The SENT Landfill Extension (SENTX) forms an integral part in the Strategic Plan in maintaining the continuity of landfill capacity in the Hong Kong for the cost-effective and environmentally satisfactory disposal of waste. ERM-Hong Kong, Limited (ERM) was commissioned to undertake the role of Environmental Team (ET) for the construction, operation/restoration and aftercare of SENTX Project (“the Project”) in accordance with the requirements specified in the Environmental Permit (EP), updated Environmental Monitoring and Audit (EM&A) Manual, the approved Environmental Impact Assessment (EIA) Report of the Project taking account of the latest design and other relevant statutory requirements.

In accordance with the updated EM&A Manual of the Project, pre-operation phase baseline monitoring was undertaken for the Project prior to commencement of the operation phase, which is scheduled to commence in late November 2021. In accordance with the updated EM&A Manual, the pre-operation phase baseline monitoring covered the following components:

Ÿ Air Quality (Dust);

Ÿ Air Quality (Ambient Volatile Organic Compounds (VOCs), Methane, Ammonia and Hydrogen Sulphide (H₂S));

Ÿ Groundwater Quality; and

Ÿ Landfill Gas.

Pre-operation phase baseline dust monitoring was conducted at 4 monitoring stations (AM1 to AM4) between 21 May and 12 June 2021, for at least 14 consecutive days before the commencement of the operation phase. The monitoring results are considered representative of the baseline condition prior to the operation phase. The Action and Limit Levels for dust (in terms of 24-hour Total Suspended Particulate (TSP) levels) were established in accordance with the updated EM&A Manual.

Baseline ambient VOCs, methane, ammonia and H₂S monitoring was conducted at 4 monitoring stations (AM1 to AM4) between 27 May 2020 and 17 February 2021, at quarterly intervals. The baseline monitoring results are considered representative of the current ambient VOCs, methane, ammonia and H₂S levels. Limit Levels for ambient VOCs, methane, ammonia and H₂S were established in accordance with the updated EM&A Manual.

Pre-operation phase baseline groundwater monitoring was conducted at 14 monitoring stations (MWX-1 to MWX-14) between 24 March 2020 and 9 March 2021, at monthly intervals. The baseline groundwater monitoring results are considered representative of the current groundwater quality levels. In accordance with the updated EM&A Manual, the Limit Levels for ammoniacal-nitrogen and COD were established based on the baseline monitoring results.

Baseline landfill gas monitoring was conducted at 36 monitoring stations (LFG1 to LFG24, P7 to P9, GP1 to GP7, GP12 and GP15) between 24 March 2020 and 26 March 2021, at monthly intervals. Owing to the unexpected elevated levels of methane detected during the pre-operation baseline monitoring, additional landfill gas monitoring was conducted in October to December 2020 and March to November 2021 to obtain additional monitoring data to establish the baseline condition. Limit Levels for methane and carbon dioxide were established based on both the baseline and additional landfill gas monitoring results.

1 Introduction

1.1 Background

The SENT Landfill Extension (SENTX) forms an integral part in the Strategic Plan in maintaining the continuity of landfill capacity in the Hong Kong for the cost-effective and environmentally satisfactory disposal of waste. The Environmental Impact Assessment (EIA) Report and the associated Environmental Monitoring and Audit (EM&A) Manual for the construction, operation, restoration and aftercare of the SENTX (hereafter referred to as “the Project”) have been approved under the Environmental Impact Assessment Ordinance (EIAO) in May 2008 (Register No.: AEIAR-117/2008) (hereafter referred to as the approved EIA Report) and an Environmental Permit (EP-308/2008) (EP) was granted by the Director of Environmental Protection (DEP) on 5 August 2008.

Since then, applications for Variation of an Environmental Permit (No. VEP-531/2017) were submitted to EPD and the Variation of Environmental Permits (EP-308/2008/A and EP-308/2008/B) were granted on 6 January 2012 and 20 January 2017, respectively, as the Hong Kong SAR Government has decided to reduce the scale of the design scheme of SENTX assessed in the approved EIA Report and SENTX will only receive construction waste. In line with the changes proposed by EPD, the landfill contractor for SENTX, Green Valley Landfill Limited (GVL), has developed a final scheme for SENTX (hereafter “the latest design”) in 2016. This latest design complies with the requirements in the Technical Memorandum of the Environmental Impact Assessment Process (EIAO-TM) and the current EP (EP-308/2008/B) conditions. A Further Environmental Permit (FEP-01/308/2008/B) (FEP) was granted to GVL on 16 May 2018.

ERM-Hong Kong, Limited (ERM) and Meinhardt Infrastructure and Environment Limited (Meinhardt) were commissioned to undertake the roles of Environmental Team (ET) and the Independent Environmental Checker (IEC), respectively, to implement the EM&A programme for the Project in accordance with the requirements specified in the EP, updated EM&A Manual ([1]), approved EIA Report ([2]) taking account of the latest design and other relevant statutory requirements.

1.2 Project Description

The SENTX is a piggyback landfill, occupying the southern part of the existing SENT Landfill (including its infrastructure area) and 13 ha of Tseung Kwan O (TKO) Area 137. A layout plan of the SENTX is shown in Figure 1.1. Under the latest design, the SENTX has a net void capacity of about 6.5 Mm³ and provides an additional lifespan of about 6 years, commencing operation upon exhaustion of the SENT Landfill (scheduled to commence operation in late November 2021). In accordance with the current EP, SENTX will receive construction waste only.

The key elements of the construction, operation/restoration and aftercare of the SENTX are described below.

Construction of SENTX

Construction works will commerce about two years prior to the operation of the SENTX. The major construction works includes:

· Site formation at the TKO Area 137 and the existing infrastructure area at SENT Landfill;

· Construction of surface and groundwater drainage systems;

· Construction of the leachate containment and collection systems;

· Construction of new leachate and landfill gas treatment facilities, site offices, maintenance yards at the new infrastructure area;

· Construction of new pipelines to transfer the leachate and landfill gas collected from the existing SENT Landfill to the treatment facilities at the new infrastructure area;

· Construction of the site access and new waste reception facilities; and

· Demolition of the facilities at the existing SENT Landfill infrastructure area.

Operation and Restoration of SENTX

The leachate and landfill treatment facilities will be commissioned and the first phase of the SENTX will start operation upon exhaustion of the SENT Landfill. Construction of the leachate containment and collection system for the subsequent phases will continue while the first phase of the SENTX is in operation. The areas that reach the finished profile will be progressively restored and landscaped.

Aftercare of SENTX

Upon the completion of final filling and restoration, the aftercare of the SENTX will begin and last for 30 years. Regular site maintenance, collection and treatment of landfill gas and leachate will be undertaken during the aftercare period to ensure that the landfill complies with the required environmental performance requirements and is safe. The restored landfill may then be developed for various passive beneficial uses (e.g. open spaces, walking trails, etc.).

Implementation Programme

The key implementation milestones of the Project are indicatively summarised in Table 1.1.

Table 1.1 Estimated Key Dates of Implementation Programme

Key Stage of the Project	Indicative Date
Start construction	2 January 2019
Commissioning of new infrastructure facilities	2020
Demolition of existing infrastructure facilities	2021
Start waste intake at SENTX	2021 or upon exhaustion of SENT Landfill, scheduled in late November 2021
Stop taking waste at SENTX	2027
End of aftercare for SENTX	2057

1.3 Purpose of the Pre-operation Phase Baseline Monitoring Report for SENTX

The purpose of this Pre-operation Phase Baseline Monitoring Report for SENTX development is to present the baseline levels of air quality (dust, ambient VOCs, methane, ammonia and H₂S), groundwater quality and landfill gas at the designated monitoring locations around the Project Site area prior to the commencement of operation phase. Such baseline conditions will be used as the basis for assessing environmental impacts, if any, and compliance monitoring during the operation/ restoration phase of the Project.

In accordance with the Section 11.2 of the updated EM&A Manual, the Pre-operation Phase Baseline Monitoring Report shall be certified by the ET Leader and verified by the IEC and submitted to EPD within 10 days of completion of the baseline monitoring and laboratory testing.

1.4 Structure of the Pre-operation Phase Baseline Monitoring Report for SENTX

The remainder of the Pre-operation Phase Baseline Monitoring Report for SENTX is structured as follows:

· Section 2 presents the methodology and findings of the baseline air quality (dust) monitoring;

· Section 3 presents the methodology and findings of the baseline air quality (ambient VOCs, methane, ammonia and H₂S) monitoring;

· Section 4 presents the methodology and findings of the baseline groundwater quality monitoring;

· Section 5 presents the methodology and findings of the baseline landfill gas monitoring; and

· Section 6 summarises the baseline monitoring events.

2 Air Quality (DUst)

2.1 Monitoring Requirement

According to the updated EM&A Manual of the Project, baseline air quality monitoring (dust, in term of Total Suspended Particulates (TSP)) shall be carried out prior to the commissioning of the operation phase to establish the baseline levels for operation phase. 24-hour TSP levels should be monitored at the four designated monitoring locations along the site boundary (i.e. AM1, AM2, AM3 and AM4) for at least 14 consecutive days before the commencement of the operation phase. Earthworks and laying of liner have been completed before the baseline monitoring and the site condition was considered representative of the baseline condition prior to the operation phase. Details of the pre-operation phase baseline dust monitoring are presented in the following sections.

2.2 Monitoring Equipment

High volume air samplers (HVSs) in compliance with the specifications listed under Section 3.2.2 of the updated EM&A Manual were used to measure 24-hour TSP levels at the dust monitoring locations. The HVSs were calibrated upon installation and maintenance to check the validity and accuracy of the results.

Table 2.1 summarises the equipment used in the pre-operation phase baseline dust monitoring programme. Copies of the calibration certificates for the equipment are presented in Annex A1.

Table 2.1 Dust Monitoring Equipment

Equipment	Monitoring Station	Model
HVS	AM1	Tiseh TE-5170 (S/N: 1190)
HVS	AM2	Tiseh TE-5170 (S/N: 1047)
	AM3	Tiseh TE-5170 (S/N: 1258)
	AM4	Tiseh TE-5170 (S/N: 1101)
Calibrator	All stations	Tisch TE-5025A (S/N: 1941)

2.3 Monitoring Locations

Pre-operation baseline dust monitoring for the Project was conducted at four monitoring stations along the site boundary (i.e. AM1, AM2, AM3 and AM4). Locations of the four monitoring locations are shown in Figure 2.1.

2.4 Monitoring Parameters and Frequency

The monitoring parameters and frequency of pre-operation phase baseline dust monitoring are presented in Table 2.2.

Table 2.2 Frequency and Parameters of Pre-operation Phase Baseline Dust Monitoring

Monitoring Station	Location	Parameter	Frequency
AM1	SENTX Site Boundary (North)	24-hour TSP	At least 14 consecutive days prior to the commencement of the operation phase
AM2	SENTX Site Boundary (West, near DP3)
AM3	SENTX Site Boundary (West, near RC15)
AM4	SENTX Site Boundary (West, near EPD building)

2.5 Monitoring Methodology

The 24-hour TSP levels were measured by the HVSs in accordance with procedures specified in the Manufacturer’s Instruction Manual. The procedures are described as follows:

Ÿ Prior to the commencement of the dust sampling, set the flow rate of the HVSs (between 0.6m³ /min and 1.7m³ /min.);

Ÿ Use fiberglass filters (Whatman G653) for TSP sampling;

Ÿ Check the power supply to ensure the sampler works properly;

Ÿ On sampling, operate the sampler for 5 minutes to establish thermal equilibrium before placing any filter media at designated air monitoring station;

Ÿ Remove the filter holding frame by loosening the four nuts and carefully center a weighted and conditioned filter with the stamped number upwards, on a supporting screen;

Ÿ Align the filter on the screen so that the gasket forms an air-tight seal on the outer edges of the filter and tighten the filter holder frame to the filter holder with swing bolts. The applied pressure should be sufficient to avoid air leakage at the edges;

Ÿ Set the programmable timer for a sampling month of 24 hours. Record the information on the record sheet, which includes the starting time, the weather condition and the filter number (the initial weight of the filter paper can be found out by using the filter number);

Ÿ After sampling, transfer the filter from the filter holder of the sampler to a sealed plastic bag and send to the laboratory for weighting. The elapsed time is also recorded; and

Ÿ Before weighting, equilibrate all filters in a desiccator for 24 hours with the temperature of 25°C ± 3°C and the relative humidity of <50% ± 5%.

2.6 Meteorological Data

Meteorological data obtained from the on-site meteorological monitoring station at the existing SENT landfill were used for the dust monitoring and are shown in Annex A2. It is considered that meteorological data obtained at the existing on-site meteorological monitoring station are representative of the Project Site area and could be used for the baseline and operation/restoration phase dust monitoring programme for the Project. On-site meteorological monitoring was suspended from 7 June to 11 June 2021 due to the removal works of the meteorological station to the new location. Meteorological data obtained from Hong Kong Observatory in June 2021 are also presented in Annex A2. At the time of reporting, the daily extract of meteorological observations at Tseung Kwan O Station (the nearest weather station monitoring prevailing wind direction and mean wind speed) in June 2021 is not available on Hong Kong Observatory website.

2.7 Baseline Monitoring Results

Pre-operation phase baseline dust monitoring was conducted at 4 monitoring stations (AM1, AM2, AM3 and AM4) between 21 May and 12 June 2021. The monitoring schedule is shown in Annex A3.

The baseline dust monitoring results are summarised in Table 2.3. The detailed 24-hour TSP monitoring results and graphical presentations are presented in Annex A4. The weather was mainly sunny and fine with occasional rainfall events during the baseline monitoring period. The operations of the existing SENT landfill and the TKO Area 137 Fill Bank are identified as the influencing factors which may affect the results of pre-operation phase baseline monitoring.

Table 2.3 Summary of Baseline 24-hour TSP Monitoring Results

Monitoring Station	Average 24-hr TSP Concentration (µg m^-3) (Range in bracket) ^(a)
AM1 – SENTX Site Boundary (North)	50 (26 – 83)
AM2 – SENTX Site Boundary (West, near DP3)	85 (40 – 196)
AM3 - SENTX Site Boundary (West, near RC15)	89 (29 – 239)
AM4 - SENTX Site Boundary (West, near EPD building)	79 (28 – 162)
Note: (a) No exceedance of Limit Levels for 24-hour TSP monitoring (refer to Table 2.4) was recorded during the pre-operation phase baseline monitoring.

2.8 Action and Limit Levels

The Action and Limit Levels were established in accordance with the updated EM&A Manual. The pre-operation baseline dust monitoring results should be referenced during the compliance check in the operation/restoration phase monitoring. Table 2.4 presents the Action and Limit Levels for dust during operation/ restoration phase of the Project.

Table 2.4 Action and Limit Levels for 24-hour TSP

Monitoring Station	Action Level	Limit Level
AM1 – SENTX Site Boundary (North)	260 µg m-³	260 µg m-³
AM2 – SENTX Site Boundary (West, near DP3)
AM3 - SENTX Site Boundary (West, near RC15)
AM4 - SENTX Site Boundary (West, near EPD building)

2.9 Event and Action Plan

Should non-compliance of the air quality criteria occur, actions in accordance with the Event and Action Plan in Table 2.5 shall be carried out.

3 Air Quality (Ambient VOCs, Methane, Ammonia and H₂S)

3.1 Monitoring Requirement

According to the updated EM&A Manual of the Project, ambient VOCs, methane, ammonia and H₂S baseline monitoring shall be conducted at the four monitoring locations along the site boundary (i.e. AM1, AM2, AM3 and AM4) at quarterly intervals for a period of 12 months prior to waste filling to establish the baseline ambient VOCs, methane, ammonia and H₂S concentrations prior to landfilling operation. Details of the ambient VOCs, methane, ammonia and H₂S baseline monitoring are presented in the following sections.

3.2 Monitoring Equipment

VOCs

Vacuum canisters fixed with a flow controller were used to collect VOCs gas samples for laboratory analysis.

Methane

Ambient air samples was captured into inert sample containers (i.e. Tedlar bags) for direct analysis using gas chromatography.

Ammonia

Sulphuric acid–treated silica gel sampling tubes was used to collect samples for the laboratory analysis for measuring ammonia concentrations.

H₂S

Cadmium hydroxide solution was used as the absorbing solution to collect H₂S in air with mid-get impringer. The air sampling flow rate was set at 1.5 L/min.

3.3 Monitoring Locations

Ambient VOCs, methane, ammonia and H₂S baseline monitoring for the Project was conducted at four monitoring stations along the Project Site boundary (i.e. AM1, AM2, AM3 and AM4). Locations of the four monitoring locations are shown in Figure 2.1.

3.4 Monitoring Parameters and Frequency

The monitoring parameters and frequency of ambient VOCs, methane, ammonia and H₂S baseline monitoring are presented in Table 3.1.

Table 3.1 Frequency and Parameters of Ambient VOCs, Methane, Ammonia and H₂S Baseline Monitoring

Monitoring Station

Location

Frequency

Parameter

AM1

SENTX Site Boundary (North)

Quarterly, for a period of 12 months prior to waste filling

· A suite of VOCs ^(a)

· Methane

· Ammonia

· H₂S

AM2

SENTX Site Boundary (West, near DP3)

AM3

SENTX Site Boundary (West, near RC15)

AM4

SENTX Site Boundary (West, near EPD building)

Note:

(a) A suite of VOCs includes:

· Trichloroethylene

· Vinyl chloride

· Methylene chloride

· Chloroform

· 1,2-dichloroethane

· 1,1,1-trichloroethane

· Carbon tetrachloride

· Tetrachloroethylene

· 1,2-dibromoethane

· Benzene

· Toluene

· Carbon disulphide

· Propyl benzene

· Ethyl benzene

· Butyl benzene

· Xylenes

· Decanes

· Undecane

· Limonene

· Terpenes

· Ethanol

· Butan-2-ol

· Dimethylsulphide

· Methyl propionate

· Ethyl propionate

· Propyl propionate

· Butyl acetate

· Ethyl butanoate

· Dichlorobenzene

· Methyl butanoate

· Dipropyl ether

· Methanethiol

· Ethanethiol

· Butanethiol

· Methanol

· Heptanes

· Octanes

· Nonanes

· Dichlorodifluoro-methane

3.5 Monitoring Methodology

3.5.1 Sampling Procedures

VOCs

Ambient air samples were drawn into the pre-cleaned and vacuum canister directly when the valve of the flow controller (with preset flow rate) was opened. After sampling, the valve will be closed manually and the canister with VOCs gas samples were transported for laboratory analysis.

Methane

Pre-cleaned Tedlar bag was placed in the vacuum chamber. Ambient air was collected in the Tedlar bag under the vacuum condition when the pump is switched on. The Tedlar bag was filled up to 90% of total capacity to avoid leakage and bag deformation. After sampling, pump is switched off and the valve of Tedlar bag was closed manually. The air samples were transported back to laboratory for analysis.

Ammonia

Calibrated personal air pump was used to pump the air through a sulfuric acid-treated silica gel sorbent tube. Gaseous ammonia in air was then trapped in the sorbent tube. The tube was transported back to laboratory for analysis.

H₂S

H₂S in air is collected in mid-get impingers by aspirating a measured volume of air through an alkaline suspension of cadmium hydroxide (as the absorbing solution). The sulphide is precipitated as cadmium sulphide to prevent air oxidation of the sulphide. Arabinogalactan is added to the cadmium hydroxide slurry prior to sampling to minimize photo-decomposition of the precipitated cadmium sulphide. The solution is transported back to laboratory for analysis.

All air samples collected for laboratory analysis were transported to the laboratory within 24 hours and analysed within 48 hours.

3.5.2 Laboratory Analytical Methods

The testing of parameters presented in Table 3.1 for all stations was conducted by ALS Technichem (HK) Pty Ltd. (HOKLAS Registration No. 066). Comprehensive quality assurance and control procedures were in place in order to ensure quality and consistency in results. The analytical methods and detection limits for VOCs, methane, ammonia and H₂S as required in the updated EM&A Manual with incorporation of the proposed updates under the Amendment Summary approved by EPD on 15 June 2020 are provided in Table 3.2.

Table 3.2 Analytical Methods and Detection Limits for VOCs, Methane, Ammonia and H₂S

Analytical Parameters	Analytical Method	Detection Limit
Methane	ASTM D1945-03/ GC-TCD & FID	0.0001%
Ammonia	NIOSH 6015	0.02 mg m^-3
Methanethiol	USEPA TO-14A/ GCMS with pre-concentrator	27 ppb
Ethanethiol	USEPA TO-14A/ GCMS with pre-concentrator	1,400 ppb
Butanethiol	USEPA TO-14A/ GCMS with pre-concentrator	1,400 ppb
Trichloroethylene	USEPA TO-14A/ GCMS with pre-concentrator	0.6 ppb
Vinyl Chloride	USEPA TO-14A/ GCMS with pre-concentrator	2.0 ppb
Benzene	USEPA TO-14A/ GCMS with pre-concentrator	2.0 ppb
Methylene Chloride	USEPA TO-14A/ GCMS with pre-concentrator	1.0 ppb
Chloroform	USEPA TO-14A/ GCMS with pre-concentrator	0.8 ppb
1,2-dichloroethane	USEPA TO-14A/ GCMS with pre-concentrator	0.2 ppb
Carbon tetrachloride	USEPA TO-14A/ GCMS with pre-concentrator	0.2 ppb
Tetrachloroethylene	USEPA TO-14A/ GCMS with pre-concentrator	0.2 ppb
1,1,1- trichloroethane	USEPA TO-14A/ GCMS with pre-concentrator	0.5 ppb
1,2-dibromoethane	USEPA TO-14A/ GCMS with pre-concentrator	0.5 ppb
Toluene	USEPA TO-14A/ GCMS with pre-concentrator	0.5 µg m^-3
Carbon disulphide	USEPA TO-14A/ GCMS with pre-concentrator	0.5 µg m^-3
Propyl benzene	USEPA TO-14A/ GCMS with pre-concentrator	0.8 µg m^-3
Ethyl benzene	USEPA TO-14A/ GCMS with pre-concentrator	0.5 µg m^-3
Butyl benzene	USEPA TO-14A/ GCMS with pre-concentrator	1 µg m^-3
Xylenes	USEPA TO-14A/ GCMS with pre-concentrator	0.5 µg m^-3
Decanes	USEPA TO-14A/ GCMS with pre-concentrator	0.7 µg m^-3
Undecane	USEPA TO-14A/ GCMS with pre-concentrator	1.2 µg m^-3
Limonene	USEPA TO-14A/ GCMS with pre-concentrator	0.4 µg m^-3
Terpenes	USEPA TO-14A/ GCMS with pre-concentrator	0.8 µg m^-3
Ethanol	USEPA TO-14A/ GCMS with pre-concentrator	3.8 µg m^-3
Butan-2-ol	USEPA TO-14A/ GCMS with pre-concentrator	0.61 µg m^-3
Dimethylsulphide	USEPA TO-14A/ GCMS with pre-concentrator	0.2 µg m^-3
Methyl propionate	USEPA TO-14A/ GCMS with pre-concentrator	0.72 µg m^-3
Ethyl propionate	USEPA TO-14A/ GCMS with pre-concentrator	0.84 µg m^-3
Propyl propionate	USEPA TO-14A/ GCMS with pre-concentrator	0.95 µg m^-3
Butyl acetate	USEPA TO-14A/ GCMS with pre-concentrator	0.95 µg m^-3
Ethyl butanoate	USEPA TO-14A/ GCMS with pre-concentrator	0.95 µg m^-3
Dichlorobenzene	USEPA TO-14A/ GCMS with pre-concentrator	1 µg m^-3
Methyl butanoate	USEPA TO-14A/ GCMS with pre-concentrator	0.84 µg m^-3
Dipropyl ether	USEPA TO-14A/ GCMS with pre-concentrator	0.84 µg m^-3
Methanol	USEPA TO-14A/ GCMS with pre-concentrator	2.6 µg m^-3
Heptanes	USEPA TO-14A/ GCMS with pre-concentrator	0.82 µg m^-3
Octanes	USEPA TO-14A/ GCMS with pre-concentrator	0.93 µg m^-3
Nonanes	USEPA TO-14A/ GCMS with pre-concentrator	0.9 µg m^-3
Dichlorodifluoro-methane	USEPA TO-14A/ GCMS with pre-concentrator	0.6 µg m^-3
H₂S	ISC Method 701	10 ppb

3.6 Action and Limit Levels

The Limit Levels are established in accordance with the approved updated EM&A Manual and are defined as WHO/USEPA/CARB’s ambient criteria if available or the odour thresholds or 1% of Workplace Exposure Limit (WEL) as stipulated in the “UK Health and Safety Executive (HSE) EH 40/2005 Workplace Exposure Limits”, whichever is lower. The pre-operation baseline ambient VOCs, methane, ammonia and H₂S monitoring results should be referenced during the compliance check in the operation/restoration phase monitoring. Table 3.3 presents the Limit Levels for ambient VOCs, methane, ammonia and H₂S monitoring during operation/ restoration phase of the Project. The detailed calculation of the Limit Levels are presented in Annex B3.

Taking into account the elevated background levels of Ethanol detected during the pre-operation baseline monitoring and the analytical detection limit of H₂S, it is proposed to establish the Limit Levels of Ethanol and H₂S from the available WHO/USEPA/CARB’s ambient criteria and 1% of WEL as stipulated in the “UKHSE EH 40/2005 Workplace Exposure Limits”, whichever is lower.

It is noted that if there is no relevant WHO/USEPA/CARB’s ambient criteria, odour thresholds and WEL available for concerned parameters. The parameters are considered to have insignificant environmental and health risk, and Limit Levels of these parameters are therefore not applicable for the operation/ restoration phase monitoring.

Table 3.3 Limit Levels for Ambient VOCs, Methane, Ammonia and H₂S Monitoring

3.7 Baseline Monitoring Results

Pre-operation phase baseline ambient VOCs, methane, ammonia and H₂S monitoring was conducted at 4 monitoring locations (AM1, AM2, AM3 and AM4) between 27 May 2020 and 17 February 2021. The monitoring schedule is shown in Annex B1.

The baseline ambient VOCs, methane, ammonia and H₂S monitoring results are summarised in Table 3.4. The detailed monitoring results at each monitoring station are presented in Annex B2.

The operations of the existing SENT landfill, the TKO Area 137 Fill Bank and the TKO Third Industrial Estate and the ambient atmosphere were noted as the possible influencing factors which may affect the baseline monitoring results.

Table 3.4 Summary of Baseline VOCs, Methane, Ammonia and H₂S Monitoring Results

			Average Concentration(Range in bracket)^(a)
Parameters	Units	Limit Level (µg m-³)	AM1	AM2	AM3	AM4
Methane	% (v/v)	NA	0.0007 (<0.0001 - 0.0015)	0.0002 (<0.0001 - 0.0002)	0.0002 (<0.0001 - 0.0002)	0.0002 (<0.0001 - 0.0002)
Ammonia	mg m^-³	180	0.03 (<0.01 - 0.08)	0.02 (<0.01 - 0.07)	0.03 (<0.01 - 0.07)	0.02 (<0.01 - 0.04)
H₂S	µg m^-³	42 ^(a)	<14	<14	<14	<14[FW1] [AL2]
Dichlorodifluoro-methane	µg m^-³	NA	2.1 (1.4 - 2.7)	2.0 (1.3 - 2.7)	2.0 (1.4 - 2.8)	1.8 (<0.6 - 2.6)
Vinyl Chloride	µg m^-³	26	<0.3	<0.3	<0.3	<0.3
Methanol	µg m^-³	2,660	24.1 (<2.6 - 42.6)	22.3 (17 - 29.1)	27.5 (19.0 - 38.0)	26.2 (15.4 - 36.0)
Ethanol[FW3] [AL4]	µg m^-³	19,200 ^(a)	18.5 (<3.8 - 33.3)	855.8 (<3.8 – 3,410.0)	111.6 (6.5 - 406.0)	216.6 (4.1 - 844.0)
Dimethylsulphide	µg m^-³	8	<0.2	0.3 (<0.2 - 0.7)	<0.2	<0.2
Carbon Disulphide	µg m^-³	150	0.9 (<0.5 - 1.5)	5.4 (<0.5 - 18.5)	0.6 (<0.5 - 0.8)	1.0 (<0.5 - 2.4)
Methylene Chloride	µg m^-³	3,530	9.8 (0.5 - 29.7)	3.5 (0.5 - 5)	2.9 (<0.4 - 6.0)	3.0 (<0.4 - 7.3)
Chloroform	µg m^-³	99	0.8 (<0.8 - 0.9)	<0.8	<0.8	<0.8
Methyl propionate	µg m^-³	353	<0.7	<0.7	<0.7	<0.7
Butan-2-ol	µg m^-³	667	0.8 (<0.6 - 1.3)	<0.6	<0.6	<0.6
1.1.1-Trichloroethane	µg m^-³	5,550	<0.8	<0.8	<0.8	<0.8
1.2-Dichloroethane	µg m^-³	210	1.9 (<0.3 - 6)	0.8 (<0.3 - 1.8)	0.7 (<0.3 - 1.6)	0.9 (<0.3 - 2.3)
Benzene	µg m^-³	33	1.4 (0.6 - 3)	1.0 (<0.5 - 1.5)	1.0 (<0.5 - 1.4)	1.2 (<0.5 - 2.1)
Carbon Tetrachloride	µg m^-³	64	0.8 (<0.6 - 0.9)	0.7 (<0.6 - 0.9)	0.7 (<0.6 - 1)	0.8 (<0.6 - 1.0)
Dipropyl ether	µg m^-³	NA	<0.8	<0.8	<0.8	<0.8
Heptane	µg m^-³	2,746	1.0 (<0.8 - 1.5)	<0.8	0.9 (<0.8 - 1.3)	30.4 (<0.8 - 119.0)
Trichloroethylene	µg m^-³	5,500	<1.1	<1.1	<1.1	<1.1
Ethyl propionate	µg m^-³	29	<0.8	<0.8	<0.8	<0.8
Methyl butanoate	µg m^-³	30	<0.8	<0.8	<0.8	<0.8
Methanethiol	µg m^-³	10	<0.4	<0.4	<0.4	<0.4
Toluene	µg m^-³	1,244	5.8 (0.6 - 15.8)	2.3 (1.4 - 2.7)	1.5 (0.5 - 2.6)	1.9 (0.7 - 3.3)
Ethyl butanoate	µg m^-³	71	<1	<1	<1	<1
Propyl benzene	µg m^-³	19	<0.8	<0.8	<0.8	<0.8
Octane	µg m^-³	7,942	<0.9	<0.9	<0.9	1.7 (<0.9 - 3.9)
Propyl propionate	µg m^-³	276	<1	<1	<1	<1
1.2-Dibromoethane (EDB)	µg m^-³	39	<1	<1	<1	<1
Butyl acetate	µg m^-³	76	3 (<1 - 11)	1 (<1 - 1)	<1	1 (<1 - 1)
Tetrachloroethylene	µg m^-³	1,380	0.9 (<0.7 - 1.2)	0.7 (<0.7 - 0.8)	<0.7	<0.7
Ethyl benzene	µg m^-³	738	2.7 (<0.5 - 8.3)	0.6 (<0.5 - 0.8)	0.6 (0.5 - 0.7)	0.6 (<0.5 - 0.8)
Nonane	µg m^-³	11,540	1.1 (<0.9 - 1.7)	<0.9	<0.9	1.0 (<0.9 - 1.3)
Ethanethiol	µg m^-³	13	<0.6	<0.6	<0.6	<0.6
Decanes	µg m^-³	3,608	1.0 (<0.7 - 1.9)	<0.7	<0.7	1.2 (<0.7 - 2.6)
Limonene	µg m^-³	212	1.0 (<0.4 - 2.2)	0.6 (<0.4 - 0.7)	0.5 (<0.4 - 0.7)	0.5 (<0.4 - 0.6)
Butyl benzene	µg m^-³	47	<1	<1	<1	<1
Undecane	µg m^-³	5,562	<1.2	<1.2	<1.2	1.8 (<1.2 - 3.7)
Butanethiol	µg m^-³	4	<1.2	<1.2	<1.2	<1.2
Terpenes	µg m^-³	NA	3.4 (<0.8 - 9.1)	<0.8	<0.8	<0.8
Xylenes	µg m^-³	534	7.3 (<0.5 - 22.5)	1.3 (0.7 - 2.3)	1.0 (<0.5 - 1.9)	1.6 (0.8 - 2.9)
Dichlorobenzene	µg m^-³	120	1 (<1 - 1.7)	<1	<1	<1
Note: (a) In accordance with Section 3.3.5 of the updated EM&A Manual, “The limit levels are defined as WHO/USEPA/CARB’s ambient criteria if available or the odour thresholds or 1% of Workplace Exposure Limit (WEL) as stipulated in the “UK Health and Safety Executive (HSE) EH 40/2005 Workplace Exposure Limits”, whichever is lower.” The limit levels established in accordance with the updated EM&A Manual were reviewed and compared against the pre-operation baseline monitoring results. Exceedance of limit level for Ethanol (980 ug/m³as established in accordance with the updated EM&A Manual) was recorded during the pre-operation phase baseline monitoring (3,410 ug/m³ at AM2 in May 2020). In addition, the limit level for H₂S (1 ug/m³as established in accordance with the updated EM&A Manual) was found below the detection limit (14 ug/m³). Taking into account the elevated background levels of Ethanol detected during the pre-operation baseline monitoring and the analytical detection limit of H₂S, it is proposed to establish the limit levels of Ethanol and H₂S from the available WHO/USEPA/CARB’s ambient criteria and 1% of WEL as stipulated in the “UKHSE EH 40/2005 Workplace Exposure Limits”, whichever is lower. It is considered that the WHO/USEPA/CARB’s ambient criteria and 1% of WEL, which are widely used by the industry and environmental and health professionals as a reference material in assessing the health risks are applicable to be adopted as SENTX limit levels for Ethanol and H₂S.

Event	Action
Exceedance of Limit Level for ambient VOCs, ammonia and H₂S at the monitoring locations	· Identify the source(s) and investigate the cause(s) of exceedance · Prepare the Notification of Exceedance within 24 hours · Inform Contractor, IEC, Project Proponent and EPD (EIAO Authority) whether the cause of exceedance is due to the Project · Discuss with Contractor and IEC for remedial measures · Ensure remedial measures are properly implemented · Assess effectiveness of Contractor's remedial measures and keep the Project Proponent and IEC informed of the results · Repeat measurement to confirm finding if exceedance is due to the Project · Increase monitoring frequency to monthly and continue until the monitoring results reduce to below limit level	· Verify the Notification of Exceedance · Check with Contractor on the operating activities and implementation of landfill gas control measures · Discuss with ET and Contractor on proposed remedial measures · Review proposals on remedial measures · Audit the implementation of the remedial measures · Audit the effectiveness of the implemented remedial measures	· Rectify any unacceptable practice · Amend working methods as required · Implement amended working methods, if necessary

4 GroundWater Quality

4.1 Monitoring Requirement

In accordance with the updated EM&A Manual, pre-operation groundwater baseline monitoring shall be conducted at all groundwater monitoring wells at monthly intervals for a period of 12 months prior to commencement of waste filling to establish the baseline condition. Further details of the pre-operation baseline groundwater quality monitoring under this Project are presented in the following sections.

4.2 Monitoring Equipment

A bladder pump with Teflon sampling tube and adjustable discharge rates was used for purging and taking of groundwater sample from the monitoring well. Filtered groundwater samples was collected by connecting a disposable in-line filter system to the tubing of the sampling pump, prior to storage and analysis.

A portable dip meter with 5mm accuracy was used for measurement of groundwater level at each well. The dip meter have an audio indicator of the water level and was checked before use.

The measurements of pH and electrical conductivity (EC) were undertaken in situ. In situ monitoring instruments in compliance with the specifications listed under Section 4.3.2 of the updated EM&A Manual were used to undertake the groundwater quality monitoring for the Project.

Table 4.1 summarises the equipment used in the baseline groundwater quality monitoring works. Copies of the calibration certificates are attached in Annex C1.

Table 4.1 Groundwater Quality Monitoring Equipment

Equipment	Model
Multifunctional meter	YSI Professional DSS (S/N: 15H102620) (S/N: 17B102764) (S/N: 20J101862)
Dip meter	Geotech Dipmeter (S/N: 80678)

4.3 Monitoring Locations

In accordance with the updated EM&A Manual with incorporation of the proposed updates under the Amendment Summary approved by EPD on 15 June 2020, groundwater baseline monitoring for the Project was conducted at 14 perimeter groundwater monitoring wells (including 5 up-gradient wells and 9 down-gradient wells) (i.e. MWX-1 to MWX-14). Locations of the groundwater monitoring locations are shown in Figure 2.1.

4.4 Monitoring Parameters and Frequency

The monitoring parameters and frequency of the pre-operation baseline groundwater quality monitoring are presented in Table 4.2.

Table 4.2 Frequency and Parameters of Baseline Groundwater Quality Monitoring

Monitoring Station	Frequency	Parameter
All groundwater monitoring wells (MWX-1 to MWX-14)	Monthly, for a period of 12 months prior to waste filling	· Water level · pH · EC · COD · BOD5 · TOC · Ammoniacal–nitrogen · Nitrate-nitrogen · Nitrite–nitrogen · TKN · TN · Sulphate · Sulphide · Carbonate · Bicarbonate · Phosphate	· Chloride · Sodium · Potassium · Calcium · Magnesium · Nickel · Manganese · Chromium · Cadmium · Copper · Lead · Iron · Zinc · Mercury · Boron

Monitoring Station

Frequency

Parameter

All groundwater monitoring wells (MWX-1 to MWX-14)

Monthly, for a period of 12 months prior to waste filling

· Water level

· pH

· EC

· COD

· BOD5

· TOC

· Ammoniacal–nitrogen

· Nitrate-nitrogen

· Nitrite–nitrogen

· TKN

· TN

· Sulphate

· Sulphide

· Carbonate

· Bicarbonate

· Phosphate

· Chloride

· Sodium

· Potassium

· Calcium

· Magnesium

· Nickel

· Manganese

· Chromium

· Cadmium

· Copper

· Lead

· Iron

· Zinc

· Mercury

· Boron

4.5 Monitoring Methodology

4.5.1 Sampling Procedures

Bladder pump with Teflon sampling tube was used for purging and collection of groundwater sample from the monitoring well. Each monitoring well was purged for 5 minutes before groundwater sampling to remove the stagnant water accumulated in the monitoring pipe itself and ensure representative groundwater is sampled. In-situ measurement of determinants, including pH and EC was taken to ensure a stable sampling conditions was achieved. Once the groundwater quality become stable (within 25% acceptable difference), groundwater samples can be taken. Where the difference of the in-situ measurement of pH and EC between the two consecutive samples exceed 25%, the first sample was discarded and further samples and readings were taken.

In accordance with the updated EM&A Manual with incorporation of the proposed updates under the Amendment Summary approved by EPD on 15 June 2020, filtered groundwater samples was collected during baseline monitoring for laboratory analysis of parameters listed in Table 4.2. A disposable in-line filter system was connected to the tubing of the sampling pump to obtain filtered groundwater samples. Following collection, water samples for laboratory analysis were stored in containers in appropriate type and size depending on the parameters to be analysed and packed in ice (cooled to 4°C without being frozen) during both on-site temporary storage and shipment to the testing laboratory. The samples were delivered to the laboratory as soon as possible and the laboratory determination works started within 24 hours after collection of the water samples. Sufficient volume of samples was collected to achieve the detection limit.

Water level measurement was carried out prior to any purging and after groundwater sampling from each monitoring wells.

4.5.2 Laboratory Analytical Methods

The testing of parameters presented in Table 4.2 for all stations was conducted by ALS Technichem (HK) Pty Ltd. (HOKLAS Registration No. 066). Comprehensive quality assurance and control procedures were in place in order to ensure quality and consistency in results. The testing method and detection limit are provided in Table 4.3.

Table 4.3 Analytical Methods and Detection Limits for Groundwater Samples

Parameter	Analytical Method	Analytical Detection Limit (mg L^-1)
COD	APHA 5220 B	2
BOD₅	APHA 5210 B	2
Total Organic Carbon	APHA 5310 B	1
Sodium	USEPA 6010C	0.05
Potassium	USEPA 6010C	0.05
Calcium	USEPA 6010C	0.05
Magnesium	USEPA 6010C	0.05
Carbonate	APHA 2320 B	1
Bicarbonate	APHA 2320 B	1
Nickel	USEPA 6020A	0.001
Manganese	USEPA 6020A	0.001
Nitrate-nitrogen	APHA 4500NO₃: I	0.01
Nitrite-nitrogen	APHA 4500NO₃: I	0.01
Sulphate	USEPA 375.4	1
Chloride	USEPA 325.1	1
Sulphide	APHA 4500S^2-: D	0.1
Chromium	USEPA 6020A	0.001
Cadmium	USEPA 6020A	0.0002
Copper	USEPA 6020A	0.001
Lead	USEPA 6020A	0.001
pH	APHA 4500H⁺: B	0.1 (pH unit)
Electrical Conductivity	APHA 2510 B	1 (µS/cm)
Iron	USEPA 6010C	0.04
Zinc	USEPA 6020A	0.01
Phosphate	APHA 4500P: B & F	0.01
Ammoniacal – nitrogen	APHA 4500NH₃: G	0.1
Mercury	USEPA 245.7	0.002
Boron	USEPA 6020A	0.01
TKN	APHA 4500Norg: D	0.1
Total Nitrogen	APHA 4500Norg: D APHA 4500NO₃: I	0.1

4.6 QA/QC Requirements

4.6.1 Calibration of In-situ Instruments

All in-situ monitoring instruments were checked, calibrated and certified by a laboratory accredited under HOKLAS or other international accreditation scheme before use, and subsequently re-calibrated at 3 monthly intervals throughout all stages of the groundwater quality monitoring programme. Responses of sensors and electrodes were checked with certified standard solutions before each use.

For the on-site calibration of field equipment, the requirements of the BS 1427:1993, "Guide to on-site test methods for the analysis of waters" was observed.

4.6.2 Decontamination Procedures

Water sampling equipment used during the course of the monitoring programme was decontaminated by manual washing and rinsed with clean distilled water after each sampling location.

4.6.3 Sampling Management and Supervision

All sampling bottles were labelled with the sample ID (including the indication of sampling station), laboratory number and sampling date. Water samples were dispatched to the testing laboratory for analysis as soon as possible after the sampling. All samples were stored in a cool box and kept at less than 4°C but without frozen. All water samples were handled under chain of custody protocols and relinquished to the laboratory representatives at locations specified by the laboratory. The laboratory determination works started within 24 hours after collection of water samples.

4.6.4 Quality Control Measures for Sample Testing

The samples testing were performed by ALS Technichem (HK) Pty Ltd. The following quality control programme was performed by the laboratory for every batch of 20 samples:

Ÿ One method blank; and

Ÿ One sample duplicate.

4.7 Baseline Monitoring Results

Pre-operation phase baseline groundwater monitoring was conducted at 14 monitoring locations (MWX-1 to MWX-14) between 24 March 2020 and 9 March 2021. The monitoring schedule is shown in Annex C2.

The baseline groundwater monitoring results of the key parameters with Limit Levels (ammoniacal-nitrogen and COD) are summarized in Table 4.4. The detailed monitoring results at each monitoring station are presented in Annex C3.

Table 4.4 Summary of Baseline Groundwater Monitoring Results (Ammoniacal-nitrogen and COD)

Location	Ammoniacal-nitrogen (mg L^-1)		COD (mg L^-1)
Location	Range	Average	Range	Average
MWX-1	0.19 - 0.74	0.40	<10	<10
MWX-2	0.02 – 3.02	0.42	<10 - 11	<10
MWX-3	0.60 – 1.01	0.82	<10 – 13	11
MWX-4	2.40 – 8.30	4.79	16 – 36	27
MWX-5	0.21 – 4.26	2.30	14 – 31	21
MWX-6	3.06 – 4.62	3.73	32 – 47	39
MWX-7	5.11 – 6.58	5.95	<10 – 49	20
MWX-8	11.00 – 15.90	13.82	30 – 55	40
MWX-9	0.40 – 7.96	5.05	14 – 75	27
MWX-10	0.01 – 0.15	0.06	<10	<10
MWX-11	<0.01 – 0.26	0.16	<10	<10
MWX-12	<0.01 – 0.05	0.02	<10	<10
MWX-13	<0.01 – 0.08	0.04	<10	<10
MWX-14	<0.01 – 0.02	<0.01	<10	<10

4.8 Action and Limit Levels

The Limit Levels for ammoniacal-nitrogen and COD are determined in accordance with requirements set out in the updated EM&A Manual which are summarized in Table 4.5.

Table 4.5 Guidelines for Establishing Limit Levels for Groundwater Quality

Parameters	Limit Level (mg L-1)
Ammoniacal-nitrogen	5 or 95%-ile of baseline data ^(a)
COD	30 or 95%-ile of baseline data ^(a)
Note: (a) If the concentration of ammoniacal-nitrogen and COD exceeds the respective limit level during baseline monitoring, the 95%-ile should be use as a limit level during impact monitoring. Should this be the case, the limit level will be well specific.

The Limit levels for groundwater quality monitoring are determined and presented in Table 4.6. The detailed calculation of the Limit Levels are presented in Annex C4.

Table 4.6 Limit Levels for Groundwater Quality

Location	Limit Levels
Location	Ammoniacal-nitrogen (mg L^-1)	COD (mg L^-1)
MWX-1	5.00	30
MWX-2	5.00	30
MWX-3	5.00	30
MWX-4	7.63	36
MWX-5	5.00	30
MWX-6	5.00	46
MWX-7	6.55	36
MWX-8	15.85	50
MWX-9	7.30	71
MWX-10	5.00	30
MWX-11	5.00	30
MWX-12	5.00	30
MWX-13	5.00	30
MWX-14	5.00	30

4.9 Event and Action Plan

Should non-compliance of the groundwater water quality criteria occur, action in accordance with the Event and Action Plan in Table 4.7 shall be carried out.

Event	Action
Exceedance of Limit Level for groundwater monitoring	· Identify source(s) of impact and investigate the cause(s) of exceedance · Prepare Notification of Exceedance within 24 hours · Inform Contractor, IEC, Project Proponent and EPD (EIAO Authority) whether the cause of exceedance is due to the Project · Discuss with Contractor and IEC for remedial measures required · Ensure remedial measures are properly implemented · Repeat measurement to confirm finding if exceedance is due to the Project · Increase monitoring frequency to weekly at monitoring well if exceedance is due to the Project until no exceedance of Limit Level	· Verify the Notification of Exceedance · Check monitoring data submitted by ET · Check Contractor's working methods · Discuss with ET and Contractor on proposed remedial measures · Review proposals on remedial measures · Audit the implementation of the remedial measures · Audit the effectiveness of the implemented remedial measures	· Divert groundwater collected at the collection sumps to the leachate treatment plant · Submit proposals for remedial measures to IEC · Rectify any unacceptable practice or design · Amend working methods as required · Implement amended working methods, if necessary

5 Landfill Gas

5.1 Monitoring Requirement

In accordance with the updated EM&A Manual, pre-operation landfill gas baseline monitoring shall be conducted at all perimeter landfill gas monitoring wells at monthly intervals for a period of 12 months prior to commencement of waste filling to establish the baseline condition.

Unexpected elevated levels of methane (ranging from 1.1% to 19.6% (v/v)) was detected at a few isolated landfill gas monitoring wells during the pre-operation baseline monitoring. Additional landfill gas monitoring was conducted under the Employer’s Change Orders, to obtain additional monitoring data to establish the baseline condition.

Further details of the pre-operation baseline and additional landfill gas monitoring under this Project are presented in the following sections.

5.2 Monitoring Equipment

Gas analysers in compliance with the specifications listed under Section 5.4.1 of the updated EM&A Manual were used to monitor the gas parameters at the landfill gas monitoring wells. The gas analysers were calibrated by a laboratory accredited under HOKLAS at yearly intervals and checked before use to ensure the validity and accuracy of the results. A portable dip meter was used to monitor the water level in the monitoring wells.

Table 5.1 summarises the equipment used in the pre-operation phase baseline and additional landfill gas monitoring programme. Copies of the calibration certificates for the equipment are presented in Annex D1.

Table 5.1 Landfill Gas Monitoring Equipment

Equipment	Model
Landfill Gas Analyser	GEM5000 (S/N: G501136)
	GA2000 (S/N: GA11956)
	GA5000 (S/N: G507306)
Dip meter	Solinst 101 (S/N: 250343)

5.3 Monitoring Locations

In accordance with the updated EM&A Manual with incorporation of the proposed updates under the Amendment Summary approved by EPD on 15 June 2020, pre-operation baseline landfill gas monitoring for the Project was conducted at 36 monitoring stations (i.e. LFG1 to LFG24, P7 to P9, GP1 to GP7, GP12 and GP15). Locations of the monitoring locations are shown in Figure 5.1.

5.4 Monitoring Parameters and Frequency

The monitoring parameters and frequency of pre-operation phase baseline and additional landfill gas monitoring are presented in Table 5.2.

Table 5.2 Frequency and Parameters of Pre-operation Phase Baseline and Additional Landfill Gas Monitoring

	Frequency	Monitoring Station	Parameter
Pre-operation phase baseline monitoring	Monthly, for a period of 12 months prior to waste filling	All landfill gas monitoring wells (LFG1 to LFG24, P7 to P9, GP1 to GP7, GP12 and GP15)	Ÿ Methane Ÿ Carbon dioxide Ÿ Oxygen Ÿ Atmospheric pressure
Additional monitoring	Three days per week (5 October 2020 to 6 November 2020)
	Two days per week (10 November 2020 to 4 December 2020)
	Weekly (10 to 28 December 2020, March to November 2021)

5.5 Monitoring Methodology

The sampling point of the landfill gas monitoring wells was connected to the gas analyser with Teflon sampling tube. The built-in gas tap of the monitoring wells was opened to allow purging of gas from the monitoring wells. Once the reading displayed on the gas analyser become stable, the values of each parameter were recorded.

5.6 Baseline Monitoring Results

Pre-operation phase baseline landfill gas monitoring was conducted at 36 monitoring stations (LFG1 to LFG24, P7 to P9, GP1 to GP7, GP12 and GP15) between 24 March 2020 and 26 March 2021. The monitoring schedule is shown in Annex D2.

During the pre-operation baseline monitoring, unexpected elevated levels of methane have been detected at a few isolated landfill gas monitoring wells, including LFG11, LFG12, LFG13, LFG15, LFG17, LFG18 and LFG19 (see Table 5.3). Methane gas was detected at a level ranging from 1.2% to 17.2% for the monitoring period between April and September 2020, exceeding the Limit Level for methane (1% by volume) as stipulated in Table 5.6a of the updated EM&A Manual. In order to obtain additional data to establish the baseline condition, additional landfill gas monitoring was conducted and scheduled between 5 October and 28 December 2020 and between 2 March and 24 November 2021 under the Employer’s Change Orders. The monitoring schedule is shown in Annex D3.

The pre-operation baseline and additional landfill gas monitoring results are summarised in Table 5.3. The detailed monitoring results are presented in Annex D4.

Table 5.3 Summary of Pre-Operation Phase Baseline (March 2020 to March 2021) and Additional Landfill Gas Monitoring Results (October to December 2020 (With Increased Frequency) and March to November 2021)

Monitoring Wells	Methane (% v/v)^(a)		Carbon Dioxide (% v/v)^(a)		Oxygen (% v/v^{) (a)}
Monitoring Wells	Pre-operation Monthly Monitoring	Additional Monitoring	Pre-operation Monthly Monitoring	Additional Monitoring	Pre-operation Monthly Monitoring	Additional Monitoring
LFG1	0.0 – 0.0	0.0 – 0.0	0.0 - 0.1	0.0 - 1.7	18.3 – 21.4	14.1 - 20.9
LFG2	0.0 – 0.0	0.0 – 0.0	0.0 - 0.6	0.0 - 2.8	19.0 – 21.3	15.0 - 21.6
LFG3	0.0 – 0.0	0.0 – 0.1	0.0 - 2.1	0.0 - 4.8	16.0 - 21.5	14.3 - 21.7
LFG4	0.0 – 0.0	0.0 – 0.1	0.0 - 3.3	0.0 - 5.5	12.7 - 20.2	12.0 – 20.7
LFG5	0.0 – 0.0	0.0 – 0.0	0.0 - 1.2	0.0 - 1.9	5.1 - 20.3	10.3 - 21.6
LFG6	0.0 – 0.0	0.0 – 0.8	0.3 - 4.6	0.1 - 7.6	7.7 – 20.5	0.3 – 21.0
LFG7	0.0 – 0.0	0.0 – 0.0	0.0 - 0.0	0.0 - 0.0	13.5 - 20.9	12.0 - 21.7
LFG8	0.0 – 0.0	0.0 – 11.6	0.0 - 0.2	0.0 - 0.9	19.4 - 21.4	0.6 - 21.8
LFG9	0.0 – 1.1	0.0 – 1.5	0.0 - 0.2	0.0 - 0.1	0.7 - 20.4	0.8 - 21.8
LFG10	0.0 - 0.0	0.0 – 2.5	0.0 - 0.1	0.0 - 0.1	10.3 - 21.5	0.2 - 21.9
LFG11	0.0 - 2.0	0.0 – 1.5	0.0 - 0.2	0.0 - 0.5	0.1 - 21.1	0.2 - 21.7
LFG12	0.0 - 12.2	0.0 – 0.4	0.0 - 0.0	0.0 - 0.0	5.8 – 21.4	14.4 - 21.7
LFG13	0.0 - 19.6	0.0 – 21.5	0.0 - 0.4	0.0 – 1.2	0.5 - 20.2	0.3 - 20.8
LFG14	0.0 - 0.1	0.0 – 4.2	0.0 - 0.0	0.0 - 0.3	13.7 – 21.3	0.3 - 20.9
LFG15	0.0 - 17.2	0.0 – 11.8	0.0 - 0.2	0.0 - 0.5	5.0 - 20.9	0.2 - 21.7
LFG16	0.0 - 0.8	0.0 – 0.2	0.0 - 0.1	0.0 - 0.5	15.0 – 20.6	13.2 - 20.9
LFG17	0.0 - 9.5	0.0 – 16.8	0.0 - 0.3	0.0 - 0.9	0.2 – 21.2	0.2 - 21.7
LFG18	0.0 - 1.3	0.0 – 0.0	0.0 - 0.2	0.0 - 0.6	15.0 - 20.1	14.7 - 20.8
LFG19	0.0 - 5.3	0.0 – 1.8	0.0 - 0.1	0.0 - 1.6	0.1 – 21.1	0.3 - 21.7
LFG20	0.0 – 0.0	0.0 – 0.0	0.0 – 2.3	0.0 – 3.1	4.7 - 19.8	3.4 - 20.8
LFG21	0.0 – 0.0	0.0 – 0.5	0.0 – 2.5	0.0 – 3.3	4.6 - 19.9	2.5 – 19.7
LFG22	0.0 – 0.0	0.0 – 0.0	0.0 – 2.4	0.0 - 2.5	0.1 – 20.8	2.9 - 20.7
LFG23	0.0 – 0.0	0.0 – 0.0	1.0 - 6.6	0.0 - 8.8	11.5 - 20.5	9.9 - 21.1
LFG24	0.0 – 0.0	0.0 – 0.0	0.1 - 2.0	0.1 – 3.2	16.8 - 20.5	14.4 - 19.9
GP1	0.0 – 0.0	0.0 – 0.1	0.0 - 4.8	0.0 – 9.1	10.8 - 20.7	2.1 - 20.7
GP2 (shallow)	0.0 – 0.0	0.0 – 0.2	0.0 - 4.9	0.0 - 9.9	10.9 - 20.8	9.8 - 21.7
GP2 (deep)	0.0 – 0.0	0.0 – 0.6	0.0 – 5.7	0.0 - 8.9	9.2 – 21.3	7.0 - 21.6
GP3 (shallow)	0.0 – 0.0	0.0 – 0.0	0.0 - 0.7	0.0 - 5.4	18.9 – 21.4	12.0 - 21.3
GP3 (deep)	0.0 – 0.0	0.0 – 0.1	0.0 - 0.4	0.0 – 4.1	19.1 - 20.9	13.1 - 21.5
GP4 (shallow)	0.0 – 0.0	0.0 – 0.0	0.0 - 0.8	0.0 – 10.1	19.0 - 21.3	8.9 - 21.7
GP4 (deep)	0.0 – 0.0	0.0 – 0.1	0.0 - 1.5	0.0 – 6.2	16.5 - 21.3	8.6 - 21.7
GP5 (shallow)	0.0 – 0.0	0.0 – 0.0	0.0 - 1.7	0.0 – 9.3	18.4 - 21.4	13.1 - 21.1
GP5 (deep)	0.0 – 0.0	0.0 – 0.0	0.0 - 3.2	0.0 - 6.0	17.8 - 21.3	17.3 - 21.7
GP6	0.0 – 0.0	0.0 – 0.0	0.2 - 5.9	3.0 - 6.9	12.7 – 20.0	7.0 - 17.0
GP7	0.0 – 0.0	0.0 – 0.0	0.0 - 2.4	0.0 – 3.0	18.0 - 21.2	12.1 - 21.4
GP12	0.0 – 0.0	0.0 – 0.0	0.0 - 0.8	0.0 - 0.8	18.4 – 21.3	18.4 - 21.5
GP15	0.0 – 0.0	0.0 – 0.0	0.0 - 0.7	0.0 - 0.1	18.9 – 21.4	19.0 - 21.5
P7	0.0 – 0.0	0.0 – 0.1	0.0 - 1.0	0.0 - 0.1	19.0 – 21.4	19.0 - 21.6
P8	0.0 – 0.0	0.0 – 0.0	0.0 - 0.2	0.0 - 0.2	19.7 – 21.4	19.0 - 21.6
P9	0.0 – 0.0	0.0 – 0.0	0.0 - 0.3	0.0 – 1.2	19.7 – 21.3	18.6 - 21.5

Elevated levels of methane (ranging from 1.1% to 19.6% (v/v)) was detected at a number of isolated landfill gas monitoring wells along the SENTX southern and western waste boundary during the pre-operation baseline monitoring, including LFG9, LFG11, LFG12, LFG13, LFG15, LFG17, LFG18 and LFG19. Nil or minimal concentrations of methane have been observed for the other perimeter monitoring wells. During the additional landfill gas monitoring, monitoring well LFG13 was observed to have consistent elevated levels of methane (up to 21.5% (v/v) on 24 November 2020) throughout the year and monitoring well LFG17 was observed to have consistent elevated levels of methane (up to 16.8% (v/v) on 30 June 2021) during the wet season. Elevated levels of methane were detected occasionally at LFG9 (up to 1.5% (v/v) on 28 April 2021), LFG11 (up to 1.5% (v/v) on 9 June 2021), LFG15 (up to 11.8% (v/v) on 21 July 2021) and LFG19 (up to 1.8%(v/v) on 16 June 2021) during the wet season of 2021 where these landfill gas wells have not been detected methane since the wet season of 2020. In addition, elevated levels of methane were newly detected at LFG8 (up to 11.6% (v/v) on 30 June 2021), LFG10 (up to 2.5% (v/v) on 21 July 2021) and LFG14 (up to 4.2% (v/v) on 30 June 2021), during the additional landfill gas monitoring in 2021.

Elevated levels of carbon dioxide (ranged from 0.0% to 6.6% (v/v)) and low level of oxygen (ranged from 0.1% to 21.4% (v/v)) have been observed in the monitoring wells during the pre-operation phase landfill gas monitoring, which could be the result of methane presented in the respective wells being oxidised to carbon dioxide or having the similar situation like the existing SENT Landfill where elevated carbon dioxide levels were measured which could be considered as natural background levels. Similar levels of carbon dioxide and oxygen were measured in the additional landfill gas monitoring.

The groundwater levels measured during the pre-operation phase baseline landfill gas monitoring are compared against the levels of the perforated section of the landfill gas monitoring wells. The groundwater levels are found within the perforated section of the monitoring wells which implies that the perforated sections were not fully submerged by groundwater, noting that the level of groundwater may vary with time. This confirms that the nil or minimal level of methane measured at the landfill gas monitoring wells were not due to the submerged perforated sections.

In May 2021, ERM was commissioned by GVL and EPD (the Employer) to undertake a desktop review to investigate the potential sources of the elevated methane levels. Given the multiple landfill gas controls implemented at the existing SENT Landfill, the absence of methane measured at the perimeter monitoring wells of SENTX located immediately next to the existing SENT Landfill (LFG1 to LFG8), it is considered very unlikely that the elevated methane measured at the concerned SENTX landfill gas monitoring wells was due to sub-surface migration of landfill gas from the existing SENT Landfill.

The desktop review also reviewed historical site investigation borehole logs at the Project Site area and it was found that pockets of organic matters are identified in the fill materials of the SENTX site. It is possible that the elevated methane levels measured at the concerned wells were due to organic matters within or around the concerned wells (especially LFG13, which continuous to show elevated methane levels).

5.7 Action and Limit Levels

The Limit Levels for methane and carbon dioxide stated in the updated EM&A Manual are presented in Table 5.4.

Table 5.4 Limit Levels for Landfill Gas Constituents

Parameters	Limit Level
Methane	1% by volume
Carbon dioxide	1.5% by volume above background ^(a)
Note: (a) Background concentrations established in baseline monitoring.

Taking into account both the pre-operation baseline and additional landfill gas monitoring results and the elevated background levels of methane (>1% (v/v)) detected in some monitoring wells, it is proposed to revise the Limit Levels of methane of the wells with elevated methane level as 1% (v/v) above background (maximum methane concentration obtained during the pre-operation baseline and additional landfill gas monitoring). For the perimeter monitoring wells with nil or negligible concentrations of methane measured, it is recommended to maintain the Limit Levels as 1% (v/v).

The maximum methane and carbon dioxide concentrations obtained during the pre-operation baseline and additional landfill gas monitoring were adopted to establish the Limit Levels as they are the actual concentrations measured during the landfill gas monitoring and reflect the baseline condition without SENTX operation. Taking into account the varying frequency and non-continuous basis of the additional landfill gas monitoring, it is reasonable to use the measured maximum methane and carbon dioxide concentrations as basis for deriving the Limit Levels during operation phase.

The Limit Levels of landfill gas monitoring at each monitoring location are established taking into account the pre-operation baseline and additional landfill gas monitoring results which shown elevated levels of methane and carbon dioxide at isolated monitoring wells and presented in Table 5.5.

Table 5.5 Limit Levels for Landfill Gas Constituents

Location	Limit Levels ^(a)
Location	Methane (% (v/v)) ^(b)	Carbon dioxide (% (v/v)) ^(c)
LFG1	1.0	3.2
LFG2	1.0	4.3
LFG3	1.0	6.3
LFG4	1.0	7.0
LFG5	1.0	3.4
LFG6	1.0	9.1
LFG7	1.0	1.5
LFG8	12.6	2.4
LFG9	2.5	1.7
LFG10	3.5	1.6
LFG11	3.0	2.0
LFG12	13.2	1.5
LFG13	22.5	2.7
LFG14	5.2	1.8
LFG15	18.2	2.0
LFG16	1.0	2.0
LFG17	17.8	2.4
LFG18	2.3	2.1
LFG19	6.3	3.1
LFG20	1.0	4.6
LFG21	1.0	4.8
LFG22	1.0	4.0
LFG23	1.0	10.3
LFG24	1.0	4.7
GP1	1.0	10.6
GP2 (shallow)	1.0	11.4
GP2 (deep)	1.0	10.4
GP3 (shallow)	1.0	6.9
GP3 (deep)	1.0	5.6
GP4 (shallow)	1.0	11.6
GP4 (deep)	1.0	7.7
GP5 (shallow)	1.0	10.8
GP5 (deep)	1.0	7.5
GP6	1.0	8.4
GP7	1.0	4.5
GP12	1.0	2.3
GP15	1.0	2.2
P7	1.0	2.5
P8	1.0	1.7
P9	1.0	2.7
Notes: (a) The Limit Levels are established based on the pre-operation phase baseline and additional landfill gas monitoring results. (b) Limit Levels of methane of the monitoring wells with elevated methane level are calculated as 1% (v/v) above background (maximum methane concentration obtained during the pre-operation baseline and additional landfill gas monitoring). (c) Limit Levels of carbon dioxide are calculated as 1.5% (v/v) above background (maximum carbon dioxide concentration obtained during the pre-operation baseline and additional landfill gas monitoring).

5.8 Event and Action Plan

Should non-compliance of the landfill gas parameters occur, actions in accordance with the Event and Action Plan in Table 5.6 shall be carried out.

Action
Limit Level being exceeded for field monitoring at the perimeter monitoring wells	Ÿ Investigate the cause(s) of exceedance Ÿ Prepare the Notification of Exceedance within 24 hours Ÿ Check monitoring data, all plant, equipment and the Contractor’s working methods Ÿ Inform Contractor, IEC, Project Proponent and EPD (EIAO Authority) whether the cause of exceedance is due to the Project Ÿ Discuss with Contractor and IEC for remedial measures required Ÿ Ensure remedial measures are properly implemented Ÿ Increase the monitoring frequency to daily if exceedance is due to the Project for monitoring wells in the areas where there is development within 250m of the SENTX Site Boundary and to weekly for other monitoring wells, until no exceedance of limit level	Ÿ Verify the Notification of Exceedance Ÿ Discuss with ET and Contractor on proposed remedial measures Ÿ Review proposals on remedial measures Ÿ Audit the implementation of the remedial measures Ÿ Audit the effectiveness of the implemented remedial measures	Ÿ Repeat field measurement to confirm findings Ÿ Check the performance of landfill gas management system Ÿ Rectify unacceptable practice Ÿ Discuss with the ET and IEC and submit proposals for remedial measures to IEC Ÿ Implement the agreed proposals Ÿ Amend proposal if appropriate

([1]) ERM (2018). South East New Territories (SENT) Landfill Extension: Environmental Monitoring & Audit Manual

([2]) ERM (2007). South East New Territories (SENT) Landfill Extension – Feasibility Study: Environmental Impact Assessment Report

	Action
Event		ET	IEC	Contractor
Exceedance of Action/Limit Level for dust monitoring		· Identify the source(s) and investigate the cause(s) of exceedance · Prepare the Notification of Exceedance within 24 hours · Inform Contractor, IEC, Project Proponent and EPD (EIAO Authority) whether the cause of exceedance is due to the Project · Discuss with Contractor and IEC for remedial measures · Ensure remedial measures are properly implemented · Assess effectiveness of Contractor's remedial measures and keep the Project Proponent and IEC informed of the results · Repeat measurement to confirm finding if exceedance is due to the Project · Increase monitoring frequency to daily and continue until the monitoring results reduce to below action level	· Verify the Notification of Exceedance · Check monitoring data submitted by ET · Check Contractor's working methods · Discuss with ET and Contractor on proposed remedial measures · Review proposals on remedial measures · Audit the implementation of the remedial measures · Audit the effectiveness of the implemented remedial measures	· Take immediate action to avoid further exceedance · Submit proposals for remedial measures to IEC · Implement the agreed proposals · Amend proposal if appropriate

Executive Summary