APPENDIX C. Draft Erosion and Sediment Control Plan

Transcription

1 APPENDIX C Draft Erosion and Sediment Control Plan

2 Waikato Power Plant Draft Erosion and Sediment Control Plan Nova 20 June 2016 Revision: 1 Reference:

3 Document control record Document prepared by: Aurecon New Zealand Limited Level 1, 286 Victoria Street Hamilton 3240 PO Box 487 Hamilton 3240 New Zealand T F E W hamilton@aurecongroup.com aurecongroup.com A person using Aurecon documents or data accepts the risk of: a) Using the documents or data in electronic form without requesting and checking them for accuracy against the original hard copy version. b) Using the documents or data for any purpose not agreed to in writing by Aurecon. Document control Report title Draft Erosion and Sediment Control Plan Document ID Project number File path C:\Users\Russell.Cathcart\AppData\Roaming\OpenText\OTEdit\EC_cs\c \Draft Sediment Control Plan Report Rev 0 issued.docx Client Nova Client contact Re v Date Revision details/status Author Reviewer Verifier (if required) Approver 0 15 June 2016 Initial submission Neill Raynor R Van Lierop 1 20 th June 2016 Final Draft submission Neill Raynor R Van Lierop R Van Lierop R Van Lierop R Cathcart R Cathcart Current revision 1 Approval Author signature Approver signature Name Neill Raynor Name Russell Cathcart Title Technical Director Title Project Leader Project File Draft Sediment Control Plan Report Rev 1 Final.docx 20 June 2016 Revision 1

4 Contents 1 Introduction 1 2 Disclaimer 1 3 Written Erosion and Sediment Control Methodology 1 Project Description 1 Estimate of Soil Loss 1 Principles to minimise sediment discharge from the site. 2 Design of erosion and sediment control devices 2 Timetable and nature of stabilisation 2 Maintenance monitoring and reporting 3 Heavy Rainfall response 3 Procedures for review and/or amendment to the ESCP 3 Identification of specific site responsibilities 3 Construction timetable 3 Appendices Appendix A Erosion and Sediment Control Plan Drawing Project File Draft Sediment Control Plan Report Rev 1 Final.docx 20 June 2016 Revision 1 Page i

5 1 Introduction This draft Erosion and Sediment Control Plan (ESCP) is intended to provide a starting point for the detailed designers to work from and to inform the council as to the general scope and intended measures that are likely to be implemented as part of this project. This document has been provided as an elaboration of what is shown on drawing SKT-C-200 which is contained in the Appendix of this document. This draft plan will be subject to refinement at the detailed design phase of project implementation. The written methodology follows the sections outlined in Section 3 of the Waikato Regional Council Erosion and Sediment Control Plan Preparation Guideline. 2 Disclaimer This draft ESCP has been prepared by Aurecon at the request of Nova and is solely for use in connection with the Waikato Power Plant Project. Aurecon has exercised due skill, care and attention in preparing this draft ESCP. Since Aurecon has no control over the development, detailed design, materials, equipment, services and methodology s undertaken by others. Aurecon does not accept responsibility if the measures indicated do not completely cover all the controls, areas and extent of what is needed on this project. Aurecon has used its experience to indicate proposed controls that would be expected on such a development from Aurecon s understanding of the project at this early stage. 3 Written Erosion and Sediment Control Methodology Project Description Nova Energy (Nova) intends to develop a nominal 360 Megawatt (MW) open cycle gas turbine (OCGT) power plant. The proposed site (the Site) is located off SH31, Kawhia Road, approximately 10 km north of Otorohonga. The project is referred to as the Waikato Power Plant. The bulk of the civil earthworks involved is related to benching the site and constructing the site access roads to the building platform and the transmission line route. Refer to drawing SKT- C-200 that shows the extent of the earthworks and most of the erosion and sediment control measures that have been identified at this point in the project. The proposed works also involves installation of culverts crossing the Ongarue Stream and associated temporary stream diversion and earthworks. Estimate of Soil Loss A Universal Soil Loss Equation (USLE) assessment will be completed as part of the development and finalising the detailed ESCP. However, as indicated in Section 3.3 below, the design approach is to minimise potential erosion hot spots through diversion of upstream catchments around the main works areas and locating the larger earthworks area on less steeply graded parts of the site. This will reduce the overall soil losses. Project File Draft Sediment Control Plan Report Rev 1 Final.docx 20 June 2016 Revision 1 Page 1

6 Principles to minimise sediment discharge from the site. The key principles relating to minimisation of sediment discharge are: Location of the main platform area on less steep land reducing the grades and erosion potential of the site. Diversion of upstream catchments around the works area in erosion-protected channels. This includes the temporary diversion of the Ongarue Stream for culvert installation. The reinstatement of contour drains on the main platform area during periods of earthworks to ensure the erosion risk is minimised. This will be implemented on a daily basis at the end of each day to control the site while personnel are not present. This is completed at the end of the working day as working areas may include some of the contour drains during the day s operations. Stabilisation of the completed areas as soon as they are finished. This is particularly applicable to the cut areas of the site around the perimeter of the platform. As the main site will be surfaced with hard fill (quarry sourced aggregate), stabilisation will be immediate. A combination of Sediment Retention Ponds (SRPs) for the main platform area, in conjunction with silt fences and other appropriate devices as required. These measures will be used to control sediment run off over all the disturbed areas. Design of erosion and sediment control devices SRPs for the main platform have been indicated in locations that can service the main platform through the various phases of construction. The main platform area has been split between two SRPs to cover a catchment areas of approximately 2.8ha each. By limiting the slopes of the main earthworks areas to less than 10% gradient and by locating the retention ponds in locations that limit the flow path to less than 200m the ponds can be sized based on the 2% of the catchment area criteria. The option of flocculation is available should controls not achieve the necessary standards. The smaller catchments around the site will be contained by silt fences placed along the contour to avoid concentrated flows. These small catchment areas are typically less than 0.3ha, or the flow path within the catchment area is less than 100m. The flow path beyond the silt fences will be to undisturbed grass prior to discharge to watercourses. In some cases additional treatment may be required prior to any watercourse. The exposed areas that would create sediment run off along the site access tracks and the transmission line access track will be localised to the road width. Management of these tracks will be split into lengths of less than 200m long or 0.5ha maximum disturbed area with each segment having appropriate devices installed dependant on the location, upstream catchment, downstream length of undisturbed grass, and topography. Timetable and nature of stabilisation The main platform and access roads will be stabilised by aggregate hard fill as a base course and will be further developed into paving and buildings. This provides instantaneous protection and is not dependent on weather or season. It is proposed to stabilise the batters and disturbed areas outside of the aggregate areas permanently with topsoil and grassed cover. Where the fast stabilisation is required for erosion control outside of the aggregated areas hay mulch or hydroseeding can be utilised to speed up the germination of the grass and stabilisation of these areas. Project File Draft Sediment Control Plan Report Rev 1 Final.docx 20 June 2016 Revision 1 Page 2

7 Maintenance monitoring and reporting Inspections of the sediment control facilities will be undertaken weekly during the construction stages and maintenance undertaken as necessary. Records of inspections and maintenance works will be kept on site for review or submission to Waikato Regional Council if requested. Additional inspections will be made prior to potential heavy rainfall events. As built records of the SRPs and catchment area sizes will be kept to confirm the retention volumes are adequate for the catchment areas. Heavy Rainfall response Weather forecasts will be reviewed on a daily basis to assess the likelihood of future heavy rainfall events. Vulnerable areas may require temporary stabilisation or protection measures and additional inspections made prior to heavy rainfall events. A rain gauge will be installed and monitored on site, when 10mm of rainfall or more has occurred in a single day the sediment control measures will be inspected to ensure they are still effective and operational. Sampling of the retention ponds during initial rainfall events will determine the effectiveness of the controls and the necessity or not of flocculation or enlargement of the SRPs. Procedures for review and/or amendment to the ESCP This draft ESCP will be reviewed and refined by the Contractor in consultation with Nova, prior to commencement of site works. Nova will implement document controls and will seek approval from Council for any changes to the ESCP. Identification of specific site responsibilities This section will be completed prior to implementation. Construction timetable This section will be addressed during detailed design. At this point, the thinking is that the Plant will be built in stages so there is a possibility that the benched earthworks for the building platform may not all be constructed at once; there could be a year or so between each stage. Project File Draft Sediment Control Plan Report Rev 1 Final.docx 20 June 2016 Revision 1 Page 3

8 Appendix A Erosion and Sediment Control Plan Drawing

9 NOTES KAWHIA ROAD APPROX BURIED GAS PIPE LINE 6m WIDE ACCESS TRACK NORTHERN PROPOSED ROAD OPTION 6m WIDE ACCESS TRACK NORTHERN PROPOSED ROAD OPTION 1. AERIAL IMAGERY SOURCED FROM LINZ DATA SOURCE. 2. EXISTING GROUND INFORMATION RECEIVED FROM POWERCO 3 LOCATIONS/SPACE BETWEEN MEASURES ARE NOT SHOWN TO SCALE. 4 SEDIMENT RETENTION PONDS MAY REQUIRE FLOCCULATION TO ACHIEVE DESIRED EFFICIENCY. 5 STAGING TO STABILISE CUT SURFACES OUTSIDE OF PLATFORM AREA BEFORE WORKS BEGIN. 6 DIVERSION PATHS UNDER TRACK AS PER CULVERT LOCATION. 7 ALL EARTH WORKS ARE EXPECTED TO BE CONTAINED WITHIN THIS CLOUDED ENVELOPE 6m WIDE ACCESS TRACK EASTERN PROPOSED ROAD OPTION SECONDARY ACCESS ROAD ON GA RU HE RY DA UN BO STR EAM LEGEND EROSION PROTECTION SILT FENCE CUT SLOPE BOUNDARY Cad File: P:\241157\3 Project Delivery\1 CADD\DRGS\CIV\ SKT-C-200.dwg Plot Date: 3/06/16 15:28:41 Name: Liam Osullivan Xrefs:..\STDS\ XR-G-A1HS..\XBASE\ XR-QUICKMAP..\XBASE\ XR-STRINGS Image Path: P:\241157\3 PROJECT DELIVERY\1 CADD\IMAGES\LINZ\ FALL L FAL DIRTY WATER DIVERSION CLEANWATER DIVERSION ONGARUHE STREAM TEMPORARY STREAM DIVERSION INDICATIVE 4-6m WIDE ACCESS TRACK TRACK FOR TRANSMISSION LINE C CULVERT PERMITTED ACTIVITY CULVERT POTENTIAL HISTORIC PLACE SEDIMENT RETENTION POND 840m³ CAPACITY EACH STABILISED CONSTRUCTION ENTRANCE EARTHWORKS SPOIL SITE DISCLAIMER THE DETAILS SHOWN ON THIS DRAWING ARE INDICATIVE OF THE TYPES OF CONTROLS WHICH MAYBE PROPOSED BUT ARE SUBJECT TO DETAILED DESIGN AND CONSTRUCTION METHODOLOGY IMPLEMENTED BY THE CONSTRUCTION CONTRACTOR. INDICATIVE 4-6m WIDE ACCESS TRACK TRACK FOR TRANSMISSION LINE C m SCALE 1:2500 CLIENT REV DATE REVISION DETAILS APPROVED DRAWN DESIGNED L.O'SULLIVAN R.VAN.LIEROP CHECKED PROJECT PRELIMINARY WAIKATO POWER PLANT NOT FOR CONSTRUCTION PROJECT No. J.KRALL TITLE APPROVED R.Cathcart A PRELIMINARY ISSUE R.Cathcart R.CATHCART DATE EARTHWORKS ENVELOPE EROSION & SEDIMENT CONTROL PLAN SCALE SIZE AS SHOWN A1 DRAWING No. REV SKT-C-200 A

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