7. HYDROGEOLOGY, HYDROLOGY AND DRAINAGEplanapps.torfaen.gov.uk/Varteg/Documents/Volume 2/ES... ·...

4339/1/ARM/caj Environmental Statement Harmers Limited Glamorgan Power November 2014 51 Varteg Hill

7. HYDROGEOLOGY, HYDROLOGY AND DRAINAGE

7.1 Introduction

7.1.1 A preliminary assessment of the hydrogeology of the site and its environs was made in order to appraise the constraints on and potential impacts of the coal recovery project on the local hydrogeological environment and to consider mitigation measures where appropriate.

7.1. Background information has been obtained from the “Reserves Assessment” (Item 12 ES Documents) which includes appendices on detailed geology and mining history and the “Supplementary Reserves Assessment” (Item 13 ES Documents) both produced by Blandford Consulting.; the report produced by Sir William Halcrow and Partners on “The Investigation into the Security of Tips 527 and 528” (Item 11) and British Coal historical mine plans. Published groundwater vulnerability maps and geological sheets covering the locality have been referred to and a site reconnaissance visit was made on 20th August 2003 to inspect the ground, drainage network, spoil tips and water features. A further visit was made to the site in order to carry out a comprehensive water features survey during February 2004, followed by a further visit in August 2014 to identify any changes in the surface water network.

7.2 Purpose of Assessment

7.2.1 The purpose of this assessment is to identify the likely impacts of the proposals on the groundwater environment. The proposals include for the removal of existing spoil tips 527 and 528 to the valley beneath Mynydd Farteg Fach and the recovery of shallow remnant coal by opencast dip-cut techniques. This assessment identifies groundwater features which may be affected by the proposals, appraises how these may be affected and, where applicable, proposes measures to monitor or mitigate the impacts.

7.2.2 In addition, the assessment identifies the hydrogeological constraints on the development proposals involving the recovery of shallow remnant coal and the remediation of the site through relocation of the current spoil tips and restoration of the mining excavation.

7.3 Hydrogeology 7.3.1 The Coal Measures are classified as a Secondary A aquifer for the purposes of

groundwater vulnerability 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 minor aquifer with an unclassified soil risk, resulting from the presence on the site of made ground arising from the former mining activities associated with the area.

7.3.2 The Castell Coch Limestone and other units of Dinantian and Visean age cropping out between the limestone and the Coal Measures are classified as a


principal aquifer of regional significance in regard to water supplies. The ground to the east of the site forming the steep valley of the Afon Llwyd comprises these strata overlain by thin granular soils and is shown as a having a high groundwater vulnerability due to the inability of these soils to adsorb contaminants.

7.3.3 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.

7.3.4 The Gellideg Rock sandstone beneath the basal seam of the OCCS is associated with a number of surface springs, although precise identification of supported springs on or near the site during the site visits was not possible.

7.3.5 Further information on the sandstone unit beneath the Garw seam has not been researched, although it is has a significant outcrop between the proposed opencast site and the Varteg Road. The Blandford Consulting report indicates that this sandstone is lenticular and spatially inconsistent. It is likely that groundwater in the sandstone is confined beneath the proposed opencast site and that locally the piezometric head is above the floor of the workings. Subject to the level of the water table / piezometric level, discharges may arise to the east of the site, surface water from the site may permeate into the sandstone subcrop but major groundwater ingresses to the excavation are considered unlikely.

7.3.6 Limited historical water level data between March 1978 and June 1979 have been acquired that pertain to either solid strata or to the superficial deposits/colliery spoil tips. These data were presented in Appendix F1 of a report by Halcrow Limited. The data indicate that groundwater was present within the colliery spoil tips 527 and 528 (piezometers V1 1b and V1 2a) and that negligible groundwater was present in those piezometers installed in the Lower Nine Feet and Yard (Bute) seams (piezometers V1 3a and V1 3b). Water within these latter piezometers is considered likely to represent nuisance water resulting from condensation or leakage of borehole casing and unrelated to local groundwater conditions. Groundwater was reported in piezometer V1 1a also set in the Yard (Bute) seam, indicating a maximum head of 365.84mAOD at this location, 1.88m above the base of the borehole. Additionally, the presence of springs, sinks and watercourses may provide a guide to likely water tables / piezometric levels.

7.3.7 Under natural conditions it is likely 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. Under these conditions the natural groundwater flow directions may have been affected and groundwater movement may be controlled by collapsed ground related to the presence of abandoned workings, remnant mine roadways or drainage adits.


7.3.8 Numerous ephemeral springs and sinks have been identified to the immediate east of the colliery spoil tips on the site. Many of these are likely to be related to variations in the thickness of older colliery spoil deposits and the variably thin superficial deposits in these areas, but also may be related to intermittent water discharges from former adits, both recorded and unrecorded, intact or collapsed, accessing the Gellideg seam, Garw seam or ironstone beds.

7.3.9 A persistent water issue was identified in the vicinity of “Stable Houses” at approximate grid reference 326290mE, 205930mN. This correlates with the approximate location of an adit indicated on historical plans and the inferred outcrop of the Garw seam/top of the underlying sandstone/base of the Garw seam roof sandstone, implying both that the spring may be fed by groundwater emanating from either sandstone formation and that the groundwater in the sandstones may be fully confined beneath the site.

7.3.10 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 limestones are in hydraulic continuity with the river and that exchanges of groundwater and surface water occur between the river and this aquifer.

7.3.11 The nearest licensed groundwater abstraction is 5km to the north east, set within the Devonian Senni Beds sandstones and conglomerates, beyond the zone of influence of activities at the proposed opencast site. There are no records of private water supplies in the vicinity of the application site.

7.3.12 A ‘well’ marked to the south of Tip 528b on an old British Coal Tip Plan is likely to comprise either a water well as indicated, penetrating the potentially water-bearing sandstone beneath the project sequence, either above or below the Garw seam or an ancient shaft into ironstone workings. It was not possible to locate this feature during the site inspections.

7.4 Hydrology and Drainage

7.4.1 The site is divided into two different catchment areas; the extraction and facilities site on the eastern part of the site and the western part of the site which is a shallow valley consisting of opencast backfill material. The proposed coal extraction total area is approximately 11.6 ha.

7.4.2 The proposed coal extraction site lies within the eastern slopes of Varteg Hill and is near the top of the Cwm Llwyd drainage catchment where the watershed runs north –south along the ridge of Varteg Hill and then northwest to Coity Mountain. The Afon Llwyd is approximately 130m below the base of the proposed site and 600m to the east and flows southwards from Blaenavon through Abersychan and Pontypool to the south.

7.4.3 Within the site boundary the catchment falls from 445m above Ordnance Datum (AOD) in the west at the ridge of Varteg Hill to 365m AOD at the base of the workings in a distance of approximately 400m, providing an average ground slope of 1 in 5.

7.4.4 As part of the scheme overburden spoil will be deposited in an area to the west of Varteg Hill at Mynydd Farteg Fach which forms the south eastern slopes of Coity Mountain. This disposal area lies within the Nant Ffrwd catchment


which sources surface water run-off from the south western slopes of Coity Mountain and flows south east to the confluence with the Afon Llwyd approximately 2.5km downstream in Abersychan.

7.4.5 Inspection of the Environment Agency for Wales website data identified the following:-

• No indicative areas of flooding within the immediate site surrounds. The nearest indicative areas that are shown are in the Afon Llwyd river corridor approximately 100m below the Varteg Road.

• Fluvial quality monitoring in Blaenavon, Abersychan and Pontypool.

7.5 Existing Drainage 7.5.1 The site was visited in August 2003 and in August 2014. Both visits

following prolonged dry spells of weather and only limited surface water features persisted. It is considered likely that only perennial groundwater discharges and surface water features would be expected to remain at this stage and that incidental, ephemeral surface water discharges associated with runoff after heavy rainfall would not be expected to be present. Anecdotal evidence from a local farmer working ground south of Salisbury Terrace indicates that rainfall incident to the site results in rapid short-lived run-off.

7.5.2 The pathways of a number of streams and ditches/drains were identified during the site visits, but most were dry. The beds of these watercourses were mostly free of vegetation or mucilage indicating likely poor quality discharges or an absence of regular flow. No ochreous staining was observed.

7.5.3 A number of ephemeral springs discharge from the spoil heaps within the proposed OCCS. These support transitory watercourses flowing towards sinks likely to be set within older low lying hummocky spoil to the east and southeast of the site forming localised marsh/mire areas. Denser vegetation and more evidence of wildlife are found in these areas. Small ephemeral ponds formed within hummocky spoil and former excavations create local habitats around the southeast extremities of the object site. There are no positive outfalls from these ponds and flows dissipate to sinks or ditches adjacent to the road.

7.5.4 Existing spoil mounds (tips 527 and 528 A and B) lie on the eastern side of Varteg Hill. Surface water run-off flows off Varteg Hill filtering through these spoil heaps and site inspection reveals small amounts of ochrous deposits in the eroded gullies. Disturbance of these is likely to result in the generation of Acidic Mine Drainage (AMD).

7.5.5 The proposed spoil tip location within Mynydd Farteg Fach currently comprises a natural valley overlain by spoil from historical workings (the Waun Hoskyn OCCS). A farm access track extends along an old railway that obscures the mouth of the valley thus forming a basin. A 600mm diameter culvert runs under the embankment permitting run-off to flow to Cwm Ffrwd. At the time of the site visit in August 2014, there was no flow from the culvert. Evidence from historical maps identifies that surface water run-off


did flow directly southwards, but this has since been diverted to discharge higher up the Nant Ffrwd catchment to the west during more recent workings. Discussions with the Council identifies that scouring occurs downstream in this catchment and is therefore sensitive in relation to flow routeing. The Nant Ffrwd flows 1.5 to 2km downstream through the Golynos Watercourse which is a manmade culvert.

7.5.6 A spring identified east of Tip 528B at the southern end of the proposed overburden dump, near “Stable Houses”, was flowing and supported a healthy mucilage. On both visits, the flow rate was too low to measure and whilst it emerged between sandstone boulders, it is not certain whether the issue is from sandstone above the Garw seam or from a collapsed adit into the Gellideg seam.

7.5.7 The existing topography of the extraction site and surrounding area dictates natural surface water run-off to generally flow from west to east. The B4246 Varteg Road runs north–south through Varteg and forms a barrier to overland drainage that flows from the site to the Afon Llwyd valley. Information from Torfaen County Borough Council (TCBC) and visual investigation indicates that there are culverts crossing the road at strategic positions along Varteg Road and these vary greatly in size, capacity and condition.

7.5.8 The site is drained by a number of small watercourses ultimately converging with the Afon Llwyd in the deeply incised valley to the east. The quality of the Afon Llwyd is monitored by the Environment Agency as part of their General Quality Assessment Scheme. The nearest monitoring sites are at Blaenavon, 2km to the north at NGR 326090,208085 and Abersychan 2.2km to the south at NGR 327190, 203885.

7.5.9 As it is considered likely that the site is characterised by rapid runoff, it is likely that discharges from the immediate site will contain high suspended solids (SS). It is also possible that runoff is characterised by acidity, elevated iron concentrations and a high chemical oxygen demand (COD). Run-off from the adjacent Varteg Hill immediately above the proposed highwall is likely to enter the opencast excavation area unless preventative measures are taken to divert these flows around the workings.

7.5.10 A road ditch collects natural surface water run-off from the north of the site and discharges via a 1200mm diameter culvert under the Varteg Road to a watercourse that flows eastwards along the old tramway route to the Afon Llwyd cascading downstream into the valley. TCBC indicate that there are scour and surcharge problems along this steep route and consideration should be given not to exacerbate this problem.

7.5.11 The side ditches along the western upstream side of the Varteg Road were heavily vegetated at the time of the site inspections. 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 via small bore culverts under the Varteg Road. Anecdotal evidence identifies that the highway ditches surcharge during intense storm periods.

7.5.12 Records held by TCBC confirm this evidence and indicate that the receiving tank on the eastern side of the Varteg Road discharges to a 15 inch diameter


culvert running southwards through Rockvilla Close and discharges to a watercourse to the south of Balance Road at NGR 326093,205128. This is a tributary of the Nant Ffrwd (See plans in Item 14 of ES Volume 3).

7.5.13 The Environment Agency advised through its response to the scoping report that it would be necessary to undertake a formal (winter) water features survey of the site, extending radially 500m from the site.

7.5.14 A comprehensive water features survey was carried out during February 2004 after a period of prolonged wet weather locally. The findings of this survey have been reported on in a separate document dated March 2004, issued under separate cover to the Environment Agency. (See Item 15, ES Volume 3).

7.5.15 Historical mining records held by the Coal Authority indicate that underground mine workings are present within the proposed coal excavation site and these could be flooded or act as subterranean drainage channels. The opencast works will expose these workings and there is an expectation of water strikes during face excavations. Where old workings have become inundated due to the closure of former drainage pathways, ochre may accumulate. Breaching of these inundated systems could lead to rapid discharges of potentially heavily contaminated minewaters, possibly laden with ochre while the former workings are drained. Once drained, significant water inflows are not anticipated. The presence of both firedamp and blackdamp should also be considered.

7.5.16 Inspection of the Welsh Water records identifies available public foul sewerage in the field to the north of Salisbury Terrace that used to drain “Twenty Houses” that have since been demolished. This sewer was not identified during the walkover survey. The pipe size and level are not detailed in the available sewer records and will require inspection and survey if likely to be used. A discharge consent will be required from Welsh Water in order to connect to this sewer. This sewer is not within the current land ownership and it is anticipated that foul sewage from the development would probably be collected on site by use of a holding tank.

7.5.17 There are no likely modifications required to the public surface water sewers

resulting from the proposed works. It is likely that watercourse diversions and attenuation structures required as part of the mining works will reduce peak flows locally in the existing public and land drainage systems during the coal extraction period.

7.5.18 There is a covered Welsh Water service reservoir adjacent to the works access

road. Connection pipework to the reservoir is routed to the north east running parallel to the track and is unaffected by the mining works, but will be affected by the site access junction provision. The junction layout design will need to maintain the existing distribution pipework system.

7.5.19 The volume of water requiring treatment will vary during the lifetime of the site, subject to the need to treat waters either entering the working area or draining from surrounding restored areas of the site. Maximum quantities can be calculated based on published statistics and data relating to rainfall, hydraulically effective rainfall (HER) and hydrogeological characteristics.


However, the extent and condition of old workings, unrecorded old workings and connections between these and other workings elsewhere will influence the volume of water which may enter the opencast excavation.

7.6 Proposed Drainage Strategy

7.6.1 The proposed drainage strategy incorporates the following principles for implementation:-

1. Drainage to areas disturbed by the mining works to be

intercepted and diverted to receive attenuation and treatment. 2. Runoff from undisturbed areas to be diverted around the works

area for infiltration into areas downstream of the working site. 3. Provision of attenuation and treatment of surface runoff after

restoration until vegetation ground cover establishment.

7.6.2 An integrated water treatment system design is required that incorporates the following considerations:-

• Storm return retention period level of service • Flow transfer pumping rates and balancing sump volumes. • Flow velocities causing scour/lining of watercourses/silt

mobilisation and settlement. • Control of particulate settlement in sumps and lagoons. • Potential treatment of Acidic Mine Drainage. • Control of discharged water quality - contact and retention

times. • Desludging or flocculent removal and disposal/recycling. • Oil and scum removal. • Process plant water use, including vehicle wash down and

effluent treatment. 7.6.3 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. Coal extraction will be followed by approximately one year of restoration and 5 years of aftercare.

7.6.4 It is proposed to collect and divert run-off drainage from the catchment

above the coal extraction area to avoid inundation and contamination from the mining 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 will also re-introduce surface water run-off to the sensitive ecologically important areas maintaining groundwater moisture content levels. Storm overflow above the infiltration trench design level will discharge to the adjacent ditch.

7.6.5 The mining 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 tend to collect at the toe of the cut face due to the geological dip and will be pumped from the face to a settling lagoon for mineral settlement and chemical/pH treatment, if required, at the nearest WTA.

7.6.6 Water springing from overburden spoil mounds may require treatment due to

the potential generation of acid mine 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 to 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.

7.6.7 Overland surface water drainage from the extended overburden mound above

Salisbury Terrace is to be intercepted by a cut-off ditch flowing southwards to the new southeast WTA intercepting the existing watercourses draining the existing and extended spoil mounds.

7.6.8 Drainage from the proposed overburden storage area within Mynydd Farteg

Fach will require attenuation and settlement to reduce the suspended solids loading. The proposal is to collect storm water run-off flows immediately downstream of the existing culvert and temporarily divert and transfer flows around Varteg Hill via a pipe/ditch to the south eastern WTA for treatment following the line of the rerouted farm access track. This will avoid the provision of an isolated chemical treatment process in the Nant Ffrwd catchment and reduce the potential risk of contamination arising from any accidental process spillages. However this will also temporarily increase the catchment area contributing to the proposed south eastern WTA and associated outfalls. Additional attenuation may be required as a result. However this strategy will provide a benefit by reducing flows that are currently causing scour problems downstream along the Nant Ffrwd and reducing flows through the Golynos Watercourse for the duration of the restoration. Subject to Torfaen CBC and NRW formal written approval 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 Nant Ffrwd. An impounding licence will be required.

7.6.9 Large volumes of run-off is generated from the area to the north of the site

which is collected in the ditch on the western side of Varteg Road and flows southwards crossing under the road via the 1200 mm 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 amount of existing contributing area reducing peak flows down this sensitive watercourse flowing east to the Afon Llwyd


7.7 Water Treatment Areas

7.7.1 Proposed water treatment areas (WTA) have been strategically placed for collection of run-off and either discharge to the existing available pipe crossings under the B4246 Varteg Road to the east and south east, or discharge overland to the Nant Ffrwd catchment to the west. The proposed water management scheme is shown on FIG 7.1 at the end of the chapter.

7.7.2 Surface water run-off contributing areas to the proposed individual water

treatment areas are summarised in Table 7.1

Table 7.1: Surface water runoff CONTRIBUTING AREAS Catchment Area

(ha) Estimated impermeability factor (%)

Intercepted run-off areas 18.2 70 Eastern WTA Spoil areas 4.2 70 Facilities area 1.4 70 South Eastern WTA Extraction works area 11.6 70 Spoil areas 2.7 70 Spoil areas (Mynydd Farteg Fach)

26.7 70

7.7.3 Suggested treatment parameters are as follows:-

• Sedimentation pond velocity < 1x10-5 m/s • Lagoon length to width aspect ratio of 5 to 1 • Lagoon depth 2m plus 0.5m freeboard. • Provision of an upstream attenuation pond with a high level

storm overflow

7.7.4 Initial indication of the consent parameters for the treated effluent by the Natural Resources Wales for a watercourse discharge consent are as follows:-

• Suspended Solids: 40-50 mg/l. • pH: to be advised based on NRW general quality assessments

of existing watercourse water quality and flows. • A volumetric discharge consent restriction of 10 l/s/ha. • Provisional level of treatment return period: 1 in 5 years with a

2 hour storm duration (based on a 3 year extraction period). • Removal of visual oils.

7.7.5 The south eastern WTA will discharge to the existing culverts crossing the

road in the local vicinity or by the provision of a connection pipe to the 15 inch diameter culvert identified by TCBC. There is an area of land between the WTA and the 15 inch diameter culvert that is believed to be owned by TCBC and can accommodate a pipeline route from the WTA. This sewer will need to


be located and surveyed on site and probably require jetting and a CCTV survey. An easement agreement with TCBC would be required.

7.7.6 Works cut-off drainage will isolate the ecological interest area designated A2.

Treated effluent will need to be diverted from the WTA to enable groundwater infiltration for this area. Prior monitoring of groundwater levels will be required to establish a recharge rate during the period of the works

7.8 Drainage related site activities

7.8.1 Foul drainage from the facilities site will discharge to an on-site holding tank. The tank will be emptied periodically and tankered away for treatment.

7.8.2 Oil and chemical storage and delivery will be in accordance with the Environment Agency Pollution Prevention Guidelines (PPG2).

7.8.3 In collaboration with the NRW, the quantity and quality of discharges from the WTAs will be monitored.

7.8.4 In collaboration with the NRW, local groundwater levels will be monitored.

7.8.5 A methodology for the containment of accidental process water spillages will be provided.

7.8.6 Protective fencing will be provided around identified ecological sites. 7.8.7 Surface water flowpaths through the site during flooding will be

considered when laying out the facilities area

7.9 Licensing and Permits

7.9.1 Any damming or culverting of a watercourse requires the prior formal written approval of Torfaen CBC under the terms of the Public Health Act 1936 and the prior formal written consent of the 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 will not normally be granted except for access crossings.

7.9.2 Under the terms of the Water Resources Act 1991, an Environmental Permit issued by 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.

7.9.3 Under the terms of the Water Resources Act 1991, an Impounding Licence may be required from the NRW for the impounding of any watercourse, ditch or stream (e.g. by dam, weir etc.) and an Abstraction Licence may be required from the Environment Agency for the abstraction of water from any inland water or underground strata.

7.9.4 All appropriate permits, consents and abstraction licences will be obtained from NRW and Torfaen CBC, as appropriate, prior to the commencement of the site works.


7.10 Controlled Waters Impact Assessment

7.10.1 There are three principal effects which the proposal to remove the spoil tips and work the underlying coal-bearing ground to the west of Varteg Road may have on controlled waters (surface water and groundwater).

7.10.2 The excavation of ground, interception of incident rainfall and groundwater and the removal to water treatment areas will result in the interruption and diversion of surface waters which would otherwise flow from west to east across the site. This will result in diminished potential recharge to sandstone horizons outcropping east of the opencast excavation including the sandstone roof and floor of the Garw seam.

7.10.3 The removal or re-shaping of the colliery spoil tips from the site of the proposed excavation, the replacement of material in the valley beneath Mynydd Farteg Fach and the replacement of excavated materials in the void following coal recovery has the potential to generate acid mine AMD. Exposure of old workings in the opencast excavation may also result in the ingress of poor quality water to the opencast site.

7.10.4 Subject to the extent of local sandstones within the local stratigraphical sequence and the current hydrogeological condition of the sandstones, there is the potential for groundwater to enter the excavation from confined sandstones present beneath the coal extraction area.

7.10.5 A qualitative impact assessment of the impact of the proposed opencast project has been carried out which identifies, in Table 7.2 below, the potential impacts of the project on controlled waters, both in the short-term during the life of the project and in the long-term following restoration of the site. Measures to mitigate potential adverse impacts are proposed, where appropriate, and the residual impacts considered following instigation of the mitigation measures.


Table 7.2 Qualitative Impact Assessment on Controlled Waters

Operation (activity) Impact (effect) Severity Mitigation measures Residual impact and severity Removal, replacement or reshaping of existing colliery spoil tips

Generation of acid mine drainage resulting in contamination of controlled receiving waters subject to nature of spoil

Potentially severe in short & medium-term

Interception of runoff from areas of disturbed ground and diversion to purpose-built water treatment areas

Negligible impact -Treated water discharge subject to discharge permit conditions.

Interception of surface water runoff from land immediately west of & above the void and incident rainfall within void area (passive dewatering)

Reduction in potential recharge to areas of ecologically important mire and permeable strata immediately east of the excavation

Potentially major in short-term

Diverted runoff to infiltration channels immediately east of the void to recharge the mire area

Potential minor positive impact -Net positive contribution to ecology of mire area east of excavation

Abstraction of (ground) water inflows to excavation

Reduction in local water tables/piezometric levels and former groundwater discharges

Minor to negligible in short-term. Temporary impact during coal extraction period.

Monitor groundwater levels in significant water-bearing horizons

Temporary minor to negligible impact - Re-instatement of groundwater levels following completion of restoration

Interception of inundated old workings and dewatering of same

Dewatering of localised minewater flow system and inflow of poor quality water to the excavation

Minor in short-term Treatment of poor quality water in water treatment areas

Negligible impact -Re-inundation of remaining old workings west of the opencast may occur following completion of restoration.


4339/1/ARM/caj Environmental Statement, Chapter 6 Harmers Limited Glamorgan Power November 2014 62 Varteg Hill

7.11 Conclusions

The geology of the sequence of strata within the coal extraction area consists principally of mudstones and coal seams with no evidence of extensive sandstone units. It is concluded that the workings will not intercept any significant groundwater inflows.

The presence to the east and beneath the floor of the proposed excavation of sandstone strata including the Gellideg Rock suggests that groundwater locally may have a significant role, where the workings are below the piezometric level of the sandstone units.

However, the topographical and structural constraints of the proposed opencast site may result in only slight impacts being experienced on the hydrogeological environment. It is considered that groundwater has only a minor impact on the proposed project.

The principal concerns in relation to the proposed opencast site in its hydrogeological setting include: water interception/diversion and surface water and groundwater drainage:

1 The interception and diversion of runoff, incident rainfall and groundwater ingress entering the excavation – flows which currently sustain the ecologically important mire areas to the east of the proposed excavation and,

2 The increased potential to generate AMD within the catchments of the Afon Llwyd and Afon Ffrwd through the disturbance of existing colliery spoil tips, ingress of poor quality water from abandoned mine workings and the excavation of virgin Coal Measures strata.

7.12 Recommendations

7.12.1 A number of recommendations can be made based on consideration of the hydrogeological environment in which the proposed opencast excavation is to be undertaken. These include:

Determine in advance of the excavation the piezometric heads within the Gellideg Rock and monitor groundwater levels within relevant water bearing units including the Gellideg Rock,

Monitor the quality of potential receiving waters at the proposed discharge points,

Design measures to exclude surface water runoff from the working area, Provide adequate water storage/treatment capacity to accommodate inrushes

and other minewater ingresses to the excavation from former mine workings and inflows of incident rainfall,

Incorporate infiltration measures into the water management drainage strategy to sustain local mire ecosystems,

Ensure adequate drainage mechanisms are installed within those areas of restored backfill, and

Monitor groundwater levels within the backfill in the restored excavation and in the valley beneath Mynydd Farteg Fach to assist in slope stability assessment.


7.13 Additional Information

7.13.1 Following the submission of the planning application in May 2004 comments were received from the Council’s Public Health Team (memo dated 27th July 2004) and the Environment Agency (letter dated 12th October 2004 from EA). Both documents are included in Item 16 of ES Volume 3). The basis of the EA’s comments was that the information contained in the ES on Hydrology and the Water Features Survey was a preliminary assessment of the hydrogeology of the site and its environs and that a number of conditions were required to be addressed in advance of the proposals proceeding.

7.13.2 To meet the requirements of the EA and Torfaen County Borough Council a Phase 1 Desk Study Report (Item 17 ES Volume 3) of the development site was carried out and submitted to the EA and Torfaen CBC in September 2005. Subsequently, an Interim Interpretative Report which included consideration of the results of a ground investigation and groundwater level monitoring carried out between August and November 2005 was submitted for comments to the EA and Torfaen Council in December 2005. Groundwater monitoring continued after this date.

7.13.3 In March 2006 comments were received from the EA on the Interim Report. The EA letter raised a number of concerns, including the need for the inclusion of information to justify the conclusions made in the Report. A meeting was subsequently held with the EA and Torfaen CBC in May 2006 to discuss the EA comments.

7.13.4 In November 2006 a further Report entitled Hydrogeological and Contaminated Land Assessment Final Interpretative Report was submitted to the EA and Torfaen Council. Groundwater and surface water quality monitoring of the site continued to be carried out.

7.13.5 The Final Interpretative Report included the results of groundwater level and groundwater and surface water quality monitoring carried out at the site between August 2005 and September 2006. The Report addresses the comments made by and concerns of the EA associated particularly with the proposed impact of the opencast workings on groundwater flow and on groundwater and surface water quality.

7.13.6 Comments were received from the EA on the Final Interpretative Report in a letter dated the 28th December 2006 (Item 18 ES ES Volume 3). This letter proposed a meeting to discuss the latest report and its recommendations and in particular the EA wished to discuss the regulation of matters through the planning permission. Following a meeting held on the 26th January 2007, a letter was sent to the EA on the 19th February 2007 with an enclosed structure of an Environmental Monitoring Plan. The EA subsequently advised Torfaen Borough Council on the 12th March 2007 they had no objections to the structure of the Environmental Monitoring Plan. Copies of the relevant correspondence and the structure of the Environmental Plan are included in Item 19 of ES Volume 3.


7.14 Response to Scoping Opinion (August 2014) 7.14.1 The EIA Scoping Opinion (Item 6 ES Volume 3) includes comments received from Natural Resources Wales (NRW) and the National Museum of Wales which are considered below.The Council also stated that the ES needs to consider the impact that the alternatives will have on the hydrogeological conditions which is included in chapter 4 .

(i) NRW Comments 7.14.2 The response from NRW dated 8th July 2014 included with the Scoping Opinion (Item 6 ES Volume 3) is very similar to the response the Environment Agency made on the previous application dated 18th November 2009 (Item 20 ES Volume 3).The NRW letter dated included in the Scoping Opinion raised the following hydrogeological and hydrological issues which need to be addressed:- ▪ Water Features Survey: A survey of all water features on and within 500 meters of the application site is requested. The survey should identify both surface water and groundwater features within the area .These will form the “controlled waters” receptors for a subsequent impact assessment. ▪ Hydrogeological Impact Appraisal: The impact of the proposed coal extraction on the controlled waters receptors should be undertaken particularly of the impacts of dewatering based on guidance in the EA Science Report SC040020SRI; “Hydrogeological impact appraisal for dewatering abstraction” dated April 2007. ▪ Water Management Plan: The plan should address surface water management on the site and of the management of groundwater pumped from the extraction area. ▪ Pollution Prevention Measures 7.14.3 The requirements of the NRW have been addressed in the supporting document to the ES entitled “Varteg Hill Reclamation & Coal Recovery Scheme ,Blaenavon ,South Wales Hydrogeological and Contaminated Land Assessment – Interpretative Report” which was updated in October 2014 and is submitted as a supporting document.

(ii) National Museum of Wales Comments 7.14.4 The National Museum of Wales has raised the issue of the potential impact of the proposed coal extraction on the operations of Big Pit in Blaenavon, in particular the potential effect on the Golynos Watercourse which drains the former workings in Big Pit. 7.14.5 The Golynos Watercourse is a mine drainage adit that was constructed in the Bottom Vein Ironstone to drain the overlying coal workings in the area to the north –north west of the site including the works from Big Pit in Blaenavon, approximately 4 kms to the north west. The Golynos Watercourse runs parallel with the valley of the Cwm Afon before discharging to the Cwm Sychan Brook to the west of Abersychan, approximately 2kms south of the Varteg site.


7.14.6 Information contained in the ES for the proposed Spring (Talywain ) Limited, British Reclamation Scheme located to the west of Abersychan indicates that the drainage adit comprises an unlined roadway cut into rock at depth s of 40-60 metres beneath the British site. 7.14.7 The abandoned mine records for the area around the proposed Varteg coal extraction site show that the former workings were drained by an adit also excavated into the Bottom Vein Ironstone. The adit discharges to the Stable House watercourse, which is located immediately to the east of the proposed coal extraction area. The Stable House watercourse is at least 20 metres below the proposed base of the coal extraction area. 7.14.8 The mine abandonment plans which are included in the Figures attached to the report entitled “Varteg Hill Reclamation and Coal Recovery, Blaenavon,SouthWales Hydrogeological and Contaminated Land Assessment” show that the Stable House Watercourse is connected to former workings in four coal seams (the Four Foot, Lower Nine Foot,Upper Seven Foot and Lower Seven Feet) which will be extracted as part of the proposed scheme and also to the Five Feet/Gellideg scheme, which is present below the base of the proposed workings. The former workings are connected to the Stable House watercourse through both Mine Pit and Mine Slope Colliery. 7.14.9 The mine abandonment plans for the area surrounding the application site do not show any reference to the Golynos Watercourse drainage. Based on the mine abandonment plans, it is concluded that the Golynos Watercourse is not in hydraulic continuity with the former workings in the vicinity of the Varteg site. All of the former workings within the seams to be extracted are drained by the Stable House watercourse, which discharges immediately to the east of the proposed coal extraction area. In the absence of any evidence of a connection to the Golynos Watercourse at the site, it is concluded that the proposed coal extraction at Varteg will have no impact on the Golynos Watercourse. 7.14.10 There is no evidence that the coal seams to be worked in the Varteg site previously have been extracted within the proposed area of extraction. Due to the shallow depth of the coal seams, particularly on the eastern side of the site, there is recognition that unrecorded former workings may be intercepted in the excavation. The recharge area for these seams is restricted to the small area of unworked land to the east of the extraction area. As this land slopes to the east, it is considered unlikely that there will be significant recharge to the coal seams and possible former workings and hence there will be negligible inflow to the workings from the up-dip area of the proposed workings to the east. 7.14.11 Ground water contours for the water –bearing sandstones present beneath the proposed coal extraction area are provided in Figures 6.9 and 6.10 of the above mentioned hydrogeological and contaminated land assessment .Based on the interpolated groundwater contours ,it is considered that groundwater in the sandstone bands present above and below the Bottom Vein ironstone ,the drainage horizon for the Stable House Watercourse and the Golynos Watercourse has no


influence on the groundwater flow ,which is to the west and south west generally consistent with the dip of the strata. The absence of any impact of the mine drainage systems on groundwater flow is attributable to the absence of any widespread former coal workings in the area of the proposed scheme, which would have been connected to the Stable House Watercourse. 7.14.12 Based on an interpretation of the hydrological conditions, the mine abandonment plans and the mine drainage systems, it is considered that the Golynos Watercourse and hence the operations at Big Pit will be unaffected by the proposed scheme. 7.14.13 The National Museum of Wales also raised a concern that the proposed opencast workings could affect workings in the Garw Coal,which is directly connected to Big Pit. There is no proposal to work the Garw Coal as part of the proposed Varteg scheme. The Garw Coal is present approximately 30m below the base of the proposed workings and hence will not be affected by the proposed scheme.

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