Glyn Rhonwy Pumped Storage 6.02 Environmental Statement Development Consent Order Volume 2
3 DESIGN EVOLUTION & ALTERNATIVES
3.1 Introduction ...... 1 3.2 Site Description ...... 3 3.3 Concept of Pumped Storage ...... 7 3.4 Site Selection ...... 8 3.5 Design Evolution ...... 9 3.6 Design Evolution: Approved Scheme ...... 9 3.7 Design Evolution: Development Consent Order ...... 17 3.8 Alternatives ...... 30
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3 DESIGN EVOLUTION & ALTERNATIVES
3.1 Introduction
3.1.1 The Development proposed within the DCO application has evolved in two principal stages. The first design evolution related to the approved scheme, with the second evolution taking place following the grant of planning permission for the approved scheme, and in advance of the submission of the DCO application.
3.1.2 Although two distinct stages are identifiable, the design of the approved scheme provided the basis for the design of the Development and as such, the two schemes are intrinsically linked. The principal reason for the design evolution that took place following the approval of the T&CPA application related to the deliverability of that scheme following the Electricity Market Reform (EMR).
3.1.3 This chapter provides an overview of the site description and of the design evolution process for the Development – an iterative process that runs from the early stages of the project through to the approved scheme (as detailed in the 2012 ES), and beyond that through to the final design of the Development as submitted. As many of the scheme elements within the Development were fully design tested as part of the evolution of the approved scheme, this chapter outlines the design process for the approved scheme to ensure that a complete explanation of the context and evolution of the Development is provided. It is the final Development design that has been assessed within this Final ES and which forms the basis of the DCO submission.
3.1.4 An iterative approach has been adopted throughout the design process which has been influenced by the conclusions and findings of the previous 2012 ES, engineering design works, responses received through the consultation process and through updated and additional survey works.
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3.1.5 The remainder of this Chapter is organised as follows:
Site Description – outlining the location, extent and physical characteristics of the Development site;
Concept of Pumped Storage – provides a basic overview of the composition of a pumped storage facility;
Site Selection – this section provides an overview of the suitability of the Glyn Rhonwy site for pumped storage;
Design Evolution – these sections provide, firstly, an overview of the evolution of the design up to the formal grant of planning permission for the approved scheme, and then secondly, how that design has evolved further into the Development subject to the DCO Application;
Rochdale Envelope – this section sets out the rationale for the maximum and minimum parameters established for the environmental impact assessment of the Development;
Alternatives - this section outlines how alternative technologies, plant and construction methodologies were considered; and
Do Nothing Scenario - this section outlines other types of electricity generation that the UK would rely on in the absence of pumped storage schemes.
3.1.6 All Figures referred to in this chapter are included in Volume 4 of this ES.
3.1.7 Design is an iterative process which is influenced by engineering, technical and economic constraints, along with likely environmental effects identified through EIA processes (undertaken for the approved scheme and for the Development subject to the DCO application). The design process has considered the consultation responses received during consultation in connection with the T&CPA application, and more recent responses received as part of the s42 and s47 consultation of the DCO application.
3.1.8 Following the grant of planning permission for the approved scheme, and the review of the scheme deliverability undertaken by the Applicant in light of the EMR, additional baseline environmental information has been
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collated and further mapping and technical constraints have been considered. Preliminary GI works have been undertaken and whilst geotechnical results are awaited, this is not expected to alter or constrain any of the main scheme elements of the Development.
3.1.9 Engineering reviews of the Development design have identified where there may be potential to optimise and improve the indicative design elements (such as the design of the turbine shaft outlined in Section 3.8.11). This design process has defined the Development subject to the DCO and informed the Rochdale Envelope (or maximum parameters) for EIA. The Order Limits and construction methods considered are therefore assessed to represent a worst-case precautionary approach.
3.2 Site Description
Introduction
3.2.1 The Development site is located to the west of Cefn Du mountain above Llyn Padarn, centred at National Grid reference SH 56268 60660.
3.2.2 The site is approximately 1.5km north west of Llanberis and 11 km south east of Caernarfon. Volume 4, Figure 1.1 shows the location of the Development, and the Order Limits shown in Volume 4, Figure 1.2.
Designations
3.2.3 The Development is located both within and in close proximity to, a number of designated sites.
3.2.4 Llyn Padarn Site of Special Scientific Interest (SSSI) is located to the east of the Development. This is shown in Volume 4, Figure 3.1. The only element of the scheme which enters the SSSI is the spillway infrastructure from the pumping station.
3.2.5 The Afon Gwyrfai Special Area of Conservation is located approximately 2 km to the south west but is connected to the Development by the Nant Y Betws watercourse. This is shown in Volume 4, Figure 3.1.
3.2.6 The Development site is located within a Landscape Character Area (LCA) (designated for its historical landscape) and also within the Dinorwig
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Landscape of Outstanding Historical Interest. This is shown in Volume 4, Figure 3.2.
3.2.7 The site is located approximately 1km from the boundary of Snowdonia National Park (SNP). This is shown in Volume 4, Figure 3.3.
Site Description
3.2.8 The Order Limits will cover an area of approximately 91.24 ha, an increase of 31.94 ha from the site area of the approved scheme (59.30 ha). This increase is a direct result of the design evolution process which is outlined further in sections 3.6 and 3.7 of this chapter.
3.2.9 The surrounding area has a number of physical characteristics which include a number of quarries, slate tips, a former World War II (WWII) munitions store, a mature plantation woodland, rough grazing land and existing highway network leading to Glyn Rhonwy Industrial Estate platform in the south and to the A4085 in the north. Ffordd Clegir separates two of the lower quarries and also forms the western boundary of the Glyn Rhonwy Industrial Estate.
3.2.10 The quarry system, of which the Development part utilises, has been numbered from Q1 in the east to Q8 in the west near Llyn Padarn, and can also be seen in Volume 4, Figure 3.4:
x Quarry 1 (Q1)– Chwarel Fawr;
x Quarry 2 (Q2) – Chwarel Cefn Du;
x Quarry 3 (Q3) – Cook;
x Quarry 4 (Q4) – Ddol;
x Quarry 5 (Q5) – unnamed but known locally as ”Film Set Quarry”;
x Quarry 6 (Q6)– Glyn Rhonwy;
x Quarry 7 (Q7) – unnamed and is a smaller quarry excavated between and to the south of Glyn Rhonwy (Q6) and the former munitions store at Quarry 8 (Q8); and
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x Quarry 8 (Q8) – former WWII munitions store (known locally as “the bombstore”).
3.2.11 The Development will utilise Q1 and Q6 to form the headpond and tailpond reservoirs respectively. Parts of Q2 and Q5 have been included within the Order Limits to permit any works which are required to seal connections to these quarries, namely from former mining tunnels. Q7 is included within the order limits but is not directly involved with the Development. Some initial works surrounding Q7 may be required, and any connection between Q6 and Q7 will be sealed, but no other physical works will be undertaken within that quarry.
3.2.12 Water has collected in two of the quarries, especially in Q6 adjacent to the Glyn Rhonwy Industrial Estate. Bathymetry surveys undertaken in 2015 estimate the depth to be approximately 17m in Q6 and approximately 7m in Q1.
3.2.13 The hillside slopes around the quarries are built up with slate waste and interspersed with the remains of outhouses and quarry workings, scattered over grazing land. The neighbouring land is mainly agricultural, with the exception of Glyn Rhonwy Industrial Estate between Ffordd Clegir and Llyn Padarn, and an existing industrial complex to the south of the Development.
3.2.14 Although development of the Glyn Rhonwy Industrial Estate has provided improved access in the vicinity of Q6 to Q8, including Public Rights of Way (PRoW) and informal footpaths, access to the overall development site is generally restricted and the quarries themselves are fenced off. In the Industrial Estate, some quarries and buildings have been known to suffer fly-tipping and vandalism in the form of graffiti and damage to the fencing to facilitate unauthorised access.
3.2.15 An overview of the history of the Development site is presented in Plate 3-1, a timeline which covers the period from pre-1840 to the present.
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Plate 3-1 Overview of usage at the Glyn Rhonwy site
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3.3 Concept of Pumped Storage
3.3.1 Pumped storage is a way of storing energy by turning electricity generated elsewhere during periods of relatively low demand into stored (or potential) energy. The stored energy can then be used to generate electricity at times of high demand. The system uses electricity to pump water from a lower reservoir to a higher reservoir (Q6 and Q1 respectively for the Development). When required, water is allowed to drive the hydro-turbines to generate electricity to meet sudden spikes in consumer demand (generally in the morning and evening). Pumping would normally happen during the night. This cycle of pumping and generating repeats on a daily basis. Pumped storage utilises electricity at night when consumer demand is low, and can be used to generate electricity at very short notice during the day when consumer demand is high, providing a flexible and valuable balancing service to the electricity System Operator, National Grid.
3.3.2 Pumped storage projects generally comprise of the following main elements:
x A headpond - upper reservoir;
x A tailpond - lower reservoir;
x A power house - containing the combined pump/turbines; and
x A penstock - the pipe connecting the headpond to the power house.
3.3.3 The Development at Glyn Rhonwy comprises of the following:
x one headpond (Q1), its dam, access shaft and spillway infrastructure to the Nant Y Betws;
x one tailpond (Q6), its dam, access shaft and spillway infrastructure to Llyn Padarn;
x a pumping station at Llyn Padarn;
x a power house at Glyn Rhonwy Industrial Estate Platform 5 (south of Q6);
x a penstock (connecting Q1 to the power house);
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x a tailrace (connecting the power house to Q6); and
x Spillway infrastructure – a discharge point from the headpond and a joint discharge/abstraction point from the tailpond.
3.4 Site Selection
3.4.1 It is uncommon to find the combination of features that make a site suitable for Pumped Storage development. The most suitable sites have unconstrained grid access, have significant elevation, suitable geology and are not subject to significant environmental constraints. Glyn Rhonwy fits these characteristics. In addition, it largely constitutes previously developed land, and feasibility and environmental assessment has concluded that potential environmental effects could be minimised or mitigated through sensitive design or the application of mitigation measures.
3.4.2 Glyn Rhonwy was selected following a detailed mapping exercise, undertaken by QBC in 2011, to examine the feasibility of pumped storage throughout Great Britain against key indicators including:
x the geology, ground conditions and terrain;
x accessibility;
x safety and feasibility of construction;
x the physical shape and sizes of the reservoirs and requirements for dams;
x the distance between the reservoirs and the distance to the distribution network;
x the environmental sensitivity of the site; and
x whether any effects of the development could feasibly be designed out or mitigated.
3.4.3 The site was also selected as its development for pumped storage was considered to be in line with both national and local planning policy. This is explained further in Document 8.01 Planning Statement.
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3.4.4 Chapter 5 Planning Policy Context provides further information on the national, regional and local (both adopted and emerging) planning policy context for the Development.
3.5 Design Evolution
3.5.1 Two stages of design evolution of the Development subject to the DCO can be identified. Table 3-1 below identifies the review stages that occurred for both the approved scheme and the Development. Further details of each review stage are then provided in section 3.6 and 3.7.
Table 3-1 Design Review Application Timing Design Review Review 1: Initial Design prepared for report November to accompany formal Scoping Request to 2011 Gwynedd Council Review 2: Engineering review following April 2012 survey works Review 3: Review following stakeholder July 2012 T&CPA consultation Review 4: Final design for planning August 2012 approval October 2012 Submission of T&CPA Application February Determination of T&CPA Application 2014 December Review 5: Engineering Review to increase 2014 generating capacity to 99.9MW Review 6: Design Review for report to January 2015 accompany formal Scoping Request to DCO SoS February – Review 7: Engineering Review March 2015 Review 8: Final Design for DCO August 2015 application
3.6 Design Evolution: Approved Scheme
3.6.1 The approved scheme was subject to a four stage design review process prior to the submission of the T&CPA application.
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Design Review 1: Feasibility & Scoping
3.6.2 An initial design of the approved scheme was established to determine the feasibility of the scheme and this was outlined in the Scoping Report submitted to Gwynedd Council in 2011. This is shown below and on Volume 4, Figure 3.5.
3.6.3 The initial design was based upon technical requirements of the pumped storage scheme, for example the amount of head (difference in altitude) needed between the headpond and tailpond, together with development constraints including proximity to residential dwellings and designated sites.
3.6.4 The initial design incorporated three dams at Q1, Q2 and Q6 with heights of 12m, 26m and 17m above ground level (AGL) respectively. An alternative option was considered which comprised an increase in the height of the dam at Q1 to 15m AGL, thereby avoiding the need for a dam at Q2, and a reduced dam height at Q6 to 8m AGL. Dams are required within the Development to increase the volume of water stored (above the natural capacity of the quarries) and to ensure that the volume of water in the headpond and tailpond are the same.
3.6.5 The penstock route was to be located on the northern side of the scheme with an overland route outside the Cook (Q3) and Dhol (Q4) quarries to avoid protected breeding birds. The penstock consisted of two 2.5m diameter pipes. Whilst the route was undetermined at that stage, it was acknowledged that installation would require either open cut trenching or drilling technology to create an underground penstock route of 1600m or 2000m respectively.
3.6.6 The power house was to be located on the western side of Ffordd Clegir in Q5. Access to the power house was proposed via the Glyn Rhonwy Industrial Estate platforms and not through Ffordd Clegir.
3.6.7 As part of a preliminary engineering review, the use of Llyn Padarn as a tailpond was investigated (in the same way that Llyn Peris is utilised for the Dinorwig hydro-electric scheme on the opposite side of Llyn Padarn). However it was recognised that Llyn Padarn is designated as a SSSI for its
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ecological value, most notably as one of only three places in the UK to support Arctic Char (Salvelinus alpines) and is also a popular recreational destination for tourists and local residents. The use of Llyn Padarn as a tailpond was therefore discounted on that basis from any further consideration.
3.6.8 In addition, the engineering and environmental constraints of locating the power house in close proximity to Llyn Padarn together with land ownership issues associated with the former munitions store would have resulted in a longer penstock. This also meant that this routing option was discounted.
3.6.9 The location of site compounds and access tracks were undetermined at this stage in the design evolution of the approved scheme.
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Design Review 2: Engineering Review
3.6.10 A second engineering review was undertaken following initial baseline environmental surveys in Spring 2012. This led to changes from the layout proposed at Design Review 1 to the layout which can be seen in Volume 4, Figure 3.6.
3.6.11 The principal change as part of Design Review 2 was the removal of the dam at Q2. The engineering review identified the potential to provide approximately 1,100,000m3 of storage in Q1 meaning that the three dams initially proposed were not required. In addition, the engineering review also identified that significant engineering and geotechnical stabilisation works would be required at Q2 and Q5. This was in addition to the ecological constraints identified in Q5. As a result, dams were now only required at Q1 (headpond) and Q6 (tailpond) which would be approximately 25m AGL and 15m AGL respectively.
3.6.12 The red line boundary still included some of Q2 to permit any required works to seal the tunnels linking Q1 and Q2. No works were proposed to be undertaken in Q2.
3.6.13 Due to the level and cost of engineering works, potential ecological effects and access, engineering and health and safety issues associated with construction at Q5, the proposed location of the power house was moved to Platform 5 of the Glyn Rhonwy Industrial Estate.
3.6.14 Two penstock / tailrace construction methods to transfer water from Q1 to Q6 were still being considered at this stage – one above ground and one below ground.
3.6.15 During this period, consultation was undertaken with the owners of private water supplies (contained within Volume 3, Appendix 9.2) together with an engineering review of the spoil mounds to the north of the quarry system. As a result, the proposed penstock route was relocated to the south. Although routing the penstock through the existing slate mounds would minimise visual effects, potential instability from construction activities and the potential effects on private water supplies justified the movement of the
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penstock and tailrace route to the south. Whether the penstock was to be above or below ground, or a combination was still undermined at this stage.
Design Review 3: Consultation Review
3.6.16 As a result of public consultation events held in June and July 2012, continued consultation with regulators, and an engineering and economic review of the survey data collated to date, it was determined that the penstock for the approved scheme should be constructed by underground tunnel excavation. The route, established at Design Review 2, would be used, albeit a more direct underground route between Q1 and Q6.
3.6.17 Both open cut trenching and tunnel excavations are standard practices for the construction of underground pipe routes, and both have been used in similar projects elsewhere. However the open cut trenching and subsequent reinstatement (which would have required a 50m working width from Q1 to Q6 for the duration of the 3.5-4 year construction period) would have significant environmental effects in comparison to tunnel excavation. This
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was considered unacceptable and therefore the open cut option was discounted following consultation with regulators.
3.6.18 At this stage, the location of the spillway pipe from Q6 to Llyn Padarn was still subject to landownership discussions, specifically related to the bombstore (Q8). A location for the pumping station was identified at a small inlet adjacent to the public car park.
3.6.19 Further mapping and engineering analysis of the construction phase identified a volume of excess spoil which would be generated by the excavation of material from Q1 and Q6, and also through the excavation of the penstock, tailrace and spillways. It was identified that the excavation from Q6 and the excess spoil from the penstock excavation could be incorporated into the dam at Q6 with minimal excess. However, a greater level of excavation (than initially estimated) was identified as being required at Q1, with approximately 690,000m3 of excess slate expected to remain once the dam was completed. Three options were considered for the management of the excess spoil with the approved scheme; (1) place material into Q2 up to a level that would not be visually intrusive; or (2) add to the existing, or create new, slate mounds which would replicate the existing slate spoil mounds which surround the site; or (3) move the excess material off site.
3.6.20 The proposed use of Q2 was discussed at a meeting with Gwynedd Council on 22nd August 2012. It was agreed with the Council and other regulators that the potential ecological, archaeological and landscape effect from placing excess material in Q2 would be too significant, as would the impacts of removal of the excess material offsite through Waunfawr. Therefore, it was agreed that the material would stay onsite and be landscaped into the existing spoil mounds at Q1.
3.6.21 Design Review 3 led to the layout as shown on Volume 4, Figure 3.7
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Design Review 4: Approved Scheme - Final Design
3.6.22 The final design review confirmed that the construction method for the penstock would be underground tunnel excavation which would remove the need for any above ground excavation for the penstock.
3.6.23 Two dams were proposed; one at Q1, approximately 25m AGL by 510m long (at the longest point), and a second at Q6, approximately 15m high from existing ground levels by 215m long (at the longest point).
3.6.24 The power house for the approved scheme was still proposed to be located on Platform 5 of the Glyn Rhonwy Industrial Estate.
3.6.25 The location of the pumping station for the approved scheme was confirmed as being at National Grid ref SH 57250 61192 on the banks of Llyn Padarn due to the proximity to deeper water and minimal effect on the car parking areas in this location.
3.6.26 The location of the spillway was confirmed as being to the south and south east of Q8, outside of the bombstore, and therefore reducing the impact on the former munitions store.
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3.6.27 The 22nd August 2012 meeting with Gwynedd Council agreed the placement of excess material south west of Q1 incorporating the existing slate mound already present.
3.6.28 This finalised design of the approved scheme is shown on Volume 4, Figure 3.8.
3.6.29 The design evolution to this final design necessitated no additional survey requirements or amendment to the technical methodologies from those agreed with statutory consultees at the Scoping stage.
3.6.30 Table 4-2 outlines the parameters of the approved scheme:
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Table 4.2 – Parameters of Approved Scheme Area Description
Q1 Capacity – 1,100,000m3 Dam Height – 25m high Dam Crest Level - 394m AOD Top Water Level – 392m AOD Lower Water Level – 342m AOD Overflow Level – 393m AOD Spillway – 400mm and 800mm discharge pipes
Q6 Capacity – 1,100,000m3 Dam Height – 15m high Dam Crest Level - 156m AOD Top Water Level – 154m AOD Lower Water Level – 121m AOD Overflow Level – 155m AOD Spillway – 450mm intake and 800mm discharge
Penstock Length approximately 1500m Diameter 4m
Excess Spoil Located south west of Q1 Mound 3 Contains a maximum of 690,000m
3.7 Design Evolution: Development Consent Order
3.7.1 Following the grant of planning permission for the 49.9MW scheme, the Applicant moved into the implementation phase. However, and as stated earlier, changes to the capacity market introduced through the EMR, necessitated a review of the scheme’s generating capacity. This review highlighted that the scheme was unlikely to be deliverable with a generating capacity of at 49.9MW and that an increased generating capacity would be required. A review of the approved scheme was therefore commissioned by the Applicant to determine the increase in generating capacity required to
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improve deliverability. From this point, a further four stages in design evolution have been undertaken to define the Development subject to the DCO application.
3.7.2 As the design evolution took the approved scheme as its baseline, this section identifies the stages in the design review process as a continuation of the design process for the approved scheme.
Design Review 5: Capacity Uplift & DCO Scoping Letter (December 2014)
3.7.3 Through an engineering review, it was confirmed that the generating capacity of the Development could be increased to 99.9MW without any substantial changes being made to the approved scheme. It was recognised at this stage that with a generating capacity above 50MW, the Development would require authorisation through a DCO application.
3.7.4 The increase in output capacity was to be achieved through an increase in the size of the turbines and associated infrastructure proposed as part of the Development. These changes were predominantly below ground and within the power house adjacent to Q6 and included the following:
x More powerful turbines with a combined output capacity of 99.9MW located within the underground turbine hall. The turbine hall remained the same size as the approved scheme and had sufficient space to house the generators required to deliver the additional generating capacity;
x Additional noise attenuation for the turbines was proposed (if required) to comply with any limits set by a DCO Requirement (which would be reflective of the limits set by planning conditions for the approved scheme); and
x A minor increase in the number of construction based deliveries to bring the larger turbines and associated infrastructure on to site. However, as the additional deliveries would have been to Q6, it was expected that the A4086 road infrastructure would accommodate the slight increase in construction delivery traffic (particularly as the planning conditions relating to traffic mitigation and management for the approved scheme
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mitigation and management were proposed to be reflected in DCO Requirements). No additional construction traffic was expected to be required for Q1.
3.7.5 It was not expected that there would be any additional spoil excavated at Q6 as the turbine hall (as approved under the T&CPA) was sufficiently sized to accommodate the additional turbines and transformers.
3.7.6 In addition, it was envisaged that the construction methods would be based on the limits, restrictions and compliance conditions imposed by planning conditions on the approved scheme. To remain consistent with the extant planning permission and retain the principles of the agreed mitigation, it was proposed that the planning conditions imposed by Gwynedd Council would provide the basis for the DCO Requirements.
3.7.7 In response to the increase generation capacity, the Applicant discussed options for connecting the project to the national grid with SP Manweb - the Distribution Network Operator (DNO). SP Manweb suggested two solutions; an Air Insulated Switchgear (AIS) substation adjacent to the turbine house, or a Gas Insulated Switchgear (GIS) substation. The AIS would be up to 80m by 100m and above ground, whereas the GIS would be more expensive but much smaller and could be housed within a building. In response the Applicant has provided for a GIS substation building in which the interface between the Development and the DNO grid connection will exist.
3.7.8 In light of the minimal changes between the approved scheme and that initially proposed for DCO approval, a letter was issued to statutory consultees setting out the scope of the EIA for the Development, and seeking their comments. This approach was agreed with PINs and further details are provided in section 2.3 of this ES.
3.7.9 The Order Limits proposed for the DCO at this stage comprised an area of 59.3ha which reflected the size of the redline site boundary for the approved scheme. The scoping letter issued to selected statutory consultees, together with a plan of the Order Limits proposed at that time, is
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included in Appendix 2.2 in Volume 3 of this ES. The Order Limits are shown in Figure 3.8, Volume 4.
Design Review 6: DCO Scoping Report (January 2015)
3.7.10 As set out in detail in section 2.3 of this ES, a formal request (accompanied by a detailed scoping report) for a scoping opinion from the SoS was submitted to PINs on the 5th January 2015. It was agreed at a meeting between the Applicant, PINS, Gwynedd Council and NRW on the 2nd December 2014 that a formal scoping opinion should be sought as the Order Limits had increased as a result of further survey and engineering work undertaken as part of Design Review 6. Further detail on the review process is set out below.
3.7.11 At this stage in the project evolution, preliminary GI works were being undertaken, together with an associated engineering review of the design. Alongside this, the Applicant commissioned a full review of the land acquisition strategy for the Development. This work provided the basis to establish a Rochdale Envelope for the purposes of the EIA. The Rochdale
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Envelope encompassed a realistic worst case scenario for construction methods, potential land take (including stabilisation works) and any other potential requirements that would need to be assessed. The design of the Development at this stage was set out in the Scoping Report submitted to PINS on the 5th January 2015, and is illustrated in Volume 4, Figure 3.9.
3.7.12 The principal changes to the scheme made at this stage in the design evolution are outlined below.
3.7.13 The Order Limits were increased to allow for construction activities connected with the new excess slate mounds to the south of Q1. An increased area to the north of Q1 was also included within the Order Limits to accommodate potential options for re-profiling the north quarry wall.
3.7.14 The area around and within Q1 is on land registered as Common Land, so an application will be made to deregister the parts of this area which will be permanently affected and fenced off. The land north and south of the penstock corridor and west of the Q1 construction compounds was identified as replacement land in terms of quality, size and access in
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relation to the land being deregistered. The land was included in the Order Limits as land negotiations had not been concluded at the time. This was to ensure that powers could be sought under the DCO to compulsorily acquire this land.
3.7.15 The Order Limits around the penstock were widened due to the potential for dolerite intrusions which may be present in this area. Dolerite is a hard rock which is more challenging to tunnel through and therefore it was assumed that two excavation methods could be required – drill and blast and Tunnel Boring Machine (TBM). The corridor in which the penstock will be constructed was also widened to 114m to allow flexibility in the penstock tunnel alignment underground. The increase was towards the south to allow maximum flexibility without any impact upon the existing quarries to the north. The alignment of the penstock will only vary if geological conditions necessitate but it will remain inside the Order Limits. The worst case aspects of both methods have therefore been included in the EIA.
3.7.16 It was also identified during this design review that the northern quarry wall at Q6 may need to be re-profiled and that further ground investigation works would be required to confirm the requirement for and scale of these reprofiling works. If reprofiling is required, this may encroach on the existing slate mounds to the north which may then also need stabilisation and reprofiling. The worst case method of stabilisation has been identified as using rock anchors and rock bolting on the quarry wall with reprofiling of the slate mound above it. This has been included as an extension to the Order Limits as a precautionary measure.
3.7.17 To further minimise the landscape impact, it was proposed that the northern edge of the Q6 dam will be reprofiled towards the slate mound to the north of Q6, in order to mimic the rolling nature of the existing slate mounds.
3.7.18 Due to the encroachment of the Q6 dam onto the Glyn Rhonwy Industrial Estate platform, and a commitment not to adversely affect Q7, it was concluded that it may be preferable to design a road originating from the lower platforms in the Glyn Rhonwy Industrial Estate, rather than within the
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dam footprint. Therefore an additional area was included for a potential replacement road to the power house, as shown in Volume 4, Figure 3.9.
3.7.19 The Order Limits were also extended at this time to allow for flexibility in the location of the pumping station and its working area. This was due to the potential to improve the pumping station design to remove any requirement for a long access track to the shore of Llyn Padarn. The pumping station was still proposed to be constructed in the manner outlined in the 2012 ES (i.e. sunken design with a small kiosk / control box above ground). The depth of the spillway infrastructure into Llyn Padarn was to remain 5m beneath the water level – this depth had been previously been agreed with Countryside Council for Wales (CCW at that time, now NRW) to be at this depth as it would avoid any potential effects on Arctic Char (by being above the thermocline), and recreational users.
3.7.20 As a result of the design review process, the development area within the Order Limits increased from 59.3ha to 91.73ha. This was the Order Limit included within the Draft ES used during the formal DCO consultation period.
Design Review 7: DCO Preliminary Environmental Information / Draft ES
3.7.21 Section 2.3 of this ES sets out the approach taken to the PEI as part of the formal consultation exercise undertaken under s42 and s47 of the PA 2008. The PEI was provided in the form of a Draft ES.
3.7.22 Subsequent to the issue of the Draft ES (February 2015) as part of the consultation period, the Applicant undertook a final review of the temporary and permanent PRoW diversions required in connection with the DCO. This identified a need to extend the Order Limits by approximately 6ha to a total of 97.77ha, this is shown on Volume 4, Figure 3.10.
3.7.23 During the formal consultation period, the Applicant continued to carry out survey work of the land within the Order Limits. This included a full topographical survey of the access route to Q1 (Green Road) and the laser mapping of the Q1 and Q6 voids to prepare a more extensive and accurate picture of the topography. Localised topographical surveys around the
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quarries were also completed to supplement the digital terrain and LiDAR mapping previously undertaken for the entire site.
3.7.24 In addition the preliminary GI works were also being undertaken at this time. However the results of these investigations did not affect the Order Limits.
Design Review 8: Proposed DCO Development
Final Order Limits
3.7.25 Since the issue of the Draft ES (February 2015), a final series of further changes have been made to the Development design and the Order Limits. These have been made in response to comments received through the formal consultation process, as a result of the extensive mapping and data collection exercise, and also to reflect a reduction in the extent of land take required for the DCO. The changes to the Development design have occurred as a result of the extensive mapping and data collection exercise. These final amendments are outlined below and shown in Volume 4, Figure
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3.11 which illustrates the Development subject to the DCO. The overall land area within the order limits has been reduced to 91.24ha.
3.7.26 During the design process, hydrological continuity (surface and sub- surface) through the quarry system from Q2 to Llyn Padarn and surrounding areas had been identified. Therefore it was considered that any sealing works in Q6 may have the potential to affect hydraulic continuity. This is assessed in greater detail within Chapter 9 Water Resources. As a precautionary measure Q5 has been included within the Order Limits. Existing tunnels between Q5 and Q6 may allow for free drainage if above the operational water level of the Development. However, if this is not the case then the inclusion of Q5 within the Order Limits will allow for installation of suitable drainage infrastructure from Q5 to Q6.
3.7.27 The area previously allocated as replacement Common and CROW land was removed from the Order Limits as more suitable land was identified to the north of Q1. This replacement land is not included within the Order Limits as land agreements are in place between the landowner and the
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Applicant. The de-registration of the common land will be subject to a separate application. More details on this are outlined in Chapter 15 Socio Economics.
3.7.28 Since the submission of the Draft ES, a bathymetric survey has been undertaken, the results of which have led to an extension of the spillway into Llyn Padarn to a depth of 5m beneath the water level contour. This is therefore a more accurate representation of the length of the spillway.
3.7.29 To enable stopping up powers to be enforced, the area within the public highways (known locally as Green Road) from Q1 to the PRoW diversions has now been included on the Order Limits. The Order Limits now also include a replacement car park for users of the area, namely Cefn Du, and the PRoW.
3.7.30 Further to consultation with Gwynedd Council, the extent of the PRoW diversions to the south of Q1 have been amended to remove the proposed diversion to the east of the disused Bryn-mawr quarry. To improve the safety of users, the route was shortened and now extends to the east of the Bryn-mawr quarry. Additional extents were added to the PRoW diversions in the far west of the Order Limits to encompass informal routes which cross the existing slate mound area.
Increase in Storage Capacity
3.7.31 Since the submission of the Draft ES, the digital mapping of the Development has been completed to provide a more accurate investigation of the Q1 and Q6 voids and topography. Combined with the bathymetry surveys which have been undertaken in Q6, and additional baseline data (namely fish and aquatic surveys also completed in Q1), the extent of the quarry voids above and below the existing water levels has been further refined.
3.7.32 The mapping of the quarry voids has identified the potential to increase the storage capacity of the reservoirs from 1,100,000m3 to up to 1,300,000m3. This increase in potential storage capacity does not materially change the proposed Development as consulted on in February 2015. Both Gwynedd
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Council and NRW were informed of this capacity change in a meeting held on the 15th July 2015.
3.7.33 This increase is entirely attributable to the improved accuracy provided by the detailed topographic surveys. The increase in capacity will deliver an increase in energy generating capacity from 600MWh to up to approximately 800MWh. The overall output generation of the proposed development remains at up to 99.9MW (as the increased storage capacity will allow the facility to operate for a longer time period) and therefore no changes to the electrical connection are required.
3.7.34 It must be noted that the increased storage capacity has not been achieved through any changes to the overall size of the dams or the above ground buildings (such as the power house). It is purely a result of the greater volume of the reservoirs which increase the length of time the scheme can operate at its maximum output of 99.9MW.
Changes to Material Volumes
3.7.35 The detailed topographic and digital mapping survey also identified that whilst the void at Q1 is larger than previously estimated, Q6 is smaller than originally estimated. Principally, at Q6, this is due to the presence of a number of geological intrusions below the surface of the water identified through the bathymetric survey - these intrusions will need to be removed to create the reservoir at Q6. Therefore, in order to provide the equivalent storage capacity in Q6 as Q1, up to approximately 650,000m3 of screened unsuitable material will need to be moved from Q6; all suitable virgin material will used for the construction of the Q6 dam.
3.7.36 SPH therefore undertook a design review, under which alternative storage areas were considered. It was considered that any storage would potentially have an adverse visual effect and be in closer proximity to residential dwellings and private water supplies. In addition, the lack of available space to store the excess material permanently in the vicinity of Q6 rendered this option unviable.
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3.7.37 In recognition of the previous commitment not to transport excess material through Waunfawr, it is therefore proposed that the excess material not utilised in the construction of the Q6 dam will be transported through the penstock utilising a conveyor. Excavation of the penstock utilises a conveyor for removal of excavated material, and this conveyor will be connected to run the full penstock length between Q6 and Q1 to carry material. This material will then be deposited within the proposed slate mounds at Q1.
3.7.38 The material excavated from Q6 will result in an increase in the volume of the slate mounds at Q1 from up to approximately 690,000m3 to up to approximately up to 935,000m3. However the slate mounds still remain in the same orientation as approved previously and as per the photomontage of Viewpoint 2 Moel Eilio (see Volume 4 Figure 6.4). The excess slate mounds will occupy a slightly larger footprint than previously proposed, but remain 4m away from the nearest public right of way (and their associated permanent diversions), 10m away from the Nant Y Betws and 2m away from the Order Limits boundary in any other non-constrained areas. The use of detailed terrain data has confirmed that there is sufficient space to accommodate this increase and a landscape assessment has confirmed that there are no additional effects.
3.7.39 The material will be subject to a contaminated land assessment (the methodology for which will be established in Chapter 8 Geology & Ground Conditions) and the material will be screened for any unexploded ordnance, as per the Ordnance Management Strategy, prior to its transportation. However given its virgin material status, it is unlikely that there will be any significant effects from its transportation. As with the Q1 slate mounds, the excavated material will be controlled via a Material Management Plan (MMP) (which is expected to be controlled by a DCO Requirement).
Changes at Q6 and Pumping Station
3.7.40 To enable the construction of the potential bifurcation valve (where the penstock splits into two tunnels to serve each turbine), a secondary access shaft and access tunnel will be sunk to enable excavation. This will be in
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addition to the main turbine shaft and tailrace but will not be used during operation other than for maintenance.
3.7.41 Whilst there was no change in the Order Limits, the location of the pumping station was moved further back from Llyn Padarn to an area of vegetation adjacent to the main car park. A secondary alternative location is also being investigated and is subject to ongoing discussions with utility companies regarding easements. This alternative location is immediately adjacent to the toilet block in front of the access to the bombstore. The DCO Work Plans (Document 2.04) have accounted for this flexibility should the secondary option be feasible from an easement and engineering perspective.
3.7.42 The final Rochdale envelope parameters are provided in Table 4-3:
Table 4.3 – Rochdale Envelope Parameters Area Description Q1 Maximum elevation of dam of 395m AOD to crest Plan width 150m and length 371m Max volume of 1,300,000m3 Max water level 392m AOD Excess Spoils Max combined volume of 935,000m3 Mounds Penstock To be tunnelled within 114m buffer and between an maximum elevation of 330m AOD to a minimum depth of 55m AOD Up to 1600m long within Order Limits (plan length) but potentially up to 1800m to allow for any underground deviations, and 4.5m internal diameter Tailrace Up to 160m long Tailrace, 4.5m internal diameter Q6 Maximum elevation of 156m AOD Plan width 95m and length 210m Max volume of 1,300,000m3 Max water level 154m AOD Power House Approximately 15m high to apex x 27m wide x 60m long
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Table 4.3 – Rochdale Envelope Parameters Area Description Turbine Hall Two underground turbines with maximum electrical output of up to 99.9MW Approximate volume of excavation 100,000m3 Switchgear 10m high to apex x 18m wide x 30m long Transformer 7m wide x 7m long x Assumed to be 10m high GIS 12m high to apex x 12m wide x 30m long Substation Gas insulated
3.8 Alternatives
Engineering Alternatives
3.8.1 Throughout the design evolution, alternatives have been considered. These are outlined in detail in Sections 3.6 – 3.7 in detail but to summarise these include:
x The use of Llyn Padarn as the tailpond – whilst the potential optimal solution in terms of engineering, this was discounted early in the scheme development due to its highly sensitive, environmental, ecological and social importance;
x An alternative to the movement of material offsite through Waunfawr resulted in the creation of the excess slate mounds and internal conveyor from Q6;
x The underground excavation of the penstock was confirmed on the basis of significantly adverse visual, environmental and archaeological effects from an open cut alternative;
x Routing of the underground penstock to avoid any potential geotechnical instability issues from drilling under existing slate mounds and close to quarries contained highly sensitive and protected ecological features; and
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x Placement of the discharge outlet into Llyn Padarn above the thermocline to avoid any potential effects on the Arctic Char.
Alternatives to the site at Glyn Rhonwy
3.8.2 As required by the Overarching National Policy Statement for Energy (EN- 1) and as advised by the SoS in Section 2.56 of his Scoping Opinion (February 2015) consideration has been given to alternatives to the Development as proposed in the DCO application. The following section details why SPH selected the Glyn Rhonwy site for the Development over other potential locations.
3.8.3 The technologies, plant and construction methodologies to be used, where definable at this stage of the development process, are detailed within this chapter and Chapter 4 Project Description. Alternative construction methods and technologies to those assessed in this ES were considered; however, they have not been carried forward or selected for the final design for various reasons, typically due to their engineering inefficiency and non- compliance with best practice guidelines.
3.8.4 Sites suitable for pumped storage are limited by the need for specific physical characteristics. Importantly, pumped storage requires at least two or more quarries or reservoirs where water can be released from a high to a low elevation. An initial source of water is also required and sites need to be reasonably close to existing electrical connections.
3.8.5 The feasibility study work undertaken by the Applicant for the development of pumped storage included a detailed mapping exercise undertaken to examine the feasibility of pumped storage throughout Great Britain, against key indicators including:
x the geology and terrain;
x accessibility;
x ground condition;
x safety and feasibility of construction;
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x the physical shape and sizes of the reservoirs and requirements for dams;
x the distance between the reservoirs and the distance to the transmission grid;
x the environmental sensitivity of the site; and
x whether any impacts of the development could feasibly be designed out or mitigated.
3.8.6 This exercise identified a number of locations where pumped storage is considered feasible, including Glyn Rhonwy. However Glyn Rhonwy was identified as a highly suitable location for pumped storage for several reasons:
x There are two quarries separated by a large height difference but geographically close to each other;
x The local geology of the Llanberis Welsh Slates formation is a reasonably impermeable seam, the use of which has already been proven by the Dinorwig Pumped Storage facility; and
x The site is only 8km from a connection point to the electricity network, which, given the other critical criteria, is considered to be relatively close.
3.8.7 The Gwynedd Unitary Development Plan (UDP) (2001 - 2016) specifically identifies pumped storage (Policy C27) as a suitable use on use of previously developed land at Glyn Rhonwy Redevelopment Site (Policy C6). The following justification is summarised from the Plan:
“Redevelopment at Glyn Rhonwy
x Nearby Llanberis already contains a reasonable number of services and community facilities together with some employment opportunities. It is also a popular tourist centre;
x The site is accessible from the local and wider area, near a regular bus service route and close to the A55 dual carriageway;
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x Creation of year-round employment opportunities could increase the expenditure in the county’s economy and would add value to existing local facilities; and
x Development would act as a catalyst for the redevelopment of other sites in the area, in addition to promoting enterprise throughout Gwynedd.”
Do Nothing Scenario
3.8.8 Pumped storage provides fast response energy in times of peak demand. Without this ability to rapidly respond to peak demand the UK would rely increasingly on baseload thermal power stations and inflexible forms of renewable energy, such as wind, to provide energy whether it is required or not. This would lead to significant inefficiencies and unnecessary green house gas emissions through unnecessary burning of fossil fuels. NPS EN- 1 supports the use of technologies such as pumped storage under the classification of “electricity storage” to provide back up to an energy market increasingly supplied by less predictable renewable energy sources. Section 3.3.12 of NPS EN-1 states
‘There are a number of other technologies which can be used to compensate for the intermittency of renewable generation, such as electricity storage, interconnection and demand-side response, without building additional generation capacity. Although Government believes these technologies will play important roles in low carbon electricity system, the development and deployment of these technologies at the necessary scale has yet to be achieved. The Government does not therefore consider it prudent to solely rely on these technologies to meet demand without the additional back-up capacity. It is therefore more likely that increasing reliance on renewable will mean that we need more total electricity capacity than we have now, with a larger proportion being built only or mainly to perform back-up functions.’
3.8.9 There are limited sites across the UK which are deemed suitable for pumped storage. To not make use of the Glyn Rhonwy site, which has been
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identified as suitable under the Gwynedd UDP, would not help in supporting the UK’s need to ensure that maximum peak demand is met, as outlined in NPS EN-1.
Project Optimisation
3.8.10 This EIA assesses the worst case scenario by making reasonable assumptions based on current knowledge and engineering design. The engineering design has been undertaken and refined where possible based on the information gained to date and there will be elements which will be subject to detailed design and further site investigation works.
3.8.11 However there is also the potential for opportunities within the design for engineering improvements and optimisation. These are indentified as follows:
x Turbine Shaft - The turbine shaft as shown in Volume 4, Figure 4.11 is considered the maximum extent of excavation. However the turbine shaft can be optimised by excavating two smaller individual shafts or a thinner single shaft opening into a larger underground turbine hall. Therefore the assessment has been made on the worst case engineering option.
x Material to be excavated - The volume of material to be excavated has been derived using a bulking factor of 1.6. This is considered to be a conservative assumption and any lesser value would be considered an improvement.
October 2015