Detailed Landfill Gas Hazard Assessment Report  

    

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Contents

1   INTRODUCTION. 1

1.1        BACKGROUND TO THIS STUDY. 1

1.2        PROCEDURES AND GUIDELINES. 2

1.3        PREVIOUS STUDIES UNDERTAKEN AT THE SITE. 2

1.4        SCOPE OF THIS STUDY. 2

1.5        STRUCTURE OF THIS REPORT. 2

2   REVIEW OF PRELIMINARY QUALITATIVE RISK ASSESSMENT. 4

2.1        APPROVED EIA REPORT. 4

3   LANDFILL GAS HAZARD ASSESSMENT METHODOLOGY. 5

3.1        GENERAL. 5

3.2        SOURCE. 5

3.3        PATHWAY. 6

3.4        TARGET. 6

4   NATURE OF NENT LANDFILL. 8

4.1        LANDFILL HISTORY. 8

4.2        HISTORICAL LANDFILL GAS AND LEACHATE CONTROL. 8

4.3        LANDFILL GAS CONTROL FOR THE NENTX. 10

5   POTENTIAL FOR THE DEVELOPMENT TO INTERCEPT LANDFILL GAS. 11

5.1        GEOLOGY AND HYDROGEOLOGY. 11

5.2        UTILITIES. 11

6   DETAILED DESIGN. 12

6.1        FOR INFRASTRUCTURE AREA. 12

6.2        DESCRIPTION OF THE INFRASRUCTURE AREA. 12

6.3        CONSTRUCTION METHODOLOGY. 13

6.4        SENSITIVE TARGET FACILITIES FOR LANDFILL GAS RISK. 13

7   QUALITATIVE ASSESSMENT OF RISK DUE TO LANDFILL GAS. 16

7.1        INTRODUCTION. 16

7.2        SOURCE. 16

7.3        NENT LANDFILL. 16

7.4        NENTX. 16

7.5        PATHWAY. 17

7.6        WITHIN LANDFILL EXTENSION SITE. 17

7.7        OUTSIDE LANDFILL EXTENSION SITE. 18

7.8        TARGETS. 18

7.9        SOURCE-PATHWAY-TARGET ANALYSIS. 25

8   RECOMMENDATIONS. 33

8.1        GENERAL HAZARDS RELATED TO LANDFILL GAS. 33

8.2        PRECAUTIONARY AND PROTECTION MEASURE - DESIGN PHASE (FOR THE CONSTRUCTION OF NENTX) 33

8.3        PRECAUTIONARY AND PROTECTION MEASURE - DESIGN PHASE (FOR THE OPERATION OF INFRASTRUCTURE AREA AT NENTX) 34

8.4        PRECAUTIONARY AND PROTECTION MEASURE - CONSTRUCTION PHASE. 34

8.5        MONITORING.. 35

8.6        PRECAUTIONARY AND PROTECTION MEASURE – OPERATION, RESTORATION AND AFTERCARE PHASES. 36

9   ENVIRONMENTAL MONITORING AND AUDIT. 37

10 CONCLUSION. 38

 

 Figures

Figure     1.1      

Project Layout Plan

Figure     1.2

250m Consultation Zone of NENTX Landfill

Figure     4.1

Typical Detail of the Composite Liner System

Figure     4.2

Location of Landfill Gas Monitoring Wells of NENT Landfill

Figure     4.3

NENTX Base Liner System

Figure     5.1

Geological Map

Figure     5.2

Preliminary Layout Plan of Proposed Utility Services of NENTX

Figure     6.1

Location of Proposed Infrastructure Building

Figure     6.2a to 6.2e

Proposed Lower/Ground Floor Plan of Infrastructure Area

Figure     7.1

Temporary Site Office of the Existing NENT

Figure     7.2

Typical Details of Gas Protection Measures

Figure     8.1

Location of Landfill Gas Monitoring Wells of NENTX

 

 


 Appendices

Appendix A           

Landfill Gas (LFG) Management System for NENTX

Appendix B          

Typical Details of Low Gas Permeability Paints

Appendix C

Typical Details of Gas Detection System

 

1                       INTRODUCTION

1.1                    BACKGROUND TO THIS STUDY

 

1.1.1                The North East New Territories Landfill Extension (the NENTX Project) is located adjacent to the existing North East New Territories (NENT) Landfill at Ta Kwu Ling. The extension site is located in a valley covering mainly the existing NENT Landfill Stockpile and Borrow Area that was formed to the east of the existing landfill as part of the original site development of the landfill, project location and layout plan shown in Figure 1.1. NENTX will be a new source of landfill gas generation and there are potential risks associated with any development close to a landfill site relating to the generation and sub-surface migration of landfill gas.

 

1.1.2                The NENTX is a designated project. The Environmental Impact Assessment (EIA) Report (AEIAR-111/2007) and an Environmental Monitoring and Audit Manual were approved on 20 September 2007. The project is governed by an Environmental Permit (EP) (EP-292/2007) which was granted on 26 November 2007. A further of EP (FEP) was applied and the FEP (FEP-01/292/2007) was subsequently granted on April 2022.

 

1.1.3                As per requirement of EP condition 2.11 and FEP Condition 2.9, the Permit Holder shall, at least one month before the commencement of construction of the Project, submit to the Director of Environmental Protection for approval a detailed landfill gas hazard assessment, which shall include a review of the preliminary qualitative risk assessment in the approved EIA report, preparation of a detailed qualitative risk assessment, preparation of detailed design of gas protection measures and the establishment of maintenance and monitoring programmes to ensure the continued performance of the proposed control measures. The submissions shall be certified by the Environmental Team (ET) Leader and verified by the Independent Environmental Checker (IEC).

 

1.1.4                Aurecon Hong Kong Limited (Aurecon) was appointed by Veolia Environmental Services Hong Kong Limited (Veolia) as the ET to undertake the detailed landfill gas hazard assessment (DLFGHA). The assessment has included a review the preliminary qualitative risk assessment as presented in the approved EIA Report and taken into account the design changes of the latest scheme, to assess the potential risk due to landfill gas migration based on the latest construction methodology and building design at the infrastructure area of NENTX and to recommend appropriate measures to ensure NENTX can be constructed and operated without undue risk to safety.

 

1.1.5                The design of the landfill gas management system and the landfill gas precautionary measures to be adopted on-site have been performed by a landfill gas specialist consultant appointed by Veolia, who has comprehensive knowledge on landfill characteristics, potential landfill gas hazards and appropriate precautionary measures to minimise hazards. Moreover, the landfill gas management system and landfill gas precautionary measures will be checked and certified by the ET Leader who leads the environmental team which includes an experienced landfill gas hazard specialist.

 

1.1.6                For the purpose of this DLFGHA Report, the NENTX schemes assessed in the approved EIA Report and the latest NENTX scheme are referred to as “the EIA Scheme” and “the latest scheme” respectively. The assessment follows the “source-pathway-target” analysis approach adopted in the approved EIA Report and the EPD’s Guidance Note on Qualitative Landfill Gas Hazard Assessment (Guidance Note).

 

1.1.7                It should also be noted that this Report is related to the potential landfill gas hazards due to the operation of the existing NENT Landfill to the construction and operation of NENTX and the operation of  NENTXof NENTX to the infrastructure facilities of the NENTX and establishment of the necessary control measures to minimise the risks identified.

1.2                    PROCEDURES AND GUIDELINES

 

1.2.1                Under Annex 7 of the Technical Memorandum on EIA Process (EIAO-TM), an evaluation of the potential risk posed by landfill gas is required for any development which is proposed within 250m of the edge of waste, known as Landfill Consultation Zone. As the NENTX site falls within the NENT Landfill Consultation Zone (see Figure 1.2), a Qualitative Landfill Gas Hazards Assessment (QLFGHA) is required to assess the potential risk due to landfill gas migration from the NENT Landfill to the construction and operation of the NENTX. This assessment considered both landfill gas sources (i.e. existing NENT Landfill and NENTX). A Practice Note for Professional Persons (ProPECC PN 3/96 “Landfill Gas Hazard Assessment for Development adjacent to Landfills”) (2) and Guidance Note on the assessment of the hazards which landfill gas may present to developments close to landfills have been issued by the EPD.

1.3                    PREVIOUS STUDIES UNDERTAKEN AT THE SITE

 

1.3.1                Number of previous studies have been undertaken at the NENTX. The documents which have been used as background material for the preparation of this assessment include the following:

 

·         Annex 7 and Annex 19 of the Technical Memorandum on EIAO (TM-EIAO);

·         North East New Territories (NENT) Landfill Extension – Feasibility Study: Environmental Impact Assessment Report, Ove Arup & Partners Hong Kong Ltd. 2007

·         Landfill Gas Hazard Assessment: Guidance Note, EPD 1997

·         ProPECC PN 3/96 “Landfill Gas Hazard Assessment for Development adjacent to Landfills (2), EPD 1996

1.4                    SCOPE OF THIS STUDY

 

1.4.1                The following tasks have been undertaken as part this assessment:

 

·         review of background information (including landfill gas monitoring data) and studies related to the NENT Landfill and the NENTX;

·         identification of the nature and extent of the NENT Landfill and NENTX which might have potential impacts on the construction and operation of NENTX;

·         identification of possible pathways through the ground, underground cavities, utilities or groundwater, and the nature of these pathways through which the landfill gas must traverse if they were to reach the NENTX; and

·         identification of the potential targets associated with the NENTX which are sensitive to the landfill gas risk.

1.5                    STRUCTURE OF THIS REPORT

 

1.5.1                Following this introductory section, the remainder of this Report is arranged as follow:

 

·         Section 2 summarises the findings and recommendations of the preliminary QLFGHA in the approved EIA Report;

·         Section 3 describes the methodology of the DLFGHA and the framework within which the identified levels of risk may be compared;

·         Section 4 describes the NENT Landfill and NENTX site, including its history and the measures taken to control landfill gas;

·         Section 5 reviews the geology and hydrogeology of the area and evaluates the potential pathways through which landfill gas may impact the targets;

·         Section 6 describes the design of the infrastructure area of NENTX and reviews the sensitivity of key elements of the development to the possible presence of landfill gas;

·         Section 7 evaluates the qualitative risk of landfill gas to the NENTX site;

·         Section 8 provides further recommendations for precautionary and protection measures to be adopted during the design, construction and operation of the NENTX based on the findings of the hazard assessment;

·         Section 9 describes the environmental monitoring and audit requirements with respect to landfill gas hazards associated with the construction, operation/restoration, and aftercare of the NENTX; and

·         Section 10 concludes the findings and recommendations of this DLFGHA.

2                       REVIEW OF PRELIMINARY QUALITATIVE RISK ASSESSMENT

2.1                    APPROVED EIA REPORT

 

2.1.1                The source-pathway-target receiver analysis was identified in the approved EIA Report (AEIAR-111/2007) shows for the existing NENT Landfill and NENT Landfill Extension Site, the overall risk level of landfill gas (LFG) hazards to targets within the landfill extension site is categorised as ‘High”.  A detailed preliminary qualitative risk assessment of LFG hazard in approved EIA Report is summarised in Table 2.1 below.

 

Table 2.1 Qualitative risk assessment of LFG hazards associated with NENT Landfill Extension

2.1.2                Precautionary and protection measures during design, construction and operation/restoration phases of the NENTX have been recommended in the approved EIA Report.

 

2.1.3                The design phase of suitable level of significant engineering measures will be required to protect the planned development and activities within. According to the LFG Guidance Note, an active gas control system supported by gas barriers and monitoring systems will be required to protect the planned development for “High” risk level. Detailed examples of these measures can be reference to EPD’s Guidance Note.

 

3                       LANDFILL GAS HAZARD ASSESSMENT METHODOLOGY

3.1                    GENERAL

 

3.1.1                A relatively simple procedure is used to evaluate the degree of risk which landfill gas may create for a particular development. The procedure is based on the Source - Pathway -Target method recommended in the Guidance Note on Landfill Gas Hazard Assessment, EPD, 1997 as described below:

 

·         Source - the location, nature and likely quantities/ concentration of landfill gas which have the potential to affect the landfill extension.

 

·         Pathway - the ground and groundwater conditions, through which the landfill gas must pass if they are to reach the development.

 

·         Target - the elements of the development that are sensitive to the effects of the landfill gas.

 

3.1.2                The landfill gas source, pathway and targets are categorised for the hazard assessment. An assessment of the overall risk is made based on the risk category as summarised in below, following the combination of existing NENT Landfill and NENTX fall into during the construction, operation, restoration and aftercare stages.

3.2                   SOURCE

3.2.1                The classification of the Source (i.e. the landfill) is determined as follows:

 

·         Minor - Landfill sites at which gas controls have been installed and proven to be effective by comprehensive monitoring which has demonstrated that there is no migration of gas beyond the landfill boundary (or any specific control measures) and at which control of gas does not rely solely on an active gas extraction system or any other single control measure which is vulnerable to failure; or

 

Old landfill sites where the maximum concentration of methane within the waste, as measured at several locations across the landfill and on at least four occasions over a period of at least 3 months (preferably longer), is less than 5 % by volume (v/v).

 

·         Medium - Landfill site at which some form of gas control has been installed (e.g. lined site or one where vents or barriers have been retrospectively installed) but where there are only limited monitoring data to demonstrate its efficacy to prevent migration of gas; or

 

Landfill site where comprehensive monitoring has demonstrated that there is no migration of gas beyond the landfill boundary but where the control of gas relies solely on an active gas extraction system or any other single control system which is vulnerable to failure.

 

·         Major - Recently filled landfill site at which there is little or no control to prevent migration of gas or at which the efficacy of the gas control measures has not been assessed; or

 

Any landfill site at which monitoring has demonstrated that there is significant migration of gas beyond the site boundary.

 

3.3                    PATHWAY

 

3.3.1                The type of pathway can be broadly classified based on various geological features of the landfill extension site such as permeability of soil, spacing, tightness and direction of fissures/ joints; topography; depth and thickness of the medium through which the gas may migrate( also affected by groundwater level); nature of strata over the potential pathway; number of media involved; and depth to groundwater table and flow patterns, etc. In general, the type of pathway can be broadly classified is as follows:

 

·       Very Short/Direct

Path length of less than 50m for unsaturated permeable strata and fissured rock or less than 100m for man-made

conduits

 

·       Moderate short/Direct

Path length of 50-100m for unsaturated permeable soil or fissured rock or 100-250m for man-made conduits

 

·       Long/Indirect

Path length of 100-250m for unsaturated permeable soils and fissured rock

3.4                    TARGET

 

3.4.1                Different types of targets may be broadly classified as follows:

 

·       High Sensitivity

Buildings and structures with ground level or below ground rooms/voids or into which services enter directly from the ground and to which members of the general public have unrestricted access or which contain sources of ignition.

 

This would include any developments where there is a possibility of additional structures being erected directly on the ground on an ad hoc basis and thereby without due regard to the potential risks.

 

·       Medium Sensitivity

Other buildings, structures or service voids where there is access only by authorised, well trained personnel, such as the staff of utility companies, who have been briefed on the potential hazards relating to landfill gas and the specific safety procedures to be followed.

 

Deep excavations.

 

·       Low Sensitivity

Buildings/structures which are less prone to gas ingress by virtue of their design (such as those with a raised floor slab).

 

Shallow excavations.

 

Developments which involve essentially outdoor activities but where evolution of gas could pose potential problems.

 

3.4.2                The above examples of the different categories should be used as a general guide only and particular aspects of a building or development may render it more or less sensitive than indicated. Account should be taken of any particular circumstances when assigning a target to one of the three categories.

 

3.4.3                A qualitative assessment of the overall risk is made based on the risk category as summarised in Table 3.1, which is extracted from Guidance Note. For the purpose of categorising the landfill extension site, the category is based upon the highest level of risk determined for any of the potential impacts identified in Table 3.1, in which the general implications fall into different overall risk categories as show in Table 3.2.

 

Table 3.1 Classification of Risk Category

Source

Pathway

Receiver Sensitivity

Risk Category

Major

Very Short/Direct

High

Very high

Medium

High

Low

Medium

Moderately short/Direct

High

High

Medium

Medium

Low

Low

Long/Indirect

High

High

Medium

Medium

Low

Low

Medium

Very Short/Direct

High

High

Medium

Medium

Low

Low

Moderately short/Direct

High

High

Medium

Medium

Low

Low

Long/Indirect

High

High

Medium

Medium

Low

Very Low

Minor

Very Short/Direct

High

High

Medium

Medium

Low

Low

Moderately short/Direct

High

High

Medium

Medium

Low

Very Low

Long/Indirect

High

High

Medium

Medium

Low

Very Low

 

                    Table 3.2 Summary of General Categorisations of Risk

Level of Risk

Implication

Very high

At the very least, extensive engineering measures and alarm systems are likely to be required. An emergency actions plan should also be developed so that appropriate actions may be immediately taken in the event of high landfill gas concentrations being detected within the development.

 

High

Significant engineering measures will be required to protect the planned development.

 

Medium

Engineering measures required to protect the development.

 

Low

Some precautionary measures will be required to ensure that the planned development is safe.

 

Very low

No protection or precautionary measures are required.

4                       NATURE OF NENT LANDFILL

4.1                    LANDFILL HISTORY

 

4.1.1                NENT Landfill is located at Ta Kwn Ling, New Territories and the landfill is one of the three strategic landfills in operation in the HKSAR and was designed with a capacity of approximately 35Mm3 of waste. The landfill commissioned in 1995 and receives municipal waste, construction waste and special waste from the North East New Territories, and Yuen Long and Sha Tin Transfer Stations solely by road, with an occupying about 108ha total site area and 64ha landfilling area of land.

 

4.1.2                The Environmental Protection Department (EPD) of the HKSAR Government 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 the extension of the existing NENT Landfill, with a target capacity of about 19 Mm3.  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 Stockpile and Borrow Area of the existing landfill.

4.2                    HISTORICAL LANDFILL GAS AND LEACHATE CONTROL

 

4.2.1                The existing NENT Landfill has been incorporated with an efficient and effective Landfill Gas (LFG) management system (Appendix A) in which a coordinated approach to LFG monitoring, collection, extraction, flaring and utilisation in accordance with international best practices for landfill operations.  The LFG extraction system includes extraction wells and pipework installed within the landfill cap connecting a pumping station on-site. It also incorporates a separate collection system connected to perimeter extraction wells isolated from the main system so that it is operated independently for migration control. The landfill contractor is undertaking routine maintenance and checking of the landfill gas extraction system to ensure it is operating satisfactorily. As the site is lined and landfill gas and leachate are collected and treated, it effectively controls sub-surface off-site migration of landfill gas and leachate. Typical details of the composite liner system (including an impermeable liner) installed at the NENT Landfill are presented in Figure 4.1.

 

Under the existing contract, Veolia will be required to continue the control and monitoring of landfill gas and leachate following closure of the landfill for a period of 30 years. Recent monitoring results from the monitoring wells located along the boundary of NENT Landfill have been reviewed.  Figure 4.2 shows the locations of monitoring wells and the landfill gas monitoring results of the existing NENT Landfill are summarised in Table 4.1.

 

Table 4.1 Summary of Landfill Gas Monitoring Results of the Monitoring Wells for Existing NENT (From January 2017 to December 2021)

Notes:

*For the gas concentration of Methane, <0.1% gas of monitoring result was detected for all monitoring wells which were under the detection limit therefore 0% of Methane gas concentration has been assumed for the Table 4.1 calculation.

 

4.2.2                Nil or minimal concentration of methane have been observed for all monitoring wells along the boundary of NENT Landfill which indicate that there is no sub-surface off-site migration of methane of the landfill.

 

4.2.3                The average Carbon Dioxide (CO2) concentrations detected in all the these monitoring wells ranged from 0.6% to 4.1% (v/v) while the maximum gas concentrations ranged from 1.8% to 9.0% (v/v). Abnormality of CO2 level was record in some monitoring wells, the cause of abnormalities were the presence of the carbonate source and natural biological activities in the soil and it was considered due to natural source and not due to landfill activities and all the abnormalities has been reviewed by the IC and it was concluded that all of them were not originated from the existing NENT Landfill.

 

4.2.4                The Site is in a valley to the southeast of the existing NENT Landfill. The Valley is encircled by three ridgelines and exits to the southwest through a small gorge.

 

4.2.5                The valley has an area of about 70 ha and overlaps with the stockpile and borrow area of the existing NENT Landfill. NENTX is designed with an estimated void space of landfill capacity of not less than 19Mm3 to receive Municipal Solid Waste (MSW) over a period of approximately 10 years. It is anticipated that construction and operation of NENTX will commence in 2022 and 2026, respectively.

4.3                    LANDFILL GAS CONTROL FOR THE NENTX

 

4.3.1                The future landfill extension itself is a source to generate significant amount of LFG during the operation and aftercare phases. With the LFG control measures in the future NENTX, it is anticipated that the source of LFG will be properly controlled within the site similar to the operation in existing NENT Landfill.

 

4.3.2                NENTX will be designed and constructed to incorporate extensive measures to contain, collect, and treat landfill gas and leachate. These measures include a composite liner system, active gas extraction systems and gas control systems in accordance with international best practices for landfill operation. These measures can effectively control sub-surface off-site migration of landfill gas and leachate. The base liner systems are designed as secure contaminant systems consisting of multi-layer impermeable liners, to contain leachate and landfill gas, LFG generated during waste deposition. Details of the base liner system designed for the NENTX is shown in Figure 4.3.

 

4.3.3                A comprehensive environmental monitoring programme will be implemented during the construction, operation, restoration and aftercare of the NENTX to monitor landfill gas generated within the NENTX and at the gas monitoring wells along the site boundary of NENTX and off-site leachate migration/ groundwater contamination. With reference to the performance standard stipulated in the NENTX contract, Veolia is required to control the migration of landfill gas such that the concentration of methane and carbon dioxide at the perimeter monitoring wells shall not exceed 1% v/v and 1.5% v/v above the background concentration (measured before the operation of the NENTX), respectively. Veolia will be required to continue the control and monitoring of landfill gas and leachate following closure of the landfill for a period of 30 years.

 

4.3.4                In conclusion, the future landfill extension itself is a source to generate amount of LFG during the Operation and Aftercares phases and another source of LFG is associated with the decomposition of MSW landfilled at NENT Landfill, which is located within (from waste boundary) from some NENTX infrastructure area.


1                           

5                       POTENTIAL FOR THE DEVELOPMENT TO INTERCEPT LANDFILL GAS

5.1                    GEOLOGY AND HYDROGEOLOGY

 

5.1.1                The NENTX site has a variable thickness of superficial deposits across the majority of its area, comprising fill, colluvium and soil derived from in-situ weathering. The solid geology of the site comprises a mixture of volcanic tuff deposits, sightly metamorphosed volcanic tuff deposits and a small area of meta-sedimentary rock. The rockhead levels within the site are largely reflected by the topography, with low-lying valleys having been formed due to the presence of geological faults.

 

Four major faults are presented within the site (see Figure 5.1):

 

Fault 1 is a located along the northern boundary of the study area and striking approximately west-northwest.

 

Fault 2 strikes north-northeast through the study area, most likely extending through the existing waste reception area to the south of the site and then following the topographic valley northeast from this. Previous works has recorded this fault as dipping at 80O to the southeast, with the material on the south eastern side having been downthrown.

 

Fault 3 follows the approximate alignment of the existing haul road through the centre of the site area, trending west-northwest to east-southeast, and extends beyond the site boundaries.

 

Fault 4 is mostly like a large splay fault associated with Fault 2. The main trend of the fault is north-northeast along the topographic valley to the east of Fault 2, with a small potion trending east-northeast to the south of the haul road before joining with Fault 2 in the low-lying area within the southern part of the site.

5.2                    UTILITIES

 

5.2.1                It is known that underground utilities (landfill gas collection pipes, electricity, telecommunications etc.)  exist in the existing infrastructure area of NENT Landfill in Portion D. Also, the new infrastructure area will integrate within the existing NENT supporting facilitates located in Portion D of the site in the future.  The utilities to be provided from existing NENTX include electricity, telecommunication cables, water mains, sewer, storm water drains, landfill gas and leachate pipes etc. along the NENTX. Electricity and telecommunication cables will be laid underground in ducts which could provide a direct man-made pathway from NENT Landfill to NENTX.  A preliminary layout plan for the proposed utility services to NENTX is presented in Figure 5.2.

 

6                       DETAILED DESIGN

6.1                    FOR INFRASTRUCTURE AREA

 

6.1.1                Based on the findings and recommendations of the preliminary QLFGHA of the approved EIA Report, Veolia has incorporated landfill gas control measures in the detailed design of the NENTX infrastructure facilities. This assessment has taken account of these control measures in the evaluation of the landfill gas hazard with respect to the nature and characteristics of the targets. The adequacy of these control measures will be evaluated and if necessary further control measures will be recommended in this Report.

6.2                    DESCRIPTION OF THE INFRASRUCTURE AREA

 

6.2.1                In accordance with the EIA and Specification requirements, the new infrastructure area (see Figure 6.1 - Location of Proposed Infrastructure Buildings and Figure 6.2a to 6.2e - the proposed ground floor plan of the infrastructure area) will integrate within the existing NENT supporting facilities located in Portion D of the site. According to the consultation zone of Guidance Notes (GN), it should be noted that the new infrastructure area is located within 250m from the existing NENT and NENTX waste boundary. Therefore, the key risk source for the new infrastructure area is the NENT and NENTX. The infrastructure area includes the following building/ structures:

 

·         Integrated Office Building

·         Operations and Maintenance Building and Maintenance Workshop Building

·         Fire Services Building

·         Process Building

 

6.2.2                As the Portion D will also house other supporting arrangements such as car parking, vehicle maintenance yards and landfill vehicle wash bay are operated in open space or non-enclosed building, there will be no or very low potential for landfill gas cumulation at these facilities. Therefore, they are not further assessed in this report.

 

6.2.3                The approximate distance from the NENTX waste boundary defined in the GN to the each of the target facilities at the new infrastructure area are presented in Table 6.1. All facilities are operated/managed by Veolia.

 

Table 6.1 Key Target Facilities in the New Infrastructure Area

Key Facilities

Approximately Distance from the NENTX

Distance from NENT

Integrated Office Building

215m

135m

Fire Services Building

205m

165m

Operations and Maintenance Building and Maintenance Workshop Building

105m

100m

Process Building

195m

30m

Remarks: Under Annex 7 of the Technical Memorandum on EIA Process (EIAO-TM) and Landfill Gas Hazard Assessment: Guidance Note, EPD 1997, an evaluation of the potential risk posed by landfill gas is required for any development which is proposed within 250m of the edge of waste, known as Landfill Consultation Zone. As the NENTX proposed infrastructure area(Integrated Office Building, Fire Services Building, Operations and Maintenance Building and Maintenance Workshop Building and Process Building) are falls within the NENT and NENTX Landfill Consultation Zone, a Qualitative Landfill Gas Hazards Assessment (QLFGHA) is required to assess the potential risk due to landfill gas migration from the NENT Landfill/ NENTX(Assessment details please refer to the below Section).

6.3                    CONSTRUCTION METHODOLOGY

 

6.3.1                Simple excavation and slope formations works will be carried out during the construction stage.  The site formation works for the landfill lining system will require some open excavations works due to slightly lower formation level for the basal liner. The temporary works will involve the formation of temporary ditches along the sides of excavations and associated drainage works, and material storage areas.

6.4                    SENSITIVE TARGET FACILITIES FOR LANDFILL GAS RISK

 

Integrated Office Building

 

6.4.1                The Integrated Office Building is designed as 3-storey building, ground floor covering a total area of approximately 500 m2. Ground level rooms include Storage, Laboratory, Female/ Male Toilets, Shower & Lockers, Accessible Toilet, Pantry, M& E Room etc. (see Figure 6.2a). These areas will be provided with mechanical ventilation or air conditioning with natural ventilation. The designed air change for each room are presented in Table 6.2.

 

Table 6.2 Designed Air Change of the Ground Floor Rooms of Integrated Building

No.

Room

No. of Air Change Per Hour (*)

1.

Lobby & Waiting Area (Reception)

5

2.

Storage

6

3.

Laboratory

10

4.

Storage Room (1)

 6

5.

Male Toilet, Shower & Lockers

15

6.

Female Toilet, Shower & Lockers

15

7.

Accessible Toilet

15

8.

Pantry

10

9.

Staff Rest Room

5

10.

Employer/ ER (Open Plan Office)

6

11.

Conference/ Meeting Room

6

12.

Conference/ Meeting Room

6

13.

Conference/ Meeting Room

6

14.

Interview Room

5

15.

M&E Room

10

16.

Special Storage Room cum Monitoring Room

6

Note:

*Refer to fresh air change rate. A higher air change rate is maintained with air re-circulation.

 

Fire & Water Services Building

 

6.4.2                The Fire Services Building is 2-story high structure, ground floor covering a total area of approximately 250 m2. Ground level rooms include Fire Services Control Room, Fire Services Pump and Tank Room, Flushing Water and Tank Room and Sprinkler and Street Hydrant Pump and Tank Room. (seeSee Figure 6.2b). These areas will be provided with mechanical ventilation or air conditioning with natural ventilation. The designed air change for each room is presented in Table 6.3.


Table 6.3 Designed Air Change of the Ground Floor Rooms of Fire & Water Services Building

No.

Room

No. of Air Change Per Hour (*)

1.

FS Control Room

5

2.

FS Pump and Tank Room

5

3.  

Flushing Water and Tank Room

5

4

Sprinkler and Street Hydrant Pump and Tank Room

5

Notes:

*Refer to fresh air change rate. A higher air change rate is maintained with air re-circulation.

 

Operations and Maintenance Building and Maintenance Workshop Building

 

6.4.3                The Operations and Maintenance Building is functional, rectangular 3-storey building, ground floor covering a total area of approximately 200 m2. Ground level rooms include Parts/ Tools Storage, Dry Gas Bottle Room, Plumbing Room, ELE Room and Pumping Room (see Figure 6.2c). These areas will be provided with mechanical ventilation. The designed air change for each room is presented in Table 6.4.

 

Table 6.4 Designed Air Change of the Ground Floor Rooms of Operations and Maintenance Building

No.

Room

No. of Air Change Per Hour (*)

1.

Workshop Area

6

2.

Parts/ Tools Storage

6

3.

Dry Gas Bottle Room

10

4.

Plumbing Room

10

5.

ELE Room

10

Notes:

*Refer to fresh air change rate. A higher air change rate is maintained with air re-circulation.

 

Process Building

 

6.4.4                The Process Building will be constructed with front and rear façades on two different site formation platform levels. The building’s Lower Ground floor will be constructed abutting a retaining wall at its rear and partly adjacent to sloping ground on one side. However, all of the Process Building’s rooms will be located above the respective ground level at the front and rear façades of the building, including the rooms of the Lower Ground floor. The building will house the electrical switch room and workshop in its lower ground floor level; blower room, toilets, changing room etc. on the ground floor. (seeSee Figure 6.2d&e). These areas will be provided with mechanical ventilation or air conditioning with natural ventilation. The designed air change for each room is presented in Table 6.5 & Table 6.6.

 

Table 6.5 Designed Air Change of the Lower Ground Floor Rooms of Process Building

No.

Room

No. of Air Change Per Hour (*)

1.

HV Switch Room

10

2.

CLP Room

10

3.

LV Room LFG

10

4.

Common Process Workshop

10

Notes:

*Refer to fresh air change rate. A higher air change rate is maintained with air re-circulation.

 

Table 6.6 Designed Air Change of the Ground Floor Rooms of Process Building

No.

Room

No. of Air Change Per Hour (*)

1.

Office  

5

2.

Storage (1)

6

3.

Storage (2)

6

5.

Common Pantry

15

6.

Hose Reel Pump Room

10

7.

Blower Room for SBRS

10

8.

SNG Plant Control Room

10

9.

SNG MCC Room

10

10.

Males Showers, Toilets & Lockers

15

11.

Disable Toilet

15

Notes:

*Refer to fresh air change rate. A higher air change rate is maintained with air re-circulation.

7                       QUALITATIVE ASSESSMENT OF RISK DUE TO LANDFILL GAS

7.1                    INTRODUCTION

 

7.1.1                This section reviews the information presented in the preceding sections and evaluates the data presented with reference to the assessment definitions given in the Guidance Note on Landfill Gas Hazard Assessment. The qualitative assessment of the potential hazard from landfill gas to the proposed targets is then concluded.

7.2                    SOURCE

 

7.2.1                The existing NENT Landfill and the NENTX will both be the source of potential risk of landfill gas migration. NENT and NENTX have the same potential for landfill gas generation.  The source of LFG at the existing NENT landfill and extension NENT Landfill are categorised as Medium. The 250m consultation zones for the NENT Landfill and the NENTX are shown in Figure 1.2.

7.3                    NENT LANDFILL

 

7.3.1                As the NENT Landfill is a large operating landfill, the landfill is a significant potential source of landfill gas. The NENT Landfill was designed and constructed to incorporate international best practices to contain, manage and control waste and landfill gas. It is operated by an experienced international waste management contractor.

 

7.3.2                The potential off-site migration of landfill gas is assessed taking into account the comprehensive and highly effective collection and management system installed and operated. It is acknowledged from the NENT Landfill Monthly Reports that the only justifiable exceedance recorded for surface gas monitoring in October to December 1997 were likely due to the proximities of monitoring locations to the active tipping faces. It was also recorded that the frequency of surface gas monitoring had been increased in accordance with the corrective actions when exceedances occurred. Hence, the potential of off-site migration of landfill gas cannot be eliminated. Given the size of the NENT Landfill, the multiple landfill gas controls implemented and the NENT Landfill was classified as a “Medium” source of potential landfill gas risk with reference to the LFG Guidance Note as presented in the approved EIA Report which is also applicable to the latest scheme.

7.4                    NENTX

 

7.4.1                The future landfill extension itself is a source to generate significant amount of LFG during the operation and aftercare phases. LFG hazards may be hazard to front-line workers within the site especially where the LFG is extracted, transported, and processed. With the LFG control measures and Waste to Energy Facility in the future NENTX, it is anticipated that the source of LFG will be properly controlled within the site similar to the operation in existing NENT landfill.

 

7.4.2                The NENTX will be designed as a containment landfill with LFG collection and management systems to eliminate any off-site migration of LFG. By virtue of the effective control and utilisation of LFG being implemented in the existing NENT landfill based on the past monitoring data, it is likely that the NENTX will be designed to adopt similar LFG control measures so as to ensure future landfill extension compliance of environmental and safety requirements.  The source of LFG at the future landfill extension was categorised as Medium.

7.5                    PATHWAY

 

7.5.1                The potential pathways through which landfill gas may enter the NENTX Site are threefold, namely:

 

·         through transmission along natural pathways such as fissures or joints in rock;

 

·         man-made pathways such as through permeable backfill in utilities trenches; or

 

·         a combination of both.

 

The likely potential for each mode of transmission are clearly dependent on the geological conditions, which are discussed below.

7.6                    WITHIN LANDFILL EXTENSION SITE

 

NATURAL PATHWAYS

 

7.6.1                The major concern is the presence of Faults 1 and 3 as shown in Figure 5.1 across the existing NENT Landfill towards the NENTX, which as natural pathways for preferential LFG migration. These pathways of fissured rock are less than 50m to the landfill extension site and are categorised as Very Short/Direct and the superficial deposits located below the formation level to the south of the landfill extension site may act as natural pathways for LFG migration towards the Waste Reception Area of the existing NENT Landfill. These pathways of unsaturated permeable strata are less than 50m to the landfill extension site and are categorised as Very Short/Direct as presented in the approved EIA.

MAN-MADE PATHWAYS

 

7.6.2                There are man-made pathways in the vicinity of the site consisting of services routes leading to the existing landfill. These pathways to sensitive receivers are classified as Very Short/Direct towards the landfill extension site in the approved EIA Report, as landfill workers could be the targets during landfill operation, piping/ conduit construction, and/ or drilling/ boring operation.

 

Also, the potential pathways or sub-surface migration of landfill gas from the NENTX waste boundary to the future infrastructure area are considered to comprise both reclamation fill and the future utilities connecting the infrastructure area. It is known that the new infrastructure area will integrate within the existing NENT supporting facilities located in Portion D of the site in the future and the underground utilities (landfill gas collection pipes, electricity, telecommunications etc.)  to be provide to the NENTX. Among all utilities, electricity and telecommunications cables will provide a direct man-made pathway for the transmission of landfill gas from NENT to NENTX. Therefore, landfill gas control measures such as seal cable duct with bentonite will be implemented to minimise the potential risk.

 

7.6.3                Considering the distance and the presence of possible migration pathways between the NENTX waste boundary and NENTX infrastructure area. And based on the detailed design of the new infrastructure area, the pathway for landfill gas migration from the NENTX waste boundary to individual target at new infrastructure area should be classified as according to the presence of possible migration pathways and distance between the target and the NENTX waste boundary: <50m as Very Short/Indirect, 50-100m as Moderately Short/Indirect, 100-250m as Long/Indirect. (seeSee Table 7.1)

7.7                    OUTSIDE LANDFILL EXTENSION SITE

 

NATURAL PATHWAYS

 

7.7.1                The presence of faults lines in NENT Landfill Extension site are identified as the potential natural pathways for potential LFG migration to the vicinities of sensitive receivers as shown in Figure 5.1. Fault 4 is the nearest fault line to Tong To Shan Tsuen at a distance of ~280m which is classified as “Long/Indirect” pathway extending from the northern bound of the future landfill extension site. Mitigation measures will include installation of proper liner to act as barriers and sealing of faults line ends to prevent off-site LFG migration.

 

MAN-MADE PATHWAYS

 

7.7.2                Although there are man-made pathways in the vicinity of the site consisting of services routes leading to the existing landfill, they are far from sensitive receivers and are classified as Long/Indirect toward the adjacent occupied development in the approved EIA Report.

 

Table 7.1 Classification of Landfill Gas Migration Pathway

Targets

Pathway Description

Classification

1. Integrated Office Building

 

Path length of 100 to 250m for unsaturated permeable soil

Long/Indirect

2. Fire & Water Services building

Path length of 100 to 250m for unsaturated permeable soil

Long/Indirect

3.Operations and Maintenance Building and Maintenance Workshop Building

Path length of 100 to 250m for unsaturated permeable soil

Long/Indirect

4.Process Building

 

Path length of 100 to 250m for unsaturated permeable soil

Long/Indirect

7.8                    TARGETS

 

WITHIN LANDFILL EXTENSION SITE

 

7.8.1                Potential receivers sensitive to LFG hazards associated with the NENT Landfill Extension include the workers and staff of NENT Landfill Extension Site. The targets identified in the latest scheme are presented below.

 

Target 1 - Construction Phase of the NENTX

 

7.8.2                As shown in Figure 1.2, some of NENTX infrastructure site falls within the 250m landfill consultation zone of the NENT Landfill. Excavation for construction of new landfill bowl and deep unventilated excavation works are expected. The excavation area and the minimal confined space and trenches, if any, are at a higher risk of exposure to landfill gas. However, in general, any excavation work or work involving the construction of trenches will use the open cut method, although there may be deep excavations. Landfill gas, if any, migrated to the site can easily be dispersed and diluted in the atmosphere. Construction works involving working in confined spaces will be undertaken by trained workers.

 

The temporary site office (see Figure 7.1) for construction phase will be provided with multiple landfill gas control measures (including provision of mechanical or natural ventilation and continuous gas monitoring system with gas alarm for all occupied on-site buildings). This target was thus classified as “High Sensitivity” in the approved EIA Report which is also applicable for the latest scheme.

 

Target 2 - Operation Phase of the NENTX (Infrastructure Area)

 

7.8.3                All of proposed new infrastructure area of NENTX will be within the 250m Landfill Consultation Zone of the NENTX and existing NENT. The assessment of potential targets for landfill gas sensitivity in the infrastructure area have been selected from the below ground and ground floor rooms of the buildings and structures. Services ducts or other confined spaces at basement or ground floor level and waste reception area of the existing NENT were classified as “high sensitivity” in the approved EIA Report.

 

OUTSIDE LANDFILL EXTENSION SITE

 

7.8.4                According to the Wo Keng Shan Outline Zoning Plan (OZP) S/NE-WKS/10 extracted from the “Statutory Planning Portal” of Planning Department (PlanD) website at https://www2.ozp.tpb.gov.hk/gos/default.aspx?planno=S%2fNE-WKS%2f10&lang=0#, the planned landuse to the south of the landfill extension site consist mainly of “Green Belt” with minor area for “Agriculture” and “Village” Type Development with the landuse governed by the Town Planning Ordinance.

 

7.8.5                The northern part of the consultation zone of NENTX falls within the Tong To Shan Archaeological Site which also imposes restrictions on any proposed development/ re-development.

 

7.8.6                There are 2 nearest LFG receivers outside the NENTX including LFG1 (Wo Keng Shan Tsuen) and LFG2 (Tong To Shan Tsuen. And LFG1 lies within the original 250m consultation zone (at ~100m from the landfill site boundary). It is therefore categorised under “High Sensitivity”) mentioned in approved EIA Report.

 

7.8.7                LFG2 is a village house marginally outside the proposed new demarcation of 250 consultation zone corresponding to the latest footprint of NENTX site area (at ~270m from the NENTX site boundary). Although it is currently abandoned and unoccupied, it will be prudent to pay due attention to the implementation of all necessary protective measures if LFG2 were occupied in future.

 

7.8.8                Based on the guidance given in EPD’s Guidance Note, the sensitivity of all targets in the infrastructure area is summarised in Table 7.2. Multiple options for landfill gas control measures will be utilised in the detailed design, for example:

 

(a)   Gas barrier

 

- impermeable gas membrane to be installed below the base slab of the building; or

 

- the internal floor slab of the ground floor rooms will be painted with low gas permeability paints (see Appendix B for the proposed products to be used); and

 

(b)   Ventilation

 

- ground floor rooms will be provided with mechanical or natural ventilation to prevent potential accumulation of landfill gas; and

 

(c)   Gas alarm

 

- all occupied on-site buildings will be provided with gas alarm (see Appendix C for the common type product to be used);

- check the fixed gas detector by the calibration gas at least once per quarter in order to

verify the accuracy and alarm function of the fixed gas detector;

- clear calibration / checking record will be maintained; and

- 2 action trigger levels will be set up (If the first action trigger level to be set at 10% LEL is

triggered, the Registered Safety Officer (RSO) will be informed. If the second action

trigger level to be set at 20% LEL is trigger, all personnel within the permanent building will

be evacuated.

                                                                                                                                                                                                                     

7.8.9                Specification of gas protection measures are shown in Figure 7.2. Taking into account the combination of landfill gas control measures that has been incorporated in the detailed design of the NENTX infrastructure area, Veolia’s expertise in landfill operation who is fully aware of the potential landfill gas hazards and with their staff well trained on the potential hazards relating to landfill gas and the specific safety procedures, the targets in the NENTX infrastructure area is conservatively classified as low.


Table 7.2 Sensitivity of all Targets in the Infrastructure Area

Targets

Description/ Proposed Mitigation Measures

Sensitivity

Preliminary analysis

With incorporation of Control Measures in the Detailed Design

Target 2.1a - Storage Room, Employer/ ER Office, Conference/ Meeting Room and Special Storage Room cum Monitoring Room of Integrated Office Building

Mitigation Measures:
- Above ground room
- Air conditioning with natural ventilation
- With gas-proofing coating apply
on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

Low

Target 2.1b - Lobby & Waiting Area, Staff Rest Room and Interview Room of Integrated Office Building

Mitigation Measures:
- Above ground room
- Air conditioning with natural ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

Low

Target 2.1c - Female/ Male Changing Room & Toilets, Accessible Toilet of Integrated Office Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access to staff only

High

Low

Target 2.1d - Laboratory and Pantry of Integrated Office Building

Mitigation Measures:
- Above ground room
- - Air conditioning with natural ventilation and with mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access to Veolia and EPD staff and invited guests/ visitors

High

Low

Target 2.1e - M&E Room of Integrated Office Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

 

 

 

Low

Target 2.2a - Fire Services Control Room, Fire Services Pump & Tank Room and Sprinkler and Street hydrant Pump & Tank Room of Fire & Water Services Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation as per Fire Services Department requirement
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

Low

Target 2.2b - Flushing Water & Tank Room and Sprinkler & Street Hydrant Pump & Tank Room of Fire & Water Services Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

Low

Target 2.3a - Workshop Area, Parts/ Tools Storage of Operation & Maintenance Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised personnel

High

Low

Target 2.3b - Dangerous Goods Storeroom, Dry Gas Bottle Room, Plumbing Room and ELE Room of Operation & Maintenance Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
for Plumbing Room and ELE Room
- Air conditioning with natural ventilation for Dangerous Goods Storeroom and Dry Gas Bottle Room
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low

Target 2.4a - HV Switch Room of Process Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With underground utilities connection
- With ignition source
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low

Target 2.4b – CLP Room of Process Building

Mitigation Measures:
- Above ground room
- With ventilation system as per CLP requirement
- With underground utilities connection
- With ignition source
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low

Target 2.4c - LV Room LFG of Process Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With underground utilities connection
- With ignition source
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low

Target 2.4d - Common Process Workshop of Process Building

Mitigation Measures:
- Above  ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low

Target 2.4e - (Infrastructure Area of the NENTX - Office of Process Building)

(category: Low sensitivity)

Mitigation Measures:
- Above ground room
- Air conditioning with natural ventilation
- With gas-proofing coating apply
on top of all ground floor slabs
- With gas alarm
- Restricted access to staff only

High

Low

Target 2.4f - Storage Room of Process Building

Mitigation Measures:
- Above ground room
- Air conditioning with natural ventilation and with mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by authorised person

High

Low

Target 2.4g - Common Pantry, Males Showers, Toilets & Locker and Disable Toilet of Process Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access to staff only

High

Low

Target 2.4h - Hose Reel Pump Room, Blower Room, SNG Plant Control Room, SNG MCC Room of Process Building

Mitigation Measures:
- Above ground room
- With mechanical ventilation
- With gas-proofing coating apply on top of all ground floor slabs
- With gas alarm
- Restricted access by competent person

High

Low


 

7.9                    SOURCE-PATHWAY-TARGET ANALYSIS

 

7.9.1                On the basis of the source, pathways and targets identified above, a source-pathway-target analysis for the latest scheme has been undertaken and is presented in Table 7.3 according to the assessment framework described in EPD’s Guidance Notes. Different combination of source, pathway, and target result in a range of overall potential hazards.

 

7.9.2                The source-pathway-target analysis shows that landfill gas risk posed by the NENT Landfill and the NENTX under the latest scheme is low to high within the NENTX waste boundary during both the construction and operation phases. Whereas the risk posed by the NENTX to NENTX infrastructure area is low with respect to the nature of the targets and the gas control measures incorporated in the detailed design of the buildings of the new infrastructure area.


Table 7.3 Qualitative Assessment of Landfill Gas Hazard Associated with the NENTX in the Latest Scheme

Source

Pathway

Target

Qualitative Risk

NENT Landfill - potential for gas generation over time, but comprehensive and proven mitigation installed.

(category: medium)

Fissured rock, Fault 1 and 3 across the NENT Landfill towards the NENTX with potential natural pathways for preferential LFG migration, distance <50m

Superficial deposits below the formation level to the south of the landfill extension fill for LFG migration towards the Waste Reception Area of the existing NENT landfill, distance <50m

(category: Very short/Direct)

Target 1a - Construction Phase of the NENTX –

·                     Excavation for construction of new landfill bowl

(category: High sensitivity)

High

NENT Landfill - potential for gas generation over time, but comprehensive and proven mitigation installed.

(category: medium)

Fissured rock, Fault 1 and 3 across the NENT Landfill towards the NENTX with potential natural pathways for preferential LFG migration, distance <50m

Superficial deposits below the formation level to the south of the landfill extension fill for LFG migration towards the Waste Reception Area of the existing NENT landfill, distance <50m

(category: Very short/Direct)

Target 1b - Construction Phase of the NENTX –

·                     Deep unventilated excavations and trenches for utility installation and basement excavation

(category: High sensitivity)

High

NENT Landfill - potential for gas generation over time, but comprehensive and proven mitigation installed.

(category: medium)

 

 

 

 

Fissured rock, Fault 1 and 3 across the NENT Landfill towards the NENTX with potential natural pathways for preferential LFG migration, distance about 100-250m

Superficial deposits below the formation level to the south of the landfill l extension fill for LFG migration towards the Waste Reception Area of the existing NENT landfill, distance about 100-250m

(category: Long/Indirect)

Target 1c - Construction Phase of the NENTX –

·                     Outbuilding, sheds and temporary structures such as construction site offices

(category: Low sensitivity)

Very Low

NENT Landfill - potential for gas generation over time, but comprehensive and proven mitigation installed.

 

(category: medium)

 

Sub-surface soil, reclamation fill materials of the unsaturated zone between the NENT Landfill and NENTX with potential direct anthropogenic conducts, distance to waste boundary, about 100-250m

 

(category: Long/Indirect)

Target 2.1a - (Infrastructure Area of the NENTX - Storage Room, Employer/ ER Office, Conference/ Meeting Room and Special Storage Room cum Monitoring Room of Integrated Office Building)

(category: Low sensitivity)

Very Low

Target 2.1b - (Infrastructure Area of the NENTX - Lobby & Waiting Area, Staff Rest Room and Interview Room of Integrated Office Building)

(category: Low sensitivity)

Very Low

Target 2.1c - (Infrastructure Area of the NENTX - Female/ Male Changing Room & Toilets, Accessible of Integrated Office Building)

(category: Low sensitivity)

Very Low

Target 2.1d - (Infrastructure Area of the NENTX - Laboratory, Pantry and M&E Room of Integrated Office Building)

(category: Low sensitivity)

Very Low

Target 2.1e - (Infrastructure Area of the NENTX - M&E Room of Integrated Office Building)

(category: Low sensitivity

Very Low

Target 2.2a - (Infrastructure Area of the NENTX - Fire Services Control Room, Fire Services Pump & Tank Room and Sprinkler & Street hydrant Pump & Tank Room of Fire & Water Services Building)

(category: Low sensitivity)

Very Low

Target 2.2b - (Infrastructure Area of the NENTX - Flushing Water & Tank Room and Sprinkler & Street Hydrant Pump & Tank Room of Fire & Water Services Building)

(category: Low sensitivity)

Very Low

Target 2.3a - (Infrastructure Area of the NENTX - Workshop Area, Parts/ Tools Storage of Operation & Maintenance Building)

(category: Low sensitivity)

Very Low

Target 2.3b - (Infrastructure Area of the NENTX - Dry Gas Bottle Room, Plumbing Room and ELE Room of Operation & Maintenance Building)

(category: Low sensitivity)

 

Very Low

Sub-surface soil, reclamation fill materials of the unsaturated zone between the NENT Landfill and NENTX with potential direct anthropogenic conducts, distance to waste boundary, about <50m

 

(category: Very short/Direct)

 

 

 

 

 

 

 

 

Target 2.4a - (Infrastructure Area of the NENTX - HV Switch Room of Process Building)

(category: Low sensitivity)