based on the results of the groundwater level monitoring, it is interpreted that groundwater beneath the site flows to the west or south west, generally consistent with the dip of the strata. Apart from the south western corner and a small area in the northern part of site, there is no evidence of previously worked coal seams within the footprint of the proposed coal extraction area. As a result, it is considered unlikely that groundwater flow beneath the majority of the site will be affected by the presence of underground workings. The strata present within the extraction area are dry. Whilst small volumes of groundwater may enter the workings via fractures and fissures in the mudstones on the northern and eastern walls of the extraction void, the groundwater catchment to the workings is very small and hence it is unlikely that significant volumes of groundwater will enter the workings from the sequence to be extracted.
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Groundwater is present in sandstone bands below the floor of the proposed coal extraction area. Two main sandstones have been identified, both of which contain groundwater confined under pressure by the overlying clay rich, Coal Measures sequence. The degree of confinement increases down dip. In the central and southern parts of the extraction area, the piezometric level in the upper sandstone unit is above the floor of the workings and there will be groundwater ingress to the deeper part of the excavation area. The piezometric level of the deeper Gellideg Rock is significantly below the floor of the proposed workings and hence groundwater in this unit will not enter the workings. It will be necessary to dewater the deeper part of the excavation to control groundwater ingress and maintain a dry operational area. Figure 8.1 shows a schematic hydrogeological conceptual site model of the proposed extraction area. There are no licensed or private groundwater abstractions in the area. The groundwater quality in the Coal Measures sequence is acidic and shows slightly elevated concentrations of various metals. Elevated iron and manganese levels have been recorded in many of the groundwater samples. Iron concentrations are below the UK Drinking Water Standard whereas all the samples exceed the standard for manganese. There are a number of ephemeral springs and seepages on the lower ground to the east and below the extraction area. It is considered that these are associated with runoff and shallow groundwater flow within the superficial deposits and the colliery spoil and not with groundwater in the Coal Measures. It is likely that these springs and seepages will be affected by the proposed coal workings.
Although the underlying Carboniferous Limestone is recognised as a sensitive principal aquifer, based on the hydrogeological conditions at the coal extraction site, it is concluded that there is no plausible linkage from the coal extraction area and the aquifer. Accordingly, it is concluded that the limestone aquifer is not at risk from the proposed development. The coal extraction area currently is drained by two ephemeral watercourses which flow in an easterly and south easterly direction. During the summer months, these watercourses are dry, consistent with the absence of groundwater discharge. Ditches on the site which flow to these watercourses show evidence of ochrous staining, consistent with acidic runoff. Colliery spoil will be deposited in a valley to the west of the coal extraction area. These operations have the potential to result in surface water runoff containing high suspended solids and possibly acidic drainage. It will be necessary to include measures in the scheme design to treat and control the runoff from the colliery spoil disposal area. Similar measures will be needed at the coal extraction area where materials will be excavated to form screening bunds on the eastern edge of the site. Acidity may be generated with the passage of water through pyritic goaf and this may be expressed by the precipitation of ochre at discharge points as iron oxidises in the presence of atmospheric oxygen. It is anticipated that the scheme will result in the storage, within the excavation, of incident rainfall in addition to the inflow of water from old workings or permeable horizons present in the high wall on the western and southern edges of the proposed opencast site. In the central and southern parts of the excavation area, there is the potential for the ingress of groundwater from the underlying Upper Sandstone unit. The potential entrainment of suspended solids within the site and dissolved species as a consequence of association with new/disturbed opencast backfill will need to be addressed in the water treatment system.
8.3 Conceptual Model for Contaminated Land The environmental liabilities associated with the scheme also include impacts on users of the site. A quantitative risk assessment has been carried out (Section 7.4), which identifies the principal aspects concerning the presence of minor ground contamination identified locally on the site and its likely impacts.
To assess the potential environmental impacts associated with the scheme development, a risk assessment has been undertaken using the source-pathway-receptor approach, promoted by DEFRA and the Environment Agency. For there to be an identifiable risk, not only must there be contaminants present on the site (source) i.e. contaminated ground but also there must be a receptor and a pathway which allows the source to impact on the receptor. All three elements must be present to form a
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contaminant linkage before there can be a potential risk to specific receptors. In accordance with standard practice, a conceptual model of the potential or actual contaminant linkages was developed for each of the two areas of the site to evaluate the likely impacts. The conceptual model of the site pertaining to contaminated land, and the impacts as a consequence of its presence, are largely focussed around the former Varteg Hill Colliery site and associated infrastructure. Based on the review of published and privately held data and the results of the ground investigation, the principal sources of contamination, likely receptors and the pathways by which contamination may reach the receptors have been identified below. 8.3.1 Sources The principal potential sources of contamination identified at the site are:
Colliery spoil arising from historical patch working across the site and modern opencast operations to the north, west and south containing elevated concentrations of soluble chemical species and acidity; Colliery spoil arising from underground mining operations tipped in and around Viponds Colliery Tips 527 and 528 containing elevated concentrations of soluble chemical species and acidity; Slightly elevated to elevated concentrations of lead, zinc and boron were identified at depth in Tip 528b. However, concentrations of soluble contaminants were low; Red shale or “red ash” arising from the spontaneous combustion of colliery spoil containing elevated concentrations of soluble chemical species and acidity; Slag derived from iron smelting operations on or near the site, used on site for railway track beds containing elevated concentrations of soluble chemical species, including B(a)P; Boiler ash, lubricants and oils originating from mechanised equipment used at the colliery and stored/maintained in colliery buildings containing elevated concentrations of chemical species and hydrocarbons; Cozalene stored on the site of the former colliery lighthouse; and, Contaminated ground in the vicinity of the former Varteg Hill Colliery, with elevated metals (copper and lead) and sulphate concentrations. However from soil analyses, it is considered that there is no evidence of widespread ground contamination in this part of the proposed coal extraction site. 8.3.2 Receptors The potential receptors that have been identified, which may be susceptible to contamination arising on or beneath the site include:
Members of the public living adjacent to the site; Tenants and users of the site; Personnel involved in the reclamation and coal recovery scheme; Carboniferous Limestone principal aquifer in the base of the Afon Llwyd; Controlled waters comprising the Cwm Ffrwd and Afon Llwyd and tributaries; Controlled waters comprising groundwater present in the Coal Measures. 8.3.3 Pathways The principal routes by which contaminants may impact on the identified receptors include:
Mobilisation in site run-off of soluble contaminants through disturbance and exposure of soils and spoil during excavation and coal extraction; Leaching of soluble contaminants present in the soils and spoil into groundwater, and; Inhalation of dust, dermal contact with, or ingestion of, contaminated soils.
An Assessment of the Impact of the Proposed Scheme on Controlled Waters
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9 An Assessment of the Impact of the Proposed Scheme on Controlled Waters
9.1 Hydrology and Hydrogeology From a review of the hydrogeological and hydrological conditions at the site, it is considered that measures will need to be included in the scheme design to manage groundwater and surface water in order to facilitate coal extraction and to minimise adverse environmental impacts.
There will be potential groundwater ingress to the proposed extraction area through:-
permeable horizons in the Coal Measures sequence within the extraction site; confined groundwater present in the sandstone units subcropping beneath the floor of the proposed coal extraction area. It is likely that significant groundwater ingress to the workings will be limited to the southern third of the site, where the piezometric level of the Upper Sandstone unit is up to 5m above the proposed floor of the workings. It is anticipated that in these areas of the site, dewatering will be required to maintain a dry operational area. Figure 9.1 shows the extent of the proposed workings where dewatering is likely to be required as a result of groundwater ingress; and,
former unrecorded coal workings. It is likely that ingress from such workings will be sporadic and short-lived following significant rainfall events. Based on an interpretation of the conceptual model, it is considered that the principal potential impacts of the proposed scheme on controlled waters are associated with:-
Ingress of groundwater to the extraction area; Impact of dewatering of the workings on groundwater level and flow; Impact of the workings on the springs east of the site; Impact of the workings on groundwater abstractions; Disruption of surface water drainage; and, Impact of contaminated drainage on groundwater and surface water quality. The main receptors potentially at risk from the development are:-
Groundwater in permeable units within the Coal Measures;
Local springs; and, The Afon Llwyd and Cwm Ffrwd. The assessment of the potential impacts of dewatering the coal extraction area has considered the issues identified in the EA Science Report SC040020/SR1, entitled ‘Hydrogeological impact appraisal for dewatering abstractions’ dated April 2007.
9.1.1 Ingress of groundwater to the extraction area Based on the results of the groundwater level monitoring carried out in the five boreholes drilled at the site in 2005, it is concluded that groundwater is present principally in sandstone units below the base of the proposed coal extraction area. Two main sandstone units have been identified – an Upper Sandstone which is present directly below the Five Feet/Gellideg seam and a deeper sandstone, the Gellideg Rock. Groundwater in both sandstone units is confined under pressure by overlying low permeability mudstones and coals.
The groundwater contours for the Gellideg Rock (Figure 6.10) show that the piezometric level is significantly below the floor of the proposed coal extraction area. Accordingly, it is concluded that groundwater in the Gellideg Rock will not enter the excavation for the opencast workings.
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The groundwater contours for the Upper Sandstone unit (Figure 6.9) show that in the deeper southern part of the excavation the piezometric level is above the floor of the proposed workings by up to 5m. In the absence of active groundwater control, there is a risk that heave of the base of the excavation may occur as the rocks above the Upper Sandstone progressively are excavated. This could result in the uncontrolled ingress of groundwater to the workings.
As the extraction site is the recharge area for the water bearing sandstones, which crop out on the western side of the Afon Llwyd valley and as groundwater flows to the south west consistent with the regional dip of the strata, it is considered, in the absence of any dewatering, that any significant groundwater inflows will be limited to the northern and eastern edges of the extraction void, along the strike of the strata. Calculations have been carried out to estimate the likely volume of groundwater which could enter the workings. If it is assumed that:- the Upper Sandstone unit is up to 5m thick; has a groundwater gradient of 1 in 7 (i); a width perpendicular to the direction of groundwater flow of 325m (W) across the site; the sandstone has a transmissivity (T) of 3-15m2/day (taken from the BGS Report WD/00/04 The physical properties of minor aquifers in England and Wales 2000). The volume of groundwater flow (Q) in the Upper Sandstone across the proposed coal extraction area is calculated using the Darcy equation:-
Q = T.i.W
as approximately 140m3/day to 700m3/day. 9.1.2 Impact of dewatering of the workings on groundwater flow Based on an appraisal of the results of groundwater level monitoring, it is concluded that groundwater in the Upper Sandstone unit, which is present at approximately 3m to 8m below the floor of the proposed coal extraction area, flows in a south westerly direction, generally consistent with the dip of the strata. To facilitate coal extraction in the southern part of the site, where the piezometric level is above the floor of the proposed workings, dewatering will be required. Dewatering of the excavation will result in a drawdown in the groundwater level. It is likely that the effects of dewatering will extend beyond the boundaries of the working area. There are no techniques accurately to determine the extent of the drawdown and the amount of drawdown caused by pumping from large excavations at varying distances from the dewatered area.
To maintain a dry operational area, it will be necessary to lower the piezometric level by up to 5m. This will be achieved through the construction of a series of ditches on the quarry floor connected to pumping sumps, from where the water will be abstracted. The sumps and ditches progressively will be lowered as the workings are deepened. During the early phases of working when the base of the excavation is above the piezometric surface of the Upper Sandstone, abstraction will be necessary largely to remove incident rainfall to the working area as runoff from the higher ground to the west will be intercepted and diverted around the excavation (Section 9.2). The site will be worked in a series of strips progressing in a northerly direction. To facilitate excavation, a series of benches will be excavated. To gain access to the lowest level of the workings in the south western part of the site, it is estimated that approximately 50% of the extraction area, approximately 7ha, will need to be opened. Based on this assumption and the rainfall records from the Cwmavon Reservoir station, it is calculated that it will be necessary to pump between 155m3/day (July) and 455m3/day (December) of water resulting from incident rainfall to maintain a dry operational area. There is no evidence of permanent groundwater in the strata present above the floor of the proposed workings and no evidence of former workings in the higher coal seams within the extraction area. Accordingly, it is considered unlikely that there will be any significant groundwater inflow to the upper levels of the workings. It is considered that impacts on groundwater flow will be limited to the effects of dewatering in the deeper parts of the workings in the south of the site.
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Whilst it is not possible accurately to predict the lateral extent of the effects of dewatering, it is likely that the dewatering will intercept the majority of the groundwater flow from the recharge area to the east and extend down hydraulic gradient in the confined zone, locally reversing the groundwater gradient. It is estimated that the volume of groundwater flow to the excavation from recharge to the east is between 140m3/day and 700m3/day.
As the hydraulic gradient in the Upper Sandstone is 1 in 7 to the south west, it is interpolated based on a piezometric head of 13m in the southern part of the site that approximately 90m down hydraulic gradient of the site, the natural piezometric level will be below that of the floor of the proposed workings. Therefore, it is concluded that the effects of dewatering will extend no more than approximately 100m down hydraulic gradient of the southern and western edges of the site. In order to estimate the likely groundwater inflow to the workings due to the dewatering, it is assumed that inflow from the up gradient half of the workings is the natural groundwater flow of 140m3/day to 700m3/day. If it is assumed that the effects down gradient are limited to a distance of 100m from the workings, the estimated groundwater inflow (Q) can be calculated using a simplified half-circle with a radius of 100m and the equation:- Q = T.i.W, where T = transmissivity (3-15m2/day) i = imposed hydraulic gradient, initially 13/100
W = width (perimeter) of aquifer (2r/2) The maximum groundwater inflow to the workings, based on the above assumptions is between approximately 120m 3/day to 610m3/day plus the natural recharge of between 140m3/day and 700m3/day. As the dewatering proceeds, the hydraulic gradient will reduce, potentially to zero. For the purpose of the calculations, a final hydraulic gradient of 0.01 is assumed. Using an hydraulic gradient of 0.01, the estimated groundwater inflow is between approximately 10m3/day and 50m3/day plus natural recharge. Based on this simplified approach, the estimated volume of groundwater ingress to the workings as a result of dewatering is between approximately 150m3/day and 750m3/day. The dewatering will impose a cone of depression on the piezometric surface, although currently it is not possible accurately to predict the extent of this effect. To determine the effect of the dewatering on the piezometric level and the local direction of groundwater flow, a groundwater level monitoring scheme will be implemented (Section 9.6). 9.1.3 Impact of the workings on the springs to the east of the site A number of small springs and seepages are present to the east of the coal extraction area on the lower ground below the extraction site. The majority of the water issues subsequently soak away into the hummocky ground further to the east. Observations of the state of these issues during 2005, 2006 and 2014 indicate that flows generally are low and that the issues frequently dry up during dry periods consistent with the absence of any significant groundwater flow to the east. Based on the results of the groundwater level monitoring in the two piezometers in borehole BH4 in the vicinity of the springs, it is concluded that the springs are not in hydraulic continuity with groundwater in the sandstone units present below the floor of the proposed workings as the recorded groundwater level is more than 5m below the level of the spring discharge. The source of the springs and seepages is attributed to shallow water flow through the colliery spoil and superficial deposits immediately above and to the west of the issues. The proposed coal extraction operations will affect much of the catchment to the springs and seepages either through intercepting surface water runoff which provides recharge to the springs or by removal of the colliery spoil on the coal extraction area. The impact will be temporary and limited to the period of coal extraction. It is considered that the springs and seepages have negligible hydrological importance. Accordingly, any impacts will be of little significance and no mitigation measures will be required.
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9.1.4 Impact of the workings on groundwater abstractions It is likely that the dewatering necessary to facilitate coal extraction in the proposed workings locally will affect groundwater levels and flow. It is interpreted that any effects will be limited to the immediate area of the site and will not extend significant distances from the extraction area. As there are no licensed or private groundwater abstractions within 5km of the site, it is concluded that the proposed coal extraction scheme will have no impact on groundwater abstractions. 9.1.5 Disruption of surface water drainage and impact of contaminated drainage on groundwater and surface water quality The opencast workings will disrupt the existing pattern of surface water drainage and also possibly locally groundwater levels and flow, principally when dewatering is needed to control groundwater inflows to the southern part of the extraction area. Surface water management controls will be implemented to minimise the impact on runoff from the site. Currently runoff from the site drains in an easterly direction by channels constructed to convey water to the Afon Llwyd. Flow in these channels is ephemeral, consistent with the absence of groundwater discharges to support the watercourses during periods of dry weather.
Surface water inflows to the extraction area will be restricted to rainfall incident to the workings and to surface water runoff from the surrounding higher ground, principally to the west. Runoff from the higher ground will be intercepted in cut-off ditches above the extraction area and directed to water treatment areas for settlement located to the north east and south east of the workings prior to being discharged to the existing drainage channels and thence to the Afon Llwyd. Water accumulating in the extraction void also will be pumped to the water treatment areas. Accordingly, incident rainfall and runoff from the site will continue to drain to the Afon Llwyd, thereby minimising any impacts on surface water flow. There is a potential that any water entering the extraction void, particularly through former coal workings, may be contaminated through the dissolution of metals by acidic groundwater. By utilising the water treatment areas, it will be possible if and when necessary, to treat the water to an acceptable quality prior to discharge. The water treatment areas also will act as settlement facilities to reduce suspended solids concentrations in the runoff water, which may increase due to incident rainfall; runoff from stripped soil areas; and, to other general site operations.
9.2 Proposed drainage strategy The proposed drainage strategy for the coal extraction scheme incorporates the following principles for implementation:- Drainage to areas disturbed by the opencast workings will be intercepted and diverted to receive attenuation and treatment. Rainfall runoff from undisturbed areas above the coal extraction area will be diverted around the excavation area for recharge into areas downstream of the working area. Continuation of attenuation and treatment after restoration until vegetation ground cover is established.
An integrated water treatment system design will be required that incorporates the following considerations:- Storm return period level of service. Flow transfer pumping rates and balancing sump volumes. Control of flow velocities to prevent scour/lining of watercourses/silt mobilisation and settlement. Control of particulate settlement in sumps and lagoons. Potential treatment of acid mine drainage. Control of discharged water quality – contact and retention times. Desludging or flocculant removal and disposal/recycling. Oil and scum removal. Process plant water use, including vehicle wash down and effluent treatment.
The duration for coal recovery is expected to be 2.5 years. The first year will include the storage and restoration of the spoil area at Mynydd Farteg Fach. The total coal extraction and restoration operations are estimated to be completed in approximately four years, following which there will be an aftercare period of five years. It is proposed to collect and divert run-off from drainage
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from the catchment above the coal extraction area to avoid flooding and contamination from the opencast activities, using open ditches and carrier drains and discharging to an infiltration trench below the works area. This will provide flow attenuation, dissipating accentuated peak flows resulting from shorter times of concentration. This process also will recharge surface water run-off to the sensitive ecologically important areas north of the extraction area maintaining groundwater moisture content levels. Storm overflows above the infiltration trench design capacity will discharge to the adjacent ditch. The extraction method will be by the exposure and excavation of progressive dip-cut cells minimising the extent of the cut face and accordingly potential volumes of groundwater ingress. Immediate coal extraction area drainage will collect at the toe of the cut face due to the dip of the strata and will be pumped to the nearest water treatment area (WTA) lagoon for the settlement of suspended solids and chemical/pH treatment. Water quality monitoring of the spring and Stable House Watercourse adit to the east of the working areas has confirmed the presence of acidic water with elevated levels of iron and manganese characteristic of Acid Mine Drainage (AMD). Water emerging from overburden spoil mounds may require treatment due to the potential generation of (AMD) from old coal deposits or ironstone waste containing high levels of sulphur. The new overburden will be disturbed spoil and percolating surface water has the potential to oxidise mobilised pyrite thus generating AMD. Initially, acid levels from percolated run-off may be high. The potential for AMD production can be reduced by restricting moisture and air flows through the spoil by controlled grading and compaction.
Overland surface water drainage from the extended overburden mound above Salisbury Terrace will be intercepted by a cut-off ditch, which directs water southwards to the new south eastern WTA. The cut-off ditch will intercept the ephemeral watercourses which currently drain the existing and extended spoil mounds. Drainage from the proposed overburden disposal area within Mynydd Farteg Fach will require attenuation and settlement and possibly chemical treatment. It is proposed that storm water run-off will be collected immediately downstream of the existing culvert and temporarily diverted around Varteg Hill via a pipe or ditch following the line of the rerouted farm access track to the south eastern WTA for treatment. This will avoid the provision of an isolated chemical treatment process in the Cwm Ffrwd catchment and reduce the potential risk of contamination arising from any accidental spillages of fuel or chemicals. This drainage ditch temporarily will increase the catchment area contributing to the proposed south eastern WTA and associated outfalls. Additional attenuation may be required as a result, but this strategy will provide a benefit by reducing flows that currently are causing scour problems downstream along the Cwm Ffrwd and reducing flows through the Golynos Watercourse for the duration of the restoration. Subject to formal written approval from Torfaen CBC and NRW, there is potential to provide permanent storm attenuation at this site by impounding storm flows in the form of a water feature as part of the restoration process. This will assist in reducing peak storm flows discharging to the Cwm Ffrwd. An impounding licence will be needed. Run-off generated from the area to the north of the site currently is collected in the ditch on the western side of Varteg Road and flows southwards crossing under the road via the 1200mm diameter culvert. The facilities area is located within this catchment and storm run-off from these areas will require isolation and diversion using cut-off ditches draining to the eastern WTA. This proposal will reduce the existing catchment area reducing peak flows down this sensitive watercourse flowing east to the Afon Llwyd.
9.3 Water treatment areas The proposed water treatment areas (WTA) strategically are placed for collection of run-off and either discharge to the existing available pipe crossings beneath the B4246 Varteg Road to the east and south east, or discharge overland to the Cwm Ffrwd catchment to the west.
The proposed WTA shown on the initial draft layout plan to the south east conflicted with an area of ecological interest identified during a subsequent ecological survey carried out as part of the Environmental Impact Assessment. It is proposed that the WTA is relocated within the site boundary adjacent to the new farm access track road junction.
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Surface water run-off contributing areas to the proposed individual WTAs are summarised in Table 9.1. Retention periods and treatment measures in the WTAs will be designed to achieve the conditions placed on any Consents to Discharge/Environmental Permits issued by NRW.
Table 9.1 Catchment areas of new Water Treatment Areas.
CONTRIBUTING AREAS
Catchment Area Estimated infiltration ( factor (%) h a )
Intercepted run-off areas from undisturbed areas not 18.2 30 requiring treatment
Eastern WTA
Spoil areas 4.2 30
Facilities area 1.4 30
South Eastern WTA
Extraction area 11.6 30
Spoil areas 2.7 30
Spoil areas (Mynydd Farteg Fach) 26.7 30
NRW requires up to four months to process an application for a Permit to Discharge. Permits will be required for both treated effluent and storm overflow discharges. NRW will require consent applications and subsequent permits for discharge, land drainage, abstraction and impounding licences prior to the commencement of the site operations. The south eastern WTA will discharge to the existing culverts crossing the road or by the provision of a connecting pipe to the 15 inch diameter culvert identified by Torfaen CBC. There is an area of land between the WTA and the culvert which is believed to be owned by Torfaen CBC and can accommodate a pipeline route from the WTA. The sewer will need to be located and surveyed and may require jetting and a CCTV survey to ensure that it is capable of carrying the flows. An easement agreement from Torfaen CBC will be required.
9.4 Drainage-related site activities Foul drainage from the facilities area will discharge to an on-site holding tank. The tank will be emptied periodically and the effluent will be tankered away for treatment.
Oil and chemical storage and delivery and refuelling operations of site plant will be in accordance with the EA Pollution Prevention Guidelines (PPG2).
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A methodology for the containment of accidental spillages of process water will be provided and Emergency Response Procedures will be developed in the event of a major contaminant incident. Protective fencing will be placed around identified ecologically sensitive sites.
Surface water flowpaths through the site during periods of flooding will be considered when laying out the facilities area.
9.5 Licensing Any damming or culverting of watercourses will require the prior formal written approval of Torfaen CBC under the terms of the Public Health Act 1936 and the prior formal consent of NRW under the terms of the Land Drainage Act 1991/Water Resources Act 1991. NRW seeks to avoid culverting and its consent for such works normally will not be granted except for access crossings. Under the Water Resources Act 1991, the prior formal written consent of NRW normally is required for any discharge of sewage or trade effluent into controlled waters or for any discharge of sewage or trade effluent from buildings or fixed plant into or onto ground or into waters which are not controlled waters. Such consent may be withheld. Under the terms of the Water Resources Act 1991, an Impoundment Licence may be required from NRW for the impounding of any watercourse, ditch or stream and an abstraction licence may be required for the abstraction of water from a controlled water or use other than dewatering of engineering works, which includes mineral workings. However, subject to the progress of legislation, a transfer licence may be required for the dewatering of the coal extraction area.
9.6 Monitoring To determine the impact of the proposed coal extraction operations on controlled waters, a scheme of environmental monitoring will be implemented prior to, during and following the coal extraction operations and restoration works. To determine the impact on groundwater level and flow, groundwater levels will be monitored in the existing boreholes on the site. Boreholes BH3 and V1/3 are located within the coal extraction area and will be lost. Boreholes BH1, BH2, BH4 and BH5 are located just outside of the coal extraction area and will continue to provide groundwater monitoring facilities. It is proposed that the groundwater level in the monitoring boreholes is monitored monthly during the period of the site operations and restoration. Surface water quality will be recorded on a quarterly basis. Samples will be taken from the two ephemeral watercourses which cross the site and which will receive discharge from the two proposed WTAs, subject to the requirements of Environmental Permits to Discharge. The proposed sampling locations are shown on Figure 9.2 and the principles of the proposed monitoring are provided at Appendix K. In addition, samples will be collected weekly from the sump in the base of the workings to assist in identifying the need for any treatment in the WTAs. The details of the final proposed monitoring scheme will be agreed in advance with NRW.
An Assessment of the Impact of the Proposed Scheme on Human Health
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10 An Assessment of the Impact of the Proposed Scheme on Human Health
10.1 Contaminated Ground No extensive areas of contaminated ground have been identified in the proposed coal extraction area. Locally elevated concentrations of lead, copper and zinc and hydrocarbons have been identified in the vicinity of the former Varteg Hill Colliery and in spoil tip 528b. Leachate tests showed that potential contaminants generally are present in immobile forms.
A quantitative risk assessment of the soils analysis results showed that a number of potential contaminant linkages have been identified. However, due to the absence of any significant sources of ground contamination and, in particular, the short period of exposure to any contaminants, it is considered unlikely that many, if not all, of these linkages will be realised. Table 10.1 sets out the potential level of risk/harm associated with the existing and probable future ground conditions at the site and land uses of adjacent areas in respect of ground contamination. The risks identified are considered to be potential risks only. For simplicity, the potential risks are designated into four levels/categories:
Very low risk – contaminants unlikely to be present.
Low risk – contaminants may be present at concentrations that are likely to have no unacceptable impact on identified receptors. Action unlikely to be needed.
Moderate risk – contaminants may be present at concentrations that are likely to have an unacceptable impact on identified receptors. Action may be needed.
High risk – contaminants may be present at concentrations that are very likely to have an unacceptable impact on identified receptors. Action likely to be needed.
Levels of contaminants in dusts generated during site works are likely to be low. For example, lead would be a contaminant of concern in airborne dusts. The highest lead concentration recorded in the soil is 1075mg/kg. At this concentration, a very high total dust level of 10mg/m3 would contain only approximately 0.001mg/m3 of lead, less than one tenth of the 8 hour time- weighted, average maximum exposure limit (MEL) given by the Health and Safety Executive. At a more likely total dust concentration of 1mg/m3, the worst case lead concentration would be less than one hundredth of the MEL. The actual concentrations of lead in dust generated during the excavation of made ground/spoil is likely to be much less than this value.
10.2 Mitigation Based on the assessment of the results of the soils analyses, it is concluded that the levels of ground contamination identified at the site do not present a significant risk to human health. It is considered that the implementation of normal site hygiene measures and the use of appropriate PPE during the coal extraction and site restoration periods will mitigate any potential adverse impacts and that no specific remedial measures are necessary to protect human health. In the unlikely event that areas of heavily contaminated soils are identified, measures will need to be adopted to reduce any adverse impacts on either human health or controlled waters. The materials should be isolated and stockpiled. Samples of the materials should be submitted for geochemical testing to determine their pollution potential and an appropriate remediation scheme prepared and agreed with Torfaen CBC.
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Capabilities on project: Environment Table 10.1: Impact Assessment and Proposed Mitigation Measures
Potential Contaminant Potential Pathway Receptors Present Level of Risk Mitigation/ Resulting Level of Residual Risk
Locally elevated lead Inhalation of dust, dermal Site operatives Low as isolated values in Implement good hygiene concentration in soils contact with, or ingestion. former mine compound area practices, utilise and in colliery spoil tip. appropriate personal Limited period of exposure to protection equipment potential contaminants. and implement measures to reduce dust generation during earthworks. Spoil tip materials to be moved to remote ‘second area ’for restoration. Residual risk level – Very low.
Locally elevated lead Inhalation of dust, dermal Members of the public Very low as isolated values in Area of workings will be concentration in soils contact with, or ingestion. adjacent to the site former mine compound area isolated from public. and in colliery spoil tip. Very Probable low availability limited exposure to potential of lead after ‘hot spot’ contaminants. excavation and replacement in remote ‘second area’. Spoil tip materials to be moved to remote ‘second area ’for restoration. Residual risk level – Very low.
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Capabilities on project: Environment Potential Contaminant Potential Pathway Receptors Present Level of Risk Mitigation/ Resulting Level of Residual Risk
On site elevated heavy Leaching from colliery Groundwater Low as the leachability test None. metal compounds waste and mobilisation in results do not show any present locally in colliery site run-off of soluble significant contaminant levels spoil contaminants through consistent with low mobility of Residual risk level – disturbance and exposure contaminants, in all but Very low. of soils and colliery spoil softest waters. The during coaling operations. groundwater underneath the site is not used for potable supplies.
On site elevated heavy Contaminated runoff from Surface water – Cwm Low as the leachability test All water draining from metal compounds excavation/mobilisation in Ffrwd and Afon Llwyd results do not show any the site will be treated present locally in site run-off of soluble and tributaries significant contaminant levels prior to discharge to colliery spoil contaminants through consistent with low mobility of reduce any chemical disturbance and exposure contaminants, in all but the contamination and of soils and colliery spoil softest of waters. suspended solids to during coaling operations. acceptable levels to comply with all Environmental Permits issued by the NRW Residual risk level – Very low.
AECOM Varteg Hill Reclamation & Coal Recovery Scheme, Blaenavon, South Wales 65
Capabilities on project: Environment Potential Contaminant Potential Pathway Receptors Present Level of Risk Mitigation/ Resulting Level of Residual Risk
Slightly elevated Leaching from Groundwater – Coal Low as the leachability test None. hydrocarbon levels in contaminated soils and Measures and results do not show any soils at the former mobilisation in site run-off Carboniferous significant contaminant levels Lighthouse, mine of hydrocarbons through Limestone consistent with low mobility of compound and mineral disturbance and exposure contaminants. Residual risk level – track of soils and colliery spoil No plausible linkage with Very low. during coaling operations. limestone aquifer.
Slightly elevated Contaminated runoff from Surface water – Cwm Low as the leachability test All water draining from hydrocarbon levels in excavation and mobilisation Ffrwd and Afon Llwyd results do not show any the site will be treated, if soils at the former in site run-off of soluble and tributaries significant contaminant levels necessary, prior to Lighthouse, mine contaminants through consistent with low mobility of discharge to reduce any compound and mineral disturbance and exposure contaminants. chemical contamination track of soils and colliery spoil and suspended solids to during coaling operations. acceptable levels to comply with all Environmental Permits issued by NRW
Residual risk level - Low
Conclusions and Recommendations
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Capabilities on project: Environment
11 Conclusions and Recommendations
11.1 Summary The principal purpose of this report is to provide additional supporting information for the Environmental Statement, which was submitted originally in 2009 as part of the application for planning permission for the proposed reclamation and opencast coal workings in the vicinity of Varteg Hill Colliery. The report has been updated to address comments made by Torfaen CBC and the suggested planning conditions specified by the Environment Agency in their letter of 18 November 2009 and comments by NRW in their letter of July 2014. The report includes the results of the site investigation works, laboratory analyses of soil and water samples, groundwater level and quality monitoring and conceptual model validation to address impacts on controlled waters and human health. Ground investigation works including 30 trial pits and 6 boreholes were carried out between 25 July and 4 August 2005. Soil samples were scheduled for geochemical analyses. Three soil samples (old spoil tip materials and made ground from the mine compound) were scheduled for leachability tests. A series of groundwater and surface water samples subsequently was collected and analysed. In addition to the existing two old piezometers (V1/3a and V1/3b), eight piezometers were installed based on the findings of geological logging and geophysical investigation results. Three piezometers (BH2a, BH4b and BH5) were equipped with data-loggers to provide a continuous record of changes in the groundwater level.
11.2 Conclusions Based on the results of the ground investigation, subsequent groundwater level and quality monitoring and a review of historical information regarding the site, the following conclusions can be drawn:-
The proposed opencast coal site will be excavated into Coal Measures strata, principally mudstone with sub-ordinate siltstone and sandstone and coal seams. Extensive and much thicker sandstone bands are present beneath the proposed floor of the coal extraction area. There is evidence of former workings, mainly in the Seven Feet (Meadow Vein) and in the Five Feet/Gellideg seams. The Coal Measures strata is overlain by a layer of made ground, typically less than 4m thick. In the southern part of the site, there are a number of colliery spoil tips in which the spoil is approximately 16m thick. Groundwater is present at the site principally in the sandstone bands below the floor of the workings. There is no evidence of significant groundwater in the upper levels of the sequence. The groundwater in the sandstone bands is confined under pressure. In the southern part of the proposed workings the piezometric surface is above the floor of the proposed workings. The depth to groundwater varies significantly across the site from approximately 4m on the eastern edge to approximately 65m on the higher ground to the west. There is evidence that the groundwater level fluctuates significantly over a short time period in a number of the boreholes. The mechanism for the significant changes in the groundwater level is unclear but may be the result of water entering the groundwater system through former ironstone and coal workings which provide preferential and rapid flow paths for groundwater recharge following heavy rainfall. It is considered that groundwater in the two principal sandstone units beneath the floor of the proposed workings flows in a south westerly and westerly direction, consistent with the dip of the strata. There is no direct hydraulic continuity between the main two water-bearing horizons. Minor springs and seepages are present to the east of the site on the upper valley sides of the Afon Llwyd. It is likely that these are associated either with flow from old adits, intermittent flow through fractures in the unsaturated zone and/or minor groundwater discharge from the overburden and superficial deposits. The Carboniferous limestone outcrops in the floor of the Afon Llwyd. The limestone is a principal aquifer. However, it is concluded that the aquifer is not in hydraulic continuity with the groundwater in the Coal Measures on the site and hence there is no plausible contaminant linkage, which could cause any impact on the groundwater in the aquifer.
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Capabilities on project: Environment
Based on the results of the soil analyses, there is no evidence of significant or widespread ground contamination at the proposed opencast site, which would place any constraint on the proposed workings. Exposure by site operatives to any contamination will be limited to a short period. Locally elevated metal concentrations (lead, copper and zinc) are associated with the made ground in the vicinity of the former Varteg Hill Colliery and at depth in spoil tip 528b. However, leachability tests show that most contaminants are not readily soluble. B(a)P was recorded above the limit of detection in 22 out of the 28 samples analysed. An elevated concentration above the C4SL value for a public open space end use was recorded in one sample. There is limited potential for combustion of the made ground and colliery spoil from the presence of coal fragments. A number of potential contaminant linkages have been identified. However, levels of ground contamination generally are low. It is considered that the levels of ground contamination recorded do not present a significant risk to either human health or to controlled waters. The existing ground conditions do not place a constraint on the proposed development and it is considered that no remedial measures are required in order to facilitate the development. Acid base accounting results show that six soil samples have negative values indicating the potential for the generation of acidic runoff, consistent with ochrous deposits on the bed of ephemeral ditches which cross the site. The results of the leachability tests of old spoil materials show no evidence of acidic water. The water quality of springs and discharge from an adit to the east of the site is acidic with elevated concentrations of iron and manganese consistent with acidic mine drainage. The groundwater samples analysed showed that three parameters are present in concentrations in excess of their respective EQS. Copper, zinc and TPH values slightly exceed the relevant levels. The groundwater is not acidic. It will be necessary to control groundwater ingress to the void, principally in the southern part of the extraction area where confined groundwater inflow from the Upper Sandstone unit beneath the floor of the workings is anticipated. All water pumped from the extraction area, consisting of incident rainfall, local surface water inflows and groundwater inflows including any potentially contaminated water from former coal workings will be pumped to water treatment areas on site prior to discharge to existing ditches and thence to the Afon Llwyd, subject to an environmental permit. The water treatment areas will provide an opportunity for the settlement of suspended solids and for any chemical treatment, such as pH adjustment, which may be required to ensure compliance with the conditions of the Permits to Discharge. It is considered that the flows to the springs to the east of the site will be adversely affected by the proposed opencast workings. The impact will be limited to the period of coal extraction. With appropriate treatment of pumped water, it is concluded that the proposed opencast coal workings will have no significant adverse impacts on groundwater or surface water flow or quality.
11.3 Recommendations 1. There is potential for the localised disturbance of ‘hot spots’ of contaminated ground. To minimise any associated risks, good site hygiene measures should be adopted and appropriate personal protective equipment used. Proposals should be prepared in association with Torfaen CBC to manage contaminated soils in the event that areas of unexpectedly high contamination are discovered. Measures also should be implemented to reduce dust generation during site operations. 2. The two water treatment areas on the eastern side of the site should be designed to facilitate, if necessary, treatment of low levels of contamination in the receiving waters from the site in order to comply with Environmental Permits to Discharge. 3. A programme of groundwater and surface water monitoring should be implemented as part of the operations at the site in discussion with NRW. Details of the proposed groundwater and surface water monitoring scheme are provided at Appendix K.