Environmental Protection Department

 

Agreement No. CE20/2004 (EP)

North East New Territories (NENT) Landfill Extension

 

Environmental Impact Assessment Report  

 

May 2007

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Contents

                                                                                                                                                                                                     

1          Introduction   1

1.1        Project Background  1

1.2        Purpose and Scope of the EIA Study  1

1.3        EIA Study Area  1

1.4        The Approach  2

1.5        Structure of the EIA Report 3

2          Description of the Project   1

2.1        General Description of the Project 1

2.2        Key Project Requirements  1

2.3        Need for the Project 2

2.4        Consideration of Alternatives  3

2.5        Site Location and Site History  11

2.6        Nature, Scope and Benefits of the Project 12

2.7        Size, Scale, Shape and Design of the Project 12

2.8        Project Timetable  14

2.9        Related Projects  15

2.10      “No Project” Scenario  15

3          Air Quality Impact   1

3.1        Introduction  1

3.2        Environmental Legislation, Standards and Guideline  1

3.3        Description of the Existing NENT Landfill and the Extension  5

3.4        Air Sensitive Receivers  11

3.5        Identification of Air Pollution Source and Environmental Impact 12

3.6        Assessment Methodology  18

3.7        Prediction and Evaluation of Air Quality Impact 30

3.8        Precautionary Measures  42

3.9        Residual Environmental Impact 44

3.10      Implication of IWMF Implementation  44

3.11      Conclusion  44

4          Noise Impact   1

4.1        Introduction  1

4.2        Environmental Legislation, Standards and Guidelines  1

4.3        Description of the Environment 4

4.4        Noise Sensitive Receivers  5

4.5        Assessment Methodologies  6

4.6        Construction, Restoration & Aftercare Noise Impact Assessment 7

4.7        Operational Noise Impact Assessment 9

4.8        Residual Environmental Impact 15

4.9        Conclusion  15

5          Water Quality Impact   1

5.1        Introduction  1

5.2        Environmental Legislation, Standards and Guidelines  1

5.3        Baseline Conditions  2

5.4        Water Sensitive Receivers  6

5.5        Assessment Methodology  7

5.6        Identification and Evaluation of Water Quality Impacts  7

5.7        Cumulative Impacts  23

5.8        Precautionary Measures  23

5.9        Residual Impacts  30

5.10      Conclusion  30

5.11      Reference  32

6          Waste Management Implications   1

6.1        Introduction  1

6.2        Legislation, Standards and Guidelines  1

6.3        Assessment Methodology  1

6.4        Identification and Evaluation of Waste Management Implications  2

6.5        Mitigation Measures  6

6.6        Residual Impacts  6

6.7        Environmental Audit 7

6.8        Implication of IWMF Implementation  7

6.9        Conclusion  7

7          Landfill Gas Hazards   1

7.1        Introduction  1

7.2        Legislation, Standards and Guidelines  1

7.3        Background Information  1

7.4        LFG Hazard Assessment 3

7.5        Protective and Precautionary Measures  13

7.6        Monitoring Requirement 20

7.7        Implication of IWMF Implementation  21

7.8        Conclusion  21

8          Landscape and Visual Impact   1

8.1        Introduction  1

8.2        Legislation, Standards and Guidelines  1

8.3        Landscape And Visual Impact Assessment Methodology  2

8.4        Baseline Study Frameworks  5

8.5        Planning and Development Control Review   11

8.6        Source of Impacts and Impact Assessment 11

8.7        Conclusion  22

9          Impact on Cultural Heritage   1

9.1        Introduction  1

9.2        Environmental Legislation & Standards  1

9.3        Description of the Study Area  1

9.4        Archaeology  2

9.5        Built Heritage  7

9.6        Identification and Evaluation of Impacts  13

9.7        Mitigation Recommendations  15

9.8        Conclusions  16

9.9        References  17

10         Ecological Impact   1

10.1      Introduction  1

10.2      Relevant Legislation and Guidelines  1

10.3      Field Survey Scope and Methodology  2

10.4      Key Ecological Issues  3

10.5      Results of Literature Review   4

10.6      Results of Field Surveys  6

10.7      Evaluation of Habitats and Species  14

10.8      Impact Identification and Evaluation  19

10.9      Impact Avoidance and Mitigation Measures  27

10.10    Residual Ecological Impacts  30

10.11    Ecological Monitoring and Audits  31

10.12    Conclusion  31

10.13    Reference  31

11         Summary of Environmental Outcome   1

11.1      Population and Environmental Sensitive Areas Protected  1

11.2      Environmental Friendly Design and Benefit 1

11.3      Key Environmental Problem Avoided  1

11.4      Environmental Protection Measures and Precautionary Measures  1

12         Environmental Monitoring and Audit Requirements   1

12.1      Introduction  1

12.2      Project Organisation  1

12.3      EM&A Manual and Implementation Schedule  1

12.4      EM&A Programme  2

12.5      Method Statements  2

13         3-Dimensional EIA   1

14         Conclusion   1

14.1      Option Evaluation  1

14.2      Air Quality Impact 1

14.3      Noise Impact 2

14.4      Water Quality  2

14.5      Waste Management 3

14.6      Landfill Gas Hazards  3

14.7      Landscape and Visual Impact 3

14.8      Cultural Heritage Impact 4

14.9      Ecological Impact 4

14.10    Environmental Monitoring and Audit 5

14.11    3D-EIA Tools  5

14.12    Overall Conclusion  5

 

 

 

Drawings

24315/01/001        Location Plan

24315/01/005        Existing NENT Landfill and Proposed Landfill Extension

24315/01/101        Landfill Extension Layout Option 1

24315/01/102        Landfill Extension Layout Option 1a

24315/01/103        Landfill Extension Layout Option 1b

24315/01/104        Landfill Extension Layout Option 2

24315/01/105        Landfill Extension Layout Option 2a

24315/01/106        Landfill Extension Layout Option 3

24315/01/107        Landfill Extension Layout Option 4

24315/13/101        Location of Air Sensitive Receivers (Assessment Points)

24315/13/102        Dust Emission Source Location (Existing NENT Landfill Final Capping + NENT Landfill Extension Phase 1)

24315/13/103        NO2, SO2 & VOC Emission Source Location

24315/13/104        Odour Emission Source Location

24315/13/105        Predicted 1-hour TSP Contour (mg/m³) at 1.5m Above Ground (Worst-case Scenario)

24315/13/106        Predicted 24-hour TSP Contour (mg/m³) at 1.5m Above Ground (Worst-case Scenario)

24315/13/107        Predicted 1-hour Averaged NO2 Contour (mg/m³) at 10m Above Ground (Worst-case Scenario : ASP ON))

24315/13/108        Predicted 1-hour Averaged SO2 Contour (mg/m³) at 10m Above Ground (Worst-case Scenario : ASP ON)

24315/13/109        Predicted 1-hour Averaged Benzene Contour (mg/m³) at Worst Affected Location (Worst-case Scenario : ASP ON)

24315/13/110        Predicted Annual Averaged Benzene Contour (mg/m³) at Worst Affected Location (Worst-case Scenario : ASP ON)

24315/13/111        Predicted 1-hour Averaged Vinyl Chloride Contour (mg/m³) at Worst Affected Location (Worst-case Scenario : ASP ON)

24315/13/112        Predicted Annual Averaged Vinyl Chloride Contour (mg/m³) at Worst Affected Location (Worst-case Scenario : ASP ON)

24315/13/113        Predicted 5-second Averaged Odour Contour at 1.5m Above Ground (Northern Tipping)

24315/13/114        Predicted 5-second Averaged Odour Contour at 1.5m Above Ground (Western Tipping)

24315/13/201        Location of Noise Sensitive Receivers

24315/13/202        Proposed Planter Wall at Wo Keng Shan Road

24315/13/203        Location of Fixed Noise Sources

24315/13/301        Location of Groundwater Monitoring Point for Existing NENT Landfill

24315/13/302        Boreholes Location Plan

24315/13/303        Location of Water Sensitive Receivers and Sampling Points for Stream Water Baseline Survey           

24315/13/304        Catchment Areas near the NENT Landfill Extension Site

24315/13/501        Geological Map of NENT Landfill Extension Site

24315/13/502        LFG Consultation Zone

24315/13/503        Monitoring of Background CO2 Levels at 25 Boreholes

24315/13/504        Existing Landfill and Landfill Extension Monitoring Plan

24315/14/001        NENT Landfill Extension & Source of Impact

24315/14/002        Landscape Character Areas (LCAs) Plan & Impact Assessment (Without Mitigation)

24315/14/003        Aerial Photograph of the Project Site and the Surroundings

24315/14/004        Landscape Resources (LRS) Plan & Impact Assessment (Without Mitigation)

24315/14/005        Tree Survey Plan

24315/14/006        Visual Envelope and Visual Sensitive Receivers (VSRs) Plan & Impact Assessment (Without Mitigation)

24315/14/007        Typical View of Visual Sensitive Receivers to Proposed Development (Sheet 1 of 2)

24315/14/008        Typical View of Visual Sensitive Receivers to Proposed Development (Sheet 2 of 2)

24315/14/009        Mitigation Plan

24315/14/010        Photo Montage of Selected View (Sheet 1 of 3)

24315/14/011        Photo Montage of Selected View (Sheet 2 of 3)

24315/14/012        Photo Montage of Selected View (Sheet 3 of 3)

24315/13/601        CHIA Issues

24315/13/602        Study Area of Option 4 (Divided into Four Sub-sections for Ease of Reference)

24315/13/603        Solid and Superficial Geology (Sheung Shui) Hong Kong Geological Survey

24315/13/604        Location of Auger Holes and Test Pits

24315/13/605        Contexts of Test Pits

24315/13/606        Archaeological Findings

24315/13/701        Location of Site of Conservation Importance and Sampling Transects and Points for Fauna

24315/13/702        Habitat Map Location of Species of Conservation interest overlaid with Option 4

24315/13/703        Photos of Habitat and Species of Conservation interest

 


 

Appendices

Appendix 2.1      EIA Study Brief ESB-114/2004

Appendix 2.2      Tentative Outline Programme

Appendix 3.1       Construction Dust Assessment

Appendix 3.2      Gaseous Emission Assessment

Appendix 3.3A    Identification of Worst Weather Condition for Odour Assessment

Appendix 3.3      Odour Emission Assessment

Appendix 3.4      Odour Emission Strength and Modelling Parameters

Appendix 3.5      Surface Roughness Calculation in the area

Appendix 3.6      Odour Hourly Emission Concentration

Appendix 3.7      Predicted 1-hour and 24-hour TSP concentration

Appendix 3.8      Predicted 1-hour, 24-hour and annual averaged NO2 and SO2 concentration (mg/m3) at ASRs under various modes of operations

Appendix 3.9      Predicted 1-hour and annual averaged VOC concentration (mg/m3) at ASRs under various modes of operations

Appendix 3.10     Predicted odour concentration

Appendix 4.1      Sound Power Level of PMEs  

Appendix 4.2      Construction Plant Inventory

Appendix 4.3      Locations of Notional Sources and Distance to NSRs

Appendix 4.4      Detail Calculation of Construction Noise Assessment

Appendix 4.5      Detail Calculation of Cumulative Construction Noise Assessment

Appendix 4.6      Compute Plot of Road Traffic Noise Model

Appendix 4.7      Noise Measurement Results of Aeration Lagoon

Appendix 4.8      Noise Measurement Results of Ammonia Stripping Plant

Appendix 4.9      Noise Measurement Results of Refuse Vehicle

Appendix 4.10     Detail Calculation of On-site Operation Noise (Un-mitigated Scenario)

Appendix 4.11     Detail Calculation of On-site Operation Noise (Mitigated Scenario)

Appendix 4.12     Detail Calculation of Existing Landfill Operational Noise

Appendix 5.1      Groundwater Monitoring Data for Existing NENT Landfill from January 2005 to March 2006

Appendix 5.2      Leachate Generated from Landfill

Appendix 7.1      LFG Protection Measures in Existing NENT Landfill

Appendix 7.2      Specific LFG Protection Measures for Building Services

Appendix 9.1      Plates

Appendix 9.2      Grave Catalogue

Appendix 9.3      Cultural Landscape Feature Recording Form

Appendix 9.4      Methodology for Preservation by Record

Appendix 10.1     Freshwater Fish known to be present in Lin Ma Hang Stream

Appendix 10.2     Bat species recorded in Ling Ma Hang or in the vicinity of the Study Area

Appendix 10.3     Plant species recorded within the Study Area

Appendix 10.4     Bird species and their abundance in the Project Area

Appendix 10.5     Bird species and their abundance in the Study Area

Appendix 10.6     Dragonfly species and their abundance in the Project Area

Appendix 10.7     Butterfly species and their abundance in the Project Area

Appendix 10.8     Dragonfly species and their abundance in the Study Area

Appendix 10.9     Butterfly species and their abundance in the Study Area


Abbreviation

 

 

ASR

Air Sensitive Receiver

BMP

Best Management Practice

BOD5

5-Day Biochemical Oxygen Demand

COD

Chemical Oxygen Demand

CRTN

Calculation of Road Traffic Noise

DIA

Drainage Impact Assessment

DO

Dissolved Oxygen

DP

Designated Project

EIA

Environmental Impact Assessment

EIAO

Environmental Impact Assessment Ordinance

EPD

Environmental Protection Department

ETWBTC

Environment, Transport and Works Bureau Technical Circular

GCL

Geosynthetic clay liner

HDPE

High density polyethylene

HKPSG

Hong Kong Planning Standards and Guidelines

IWMF

Integrated Waste Management Facilities

MSW

Municipal solid waste

NCO

Noise Control Ordinance

NENT

North East New Territories

NSR

Noise Sensitive Receiver

OZP

Outline Zoning Plan

PCB

Polychlorinated Biphenyl

ProPECC

Environmental Protection Department Practice Note for Professional Persons

SBA

Stockpile and Borrow Area

SBR

Sequencing Batch Reactor

SENT

South East New Territories

SPL

Sound Pressure Levels

SS

Suspended Solid

SWHSTW

Shek Wu Hui Sewage Treatment Works

SWL

Sound Power Levels

TKN

Total Kjeldahl Nitrogen

TM-EIAO

Technical Memorandum on Environmental Impact Assessment Process (Environmental Impact Assessment Ordinance, Cap. 499, S.16)

TM-Places

TM for the Assessment of Noise from Places other than Domestic Premises, Public Places or Construction Sites

TM-PP

Technical Memorandum on Noise from Percussive Piling

TM-DA

Technical Memorandum on Noise from Construction Work in Designated Areas

TM-GW

Technical Memorandum on Noise from Construction Work other than Percussive Piling

TM-Water

Technical Memorandum on Standards for Effluent Discharged into Drainage and Sewerage System, Inland and Coastal Waters

TN

Total Nitrogen

TOC

Total Organic Carbon

TSS

Total Suspended Solid

TTSAS

Tong To Shan Archaeological Site

USEPA

United State Environmental Protection Agency

WCZ

Water Control Zone

WENT

West New Territories

WHO

World Health Organization

WPCO

Water Pollution Control Ordinance

WRFP

Waste Reduction Framework Plan

WSR

Water Sensitive Receiver

WQI

Water Quality Indexes

WQO

Water Quality Objective

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


1                  Introduction

1.1                 Project Background

Currently, about 6 million tonnes of waste are disposed each year at the three strategic landfills in Hong Kong, including the West New Territories (WENT) Landfill, the South East New Territories (SENT) Landfill, and the North East New Territories (NENT) Landfill.

At time of commissioning, the three landfills with a total capacity in the order of 140 Mm³ were expected to be able to meet the waste disposal needs of Hong Kong until 2020 or beyond.  The actual waste disposal rate at the landfills has been, however, higher than expected.  It is thus projected that the three existing landfills would last only until early-to-mid next decade.

To tackle the problem, further efforts have been taken to reduce and recycle waste.  Also, the HKSAR Government has planned to develop Integrated Waste Management Facilities (IWMF) to substantially reduce the volume of waste requiring landfill disposal.  Yet these measures could not obviate totally the need for new landfill capacity in Hong Kong, especially as the implementation of IWMF will take time and as its residues will still need to be disposed.

The Environmental Protection Department (EPD) of the HKSAR Government therefore commissioned a Study in Year 2000 on the Extension of Existing Landfills and Identification of Potential New Waste Disposal Sites.  Amongst the potential sites recommended in this territory-wide study is an extension of the existing NENT Landfill, with a target capacity of about 19 Mm³.  As shown in the attached Drawing No. 24315/01/001, the proposed Extension, of about 70 ha, is located immediately east of the existing NENT Landfill.  A large proportion of the Extension area is in fact the borrow/stockpiling area of the existing landfill.  Drawing No. 24315/01/005 depicts the general topography at/around the Extension site, showing that it is generally in the form of a bowl bounded by Robin’s Nest and Wo Keng Shan.

In February 2005, EPD appointed Ove Arup & Partners Hong Kong Ltd. to undertake a detailed feasibility study for the NENT Landfill Extension (hereafter referred to “the Project”), with the following key tasks: formulation and evaluation of layout options for the landfill extension; EIA study; and conceptual design of landfill facilities.

1.2                 Purpose and Scope of the EIA Study

The purpose of this EIA Study is to provide information on the nature and extent of environmental impacts arising from the construction, operation, restoration and aftercare stages of the NENT Landfill Extension, and to contribute to decisions on the overall acceptability of the Project, after the implementation of environmental mitigation measures.

The NENT Landfill Extension is a Designated Project under Schedule 2, G.1, of the EIAO : “A landfill for waste as defined in the Waste Disposal Ordinance (Cap. 354)”.  The EIA study, undertaken under the NENT Landfill Extension Feasibility Study, has therefore been carried out in strict accordance with the EIAO, including the requirements stipulated in EIA Study Brief No. ESB-114/2004 issued under the EIAO.

Drawing No. 24315/01/001 shows the location of the Project site.

1.3                 EIA Study Area

The EIA study areas for the impact assessments on air quality, noise, water quality, landfill gas, ecology, landscape & visual and cultural heritage as defined in accordance with the requirements in the EIA Study Brief and are presented in Table 1.1 below.

Table 1.1: Study areas for various assessments

Aspect

Study Area

Remarks

Air Quality

within 500m from the Project Boundary

According to the study brief requirements with additional ASRs selected between 500 to 2000m.

Noise

within 300m from the Project Boundary

According to the study brief requirements with additional NSRs selected between 300 to 1800m.

Water Quality and

Aquatic Ecology

within 500m from the Project Boundary

According to the study brief requirements, with additional WSRs such as nearby watercourses, the associated water systems and the coastal water of Deep Bay and Starling Inlet.

Landfill gas

within 250m from the Project Boundary

According to the study brief requirements

Landscape

within 500m from the Project Boundary

According to the study brief requirements

Visual

visual envelope

According to the study brief requirements

Cultural Heritage

within 50m from the Project Boundary

According to the study brief requirements

Terrestrial Ecology

within 500m from the Project Boundary

According to the study brief requirements.

1.4                 The Approach

The EIA study has been prepared in accordance with the guidelines provided in Annex 11 of the TM-EIAO for the report contents and Annexes 12 to 19 for the impact assessments of various environmental issues. The general approaches and methodologies adopted for this EIA study are described below.

1.4.1            Description of the Environment

The characteristics of the existing environment were reviewed for identification and prediction of environmental impacts. Baseline surveys were conducted to determine the existing environmental conditions on the Project site and in any environs likely to be affected by the Project. The baseline conditions of the key issues as identified in the EIA Study Brief including air quality, noise, water quality, landscape & visual, cultural heritage and ecology are described in the assessment.

1.4.2            Impact Prediction

The EIA Study was undertaken in accordance with the guidelines on assessment methodologies given in Annexes 12 to 19 of the TM-EIAO. Quantitative predicting tools were employed for assessing the environmental impacts in respect of construction dust, operational air quality, construction noise, operational noise and water quality. The predictions were conducted based on well-recognized methods such as Arup plant noise impact analysis for construction activities, CRTN for evaluating operational road traffic noise impact, ISCST3 for evaluating fugitive and odorous source impacts, and hydrogeological model for evaluating the change of groundwater flow regime.

The applied methodologies for the Project had previously been adopted in other EIA studies. They have been generally accepted for use in predicting environmental impacts and for comparison of assessment results with the TM-EIAO requirements. Limitations are however envisaged of these methodologies. The accuracy of the prediction result will be affected by the degree of uncertainty in input data such as construction plant, air emission inventories and predicted traffic flow. Quantitative uncertainties in the prediction have been considered when drawing conclusion from the assessment results. In carrying out the prediction, realistic worst-case assumptions have been made in order to provide a conservative assessment of environmental impacts.

1.4.3            Impact Evaluation

The predicted changes and effects as a result of the Project were evaluated with respect to the criteria described in Annexes 4 to 10 of the TM-EIAO, and were in quantitative terms as far as practicable.

1.4.4            Impact Mitigation

Mitigation measures have been identified and evaluated to avoid, minimize or remedy the impacts. Priority was given to avoidance of impacts as a primary means of mitigation. The effectiveness of mitigation measures was assessed and the residual environmental impacts identified. Evaluation of impact was made with respect to the criteria described in Annexes 4 to 10 of the TM-EIAO, in quantitative terms as far as practicable.

1.5                 Structure of the EIA Report

The structure of this EIA Report is outlined below for ease of reference:

Chapter

Title

Aims

1

Introduction

To provide project background, purpose and scope of the EIA Study and to define the EIA study area.

2

Description of the Project

To describe the project requirements, consideration of alternative and major activities in the Project.

3

Air Quality Impact

To assess the potential air quality impact of the Project and suggest mitigation measures.

4

Noise Impact

To assess the potential noise impact of the Project and suggest mitigation measures.

5

Water Quality Impact

To assess the potential water quality impact of the Project and suggest mitigation measures.

6

Waste Management Implications

To assess the potential waste management implications of the Project and suggest mitigation measures.

7

Landfill Gas Hazards

To assess the potential hazards arising from landfill gas migration and suggest precautionary measures.

8

Landscape and Visual Impact

To assess the potential landscape and visual impacts of the Project and suggest mitigation measures.

9

Impact on Cultural Heritage

To assess the potential impacts of the Project on cultural heritage and suggest mitigation measures.

10

Ecological Impact

To assess the potential ecological impacts of the Project and suggest mitigation measures.

11

Summary of Environmental Outcome

To summarise the key environmental outcomes arising from the EIA Study.

12

Environmental Monitoring and Audit Requirements

To define the scope of the EM&A requirements for the Project.

13

3-Dimensional EIA

To describe the 3-Dimensional EIA for this Study.

14

Conclusion

To conclude the assessment results of the EIA Study.


2                  Description of the Project

2.1                 General Description of the Project

The development of the NENT Landfill Extension (hereafter referred to “the Project”) will involve the following works:

·         Site formation and preparation.

·         Installation of liner system.

·         Installation of leachate collection, treatment and disposal facilities.

·         Installation of gas collection, utilization and management facilities.

·         Utilities provisions and drainage diversion.

·         Operation of landfill.

·         Restoration and aftercare in subsequent stages.

·         Measures to mitigate environmental impacts as well as environmental monitoring and auditing to be implemented.

2.2                 Key Project Requirements

The key project requirements for the NENT Landfill Extension are:

·         Development of a sanitary landfill that covers an area of about 70 ha with an estimated void space (landfill capacity) of 19Mm3;

·         Provision of a liner system for the landfill to prevent contamination of land and water resources;

·         Provision of a leachate collection, treatment and disposal facilities with sufficient capacity for handling the leachate arising from the landfill extension;

·         Provision of landfill gas collection, utilisation and management facilities;

·         Provision of utilities, drainage and road network necessary for the proper operation of the Project;

·         Provision of facilities (both civil works and electrical & mechanical equipment) for waste reception, inspection, charging, handling and compaction, and plant maintenance;

·         Provision of facilities for site administration;

·         Operation of the landfill in compliance with all relevant engineering, geotechnical and environmental standards;

·         Restoration of the landfill in compliance with all relevant engineering, geotechnical and environmental standards;

·         Provision of aftercare for the landfill for a period of about 30 years;

·         Carrying out environmental monitoring and audits throughout construction, operation, restoration and aftercare of the landfill; and

·         Implementation of environmental measures necessary for the protection of the surrounding environment.

2.3                 Need for the Project

2.3.1            Growing Wasteloads

Waste is a common problem of affluent societies. Especially when people can afford greater convenience and more purchases, they tend to generate a higher volume of waste per capita. Hong Kong is no exception to this. Like many other modern cities, Hong Kong has seen its wasteloads increase following the economic growth.  Municipal wasteloads have grown on average of about 3% per year since 1986.  With the population growth at 0.9% each year, the waste generation rate has risen from 1.96 kg per person per day in 1996, to 2.27 kg in 2004 (Figure 2.1).

Text Box:

 

 

MSW Generation: 3% average annual growth

Population: 0.9% average annual growth

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Figure 2.1  Waste line grew from 1996 to 2004 [extracted from EPD” Policy Framework for the Management of MSW (2005-2014)”]

 

Hong Kong’s waste arising have exceeded the expected amount. At the time when the three existing strategic landfills, SENT Landfill, NENT Landfill and WENT Landfill, were planned, it was forecasted that the daily amount of waste to be disposed of at landfills would rise from 12,500 tonnes in 1989, to 14,000 tonnes in 1997 and 16,700 tonnes by 2001. By 1997 the three strategic landfills were already taking in 16,000 tonnes of waste every day. Should this trend continue, the landfills will be full by 2015, instead of lasting until 2020 as they were originally designed for.

Although all measures outlined in the Policy Framework for the Management of Municipal Solid Waste (2005-2014) including source separation, MSW charging, waste recycling, IWMF, etc. would help extend the lives of the three landfills, the residues from the IWMF will still require sites for final disposal and landfill site is therefore necessary. 

 

The reality is that HK, like all other developed cities around the world, will need landfills as the final means of disposal.  Assuming the Government’s target of reducing the waste going to landfill site from 60% in 2004 to 25% by 2014 will be achieved, some 4000 tonnes per day of waste still needs to be disposed of at landfill sites. Therefore, outlets for landfill sites for final disposal of solid waste are still required.  Extensions of existing landfill sites have been identified as an indispensable element for the management of waste in Hong Kong.  Justifications of the need for providing additional void space for waste disposal by developing extension at the existing NENT Landfill are provided in the following sections.

2.3.2            Justification of Developing Extension at NENT Landfill

With a clear Government strategy to achieve sustainable management of the MSW in the next 10 years, it is anticipated that the amount of solid waste requiring landfill disposal will start to reduce gradually.  Having said that, there will still be millions of tonnes of un-recyclable or unrecoverable waste requiring disposal each year. With the three existing strategic landfills envisaged to be exhausted between Year 2011 to 2015 and the long lead time required for developing new landfills, there is a need to identify an intermediate solution.

EPD had therefore commissioned a study in February 2000 to explore the potential of extending the existing landfills and identify potential new landfill sites.

Given that it will take many years to confirm suitability of a new landfill location, extensions of the existing landfills were considered a practicable, necessary and urgent intermediate solution.  Key advantages of the extension schemes include:

·         Availability of existing supporting infrastructure and therefore less lead time for the development.

·         Availability of existing supporting infrastructure and therefore more cost effective for the development.

·         Availability of accurate information and hence lower level of risk in capital and operating costs estimation.

·         Availability of existing environmental monitoring data and hence more reliable for confirming environmental acceptability of the Project.

·         Availability of existing supporting infrastructure and therefore less requirements on land resumption for the development.

·         Availability of existing supporting infrastructure and therefore potentially less impact on the environment in comparison with a new green field site scheme.

·         Established site specific procedures for operation and environmental impact control.

These key advantages are recognised at the NENT Landfill for the proposed extension.

2.4                 Consideration of Alternatives

2.4.1            Alternative Extension Layout

In working out the most desirable layout for NENT Landfill Extension, a number of layout options were formulated, evaluated and then compared for selection, based on various evaluation criteria and an evaluation framework agreed with relevant stakeholders in advance.

The key issues and constraints identified during the course of study were taken into account in formulation of landfill extension layout options.  A total of 4 broad options (as well as related sub-options) were thoroughly evaluated and discussed at a Value Management Workshop on 2 December 2005, attended by relevant stakeholders. Key features of the various options are recapitulated below.

2.4.2            Broad Layout Option 1

2.4.2.1       Option 1

Option 1 adopts a similar rationale as the proposed conforming scheme in the EPD’s preliminary study under “Agreement No. CE45/99, Extension of Existing Landfills and Identification of Potential Waste Disposal Sites, Final Strategic Environmental Assessment Report”.  It achieves a landfill capacity of 17Mm³, and infringes a minor part of the Tong To Shan Archaeological Site (TTSAS). The area of built heritage affected will only be limited to the secondary features of boulder paths and stone terraces.  The main archaeological features will be untouched (see Drawing No. 24315/01/101 for layout).  The key parametric indicators of this option are outlined below in Table 2.1.

Table 2.1: Summary of Option 1

Waste receiving area

60 ha

Maximum fill level

+245 mPD

Site formation complexity

Cut volume 5.9 Mm³, Fill volume 2.3 Mm³

Landfill capacity

17.4 Mm³

2.4.2.2       Option 1a

Option 1a is similar to Option 1 except with the slight extension to the southern boundary and the increase in fill level to meet the target landfill capacity of 19Mm³.  The design is achieved by raising the eastern part of the landfill extension by approximate 10m relative to the original design to reach a maximum level of +255mPD (see Drawing No.  24315/01/102).  The maximum height of the adjacent Wo Keng Shan is about +297mPD.  It is envisaged that the visual impact due to a 10m raise would be insignificant.  The key parametric indicators of this option are outlined in Table 2.2.

Table 2.2: Summary of Option 1a

Waste receiving area

61 ha

Maximum fill level

+255 mPD

Site formation complexity

Cut volume 6.0 Mm³, Fill volume 2.2 Mm³

Landfill capacity

20.2 Mm³

2.4.2.3       Option 1b

Option 1b is derived based on Options 1 and 1a, with the same encroachment to TTSAS, to further increase the landfill capacity. The design is achieved by the slight extension to the south boundary and the increase in fill level to +300mPD (see Drawing No. 24315/01/103).  This roughly matches with the maximum elevation of +297mPD of the adjacent Wo Keng Shan.  The key parametric indicators of this option are outlined in Table 2.3.

Table 2.3: Summary of Option 1b

Waste receiving area

61 ha

Maximum fill level

+300 mPD

Site formation complexity

Cut volume 6.0 Mm³, Fill volume 2.2 Mm³

Landfill capacity

25.2 Mm³

 


2.4.3            Broad Layout Option 2

2.4.3.1       Option 2

Option 2 avoids the encroachment on TTSAS and keeps the peak level the same as Option 1 (i.e. +245mPD).  This will reduce the actual landfill capacity to 16.8Mm³ (see Drawing No. 24315/01/104).  The key parametric indicators of this option are outlined in Table 2.4.

Table 2.4: Summary of Option 2

Waste receiving area

55 ha

Maximum fill level

+245 mPD

Site formation complexity

Cut volume 4.7 Mm³, Fill volume 2.0 Mm³

Landfill capacity

16.8 Mm³

2.4.3.2       Option 2a

Similar to Option 2, Option 2a also avoids the encroachment on TTSAS and again falls short of meeting the target capacity of 19Mm³.  The design deviates from Option 2 by raising the eastern part of the landfill extension by approximate 10m to reach a maximum level of +255mPD (see Drawing No. 24315/01/105).  The key parametric indicators of this option are outlined in Table 2.5.

Table 2.5: Summary of Option 2a

Waste receiving area

55 ha

Maximum fill level

+255 mPD

Site formation complexity

Cut volume 4.7 Mm³, Fill volume 2.0 Mm³

Landfill capacity

18.4 Mm³

2.4.4            Broad Layout Option 3

Archaeological survey conducted on the site has identified a number of large graves in the heart of the landfill extension. Option 3 is developed with extensive reinforced earth wall at the northern boundary to avoid the need for clearance of these existing large graves (Drawing No. 24315/01/106). The landfill capacity will however be reduced to only 11.1Mm³.  The key parametric indicators of this option are outlined in Table 2.6.

Table 2.6: Summary of Option 3

Waste receiving area

50 ha

Maximum fill level

+245 mPD

Site formation complexity

Cut volume 3.7 Mm³, Fill volume 2.8 Mm³

Landfill capacity

11.1 Mm³

2.4.5            Broad Layout Option 4

Option 4 is developed with the northwestern and southeastern boundary extended to reach the ridgeline to maximize the landfill capacity.  The northern boundary is also set back to minimize the impact to woodland as well as TTSAS (see Drawing No. 24315/01/107).   The landfill capacity can achieve 21.4Mm³ while encroachment on the Lin Ma Hang catchment can be totally avoided.  The key parametric indicators of this option are outlined in Table 2.7.

Table 2.7: Summary of Option 4

Waste receiving area

63 ha

Maximum fill level

+255 mPD

Site formation complexity

Cut volume 6.2 Mm³, Fill volume 2.2 Mm³

Landfill capacity

21.4 Mm³

 

2.4.6             Selection of Preferred Scenario

2.4.6.1             Evaluation Criteria

These options were evaluated / assessed in accordance with the following factors and main criteria :

·         Waste management needs of 19Mm3 void space for the NENT Landfill Extension;

·         Engineering considerations including site formation complexity, constructability, drainage impact and maintenance;

·         Environmental issues such as noise, air quality, ecology, landscape and visual, waste management, cultural heritage, water quality, etc.

·         Social issues such as afteruse flexibility, cost of disposal, land resumption and graves clearance. 

2.4.6.2       Waste Management Needs

Under the previous study ”Agreement No. CE45/99, Extension of Existing Landfills and Identification of Potential Waste Disposal Sites, Final Strategic Environmental Assessment Report”, the “Strategic Plan” for the development of NENT Landfill Extension required a void space (landfill capacity) of 19Mm3 to be provided.  Options 1, 2, 2a and 3 cannot achieve this target volume.  Options 1a, 1b and 4 can achieve this target and are therefore preferred.

2.4.6.3       Engineering Considerations

The major engineering considerations relate to construction practicability, drainage impact to downstream rivers and requirements on operation and maintenance of the various facilities are discussed as follows:

 

Construction Practicability

The optimum engineering design of a landfill site is to maintain a balance in cut and fill material over the entire construction and operation periods. Importing or exporting construction material is not preferred.  In this regard, all the four broad options including sub-options can achieve this requirement.

According to the recent ground investigation (GI) data, there is no particular geological constraint in the proposed landfill extension site.  Site formation and retaining structures for all options are feasible to construct. All options will experience the same founding condition and reinforced fill slopes will be adopted for retaining structures taller than 10m

Although Options 1, 1a, 1b, 2, 2a and 4 require the construction of reinforced earth wall, they do not affect the site formation planning and are therefore preferred.  By contrast, Option 3 requires construction of a long reinforced earth wall at the north within a small site area, hence imposing great difficulties on the phasing and sequencing of the site formation works.  Option 3 is therefore less preferable.

Drainage Impact to Downstream

All options affect the existing landform and may have impact to the adjacent drainage systems at both Lin Ma Hang Stream and Ping Yuen River.   

According to the Drainage Impact Assessment (DIA) conducted for this Project, the diversion of catchment in some options will result in increased water level in Ping Yuen River and decreased water level in Lin Ma Hang Stream. In other words, the less the impact on stream and river, the more preferable the option.

Options 2, 2a, Option 3 and Option 4 that have no drainage impact to Lin Ma Hang Stream are therefore preferred.  Option 1, 1a and 1b have drainage impact to both Lin Ma Hang Stream and Ping Yuen River and are therefore less preferable.

Operation and Maintenance

The operation and maintenance requirements for various facilities such as treatment facilities, drainage system, E&M equipment, water quality, leachate and landfill gas monitoring equipment, etc. are similar for all the 4 options.

Option 1, 1a and 1b are preferred as they have only a small section of reinforced earth wall, which requires less maintenance works.  Options 2, 2a, 3 and 4 require more substantial maintenance works for the reinforced earth wall and the associated drainage system, and are therefore less preferable.

2.4.6.4       Environmental Issues

The major environmental considerations relate to water quality, ecology, archaeology and cultural heritage, landscape and visual etc. at various project phases are discussed as follows:

Water Quality Impact

Some of the landfill extension options may encroach to both Lin Ma Hang and Ping Yuen Catchments.  There may be certain degree of influence of water flow/yield on Lin Ma Hang Stream and Ping Yuen River.  In case of any accidental overflow from the treatment plant or accidental leakage through the liner, there might be short-term impact on the adjacent streams.

Options 2, 2a, 3 and 4 with no encroachment to Lin Ma Hang Catchment are therefore preferred whereas, Option 1, 1a and 1b with encroachment to both Lin Ma Hang Catchment and Ping Yuen Catchment are less preferable.

Ecological Impact

Some of the landfill extension options may cause minor ecological impacts to the Lin Ma Hang Stream due to reduction in water level and loss of woodland and shrubland.  Option 1, 1a and 1b will cause minor ecological impacts to Lin Ma Hang Stream due to a 15mm drop in water level and are therefore less preferable.  Options 2, 2a, 3 and 4 will have neither encroachment nor ecological impacts on Lin Ma Hang Stream, and are preferred options.    

Woodland of over 1 ha is considered as an important habitat.  Option 1, 1a and 1b will cause a significant loss of woodland of more than 5ha and are thus less preferable.  For other options, the impact on loss of woodland, ranging from 2 to 4 ha, are considered to be moderate in term of ecological value. Compensatory woodland planting would be provided.  These options are therefore preferred with mitigation measures being in place.

With consideration of a cumulative combination of ecological impacts (drop in water level and loss in woodland), Options 1, 1a, 1b and 4 are less preferable.  Options 2, 2a and 3 are preferred.

Archaeological and heritage Impact

Some of the landfill extension options may encroach into TTSAS affecting secondary features such as boulder paths and boulder terraces.  A total of 21 graves including 10 old graves will be affected and will need to be removed. In terms of impacts to graves, all options have the same grade as these can be mitigated by detailed preservation by record as agreed with AMO, LCSD.

Option 1, 1a and 1b will encroach into TTSAS by about 5 ha, affecting of 200m boulder paths and 2 numbers of boulder terraces. Nonetheless, these affected areas comprise mainly secondary features and can be mitigated by detailed preservation by record (as agreed with AMO).  Therefore, these options are less preferable.

Options 2, 2a and 3 will have no impact to the TTSAS and are therefore preferred.  Similarly, Option 4 affects only 30m of boulder path (secondary feature only) which can be mitigated by detailed preservation by record.  The impact on Option 4 is therefore also minimal and this option is preferred. 

Landscape and Visual Impact

Option 1a will have a total area of about 61 ha which encroaches into about 5.16 ha of woodland near the ridge of Wong Mau Hang Shan, Shui Ngau Tso and northeast of Wo Keng Shan.  The final height of the landfill is about +255mPD.  

Option 2a will have a total area of about 54 ha which encroaches into about 3.08 ha woodland near the ridge of Shui Ngau Tso and northeast of Wo Keng Shan.  The final height of the landfill is about +255mPD.

Option 3 will have a total area of about 50 ha which encroaches into about 3.05 ha of woodland near Shui Ngau Tso and northeast of Wo Keng Shan.  The final height of the landfill is about +245mPD which is similar to the adjacent Wong Mau Hang Shan. 

Option 4 will have a total area of about 63 ha and encroach into about 3.7ha of woodland near the ridge of Shui Ngau Tso and northeast of Wo Keng Shan.

In fact, the visual impact to the adjacent areas for all options is similar with slight impact (also see Chapter 8).

Other environmental considerations

Other environmental considerations, including air, noise, waste, landfill gas, have been reviewed.  The potential impacts for all options are similar in order and can all be mitigated by suitable mitigation measures. 

2.4.6.5             Impact on Community

The major community considerations relate to flexibility for aftercare, unit cost per disposal, needs for land resumption and needs for graves clearance at various project phases are discussed as follows:

Flexibility for Afteruse

The proposed extension is expected to last for about 10 to 12 years.  Options that can offer higher flexibility to the potential afteruse of the landfill are preferred.

Options 1, 1a, 1b and 4 will cover areas of 60 ha to 63ha in size.  The gradients of the final landfill profile for these options are gentle and suitable for all type of afteruse activities.  These options would not impose any restriction/limitation to the afteruse planning. They are the preferred options.

Option 2 and 2a will cover an area of 55 ha only. The gradient of the final landfill profile is gentle with slight variation.  This option would not impose any restriction/limitation to the afteruse planning.  However, this option has less planning flexibility in view of the smaller landfill area and is therefore less preferable.

Similarly, Option 3 has the smallest landfill area of only 50 ha with steep gradient at certain locations.  The steep slope may inevitably impose additional constraints to the potential afteruse and the planning flexibility of other facilities such as bowling greens and multi-purposes grass pitches. This option is therefore also less preferable.

Unit Cost per Disposal

The unit cost per disposal is the capital cost divided by the actual landfill capacity, which is the cost required to produce a 1m3 landfill capacity.  The higher the unit cost per disposal, the higher the chance of illegal dumping.

The anticipated unit cost per disposal (m³) for Options 1, 1a, 1b, 2, 2a and 4 are of similar order, which is about half of that for Option 3. Based on the above cost estimation, Options 1, 1a, 1b, 2, 2a and 4 are “preferred”; while Option 3 is “less preferable”.

Needs for Land Resumption

All Options will affect the same number of private lots.  Nonetheless, Option 1, 1a and 1b affect a Government Hilltop Survey Tri-Station (GLA) and are therefore less preferable.  Hence, Options 2, 2a, 3 and 4 are preferred.

Needs for Graves Clearance

According to recent survey, there are a large number of graves including some old graves lying within the extension site.  All options affect almost the same number of graves including old graves except for Option 3 which affect a much smaller number of graves (9 to 10 graves less).  Option 3 is therefore preferred.  All other options are less preferable since a longer lead time would be required on liaison in the graves clearance process.

2.4.6.6       Overall

Amongst the three options in Broad Layout Option 1, Option 1a is the most preferred.  Similarly, Option 2a is the most preferred option under Broad Layout Option 2.  Accordingly, Option 1a and Option 2a were therefore directly compared with Option 3 and Option 4, so as to arrive at the most favourable layout for NENT Landfill Extension.  A summary of the final round of layout options selection is tabulated below.

Table 2.8: Summary of reasons for option evaluation

Criteria 

Option 1a

Option 2a

Option 3

Option 4

(A) Waste Management Needs

20.2 Mm³ - achieving the target requirement of 19Mm3 .

(Preferred)

18.4 Mm³ - marginally falls short of meeting target requirement of 19Mm3 .

(Less Preferred)

 

11.1 Mm³ - falls short of meeting target requirement of 19Mm3 .

(Less Preferred)

21.4 Mm³ - achieving the target requirement of 19Mm3 .

(Preferred)

(B) Engineering

Construction Practicability

No imported fill material is required for the site formation works;

Require short (100m) reinforced earth wall with max. height of 15m.

(Preferred)

No imported fill material is required for the site formation works;

Require relatively long (400m) reinforced earth wall with max. height of 25m.

(Preferred)

No imported fill material is required for the site formation works;

Require relatively long reinforced earth wall (with max. height of 25m) in a relatively small site and impose difficulties in site formation phasing.

(Less Preferred)

 

No imported fill material is required for the site formation works;

Require relatively long reinforced earth wall (with max. height of 25m) but will not impose difficulties in site formation phasing.

(Preferred)

Drainage Impact to Downstream

Impact to both Lin Ma Hang Stream and Ping Yuen River.

(Less Preferred)

Impact to Ping Yuen River (no impact on Lin Ma Hang).

(Preferred)

Impact to Ping Yuen River (no impact on Lin Ma Hang).

(Preferred)

Impact to Ping Yuen River (no impact on Lin Ma Hang).

(Preferred)

 

Operation and Maintenance

Require maintenance of a short reinforced earth wall and associated drainage system (100m).

(Preferred)

Require maintenance of a relatively long reinforced earth wall and associated drainage system (400m).

(Less Preferred)

Require maintenance of a relatively long reinforced earth wall and associated drainage system (510m).

(Less Preferred)

Require maintenance of  a relatively long reinforced earth wall and associated drainage system (590m).

(Less Preferred)

(C) Environmental

Water Quality Impact

Impact to both Lin Ma Hang Stream and Ping Yuen River

(Less Preferred)

Impact to Ping Yuen River (no impact on Lin Ma Hang)

(Preferred)

Impact to Ping Yuen River (no impact on Lin Ma Hang)

(Preferred)

 

Impact to Ping Yuen River (no impact on Lin Ma Hang)

(Preferred)

Ecology Impacts

Minor impact to the Lin Ma Hang Stream & its catchment;

Relatively large scale  of woodland loss (5.16ha);

No impact to Lin Ma Hang Lead Mines;

Minor impact to the  Robin’s Nest countryside;

 (Less Preferred)

No impact to the Lin Ma Hang Stream & its catchment;

Small scale of woodland loss (3.08ha)

No impact to Lin Ma Hang Lead Mines;

Minor impact to the Robin’s Nest countryside;

 (Preferred)

 

No impact to the Lin Ma Hang Stream & its catchment;

Small scale of woodland loss (3.05ha)

No impact to Lin Ma Hang Lead Mines;

Minor impact to the Robin’s Nest countryside;

(Preferred)

No impact to the Lin Ma Hang Stream & its catchment;

Medium scale of woodland loss (4.01ha)

No impact to Lin Ma Hang Lead Mines;

Minor impact to the Robin’s Nest countryside;

 (Less Preferred)

Archaeological and Heritage Impact

Encroach into small (non-core) portion  of TTSAS (5ha).

Affect 21 graves including 10 old graves (no impact on cultural heritage value).

(Less Preferred)

No impact to TTSAS.

Affect 20 graves including 9 old graves (no impact on cultural heritage value).

(Preferred)

No impact to TTSAS.

Affect only 9 graves and avoid all old graves (no impact on cultural heritage value).

(Preferred)

Encroach into very small (non-core) portion  of TTSAS (2ha).

Affect 20 graves including 9 old graves (no impact on cultural heritage value).

(Preferred)

Landscape & Visual

Total landfill area is 61ha; final fill level at +255mPD.

(Insignificant landscape & visual impact)

Total landfill area is 55ha; final fill level at +255mPD.

(Insignificant landscape & visual impact)

Total landfill area is 50ha; final fill level at +245mPD.

(Insignificant landscape & visual impact)

Total landfill area is 63ha; final fill level at +255mPD.

(Insignificant landscape & visual impact)

Other Environmental Considerations, such as air, noise, landfill gas, waste

Neutral to various options – minor impact which can be mitigated by suitable mitigation measures.

(similar impact to other options)

Neutral to various options – minor impact which can be mitigated by suitable mitigation measures.

(similar impact to other options)

Neutral to various options – minor impact which can be mitigated by suitable mitigation measures.

(similar impact to other options)

Neutral to various options – minor impact which can be mitigated by suitable mitigation measures.

(similar impact to other options)

(D) Impact on Community

Flexibility for afteruse

Largest landfill area (61ha) with gentle slopes/ gradient – good for all kinds of afteruse.

(Preferred)

Smaller landfill area (55ha) with gentle slopes/gradient, but vary in landfill profile and hence less planning flexibility.

(Less Preferred)

Smallest landfill area (50ha) with steep slope and extensive earth wall.  Hence, impose constraints to the potential afteruses.

(Less Preferred)

Highest landfill area (63ha) with gentle slopes/ gradient – good for all kinds of afteruse.

(Preferred)

Unit Cost per Disposal

Comparable with other options except Option 3.

(Preferred)

Comparable with other options except Option 3.

(Preferred)

Higher disposal cost leading to higher chance of illegal dumping.

(Less Preferred)

Comparable with other options except Option 3.

(Preferred)

Need for Land Resumption

Affect private lands and survey station

(Less Preferred)

Affect only private lands (no impact on survey station)

(Preferred)

Affect only private lands (no impact on survey station)

(Preferred)

Affect only private lands (no impact on survey station)

(Preferred)

Need for Graves Clearance

Affect 21 graves including 10 old graves (no impact on cultural heritage value)

(Less Preferred)

Affect 20 graves including 9 old graves (no impact on cultural heritage value)

(Less Preferred)

Affect 9 graves and aovid all old graves (no impact on cultural heritage value)

(Preferred)

Affect 20 graves including 9 old graves (no impact on cultural heritage value)

(Less Preferred)

As Option 4 was evaluated as a preferred option for the largest number of aspects, it was selected as the overall most preferred option.  See Drawing No. 24315/01/107 for the layout of Option 4.

2.4.7            Alternative Construction Methods and Sequences of Works 

Different construction methodology and sequences of works were studied, giving careful consideration on environmental impacts including noise, ecology, archaeology, etc.

It is recommended to adopt a balanced cut-and-fill site formation for constructing the landfill bowl within the existing valley.

The NENT Landfill Extension will be developed in three phases to allow progressive use of the overall landfill area.  Each phase will be constructed, operated and restored at a rate dependent on the delivery of waste.  Simultaneous construction, operation and capping activities will therefore occur in different parts of the site.

During the construction stage, mobilisation & preparation / establishment will be carried out by the DBO Contractor.  A balance between cut-and-fill quantities will be adopted to optimise the reuse of excavated materials, i.e. to minimise import or export of materials.  The process involves temporarily stockpiling of excavated materials on site for use as daily cover during the operation phase and final capping during the restoration phase.  This will reduce construction materials / waste to be delivered to public fill bank.  Where necessary (to be triggered by EM&A programme), daily cover and temporary cover will be provided to reduce potential impact on air and water qualities during the operation phase of the Project.

Alternative construction methods such as blasting have also been evaluated but found to be not desirable from an engineering perspective.  The balancing of cut-and-fill limits the usable area of the landfill site and therefore the amount of stockpiled materials.  Blasting will generate a significantly larger volume of excavated and stockpiled materials, and the usable area of the landfill site will be much reduced.  There is also a safety concern if blasting is conducted in close proximity to the tipping area, as refuse collection vehicles and operators might be at risk if the buffer distance provided is not sufficient. 

2.5                 Site Location and Site History

2.5.1            Site Location

The landfill extension site of the selected layout is approximately 70 ha in size and located in a valley to the south of the existing NENT Landfill. The valley is encircled by three ridgelines and exits to the southwest through a small gorge, at approximately +50mPD.

On its south-eastern side, the site is enclosed by a major ridgeline, which runs from Wo Keng Shan (+297mPD) to Robins Nest (+492mPD). A smaller ridge intersects this main ridgeline and forms the northern flank of the Project area. This ridge overlooks To Tong Shan Settlement District and Lin Ma Hang Village. It reaches an elevation of +205mPD at its western end, just beyond the boundary between the existing NENT Landfill and the extension site. Two saddles, with minimum elevations of approximately +120mPD, are located about half way along this smaller ridge.

The ridge separating the site from the existing NENT Landfill forms the north-western boundary of the Project area. This ridge runs from an elevation of +205mPD at its northern end to a level of +65mPD at the point where it intersects the existing haul road in the south-western corner of the site (Drawing No. 24315/01/001).

The slopes overlooking the main valley of the site are sparsely vegetated with a cover of grass and shrubland. Occasional groups of pine trees and localised dense vegetation are also found along stream courses.

2.5.2            Site History

The proposed extension is mainly covered by the existing NENT Landfill Stockpile and Borrow Area that was formed to the east of the existing landfill as part of the original landfill development.  The aerial photographs of the site reveals that several large cut slopes, many of which have been subsequently covered with stockpiled material, and a haul road (Shek Tsai Ha Road) have been formed within. The stockpile area is mostly located within the eastern portion of the site and is bound by concrete drainage channels. Other than the haul road and scattered gravesites, the remaining site area comprises natural terrain that has seen little interference from human activity.

2.6                 Nature, Scope and Benefits of the Project

2.6.1            Nature of the Project

The nature of the Project is to develop a landfill extension for waste as defined in the Waste Disposal Ordinance (Cap. 354).

2.6.2            Scope of the Project

The scope of the Project is to provide a landfill extension of about 70 hectares with a target void space of at least 19 million cubic metres on the eastern side of the existing NENT Landfill. On top of site formation and preparation works; there will be provision of installation of liner system; leachate collection, treatment and disposal; gas collection and management; utilities provisions; drainage diversion; restoration and aftercare. Environmental mitigation measures, monitoring and auditing are provided.

2.6.3            Benefits of the Project

The development of NENT Landfill Extension ensures the continued provision of final disposal site for solid waste after the three existing landfills are full by 2015.

It also avoids illegal dumping of construction waste and municipal waste that may cause serious environmental problems.

With waste-to-energy facility (such as Landfill Gas Export Scheme), landfill gas can be converted to reusable energy that brings benefits to the community.

The Project site is equipped with waste handling facilities at NENT Landfill, waste recycling factories in the nearby area, sewage treatment facility at Shek Wu Hui Sewage Treatment Works, and a landfill gas waste-to-energy facility nearby. The availability of these existing supporting facilities can shorten the lead time and land resumption requirement for a new landfill development in a green field site. 

Substantial saving in cost can also be achieved by pooling together the existing NENT Landfill infrastructure and facilities by carrying out suitable conversion works under suitable contractual arrangement.

There are some small-scale waste recycling factories around the existing NENT Landfill, skilful workers and special equipments have been allocated in the region. Therefore, there will be social and economic benefit of the Project, if these workers and equipments can be tied in with the NENT Landfill Extension (e.g. sustainable for local employment).

2.7                 Size, Scale, Shape and Design of the Project

The landfill extension site is a bowl-shape area with a large void space in the middle for waste filling. The northwestern and southeastern boundaries of the landfill extension site follow the ridgelines to maximize the landfill capacity.  Some set back of the northern boundary is included to minimize the impact to woodland and Lin Ma Hang Catchment. The total site area is about 70 ha and the final height of the landfill would be +255mPD (see Drawing No. 24315/01/107).

The key design features are listed as follows and summarised in Table 2.10:

·         Bottom liner system - to separate rubbish and leachate from groundwater;

·         Landfill cells – to store waste within the unit;

·         Storm water drainage system - to collect rain water run off on the landfill;

·         Leachate collection system - to collect liquid leaching from the waste mass and convey it to a leachate treatment plant prior to discharging to Shek Wu Hui Sewage Treatment Works;

·         Gas collection system - to collect gases formed during the decompositon of waste. These gases will be treated and utilised for production of electricity on site.

·         Covering and capping - to seal off the top of the landfill with a gas venting layer, an impermeable mineral layer, a drainage layer of at least 0.5 metre and at least one metre of top soil.

Table 2.10: Summary of key design elements

Total size

63 ha

Final height

+255 mPD

Shape

Bowl shape at the existing NENT Landfill Stockpile and Borrow Area

Site formation complexity

Cut volume 6.2 Mm³, Fill volume 2.2 Mm³

Actual waste capacity

21.4 Mm³

Key elements of design

•     Site formation and preparation

•     Installation of liner system

•     Installation of leachate collection, treatment and disposal facilities

•     Installation of gas collection, utilization and management facilities

•     Utilities provisions and drainage diversion        

 

Various activities during construction, operation, restoration and aftercare of landfill are discussed in the following sub-sections.

2.7.1            Construction Phase and Activities 

Simple excavation and slope formation works will be carried out during the construction stage.  The permanent works comprise cut and fill earthworks, slope formation and earth wall construction.  The temporary works will involve the formation of temporary ditches along the sides of the excavations and associated drainage works, and material storage areas.

During site formation, sediment will be contained in permanent detention ponds/silt traps that will be constructed according to landfill phasing. Final design and location of sediment traps are yet to be decided, but are likely to be down gradient of each landfill phase or in the downstream valleys near the existing waste reception area.  Where possible they will be maintained during the operation of each phase to ensure the effective control of operational soil erosion problem.

2.7.2            Operation Phase and Activities 

During operation, waste will be disposed of at individual landfill cells.  Deposited waste will be compacted to thin layers.  The works will be maintained at a gradient of not greater than 1 in 3 to ensure the effectiveness of the compaction equipment.  Daily cover (about 150mm if soil cover used) will be applied to control environmental nuisances such as windblown litter, odour, vermin, flies and birds.

There are other more effective alternative biodegradable materials for use as daily cover. They include:

·         heavy duty reusable and biodegradable sheets;

·         non reusable plastic films;

·         geotextiles; and

·         foams and sprays.

Advantages of using alternative daily cover over traditional methods include preservation of landfill capacity and soil material; biodegradable and less permeable to water and gas (reduce water infiltration, odour and dust emission).

2.7.3            Restoration Phase and Activities

Restoration is a process to restore a landfill site to a condition suitable for afteruse.

After completion of waste filling, final capping will be applied to minimise infiltration of rainwater into the waste body thus reducing the amount of leachate generated.  The capping system normally includes a number of components including topsoil, subsoil, drainage layer and barrier layer. 

2.7.4            Aftercare Phase and Activities

Aftercare is the work done after the replacement of the soil and includes cultivations, fertilisation, planting, construction of pathways, access points, vegetation maintenance and monitoring.

Landscaped berms will be created and tree planting will be provided during the aftercare period for aesthetic purpose.

2.8                 Project Timetable

The Landfill Extension will start receiving waste only when the existing NENT Landfill has ceased operation.  The timing of this has yet to be determined as it depends on the rate of waste deliveries in the forthcoming period.  Based on current prediction, the Existing Landfill will probably run out by early-to-mid next decade, by which time the Landfill Extension shall start operation. 

Taking account of the time needed for mobilization and preparatory works prior to commencement of receipt of waste, it may be necessary to award the Landfill Extension contract towards the end of this decade, in order to ensure that new landfill space will be available before the capacity of the existing landfill runs out. 

It is anticipated that the DBO (Design-Build-Operate) contract form, which has hitherto worked well for the existing waste management contracts (notably the three strategic landfill contracts and the refuse transfer station contracts), will be adopted for NENT Landfill Extension.  Detailed design and formulation of technical details for the construction, operation, restoration and aftercare of the NENT Landfill Extension will be carried out by the DBO Contractor, in accordance with requirements stipulated in the Specification and other documents of the DBO Contract.

Even though there will not be any overlapping in operation between the Landfill Extension and the Existing Landfill, the two contracts will still overlap.  Clearly the initial development (notably the initial site formation) for the NENT Landfill Extension will overlap and hence interface with the final operational period of the Existing NENT Landfill as well as part of its restoration & aftercare, whereas the early operation period of the NENT Landfill Extension plus continuation of its development works will overlap/interface with the remaining restoration of the Existing Landfill and the main part of its aftercare.

A tentative outline programme for implementation of the NENT Landfill Extension is shown in Appendix 2.2.  As pointed out above, the exact timing of the various activities may vary, depending on actual volume of waste to be delivered in the forthcoming years.

2.9                 Related Projects

The existing NENT Landfill would be the only related project for the purpose of this study.

2.10             “No Project” Scenario

The current site mainly located within the borrow area of the existing NENT Landfill. Based on the site inspection, some of the nearby areas are used for waste recycling activities. Under the “no project” scenario, the site will be operated as a restored landfill for 30 aftercare period. During this period, raw leachate will still be generated and collected to the open lagoons. Landfill gas will also generate during this period. Part of the LFG will be extracted for leachate treatment in the Ammonia Stripping Plant.  Restoration planting will be carried out in phase after the final capping.  Maintenance vehicle will be visiting the site for periodic inspection and maintenance.  Subject to the detailed design for restoration, the area might be used for recreational use in the medium-term future after the soil is settled and stabilised.

 

 


3                  Air Quality Impact

3.1                 Introduction

This chapter presents the impact assessment on potential air quality aspects for the construction, operation and restoration and aftercare stages of the Project. Control measures for construction related activities have been recommended, in accordance with the requirements specified in the Air Pollution Control (Construction Dust) Regulation. Proper emission control limits for stack emissions from ammonia stripping plant, flare and landfill gas (LFG) power generator will be in place for the extension site, similar to the current NENT Landfill operation. Together with the implementation of good site practice for the tipping operation, the air quality impact will be controlled to within Hong Kong Air Quality Objectives (HKAQOs).

The assessment has been conducted in accordance with the requirements of Annex 4 and Annex 12 of the TM-EIAO, as well as the requirements set out under Clause 3.4.1 of the EIA Study Brief.

3.2                 Environmental Legislation, Standards and Guideline

The relevant legislation and associated guidance notes applicable to the study for the assessment of air quality implications include:

·         Environmental Impact Assessment Ordinance (Cap. 499) and Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO);

·         Air Pollution Control Ordinance (APCO) (Cap. 311) Air Pollution Control (Construction Dust) Regulation (Cap. 311R);

·         Hong Kong Planning Standards and Guidelines (HKPSG);

·         World Health Organisation (WHO); and

·         United State Environmental Protection Agency (USEPA) references.

3.2.1            Air Quality Objectives

The principal legislation for controlling air pollutants is the Air Pollution Control Ordinance (Cap. 311) and its subsidiary regulations, which define statutory Air Quality Objectives (AQOs) for 7 common air pollutants. The AQOs for these air pollutants are tabulated in Table 3.1 below.

Table 3.1 : Hong Kong Air Quality Objectives

           

Pollutant

Concentration in micrograms per cubic metre [1]

(Parts per million, ppm in brackets)

1 Hour [2]

8 Hour (3]

24 Hours [3]

3 Months [4]

1 Year [4]

Sulphur Dioxide

800

(0.3)

 

350

(0.13)

 

80

(0.03)

Total Suspended Particulates (TSP)

500 [7]

 

260

 

80

Respirable Suspended Particulates (RSP) [5]

 

 

180

 

55

Carbon Monoxide

30,000

(26.2)

10,000

(8.7)

 

 

 

Nitrogen Dioxide

300

(0.16)

 

150

(0.08)

 

80

(0.04)

Photochemical Oxidants (as ozone) [6]

240

 

 

 

 

Lead

 

 

 

1.5

 

 


Notes:

[1]    Measured at 298°K and 101.325 kPa.

[2]    Not to be exceeded more than three times per year.

[3]    Not to be exceeded more than once per year.

[4]    Arithmetic mean.

[5]    Respirable suspended particulates means suspended particulates in air with a nominal aerodynamic diameter of 10 micrometres or smaller.

[6]    Photochemical oxidants are determined by measurement of ozone only.

[7]    Not an AQO. TM-EIAO suggested short-term averaging level for 1 hour is 500ug/m³. There is no exceedance allowance for 1-hour TSP guideline level.

 

3.2.2            Air Pollution Control (Construction Dust) Regulation

The Air Pollution Control (Construction Dust) Regulation identifies those processes that require special dust control.  The Contractor of this Landfill Extension is required to inform the EPD prior to carrying out such processes and to adopt dust reduction measures while carrying out "Notifiable Works" or “Regulatory Works”, as defined under the regulation.  Works relevant to this Project are the site formation activities, for which TSP concentration shall not exceed 500 ug/m3.

3.2.3            Odour Criteria

In accordance with Annex 4 of TM-EIAO, the limit of 5 odour units (OU) based on an averaging time of 5 seconds for odour prediction assessment shall not be exceeded at any receivers.

3.2.4            Other Pollutants

Other pollutants that are not covered by the Hong Kong AQOs but may impose a health risk concern have also been considered.  The criteria / guideline values related to carcinogenic and non-carcinogenic health risk evaluation are established from the following order of reference:

·         World Health Organization (WHO);

·         United States Environmental Protection Agency (USEPA); and

·         California Environmental Protection Agency (CEPA).

 

The guidelines for the assessment of carcinogenic health risk from exposure to air toxics are based on the WHO and USEPA Integrated Risk Information System (IRIS)’s acceptable lifetime risk.    

Long-term monitoring for 38 species of VOC relating to the landfilling operation is being conducted by NENT Landfill. Nonetheless, emission for 18 species of these VOC is found to be insignificant and below the detection limit. Out of the remaining 20 species of VOC, only 8 species have documentary concern related to carcinogenic and non-carcinogenic health risk. The unit risk factor and reference dosage for the 8 related VOCs are tabulated in Table 3.2.


Table 3.2: Unit factors and reference dosage from available WHO/IRIS/CEPA database on related VOCs

Substance [1]

Molecular Weight g/mol [4]

Unit Factor per μg/m3  [3]

Reference dosage [2,4,5,6, 7]

Benzene

(CASRN 71-43-2)

78.11

6x10-6

Chronic Inhalation Exposure (RfC):  30 μg/m3 (9.4ppbv) (IRIS)

Acute: 1.3 x 103   μg/m3 (406.9ppbv) (CEPA)

1,4-Dichlorobenzene (CASRN 106-46-7)

147.01

-

Chronic Inhalation Exposure (RfC):  8x102 μg/m3 (133.1ppbv) (IRIS)

Ethyl Benzene (CASRN 100-41-4)

106.16

 

Chronic: 22,000 μg/m3 for 1 year averaged

All based on WHO (Geneva)

Chronic Inhalation Exposure (RfC):  1000 μg/m3 (230.3ppbv) (IRIS)

Toluene

(CASRN 108-88-3)

92.14

-

Acute: 1 x 103   μg/m3 for 30min averaged (odour threshold) (265.4ppbv), based on S5.14 of WHO

Chronic: 260 μg/m3 (69ppbv) of 1 week, based on S5.14 of WHO

Vinyl chloride (CASRN 75-01-4)

62.5

1.0x10-6

Chronic Inhalation Exposure (RfC):  100 μg/m3 (IRIS)

Acute: 1.8x105 μg/m3 (70,416ppbv) (CEPA)

Xylenes

(CASRN 1330-20-7)

106.16

-

Acute: 4800 μg/m3 for 24 hour averaged

Chronic: 870 μg/m3 for 1 year averaged

All based on WHO (Geneva)

Chronic Inhalation Exposure (RfC):  100 μg/m3 (23.0ppbv) (IRIS)

Tetrachloroethylene (CASRN 127-18-4)

165.8

-

Acute: 8000 μg/m3 for 30 min averaged; 250 μg/m3 for 24 hour averaged based on WHO (Geneva)

Methylene Chloride / Dichloromethane (CASRN 75-09-2)

84.93

-

Acute: 3mg/m3 for 24 hour guideline;

Chronic: 0.45mg/m3 for a weekly guideline

All based on S5.7 of WHO

Note:    [1]. CASRN – Chemical Abstracts Service Registry Number

            [2]. RfC – Reference Concentration

            [3]. If WHO standard is available, it will be applied first

            [4]. C ppbv  = C ug/m3  x 24.45 / Molecular Weight

            [5]. WHO represents Air Qualiy Guideline for Europe, WHO

            [6]. WHO (Geneva)  represents Guidelines for Air Quality, WHO, Geneva, 2000

            [7]. CEPA represents California Environmental Protection Agency

 

3.2.4.1             Carcinogenic Health Risk Assessment

Emissions pertinent to this Project are benzene and vinyl chloride which are key control parameters from the Ammonia Stripping Plant (ASP), flares and LFG generators.  Tables 3.3 and 3.4 show the unit risk factors for non-criteria key pollutants of benzene and vinyl chloride and guidelines for assessment of individual risk.

Table 3.3: Unit risk factors guideline for non-criteria pollutants

Pollutant

Unit Risk ((μgm-3 ) -1 )

Benzene

6x10-6

Vinyl Chloride

1.0x10-6

 


Table 3.4: Risk guidelines for carcinogenic health risk assessment

Acceptability of Cancer Risk

Estimated Individual Cancer Risk Level

Individual Lifetime Risk

(A)

Individual Risk Per Year

(B) = (A)/70

Significant

>10-4

>1.4x10-6

Risk should be reduced to As Low As Reasonably Practicable (ALARP)

>10-6  & <= 10-4

>1.4x10-8  & <=  1.4x10-6

Insignificant

£10-6

£1.4x10-8

3.2.4.2             Non-Carcinogenic Health Risk Assessment

Non-carcinogenic health risk guidelines apply to the assessment of chronic and acute health risks.

Chronic Health Risks

Using the chronic health risk assessment approach, the chronic reference concentrations for benzene and vinyl chloride are summarized in Table 3.5 and their acceptability criteria in Table 3.6.

Table 3.5: Chronic reference concentrations for benzene and vinyl chloride

Pollutant

Chronic Reference Concentration (ACA )

(Annual Average)

Benzene

30 μg/m3 (9.4ppbv) (a)

Vinyl Chloride

100 μg/m3 (39.12ppbv) (a)

Note: (a) Yr 2000 updated standard from Integrated Risk Information System (IRIS), USEPA

 

Table 3.6: Acceptability criteria for chronic non-cancer health risks

Acceptability

Assessment Results (a)

Chronic non-cancer risks are considered “Insignificant”

ACA £RCC

Chronic non-cancer health risks are considered ‘Significant”.  Detailed assessment of the control requirements and further mitigation measures are needed

ACA >RCC

Note: (a) ACA and RCC  represent annual average concentration and chronic reference concentration respectively.

 

Acute Health Risks

Using the acute health risk assessment approach, the acute reference concentrations for benzene and vinyl chloride are summarized in Table 3.7 and their acceptability criteria in Table 3.8.

Table 3.7: Acute reference concentrations

Pollutant

Acute Reference Concentration (ACHM)

(1-hour average, μg m-3  )

Benzene

1.3 x 103 (a)

Vinyl Chloride

1.8x105 (a)

Note :  (a)  California Air Resources Board – Air Toxic Hot Spots Program Risk Assessment Guidelines, Part I – Technical Support Document for the Determination of Acute Reference Exposure Levels for Airborne Toxicants, May 2000.

 

Table 3.8: Acceptability criteria for acute non-cancer health risks

Acceptability

Assessment Results (a)

Acute non-cancer risks are considered “Insignificant”.

ACHM £RCA

Acute non-caner health risks are considered “Significant”.  Detailed assessment of the control requirements, and further mitigation measures are needed.

ACHM >RCA

Note:   (a)  ACHM  and RCA  represent maximum hourly average concentration and acute reference concentration respectively.

 

3.3                 Description of the Existing NENT Landfill and the Extension

3.3.1            Existing vehicles trips generated from NENT Landfill

Based on the latest information, daily vehicular trip generation is in the order of 500 veh/day (or max peak hourly flow of 90 veh/hr) travelling to and from the existing NENT Landfill.  Owing to the low traffic flow, vehicular emission impact is not a key issue for the existing NENT Landfill operation.

In addition, most of the refuse collection vehicles (RCV) for MSW and sludge are of enclosed-type and odorous gases are well contained during transit under normal circumstances.  For sludge vehicles / special vehicles that required admission ticket,  special condition can be imposed on the cleanliness of vehicle and disposal period to avoid adverse cumulative impact. With reference to the existing NENT Landfill experience, potential odour impact from RCVs can be adequately controlled and unlikely to be an issue. 

3.3.2            Existing plants operation

Current NENT Landfill operation emits gaseous emissions from Ammonia Stripping Plant (ASP), flare system and landfill engine. The flare system operates only when the ASP is not in use or when excessive LFG is pending for treatment. With the development of Landfill Gas Export Scheme (LFGES), the need for flaring over any extensive period would be unlikely in practice. Monthly monitoring at the inlet and outlet of the flaring system is conducted to verify the destruction efficiency.  Past monitoring results suggest that emission from flaring system has complied with the control limits.

3.3.3            Existing monitoring and audit findings

EM&A records for TSP and VOCs monitoring over the previous 9 years have been reviewed. TSP monitoring is conducted once every 6 days in three locations (See Drawing 24315/13/504 for existing dust monitoring locations D1 to D3).  Whereas, VOC monitoring is conducted once every 3 months in four locations around the site boundary (See Drawing 24315/13/504 for existing VOC monitoring locations V1 to V4), and one location at source within the gas well (See Drawing 24315/13/504 for existing gas wells locations W1 to W30). 

The sampling methodology was stipulated in Section 35.10.2 of the NENT Landfill Monitoring Plan.  Equipment specified in Method T014/T015 of USEPA and corresponding methods for the determination of Toxic Organic Compounds in ambient air were adopted for monitoring the existing landfill.  VOC will be collected in 6L stainless steel canisters coated internally with silica.  Methane will be trapped using a low-flow rate pump to a 1L Tedlar bag for direct analysis on a gas chromatography.  Analysis will be carried out by a laboratory equipped with a capillary gas chromatography linked to a mass spectrometer.

Key observations from the past monitoring records are summarised in Table 3.9 for TSP and Table 3.10 for VOC.  The dust and LFG monitoring locations of the existing NENT Landfill is shown in Drawing No. 24315/13/504.  In accordance with the long-term monitoring record, there is no exceedance of TSP since Year 1996. With the implementation of dust control measures and periodic EM&A monitoring, the performance of dust suppression measures are found to be sufficient and no adverse impact would be anticipated.


Table 3.9: Dust monitoring record for existing NENT Landfill operation

Monitoring ID

Location

Monitoring Parameters

Frequency

Observations

Mitigation Measures

D1

beside canteen

TSP/RSP

Once very 6 days. Increase to 3 days cycle in case of exceedance event

No exceedance since 1996

Increase water spraying frequency in tipping area and haul road by water trucks and sweeper trucks

 

Apply automatic water spraying system

 

Minimize the exposure duration of cut slopes and temporary capped areas by early hydroseeding.

D2

grassland beside Lagoon#1

No exceedance since 1996

D3

near Tung Lo Hang Village

There were 2 abnormalities  occurred from 97 until present due to dry weather and high traffic rate of haul road M3.  The abnormalities were rectified immediately and Independent Consultant was satisfied with the results.

Remark :    The established EM&A mechanism and good site practice in existing NENT Landfill effectively contain any dust problem on site in a timely manner.

 

Table 3.10: VOC monitoring information for existing NENT Landfill operation

Monitoring ID

Location

Monitoring Parameters

Frequency

Observations

Mitigation Measures

V1

 

 

 

 

 

East of the landfill area

38 VOCs  including 8 prominent VOCs:

•  Benzene;

•  Dichlorobenzenes;

•  Dichlorodifluor-methane;

•  Ethylbenzene;

Quarterly basis in March, June, September and December at four boundary locations and one gas well.

 

Only one abnormality was observed out of 1440 data ( 9-year monitoring data) [1]

 

Site investigation has identified neither potential leakage from the pipelines nor defect in extraction system.

 

No exceedance was identified in subsequent special monitoring.

V2

North of the landfill area

•  Methylene Chloride;

•  Toluene; and

•   Methane.

If the monitoring results show abnormality, site inspection and special monitoring will be conducted.

Only four abnormalities were observed out of 1440 data ( 9-year monitoring data) [1]

V3

West of the landfill area

 

 

Only five abnormalities were observed out of 1440 data ( 9-year monitoring data) [1]

V4

South of the landfill area

 

 

Only one abnormality was observed out of 1440 data ( 9-year monitoring data) [1]

Remark : [1] -    VOC monitoring data and emission trend at source (within gas well) were compared with the results at the site boundary. Independent Consultant (IC) confirmed that the handful number of abnormal readings were not caused by / related to landfill operation.

Only 11 abnormalities out of 7200 monitoring data were observed over the past 9 years.  For all these 11 abnormalities, the VOC levels at the gas well (source) were lower than that at the site boundary. Special monitoring had been conducted immediately and no exceedance was observed.  An Independent Consultant (IC) had reviewed all these monitoring results and the findings for the site inspection by Environmental Team.  It was concluded that the abnormal readings of VOC were not due to the operation of existing landfill. There were existing pig farm, recycling workshops and woodland in the nearby area that would also have emission of the same VOC elements.  The reasons for the cause of the abnormality were originated from external sources. The reasons were justified and accepted by the IC, and these IC reports have been sent to EPD for review. Therefore, these abnormalities (i.e. non genuine cases) in VOCs have been discarded in this assessment.

The 9-year VOCs concentrations at the 4 monitoring points of the NENT Landfill site boundary are also tabulated in Table 3.11.  It is observed that all VOC levels were within the contractual trigger levels which had been verified by the Independent Consultant.

The nearest ASR is located more than 300m away from the NENT Landfill site boundary.  Taking into consideration the dispersion from the boundary to the ASRs, it is envisaged that the VOC level at ASRs will be further reduced significantly.  During landfill restoration, the existing NENT Landfill will be capped with plastic sheet together with a thick layer of covering soil similar to other landfill under restoration, the VOC emission will be insignificant.

By the time when the NENT Landfill Extension is in operation, existing NENT will be capped with thick soil and equipped with active LFG extraction system, the surface emission from existing NENT will not be an issue based on the observation from the restored landfills in HK. In order words, the ambient VOC level would be significantly lower than the past monitoring data after restoration of existing NENT.

Table 3.11: 9-year averaged VOC concentration at the site boundary of the existing NENT Landfill     (from Year 1997 to Year 2005)

Pollutants

Events

9-year monitoring data at the site boundary (in ppbv except methane) [a]

 

V1

V2

V3

V4

1_2-Dibromoethane

(CASRN 106-93-4)

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

1_1_1-Trichloroethane (CASRN 71-55-6)

Monitoring result range

<1 * – 1.2

1

<1 * – 1.2

<1 * – 1.1

Long-term average

1

1

1

1

Benzene

(CASRN 71-43-2)

Monitoring result range

<1 * – 2.8

<1 * – 1.8

<1 * – 8.2

<1 * – 2

Long-term average

1.2

1.1

1.5

1.1

Butan-2-ol

(CASRN 71-36-3)

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Butanethiol

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Butyl acetate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Butyl benzenes

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Carbon Disulphide

Monitoring result range

<1 *

<1 *

<1 *

<1 *

(CASRN 75-15-0)

Long-term average

<1 *

<1 *

<1 *

<1 *

Chloroform

(CASRN 67-66-3)

Monitoring result range

<1 * – 13

<1 * – 1.9

<1 * – 14

<1 *

Long-term average

1.6

1.1

1.3

<1 *

Decanes

Monitoring result range

<1 *

<1 * – 1.1

<1 *

<1 * – 3.2

Long-term average

<1 *

1

<1 *

1.1

Dichlorobenzene

(CASRN 106-46-7)

Monitoring result range

<1 * – 8.1

<1 * – 16

<1 * – 16

<1 * – 17

Long-term average

1.4

2.4

2.7

3.4

Dichlorodifluoromethane (CASRN 75-71-8)

Monitoring result range

<1 * – 21

<1 * – 83

<1 * – 82

<1 * – 12

Long-term average

3.5

12.3

6.4

2.0

Dimethyl sulfide

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Dipropyl ether

(CASRN 111-43-3)

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Ethanethiol

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Ethanol

Monitoring result range

<100 *

<100 *

<100 *

<100 *

Long-term average

<100 *

<100 *

<100 *

<100 *

Ethyl Benzene

(CASRN 100-41-4)

Monitoring result range

<1 * – 44

<1 * – 6.4

<1 * – 70

<1 * – 65

Long-term average

3.4

2.1

6.2

5.1

Ethyl Butyrate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Ethyl Propionate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Limonene

(CASRN 5989-27-5)

Monitoring result range

<1 *

<1 *  4.2

<1 * – 3.5

<1 * – 2.8

Long-term average

<1 *

1.5

1.1

1.1

Methane

Monitoring result range in ppmv

0.5 – 32

0.05 – 55

1.8 – 56

0.5 – 57

Long-term average      in ppmv

6.7

7.1

9.0

13.9

Methanethiol

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Methanol

(CASRN 67-56-1)

Monitoring result range

<100 *

<100 *

<100 *

<100 *

Long-term average

<100 *

<100 *

<100 *

<100 *

Methyl Butyrate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Methyl Propionate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Methylene chloride

Monitoring result range

<1 * – 53

<1 * – 73

<1* – 230

<1 * – 84

Long-term average

9.1

12.5

27.8

12.1

n-Heptane

(CASRN 142-82-5)

Monitoring result range

<1 * – 5.4

<1* – 900

1 – 95

<1 * – 23

Long-term average

1.2

44

7.2

2.6

n-Octane

Monitoring result range

<1 *

<1* – 760

<1 * – 54

<1 * – 5.8

Long-term average

<1 *

37.2

3.5

1.2

Nonane

Monitoring result range

<1 *

1 – 92

1– 18

1– 2.3

Long-term average

<1 *

5.3

1.8

1.1

Propyl Benzene

Monitoring result range

<1*– 36

<1* – 21

<1* – 6.6

<1* – 28

Long-term average

3.2

3.5

1.4

3.5

Propyl Propionate

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Terpenes

Monitoring result range

<1* – 1.7

<1* – 1.5

<1* – 1.5

<1* – 2

Long-term average

1.0

1.0

1.0

1.1

Tetrachloroethylene

(CASRN 127-18-4)

Monitoring result range

<1* – 2.6

<1 * – 2.9

<1 * – 2.7

<1 *

Long-term average

1.1

1.1

1.1

<1 *

Toluene

(CASRN 108-88-3)

Monitoring result range

<1* – 120

<1* – 42

<1* – 160

<1* – 78

Long-term average

15.1

11.1

23.4

18.6

Trichloroethylene

(CASRN 79-01-6)

Monitoring result range

<1 *

<1 * – 2.8

<1 *

<1 * – 1.7

Long-term average

<1 *

1.1

<1 *

1.0

Undecane

Monitoring result range

<1 *

<1 *

<1 *

<1 *

Long-term average

<1 *

<1 *

<1 *

<1 *

Vinyl chloride

(CASRN 75-01-4)

Monitoring result range

<1* – 2.8

<1 *

1 – 13

<1 *

Long-term average

1.1

<1 *

1.6

<1 *

Xylenes

(CASRN 1330-20-7)

Monitoring result range

<1* – 64

<1* – 12

<1* – 110

<1* –120

Long-term average

5.1

3.6

10.7

8.7

Remark    (a) : lowest detection limit is 1ppbv for all pollutants; except for methanol and ethanol which is 100ppbv.

                 *  : Below detection limits (assume to take the lowest detection limit as the monitoring result)

Owing to the lack of background monitoring data at the region/ASR, the long-term monitoring data of benzene and vinyl chloride at the site boundary are taken as the background as a conservative estimation. A background benzene and vinyl chloride concentrations of 1.225ppbv (3.9ug/m3) and 1.175ppbv (3ug/m3) are adopted, respectively. In fact, these values have included the contribution from surface gas emission, if any, from the tipping area.

Odour complaint records from existing NENT Landfill site office and EPD Environmental Compliance Division have been checked, and there were only 2 odour complaints in the existing NENT Landfill region in the past 5 years. Detailed investigations were conducted by the Independent Consultant and Environmental Team of the existing NENT Landfill and it was concluded that NENT Landfill was not the source of the odour nuisance.

Benzene, Vinyl Chloride and Non-methane Organic Carbon (NMOC) have also been monitored at the flare of the existing NENT Landfill, and the monitoring results are summarised below.


Table 3.12: Monitoring data from flare system

Pollutants

NMOC

Vinyl Chloride

Benzene

6-year Monitoring Results

Inlet

Outlet

Inlet

Outlet

Inlet

Outlet

Max (ppmv)

4800

33

1.6

<0.006

1

<0.006

Min (ppmv)

330

0.03

0.2

<0.001

0.2

<0.001

Average (ppmv)

2182

6.1

0.553 (1413 mg/m3)

0.0026 (6.646 mg/m3)

0.493 (1574.98 mg/m3)

0.0029 (9.265 mg/m³)

Removal Efficiency [aver value (inlet - outlet)/inlet]

99.7%

99.5%

99.4%

 

Owing to the lack of monitoring data for ASP and power generator, reference has been made with the typical control efficiency under Table 2.4-3, AP-42 of USEPA as the best estimate. The typical controlled efficiency of 99.6% and 99.8% are proposed for halogenated species and non-halogenated species for boiler/stream turbine. As compared to the controlled efficiency of 99.5% and 99.4% for halogenated species and non-halogenated species for flare, the efficiency in flare is on a conservative side. Therefore, the controlled efficiency for ASP and power generator will assume to be the same as that for the flare. 

3.3.4            Proposed Plant for Landfill Gas Export Scheme in Existing NENT Landfill

The contractor of the existing NENT Landfill has signed an agreement with Hong Kong China Gas Co. (HKCG) for the Landfill Gas Export Scheme (LFGES). Under this LFGES, NENT Landfill shall supply a large quantity of LFG as fuel for production of towngas. The ultimate aim of the scheme is to enhance the environment and utilise as much LFG as possible as fuel. The entire system will extract most of the LFG from gas wells.   

In order to maximise the extraction to achieve a cost-effective export scheme, the following practices have been implemented since Year 2007 to improve the extraction efficiency (means higher LFG production rate and higher energy recovery) as much as possible:

·         Formulation of a working team to review all processes, control practice and extraction system in order to maximum the efficiency of the system.

·         Maintain a slightly negative pressure within the entire tipping area (by suction).

·         Increase the number of gas-extraction wells by reducing the radius of the catchment from 50m each to 25m.

·         Improve the extraction efficiency by checking/reinstating gas wells with abnormally low extraction rate as a result of blockage/soil movement or sedimentation.

·         Increase the coverage of inactive tipping area with HDPE sheet which can enhance the anaerobic decomposition (reduce air getting in).

·         Extract LFG at newly-opened active tipping area (the only free opening for surface VOC emission).

At the restoration phase, no surface gaseous emission is anticipated after laying of plastic sheet and thick soil cover based on the observations from other restored landfills in HK.

3.3.5            Ambient air quality from EPD monitoring station

The nearest EPD air quality monitoring station to this Project is the Tai Po Monitoring station at Tai Po Government Office Building. According to EPD’s report on “Air Quality in Hong Kong” the area type of NENT Landfill Extension is under the “New Town” category.

Air quality data at the Tai Po Monitoring Station between 2000 to 2005 has been extracted. Table 3.13 below shows the average concentration of major air pollutants at the monitoring station.


Table 3.13: Background pollutant concentrations (5-year annual averaged)

Pollutant/ Year

2000

2001

2002

2003

2004 (a)

2005

5-year Averaged Concentration (ug/m3)

NO2

47

50

48

52

N.A.

49

49.2

SO2

12

13

11

14

N.A.

19

13.8

TSP

63

68

61

71

N.A.

61

64.8

RSP

48

50

46

54

N.A.

51

49.8

Note: (a)   Annual averaged monitoring data for Tai Po is not available at Year 2004 due to upgrading of system.

 

3.4                  Air Sensitive Receivers

Air sensitive receivers (ASRs) were identified in accordance with the guidelines in Annex 12 of the TM-EIAO. Existing ASRs were confirmed through site visits and review of survey maps. There were no planned ASRs on the latest Outline Zoning Plan. Representative ASRs within a distance of 500m from the Project boundary have been selected for the assessment.  Their respective locations are shown in Drawing No. 24315/13/101 and Table 3.14 below.

Table 3.14: Summary of representative air sensitive receivers

Assessment Point No.

Assessment Point Description

Use

No. of Storey (including roof)

Shortest Horizontal Distance to Waste Boundary, m

ASR1

Wo Keng Shan Tsuen

Residential

3

420

ASR2

Village houses at Junction of Ng Chow Road and Wo Keng Shan Road

Residential

3

1040

ASR3

Cheung Shan Monastery

Religions

1

820

ASR4

Man Uk Pin

Residential

3

1130

ASR5

Man Uk Pin

Residential

3

1200

ASR6

Miu Keng

Residential

3

990

ASR7

Heung Yuen Wai

Residential

3

1240

ASR8

Tsung Yuen Ha

Residential

3

1790

ASR9

Ha Heung Yuen

Residential

3

1330

ASR10

Lin Ma Hang

Residential

3

900

ASR11

Tung Lo Hang

Pig Farm/ Residential

2

800

ASR12

Chuk Yuen

Residential

3

2000

ASR13

Nga Yiu Ha

Residential

3

1080

ASR14

Ping Yeung

Residential

3

960

ASR15

Ping Che

Residential

3

1890

ASR16

Ping Che Kat Tin

Residential

3

1870

ASR17

Kan Tau Wai

Residential

3

2250

ASR18

Tong Fong

Residential

3

2150

ASR19

Fung Wong Wu

Residential

2

2500

ASR20

Lei Uk

Residential

2

2450

ASR21

Chow Tin Tsuen

Residential

2

2750

ASR22

Tai Po Tin

Residential

2

2400

ASR23

Ha Shan Kai Wat

Residential

2

2800

ASR24

Sheung Shan Kai Wat

Residential

2

3000

ASR25

Tai Tong Wu

Residential

2

1650

ASR26

Loi Tung

Residential

2

1700

ASR27

Tong To Shan Tsuen     (derelict  and vacant)

Derelict  and Vacant

3

450


      3.5                 Identification of Air Pollution Source and Environmental Impact

3.5.1            General Modes of Construction/Operation

Based on the practice in existing NENT Landfill operation and the construction/operational programme for future NENT Landfill Extension operation, the construction and operational events are summarised in Tables 3.15, 3.15a and 3.16 respectively. The existing and future landfill development phasing is illustrated in Appendix 2.2 and Drawing 24315/13/203.

Table 3.15: Summary of general modes of construction / capping activities

Stage

Mode of Construction

Period

Dust Impact

Remark

1

•   Operation + Capping of Existing NENT Landfill – from end 2008 (assumed as worst case)

•   Site clearance - end 2008 to mid 2009

•   Excavation & site formation - mid 2009 to end 2009

•   Installation of liner, leachate & LFG systems - end 2009 to end 2010

About 24 months

•   Existing NENT Landfill : About 3,000m²  of active area for capping/stockpiling; including the 40m x 30m operation area.

•   Phase 1 area of NENT Landfill Extension : About 20% of Phase I area under active site formation works.

•   Phase 2 area of NENT Landfill Extension : No activity.

•   Phase 3 area of NENT Landfill Extension : No activity.

•   Worst-case scenario with the cumulative impact from existing NENT Landfill and its extension, active site areas in NENT and NENT Extension are closest to ASR.

•   Need advance work and involve larger construction area during critical period.

•   Setback distance of Stage 1 is closest to ASR.

2

•   Site clearance – early 2010 to end 2010

•   Excavation & site formation - end 2010 to mid 2012

•   Installation of liner, leachate & LFG systems- mid 2011 to end 2012

About 36 months

•   Existing NENT Landfill : Aftercare and no construction activity.

•   Phase 1 area of NENT Landfill Extension : 40m x 30m operation area.

•   Phase 2 area of NENT Landfill Extension : About 20% of Phase 2 area under active  site formation works.

 •   Phase 3 area of NENT Landfill Extension : No activity.

•   More float time for construction and smaller construction area

Setback distance of Stage 2 to ASR is further away than  Stage 1.

•   Less impact than Stage 1 and detailed model will not be conducted.

3

•   Site clearance - early 2013 to end 2013

•   Excavation & site formation - mid 2013 to end 2014

•   Installation of liner, leachate & LFG systems – early 2014 to end 2015

About 36 months

•   Existing NENT Landfill : Aftercare and no construction activity.

•   Phase 1 & 2 areas of NENT Landfill Extension : 40m x 30m  operation area.

•   Phase 3 area of NENT Landfill Extension : About 20% of Phase 3 area under active  site formation works.

•   Less impact than Stage 1 and detailed model will not be conducted.

4

•   Installation of final capping - early 2020 to end 2021

•   Planting and Landscaping - early 2021 to end 2022

about 24 months for capping and 24 months for planting

•   Existing NENT Landfill : Aftercare and no construction activity.

•   NENT Landfill Extension : About 3,000m²  of active excavated area for capping.

•   Less impact than Stage 1 and detailed model will not be conducted.

 

 


Table 3.15a: Identification of worst-case scenario for construction / capping activities

 

Existing NENT Landfill / Landfill Extension

Existing NENT Landfill

Landfill Extension Phase 1 Area

Landfill Extension Phase 2 Area

Landfill Extension Phase 3 Area

Earthwork activities

Operation 0.00018 Mm³

(40x30x0.15 m³ )

Capping

0.7 Mm³

(0.7 Mm³ fill)

Site formation

2.7 Mm³

(1.5 Mm³ cut + 1.2 Mm³ fill)

Site formation

2.8 Mm³

(1.9 Mm³ cut + 0.9 Mm³ fill)

Site formation

2.9 Mm³

(2.8 Mm³ cut + 0.1 Mm³ fill)

Programme

Everyday

24 months

15 months

30 months

24 months

Earthwork activities per month

(Dust Impact)

0.0054 Mm³

0.03 Mm³

0.18 Mm³

0.10 Mm³

0.12 Mm³

Notes :

1. The earthwork activity in operation is considered negligible in comparison with the site formation activities.

2. In Stage 1 (Existing NENT + Extension Phase 1), total earthwork involved is estimated to be 0.21 Mm³ per month, and is close (~ 500m) to Wo Keng Shan Village.

3. In Stage 2 (only Extension Phase 2 with dusty construction), total earthwork involved is estimated to be 0.10 Mm³ per month.  Phase 2 has more float time and thus the active construction area can be reduced. Thus the impact will be less than that in Stage 1.

 

Table 3.16: Summary of general modes of operation activities and identification of worst-case scenario

Stage

Mode of Operation

Period

Gaseous Emission and     Odour Impact

Remark

A

•   Existing NENT Landfill close down without tipping activities

•   Waste filling (within Phase 1 area) - end 2010 to end 2012

 

about 27 months

•   Existing NENT Landfill : No operational activity.

•   Phase 1 area of NENT Landfill Extension : In operation with active tipping area about 40m x 30m.

•   Phase 2 area of NENT Landfill Extension : No operational activity.

•   Phase 3 area of NENT Landfill Extension : No operational activity.

•   Existing NENT will be capped with no detectable surface gas and odour emission.

•   Less landfill gas and leachate generation than Stage C due to smaller waste filling volume.

•   Odour from the same active tipping area.

B

•   Waste filling (within Phases 1 and 2 areas) - early 2013 to end 2015

About 36 months

•   Existing NENT Landfill : No operational activity.

•   Phase 1 & 2 areas of NENT Landfill Extension : In operation with active tipping area about 40m x 30m.

•   Phase 3 area of NENT Landfill Extension : No operational activity.

•   Less landfill gas and leachate generation than Stage C due to smaller waste filling volume.

•   Odour from the same active tipping area.

C

•   Waste filling (within Phases 1 to 3 areas) -early 2016 to end 2020

About 60 months

•   Existing NENT Landfill : No operational activity.

•   Phase 1, 2 & 3 areas of NENT Landfill Extension : In operation with active tipping area about 40m x 30m – worst-case with largest area (both active and inactive tipping areas) – can be controlled by good extraction system and coverage by plastic sheet.

•   Max number of operational plants adopted for the entire lifecycle (LFG, ASP and flares) – in practice with largest amount of gas generation due to cumulative of waste and maturity of the landfilling condition.

•   Worst case for gaseous emission assessment.

•   Odour from the same active tipping area.

 

D

•   Aftercare (Landfill gas and Leachate will be reduced)     2023 (for 30 years)

 

About 30 years

•   Very light activities within the capped area. Active control system for landfill gas and leachate will be operated without causing adverse environmental impact.

•   No detectable surface gas and odour emission will be anticipated based on the observations from other restored landfills in HK.

•   Less impact than Stage C.

•   No odour from restored landfill.

 

3.5.2            Source Identification

On-site and off-site air pollution sources during construction, operation, restoration and aftercare of the Project are summarised in Table 3.17 and 3.18 below:

Table 3.17: Sources of air pollution from Construction and Restoration Phases

Sources of air pollution

·         Various construction activities during daytime

·         Wind erosion

 

Table 3.18: Sources of air pollution from Operation Phase

Sources of air pollution

·         Road traffic (insignificant due to very low traffic flow. There is no increase in total flow between the existing landfill and its future extension).

·         Potential dust emission arising from daily operations (included in the general construction activities)

·         VOC emission from active tipping area.

·         Gases emission from flare, LFG power generator and ammonia stripping plants.

·         Odour emission from leachate treatment facilities.

·         Odour emission and surface gas emission from waste tipping operation.

3.5.3            Construction Phase

Heavy construction activities during daytime include site clearance, ground excavation, cut and fill (i.e. earth moving) operations, construction of the associated facilities and temporary road access within the site.  In addition, wind erosion of all open sites including stockpiling will have potential impact.

Quantitative assessment on the impact of the identified sources on the ASRs is conducted.

3.5.4            Operation Phase

3.5.4.1             Vehicles

Current daily vehicular trip generation travelling to and from the existing NENT Landfill site along Wo Keng Shan Road is in the order of 500 veh/day. About 90 veh/hour is predicted from the NENT Landfill Extension during the peak operation hour.  Given the more than 5m setback distances between Wo Keng Shan Road and ASRs, it is in compliance with the HKPSG requirements for vehicular emission control.  As there will not be any overlapping of operation phases between NENT Landfill and its extension, adverse vehicular emission impact is not anticipated and quantitative assessment is not required.

In general, most of the refuse collection vehicles (RCV) for MSW and sludge are of enclosed-type and odorous gases are well contained during transit under normal circumstances.  Sludge vehicles / special vehicles that required admission ticket, and special condition can be imposed on the cleanliness of vehicle and disposal period to avoid adverse cumulative impact. With reference to the existing NENT Landfill experience, potential odour impact from RCVs can be adequately controlled and unlikely to be an issue.  Quantitative assessment is therefore not required.

In accordance with the HKPSG requirements, the minimum setback distance from earth moving activities to ASRs is 50m. Since the distance between the NENT Landfill Extension and the nearest ASRs is more than 300m, dust emission impact from landfill will be insignificant. In addition, all vehicles will be cleansed by wheel washing facility up to half of the vehicle height before leaving landfill, and soil brought away from landfill is thus not anticipated. Vehicle containing dusty material will also be covered by sheet to avoid any potential nuisance.  Any dusty discharge on road is a violation of the Public Health & Municipal Ordinance.  Therefore adverse off site dust impact is not anticipated.

3.5.4.2             Ammonia Stripping Plant, LFG Power Generator and Flaring Systems

The ammonia stripping plant and the thermal destructor at the existing NENT Landfill is an integrated unit (Figure 3.1 for illustrative diagram). When raw leachate passes through the ammonia stripping tower, ammonia dissolved in leachate will be removed. The ammonia laden air is combusted with landfill gas in the thermal destructor. Given particulate matter in the combustion process is negligible, emissions of ASP from the stacks are expected to be insignificant.

In accordance with US Environmental Protection Agency, AP-42 "Compilation of Air Pollutant Emission Factors" data, the thermal destructor is designed to destroy over 99% of VOCs (including methane, vinyl chloride, benzene and other non-methane hydrocarbons) in the landfill gas and exhaust from the ammonia stripping tower. Resulting discharge of benzene and vinyl chloride is reduced to a low limit. Similarly, all gaseous ammonia are completely oxidised to nitrogen and water.

 

 

Text Box:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 Figure 3.1     Schematic Diagram of the Thermal Destructor (Within Ammonia Stripping Plant)

 

LFG extracted from NENT Landfill is utilised on site as the fuel source for LFG power generator and will be exported to HKCG for commercial use.  The existing LFG power generator plant consists of 2 JGC 320 GS-B21 engine modules which can produce approximately 1.8 MW of electricity. The plant is running in pure isolated operation 24 hours a day because system connection to power grid is not allowed.

An agreement was formed between the contractor of the existing NENT Landfill and The Hong Kong & China Gas Company (HKCG) to export the LFG from NENT Landfill for towngas production. Landfill gas flaring system is installed in the existing NENT Landfill purely for the thermal destruction of surplus landfill gas. Under normal operating condition, all the available LFG will be fully utilised and no surplus LFG will be incinerated in the flaring system.  As it is still early stage to formulate a LFG Export Scheme from future NENT Landfill Extension, the following assessment using similar flaring system as the existing landfill will be the worst-case scenario.  In fact the flaring system for the extension site would be much smaller than the existing landfill because the total waste volume of the extension site is much less than the existing landfill.

NO2, SO2, Vinyl Chloride and Benzene as the key control parameters will be quantitatively modelled to assess their potential impact.

3.5.4.3             Leachate Treatment Facilities

Raw leachate temperature rises as a result of the bacteriological reaction during decomposition of waste.  Its temperature is further increased by mixing with the treated effluent from the ammonia stripping plant (heating process).  Leachate temperature is therefore well above the atmospheric temperature.  Effect of atmospheric temperature variation has little influence on odour emission from leachate treatment plant.  Odour samples collected for quantitative analysis is therefore not subjected to temperature adjustment.

To plan for the worst case scenario with cumulative impact from the restored landfill and the NENT Landfill Extension, a new on-site leachate treatment facility is assumed within the NENT Landfill Extension to serve the extension site, while the existing leachate treatment plant is retained to serve the existing landfill under restoration.  The new leachate treatment facilities are located at the lowest elevation in order to cater for a gravity leachate collection system.  It will be located close to the waste reception area of the existing NENT Landfill and Wo Keng Shan Tsuen.  A quantitative assessment model is adopted for the odour impact evaluation of the two leachate treatment plants.

It is also noted that there would be upgrading works under the existing NENT Landfill Project to improve the existing leachate treatment plant.  The proposed improvements include:

·         Provision of ventilated cover for the existing lagoons and emissions are extracted to suitable odour removal filters with odour removal efficiency of 99%. 

·         Ferric nitrate or sodium hypochlorite can be added to oxidise the odourous chemical in the leachate. The pH value of leachate can be controlled to a suitable value from future on-site experiment such that the generation of any odourous H2S and ammonia can be optimised.

·         For the gaseous extraction system, the wind speed immediately above the leachate surface should be kept to minimal (in the order of 1E-3 m/s) such that the odour emission strength from lagoon can be minimised. Suitable treatment system should be provided for odour removal. The ventilated gaseous emission from lagoons should be provided with 5-10 air change per hour for further dilution before discharge.  

·         The notional centre of the future discharge point (e.g. stack) shall be located at a location with maximum setback distance from the ASRs and further away from the notional centre of the lagoons. The location of discharge point and discharge height should be determined at the detailed design stage to ensure that the odour criterion at the ASRs will not be exceeded. 

This will provide an environmental benefit to nearby environment in terms of visual and odour improvement.

As regards the leachate treatment facilities for the Landfill Extension (assuming conservatively that a new plant will be implemented), it is anticipated that the new plant will be built to the improved condition as described above, right from the beginning of its operation.   Treatment method such as Sequencing Batch Reactor could be adopted for future lagoon.

Based on the preliminary estimation, owing to the capping of the existing NENT Landfill, leachate generation will be much reduced from currently 800m3/day to 350m3/day in the future.  Most of the existing plants in NENT Landfill will not be operated in full scale. The leachate generation from NENT Landfill Extension will be gradually increased from 0 to about 800m3/day when all three phases of the landfill site are fully filled.

 

 

 

3.5.4.4             Waste Tipping Operation

Based on long-term operational practice in existing NENT Landfill, active tipping face during daily operation is normally exercised in a cell of 40mx30m in size while most of the inactive areas are covered by impermeable sheets.  Dust emissions from the operation plants are minor and have been included as a cumulative source in the construction dust assessment.  Potential odour impact is associated with the prevailing climate condition and is expected to be the worst-case in stable and calm weather.  A quantitative assessment model is adopted for the odour impact evaluation of waste tipping operation.

Most of the waste received at NENT Landfill is municipal solid waste, with moisture content varies from 35 to 70%.  There are other waste types with extremely high moisture
content of 70-85% (e.g. sludge, livestock waste and dredged mud) disposed
of at NENT.  Waste received in NENT Landfill is wet in nature in particular during humid and wet season in Hong Kong.

Previous waste-statistical data have been reviewed as shown in Table 3.19.  Such data on waste composition show that Special-Waste + Sludge amount to approximately 10% or less of the total.

Table 3.19 : Composition of Waste Disposal to NENT Landfill (in tpd)

Year

2000

2001

2002

2003

2004

2005

Landfilled Construction Wastes (LCW) + Municipal Solid Wastes (MSW)

3441

3452

3530

3064

2721

2656

Special-Waste + Sludge

132

144

149

186

215

303

TOTAL

3573

3596

3679

3250

2936

2959

% of LCW + MSW

96.3%

96.0%

96.0%

94.3%

92.7%

89.8%

% of Special Waste + Sludge