DRAINAGE, EROSION AND SEDIMENT CONTROL PLAN SUBCONTRACTOR’S CI TINA RIVER HYDROPOWER DEVELOPMENT PROJECT HEC-CDSB-CESMP- CPP-010 REV. 5 PAGE 1 OF 29 Drainage, Erosion and Sediment Control Plan Person Responsible HEC Construction Manager and HEC HSE Manager REV. DATE (dd/mm/yyyy) DESCRIPTION PREPARED CHECKED APPROVED 1 15/10/2019 Version 1 draft for Lenders’ Review HEC HEC 2 30/04/2020 Version 2 issued for OE’s review HEC HEC 3 02/06/2020 Version 2 issued for Lenders’ Review – Access Road Lot 1 HEC OE(JG) 4 10/09/2020 Version 3 issued for Lenders’ Review – Access Road HEC OE(JG) 5 03/11/2020 Version 3 resubmitted for Lenders’ approval (Access Road) HEC OE (JG)
2.3 DESCRIPTION OF POSITION AND RESPONSIBILITIES 12
3 RISK ASSESSMENT AND MANAGEMENT 17
4 REPORTING AND AUDITING 23
4.1 REPORTING 23
4.2 AUDITING 24
ANNEX A – VISUALISATION OF THE WATER CROSSING STRUCTURES IDENTIFIED
IN THE CURRENT ROAD DESIGN 26
ANNEX B – EXISTING DRAINAGE FACILITY 27
ANNEX C – CALCULATION SHEET FOR SEDIMENT BASIN SURFACE AREA 28
ANNEX D – DRAINAGE DESIGN FOR ACCESS ROAD (SUMMARY) 29
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ACRONYMS
Name Description BOOT Build, Own, Operate and Transfer CESMP Construction Environmental and Social Management Plan DESCP Drainage, Erosion and Sediment Control Plan DIA Direct Impact Area EDCF Economic Development Cooperation Fund EIA Environmental Impact Assessment EPC Engineering, Procurement and Construction E&S Environmental and Social ESC Erosion and Sediment Control ESCP Erosion and Sediment Control Plan ESIA Environmental and Social Impact Assessment ESMP Environment and Social Management Plan GIIP Good International Industry Practice
GRM Grievance Redress Mechanism
HEC Hyundai Engineering Corporation Limited HSE Health, Safety and Environmental IA Implementation Agreement IPP Independent Power Producer K-water Korea Water Resources Corporation LTA Lenders Technical Advisor masl Meters above sea level MMERE Ministry of Mines, Energy and Rural Electrification MW Mega Watt OE Owner’s Engineer (Stantec New Zealand) PO Project Office PPA Power Purchase Agreement PS Performance Standard SIEA Solomon Islands Electricity Authority SIG Solomon Islands Government THL Tina Hydropower Limited TRHDP Tina Hydropower Development Project (the Project)
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1 INTRODUCTION
The Tina River Hydropower Development Project (TRHDP or “Project”) is a hydropower development located in Central Guadalcanal, Solomon Islands, managed by a dedicated Project Office (PO) under the national Ministry of Mines, Energy and Rural Electrification (MMERE).
Tina Hydropower Limited (THL) was established by Korea Water Resources Corporation (K-water) and Hyundai Engineering Company (HEC). THL will Build, Own, Operate and Transfer (BOOT) the Project under an Implementation Agreement (IA) and a Power Purchase Agreement (PPA) with the Solomon Islands Government (SIG) and Solomon Islands Electricity Authority, respectively. The BOOT concession is expected to last for a 30-year period, following commissioning.
HEC will be responsible for the Engineering, Procurement and Construction (EPC) of
the Project, while THL will be responsible for the Operation and Maintenance contract.
THL will sell electricity to the Solomon Islands Electricity Authority (SIEA) trading as
Solomon Power, the state-owned power utility, for the duration of the concession. At
the end of the concession, the hydropower infrastructure will be transferred to the SIG
or SIEA.
1.1 PURPOSE AND SCOPE
This Drainage, Erosion and Sediment Control Plan (DESCP) is one of a series of
environmental and social management plans (ESMPs) that have been developed to
address key environmental and social aspects of the Project. The purpose of this DESCP
is to set out planning and control measures, monitoring and reporting to minimise
erosion, prevent off-site sedimentation and mitigate the residual impacts on and of
stormwater runoff during project construction.
The DESCP has been prepared based on the information and requirements described
in the Environmental and Social Impact Assessment (ESIA) dated August 2017, the
Environmental Impact Statement (EIS) dated July 2019, and specialist erosion and
sediment control advice.
The plan sets out:
• The principles of erosion and sediment control;
• Practical measures to minimise erosion and retain sediment on site, thereby helping to protect water quality, the ecosystem and ecosystem services;
• Controls to manage site drainage (see Annex D)
• A monitoring program to guarantee efficacy of this management plan;
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This DESCP applies to activities conducted by HEC and all subcontractors involved in
related project construction activities.
1.2 DEFINITIONS
Drainage The natural or artificial removal of either surface or sub-
surface water from land.
Employee(s)
Any person(s) who is/are directly employed by the PO, THL or HEC to work on the Project and who receives, or is entitled to receive, remuneration.
Employer / Owner Tina Hydropower Limited (THL); the Project Owner, which will take over operation of the hydropower facility once it is constructed.
EPC Contractor The engineering, procurement and construction
contractor for the TRHDP; Hyundai Engineering
Corporation Limited (HEC).
Erosion The wearing away of the land by geological processes such
as rainfall, running water and wind.
Runoff The portion of precipitation that becomes surface flow.
Sediment Material of varying size, both mineral and organic, that is
or has been moved and deposited in a new location by the
action of water, wind, gravity or ice.
Stakeholder
Individuals or groups who are affected or likely to be affected by the project (project-affected parties); and may have an interest in the Project (other interested parties).
Subcontractors All companies, persons working directly for these companies, or employed by an employment agency, that are under contract to carry out work for HEC, as part of the construction workforce.
Suspended Solids Sediment being transported by water or air that is held in
suspension.
Worker(s) Person(s) engaged in Project activities, including both
employees and contractors
1.3 PROJECT OVERVIEW
The Project consists of a 53 meter high Roller Compacted Concrete dam (from riverbed
to dam crest) in the central area of Malango Ward of Central Guadalcanal, located 20
km southeast of Honiara, at an elevation of approximately 122 meters above sea level
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(masl) and roughly 30 river km from the sea. It also incorporates a 3.3 km tunnel to a
powerhouse and a tailrace at elevation 73 masl, centreline elevation, according to
Technical Proposal. The reservoir formed by the dam will extend upstream
approximately 2.6 km and will have a surface area of about 0.31 km2 at an elevation of
175 masl. The powerhouse will be located 5.4 km downstream from the dam on the
left bank of the Tina River, and water will be diverted to the powerhouse from the
reservoir through the underground tunnel. Initially, the powerhouse will have 3
turbine/generator units, each with a capacity of 5 Mega Watt (MW), allowing a
maximum discharge of about 18 m3/s and a minimum discharge of 2.4 m3/s. An
environmental flow of 1 m3/s will be maintained between the dam and the
powerhouse tailrace, a distance of 5.7 km.
1.4 PRINCIPLES OF EROSION AND SEDIMENT CONTROL
The underlying principles of erosion and sediment control are to (i) minimize erosion
and (ii) prevent off-site sedimentation. Erosion control relies upon good project design
and the installation of adequate site drainage to control runoff safely above, through
and off the site, in manageable volumes before erosive velocities are reached.
Similarly, sediment control relies on good erosion control to minimize the volume of
sediment produced, and installing more than one basin or trap so that in the event of
failure most sediment will still be retained on site.
Project activities that can increase the erosion hazard are:
• Construction of new access roads; Vegetation clearance;
• Soil disturbance, excavation and movement;
• Drainage / river diversion; and
• Vehicle and machinery traffic.
During detailed project design consideration will be given to the establishment of
stable landforms. Attention will be given to stable road design relating to road grades,
cut batter and fill embankment stability, and drainage. Detailed design will incorporate
the design of sediment controls, including sediment basins (Annex C) for construction
sites, work areas and associated project facilities as required. Drains and sediment
basins will be sized for site conditions (slope, soil type, catchment) and the return
period in accordance with good engineering practice.
To determine the required surface area for the sediment basins, the following standard
equation will be used:
As = 1.2Q/Vs (Eq. 1)
Where:
As = Minimum surface area for trapping soil particles of a certain size (m2)
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Vs = Settling velocity of the design particle size chosen (m/sec)
1.2 = Factor of safety recommended by the United States Environmental
Protection Agency (USEPA) to account for the reduction in basin efficiency due
to turbulence and other non-ideal conditions.
Q = CIA*1/360 (Eq.2)
Where:
Q = Discharge rate measured in cubic meter per second
C = Runoff coefficient (unitless)
I = Peak rainfall intensity for the 10-year, 6-hour rain event (mm/hr)
A = Area draining into the sediment basin in ha
The design particle size will be the coarse silt sized (0.05 mm) particle, and the Vs used
should be 100 percent of the calculated settling velocity. Also, the basin length
(distance between the inlet and the outlet) should be a minimum of twice the basin
width and the depth will be 1.0m for safety reasons.
According to the above methodology, surface area of each sediment basin has been
estimated as shown in Table 1-1.
Table 1-1 Estimated Surface Area per Sediment Basin1
Type Surface area (m2) Remark
Lot 1 Max. 49 Total 29ea
Min. 2
Average 14
Lot 2 Max. 84 Total 24ea
Min. 1
Average 16
Lot 3 Max. 16 Total 10ea
Min. 3
Average 10
1 Note: Surface area, number and location may be revised during detailed design.
Basins will have primary and secondary treatment, and sufficient capacity to settle out
suspended sediment before discharging.
Identification of water drainage has been conducted in association with the
watercourse crossing design. Visualisation of the water crossing structures identified
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in the current road design is available in Annex A. A summary of the planned drainage
design is included in Annex D.
1.5 APPLICABLE STANDARDS
The Applicable Standards for this DESCP are as follows:
Legislation
• Solomon Islands Water Authority Act 1992;
• Solomon Islands River Water Act 1964;
• Solomon Islands Safety at Work Act 1982;
• Solomon Island Environmental Act 1998;
• Solomon Island Environment Regulations 2008;
• Solomon Island Provincial Government Act 1997; and
• Solomon Island Roads Act 1996;
International standards and guidelines
• World Bank Performance Standard (PS) 1: Assessment and Management of Environmental and Social Risks and Impacts, 2012;
• World Bank PS3: Resource Efficiency and Pollution Prevention, 2012;
• World Bank Group Environmental, Health, and Safety (EHS) General Guidelines, 2007;
• World Bank Group’s General Environmental, Health, and Safety (EHS) Guidelines (1.3): Wastewater and Ambient Water Quality;
• Asian Development Bank Safeguard Policy Statement (June 2009) Appendix 1, Safeguard Requirement 1: Environment;
• World Bank Operational Policy and Bank Procedure 4.01: Performance Standard 1, Environmental Assessment;
• Economic Development Cooperation Fund (EDCF) Safeguard Policy (2016);
and
• The World Bank Environmental and Social Framework, World Bank, 2016.
HEC policies and procedures
• HEC-AH-H04-H02 HSE Management of Subcontractors;
• HEC-AH-H04-H05 HSE Training and Awareness Procedure;
• HEC-AH-H04-H09 HSE Monitoring and Measurement Procedure; and
• HEC-AH-H04-H13 HSE Audit Procedure.
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Where both national and international standards are applicable, the Project will apply the most stringent standard.
1.6 LINKS TO OTHER MANAGEMENT PLANS
HEC has a comprehensive set of internal HSE procedures which will be implemented
on site. For the purpose of the TRHDP, where there is any conflict between the
mitigation measures and management approaches described in ESMPs, the TRHDP
ESMP requirements will take precedence over HEC internal procedures.
Table 1-2 below lists other ESMPS which are integrated with, and most relevant to,
this DESCP.
Table 1-2: Links to other management plans.
Management Plan Relevance
Construction Environmental and
Social Management Plan (CESMP;
P1)
Refer to this plan for presentation of organizational
charts, detailed description of the audit process,
description of process to amend the management
plans.
Forest clearance plan
(FCP; C3)
Refer to this plan for mitigation measures to limit
drainage of sediments when clearing a vegetated
area.
Post-construction rehabilitation
and revegetation plan
(PCRRP; C4)
Refer to this plan for mitigation measures related to
cleared areas.
Water Supply Replacement Plan
(WSRP; C7)
Refer to this plan for strategies to replace water
sources for downstream users when likely to be
affected by sediment drainage.
Watercourse Crossing Management
Plan
(WCMP; C8)
Refer to this plan for description of mitigation
strategies to guarantee proper drainage during
construction of access roads.
Spoil and Topsoil Management Plan
(STMP; C9)
Refer to this plan for the description of mitigation
strategies to limit soil erosion in stockpiles, and
disposal of spoil from excavations.
Suspended sediment monitoring
plan
(HESSMP; M1)
Refer to this plan for the monitoring activities
related to sediment drainage.
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Management Plan Relevance
Water quality monitoring plan
(WQMP; M2)
Refer to this plan for the monitoring activities
related to water quality.
Fish, Algae, and Macro-Invertebrate
Monitoring Plan
(FAMMP; M3)
Refer to this plan for the monitoring of biota
inhabiting natural water bodies within the Tina River
catchment.
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2 ROLES AND RESPONSIBILITIES
2.1 INTRODUCTION
Having an appropriate organizational structure in place, with all people having defined
roles and responsibilities, is essential to ensuring the overall success of this DESCP.
The HEC Construction Manager, with inputs from HEC HSE Manager, will be ultimately
responsible for the implementation and maintenance of this DESCP. HEC are
responsible for all checks/approvals of all works. THL reviews inspection reports
weekly and conducts spot-checks (on a weekly basis)and signs off on major works (like
disposal areas and final landform for rehabilitation).
HEC expects to hire subcontractors for the design of civil works, dam works, tunnel
works and road works. A series of companies have been shortlisted based on their
reputation and experience.
Sungpoong and Dongbu Engineering were contracted for access road construction and
engineering respectively. Korea Engineering Consultants Corp. was also selected for
main construction engineering.
2.2 SUBCONTRACTOR(S)
HEC will ensure that each subcontractor will be responsible for the execution of the
DESCP.
HEC contracted with subcontractors that are reputable and legitimate enterprises,
appropriately trained in drainage, erosion and sediment control, and licensed by the
relevant government regulatory agencies. Each subcontractor will be responsible for
the execution of the DESCP as applicable to their role in the project. It was a
requirement for the subcontractor to demonstrate to HEC as part of the tendering
process the way their role in the plan will be implemented. Such actions became a
contractual commitment between the subcontractor and HEC.
Selection of subcontractors were conducted according to HEC’s internal corporate
procedure - HSE Management of Subcontractors (HEC-AH-H04-H02).
2.3 DESCRIPTION OF POSITION AND RESPONSIBILITIES
A description of the key positions and their responsibilities are in Table 2-1.
Table 2-1: Position and Responsibilities.
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Position Responsibilities
HEC Project
Manager
(Mr Eu Man
Moon)
• Ensure adequate resources are provided to successfully implement
this DESCP.
• Ensure that all HEC project managers and subcontractors understand
and fulfil their DESCP responsibilities.
HEC
Construction
Manager
(Mr Yoo Jae
Bong)
• Ensure that the HEC HQ Design Team integrates E&S mitigation
measures (including stormwater control structures) into the final
project design.
• Participate in site inspections to plan and confirm the detailed design
of E&S site measures.
• Review and approve detailed site plans incorporating E&S measures.
• Participate in site inspections in the early stages of works at each site
with the HEC HSE Manager, subcontractors and THL.
• Review and approve HSE reports.
• Audit subcontractor performance.
HEC HSE
Manager
(Mr Dae Yong
Kim)
• Maintain this DESCP.
• Lead site inspections with the HEC Construction Manager to plan and
confirm the detailed design of E&S site measures.
• Identify the area that may be affected by stormwater and record
these impacts after stormwater
• Prepare detailed site plans integrating E&S measures into final design
drawings and submit these to the HEC Construction Manager.
• Lead daily site inspections in the early stages of works at each site
with subcontractors and THL.
• Lead weekly site inspections with subcontractors and THL during
construction (following early works).
• Prepare weekly and incident HSE Performance Reports.
• Audit subcontractor E&S performance.
HEC E&S
Supervisor
(Ernest Kolly)
• Undertake field inspections to monitor drainage, erosion and
sediment control.
• Contribute to weekly and incident HSE incident reports prepared by
the HEC HSE Manager.
• Ensure the HEC E&S team conducts all monitoring and reporting as
set out in the ESMPs.
HEC Training
Supervisor
(Mr Patrick Kekete)
• Train HEC staff and subcontractors, particularly those involved in
vegetation clearance and earthworks, on drainage, erosion and
sediment controls with the assistance of the HEC HSE Manager.
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Position Responsibilities
Subcontractors
– Sungpoong,
Dongbu
Engineering,
and Korea
Engineering
Consultants
Corp.
• Specifications for Site Erosion and Sediment Controls at individual
work areas shall be included in Method Statements
• Undertake all civil works and install all related E&S control measures
in accordance with this DESCP and detailed site plans.
• Maintain E&S control measures in good working order, and modify
these controls as needed.
• Notify HEC of any E&S incidents and proposed correction actions, and
record these in an incident log.
• Undertake the agreed corrective actions in a timely manner.
Owner’s
Engineer (OE) -
Stantec New
Zealand
• Review DESCP for compliance with the E&S Standards and Good International Industry Practice (GIIP).
• Monitor and audit project delivery and HEC activities in accordance with the detailed project design, method statements, DESCP, related ESMPs, and detailed site plans.
• OE Site Engineer (Vilive Anise and/or William Waddell) will undertake regular site supervision, and report any E&S non-compliances to the HEC HSE Manager, THL E&S Manager and OE Environmental & Social Safeguards (ESS) Lead (Jessica Grinter – Off Shore).
• Audit HEC performance with respect to the requirements of the
EPC Contract, and health, safety, environmental and social
obligations (including but not limited to the E&S Standards, and
Schedule 7 of the EPC Contract). Auditing will include a site visit
conducted every six months from commencement of
construction, for the duration of the construction phase, by the
OE ESS Lead at minimum.
THL E&S
Manager
(to be
confirmed;
currently Mr
Jihun Lee, CFO
is primary
contact)
• Review DESCP compliance with the E&S Standards and GIIP.
• Participate in daily site inspections in the early stages of works at each
site with HEC and subcontractors.
• Participate in weekly site inspections with HEC and subcontractors
during construction (following early works).
• Prepare monthly E&S performance reports, advising HEC of any non-conformances and required corrective actions.
• Audit HEC compliance with the DESCP.
• Sign off on completed spoil disposal sites when:
• all required permanent retaining structures, drains, etc have been installed;
• initial site revegetation works have been completed; and
• adequate perennial vegetation has been established on the disposal site.
PO E&S
Monitoring
team (with
Monitor that HEC and THL have:
• complied with all requirements, guidelines, procedures, timetables and other specifications set forth in the DESCP at all times
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Position Responsibilities
Lenders
Technical
Advisor - LTA)
• obtained, maintained and complied with all applicable laws, regulations, permits, licences and consents.
• Audit HEC and THL E&S performance.
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3 RISK ASSESSMENT AND MANAGEMENT
A risk assessment was conducted to identify the project activities which might present
a hazard or risk relating to drainage, erosion and sedimentation, and assess the
potential impacts which may arise. A range of mitigation measures and management
approaches were then identified, to achieve a reduction in the initial perceived risk.
The objective in implementing these measures and approaches is to reduce the level
of residual risk to a lower (and acceptable) level.
The following tasks were undertaken to analyse and evaluate risks and identify
potential impacts:
• Identify all activities and sub-activities associated with construction of the Project;
• Assess the likely impact of the activity on the environment, safety and security of
workers and the public, and social/cultural aspects of the Project setting;
• Determine the possible consequences if each impact were to occur;
• Assess the likelihood of each impact occurring in the absence of any controls;
• Consider the severity of impact/s;
• Determine a risk level based on a 5 X 5 risk assessment matrix.
• Document current and future mitigation measures that need to be implemented to
bring the level of risk down to an acceptable level (including consideration of the
findings of the Environmental and Social Impact Assessments (ESIAs) dated August
2017 and July 2019); and
• Re-evaluate to determine the residual risks once the mitigation measures have
been implemented.
HEC and THL applied a modified version of the Risk Ranking Table from the IFC EHS Guidelines (Table 2.1.1) to assess the environmental, health and safety, security and social risks which could be encountered due to construction activities. The matrix applied is presented in Table 3-1 below.
The initial risks identified for each activity; associated impacts, and residual risks (after
implementation of mitigation measures) have been captured in a ‘live’ risk register,
which is maintained on Project Space, the online document management system
administered by HEC for the Project. The activities, risks and impacts presented in
ESMPs are consistent with those listed in the register. The register will be used by HEC,
THL and the OE as a tool to monitor the effectiveness of mitigation measures in
reducing risk across the Project, and will be regularly reviewed and updated as the
Project progresses.
The mitigation measures and management procedures described in this section provide the approach to control and minimise the impacts from drainage, erosion and sedimentation during construction. HEC is committed to implementing the identified mitigation measures and management procedures in order to not cause
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exceedance of the applicable standards, and to avoid impacts on the local community and the environment.
The mitigation measures and management measures that are relevant to HEC on-site activities are shown in Table 3-1.
Should excessive drainage, stormwater, erosion and sedimentation impacts arise from site activities following the implementation of the proposed measures, HEC will review the need for additional measures and update this DESCP accordingly.
Table 3-1 5 X 5 Risk Assessment Matrix
Likelihood Consequences
Insignificant
Negligible impacts to a minimal area
of low environmental
or social significance, managed by
internal control
procedures
Minor
Minor or minimal short-term impacts
to the environment
and social areas
Moderate
Significant impacts to the
wider environment
or social areas, where short-term restoration works are
needed
Major
Major, persistent
and/or extensive
impacts to the environment
or social areas where longer
term remediation is required (> 6
months)
Catastrophic
Catastrophic and
irreversible environmental
damage to social areas or environment
A. Almost certain
Very high likelihood
the risk will occur
(>75%)
Moderate High Extreme Extreme Extreme
B. Likely
High likelihood
the risk will occur
(51 - 75%)
Moderate High High Extreme Extreme
C. Possible
Medium likelihood
the risk will occur
(21 - 50%)
Low Moderate High High Extreme
D. Unlikely
Low likelihood
Low Moderate Moderate High High
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the risk will occur
(5 - 20%)
E. Rare
Very low likelihood
the risk will occur
(<5%)
Low Low Low Moderate Moderate
Mitigation measures were selected to achieve the following:
• In the cases where risk level was assessed as a Moderate or High – reduce risk
to Low;
• In the cases where risk level was assessed as Low – ensure risk level does not
increase; and
• In the cases where risk level was assessed as Extreme – modify the project to
avoid critical risk activities.
The impacts associated with construction of the Project, and particularly in relation
to the scope of this Plan, are included in Table 3-2, along with assigned mitigation
measures / management approaches. The table also outlines the monitoring actions
that will be applied to continually evaluate the effectiveness of these measures and
approaches for the duration of construction.
As noted in Section 1.6, this DESCP has links to several other plans. In particular,
Table 3-2 below cross-references measures from (and should be read and
implemented in conjunction with):
• Hazardous Materials Management Plan (HMMP; P13)
• Spill Prevention and Emergency Response Plan (SPERP; P14)
• Watercourse Crossing Management Plan (WCMP; C8)
• Spoil and Topsoil Management Plan (STMP; C9)
• Suspended Sediment Monitoring Plan (SSMP; M1)
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Table 3-2 Mitigation / Management and Monitoring Procedures
1 Detailed design review • Project engineering design shall be reviewed to ensure long-term stability of final project landforms. HEC Project Manager, HEC Engineering Team, HEC HSE Manager
• Sign-off of detailed project designs HEC Engineering Team
2 Detailed project planning • Sedimentation basins will be delineated (and HEC will assess whether these may drain to the watershed of any community water sources identified through the Water Supply Replacement Survey (refer to details in the Water Supply Replacement Plan, WSRP; C7).
• Detailed specifications for Site Erosion and Sediment Controls at individual work areas shall be included in Method Statements and submitted for engineering review by HEC Engineering Team and OE prior to commencement of construction. These specifications will include at minimum sediment basin dimensions and capacity, culvert dimensions and capacity, diversion drain cross-section and grade, disturbed areas, and a description of implementation activities and design details for the measures (e.g. timing/sequencing of works, sediment basin volume calculations, temporary measures, stabilisation/revegetation works).
• Method statements shall detail the design of each sediment basin to be installed to settle out coarse and suspended sediment, including primary and secondary treatment, and sufficient capacity to settle out suspended sediment before discharging
• Design will include methods to settle out coarse and suspended sediment, including primary and secondary treatment.
HEC Construction Manager, HEC Engineering Team, HEC HSE Manager
• Sign-off of sedimentation basin design and method statements
HEC Engineering team and HEC HSE Manager OE (review)
3 Site Preparation • Site boundaries and initial erosion and sediment control measures such as drains, diversion banks, sediment basins and traps shall be surveyed and pegged by HEC or its nominated subcontractor. HEC shall then seek approval of the siting and layout of the site and controls from by THL.
• THL shall inspect each site to be cleared prior to the commencement of any clearing, and approve sites that have been clearly marked in accordance with the permit to clear, vegetation clearance plan and the initial erosion and sediment controls have been correctly installed, issuing a Notice to Proceed.
• All staff involved in earthworks and the operation of other machinery and vehicles on site shall be walked through the layout of the pegged control measures on each site, and instructed on strict adherence to site clearance, erosion and sediment controls.
• Initial erosion and sediment controls shall be installed prior to the commencement of site vegetation clearance (or where vegetation clearance is required to install the controls immediately after clearance), before the commencement of bulk earthworks.
• Vegetation and topsoil shall be progressively removed and stockpiled from each site in a controlled manner immediately before major earthworks are commenced to minimize the period of time that land is exposed to erosion.
• Cleared vegetation shall be stockpiled in accordance with the Forest Clearance Plan (FCP, C3) to minimise site erosion, enable the salvaging of logs as necessary and provide a source of mulch and seed for later revegetation. Stockpiling shall only occur on previously disturbed areas to avoid additional vegetation clearance and ground disturbance unless such areas are unavoidable. Wherever possible vegetation shall be stockpiled on the contour to spread overland runoff and catch sediment.
• Earthworks shall be strictly undertaken within marked areas, avoiding vegetation and soil disturbance beyond these designated sites.
• Access shall be strictly controlled to and from each site via designated entry/exit points.
• Permanent and temporary drains shall be installed as early as possible to control runoff.
• Initial erosion and sediment controls installed on each site shall be inspected by THL, who shall issue a Notice to Proceed for the related construction activity if the controls are installed in accordance with the detailed approved site plan.
HEC Construction Manager and Subcontractor - pre-site clearance THL – pre-site clearance HEC HSE Manager Subcontractors Subcontractors Subcontractors Subcontractors Subcontractors Subcontractors THL E&S Manager (prior to commencing construction activity)
• Site inspections as needed, moving to joint weekly site inspections after the initial works (weekly HSE performance reports prepared by HEC HSE Manager)
HEC Construction Manager, HEC HSE Manager, Subcontractors, THL (Daily inspections, moving to weekly frequency)
4 Erosion and drainage control
• Minimal ground disturbance and vegetation clearance shall occur by limiting each site to the minimum area required, clearly pegging / marking out the boundary and strictly controlling vegetation clearance and site access.
• Construction activities will be programmed to limit the period of time that soil is exposed, particularly during the wet season.
• All vehicles and machinery shall be restricted to designated accessways and areas to prevent additional ground disturbance.
• Adequate permanent and temporary drainage shall be installed to divert runoff above the site and control it through and off the site. Specific measures shall include:
• installation of permanent lined drains as soon as possible;
• cut-off drains (earth or vegetated spoon drains or diversion banks) installed above disturbed areas to safely direct run-on from entering the site;
• flow velocities in unlined drains kept low to prevent scouring by running the drains at a low grade;
• temporary drains/banks (earth spoon drains or diversion banks) installed across large construction areas subject to earthworks or ongoing disturbance, to break the site into sub-drainage areas, reducing overland runoff distances/volumes/velocities;
• side drains and road camber installed to direct runoff into side drains and safely convey it to crossroad drains;
HEC Construction Manager Subcontractors Subcontractors Subcontractors
• Site inspections as needed, moving to joint weekly site inspections after the initial works (weekly HSE performance reports prepared by HEC HSE Manager)
HEC Construction Manager, HEC HSE Manager, Subcontractors, THL (Daily inspections, moving to weekly frequency)
DRAINAGE, EROSION AND SEDIMENT CONTROL PLAN SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT HEC-CDSB-CESMP-CPP-010 REV. 5 PAGE
• permanent drains lined and fitted with outlet protection to prevent scouring, installed as soon as possible;
• installed drains discharged into stable natural drainage lines wherever possible; • road sections with a high risk of erosion (e.g. steeper grades) gravelled or sealed;
• installation of retaining structures (rock walls, gabions, etc) to stabilize cuttings and embankments; and
• use of temporary erosion control measures (e.g. temporary diversion banks; plastic sheeting on exposed batters).
• The disturbance of stable drainage lines shall be avoided by marking off these areas from adjacent construction sites to ensure machinery and vehicles do not enter these areas.
• Existing stable drainage lines shall be used for trunk drainage where possible.
• Sufficient cross drains will be installed to avoid erosion. Drains will not be hydraulically connected to streams. Instead, they will exit via ditches into stable, vegetated areas or discharge into settling ponds.
• If a drainage line crossing is required it will be aligned at right angles to the flow path and kept to the minimum width for the purpose, with the design and control measures in accordance with the Watercourse Crossing Management Plan (WCMP; C8).
• Cutting and filling will be completed to final cross-sections at each site/discrete section as soon as possible, ideally in one continuous activity, to create the final landform and enable site stabilisation works to be undertaken as early as possible.
• Erosion and sediment controls shall be maintained in good working order.
• Erosion and sediment controls shall be inspected weekly and after each major rainfall event to identify any issues and required corrective or additional measures.
• Corrective measures will be installed as soon as possible after they are identified.
• Erosion control on steep slopes subject to gully erosion will be carried out by appropriate erosion control good practices. These measures rely on (i) storm water control design (peripheral drainage), (ii) design of the slope (including berms), (iii) run-off control by revegetation and (iv) stabilisation of sensitive areas by engineering methods.
5 Sediment control • Sediment controls shall be installed across construction sites to remove sediment before runoff discharges from the site, based on the principle of dividing the catchment into manageable areas (rather than relying on a single trap at the bottom of the site that may fail).
• All runoff from project work sites shall be directed into sediment traps or basins to remove coarse and suspended sediment from runoff before it is discharged from the site.
• Sediment fences, traps and basins with adequate capacity shall be installed on each construction site, material storage area, camp site and other disturbed areas.
• Sediment basin volume and dimensions will be designed based on catchment area, estimated storm discharge (e.g. two-year return period) and soil particle size, in accordance with good practice.
• Sediment basins will be fitted with a runoff overflow pipe and spillway that either discharges into a secondary basin (as needed) or into a stable natural watercourse or broad open area.
• Sediment basins shall be accessible by machinery so they can be cleaned.
• Where significant sediment volumes may be generated basins shall have primary and secondary treatment to settle out suspended sediment before discharge.
• Sediment basins, traps and fences shall be inspected weekly and after each major storm event to check that they are operational and have sufficient trapping capacity.
• Sediment storage capacity in basins shall be monitored and documented each week and after each major rainfall event to determine when dredging is required.
• Sediment basins, traps and fences shall be cleaned of sediment when 50% of their available capacity is full.
• Sediment shall be disposed of without creating a safety or erosion hazard, or degrading land (e.g. disposal in the spoil disposal site is permitted, but not on agricultural land).
• Removed sediment will either be deposited into an adjacent trench to dry or moved to the final disposal site.
• Where installed sediment controls are deemed inadequate, modifications to these controls or additional controls shall be designed and installed.
Subcontractors Subcontractors Subcontractors HEC Engineering Team and Subcontractors Subcontractors Subcontractors HEC HSE Manager and Subcontractors Subcontractors Subcontractors Subcontractors HEC Construction Manager and Subcontractor
• Daily site inspections as needed, moving to joint weekly site inspections after the initial works (weekly HSE performance reports prepared by HEC HSE Manager)
6 Topsoil management • All topsoil shall be stripped from construction and ancillary sites immediately prior to the use of each site, including stripping any temporary work areas.
• Topsoil shall be stockpiled for reuse in site revegetation.
• If excess topsoil is available it may be used for local community facilities (e.g. playing fields, communal areas).
• Topsoil shall be stored separately from spoil (subsoil, rock, etc) in flood-free areas at least 20 m from the Tina River, streams and drainage lines.
• Topsoil shall be stockpiled in bunds with slopes not exceeding 1:2 (V:H).
• Daily site inspections as needed, moving to joint weekly site inspections after the initial works (weekly HSE performance reports prepared by HEC HSE Manager)
HEC Construction Manager, HEC HSE Manager, Subcontractors, THL
DRAINAGE, EROSION AND SEDIMENT CONTROL PLAN SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT HEC-CDSB-CESMP-CPP-010 REV. 5 PAGE
• Topsoil stockpiles to be retained for greater than 3 months shall be seeded with a cover crop (e.g. rice, sorghum) or covered with mulch within a fortnight of stockpile formation to minimise the erosion hazard.
Subcontractor
7 Stockpiling construction materials
• Erodible construction material (sand, soil, etc) shall be stockpiled:
• on relatively flat and flood-free areas;
• outside the normal Tina River flood zone (1:5 year flood);
• at least 20 m from a stream or watercourse (except for temporary stockpiling that may be permitted adjacent to a river extraction site during the dry season);
• on sites already devoid of trees and at least 10 m away from retained vegetation; and
• not directly upslope of houses and other structures.
• Stockpiling on communal or private land shall only occur with the written permission of the community and with THL approval of the site.
• Depending on the site, drainage will be installed to prevent run-on entering the storage area.
Subcontractor Subcontractor Subcontractor
• Joint weekly site inspection (weekly HSE performance reports prepared by HEC HSE Manager)
HEC Construction Manager, HEC HSE Manager, Subcontractors, THL
8 Site rehabilitation • THL shall inspect and approve each final landform prior to the commencement of site stabilization works.
• Project sites shall be progressively stabilised, with each disturbed area shall be rehabilitated as soon as possible following the completion of construction activities on that site or sub-site area: within one month of the completion of construction or project use of the site during the dry season and within two weeks of completion during the wet season, thereby minimizing the period of soil exposure.
• Final landforms shall be topsoiled and seeded or planted to promote revegetation. Minimum treatment shall include had seeding or sowing (i) a cover crop for rapid ground cover and (ii) perennial species for long-term soil stabilisation. Additional treatment may include planting tree and shrub seedlings and mulching the ground surface.
• Site vegetation shall be maintained until sufficient permanent ground cover has been established. This will entail monitoring the site for at least one year and replanting areas with insufficient ground cover (75% or greater cover).
THL – prior to site stabilisation Subcontractor - progressively as each discrete area is completed Subcontractor HEC or Subcontractor – for 1 year following initial revegetation works
• Joint weekly site inspections during works (weekly HSE performance reports prepared by HEC HSE Manager)
• Monthly site inspections (quarterly revegetation reports prepared by HEC HSE Manager)
HEC Construction Manager, HEC HSE Manager, Subcontractors, THL HEC and Subcontractor
.
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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4 REPORTING AND AUDITING
4.1 REPORTING
The DESCP establishes an internal and external reporting structure summarised in
Table 4-1.
Internally, the reporting hierarchy proceeds as follows: Subcontractor reports to the
HEC Construction Manager, who reports to the HEC Project Manager. Externally, HEC
reports directly to THL and the OE; THL in turn reports to the PO, Lenders and relevant
authorities.
The subcontractor is responsible for reporting to the HEC Construction Manager
regarding design and implementation of ESC structures. Moreover, the subcontractor
will report its HSE performance following the procedures and templates detailed in the
Workers’ Health and Safety Plan (WHSP; P8) and CESMP (P1).
Monitoring of the efficacy of the mitigation measures will be conducted according to
Table 3-2 above; along with the Suspended Sediment Monitoring Plan (SSMP; M1) and
the Water Quality Monitoring Plan (WQMP; M2).
At least one month prior to the anticipated commencement of the wet season, a
review of the effectiveness and adequacy of the existing erosion and sediment controls
will be made and any necessary modification and/or augmentation of controls carried
out.
Table 4-1 Reporting structure for the DESCP
Preparation Review Content Frequency
Internal
Subcontractor HEC Construction Manager
• Controls to be implemented on site, in order to comply with the DESCP (e.g. map the location of sediment fences)
Once at Detailed Design stage
Subcontractor HEC Construction Manager
• Completion of ESC checklist to monitor correct implementation of mitigation strategies
• Incident Report Form if any accidental flooding occurs due to poor management of stormwater mitigation measures.
• HSE Performance Report
Weekly
HEC E&S Team HEC Construction Manager
• Visual inspection report of ESC
• Revision of ESC Checklist
Weekly
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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Preparation Review Content Frequency
HEC Construction Manager
HEC Project Manager
• Results of visual inspection of ESC
• Collection and distribution of Incident Report Forms prepared by the subcontractor.
Weekly
External
HEC Construction Manager
THL • Results of visual inspection of ESC • HSE Performance Report (monthly
collection)
• Collection of Incident Report Form.
Monthly
4.2 AUDITING
HEC will be subject to internal and external audits. The internal audit will be conducted
by HEC Headquarters to the on-site team according to HEC’s corporate internal HSE
Audit Procedure (HEC-AH-H04-H13). The internal examinations regularly performed by
the on-site HEC staff are referred as inspections. External audits will be conducted by
the E&S Manager from THL, E&S Safeguards Manager from the PO, and the Owner’s
Engineer (OE).
The detailed structure and content of the auditing process is presented in the Project
Construction Environmental Social Management Plan (CESMP; P1). Table 4-2 presents
a summary of the process.
Table 4-2 Summary of auditing process.
Auditor Auditee Frequency
THL E&S Manager HEC Every three months
PO E&S Safeguards Manager and Monitoring team (with LTA)
HEC and THL Every three months
HEC Headquarter HSE Team HEC on-site team Every six months
HEC HSE Manager Subcontractor Every three months
HEC HSE team (with THL) On-site workers Every week
OE HEC Every six months
External and internal auditors shall notify by email the HEC Project Management Team
(Project Manager, Construction Manager and HSE Manager) about upcoming audit
events. This will provide a mechanism to communicate the schedule, activities and
objectives of the audits. If urgent, the Project Site may be notified via phone or fax.
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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The audit process involves reviewing on-site activities to assess compliance with the
management plans and / or HEC internal standards. The auditor will review all records
of previous audits and evaluate historic compliance and the use of appropriate
corrective actions.
Findings from the audit will be summarised in an audit report. A copy of the resulting
audit report is to be made available upon request for reference and, where necessary,
implementation of any identified corrective actions.
The Key Performance Indicators to be considered when auditing this management plan
are:
• Number of incompliances recorded;
• Number of incompliances resolved;
• Stockpile location according to ECSP;
• Stockpiles adequately protected against erosion;
• Number of stockpiles not compliant with ECSP;
• Settling ponds location and design according to ECSP;
• Number of damaged settling ponds;
• The used tarpaulins and geotextiles provide adequate protection to the
covered material;
• Design of stormwater management structures according to ESCP;
• Instances of stormwater ‘pooling’ observed;
• Number of drains obstructed;
• Number of damaged drains; and
• Number of drainage channels that disrupt water supply of local communities.
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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ANNEX A – VISUALISATION OF THE WATER CROSSING STRUCTURES IDENTIFIED IN
THE CURRENT ROAD DESIGN
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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ANNEX B – EXISTING DRAINAGE FACILITY
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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ANNEX C – CALCULATION SHEET FOR SEDIMENT BASIN SURFACE AREA
DRAINAGE, EROSION
AND SEDIMENT
CONTROL PLAN
SUBCONTRACTOR’S CI
TINA RIVER HYDROPOWER DEVELOPMENT PROJECT
HEC-CDSB-CESMP-
CPP-010 REV. 5
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29 OF 29
ANNEX D – DRAINAGE DESIGN FOR ACCESS ROAD (SUMMARY)
