Glyn Rhonwy Pumped Storage Development Consent Order

Appendix 9.1 Water Framework Directive Assessment

Table of Contents

1 Introduction ...... 1 2 Approach and Methodology ...... 6 3 Environmental Baseline ...... 13 4 WFD Appraisal ...... 23 5 Summary and Conclusion ...... 35 References ...... 37 Glossary ...... 38 Appendix A Study Area Water Bodies ...... 39 Appendix B Water Balance Technical Note ...... 40 Appendix C Water Quality Data and Analysis ...... 51

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1 Introduction

This Water Framework Directive (WFD) Appraisal has been prepared to support the preparation of an Environmental Statement and an application for a Development Consent Order (DCO) for a proposed pumped storage development near Llanberis.

1.1 Description of the Proposed Scheme Snowdonia Pumped Hydro Ltd (SPH) proposes to construct and operate a pumped storage hydropower plant using existing former quarries to the west of Llyn Padarn and to the northwest of Llanberis. The extent of the Development and the location of any nearby Water Framework Directive (WFD) designated water bodies are shown by the figure in Appendix A. Please refer to Chapter 4 Project Description of the Environmental Statement for further details.

1.1.1 Construction Chapter 4 Project Description of the Environmental Statement presents an overview of the construction method with details of mitigation measures described in the Code of Construction Practice (Appendix 16.1 of the Environmental Statement). The following are specific details relevant to this assessment. It is estimated that the headpond (henceforth referred to as Q1 – see Photo 1) currently holds approximately 500 m3 of water, and the tailpond (henceforth referred to as Q6 – see Photo 2) approximately 100,000 m3 of water (this is a worst case assumption based on an estimate of 50,000 m3 of water in the standing water column and a further 50,000 m3 in the voids of the slate waste believed to reside in the bottom), respectively (Please refer to Appendix A). This water will need to be removed prior to construction works, together with any ongoing dewatering of natural runoff and groundwater seepage.

Photo 1 Q1 Headpond Photo 2 Q6 Tailpond

It is preferred that this water will be discharged to Llyn Padarn via a temporary above ground pumping main until either the existing scour pipe is completed or the existing system that drains the quarry is fully understood. Water quality in Llyn Padarn will be monitored during the discharge operation, the scope of which will be agreed when an application for a discharge consent is made under the Environmental Permitting (England and Wales) Regulations 2010 (as amended).

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1.1.2 Commissioning It is proposed to abstract water from Llyn Padarn to commission the pumped storage scheme proposed at Glyn Rhonwy by Snowdonia Pumped Hydro. In July 2015 Snowdonia Pumped Hydro obtained an abstraction license from NRW under the Water Resources Act 1991 (as amended) for the following (yet to be utilised): - Permission to abstract up to 2,000 m3/day from Llyn Padarn; and

- Permission to abstract up to 550,000 m3 in a 12 month period (equivalent to 1,507m3/day for the full year).

An additional condition was that no abstraction from Llyn Padarn should occur when river levels in the downstream Afon Seiont are less than 0.343 m at the Peblig Mill gauging station (henceforth referred to as the ‘hands off flow’). It had previously been estimated that 1.1 million m3 (Mm3) of water will be required to fill the quarries during the commissioning period. Subsequent to gaining the current abstraction licence Snowdonia Pumped Hydro identified from recent bathymetric surveys of the quarry system that a greater volume of 1.3 Mm3 can now be stored It is now proposed to abstract water at a rate of up to 3,300 m3 per day within a total period of approximately 18 months, depending on licence conditions linked to the lake water level, flows along the Afon Seiont and environmental considerations yet to be agreed with NRW. The abstraction of water from Llyn Padarn will require an amendment to the existing abstraction licence. Until this is determined it has been assumed by this assessment that abstraction will be made at the maximum proposed rate providing there is sufficient water in Llyn Padarn to maintain the hands off water level on the Afon Seiont at the Peblig Mill gauging station, as required by the current approved abstraction licence. A new intake and pumping station would be located at approximately SH 57150 61200 in the centre of the southern bank of the lake. The intake will extend approximately 30 m into the lake and approximately 5 m wide at its largest extents. It will be positioned so that it is at least 5 m below the average minimum water level of the lake and a similar depth above the typical shallowest depth of the thermocline in order to avoid potentially adverse impacts on ecological and recreational receptors. The intake (and adjacent outfall) pipe will be buried, being constructed using an open cut method but within a dry working area supported by a coffer dam and an outer silt curtain.

1.1.3 Operation Throughout the following section please refer to Chapter 4, Project Description, and the scheme drawings presented in Appendix 4.2-4.15 of the Environmental Statement. Once in operation, water will generally be allowed to drain from Q1 through the penstock, turbines and the tailrace to Q6 during peak daytime demand. Water will then be pumped back to Q1 during the night exploiting cheaper electricity rates. However, it is highly likely that both reservoirs will be part filled for the majority of the time. The scheme is a ‘closed system’ with water being constantly recycled between Q1 and Q6 and vice versa. However, it will be necessary to ‘bleed off’ excess water that enters the quarry from direct rainfall and runoff from the quarry walls. It is also necessary to provide a way to rapidly drain down each reservoir in an emergency (i.e. as a result of concerns over dam safety), other than by transferring to the other reservoir. To do this two overflows (i.e. pipes to outfalls) will be constructed, one from Q6 to Llyn Padarn and from Q1 to the Nant-y-Betws stream. From Q6, the overflow will be an approximately 800 mm diameter pipe that will be buried beneath the littoral margins of Llyn Padarn before emerging from the bed at a water depth of at least 5 m below the minimum average lake water level (and thus into water above that typically used by Arctic charr for spawning) to where a concrete headwall, diffuser head with suitably sized fish screen will be fitted. From Q1 the overflow will consist of approximately 800 mm (overflow) and 450 mm (combined scour and Rising Main) diameter pipes that will discharge to the Nant-y-Betws stream via a stilling basin and an outfall fitted with flow disruptors (to reduce flow velocity and dissipate energy) and a trash screen. It has been agreed with NRW that the detail design of this outfall can be subject to a Requirement of the DCO. This will ensure that adequate measures are fitted to the outfall to minimise any risk of erosion occurring in the Nant-y-Betws.

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Under normal operation, excess water that builds up in the system from natural runoff will be syphoned off from Q6 using an overflow positioned just above the maximum operational water level (i.e. 154 mAOD) and discharged to Llyn Padarn via an overflow. Should this not be possible due to a failure of the pumping system, restriction on the discharge from Q6 to Llyn Padarn, or a large sudden storm event, excess water in Q1 could be discharged via an overflow (set just above the maximum operational water level of 392 mAOD) to the Nant-y-Betws stream. However, this scenario is extremely unlikely as the optimal position would be to discharge from Q1 to Q6 in these events by opening the penstock between the two reservoirs. Only if the penstock was unavailable and the headroom in Q1 utilised, would the relief valve then release to the Nant-y-Betws. Excess water will be syphoned off from the pumped storage system in response to rainfall and natural runoff into each reservoir, which will be similar to the current (i.e. without the development) runoff regime to the Llyn Padarn. Detailed design of the excess water overflows is yet to be undertaken, but they will be designed to accommodate a Probable Maximum Flood flow (approximately a 1 in 10,000 year storm) with a maximum discharge rate of 0.15 m3/s along the Q1 overflow and 1.6 m3/s for the Q6 overflow, respectively. If required the overflows will incorporate energy dissipation features (e.g. over-widened channel with flow disruptors) to retard the flow and avoid excess erosion of the Nant-y-Betws stream. An Excess Water Management Strategy will be prepared and it has been agreed with NRW that this shall be a pre-construction requirement of the DCO. During an emergency situation, the principle method for quickly draining down Q1 would be the penstock through the turbines to Q6. The draw off and pumping facility has the capacity to transfer water between the two reservoirs within a matter of hours. However, under certain exceptional circumstances when there is an immediate need to rapidly lower the water level in either reservoir (i.e. potential risk of dam breach), while at the same time it is not possible to pump water from Q6 to Q1 or allow water to drain through the turbines from Q1 to Q6, water can be released by a relief valve at the base of each reservoir down the overflows to either Llyn Padarn or the Nant-y-Betws stream. For Q1, water drained via the relief valve will go down the overflow into the Nant-y-Betws at approximately a maximum rate of 0.6 m3/s. For Q6 water drained via the relief valve would go into Llyn Padarn at approximately a rate of 0.3 m3/s. Both relief valves are designed to drain the reservoir by 100% of the impounded volume (i.e. the total volume of water held back by the dams and not the total water stored in the reservoir) within seven days and each would be fitted with a coarse debris screen. The use of the relief valve in an emergency from Q1 or the relief value in Q6 is considered to be a highly unlikely event. The risk of an emergency is reduced by constant monitoring of the pore water pressure within the dams plus the maintenance and inspections required under the Reservoirs Act 1975 (as amended). Under the Reservoirs Act 1975 (as amended) it will be necessary for both dams to be inspected at least once per year. A major inspection of the dam will be required approximately every 10 years during which a partial or full draining down of the reservoir may be required. Maintenance works will be planned well in advance so that they can be undertaken in the optimum period which would be determined according to a number of factors including the nature of the works, limiting operational disruption and avoiding the need for discharging to the natural water environment. Preferentially, major dam inspections and maintenance work shall be carried out for each dam at different times of the year in order that the ‘free’ reservoir can be used for storage. However, during maintenance there is a greater possibility of more frequent small discharges of natural runoff to either Llyn Padarn or the Nant-y-Betws, depending on which reservoir is being inspected or maintained. In the long term it is assumed that the water quality of both reservoirs will be similar to the quality of water in the existing quarries, although there may be less leaching of metals and other ions as the quarries will be lined. The water quality of both reservoirs will be tested on a regular ongoing basis during operation and analysed for a suite of chemical determinands to be agreed with NRW. Long term water quality monitoring will provide a robust baseline from which to evaluate the risk of spills to Llyn Padarn, and less frequently the Nant-y-Betws and the Afon Gwyrfai. By committing to this water quality monitoring, it will be possible to gain a greater understanding of water quality and identify trends, ensuring that action, should it be required, can be taken rather than investigating the potential effects post-spill, something that would be more difficult. Water quality monitoring of Llyn Padarn before abstraction commences and throughout the process will help to avoid abstracting during short term periods of very poor quality that may occur for a short periods following prolonged wet weather when there will be additional wash out of the catchment and a greater risk of stormwater spills from Llanberis Sewage Treatment Works (WWTW) and other intermittent discharges. Consideration may also be given to reducing the rate of abstraction immediately

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following the autumn lake overturn when water quality is also likely to deteriorate (i.e. low oxygen water containing elevated levels of nutrients and metals that have built up in the hypolimnion are released throughout the water column). However, since water will be abstracted at a relatively slow rate over a long period of time, short term deterioration in water quality will tend to be offset by abstraction at times of better quality. The water abstracted from Llyn Padarn will also be diluted by natural runoff into Q1 and Q6.

1.2 Water Framework Directive The WFD was transposed into law in England and Wales by the Water Environment (Water Framework Directive) Regulations 2003. These regulations implement a holistic approach to the management, protection and monitoring of the water environment, and requires that all water bodies achieve ‘good status’ by 2015.

Good status comprises either good ecological status or good ecological potential (if the water body is designated as heavily modified or artificial) and good chemical status. ‘Good’ in this context is defined as a slight variation from undisturbed natural conditions. ‘High’ ecological status (which is higher than the target) equates to pristine natural conditions. There are also three classes which are less than good – moderate, poor or bad ecological status / potential. The classification of all water bodies, including relevant pressures and risks, as well as the actions (or measures) required to ensure that all the water bodies achieve their WFD objectives are set out in a series of statutory River Basin Management Plans (RBMPs) that were first published in December 2009 by NRW (as EAW). The Glyn Rhonwy Pumped Storage Scheme is within the Western Wales River Basin Management Plan (RBMP). NRW are currently consulting on the second cycle RBMP which is due to be published later in 2015.

1.2.1 Water Framework Directive Objectives The objectives of the WFD for surface waters are:

- Prevent deterioration in the status of water bodies; - Aim to achieve good ecological and chemical status in water bodies by 2015; - For water bodies that are designated as artificial or heavily modified, aim to achieve good ecological potential and good chemical status by 2015; - Comply with objectives and standards for Protected Areas where relevant; and - Reduce pollution from priority substances and cease discharges, emissions and losses of priority hazardous substances.

For groundwater bodies, the WFD objectives are:

- Prevent deterioration in the status of water bodies; - Aim to achieve good quantitative and chemical status by 2015; - Implement actions to reverse any significant and sustained upward trend in pollutant concentrations; - Comply with objectives and standards for Protected Areas where relevant; and - Prevent or limit the input of pollutants into groundwater.

This assessment aims to determine whether the proposed pumped storage scheme could affect the status of one or more WFD water bodies by:

- Causing deterioration, defined as a drop in status class of one or more of the WFD parameters at the level of the water body (whether or not this results in an overall reduction in status / potential); and / or - For water bodies not at Good Ecological Status or Potential, prevent it from improving and thus achieving its WFD target.

Any implications for Protected Areas or for other (e.g. adjacent) water bodies will also be considered in line with the objectives set out above, and any other potential conflicts with the proposed RBMP Programme of Measures (i.e. the actions to be taken to achieve the WFD objectives) will be highlighted and resolved.

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Please note that there will be no release of chemical pollutants during the operation of the scheme and thus we will not consider any further the objective to reduce pollution from priority substances and cease discharges, emissions and losses of priority hazardous substances.

1.2.2 Preventing Deterioration in Status or Potential Deterioration in WFD terms refers to a change between status classes – for example, from high to good status or from moderate to poor status. Preventing deterioration in status is a strict requirement of the WFD. There is only one possible exception to this requirement for water bodies other than those at ‘high status’. This is the situation where physical modification to water body is required to support certain sustainable human activities (including flood defence) and where the criteria set out in Article 4.7 of the WFD are met.

1.2.3 Meeting the ‘Aim to Improve’ Objective If a water body is not already at Good Ecological Status or Potential, the RBMP may set out the measures required to achieve Good Ecological Status or Potential or it may set an alternative objective for the water body (which must be justified on grounds of technical feasibility or disproportionate cost). It is important to identify whether the proposed pumped storage scheme could prevent any intended improvements being realised and to resolve any such potential conflicts. At the same time, consideration of whether there is the possibility of any synergistic benefits with WFD measure that could help improve status in failing water bodies, although this is unlikely due to the nature of the proposal.

1.2.4 WFD Objectives for Groundwater Bodies Groundwater bodies are classified in terms of their chemical (quality) and quantitative status. There are only two classes for groundwater status – good and poor, the outcome being set at the lower of either chemical or quantitative status. The specific criteria that must be met for a groundwater body to be classed as being at good quantitative status and good chemical status are set out in the WFD and further elaborated in the Groundwater Directive (2006/118/EC (replacing 1980/68/EC)). These criteria have been developed in the UK into a series of tests, which are triggered when a relevant risk is identified (i.e. the identification of a risk leads to investigations to determine whether or not the criteria specified in the test are met).

1.2.5 Achieving Objectives for Protected Areas The WFD identifies areas requiring special protection under other EC Directives and water used for the abstraction of drinking water as Protected Areas. Under Article 4 of the Directive, Member States are required to achieve compliance with any standards and objectives set for each Protected Area by the end of 2015 unless otherwise specified in the other EC Directive. In addition, in the UK water dependent SSSIs should also be considered alongside Protected Areas when assessing the compliance of a proposed Development with WFD objectives.

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2 Approach and Methodology

This section describes the approach and methods used to assess the compliance of the proposed Development with the WFD.

2.1 Approach There is no formal guidance for the appraisal of compliance of proposed infrastructure projects with the objectives of WFD designated water bodies. Thus, we have adopted an approach based on our experience with other schemes and consultation with NRW to identify the key issues and scope of assessment. The study area has been reviewed to identify what WFD designated water bodies might be affected by the proposed Development. The appraisal is based on 2014 WFD classification data provided to AECOM by NRW in May 2015. A qualitative appraisal supported by a review of water quality, ecological, bathymetry and flow data has been carried out of the Development’s construction and operation to understand the likely consequences of the Development on the objectives of hydrologically connected or relevant adjacent (that could be indirectly impacted) WFD designated water bodies. This has also considered any relevant Protected Areas that apply to each water body. For water bodies that are not at Good Ecological Status or Potential we have also assessed compliance with proposed mitigation measures to determine if the proposed Development could prevent improvement, at the water body level.

2.2 Consultation The following summarises the relevant consultations carried out as part of the original planning application made under the Town and Country Planning Act 1990 and more recent consultation carried out under the current DCO application.

2.2.1 Town and Country Planning Application A Scoping Report for the approved 49.9 MW scheme was submitted to Gwynedd Council in November 2011 as part of the 2012 EIA. Responses to the Scoping Report were made by Gwynedd Council and by NRW (as EAW). These can be seen in Volume 3, Appendix 2.2 of the Environmental Statement. The response from NRW (as EAW) included advice in respect of the need for a licence to abstract water from Llyn Padarn for the initial filling of the reservoir. A specific comment was made regarding the need to assess the impact of the management of excess water and to assess the impacts of the Development on the current drainage pattern. A subsequent meeting was held with NRW in May 2012 to discuss the approach for the assessment of the development on water resources.

At a meeting on the 29th May 2012, NRW (as EAW) agreed in principle to the proposed abstraction regime from Llyn Padarn, providing the ‘hands off flow’ is maintained down the Afon Seiont. NRW (as EAW) also provided qualitative comments on recent water quality issues and risks to future water quality in Llyn Padarn, such as the ongoing work with Welsh Water to improve treatment at Llanberis WwTW and to resolve problematic Combined Sewer Overflows. In particular, NRW (as EAW) noted that Llyn Padarn was enriched against its ideal oligotrophic - mesotrophic status and that this was not reflected in the 2009 WFD classification due to when data had been gathered. Finally, NRW (as EAW) suggested that consideration of the potential to ‘seed’ an algal bloom in Llyn Padarn was considered by the assessment of this scheme. The Scoping response from Gwynedd Council included the requirement to assess the potential impact of the Development on Llyn Padarn SSSI as a result of discharges of polluted water or changes to the temperature of the lake. The Countryside Council for Wales (CCW) were consulted in 2012 by Etive Ecology who had been commissioned to undertake an impact assessment of the potential effects of the proposed scheme on the freshwater ecology of Llyn Padarn. They provided bathymetric data (including depth-volume and hydrographic curves) of Llyn Padarn, surveyed sometime in 2010 / 2011 (uncertain) and macrophyte survey data for 2003 and the 2009 SSSI condition assessment.

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2.2.2 DCO Application The formal Scoping Report for the Development was submitted to the Planning Inspectorate (PINS) on the 5th January 2015. In addition to stating the need to update the previous 2012 impact assessment to reflect any changes to the Development, planning policy, guidance and consultation, a number of additional comments were made relating to water quality and ecological effects that are relevant to the scope of the WFD assessment including:

- The depth of any discharge to Llyn Padarn and its typical seasonal stratification should be considered; - Potential geomorphic effects of discharges on Llyn Padarn should be considered; - Potential effects on bathing waters in Llyn Padarn should be considered; - A water quality sampling programme including water quality and sediment samples from Q6 should be undertaken; and - An assessment of the risk to the Afon Gwyrfai from any water transfer from Llyn Padarn and Q1 should be undertaken.

A meeting was held with NRW on 22nd January 2015 where the need for an abstraction license and the requirement for any further consents and permits were discussed. It was confirmed that a Water Activity Permit (i.e. a discharge consent) would be needed for the discharge of existing water in Q6 to Llyn Padarn. NRW also advised that should the water in Q6 be contaminated during operation (including temperature differences) then an environmental permit would be required prior to any discharge. The permit would set out NRWs requirements for treatment. A second meeting with NRW was held on the 30th March 2015 to discuss a range of matters concerning water resources, water quality, ecology and landscape:

- At this meeting it was agreed that the intake from Llyn Padarn would be positioned above the thermocline at a minimum depth of 5 m. AECOM also confirmed that the level and frequency of discharges during operation are unpredictable as they relate to the pattern of rainfall in any given year and it was agreed that the Excess Water Management Strategy can be a Requirement on the DCO, although the Environmental Statement will need to include an Appropriate Assessment; - SPH confirmed that water being discharged will not be of a temperature significantly different from the surface water in the receiving water bodies, but that the Environmental Statement will include an assessment of any potentially adverse effects from a hydrological connection between the two receiving water bodies and the quarries; - NRW raised concerns regarding the potential to mobilise sediment from the quarries to Llyn Padarn, specifically Q6 where there is the potential for munitions to be present. At this stage water will be filtered, monitored with further treatment if required. Any waste classed as hazardous will need to be taken to an appropriately licensed site for disposal; - NRW stated that Q1 and Q6 should be subjected to a fish survey due to the uncertainty of species that may or may not be present within quarry water bodies. In addition, the importance of Arctic charr should reflect the uniqueness and rarity of the population found in Llyn Padarn; and - SPH confirmed that they expected to use mains water supply (supplemented with water bowsers if pressure low) during construction other than the filling of the reservoirs.

Subsequently, NRW wrote to AECOM on the 24th April 2015 to confirm a number of matters discussed on the 30th March 2015. This included confirmation that water discharges from Q1 and Q6 will be subject to permitting under the Environmental Permitting (England and Wales) Regulations 2010 (i.e. two for dewatering Q1 and Q6, two for emergency release via the relief valve from Q1 and Q6, in addition to normal operational discharges to Llyn Padarn and the Nant-y-Betws and the abstraction licence from Llyn Padarn), providing details of the procedure and highlighting the likely need to use valid data and predictions that may require modelling. In addition, the Excess Water Strategy must include:

- “When releases are likely to be made and at what baseline conditions; - The receiving watercourse(s) should be assessed for their capacity along with structures. Releases should not be made which are likely to lead to incidents of flooding in the catchment; - Scour releases would be similar and require assessment and agreement as a 'Requirement' in the DCO; and - Any possible erosion of land due to releases should also be considered and addressed accordingly. Energy dissipation may also be required.”

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A third meeting with NRW took place on the 15th July 2015 to discuss ongoing aquatic ecology surveys and water quality sampling as well as other scheme progress. Further to this meeting NRW’s water quality specialist provided the following additional comments on the application:

- In commenting on the on-site water quality survey data provided at the time, NRW were in agreement that the data did not show any anomalies or departures from EQS values; - Runoff from areas where there is slate wastes needs to be carefully controlled, especially when crushed, since this could give rise to high suspended sediment loads. Slate is also high in aluminium that can be toxic to fish, especially when the pH is low. The potential impacts on the Llyn Padarn and the Afon Gwyrfai need to be considered and NRW would expect mitigation measures on site to deal with this specific issue. - NRW expect that a programme of catchment water quality monitoring is undertaken prior to and during the construction phase. This should include the preparation of an Action Plan in the event that adverse or unusual monitoring results are observed. The sampling programme should consider the following parameters: Total and dissolved metals, suspended solids, chemical oxygen demand (COD), and biochemical oxygen demand (BOD); and - The installation of a coffer dam in Llyn Padarn required for the installation of the abstraction pipe and overflow may require an Environmental Permit.

Finally, NRW issued a full licence to abstract water from Llyn Padarn in July 2015. The licence was for a total abstraction of 1.1 million m3 of water from Llyn Padarn limited to 2000 m3 / day and 550,000 m3 / year in the aggregate (i.e. abstraction at maximum rate allowed for only 275 days per year). Abstraction is prohibited unless the level of water in the Afon Seiont as measured at the Peblig Mill Gauging Station (NGR SH 49450 62269) is equal to or greater than 0.343 m. An application for a Flood Defence Consent under Section 109 of the Water Resources Act 1991 (as amended) has also been granted by NRW for the installation of the abstraction pipe, overflow and any other structures or works that could affect Llyn Padarn within the byelaws distance from the lake margin. However, as the scheme has changed slightly the licence will be reviewed to determine if a variation or a revised licence is required.

2.3 Scope of Assessment This assessment has considered the potential implications of the proposed Development on the WFD objectives for nearby water bodies. It is intended that the development will be a closed system and during routine operation there will be no further abstractions from any water body. Excess water can be discharged along two separate overflows serving Q1 and Q6, respectively, but in operation this would be predominantly from Q6 to Llyn Padarn, and only from Q1 to the Nant-y-Betws if this is not possible (i.e. it is unlikely)

There could also be discharges from Q1 or Q6 should there be the need to rapidly draw down either reservoir (i.e. if there was a risk of potential dam failure) and it not being possible to transfer water between them. However, this is considered an unlikely and rare event and operational procedures will minimise the risk of this ever occurring. However, as this could be a reasonable worst case scenario it has also been considered by the assessment. During construction existing quarry water will be pumped out of Q1 and Q6 where it would drain via a temporary pipeline to Nant-y-Betws and to Llyn Padarn, respectively. Groundwater seepage and rainwater entering the two quarries, which could become laden with silt and potentially other pollutants (e.g. construction materials, oils and chemicals) will also need to be dewatered to maintain a dry working area. Standard mitigation measures defined by best practice (e.g. Environment Agency Pollution Prevention Guidance) will be applied (please refer to the Construction Code of Practice presented in Appendix 16.1 of the Environmental Statement). These proven measures will be effective in managing the risk of pollution to WFD designated water bodies. Therefore, in the context of these mitigation measures and since the WFD is focused on long term non-temporary effects, potential short term and temporary effects associated with construction activities (including the potential adverse impacts on the Llyn & Eryri WFD groundwater body) have not been considered in detail any further. For more information and a full assessment of impacts associated with the construction phase please refer to Chapter 9 of the Glyn Rhonwy Pumped Storage Scheme Environmental Statement (AECOM, 2015).

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Although the abstraction of water from Llyn Padarn to initially fill the pumped storage scheme will occur during the construction and commissioning phase, due to the volume of water to be abstracted and the length of time over which it will take place (i.e. one to two years) it has been included in the assessment. We have also considered the dewatering of the both quarries in order to prepare a dry working environment and the potential discharge of this water from Q1 to the Afon Gwyrfai via the Nant-y-Betws stream, and from Q6 to Llyn Padarn.

Overall, the following possible impacts on WFD designated water bodies have been considered: 1) The effects on Llyn Padarn from the discharge of existing quarry water in Q6; 2) The effects on Llyn Padarn from the abstraction of commissioning water; 3) The effects on Llyn Padarn from the construction of a permanent intake and outfall structures; 4) The effects on Llyn Padarn from routine discharges of excess storm water from Q6; 5) The effects on Llyn Padarn from rapidly draining down Q6 in an emergency; 6) The indirect effects on the Afon Seiont from the abstraction of commissioning water from Llyn Padarn; 7) The effects on Afon Gwyrfai from the discharge of existing quarry water in Q1; 8) The effects on the Afon Gwyrfai from routine discharges of excess storm water from Q1; and 9) The effects on the Afon Gwyrfai from rapidly draining down Q1 in an emergency.

For all water bodies that might be directly or indirectly (i.e. adjacent water bodies such as the Afon Seiont that might be impacted by the abstraction from Llyn Padarn) affected by the proposed Development we have considered the potential affects of the scheme on WFD biological quality elements (BQE), supporting physico-chemical, and hydromorphological parameters insofar as they are required to support Good Ecological Status or Potential. We have also taken into account any relevant Protected Area designations including water dependent SSSIs. For discharges to Llyn Padarn a key aspect of the assessment has been the possibility that discharges from the Development could be at a warmer temperature with consequences for the Arctic charr population. For discharges to the Afon Gwyrfai catchment we have specifically considered the risk of transferring water from a different catchment and water body type, particularly nutrient levels. For all discharges we have considered the risk that water in the pumped storage scheme will become increasingly acidic due to the oxidation of naturally occuring sulphides. Nant Peris is a freshwater river that previously flowed into Llyn Peris, but is now diverted into the Afon-y-Bala by a tunnel. It is currently at Moderate Ecological Status due to copper and zinc levels, and is not expected to achieve Good Ecological Status until 2027 due to the implementation of mitigation measures to improve zinc levels being technically unfeasible. Upstream of the Proposed Development it shall not be affected by the development and will not be considered any further. NRW (as EAW) has also identified the possibility that runoff from the pumped storage scheme into Llyn Padarn could result in ‘seeding’ an algal bloom within the lake. However, this is considered unlikely due to the size and frequency of discharges and the likely quality of that discharge and that fact that aquatic ecology surveys of Q1/Q6 have not identified anything of concern. This issue will therefore not be considered any further. Another aspect of WFD assessment is the consideration of alien or ‘invasive’ plant and animal species. The invasive plant species Nuttall’s Waterweed (Elodea nuttallii) has been identified in Llyn Padarn and is considered to be a high impact alien species under the WFD. It is also a Schedule 9 species for which it is an offence to spread. However, it requires reasonably shallow water to grow in, so although the scheme will carefully remove it from any working or operational areas in Llyn Padarn, should it be drawn into Q1/Q6, it is unlikely to be able to successfully grow or survive in the deep water environment, which would be a relatively hostile habitat (given the closed-loop system and daily changes in water levels). Please refer Chapter 6 – Ecology of the Environmental Statement and the Habitats Regulation Assessment in Appendix 6.1 for a more detailed assessment of invasive species and other ecological issues.

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2.4 Method All WFD designated water bodies that could be affected by the proposed pumped storage scheme have been identified following a review of online maps, NRW data and the Western Wales RBMP (Environment Agency Wales 2009). From the same sources we have reviewed the 2014 WFD classification, targets, and currently proposed mitigation measures for water bodies not at Good Ecological Status or Potential. We have also identified and reviewed the citations and any data for relevant Protected Areas. All relevant scheme information, reports and previous correspondence have been reviewed and used to screen each water body to determine possible mechanisms by which the Development may impact on WFD objectives. All water bodies that might be directly affected (including relevant water dependent Protected Areas) and neighbouring water bodies that might experience indirect effects, have been assessed against the core WFD objectives for that water body, including deterioration of relevant ecological, supporting physico-chemical and hydromorphological parameters. For those water bodies not at Good Ecological Status or Potential we have also considered the failure to improve objective by assessing the proposed development against proposed mitigation measures. Finally, AECOM has consulted NRW extensively on water quality, water resource and ecological matters and obtained from them latest water quality data for Llyn Padarn and the Afon Gwyrfai.

2.4.1 Data Sources The following data sources have been used to inform this assessment:

- AECOM (February, 2012) A Report of a Hydrogeological Site Walkover Investigation by AECOM (see Vol 3, Appendix 7.1); - AECOM (2012) Water quality sampling at four locations around Q6 and Q7 for range of physico-chemical, metal, and major ion parameters; - Bennion, H., Burgess, A., Roe, K., Yang, H., and Thomas, R (2010) Palaeoecological Study of Llyn Padarn, CCW Contract Science Report No. 918 39pp, ENSIS Ltd, University College London; - British Geological Survey (BGS) 1:50,000 scale map, Sheet 106 Bangor; - BGS 1:10,000 scale map SH56SE; - CCW (2012) Bathymetic data for Llyn Padarn; - Daily Llyn Padarn levels from September 2007 to August 2015 (NRW, 2015); - Daily mean flows in the Afon Seiont (at Peblig Mill) from August 1976 to August 2015 (NRW, 2015); - Daily mean flows in the Afon Peris (at Nant Peris) from March 1982 to August 2015 (NRW, 2015); - 15 minute river levels in the Afon Seiont (at Peblic Mill) from October 2009 to August 2015 (NRW, 2015); - 15 minute river levels in the Afon Peris (at Nant Peris) from October 2009 to August 2015 (NRW, 2015); - Llyn Padarn bathymetry data and associated level-storage table ((NRW, 2015); - Environment Agency Wales (2006) The Llyn and Eryri Catchment Abstraction Management Strategy; - Environment Agency Wales (2009) River Basin Management Plan: Western Wales River Basin District; - Environment Agency Wales (2014) Draft Cycle 2 River Basin Management Plan: Western Wales River Basin District; - ESI (June, 2011) Pumped Storage Hydroelectric Development: Hydrogeological desk study, report reference 60524TN1; - Etive Ecology (September 2012) Glyn Rhonwy Pumped Storage Scheme: Llyn Padarn Freshwater Ecology Impact Assessment, Produced for Quarry Battery Ltd; - Goldsmith, B., Henderson, G., Shilland, E.M., Dowman, S., Tomlinson, M. & Harwood, A. (ENSIS Ltd. May 2015) Aquatic Surveys: Glyn Rhonwy Quarries Q1 and Q6 - Interim report to AECOM; - NRW (2015) Water quality for the Afon Gwyrfai January 2004 to April 2015 from a station just downstream of where the Nant- y-Betws confluence (NGR SH 52620 59030); - NRW (2015) Water quality data for Llyn Padarn January 2004 to April 2015 from station close to the outfall to the Afon Seiont (NGR SH 55954 62329); - NRW (2015) 2014 WFD classifications including new standard river specific SRP targets; - NRW (2015) 2014 Bathing Waters Monitoring Data; - Online Ordnance Survey Maps (http://www.bing.com/maps/);

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- Thomas, R.H, and Holt, R. (2011) Diver Observations on Arctic charr (Salvelinus alpinus L.) Spawning Grounds in Llyn Padarn SSSI. CCW Staff Science Report No. 11/8/2; and - Various correspondences with statutory consultees and other relevant stakeholders.

2.4.2 Water Quality Analysis Water quality for the Afon Gwyrfai was obtained from NRW for the period January 2004 to April 2015 from a station just downstream of where the Nant-y-Betws confluence (NGR SH 52620 59030) and a Welsh Water Waste water Treatment Works (WwTW). This has been compared with surface water quality data for Llyn Padarn (obtained from NRW for the same period) collected from close to the outfall to the Afon Seiont (NGR SH 55954 62329). Water samples from Llyn Padarn were collected from a depth of at least 30 cm below the lake surface and are considered to be representative of the well mixed epilimnion (during summer stratification) or the fully mixed winter water column (when the lake is non-stratified). It has therefore been assumed that this water quality record is a fair and reasonable representation of the likely water quality of water that would be abstracted by the Development during commissioning. Mean averages, minimum and maximum reported concentrations and summary statistics have been compared for parameters where data was available for Llyn Padarn and Afon Gwyrfai (less than results have been included as at the limit of detection). This includes physico-chemical parameters (dissolved oxygen (DO), pH, conductivity, temperature, hardness, and alkalinity), indicators of organic pollution (BOD, ammonia and ammonium), nutrients (soluble reactive phosphorous (SRP) or Molybdate Reactive Phosphorous (MRP)), nitrate, nitrite and total oxidised nitrogen), and some heavy metals (magnesium, copper and zinc) and ions (e.g. sulphate). Summary statistics have been prepared using all of the available data (long term) and for the period 2013 to April 2015 (short term). The short term data is included to take account of recent trends that may not be apparent in the longer term data record and is more in line with annual averages used for determining EQS. The available water quality data for the Llyn Padarn has also been compared with available WFD Environmental Quality Standards (EQS) relevant to the Afon Gwyrfai river typology taken from The Water Framework Directive (Standards and Classification) Direction (England and Wales) 2015. This includes: DO, BOD, ammonia, pH, temperature, ammonia, chromium, copper, zinc, and phosphorus (in accordance with the 2015 standard update). Selected other parameters have been compared against other non WFD EQS where data was available (e.g. for lead, cadmium, suspended solids and sulphate in Llyn Padarn, although no corresponding data was available for the Afon Gwyrfai). Standards have been drawn from the following sources:

- The River Basin Districts Typology, Standards and Groundwater threshold values (Water Framework Directive) (England and Wales) Directions, 2010 - Freshwater AA; - SEPA - Supporting Guidance (WAT-SG-53) Environmental Standards for Discharges to Surface Waters. v4.0. Apr 2013. Fresh EQS – AA; - SEPA - Supporting Guidance (WAT-SG-53) Environmental Standards for Discharges to Surface Waters. v4.0. Apr 2013. Fresh EQS – MAC; and - PNEC derived for EU REACH registration dossiers – Freshwater.

Water quality sampling of Q6 was originally undertaken in July 2012 and then again in 2015, alongside samples from Q1, by ENSIS Ltd to a scope agreed between AECOM and NRW. The full results of the analyses are described in Chapter 9 Water Environment of the Environmental Statement and summarised in Appendix C. Water samples were taken from the water’s edge where the water is at least a metre in depth using a throw bottle, aiming to collect water from at least 5 m from the edge. Eleven samples have been collected thus far from Q6. Four samples in total have been collected from Q1, including two repeats due to the difficulty accessing the quarry. This sampling frequency was agreed with NRW as part of the water sampling protocol (within the outline Water Management Plan (Appendix 16.1.1). As there is no evidence of stratification in either quarry it is assumed that the water samples are representative of the whole water body.

2.4.3 Limitations The Cycle 2 Western Wales River Basin Management Plan will not be issued until December 2015 and thus this assessment has been completed based on the latest 2014 WFD classifications.

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The following limitations apply to the review of water quality data for Llyn Padarn, which could result in some uncertainty in the analysis:

- Outliers have not been removed from the data sets. It is possible that the presence of low lying outliers could reduce the overall average and give the impression of better water quality in the lake; - Sampling frequency varies for some parameters. Generally, sampling is at least monthly, but for the periods January 2004 to December 2004 and January 2010 to February 2013 some parameters were sampled twice a month or weekly. The increased frequency of sampling in these periods could introduce a bias in the mean; - There are some data gaps principally affecting manganese, copper (filtered), total zinc, lead, cadmium and chromium; - For some metals the available data alternates over time between filtered and unfiltered results; - BOD is not routinely monitored since the end of 2010; - Where the sample result was below the Limit of Detection (LOD) this has been included in summary statistics as the value of the LOD, which could potentially increase the mean average; and - There was a change in the way Total Phosphorus was analysed from the start of 2008. The long term average includes all data, but to eliminate this potential source of error the short term data set only includes data from January 2013 to April 2015.

The following limitations apply to the review of water quality data for the Afon Gwyrfai, which could result in some uncertainty in the analysis:

- Outliers have not been removed from the data sets at this point in time. It is possible that high outliers could result in the mean underestimating reality; - There is no water quality data for 2011 and 2012; - SRP was only monitored between January 2005 and January 2006; - Conductivity and alkalinity not routinely monitored pre-2007 or between May 2010 and December 2010; - BOD, copper (filtered) and total zinc were not routinely monitored since 2011; and - Where result was below LOD this has been included in summary statistics as the value of the LOD which potentially increased the mean etc.

Finally, no water quality or flow data has been provided by NRW for the Afon Seiont.

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Photo 3 Overflow from Llyn Padarn to the Afon Rhythallt Figure 1 Llyn Padarn Depth-Volume Curve (CCW, 2012)

Photo 4 View of Llyn Padarn from the overflow looking Figure 2 Llyn Padarn Hypsographic Curve (CCW, 2012) southeast

Llyn Padarn is classified under the WFD (ID GB31033730) as a low alkalinity, shallow lake, which is a relatively uncommon typology. Despite the relatively shallow depth of the lake NRW (formerly EAW and CCW) investigations have identified that Llyn Padarn experiences thermal summer stratification and it is believed to be a warm monomitic lake (i.e. overturning once in autumn with water temperatures never falling below 4C). It is heavily modified and currently at Moderate Ecological Potential due to dissolved oxygen levels and not all mitigation measures being implemented, but has good chemical status. Llyn Padarn is linked at its south-eastern end by the Afon Bala aqueduct to the upstream Llyn Peris, which is the lower reservoir of the Dinorwig Hydro Power Station. Excess water overflows to Llyn Padarn and water levels within Llyn Padarn are therefore maintained below those in Llyn Peris. The outflow of Llyn Padarn is on the northern shore and is called Afon Rhythallt (or Seiont according to the WFD classification), which becomes the Afon Seiont below Pont Rhythallt near Llanrug. 14

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Llyn Padarn is also designated as a SSSI primarily for its rare and genetically unique population of Arctic charr (Salvelinus perisii), nationally scarce water plant Floating Water-plantain (Luronium natans) and exposed Cambrian rocks. Arctic charr are known to spawn in the Afon y Bala area at the southern area of the lake, although there are indications that other spawning sites around the littoral margins of the lake to depths of approximately 8 m may also be used. An investigation by CCW with hydroacoustic and scuba dive surveys in December 2010 implied that Arctic charr may use the littoral edge around the ‘sidings’ at SH 57166 61213 and extending to the northwest, close to where the intake and outfall structures are proposed. No Arctic charr eggs were identified and the presence of suitable habitat (lake depth and shoreline composition) alone does not confirm the area as a spawning site, although CCW acknowledge that this type of survey is difficult and it is possible that the main spawning run for that year had not yet taken place. Further investigations of water quality and hydroecology by CCW in 2010 suggest that oxygen levels in the deeper hypoliminion are typically depleted during the mid-late summer and could be contributing to the declining Arctic charr numbers that preferentially inhabit the cooler water (CCW, 2010). Waters will naturally be oligotrophic to mesotrophic (i.e. low to moderate in nutrients), with slightly acidic to neutral pH and low conductivity, although there is evidence of increasing mesotrophic conditions since the mid-1800s and this enrichment has contributed to a vulnerability to episodic eutrophic problems and algal blooms that can be triggered by a sudden increase in nutrient availability together with conducive hydrological and weather conditions. The last bloom occurred between May and October 2009 and according to NRW “was caused by a combination of weather conditions and nutrients (phosphorous) entering the lake, particularly from the nearby sewage treatment works and storm overflow.”

Evidence from the investigations undertaken by NRW into Llyn Padarn and the more recent PROTECH modelling of the lake system, identified that the Llanberis WwTW was responsible for the environmental damage. However, the immediate risk of continuing damage has been eliminated by the following mitigation measures: 1) NRW has installed a continuous water quality monitoring station on the lake in order to track daily changes in lake quality from the lake bottom to its surface and has commissioned modelling work to understand the nutrient pressures on the lake both historically and in the future. 2) In 2010 NRW required Dŵr Cymru Welsh Water (DCWW) to comply with a regulator-initiated permit variation to reduce permitted total phosphorous levels in the Llanberis WwTW final treated effluent from 1.6 mg/l to 1 mg/l (as an annual average). NRW also identified improvements required for Llanberis WwTW and the sewer network. These will include further reductions to both (i) the permitted Total Phosphorous limit (reduced to 0.5 mg/l as an annual average from the current 1 mg/l); and (ii) the frequency and timing of untreated storm discharges to the lake. These improvements will be delivered by DCWW in the AMP6 capital investment programme between April 2015 and March 2020. 3) DCWW have undertaken sewer network modelling of the Llanberis network to understand its operation and identify potential impacts on the lake. The modelling was used to assess the apportionment of Total Phosphorus loadings into the lake. They required the removal of a phosphorous-enriched trade effluent to sewer emanating from Siemens Healthcare Diagnostics Ltd. and have implemented other practical short-term solutions to improve the quality of the effluent discharged from Llanberis WwTW to prevent the risk of future algal blooms. They have also identified and undertaken repairs on the sewerage network within Llanberis and made improvements to sewage pumping stations which has reduced the flow of sewage to the works, and have constructed an inlet works at Llanberis WwTW and have also improved treatment of final effluent by adding two additional DynaSand sand filters at the site in addition to the 2 No. sand filters already on site. Finally, specialist phosphorus removal technology Blue-PRO has been trialled at the site and flow meters installed to measure the volume of storm water discharges. Such measures have contributed to the phytoplankton quality element in the WFD classification of ecological status returning to ‘good’ status in the 2013 and 2014 (draft) classifications. According to the bathymetric data provided by CCW (2012) Llyn Padarn contains just over 15 million m3 of water. The margins of the lake are generally deeper than the photic zone other than in the northwest corner where it shoals and overspills into the Seiont, as well as a few isolated pockets north of Llanberis and in the southeast corner. The water depth of the majority of the northwestern third of the lake and the lake margins are approximately 8 m to less than 20 m deep, and the main basin lies in the southeast portion of the lake, with a spine of deeper water (more than 20 m) running north approximately two thirds of the lakes length.

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Photo 5 Afon Seiont near Peblig Mill

There are a number of small tributaries draining land to the north and south of the Afon Seiont that will contribute to the flow recorded at Peblig Mill, although it is considered that the majority of flow originates from Llyn Padarn. The Afon Seiont (lower) is currently at Good Ecological Status and Chemical Status. No water quality data or details of any WFD mitigation measures were provided by NRW for the Afon Seiont.

3.4 Afon Gwyrfai The Afon Gwyrfai has headwaters from the glacial tarn Llyn y Gader, which flows into the Llyn Cwellyn, a deep (approximately 37 m) glacial ribbon lake covering approximately 870,000 m2. Like Llyn Padarn, Llyn Cwellyn is also an oligotrophic to mesotrophic lake with low alkalinity and contains a natural population of Arctic charr. The Afon Gwyrfai is 21 km in length and discharges into Fyord Bay just to the south of the village of Saron. NRW operate a gauging station at Bontnewydd approximately 5 km downstream of the confluence with the Nant-y-Betws upland stream, which drains the slopes to the south of Q1 and into which any overflow will be drained to. According to the National River Flow Archive, the river catchment is steep, on impermeable geology, and with a high proportion of grassland / rough moorland (70%). A flow record dating between 1970 and 2005 is available, although there may be increased error with the measurement of low flows, and the abstraction of raw water from Llyn Cwellyn for potable supplies has affected flows along the Afon Gwyrfai.

The Afon Gwyrfai is also designated as part of the Afon Gwyrfai and Llyn Cwellyn SAC and SSSI for its water dependent species and habitats including: Atlantic salmon (Salmo salar), clear water lakes with aquatic vegetation of poor to moderate nutrient levels, floating water plantain, otter, and floating vegetation often dominated by water-crowfoot. Surface water quality data for the Afon Gwyrfai was obtained from NRW for the period January 2004 to April 2015 from a station just downstream of where the Nant-y-Betws confluence (NGR SH 52620 59030) and is summarised in Appendix A.

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and so this is likely to overestimate the average dissolved iron content). Furthermore, as with the samples from Q6, the only organic compound present above the limit of detection was phenol at approximately 0.06 µg/l. Overall, the 2015 water quality results for Q6 were similar to the water quality result reported in July 2012 (AECOM, 2012). No water quality sample was collected from Q1 in 2012 due to the difficulties gaining access. However, these water samples only provide a ‘snap shot’ of water quality, although given the nature of the water body (i.e. lake) and limited inputs and outputs, water quality may be relatively stable. There was no evidence of any significant sedimentation (sampling was attempted but no discernible samples could be collected) or stratification in either quarry and the results are assumed to be analogous throughout both quarry water bodies.

3.6 Protected Areas This section identifies any relevant Protected Areas with a hydrological connection to the proposed Development and the potential that they could be impacted. Protected Areas include sites defined by other European Directives plus water depending SSSIs protected by national legislation. For convenience, Protected Areas have been discussed as either ‘ecological’ or ‘non- ecological’ sites.

3.6.1 Ecological Protected Areas Ecological Protected Areas include SACs, SPAs, SSSIs, freshwater and shellfisheries. Water dependent nature conservation Protected Areas (including SSSIs) within the study area that have a hydrological connection to the scheme include:

- Afon Gwyrfai and Llyn Cwellyn SAC / SSSI; - Menai Strait and Conwy Bay SAC; - Llyn Padarn SSSI; - Seiont SSSI; - Salmonid fisheries; and - Shellfish waters.

The following describes the overall objectives of the various European Directives that have introduced the relevant types of Protected Area found within the study area: The objective for Natura 2000 Protected Areas identified in relation to relevant areas designated under the Habitats Directive is to ‘protect and, where necessary, improve the status of the water environment to the extent necessary to achieve the conservation objectives that have been established for the protection or improvement of the site’s natural habitat types and species of Community importance in order to ensure the site contributes to the maintenance of, or restoration to favourable conservation status.’

The objective for Natura 2000 Protected Areas identified in relation to relevant areas designated under the Birds Directive is to ‘protect and where necessary improve the water environment to the extent necessary to achieve the conservation objectives that have been established for the protection or improvement of the site in order to ensure that the site contributes to the conservation (survival and reproduction in their area of distribution) of birds species listed in Annex I of the Birds Directive.’ The objective for freshwater fish waters designated under the Freshwater Fish (Consolidated) Directive is ‘to protect or improve the quality of running or standing freshwaters to enable them to support fish belonging to indigenous species offering a natural diversity or species the presence of which is judged desirable for water management purposes by the competent authorities of the Member States.’ The objective for shellfish waters designated under the Shellfish Water Directive is ‘to protect and, where needed, improve the quality of shellfish waters in order to support shellfish (bivalve and gastropod molluscs) life and growth, and thus contribute to the high quality of shellfish products directly edible by man.’ Table 6 provides a description of each ecological Protected Area and whether they are relevant or not to this assessment and should be considered further. 20

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Photo 6 water sports in the ‘lagoons’ on Llyn Padarn

The objectives for Drinking Water Protected Areas (DrWPAs) are to ‘ensure that, under the water treatment regime applied, the drinking water produced meets the requirements of the Drinking Water Directive, and ensure necessary protection in the DrWPA with the aim of avoiding deterioration in water quality in order to reduce the level of purification treatment required in producing drinking water.’ According to the RBMP the Afon Seiont, Afon Gwyrfai and the Llyn & Eryri groundwater body are all included within DrWPAs. However, no potable water is currently abstracted from Llyn Padarn, it is not anticipated that the scheme will impact any local raw water supplies, and thus this Protected Area shall not be considered any further.

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cumulative lake levels falls are unlikely to occur. In any case, once the lake level corresponding to the hands-off flow is reached abstraction would stop and it is not predicted that significant littoral areas of the lake would be exposed (although there is some uncertainty regarding the area close to the outfall that was not surveyed, although observations suggest it would not dry up completely and hydrological connectivity with the Afon Rhythallt would be maintained); - The hands off flow condition is predicted to occur around 15% of the time during an extreme dry year (such as if an extreme dry year like in 2010 were to occur during the construction period) under the ‘without abstraction’ scenario. We note that a conditions of the current abstraction licence granted by NRW abstraction at the maximum rate is limited to only 275 days or 75% of the year; - It is considered that there would be no significant effect of the abstraction on lake levels in Llyn Padarn. This is due to the hands off flow condition, linked to levels in the downstream Afon Seiont. Consequentially it is considered that there would be no effect on aquatic receptors in the lake (including at its margins); - If the construction period and abstraction were to extend over a dry year then it is possible that the hands off flow condition on the licence would be in place for around 20% of the time (and most probably occurring during the spring and summer). Natural runoff into the quarries, during wetter periods of the year may provide a replacement source of water so that they may be filled within the current 18 month programme; and - Overall, the abstraction regime is not considered to have any significant impact on lake water levels (and therefore littoral habitat quality and extents) and water quality (as it is affected by changing water levels), and thus will not result in the deterioration of any of the BQE present and physico-chemical supporting parameters or likelihood of failing to meet at least good status for lake water levels.

In order to abstract water for the commissioning of the pumped storage scheme a new overflow and intake will be constructed. The overflow will be buried beneath the lake bed with only the new intake / outlet structure residing on the bed itself. In total, only 0.013% of the lake bed will be lost and in an area where Luronium natans are not present (nearest population more than 100 m away). The lake bed in this location is relatively steep and this coupled with a restricted rate of discharge will minimise the risk of any scouring occurring. Other than an emergency situation (including high rainfall events) the rate of routine runoff bleeding from the pumped storage scheme will be relatively small compared to the volume of water stored in Llyn Padarn, and thus unlikely to result in any significant change in water quality. Routine discharges will also be similar to the current ‘natural’ runoff from the catchment to Llyn Padarn (please note that it is believed that runoff collecting in Q1 currently drains to Llyn Padarn via existing drains, rather than to the Afon Gwyrfai, despite topographically being within this catchment). Based on an incident rainfall of 1,867 mm per year and approximately 465 mm evaporation there will be a net accumulation of approximately 161,000 m3 of rainwater in Q1 and 315,000 m3 of rainwater in Q6 (i.e. 476,000 m3 in the entire system). It is expected that a total volume of rainwater averaging this amount will be discharged to Llyn Padarn annually from the pumped storage scheme (and only from Q1 to the Afon Gwyrfai under exceptional circumstances) which would equate to approximately 1200 m3 per day. This is an insignificant amount when compared to the c. 15 Mm3 of water contained in Llyn Padarn. Indeed, to put it into context if all of the natural runoff expected to be bled from Q1 and Q6 was discharged to Llyn Padarn in one go this would represent less than 0.03% of the total lake volume. In reality, this runoff would be unevenly distributed throughout the year and moderated by other factors (e.g. storm intensity, operational water levels in Q1 and Q6 etc.). However, when spills would occur it is expected that the water levels and flows in the Llyn Padarn, Afon Seiont and Afon Gwyrfai would be higher offering a greater potential for dilution and dispersion.

Although very unlikely, under certain circumstances there could be the need for the rapid discharge of water from Q6 to Llyn Padarn via the relief valve. This might occur following a sudden and intense rainfall event or as a worst case in the unlikely event that the dam for Q6 was at risk of breaching and it was not possible to pump water from Q6 to Q1. Water would be discharged at a rate of 0.3 m3 per second meaning that a constant discharge of just under 26,000 m3 per day for up to seven days in order to drain 100 % the impounded volume in Q6. However, any discharge is still likely to be small when compared to the typical volume of water stored in Llyn Padarn, and as discussed earlier it is unlikely to be contaminated with excessive nutrients or other pollutants, be low in oxygen, or significantly elevated in temperature. A coarse sediment screen would be placed on the relief valve to prevent any sediment in the bottom of the reservoir being drawn through. Such very intense sudden rainfall events would be less frequent and the risk of a dam breach considered a ‘one-off’ event and unlikely to result in long lasting effects that could prevent WFD targets annually or in the longer term. Operational procedure will also require constant monitoring of dam water pressure meaning that any risk of failure would be identified long before there was a risk of it actually occurring. Another consideration related to the emergency discharge is suspended sediment. Water abstracted from Llyn Padarn will be screened to prevent entrainment of fine sediment and transportation of this material into the pumped storage system. Surveys of Q1 and Q6 have also confirmed that both lakes are oligotrophic and are lacking in any fine sediment, which is indicative of the likely trophic status that will develop over time and implies that low productivity. A coarse screen will be positioned on the relief valve to prevent ingress of larger material that may accumulate on the bed of the quarry. In addition, the rate of runoff from an emergency spill will be controlled through a discharge consent and mitigated in order not to cause excessive and unacceptable

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erosion of Nant-y-Betws and the mobilisation of fine sediment downstream. Therefore, sedimentation effects are unlikely to be an issue and have not been considered any further. Finally, upon initial filling loose fine particulates of concrete from the construction of the dams and reservoirs will be washed into the standing water body in the reservoir and could slightly increase the pH and alkalinity of the water. However, this effect would diminish over time following natural runoff into the quarry system and is unlikely to impact Llyn Padarn due to the relatively low rate that excess water would be discharged (i.e. high dilution in Llyn Padarn) and the intermittent nature of that discharge.

Aluminium

Historically, aluminium has not been considered as one of the primary metals that may have toxic effects on the aquatic environment due to its relative abundance and low toxicity at typical pH and temperature conditions. However, recent research carried out by the Environment Agency suggests that aluminium effects might still be significant, and not just at low (i.e. pH <5.5) pH conditions (Environment Agency, 2008), although they acknowledge that aluminium toxicity remains poorly understood and as yet there are no non-drinking water UK standards. Nevertheless, although not a relevant WFD parameter itself, since high concentrations of bioavailable aluminium can cause physiological effects on biological quality elements (e.g. macroinvertebrates, fish and flora, and in particular may precipitate on the gills of fish) the risk that aluminium rich runoff might be released during construction of the development has been considered. Slate contains high levels of aluminium that could be leached by surface water runoff and conveyed to Llyn Padarn. The release of dissolved and particulate aluminium in runoff during construction would be exacerbated on the site by activities to crush, work or transport slate as part of excavations and earthworks to construct dams, and from the stockpiling of unused material. Leachate tests on 40 soil samples taken from trial pits close to Q1 and Q6 have variable concentrations between 170 ug/l to a maximum of 260 ug/l, with a mean of 100 ug/l (please refer to Tables C3 and C4 in Appendix C). In comparison, the average concentration of aluminium-filtered and aluminium total in Llyn Padarn based on predominantly weekly sampling between September 2011 and March 2013 by NRW was 17.7 ug/l (ranging 11.1 ug/l to 24.8 ug/l) and 35.8 ug/l (ranging 16.5 ug/l to 138 ug/l), respectively (please see Table C1 in Appendix C). It should be noted that the long term average of pH in Llyn Padarn is circumneutral, with the pH of water currently residing in Q1 and Q6 being slightly more alkaline.

Based on the soil leachate tests and the available background water quality data, it is possible that if left unmitigated, construction site runoff could contain high levels of dissolved and particulate aluminium that could exceed background levels by as much as ten times. Although pH is circumneutral, and despite uncertainty over the toxic effects of aluminium in the aquatic environment, it is plausible that the discharge of aluminium rich construction site runoff could result in short term and temporary adverse effects on biological quality elements in the Llyn Padarn, although there would be considerable dilution of runoff in Llyn Padarn. The risk to Llyn Padarn would also be limited by the need to attenuate and discharge construction site runoff to a rate agreed with NRW, or by discharging intermittently to allow the discharged water to disperse. The Development will adopt a precautionary approach to minimise the formation of and conveyance of aluminium rich surface water (e.g. carefully control the extent, location and method of excavating, crushing, and moving slate material). It is also proposed to set up a temporary construction site drainage system that will intercept, attenuate and settle fine sediment from construction site runoff in accordance with best practice guidance (e.g. CIRIA C648 etc.). Where space allows this may include sedimentation lagoons, but where space is limited other measures (e.g. filtration through straw bale) or if necessary proprietary systems (including Siltbusters or chemical treatment tanks) may be used in combination to effectively treat suspended sediment and dissolved metals in runoff. These measures will be described in detail in a Water Management Plan (including a Silt Management Plan) to be prepared prior to construction works. Measures will be agreed with NRW as part of the application for an Environmental Permit, and if required a water quality monitoring programme will be implemented on site in accordance with any permit conditions.

Specific Pollutants – Copper and Iron

Water quality testing of both quarries (ENSIS 2015) has also not revealed any evidence of high levels of contamination, other than elevated levels of dissolved copper which exceeded the 1 ug/l annual average bioavailable standard for oligotrophic water bodies (i.e. Llyn Padarn). Dissolved copper ranges between 2.1 ug/l and 3.6 ug/l with an average of 2.8 ug/l in Q1, and ranges between 5.7 and 9.0 with an average of 7.01 ug/l in Q6 (i.e. more than twice the concentration of Q1). In comparison, the long term average in Llyn Padarn is 1.1 ug/l, which also just exceeds the current standard, although for 2014 copper was classified as meeting good status. It is believed that copper is being leached from the surrounding rocks and potentially from the UXO in the quarry, and which would be removed should the scheme be developed.

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Dissolved iron concentrations in Q6 averaged 20 ug/l, but had a wide range between 4 ug/l and 120 ug/l. If the maximum value was not included the average reduces to 13.4 ug/l, although this still would exceed the annual average EQS for surface waters of 1 ug/l (bioavailable). NRW were unable to provide any data on iron concentrations in Llyn Padarn and so a comparison has not been possible. Should Q1 and Q6 be dewatered and the water discharged to Llyn Padarn via the Development and become fully mixed it would have a negligible effect on the overall copper and iron concentration of the lake under stratified or un-stratified conditions due to the available dilution. Around the location of the discharge there may be a temporary increase in dissolved copper and iron concentrations, but this would be short lived while the discharge is occurring and for a short period afterwards until the runoff has been dispersed. Due to the mobility of copper it would typically flush through the lake system quickly becoming increasingly diluted and dispersed and would not persist in the long term as this is a ‘one off’ discharge (please note that the standard is an annual average and higher concentrations in the short term can be tolerated by BQE). Any discharge to Llyn Padarn will be in accordance with an Environmental Permit agreed with NRW. If required, the need for specific mitigation measures will be agreed with NRW as part of the permitting process. This may include restrictions on the rate of discharge, intermittently discharge to allow time for dispersion, or pre-treatment on site in advance discharging. In the longer term, it is possible that the water in the pumped storage scheme would reflect the copper and iron concentrations observed in the current quarry water, although by lining the reservoir the ability of metals to leach from surrounding rocks is reduced, and the operation of the pumped storage scheme should not introduce any new sources of copper or other metals. The risk should also be considered in the context of existing drainage from these quarries to Llyn Padarn, albeit the flow pathways and rates are uncertain. The volume of discharge would be greater in an emergency situation, but this would be a ‘one-off’ event similar to the initial draining of the quarries that is unlikely to cause the annual EQS to be exceeded and no persistent long lasting adverse effects. Overall, despite copper levels in Llyn Padarn already exceeding the annual average EQS, based on the data available for Q6 the discharge of existing quarry water or future intermittent or emergency discharges of excess reservoir water are not likely to result in deterioration or prevent improvement with respect to the copper WFD EQS or BQEs, at the water body level.

Nutrients

The BQE relevant to and monitored for Llyn Padarn are principally indicators of nutrient status, and to a lesser extent acidification and hydromorphology. The water quality of Q6 is generally low in nitrates, nitrite and ammoniacal nitrogen, although levels of total phosphorus were higher, averaging approximately 36 ug/l in Q6 (ranging from 20 ug/l to 67 ug/l). It is not clear why total phosphorus concentrations are relatively high in Q6 or where it is being sourced given the surrounding landscape, land use and low productivity in the quarry. However, as this discharge would be a one-off event and given the dilution that would occur in Llyn Padarn no significant impacts are predicted on water quality or supporting BQE. To put this discharge into context, the concentration of total phosphorus in quarry dewaters is significantly lower than the current total phosphorus consent limit from Llanberis WwTW which is 0.5 mg/l (i.e. 500 ug/l). The operation of the pumped storage scheme will not result in any change to the nutrient status of Llyn Padarn since the Development will not contribute any significant nutrient loading to the lake. The water held in the pumped storage scheme would have been originally sourced from Llyn Padarn and through operation will not gain any significant nutrients from the quarry environs. Over time and with continued natural runoff it is expected that the nutrient status of the water within the pumped storage system will reflect the current oligotrophic-mesotrophic conditions in Q1 and Q6. Furthermore, due to the low nutrient inputs and regular mixing of water there is a low risk of algal blooms occurring in either Q1 or Q6 and thus it is unlikely that the operation of the pumped storage scheme could ‘seed’ a bloom in Llyn Padarn.

Acidification

During operation and over time there is the possibility that sulphides are oxidised due to the repeated passing of water through the turbines and that this could lead to the water becoming more acidic. Sulphides originate from the anaerobic decay of organic matter or may come from sewage discharges. The levels of sulphur measured as sulphate in Llyn Padarn are very low and stable (the long term mean average is 3.8 mg/l with a small standard deviation). Based on the water sampling undertaken for this development, current sulphate levels in Q1 and Q6 are comparable to Llyn Padarn (i.e. averaging 3.4 and 4 mg/l, respectively) reflecting the mesotrophic-oligotrophic conditions. Therefore, in light of no other obvious and substantial sources of sulphate it is considered that the risk of this occurring is low. Long term water quality monitoring will include pH and if it was observed that water in the reservoirs was becoming increasingly acidic options to dose the reservoirs with a suitable alkaline could be undertaken in the future.

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Temperature

NRW have also raised concerns regarding the risk of discharging water of elevated temperature since this could impact on Arctic charr habitat and populations within Llyn Padarn. Once the Development is fully commissioned with 1.3 Mm3 of water, this will pass between Q1 and Q6 in order to provide the battery storage and generate electricity at peak times. No water is directly discharged into Llyn Padarn from the turbines and so it is unlikely that the discharge will be heated. The following points outline how the proposed Development is different from the adjacent Dinorwig pumped storage scheme and why there is unlikely to be any potential significant effects from heated water:

- Scale - The scale of the Development is considerably smaller than that of Dinorwig. This is in terms of both the power output (99.9MW compared to 1800MW) and, more importantly, the volume of water that is processed and discharged. Llyn Peris is the tailpond for the Dinorwig scheme whereas Llyn Padarn will only receive intermittent overflow from the much smaller Development. This discharge would be above the thermocline in the well-mixed zone where small inflows of water with a slightly different temperature can be quickly assimilated. Consequently, any potential impact of the Development will be significantly reduced in comparison to that of Dinorwig; - Heat source: Solar exposure - The bathymetry of Llyn Peris, the lower reservoir at the Dinorwig facility, is a relatively shallow and wide. This basin undergoes significant drawdown during operation, exposing dark rocks to heating from the sun. It may be possible that this is a driver for increased water temperature in Llyn Peris, as the heat stored is transferred to the surrounding water once re-filled. The Glyn Rhonwy Development is quite different. The lower volume at Q6 is much more narrow, deep and shaded. It is therefore more likely that the water in Q6 will remain cool. While Llyn Peris has an area of around 60 hectares, Q6 has an area of around 3 hectares. Llyn Peris stores 7 Mm3 increasing to >9 Mm3 (following a recent upgrade) of water, while Glyn Rhonwy will store 1.3 Mm3, so the Development has approximately 1/7 the volume but 1/20 the surface area. This very different volume to surface area ratio means the water in Glyn Rhonwy is much less exposed to the sun than the water of Llyn Peris; - Heat source: Geothermal gradient - The penstock proposed for the Development is shallower than that used by Dinorwig. This may be relevant because generally the deeper the tunnel, the warmer it gets with the average gradient around 25oC to 30oC per km depth. Though heat transfer from the rocks to the water will be limited by the surface area of contact, and the conductivity of the surrounding rocks, it is possible that Llyn Peris is warmed by the mountain itself. The tunnels of Dinorwig reach a depth of some 450 m, and are roughly 2.4 km long. At Glyn Rhonwy the tunnels will be between 50 and 80 m deep and are around 1.6 km long; - Configuration - The configuration of the Development is considerably different. Once the water has passed through the turbine it will flow into Q6 where it will be stored until it is ready to be pumped back up to Q1. Only when there is excess water during periods of high rainfall will discharge from the Development into Llyn Padarn be required. We believe that the discharge will be very similar in terms of rate and temperature as to present drainage conditions as the relief valve is close to the maximum water level within the reservoirs; - Penstock and Tailrace Lining – The inside surface of the penstock and tailrace will be appropriately lined to ensure a smooth surface to reduce friction as much as is practically possible and thus loses of potential energy to warming up the water passing through them.

The scheme is fundamentally different to the nearby Dinorwig power station in that it is a closed system with Q6 being the bottom reservoir, not Llyn Padarn. The scheme has also been designed to be low friction, which will minimise any warming of water pumped through the system. It is difficult to predict the temperature range of the water that will be held within the pumped storage system, and which will be allowed to spill into Llyn Padarn. Water temperature will vary diurnally / seasonally and will be moderated by the bathymetry of the reservoirs, the operation of the plant / mixing, and the altitude of the quarries. Without a significant source of additional heat, it is anticipated that the water held within the pumped storage scheme will be controlled predominantly by natural factors such as climate and bathymetry. In addition, water that will be discharged will be siphoned off from near to the surface where it is most likely to be acclimatised to the surrounding air temperature and comparable to the surface waters in Llyn Padarn. During the winter, should the water temperature within the pumped storage scheme be elevated above what would be expected naturally, the relatively low rate and volume of any overflow will be effectively buffered by the much large volume of water within Llyn Padarn, which would be fully mixed. Overall, the strong seasonal variation exhibited by monitoring of Llyn Padarn’s surface water temperature record is likely to be much more significant for controlling the status of BQEs and other physico-chemical parameters. Therefore, with the dilution potential offered by Llyn Padarn, rainfall and the relative rate and volume of discharges from the pumped storage scheme, no significant changes in water quality in terms of nutrients, contaminants or acidity is predicted, and thus no deterioration of any BQEs or failure to meet chemical EQS as a consequence of the proposed Development.

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Excess water will preferentially be bleed from Q6 to Llyn Padarn rather than from Q1 to the Nant-y-Betws stream, and thus regular discharges to the Afon Gwyrfai are unlikely and each spill could be considered as a ‘one-off’ event. In terms of routine runoff, net annual runoff to Q1 is predicted to be approximately 160,000 m3, which equates to approximately 438 m3 per day and less than 2 % of the Q95 flow in the Afon Gwyrfai (as monitored approximately 5 km downstream at Bontnewydd. Runoff from Q1 will fluctuate in response to rainfall patterns and system operations, and a greater volume may be released over the short term (hours or days) compared to this scenario in response to rainfall. However, when a spill occurs to the Afon Gwryfai the flows in the receiving watercourse will be proportionately elevated in response to the same storm event and this will provide increasing dilution of the runoff from Q1. The mean average water quality of Llyn Padarn (over the long term and over the past couple of years) has been compared with the mean average water quality in the Afon Gwyrfai to assess the risk of water being transferred between catchments. This is considered appropriate since the variations exhibited by some parameters (e.g. copper, zinc, TP, SRP and pH) would be moderated by the relatively slow rate and long period of abstraction. This data comparison has shown that there are no obvious or significant differences in water quality between the two water bodies. The water quality in Llyn Padarn would meet the Good Ecological Status WFD river standards for the Afon Gwyrfai, other than for copper. However, although the long term mean of copper (filtered) for Llyn Padarn just exceeds the annual average WFD river standard, it is currently less than the current Afon Gwyrfai mean average. High concentrations of copper can be toxic to aquatic organisms especially in soft water as occurs in this catchment, although higher concentrations can be tolerated for shorter period without having a significant impact on BQEs in the long term. However as the copper data for the Afon Gywrfai is limited (i.e. no data since 2011), in order to reach a robust conclusion, it is proposed to include this catchment within the pre-construction water sampling programme to gain sufficient baseline information on the catchment water quality prior to construction starting. If required, the rate or frequency of discharges could be controlled to ensure that there is sufficient dilution and dispersion in river. Water abstracted from Llyn Padarn (including any contaminants) to fill the pumped storage scheme will be augmented by natural runoff which will help to dilute any parameters of concern. This will continue year on year as natural runoff continues to fill Q1 meaning that the concentration of certain parameters of concern and the lake characteristic of the water will diminish over time. In the long term the water quality of Q1 is expected to take on a similar character to the quality of water that currently resides in the quarry and reflecting the natural conditions, albeit with the added influence of the operation of the pumped storage system. Thus, the risk of excess nutrients etc. being passed from Llyn Padarn to the Afon Gwyrfai will diminish over time, and furthermore with the normal working scenario of discharging to Q6 / Llyn Padarn as opposed to the Nant-y-Betws. Furthermore, if there was contamination in Q1, it would most likely be in a dissolved form meaning that upon discharge it is likely to disperse and be conveyed rapidly along the Afon Gwyrfai. Any impact on water quality would most likely be short term with the quality and ecology returning quickly to normal once the discharge has ended. As discussed earlier, there is a risk that aluminium rich runoff is discharged to the Afon Gwyrfai, which could result in adverse effects on aquatic fauna. It is not possible to compare the leachate tests from soils found in the quarry with background dissolved aluminium levels in the Afon Gwyrfai as NRW have not been able to provide any data. The long term average pH for the Afon Gwyrfai is circumneutral meaning that the risk from metal toxicity is lower. The risk to the Afon Gwyrfai would also be lower than for Llyn Padarn as it is not proposed to routinely discharge construction site runoff to this watercourse with the main risk coming from the construction of stockpiles of slate, although these would be at least 10 m from the Nant-y-Betws. The Afon Gwyrfai also has a greater potential to disperse the discharge quickly. However, as discussed earlier, a precautionary approach to minimise the formation of, and conveyance of aluminium rich surface water (e.g. carefully control the amount, location and method of excavating, crushing, and moving slate material) will be adopted with suitable mitigation measures and monitoring as required. Any discharge would also require a discharge consent from NRW.

Upon initial filling loose fine particulates of concrete from the construction of the dams and reservoirs will be washed into the standing water body in the reservoir and could slightly increase the pH and alkalinity of the water. However, this effect would diminish over time following natural runoff into the quarry system and is unlikely to impact the Nant-y-Betws and the Afon Gwyrfai due to the relatively low rate that excess water would be discharged and the infrequency nature of that discharge.

Nutrients

Phosphorus exists in organic / inorganic and soluble, and sediment-bound forms. It is typically the limiting nutrient controlling biological productivity in freshwaters, although not all forms are readily bioavailable to plants and phytoplankton. The soluble reactive form (SRP or orthophosphate-filtered) is the most bioavailable, but since this is readily taken up by plants and phytoplankton it is not considered a good indicator of nutrient status in lakes and total phosphorus should be used instead. This is problematic for comparison with the Afon Gwyrfai since the current standards for WFD compliance for phosphates in rivers is

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set for SRP. The following considers the potential impact of dewatering Q1 and transferring water from Llyn Padarn to the Afon Gwyrfai catchment. The BQE relevant to and monitored for the Afon Gwyrfai are principally indicators of nutrient status, and to a lesser extent acidification and hydromorphology. The water quality of Q1 is generally low in nitrates, nitrite and ammoniacal nitrogen, although levels of total phosphorus were higher, averaging 65.5 ug/l (stable) in Q1. It is not clear why total phosphorus concentrations are relatively high in Q1 or where it is being sourced given the surrounding landscape, land use and low productivity in the quarry. However, as there is only 500 m3 of water to be dewatered from Q1 this would be rapidly diluted and dispersed by the prevailing flow in the Afon Gwryfai, which would receive it indirectly via the Nant-y-Betws stream. In Llyn Padarn, the long term and short term mean averages of total phosphorus are both 0.009 mg/l with a relatively small standard deviation of 0.003 mg/l and 0.005 mg/l, respectively. Both averages are just below the annual average WFD standard for Good Ecological Status in lakes (0.01 mg/l) and significantly lower the permit limits typically applied to sewage treatment works operating the best available techniques (i.e. 0.5 to 1 mg/l total phosphorus). However, unlike a sewage treatment works any discharge from Q1 would be intermittent but unlikely to occur due to the preferential discharge of excess water to Llyn Padarn. As NRW does not monitor total phosphorus in the Afon Gwyrfai there is no data against which to compare with water from Llyn Padarn. Therefore, as a proxy we have also compared MRP for which we do have more data. The long term and short term mean averages for MRP and the range of results are broadly similar for Llyn Padarn and the Afon Gwyrfai suggesting that both have a similar nutrient status. We have also compared SRP and generally the nutrient levels in the Afon Gwyrfai were slightly higher, although we only have a short data record from the Afon Gwyrfai (i.e. 13 monthly samples between January 2005 and February 2006). Despite the limitations of the available data, both MRP and SRP suggest that there would be no significant impact on nutrient status from discharges from Q1. The existing water in Q1 is oligotrophic reflecting the limited allotrophic supply and autotrophic production and it is thought over time both reservoirs will adopt a similar character (i.e. will trend towards oligotrophic conditions). This together with the initial and ongoing dilution of the stored water abstracted from Llyn Padarn by low nutrient rainfall means that there is unlikely to be an impact on the nutrient status of the Afon Gwyrfai. NRW’s (as EAW) 2010 investigation into the 2009 algal bloom included nutrient depth profiling between August 2009 to December 2010. Seventeen monitoring visits were made with samples collected at a range of depths for TP and SRP. Although limited in temporal coverage, this data allows a check on whether there would be any difference in water quality at the depth of the intake, which would be a minimum of 5 m below normal water level of the lake. Generally, at this depth above the thermocline TP and SRP results were broadly in line with the long and short term mean average results discussed earlier. A significant peak in SRP in August 2010 (>0.2 mg/l) was explained by preceding wet weather increasing runoff from the catchment and the likelihood of spills from Llanberis WwTW combined with strong winds encouraging river water to spread further across the surface of the lake. Although an isolated event it highlights the need to monitor water quality during abstraction to try and avoid initially abstracting poorer quality water higher in nutrients (i.e. during wet weather, following storm water spills or potentially lake mixing in late autumn when stratification breaks down). However, due to the slow rate of abstraction over a long period of time any short term peaks will be moderated by longer periods of better water quality and thus the mean average water quality from the data are more likely to be representative of the final quality of abstracted water.

Acidification

A water quality sample collected from the existing Q1 reservoir water in spring 2015 reported a pH of 8.04 (mild-moderately alkaline). This is within the range of pH recorded in the Afon Gwyrfai, although the mean is typically more circumneutral. The pH of water in Llyn Padarn is circumneutral (mean average 7.14 pH units) and there is no evidence of historical acidification (Bennion et al; 2010). This compares with a mean average pH of 6.88 in the Afon Gwyrfai, which is also circumneutral. Both results are compliant with the WFD standard for High Ecological Status in a cold water river. On rare occasions the pH of Llyn Padarn has exceeded 9 pH, although it is suspected that these short lived events might be associated with algal blooms or increase algal productivity in the summer (e.g. the Anabaena bloom in 2009 photosynthesis best at > pH 9 (EAW, 2010)) that are relatively short lived and would most likely require abstraction to be temporarily halted in any case. Consideration has also been given to the risk of acidification from the operation of the pumped storage scheme. Sulphides originate from the anaerobic decay of organic matter or may come from sewage discharges. It is possible that the high oxygenation of water caused by repeatedly passing through the turbines could encourage the formation of sulphur based acids. However, although only 6 samples have been collected the levels of sulphur measured as sulphate in Llyn Padarn appear to be low (mean average 3.8 mg/l with small standard deviation). It is therefore considered that the risk of this occurring is low. Future

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monitoring of water quality in the pumped storage system will help monitor trends and of there was evidence of increasing acidification action could be taken to periodically dose the water with a suitable alkaline, in consultation with NRW. Overall, the pH of existing quarry water and the mean and range of pH for Llyn Padarn is broadly comparable to the mean and range of pH recorded for the Afon Gwyrfai and it is considered that there is onoly a low risk of increasing acidification from the oxidation of sulphides. Discharges of excess water would preferentially be from Q6 to Llyn Padarn. However, should there be a discharge from Q1 to the Afon Gwyrfai catchment it would be infrequent, temporary and diluted in river. Therefore, it is not thought that discharges from Q1 would result in any significant effect on the watercourse. Regular monitoring of the water in Q1 will include pH and if this begins to trend to more acidic conditions measures could be taken to dose the water with a suitable alkaline.

Emergency discharge of water from Q1

Under certain but unlikely circumstances (i.e. potential dam safety issue and inability to transfer water to Q6) there could be the need for the rapid discharge of water from Q1 to the Afon Gwyrfai via an overflow and outfall to the Nant-y-Betws stream. Water quality issues would be the same as discussed earlier, albeit a potentially greater volume of water would be discharged that could result in a more immediate impact and not necessarily with any increase of in channel dilution in response to a storm. Nevertheless, the water quality data reviewed does not suggest that there would be any significant level of contamination in the discharge and the event would effectively be a ‘one-off’ with no long lasting effects, providing appropriate measures are put in place to prevent scour and erosion in the Nant-y-Betws stream to prevent mobilisation of fine sediments downstream and into the Afon Gwyrfai. Water abstracted from Llyn Padarn will be screened to prevent entrainment of fine sediment and transportation of this material into the pumped storage system and a coarse screen will also be positioned across the relief valve to prevent ingress of larger material that may accumulate on the bed of the quarry. The rate of runoff will be limited to a rate agreed with NRW under an Environmental Permit to ensure that excessive and unacceptable erosion of Nant-y-Betws does not occur. Therefore, sedimentation effects are unlikely to be an issue and have not been considered any further.

Specific Pollutants – Copper and Iron

The Afon Gwyrfai is monitored for a range of hydrocarbons, pesticides, and metals, all of which are at High Status. The proposed Development will not introduce any of these substances and thus no change to these chemical parameters is predicted. However, initially the estimated 500 m3 of water in Q1 will be discharged to the Afon Gwyrfai via the Nant-y-Betws stream and in the longer term it is expected that over time the quality of water in Q1 may adopt characteristics similar to the quality of water currently in Q1. Four water quality samples have been collected from Q1 (which is currently difficult to access) and thus provide only a ‘snap-shot’ of water quality. Analysis of the results suggest that the water quality is generally good, although dissolved copper and dissolved iron are elevated in both and above the relevant EQS. Average dissolved copper concentrations were 2.8 ug/l and the average iron concentration was 5 ug/l, both of which exceed the 1 ug/l annual average EQS for surface waters. Please note that the iron data includes two samples where the dissolved iron concentration was reported below the 4 ug/l limit of detection and thus the actual average is likely to be lower than 5 ug/l. However, as the initial dewatering discharge would be a ‘one off’ event of only an estimated 500 m3, which would be expected to become rapidly diluted and dispersed by the flow in the Afon Gwyrfai, and since future operational discharges would likely be infrequent (i.e. preference for excess water to be discharged to Llyn Padarn) and relatively small, no significant impact on water quality or BGE in the Afon Gwyrfai is predicted. Any discharge of dewaters to the Nant-y-Betws stream will be in accordance with an Environmental Permit agreed with NRW. If required, the need for specific mitigation measures will be agreed with NRW as part of the permitting process. This may include restrictions on the rate of discharge, intermittently discharge to allow time for dispersion, or pre-treatment on site in advance of discharging.

4.3.2 Failure to Improve Although the Afon Gwyrfai is at Good Ecological Potential we note that NRW are yet to complete the mitigation measures assessment. Therefore, we have undertaken as appraisal of the proposed Development against existing proposed mitigation measures. Of those listed in Table 5 only the proposed measures to maintain a sediment management regime to avoid degradation of the natural habitat characteristics of the downstream river was identified as being relevant. Although the main driver for this measure would be flows from Llyn Cwellyn the measure is relevant because of the potential for emergency spills from Q1 to cause erosion

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5 Summary and Conclusion

The following is a summary of the key findings of this appraisal, including conclusions and any recommendations for further assessment:

5.1 Llyn Padarn Llyn Padarn is a HMWB that is currently at Moderate Ecological Potential due to dissolved oxygen levels and not all mitigation measures having been implemented. This appraisal has assessed the compliance of the proposed Development against the objectives for this water body considering the potential effects of water abstraction, dewatering Q1 and Q6, construction site runoff, routine and emergency discharges, and physical impacts from new structures. It has also considered the compliance with proposed mitigation measures (i.e. prevention of improvement objectives) and SSSI objectives (principally for Arctic charr and floating water plantain). Abstraction of raw water from Llyn Padarn has been agreed in principle with NRW who issued a licence in July 2015 to abstract up to 2,000 m3 per day subject to conditions including a 'hands off' water level as measured at the Peblig Mill gauging station on the Afon Seiont. Since this licence was issued the total volume of water that could be stored in the pumped storage scheme has increased and it is now proposed to abstract up to 3,300 m3 per day over a period of up to 18 months. A water balance study has been undertaken of this new rate and is presented in Appendix B. This shows that water can be abstracted at this rate whilst maintaining the hands off water level and without significant impacts on Llyn Padarn. It has therefore been concluded that the proposed abstraction would be compliant with the WFD.

Water currently in Q6 that will be discharged to Llyn Padarn is generally good, although dissolved copper, dissolved iron and total phosphorus levels are elevated in both and above the relevant EQS. It is believe that Q6 already drains to Llyn Padarn via old mine workings and fractures in the bedrock, although directly discharging the water will likely increase the rate of discharge above natural flows. However, the discharge would be a ‘one off’ event and the effluent would be significantly diluted and dispersion in Llyn Padarn and no long term effects on aquatic organisms is predicted. Any discharge to Llyn Padarn will be in accordance with an Environmental Permit agreed with NRW. If required, the need for specific mitigation measures will be agreed with NRW as part of the permitting process. This may include restrictions on the rate of discharge, intermittently discharge to allow time for dispersion, or pre-treatment on site in advance of discharging. Overall, the future quality of water in the pumped storage scheme is unlikely to contain excessive levels of nutrients, contaminants or high levels of suspended sediment, or be significantly different in pH or temperature to the water quality of Llyn Padarn. With the dilution potential of Llyn Padarn and taking account of the relative rate and likely volume of discharges, no significant changes in water quality in Llyn Padarn is predicted, and thus no deterioration of any BQEs or failure to meet chemical EQSs as a consequence of the proposed Development. In addition, no evidence of any alien species have been identified in Q1 or Q6 by aquatic ecology surveys carried out for this Development, and measures will be undertaken to avoid Nuttal’s Waterweed being abstracted from Llyn Padarn. During construction there is the possibility of site runoff becoming enriched with aluminium from the surrounding slate waste, especially where this has been worked or crushed. To reduce the risk to the aquatic environment it is proposed to carefully manage construction site runoff to reduce this risk as far as reasonably possible and to only discharge construction site runoff to Llyn Padarn in accordance with an Environmental Permit agreed with NRW. In addition to the application of standard treatment of construction site runoff, other measures to reduce the risk could be to discharge at a suitably slow rate or intermittently allowing the discharged waters to disperse. The proposed new intake and outfall structures will result in the permanent loss of a small area of lake bed, although as the connecting pipework will be buried the physical impact of the Development has been minimised and the overall effect is considered to be insignificant. Both structures will be located above the thermocline but sufficiently deep to avoid disrupting the activities of other lake users. The new intake will be fitted with a suitable screen to prevent ingress or abrasion of fish, particularly Arctic charr. The depth of the lake bed falls relatively quickly at the location of the outfall meaning that the potential for scour is low.

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5.2 Afon Seiont The Afon Seiont originates from the outfall from Llyn Padarn and is currently at Good Ecological Status. It was also a salmonid river under the Freshwater Fish (Consolidated) Directive, which has now been subsumed by the WFD. The Afon Seiont will not be directly impacted by the Development, but has been considered as an adjacent designated WFD water body that could be impacted indirectly through changes to the flow regime and water quality in Llyn Padarn. Abstraction from Llyn Padarn will be controlled so that the flow regime downstream along the Afon Seiont is not significantly affected and water levels are maintained above 0.343 m at the Peblig Mill gauging station as required by the current abstraction licence. The abstraction will only take place for up to 18 months and thus is unlikely to result in any long term permanent effects. In terms of water quality, the changes in water level within Llyn Padarn are negligible and are not expected to alter the physio- chemical quality of the lake when compared to EQSs. In addition, it is not expected that discharges from the construction and operation of the proposed Development will significant effect lake water quality providing suitable mitigation measures are adopted. Therefore, the proposed Development is not expected to cause deterioration of any WFD parameter relevant to the Afon Seiont and it is considered to be compliant with the objectives for this water body and any water dependent Protected Areas.

5.3 Afon Gwyrfai The Afon Gwyrfai is a lake fed river whose flow has been modified by water storage for drinking water supplies, and which is thus a HMWB. In undertaking this appraisal we have also considered the potential compliance with the objectives for the SSSI and SAC designations that apply. The proposed Development will not have any direct effects on this river, with the potential for indirect effects on WFD parameters to occur from discharges of existing quarry water, construction site runoff, overflow discharges (routine operation) or emergency release of flows using the relief valve via the Nant-y-Betws upland stream. Water currently in Q1 that will be discharged to the Afon Gwyrfai via the Nant-y-Betws stream is generally good, although dissolved copper, dissolved iron and total phosphorus levels are elevated in both and above the relevant EQS. However, the discharge would be a ‘one off’ event and there is only an estimated 500 m3 in the quarry which is expected to be rapidly diluted and dispersed by the flow in the Afon Gwyrfai. Any discharge of dewaters to the Nant-y-Betws stream will be in accordance with an Environmental Permit agreed with NRW. If required, the need for specific mitigation measures will be agreed with NRW as part of the permitting process. This may include restrictions on the rate of discharge, intermittently discharge to allow time for dispersion, or pre-treatment on site in advance of discharging.

During the operation of the proposed Development discharges from Q1 are not predicted to contain significant concentrations of any pollutants, be enriched in nutrients, have a low pH, or have high levels of suspended sediment. Excess water will also preferentially be discharged from Q6 to Llyn Padarn rather than from Q1 to the Nant-y-Betws stream, and thus regular discharges to the Afon Gwyrfai are unlikely. Overall, the risk from operational discharges to the Afon Gwyrfai is low and no significant impact on WFD parameters has been predicted. The rate of flows from the Q1 overflow will be controlled to ensure that they do not lead to further erosion of the Nant-y-Betws stream and the mobilisation of fine material downstream and into the Afon Gwyrfai. It has been agreed with NRW that the detailed design of the outfall can be subject to a DCO Requirement. The detailed design will consider the risk of hydromorphological impacts so that suitable measures can be incorporated into the final design.

Overall, the proposed Development is considered to be compliant with all WFD objectives for the Afon Gwyrfai water body, taking into account mitigation measures and Protected Areas.

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References

AECOM (February, 2012) A Report of a Hydrogeological Site Walkover Investigation by AECOM (Volume 3, Appendix 7.1); AECOM (2012) Water quality sampling at four locations around Q6 and Q7 for range of physic-chemical, metal, and major ion parameters;

Bennion, H., Burgess, A., Roe, K., Yang, H., and Thomas, R (2010) Palaeoecological Study of Llyn Padarn, CCW Contract Science Report No. 918 39pp, ENSIS Ltd, University College London;Water quality data for Llyn Padarn. British Geological Survey 1:50,000 scale map, Sheet 106 Bangor. British Geological Survey 1:10,000 scale map SH56SE. Centre for Ecology and Hydrology (2012) Daily flows from the upper Afon Rhythallt (i.e. the Seiont) from Peblig Mill (http://www.ceh.ac.uk/data/nrfa/index.html). Countryside Council of Wales (2012) Bathymetic data for Llyn Padarn. Countryside Council of Wales (2010) Palaeoecological Study of Llyn Padarn, CCW Contract Science Report No. 918. Environment Agency Wales (2012) Llyn Padarn water level data. Environment Agency Wales (2010) Llyn Padarn Investigations 2010.

Environment Agency Wales (2006) The Llyn and Eryri Catchment Abstraction Management Strategy. Environment Agency Wales (2009) River Basin Management Plan: Western Wales River Basin District. Environment Agency (2008) Environmental Quality Standards for trace metals in the aquatic environment, Science Report – SC030194. ESI (June, 2011) Pumped Storage Hydroelectric Development: Hydrogeological desk study, report reference 60524TN1. Etive Ecology (September 2012) Glyn Rhonwy Pumped Storage Scheme: Llyn Padarn Freshwater Ecology Impact Assessment, Produced for Quarry Battery Ltd. Goldsmith, B., Henderson, G., Shilland, E.M., Dowman, S., Tomlinson, M. & Harwood, A. (ENSIS Ltd. May 2015) Aquatic Surveys: Glyn Rhonwy Quarries Q1 and Q6 - Interim report to AECOM - May 2015. Natural Resources Wales (2015) Water Quality Data and 2014 WFD Classifications. Natural Resources Wales (2014) Draft Cycle 2 River Basin Management Plan: Western Wales River Basin District. Thomas, R.H, and Holt, R. (2011) Diver Observations on Arctic charr (Salvelinus alpinus L.) Spawning Grounds in Llyn Padarn SSSI. CCW Staff Science Report No. 11/8/2. Online Ordnance Survey Maps (http://www.bing.com/maps/); UK Technical Advisory Group on the WFD (2013) Updated Recommendations on Environmental Standards for Phosphorus in Rivers - River Basin Management Plan (2015-2021) – Final Report. UK Technical Advisory Group on the WFD (2013) Final Recommendations on New and Updated Biological Standards. UK Technical Advisory Group on the WFD (2013) Updated Recommendations on Environmental Standards - River Basin Management Plan (2015-2021) – Final Report. UK Technical Advisory Group on the WFD (2008) UK Environmental Standards and Conditions (Phase 1) Final Report. UK Technical Advisory Group on the WFD (2008) UK Environmental Standards and Conditions (Phase 2) Final Report.

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AECOM Pumped Storage Scheme WFD Compliance Appraisal 38

Glossary

AOD Above Ordnance Datum BOD Biochemical Oxygen Demand BQE Biological Quality Element (WFD parameter) CCW Countryside Council for Wales (now NRW) DCO Development Consent Order DCWW Dŵr Cymru Welsh Water

DO Dissolved Oxygen DrWPA Drinking Water Protected Area EAW Environment Agency Wales (now NRW) EIA Environmental Impact Assessment EQS Environmental Quality Standard GES Good Ecological Status HES High Ecological Status HOF Hands off Flow HMWB Heavily Modified Water Body LOD Limit of Detection (of chemical analysis)

MRP Molybdenum Reactive Phosphate (unfiltered orthophosphate) MW Megawatts of electricity NGR National Grid Reference NRW Natural Resources Wales PINS Planning Inspectorate RBD River Basin District RBMP River Basin Management Plan SAAR Seasonally Adjusted Annual Rate SAC Special Area of Conservation SPA Special Protection Area

SPH Snowdonia Pumped Hydro SRP Soluble Reactive Phosphate (filtered orthophosphate) SSSI Site of Special Scientific Interest TP Total Phosphorus UKTAG UK Technical Advisory Group (for WFD)

WFD Water Framework Directive WwTW Waste water treatment works

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AECOM Pumped Storage Scheme WFD Compliance Appraisal

Appendix A Study Area Water Bodies

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Appendix B Water Balance Technical Note

Introduction

This technical note supports the wider study to assess the potential effects of the proposed Glyn Rhonwy Pumped Storage Scheme on water resources presented in Chapter 9 of the Environmental Statement. The proposed abstraction is to occur at Llyn Padarn and would be used for commissioning the pumped storage scheme proposed at Glyn Rhonwy by Snowdonia Pumped Hydro. In July 2015 the client obtained an abstraction license (hereon referred to Abstraction Regime 1) for the following (yet to be utilised):

3 - Permission to abstract up to 2,000 m /day from Llyn Padarn; and 3 3 - Permission to abstract up to 550,000 m in a 12 month period (equivalent to 1,507m /day for the full year).

NRW have added a hands off flow (HOF) condition to the licence requiring that no abstraction from Llyn Padarn should occur when river levels in the downstream Afon Seiont are less than 0.343 m at the Peblig Mill gauging station. It has previously been estimated that 1.1 Mm3 (equivalent to 2 years supply based on Abstraction 1) will be required to fill the quarries during the commissioning period. It is considered that natural runoff would augment the supply from Llyn Padarn, so that 2 years abstraction from the lake would not be required. Subsequent to gaining a licence for Abstraction 1 the client is considering applying for a higher rate of abstraction from Llyn Padarn (hereon referred to as Abstraction Regime 2), as follows:

3 - Permission to abstract up to 3,300 m /day from Llyn Padarn; and 3 3 - Permission to abstract up to 1,205 Mm in a 12 month period (equivalent to 3,300 m /day for the full year).

It is assumed that the hands off flow constraint would also apply to Abstraction Regime 2.

Following more recent bathymetric surveys of Q1 and Q6, it is now proposed to abstract up to 1.3 Mm3, rather than 1.1 Mm3, to fill the quarry during the commissioning period. Again, this will likely be topped up by natural runoff during abstractions. The purpose of this Technical Note is to understand the impact of the conditions imposed by the current approved licence, and to examine the hydrological effect of Abstraction Regime 2. If there is a significant effect the wider environmental effects will be considered. Catchment Overview

The study area is indicated in Figure 1 below. Llyn Padarn and the Afon Peris lie within the catchment of the Afon Seiont. Flow in the catchment generally flows in west-northwesterly direction. Flow is measured at two locations within the catchment as outlined in Figure 1 (Afon Seiont at Peblig Mill and Afon Peris at Nant Peris). The Afon Seiont gauge is located close to the tidal limit and so catchment descriptors for this site represent the catchment as a whole. As such the catchment is approximately 80 km2 and has a median altitude of 281 m AOD (maximum of more than 1,000m AOD). Grassland accounts for 65% of the catchment whilst woodland and mountain/heath/bog both account for 10% each. Urban areas account for 1% of the catchment. Rainfall within the catchment is very high, with the 1961-1990 SAAR being 2,280 mm. A site visit was undertaken on the 28th July 2015. During this it was confirmed that the outflow from Llyn Padarn into the Afon Rhythallt occurs under a road bridge. The road bridge (Plate 1) results in some backing of up flow upstream of it, although does not constrain water fully (i.e. unlike a dam could).

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AECOM Pumped Storage Scheme WFD Compliance Appraisal

Plate 1: Downstream end of Llyn Padarn and its outflow under a road bridge (taken on the lake side)

During the site visit, and following subsequent investigations, it was determined that the Afon Peris bypasses Llyn Peris (although during exceptionally high flows some flow is directed into Llyn Peris which is serving as flood storage). The water level in Llyn Peris is controlled as part of the operation of the First Hydro Dinorig Pumped Storage power station. The outflow from Llyn Peris is controlled via three large bascule gates (Plate 2) and levels on the day of the site visit were significantly below the outflow (Plate 3), so that the llyn was not contributing to flow downstream.

Plate 2: Llyn Peris 1 of 2 Outflow Control Structures (looking upstream)

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Plate 3: Downstream end of Llyn Peris (down catchment to the right)

Hydrological Baseline

Hydrological Data

The following hydrological data were obtained from NRW:

- Daily Llyn Padarn levels from September 2007 to August 2015 - Daily mean flows in the Afon Seiont (at Peblig Mill) from August 1976 to August 2015 - Daily mean flows in the Afon Peris (at Nant Peris) from March 1982 to August 2015 - 15 minute river levels in the Afon Seiont (at Peblig Mill) from October 2009 to August 2015 - 15 minute river levels in the Afon Peris (at Nant Peris) from October 2009 to August 2015 - Llyn Padarn bathymetry data (survey undertaken in 2011 by ENSIS/ ECRC on behalf of CCW) and associated level- storage table.

Llyn Padarn

A level1 duration curve derived from the Llyn Padarn level monitoring is provided as Figure 2. This indicates the percentage of time that levels are exceeded. The duration curve indicates that lake levels are usually between 102.5 m and 103.5 m AOD (the minimum recorded level is 102.5 m AOD whilst the maximum recorded level is 104.1 m AOD) and that levels are less than 102.59 m AOD for 5% of the time and 102.61 m AOD for 10% of the time. Levels are greater than 103.04 m AOD for 10% of the time and greater than 103.16 m AOD for 10% of the time.

Figure 3 presents the information collected during the 2011 bathymetry survey. The data presented has levels with regard to a relative datum, assumed to be the surface water level on the day of sampling, rather than with regard to an absolute datum (e.g. Ordnance Datum). Nevertheless it is still informative. As described above, lake levels are unlikely to vary by more than 1 m. As such even if the survey was undertaken at a time of high lake levels it is unlikely that areas with depths of more than 1m would become exposed (i.e. only the areas in red and orange are envisaged to become exposed during dry periods). The margins of the lake have not been surveyed and neither has the area surrounding the outflow. The site visit confirmed that the littoral areas and the area surrounding the outfall are relatively shallow and much of these areas would likely become exposed during extreme dry periods.

1 Specifically a stage duration curve as with regard to an absolute datum (ordnance datum) rather than a relative datum.

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end of April until the end of June flows in the downstream Afon Seiont were generally less than 1 m3/s indicating that flow contributions from upstream (including Llyn Padarn) were low. As mentioned above the bathymetrys survey did not extend to the shallower area around the Llyn Padarn outflow. During the site visit (28th July 2015) Llyn Padarn levels were approximately 103 m AOD. As apparent in Figure 2, lake levels could be expected to be up to 0.5 m lower than this. Based on the site visit it is considered that flow would still occur under the bridge at the Llyn Padarn outflow at levels 0.5 m that observed during the site visit although flow would likely be low. This suggests that the lake is in connectivity with the downstream Afon Rhythallt at all times providing flow contributions. Once a period of rainfall occurred, between 28 June 2010 and 2 July 2010 ending the dry period, at the start of July 2010 lake levels rose quickly by 0.27 m (equivalent to 0.067 m/day) whilst storage increased by around 67,000 m3/day during this period. The Afon Seiont measured records indicates that when river levels have been measured at around 0.343 m (i.e. the hands off flow), the median flow is approximately 0.9 m3/s. Similarly when river level stage is 0.343 m or lower Llyn Padarn levels are up to 102.61 m AOD.

Hydrological Impact Assessment

Selection of a historic year for a worst case assessment

Given the strong correlation between lake levels and river flows, it is considered that the longer term record flow records can be used as a proxy for lake levels. This has been undertaken to ascertain how dry 2010 was compared to previous years (back to 1976 when the flow record for the Afon Seiont began). The two lowest flows (0.144 m3/s and 0.148 m3/s) occurred in 2010. Of the 50 lowest flows 10 occurred during 2010, 14 occurred in 1995, nine occurred in 1976, six occurred in 1983, four occurred in both 2003 and 2006, two occurred in 1984, whilst one occurred in 1989. This suggests that 2010 was one of the driest years within the past 40 years and it would be unlikely that a drier year would occur during the construction period. The 2010 records have thus been used as a basis for a worst case assessment of the hydrological impacts of Abstraction Regime 2. The 2010 record itself is used as the basis of a ‘without abstraction’ scenario.

Effect of the hands off flow on Llyn Padarn Abstraction

The 6 years of 15 minutes river level data for the Afon Seiont at Peblig Mill was reviewed with regard to the hands off flow restriction on the Llyn Padarn abstractions (either under Abstraction Regime 1 or 2 when flow would not be permitted when river levels are less than 0.343 m). The mean level for each day was determined. Of the 2,161 days where data was available river level was less than 0.343 m on 137 days (6.3% of the time). During 2010, river level was less than 0.343 m on 55 days (15.1% of the time). This suggests that the hands off flow condition would be in place for around 15% of the time during an extreme dry year (such as if an extreme dry year like in 2010 were to occur during the construction period) under the ‘without abstraction’ scenario.

Effect of Abstraction Regime 2 on lake levels

The hands off flow should help ensure that connectivity remains between Llyn Padarn and the Afon Rhythallt. The system has shown to be flashy and flow downstream of Llyn Padarn is well correlated to lake levels, as expected given the lack of an impoundment at the end of the lake. Given this it is anticipated that the short term effect of the abstraction would be to reduce the amount of flow that is conveyed downstream (e.g. the daily effect of 3,300 m3 abstraction would be to reduce flow downstream by as much as the volume that has been abstracted) rather than cumulatively reducing lake levels. The hands off flow would likely ensure that abstraction would cease when lake levels are around 102.6 m AOD or below. This would help ensure that the abstraction would not reduce the lowest lake levels below what they would be normally be (without abstraction), i.e. not below 102.5 m AOD.

There would likely be a short term effect on Llyn Padarn levels although this would not be significantly expected to accumulate given that hydrological records in the catchment indicate a reasonably swift passage of water through the lake and catchment in response to rainfall events. An abstraction of 3,300 m3 equates to a reduction in lake level of

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AECOM Pumped Storage Scheme WFD Compliance Appraisal

around 0.003 m on a given day. As this effect would not be expected to accumulate with continued abstraction over long periods of time, the effect is not considered to be significant. A conservative assessment2 of the predicted effect of the abstraction on Llyn Padarn storage during an extreme dry period is presented in Figure 7. This indicates that as lake level and storage drops quicker as a result of the abstraction, so the point where the hands off Flow condition of the Abstraction Regime licence applies would be reached sooner (by approximately a fortnight). Thus, should there be a short term cumulative fall in lake level the HOF would eventually apply and abstraction would have to stop until lake levels rise again. Given the above it is considered that there would be no significant effect of Abstraction Regime 2 on lake levels in Llyn Padarn. This is strongly due to the hands off flow condition, linked to levels in the downstream Afon Seiont. Consequentially it is considered that there would be no effect on aquatic receptors in the lake (including at its margins).

If the construction period and abstraction where to extend over a dry year then it is possible that the hands off flow condition on the licence would be in place for around 20% of the time (and most probably occurring during the spring and summer). Natural runoff into the quarries, during wetter periods, may provide a replacement source of water so that they may be filled within the desired timeframes.

Effect of Abstraction Regime 2 on flow in the downstream Afon Rhythallt and Afon Seiont

The Afon Seiont measured records indicate that when river levels have been measured at around 0.343 m, the median flow is approximately 0.9 m3/s (corresponding to the Q90/ exceeded for 90% of the time). This has been used to inform an assessment of how flow in the Afon Seiont may be affected under Abstraction Regime 2. This is illustrated in Figure 7. The hands off flow condition of the proposed licence would help ensure that the lowest flows in this river and the upstream Afon Rhythallt would not be reduced as a result of the abstraction. Moderately low flows, greater or equal to the Q90 may be reduced as a result of the abstraction by up to 4%. This would likely manifest as a reduction in river velocities rather than a reduction in level and is not considered to be significant (with flow naturally being reduced to a greater extent on a regular basis/ 10% of the time). The abstraction would also not have any impact on the pattern of flows, which can be important for certain fish species. Given the above, it is considered that Abstraction Regime 2 would have no significant hydrological or environmental effects on the downstream Afon Rhythallt or Afon Seiont.

Effect of Abstraction Regime 1 on lake levels and flow in the downstream Afon Rhythallt and Afon Seiont

The effect of Abstraction Regime 1 on lake levels and downstream flow is considered to be lower than that of Abstraction Regime 2, which is considered to be negligible. The hands off flow condition also applies to Abstraction Regime 1 and is a strong reason for determining there to be no significant impacts associated with Abstraction Regime 1.

2 In that the full impact of the abstraction is observed in both the downstream flow and lake storage records, noting that it would most likely predominantly occur in the former and not to the full magnitude in both

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Figures

Figure 1: Glyn Rhonwy Water Balance Study Key Locations

Figure 2: Llyn Padarn at Llanberis Level (Stage) Duration Curve

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Figure 3: Llyn Padarn Bathymetry (based on 2011 survey data collected by ENSIS)

Figure 4: Afon Seiont at Peblig Mill Flow Duration Curve

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Figure 5: River Flows and Llyn Padarn Levels measured in the Afon Seiont catchment (September 2007 to August 2015)

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Figure 6: River Flows and Llyn Padarn Levels measured in the Afon Seiont catchment (2010)

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Figure 7: River Flows and Llyn Padarn Levels measured in the Afon Seiont catchment (2010)

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Appendix C Water Quality Data and Analysis

Including:

- Table C1 Llyn Padarn Water Quality Analysis; - Table C2 Afon Gwyrfai Water Quality Analysis; - Table C3 Water Quality Results from Q1; and - Table C4 Water Quality Results from Q6.

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3) N/A refers to where no EQS exists. Underlined analytical parameters are those with WFD standard.

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