Proposed Removal of the St Mellons Tanks Combined Sewer Overflow (CSO) Marine Outfall

Transcription

1 Dŵr Cymru Welsh Water Non Technical Summary 21 August 2013 Proposed Removal of the St Mellons Tanks Combined Sewer Overflow (CSO) Marine Outfall

2 Contents 1 Introduction 2 Site and Surrounding Area 3 Description of Development 4 Approach to the nvironmental Statement 5 Coastal Processes and Geomorphology 6 Water and Sediment Quality 7 Flora and Fauna 8 Historic nvironment 9 Conclusions 2 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

3 1. Introduction This document comprises the Non-Technical Summary (NTS) of the nvironmental Statement (S) for the proposed partial removal of the St Mellons Tanks Combined Sewer Overflow (CSO) long sea outfall, which has been prepared to accompany an application for full planning submitted to Newport City Council and a separate marine licence application to Natural Resource Wales (NRW) on behalf of Dŵr Cymru Welsh Water (DCWW). The proposed development seeks full planning permission for the partial removal of the St Mellons Tanks CSO long sea outfall pipeline to a revised consented discharge point. The proposed removal is needed due to the current poor condition of the pipeline, which is broken in several places, resulting in the pipe discharging landward of the presently consented location. The purpose of the S is to identify, describe, and assess the potential environmental impacts that may arise as a result of the proposed development, and to outline measures to reduce any significant impacts. This NTS describes the site and its context and the proposed development. It also provides an overview of the environmental assessment process, and a summary of the assessments carried out for the following topics: Coastal Processes and Geomorphology; Water and Sediment Quality; Flora and Fauna; Historic nvironment. Consultation with the Local Planning Authority (LPA) and Natural Resources Wales (NRW), led to the following topics being excluded from the S as any potential effect from the proposed development was considered to be Negligible: Air Quality; Climate; Coastal Protection and Flood Defence; Geology, Soils and Contamination; Human Beings; Hydrology, Hydrogeology and Water Resources; Landscape and Visual Assessment; Noise and Vibration; Transport; and Waste. Figure 1 - Views South over the Severn stuary towards the St. Mellons long Sea outfall pipeline and wooden piles Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 3

4 2. Site and Surrounding Area The long sea outfall pipeline is located within the Severn stuary, and lies approximately 2km south of St Mellons, Cardiff. The site lies within the administrative area of Newport City Council. The site is set entirely within the Severn stuary marine environment. The inland area immediately surrounding the site comprises agricultural land, reclaimed marshland and networks of drainage ditches. The nearest residential area is located at St Mellons approximately 1.6km to the north. A number of business parks are also located approximately 1km to the north of the site. The site is located adjacent to the Gwent Levels - Rumney and Peterstone Site of Special Scientific Interest (SSSI), the Gwent Levels Historic Landscape of Outstanding Historic Interest, and within the Severn stuary and the Severn stuary uropean Marine Site (MS), which encompasses several uropean nature conservation designation sites. These are: The Severn stuary / Môr Hafren Special Area of Conservation (SAC); The Severn stuary Special Protection Area (SPA); and The Severn stuary Ramsar site. In addition, the intertidal area of the Wentlooge levels is a continuation of the historic landscape of the Registered Gwent Levels of Outstanding Historic Importance. A single lane track connects the site with the B4239 Wentlooge Avenue which connects Newport and Cardiff. The project location is shown on Page 4. The proposed development area constitutes 1.7 ha a relatively very small area in the context of the Severn stuary, uropean Marine Site and mudflat area. Figure 2 - Views south overlooking the inland area surrounding the site, with distant views of the Severn stuary 4 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

5 A3! Torwick Reen Wentloog Avenue Headworks chamber building : N River Severn stuary Mean Low Water : N Contains Ordnance Survey data Crown copyright and database right 2013 This map is based upon the Ordnance Survey material with the permission of Ordnance Survey on behalf of The Controller of Her Majesty's Stationery Office, Crown copyright Licence Number: WU Figure 3 - Site location plan showing the Planning Application Boundary (red line) and the Marine Licence Application Boundary (black dashed line) Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 5

6 3. Description of Development The proposed development seeks full planning permission for the partial removal of the St Mellons Tanks CSO long sea outfall to a revised discharge point closer to the shoreline. The objective is to ensure that the storm sewage discharges are released in a controlled manner at a consented discharge point. At present, storm sewage is intermittently discharging through broken sections of the outfall pipe, rather than at the currently consented discharge point. It is proposed that a maximum of up to 725m of redundant cast iron pipeline would be removed with a revised consented discharge location located approximately 375m from the outfall headworks chamber. It is proposed that the pipeline would be removed using an excavator mounted on a barge. The barge would carry the removed outfall pipe sections to the Queen Alexandra Dock at the Port of Cardiff, where it would be taken to a licenced waste transfer facility and recycled. All works would be carried out and contained within a 25m works corridor along the pipeline. Following the completion of the proposed works, the long sea outfall would continue to operate as before, discharging storm sewage intermittently, which would be flushed away on each high tide. As part of operational maintenance, the outfall would continue to be inspected on a regular basis from the shore. The proposed works would be carried out in phases over 8-12 weeks during the summer of Consideration of Alternatives The S must demonstrate that alternatives to the preferred solution have been considered during the assessment process. The alternative approaches considered for the proposed development include: Do Nothing; Re-constructing the outfall; Relocation of the outfall alignment; Construction of a buried pipeline; Removal of the pipeline by a tracked excavator. Following a process of consultation with Natural Resources Wales and through the development of the project design, the preferred proposal of partially removing the pipeline has been selected in order to mitigate potential impacts to the mudflats, water and sediment quality in the Severn stuary MS, SSSI and Gwent Levels - Rumney and Peterstone (SSSI). Figure 4 - View seaward from the shoreline over the long sea outfall pipeline Figure 5 - Partially buried long sea outfall pipeline 6 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

7 4. Approach to the nvironmental Statement The nvironmental Statement has been prepared in accordance with the requirements of the Town and Country Planning (nvironmental Impact Assessment) (ngland and Wales) Regulations 1999 (as amended), Marine Works (nvironmental Impact Assessment) Regulations 2007 (as amended), and in line with best practice guidance provided in the Institute of nvironmental Management and Assessment (IMA) Guidelines for IA (2004). IA Scoping and Consultation Formal IA scoping was completed prior to the assessment of impacts in order to identify likely significant environmental issues arising from the proposed development, the baseline information to be gathered and the assessment methodology to be undertaken for each topic. Consultation with statutory and non-statutory key consultees was undertaken during the initial baseline data gathering and scoping stages and continued throughout the course of the IA. An IA Scoping Report was submitted to Newport City Council on 23 April 2013 and Natural Resources Wales on 24 April The formal scoping responses were received on May Assessment Methodology The assessments carried out within the S consider the likely significant effects on the environment during the construction and operation of the proposed development, taking account of both direct and indirect effects and beneficial and adverse effects. For each topic, reference is made to existing baseline conditions. This then forms the basis against which assessments of any likely significant environmental effects arising from the proposed development have been assessed. Other developments, including those approved or under construction in the area have been identified, and the potential for cumulative impacts have also been assessed. Where likely significant adverse effects have been identified during the assessment, measures have been proposed (mitigation) to prevent or reduce effects and the residual impacts have been assessed. Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 7

8 5. Coastal Processes and Geomorphology Introduction The Coastal Processes and Geomorphology assessment considers the potential effects on coastal hydrodynamics and geomorphology as a consequence of the proposed development during its construction and operation. Assessment The assessment has been completed as a desk-based study, utilising available literature. Coastal processes are not considered to be a receptor sensitive to change, but they can affect ecological interests, water and sediment quality. Therefore, the methodology considers the magnitude of potential changes in coastal processes. xisting Conditions The Severn stuary is subject to a large tidal range and relatively strong currents. The wave climate is mainly locally wind-generated, with exposure to Atlantic swell waves. An extensive mud-belt occurs at the study site with the intertidal mudflats composed of peat and estuarine clay deposits. The long term trend for erosion of the mudflats is illustrated by the exposure of the previously buried outfall pipe. Figure 6 - xisting condition of long sea outfall Likely ffects upon the nvironment The methods used to remove the pipeline are temporary and would have no direct footprint on the mudflats. They are also small scale in comparison to the estuary. Therefore, changes and effects on coastal processes are considered Negligible. The same conclusion is reached for the operation phase of the development as the new discharge consent location and the absence of the pipeline is expected to result in Negligible and temporary changes in local coastal processes and sediment transport patterns. Mitigation and Residual ffects Construction mitigation is achieved via good design and adopting best practice construction techniques, the residual effects of which are considered to be Negligible. There would be Negligible changes during operation with no residual effects 8 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

9 6. Water and Sediment Quality Introduction The Water and Sediment Quality assessment considers the potential effects on water and sediment quality as a consequence of the proposed development during its construction and operation phases. Assessment The assessment has been completed as a deskbased study, utilising available literature and data supplied by Natural Resources Wales. The assessment considered the implications of sediment disturbance and any increase in suspended sediment. It considers the existing water and sediment quality status of the study area against recognised standards, and water quality objectives in place in relation to the status of the waterbody (via the Water Framework Directive (WFD). Potential changes in water and sediment quality, as a consequence of an accidental spillage or pollution incident were also identified. A WFD Compliance Assessment has been completed and is included within the nvironment Statement. xisting Conditions Data provided by Natural Resources Wales showed that average concentrations of dissolved contaminants in estuarine water (trace metals, trace organics and radiological contaminants) are all below nvironmental Quality Standards (QS) thresholds and are in compliance with the WFD. The site has Good Chemical Status and the WFD objective of achieving Good cological Status by 2027 is on target. In terms of estuarine sediments, a number of compounds exceed environmental threshold levels. The existence of contamination in the Severn stuary is attributed to a long history of industrial development and discharges into the estuary and the fine sedimentary characteristics of the estuary. Likely ffects upon the nvironment For both construction and operation phases of the development, the effects on water and sediment quality are considered to be Negligible. This is based on construction activities lasting for a short duration and over a relatively small area. Hence, this should result in a very brief and highly localised sediment disturbance and suspended sediment load. Since the natural environment of the estuary is characterised by frequent and regular sediment exchanges between the seabed and estuarine water column, construction effects should not be discernible from the existing conditions. The WFD Compliance Assessment also concluded that the proposed development is compliant with WFD requirements, based on the sensitive construction methodology and no change in the existing discharge characteristics. Mitigation and Residual ffects Negligible effects are predicted from construction. Mitigation is achieved via good design and adopting best practice construction techniques, the residual effects of which are Negligible. Best practice construction techniques have been considered to mitigate against construction impacts. No mitigation measures are considered necessary for the operation phase of the development. The residual effects of the proposed development during its construction and operation phase are considered to be Negligible. Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 9

10 7. Flora and Fauna Introduction The Flora and Fauna assessment considers the potential construction and operational impacts on ecological features of the Severn stuary from the proposed development. Assessment Baseline conditions were established by means of ecological desk based assessment and Phase 1 Habitat Surveys. The assessment was conducted in line with best practice guidance in the Guidelines for cological Impact Assessment in the United Kingdom published guidance by the Institute of cology and nvironmental Management. xisting Conditions The proposed development is located within the Severn stuary MS and the Severn stuary SSSI and adjacent to the Gwent Levels Rumney and Peterstone SSSI. These sites are designated for a number of uropean protected bird species (e.g. curlew, redshank, dunlin, pintail, shelduck and ringed plover), fish species (e.g. river lamprey, sea lamprey, Atlantic salmon, sea trout and allis shad) and habitats (e.g. reens, saltmarsh and mudflat habitats). Likely ffects upon the nvironment The 25m working corridor and sensitive construction techniques means that the proposed works should have a Negligible effect on the environment within the designated sites identified above. The proposed works are scheduled to take place outside of the wintering bird season and therefore would avoid any impact on those bird species listed under the Severn stuary MS citation as over wintering species. However, ringed plover are listed as on passage species and have been identified within 2km of the proposed works and therefore have the potential to be impacted by the proposed works. Despite this, the assessment has determined that the proposed development would have a Negligible impact on flora and fauna within the Severn stuary due to the small scale nature of the proposed works, the limited potential for disturbance and the large expanse of alternative habitat present within the Severn stuary. Mitigation and Residual ffects Mitigation proposals include sensitive construction methods and working outside of the breeding bird season. As a result, there is expected to be no residual effect on ecological receptors within the Severn stuary MS and SSSI and Gwent Levels Rumney and Peterstone SSSI as a result of the proposed development. Figure 7 - Views south over the estuary with saltmarsh in the foreground 10 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

11 8. Historic nvironment Introduction The Historic nvironment assessment considers the potential construction and operational impacts on historic features from the proposed development. Historic baseline data was gathered for the site. A range of desk-based sources have been utilised in establishing the baseline. Where appropriate, mitigation measures are proposed. Assessment Baseline conditions were established by means of reviewing archaeological desk based data, including: Glamorgan Gwent Archaeological Trust Historic nvironment Record; Cadw datasets for designated heritage assets; Aerial Photographs held by Royal Commission on the Ancient and Historical Monuments of Wales; and Historic Ordnance survey maps. The assessment was undertaken in line with the Design Manual for Roads and Bridges (DMRB) Volume 11, Section 3, Part 2 Cultural Heritage 1. DMRB assessment criteria, although designed for trunk road schemes, has become the standard for historic environmental impact assessment and is therefore applicable for this IA process. xisting Conditions The outfall is located within the Gwent Levels Historic Landscape of Outstanding Historic Interest, which is an extensive low lying area of estuarine alluvium and represents the largest and most significant example in Wales of a hand-crafted landscape. The area surrounding the proposed development is considered to be populated with archaeological remains dating from the Neolithic period to the 20th century. The baseline assessment identified no heritage assets within the proposed development, although the potential for undiscovered archaeological remains cannot be discounted. Likely effects upon the environment The assessment indicates that any archaeological remains would have been impacted by the original construction of the outfall pipe. Therefore, the likely effect of the proposed development is assessed as Negligible. Mitigation and residual effects Mitigation proposals include sensitive construction methods to reduce the likelihood that the proposed development would impact upon any archaeological remains. 1 Highways Agency (2007) Design Manual for Roads and Bridges (DMRB) Volume 11 Section 3, Part 2 Annexe 5 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 11

12 9. Conclusions The nvironmental Statement has been prepared to accompany an application for full planning permission for the proposed partial removal of the St Mellons Tanks CSO long sea outfall. The assessment considers the likely significant environmental effects during construction and operation of the proposed development based on the description of the baseline conditions and against set criteria. Measures have been indicated to mitigate any adverse effects identified. A summary of the significant effects and mitigation measures are provided below. The construction phase would have a temporary Negligible effect on water quality and sediment, the historic environment, coastal processes and flora and fauna due to the timing of the works and the sensitive construction techniques proposed; The key mitigation measures that have been proposed during construction include a 25m working corridor, no land based vehicles taken onto the mudflats, works to be carried outside the wintering bird season, no storage of materials and pipe removal to occur from the barge; The operation phase would have a Negligible effect on water quality and sediment, the historic environment, coastal processes and flora and fauna. This is due to the operation of the outfalls remaining the same with only periodic routine inspections of the outfalls from the land, as per the existing situation. No mitigation measures are therefore necessary. In conclusion, the environmental effects of the development would be of Negligible significance taking account of the proposed construction methodology and the mitigation proposals incorporated within the scheme. Where to find out more All of the planning submission materials for the proposed development, including this NTS and the S, are available for inspection at Newport City Council s Planning Department and on their website ( Planning Application Newport City Council Civic Centre Newport South Wales NP20 4UR Copies of the S, NTS and other documents that accompany the planning application and marine license application for this proposed development are also available for purchase by ing Martin Kilroy at DCWW at Martin.Kilroy@dwrcymru.com at a cost of - S 150, NTS 10 or electronic copies on CD ( 10). 12 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall

13 Proposed Removal of the Kimberley Road Combined Sewer Overflow (CSO) Marine Outfall 13

14 For further information on this submission please contact: Martin Kilroy Project Manager DCWW (Depot Building) Pentwyn Road Nelson Treharris CF46 6LY