4                                            Air Quality impact Assessment

4.1                                      Introduction

This section presents an assessment of the potential air quality impacts arising from the construction, operation, restoration and aftercare of the proposed Extension.

During the construction phase, dust nuisance arising from blasting, excavation and filling, slope stabilisation, site formation, stone crushing and vehicle movements on the site is a potential concern.  Potential sources of air quality and odour impacts during the operation, restoration and aftercare phases of the Extension will include waste filling activities, the landfill gas (LFG) treatment facility, the new leachate treatment plant (LTP) and the LFG generator. 

Representative Air Sensitive Receivers (ASRs) have been identified and an assessment of the potential air quality impacts has been conducted.  Adjacent emission sources such as industrial emissions from Tseung Kwan O Industrial Estate (TKOIE), restoration of existing SENT Landfill and the future operations in TKO Area 137 during construction operation/restoration and aftercare phases of the Extension have also been taken into consideration.  Mitigation measures have been recommended, where appropriate, to reduce the impacts. 

4.2                                      Legislation Requirement and Evaluation Criteria

4.2.1                                Air Pollutants Covered by Hong Kong Air Quality Objectives (HKAQOs)

The principal legislation for the management of air quality in Hong Kong is the Air Pollution Control Ordinance (APCO) (Cap. 311).  Under the APCO, the Hong Kong Air Quality Objectives (HKAQOs), which are presented in Table 4.2a, stipulate the statutory limits for air pollutants and the maximum allowable numbers of exceedences over specific periods.


Table 4.2a      Hong Kong Air Quality Objectives (mg m-3) (a)

Air Pollutant

Averaging Time

 

1 Hour (b)

8 Hour (c)

24 Hour (c)

1 Year (d)

Total Suspended Particulates (TSP)

-

-

260

80

Respirable Suspended Particulates (RSP) (e)

-

-

180

55

Sulphur Dioxide (SO2)

800

-

350

80

Nitrogen Dioxide (NO2)

300

-

150

80

Carbon Monoxide (CO)

30,000

10,000

-

-

Notes:

(a)     Measured at 298K (25°C) and 101.325 kPa (one atmosphere)

(b)     Not to be exceeded more than three times per year

(c)     Not to be exceeded more than once per year

(d)     Arithmetic means

(e)     Suspended airborne particulates with a nominal aerodynamic diameter of 10 micrometres or smaller

The Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM) also includes an hourly TSP criterion of 500 mg m-3 for construction dust impacts and an odour criterion of 5 Odour Units (OUs) for a 5-second averaging period for odour impact assessment.

The criteria outlined in Table 4.2a and in the EIAO-TM were used to assess the potential air quality impacts associated with the Extension. 

The measures set out in the Air Pollution Control (Construction Dust) Regulations should be followed to reduce dust impacts from this Project.

If a stone crushing plant of a capacity greater than 5,000 tonnes per year is needed, a licence must be obtained under the Air Pollution Control (Specified Process) Regulation and the control measures set out in the Guidance Note on the Best Practicable Means for Mineral Works (Stone Crushing Plants) (BPM 11/1) should be followed.

Should the fuel consumption rate of a premises/process with chimney emission exceed the specified fuel consumption rates stated in the Air Pollution Control (Furnaces, Ovens and chimneys) (Installation and Alternation) Regulations, an approval of chimney installation/alternation should be obtained from the EPD prior to the operation.

4.2.2                                Air Pollutants Not Covered by HKAQOs

For those pollutants not covered by the HKAQOs, health risk criteria recommended in the international guidelines, such as those promulgated by the World Health Organisation (WHO), the United States Environmental Protection Agency (US EPA) and the California Air Resources Board (CARB) have been considered.  The criteria/guideline values were selected in the following order of preference:

·           WHO;

·           US EPA; and

·           CARB.

Cancer Health Risk Assessment

Of the non-criteria substances emitted during the operation/restoration and aftercare phases, benzene and vinyl chloride are considered carcinogenic.  Table 4.2b shows the Unit Risk Factors (URFs) for the carcinogenic substances considered in this assessment.

Table 4.2b      Guideline Unit Risk Factors for Carcinogenic Substances

Substance

Unit Risk Factor (mg m-3)-1

Benzene

7.8x10-6 (a)

Vinyl Chloride

8.8x10-6 (b)

Notes:

(a)     Reference to US EPA – Integrated Risk Information System – On-line data as in October 2007.  The URF of benzene is in a range of 2.2x10-6 – 7.8x10-6 per mg m-3.  Upper range of URF is adopted for the worst case assessment (http://cfpub.epa.gov/iris/quickview.cfm?substance_nmbr=0276).

(b)     Reference to US EPA – Integrated Risk Information System – On-line data as in October 2007.  The URFs of vinyl chloride are 4.4x10-6 per mg m-3 for the exposure during adulthood and 8.8x10-6 per mg m-3 for the exposure from birth.  Higher URF is adopted for the worst case assessment (http://cfpub.epa.gov/iris/quickview.cfm?substance_nmbr=1001).

The risk assessment guidelines for assessing the carcinogenic health risks from exposure to air toxics are summarised in Table 4.2c.

Table 4.2c      Risk Assessment Guidelines for the Assessment of Carcinogenic Health Risks

Acceptability of Cancer Risk

Estimated Individual Lifetime Cancer Risk Level

Significant

> 10-4

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

> 10-6 – 10-4

Insignificant

£ 10-6

Non-Cancer Health Risk Assessment

Benzene and vinyl chloride have the potential to cause chronic and/or acute impacts for long and/or short-term exposures, respectively.  The reference chronic and acute concentrations of these pollutants are summarised in Table 4.2d.

Table 4.2d      Guideline Values for Chronic and Acute Reference Concentrations

Substance

Chronic Reference Concentration (Annual Average in mg m-3)

Acute Reference Concentration (Hourly Average in mg m-3)

Benzene

30 (a)

1,300 (b)

Vinyl Chloride

100 (a)

1.8x105 (b)

Notes:

(a)     US EPA – Integrated Risk Information System – On-line data as in October 2007

(b)     California Environmental Protection Agency, Air Resources Board (ARB)/Office of Environmental Health Hazard Assessment (OEHHA) (http://www.oehha.ca.gov/air/acute_rels/allAcRELs.html).

The risk assessment guidelines also recommend criteria to assess the acceptability of chronic and acute non-cancer health risks and these are summarised in Tables 4.2e and 4.2f, respectively.

Table 4.2e      Acceptability of Chronic Non-Cancer Health Risks

Acceptability

Assessment Results (a)

Chronic non-cancer risks are considered “Insignificant

ACA £ RCc

Chronic non-cancer health risks are considered “Significant”.  A more detailed assessment of the control requirements and further mitigation measures are needed.

ACA > RCc

Note:

(a)     ACA and RCc represent annual average concentration and chronic reference concentration, respectively.

Table 4.2f       Acceptability of Acute Non-cancer Health Risks

Acceptability

Assessment Results (a)

Acute non-cancer risks are considered “Insignificant

ACHM £ RCA

Acute non-cancer health risks are considered “Significant”.  A more detailed assessment of the control requirements and further mitigation measures are needed.

ACHM > RCA

Note:

(a)     ACHM and RCA represent hourly average and acute reference concentrations, respectively.

4.3                                      Baseline Conditions and Background Air Quality

4.3.1                                Baseline Conditions

The proposed Extension is located to the south of the existing SENT Landfill.  The TKOIE is located to the north west of the Extension (see Figure 4.4a).  The TKO Area 137 Fill Bank currently occupies part of the Extension site and the area south of the Extension.  TKO Area 137 has been zoned for industrial activity (Deep Waterfront Industry) according to the Outline Zoning Plan (OZP) No. S/TKO/15 gazetted in November 2004.

No residential dwellings have been identified within 500m of the Extension site boundary.  The nearest residential use (LOHAS Park), which is under construction, is located at about 1.8 km from the Extension site boundary.

The existing air quality in the vicinity of the Extension is affected by:

·           Emissions from facilities in the TKOIE;

·           Dust, odour and stack emissions from the SENT Landfill;

·           Dust nuisance from TKO Area 137 Fill Bank;

·           Vehicular emissions on Wan Po Road (both to and from the SENT Landfill and TKO Area 137 Fill Bank); and

·           Background air quality in the Pearl River Delta.

During the operation of the Extension, the existing SENT Landfill will be closed.  A capping system which will comprise (from bottom to top), as soil layer, a non-woven geotextile, an HDPE liner (impermeable liner), a sub-soil drainage layer and a final cover soil layer, will be installed.  The LFG and leachate generated from the existing SENT Landfill will be collected by the leachate and LFG collection system and conveyed to the new LTP and LFG treatment facility for treatment.  Therefore, no odour will be anticipated to be emitted from the restored area of the existing SENT Landfill.

4.3.2                                Background Air Quality

EPD does not operate any Air Quality Monitoring Stations (AQMSs) in the Tseung Kwan O area.

For TSP, RSP, NO2 and SO2, the past six years (2001 - 2006) of air pollutant data([1]) recorded at the Kwun Tong AQMS (see Table 4.3a), which is the nearest EPD AQMS to the Extension, have been used to characterise the background air quality for the impact assessment.  For CO, the past six years (2001 – 2006) of air pollutant data recorded at the Mongkok AQMS have been used as no CO monitored at Kwun Tong AQMS.

Table 4.3a      Background Air Quality

Air Pollutant

Background Concentration (mg m-3)  

Total Suspended Particulates (TSP)

78 (a)

Respirable Suspended Particulates (RSP)

57 (a)

Nitrogen Dioxide (NO2)

66 (a)

Sulphur Dioxide (SO2)

18 (a)

Carbon Monoxide (CO)

1,294 (b)

Benzene

2.1 (c)

Vinyl Chloride

5.1 (c)

Notes:

(a)     From six years (2001-2006) annual average data on air pollutant concentrations measured at the EPD Kwun Tong AQMS (http://www.epd-asg.gov.hk/english/report/aqr.php).

(b)     Since no CO data is recorded at EPD Kwun Tong AQMS, therefore, the CO data recorded at Mongkok AQMS is used.

(c)     Reference to Table 4.5f.  The maximum average benzene and vinyl chloride concentrations measured at the ambient VOC monitoring stations at the existing SENT Landfill for the past 5 years (2002 – 2006) were used. 

Ambient benzene and vinyl chloride concentrations are measured at the ambient monitoring stations at the existing SENT Landfill.  The locations of the ambient monitoring stations are shown in Figure 4.3a.  In accordance with the Environmental Management Plan (EMP) of the existing SENT Landfill, benzene and vinyl chloride levels are measured at quarterly intervals.  The measured data of benzene and vinyl chloride at the existing SENT Landfill monitoring stations were used to establish the background concentrations of these pollutants in the Study Area (see Table 4.3a).

As the existing SENT Landfill will be closed during the operation of the Extension, there will be no other similar odour sources identified within 500m of the Extension site boundary.  Hence, no background odour is anticipated.

4.4                                      Air Sensitive Receivers

Table 4.4a and Figure 4.4a show the ASRs or those buildings that may be affected.  Representative ASRs were identified in line with the requirements set out in the EIA Study Brief (ESB-199/2004) and Annex 12 of the EIAO-TM.  The list includes existing and planned buildings within 500m of the Extension and ASRs along the Wan Po Road and Chiu Shun Road, in accordance with the requirements of Section 3.4.1.2 of the EIA Study Brief.  Planned developments were identified with reference to the latest Outline Zoning Plans (No. S/TKO/15 gazetted in November 2004).

For the assessment of construction dust and gaseous emission, the Study Area is defined as 500m from the Extension site boundary.

Table 4.4a      Identified Representative Air Sensitive Receivers

ASR

Location

Approx. Distance from Extension Site Boundary (m)

Type of Uses (a)

Approx. Max. Height above Ground (m)

Construction Dust (d)

Gaseous Emission (d)

Odour

A1-1

Proposed C&DM Handling Facility

150

I

30 (c)

Ö

Ö

Ö

A1-2 (1)

Planned Industrial Uses in TKO 137 (south of Extension) – 1

10

I

30 (c)

Ö

Ö

Ö

A1-2 (2) (b)

Planned Industrial Uses in TKO 137 (south of Extension) – 2

200

I

30 (c)

Ö

Ö

Ö

A1-3 (1)

Planned Industrial Uses in TKO 137 (south of TVB City) – 1

90

I

30 (c)

Ö

Ö

Ö

A1-3 (2) (b)

Planned Industrial Uses in TKO 137 (south of TVB City) - 2

200

I

30 (c)

Ö

Ö

Ö

A2

TVB City

110

C

30

Ö

Ö

Ö

A3

HAESL

410

I

30

Ö

Ö

Ö

A4

HAECO Component Overhaul Building

470

I

30

Ö

Ö

Ö

A5

Exhibition Services & Logistics Centre

690

I

30

-

-

Ö

A6

Gammon Skanska

950

I

30

-

-

Ö

A7

Yan Hing Machinery Industrial Building

400

I

30

Ö

Ö

Ö

A8

Apple Daily

505

C

30

Ö

Ö

Ö

A9

Mei Ah Industrial Building

530

I

30

-

-

Ö

A10

Asia Netcom

590

C

30

-

-

Ö

A11

Wellcome Storage

580

I

30

-

-

Ö

A12

Avery Dennison Machinery

600

I

30

-

-

Ö

A13

Hitachi

700

I

30

-

-

Ö

A14

Next Media Co. Ltd

740

C

30

-

-

Ö

A15

Varitronix

850

I

30

-

-

Ö

A16

Four Seas Food Processing Co. Ltd

1,060

I

30

-

-

Ö

A17

Committed HSBC Office

1,000

C

30

-

-

Ö

A18

Eastern Pacific Electronics

1,250

I

30

-

-

Ö

A19

Committed Tung Wah Group of Hospital Aided Primary & Secondary School

1,470

E

20

-

-

Ö

A20

LOHAS Park

1,830

R

200

-

-

Ö

A21

Chiaphua-Shinko Centre

1,860

I

30

-

-

Ö

A22

Shaw Film Studios

2,290

C

30

-

-

Ö

A23

Oscar by the Sea

3,160

R

170

-

-

Ö

A24

Tseung Kwan O Sport Ground

3,810

Rec

1.5

-

-

Ö

A25

Tseung Kwan O Town Park

4,050

Rec

1.5

-

-

Ö

A26

Leung Sing Tak Primary School

4,010

E

20

-

-

Ö

A27

Nan Fung Plaza

4,070

R

130

-

-

Ö

A28

St Andrew’s Church

4,160

Church

20

-

-

Ö

A29

Fung Ching Memorial Primary School

4,190

E

20

-

-

Ö

A30

On Ning Garden

4,260

R

120

-

-

Ö

A31

Sheung Ning Playground

4,240

Rec

1.5

-

-

Ö

A32

Tseung Kwan O Swimming Pool

4,530

Rec

1.5

-

-

Ö

A33

La Cite Noble

3,930

R

140

-

-

Ö

A34

Yuk Ming Court

3,980

R

110

-

-

Ö

A35

Ming Tak Estate

4,130

R

110

-

-

Ö

A36

Tin Ha Wan Village

3,950

R

10

-

-

Ö

A37

Tseung Kwan O Hospital

4,260

Hospital

25

-

-

Ö

A38

Ocean Shore Phase I

3,900

R

160

-

-

Ö

A39

Choi Ming Estate, Choi Yiu Court

3,820

R

155

-

-

Ö

A40

Park Central Block 1

3,530

R

185

-

-

Ö

A41

Bauhinia Garden Block 5

3,200

R

165

-

-

Ö

A42

Heng Fa Chuen

3,300

R

70

-

-

Ö

A43

Island Resort

2,400

R

160

-

-

Ö

Notes:

(a)       I = Industrial premises, R = Residential developments, C = Commercial premises, and Rec = Recreational facilities

(b)       As the type of industrial uses in the TKO Area 137 is not available (except the C&DM Handling Facility) at the time of the EIA Study, the HKPSG recommended setback distance of 200m from the major odour source (ie the SENT Landfill Extension) is included.  The potential air quality impact within and outside the 200m buffer area has been assessed.

(c)       Planning Department has been consulted with respect to the building height restriction of TKO Area 137.  It was agreed that the consultant should assume that the maximum height of the buildings at TKO Area 137 will be 30m. 

(d)       Representative ASRs within 500m from the Extension site boundary will be included in the assessment of the construction dust impact and impact due to gaseous emission.

4.5                                      Potential Sources of Impacts

4.5.1                                Construction Phase

Nuisance from dust generating activities has the potential to arise during construction.  The major construction works include blasting, slope stabilization, excavation and filling, site formation, stone crushing and vehicle movements on the site.  Blasting, materials handling during slope cutting and site formation, rock crushing and wind erosion of the filled area will be the major dust generating activities during the construction of the Extension. The construction works area is shown in Figure 4.5a.

Blasting will take place for the slope cutting at the area currently occupied by the TKO Area 137 for about 107 days between the third quarter of 2011 and end of 2012.  One blast will be made each day.  A total of about 320,000 m3 of rock will be generated and approximately 3,000 m3 of rock will be generated per day.  It should be noted that all construction works will be ceased during the blasting due to site constraint and safety reason.

Due to limited space at the Extension site, most of the rocks will be exported off-site.  A small rock crushing plant will be employed on-site to crush the blasted rocks (about 155,800 m3) into 25mm – 100mm in size and used as leachate drainage stones for the Project and the rest of the blasted rock will be broken down to about 250 mm in size for disposal off-site.  During this process, watering will be carried out and no fugitive emission will be generated.  Dust will be generated from the rock crushing activities screening and at the conveyor transfer point.  With the provision of enclosure for the conveyor belt and watering at the conveyor transfer point, no fugitive dust emission is anticipated.  Other dust control measures recommended in the Guidance Note on the Best Practicable Means for Mineral Works (Stone Crushing Plants) (BPM 11/1) will also be implemented at the rock crusher, and hence dust will only be emitted from the crushing and screening processes. 

Should the processing capacity of the rock crusher exceeded 5,000 tonnes per day, it will be classified as a Specified Process (SP) and a licence will be required for the operation under the Air Pollution Control (Specified Process) Regulations. 

About 770,000 m3 of excavated soil will also be generated during the slope cutting period between the third quarter of 2011 and end of 2012 (around one and a half years).  Some of which will be reused for site formation works (about 475,000 m3).  Due to limited space at the Extension, a small portion of the surplus soils (10,000 m3) will be stockpiled on-site for subsequent use as daily or intermediate cover materials for the Phase 1 operation of the Extension.

Throughout the construction period, good site practices and dust control measures stipulated in the Air Pollution Control (Construction Dust) Regulations will be implemented to reduce the dust emission as much as possible.  The site-specific good site practices and dust control measures are recommended in Section 4.8.1.

4.5.2                                Operational/Restoration Phase

Section 3 details the activities that will take place during operation and restoration of the Extension.  As the restoration will take place progressively, whilst operations are ongoing on other parts of the site, these two phases have been considered together in the assessment.

The potential sources of air quality and odour impacts arising from the Extension during the operational/restoration phase include:

·           Gaseous emissions from the new LFG treatment facility, the thermal oxidizer of the LTP and generator at the new infrastructure area;

·           Vehicular emissions from traffic associated with the Extension;

·           Fugitive emissions from the active tipping face; and

·           Odour emissions arising from Waste Filling Activities and Operation of LTP.

Gaseous Emissions from the LFG Treatment Facility

LFG is a by-product of the waste decomposition process when this takes place under anaerobic conditions.  Typically, this comprises methane (CH4), carbon dioxide (CO2) and trace amounts of other gases (eg volatile organic compounds (VOCs), hydrogen sulphide (H2S), etc).  The proportions of these compounds vary over the life of the landfill and from landfill to landfill.  The quantity also varies from little or none in the early years of operation, rising to a peak during the operational period, before gradually declining over time following restoration of the landfill.

During the operation/restoration phase, the majority of the LFG generated will be collected by the extensive LFG collection system and used on-site (as the first priority) or flared off.  The LFG will be pre-treated (removal of moisture) prior to utilization or flaring in order to minimize corrosion to the equipment.

The LFG treatment facility will comprise two flares (each with a maximum capacity of 10,000 m3 hr-1) located at the south-eastern boundary of the site (see Figure 4.5b).  During the operation/restoration phase, the LFG collected will mainly be used in the LTP and LFG generator (IMW) to supply power for the facilities in the Infrastructure Area and the remainder will be diverted to the on-site utilization plant or flares at the LFG treatment facility.  Based on the outline design of the LTP, the plant will consume a maximum of 3,125 m3 of LFG per hour and the LFG generator will consume about 1,500 m3 of LFG per hour.  If not utilized for other beneficial uses, the remaining LFG (a maximum of 15,375 m3 hr-1) will be flared.  For the worst case assessment, it is assumed that the LFG flares will be operated at their maximum design capacity (ie 10,000 m3 hr-1 each).  The combustion temperature of the flares will be about 850°C.  At this temperature, methane, VOCs and the trace pollutants (such as H2S) will be oxidised and destroyed.  After flaring, trace amount of nitrogen dioxide (NO2), carbon monoxide (CO), sulphur dioxide (SO2) from the oxidation of H2S, benzene, vinyl chloride and non-methane organic compound (NMOCs) will be emitted and the potential impacts of these air pollutants have been assessed in the following section.

The diameter and height of each flare stack will be 3.8m and 25m above the ground, respectively.  The exit flowrate and velocity of the exhaust gas for each flare will be about 499,582 m3 hr-1 and 12.24 m s-1 at 850°C.  Table 4.5a shows the performance standards to which the flares will be operated to maintain a destruction efficiency of at least 99%.
Table 4.5a      Designed Performance Standards of the LFG Flare

Parameter

Performance Standards

Emission limit for nitrogen oxides (NOx)

11.28 mg m-3 (a) (b)

Emission limit for carbon monoxide (CO)

28.19 mg m-3 (a) (b)

Emission limit for sulphur dioxide (SO2)

1.55 mg m-3 (a)

Emission limit for benzene

2.98x10-3 mg m-3 (a) (c)

Emission limit for vinyl chloride

1.88x10-3 mg m-3 (a) (c)

No. of flares

2

Stack height

25 m

Stack diameter

3.8 m

Exit temperature (d)

850°C

Exhaust gas flowrate

499,582 m3 hr-1 (a)

Exhaust gas velocity

12.24 m s-1

Notes:

(a)       Emission limit of air pollutant in exhaust gas.  For SO2, please refer to Annex A1 for detailed calculations.

(b)       Emission limits were estimated based on the specification of flares operating in the existing SENT Landfill.

(c)       Emission limits for benzene and vinyl chloride were estimated from the maximum concentrations of benzene and vinyl chloride in raw LFG measured at the inlet of the flare at the existing SENT Landfill.  The maximum emissions of vinyl chloride and benzene were 4.4 ppm and 5.6 ppm, respectively.  In accordance with the existing SENT Landfill Contract Specification, at least 99% of VOC destruction efficiency should be maintained.  The emission limits are estimated based on the emission concentrations in the inlet, LFG flowrate, exhaust flowrate and the VOC removal efficiency.  Please refer to Annex A1 for the detailed calculations.

Gaseous Emissions from Thermal Oxidizer of LTP

Leachate will be collected from the Extension and the restored existing SENT Landfill and pumped to the LTP in the new infrastructure area.  The LTP will consist of four buffer storage tanks, two ammonia stripping towers and two thermal oxidisers (ie, one duty and one standby), a stripped leachate storage tank, two SBR tanks and a sludge holding tank.  Except for the SBRs, all tanks will be enclosed and the air exhaust from the tanks will be diverted to the thermal oxidiser as part of the air intake. 

The raw leachate will be stripped in the ammonia stripping towers.  The ammonia laden air and the exhaust air of the enclosed tanks will be oxidised and destroyed in the thermal oxidiser (which will operate at 850°C) prior to discharge to the atmosphere.  Under this combustion temperature, the ammonia gas will be completely destroyed ([2]).

LFG will be used as a fuel for the thermal oxidiser.  The estimated maximum LFG consumption will be 3,125 m3 hr-1 assuming that the LTP is operating at its maximum capacity of 1,500 m3d-1 ([3]), and 50 m3 of LFG is required for each cubic metre of leachate treated.  A worst case assumption has been adopted whereby the emissions of nitrogen oxides (NOx), sulphur dioxide (SO2) (product of decomposition of any residual H2S at high temperature), carbon monoxide (CO), benzene, vinyl chloride and NMOCs are assumed to be same as those for the flares (see Table 4.5a).

The physical parameters and emission data of thermal oxidiser are summarized in Table 4.5b.

Table 4.5b      Stack Emissions and Physical Parameters of the Thermal Oxidiser

Parameter

Thermal Oxidiser of the LTP

Emission limit for NOx

28.4 mg m-3 (a)

Emission limit for CO

70.91 mg m-3 (a)

Emission limit for SO2

3.9 mg m-3 (a)

Emission limit for benzene

7.51x10-3 mg m-3 (a)

Emission limit for vinyl chloride

4.73x10-3 mg m-3 (a)

No. of Stack

2 (one duty and one standby)

Stack height

9.76 m (c)

Stack diameter

1.12 m (c)

Exit temperature

171.6 °C (c)

Exhaust gas velocity

17.5 m s-1 (c)

Exhaust gas flowrate

62,068 m3 hr-1

Notes:

(a)       All emission limits are under its exhaust gas condition.

(b)       Refer to the detailed calculations presented in Annex A1.

(c)       With reference to the design of the Thermal Catalytic Units of the existing Bioplant at SENT Landfill.

Gaseous Emissions from LFG Generator

A generator fuelled by LFG will be installed to provide power for on-site plant and equipment.  Taking account of the anticipated power requirements of the infrastructure area of the Extension, the capacity of the generator will be about 1MW which is similar to the generator used in the existing SENT Landfill.  The physical parameters and emission data of generator, reference to the LFG generator operating in the existing SENT Landfill, are summarized in Table 4.5c.

Table 4.5c      Stack Emissions and Physical Parameters of the LFG Generator

Parameter

LFG Generator

Engine power

1MW (a)

LFG input to generator

1,500 m3 hr-1 (a)

Emission limit for NOx

0.14 lb mmBTU-1 (b)

Emission limit for CO

0.44 lb mmBTU-1 (b)

Emission limit for SO2

0.045 lb mmBTU-1 (b)

Emission limit for benzene

2.1x10-5 lb mmBTU-1 (b)

Emission limit for vinyl chloride

1.6x10-6 lb mmBTU-1 (b)

No. of Stack

2 (one duty and one standby)

Stack height

28 m

Stack diameter

0.305 m (a)

Exit temperature

454°C (a)

Exhaust gas velocity

48.6 m s-1 (a)

Notes:

(a)       Reference to the generator being operated at the existing SENT Landfill.

(b)       Reference to the Compilation of Air Pollutant Emission Factors, AP-42, 5th Edition, Table 3.1-1 and 3.1-2b.

Summary:  Under normal operations, LFG collected from the Extension will be primarily used as fuel for the LTP and generator.  The remainder will be utilised or flared.  Table 4.5d summarises the emission data of each facility and the location of these facilities is shown in Figure 4.5b.  The detailed calculation is summarized in Annex A1.

Table 4.5d      Summary of Gaseous Emission Inventory for the Flares and Thermal Oxidiser During Operation/Restoration Phase (a)

Parameter

Flare

Thermal Oxidiser

LFG Generator

No. of emission points

2

1 (one duty and one standby)

1 (one duty and one standby)

Stack height (m)

25

9.76

28

Stack diameter (m)

3.8

1.12

0.305

Exhaust gas velocity (m s-1)

12.24

17.5

48.6

Exhaust gas flowrate (m3 s-1)

499,582

62,068

12,780

Exit temperature (°C)

850

171.6

454

Emission limit for NOx (b)

11.28 mg m-3

28.4 mg m-3

0.14 lb mmBTU-1

Emission limit for CO (b)

28.19 mg m-3

70.91 mg m-3

0.44 lb mmBTU-1

Emission limit for SO2 (b)

1.55 mg m-3

3.90 mg m-3

0.045 lb mmBTU-1

Emission limit for benzene (b)

2.98x10-3 mg m-3

7.51x10-3 mg m-3

2.1x10-5 lb mmBTU-1

Emission limit for vinyl chloride (b)

1.88x10-3 mg m-3

4.73x10-3 mg m-3

1.6x10-6 lb mmBTU-1

Emission rate for NO2 (g s-1)

0.31 (c)

0.10 (c)

0.11 (c)

Emission rate for CO (g s-1)

3.91

1.22

1.721

Emission rate for SO2 (g s-1)

0.22

0.07

0.176

Emission rate for benzene (g s-1)

4.14x10-4

1.29x10-4

8.22x10-5

Emission rate for vinyl chloride (g s-1)

2.61x10-4

8.15x10-5

6.26x10-6

Notes:

(a)       Detailed calculations are summarized in Annex A1.

(b)       All emission limits are under its exhaust gas condition.

(c)       Assuming 20% of NOx is NO2.

Vehicular Emissions from Traffic Associated with the Extension

The waste arising forecast indicates that a maximum of 134 vehicles per hour([4]) will be generated from the operation of the Extension which will be about 19% on the Wan Po Road south of Chung Wang Street and about 2.4% on the Wan Po Road south of Pak Shing Kok Road as compared to forecasted background traffic in 2018 (refer to Annex B2-3).  It is anticipated that this limited increase in traffic flow will not result in adverse air quality impacts at the identified ASRs.

Fugitive Emissions at Landfilling Area in the Extension

The landfill activities during the operation/restoration phase of the Extension will generate fugitive dust and gaseous emissions from (1) the construction of drainage channels and sumps, LFG and leachate extraction wells and collection systems; (2) haul roads; and (3) operation of the construction equipment.  Landfill surface emission from the active tipping face is also a potential fugitive emission source.

Fugitive Dust Emissions:  Fugitive dust will be emitted from the placement of cover materials, construction of LFG and leachate collection pipes and wells, traffic movements on the unpaved haul roads and traffic movements at the waste reception area.  The quantities of soil and rock to be handled for different phases of the Extension are summarized in Table 4.5e. 

Table 4.5e      Total Soil and Rock Fill Requirements

Phase

Total Fill Requirement (m3)

Fill Requirement Per Day (m3d-1) (a)

 

Soil

Rock

Soil

Rock

1

365,600

60,500

1,000

165.8

2

453,100

60,500

1,240

165.8

3

478,700

60,500

1,310

165.8

4

557,900

60,500

1,530

165.8

5

590,800

60,500

1,620

165.8

6

658,800

60,500

1,800

165.8

Total

3,104,900

363,000

-

-

Note:

(a)     For each phase, no. of day is 365.

The management of fugitive dust at the Extension will be similar to that being implemented at the existing SENT Landfill and will include immediate compaction of the fill area; regular damping down of the surface of the haul road; provision of vehicle washing facility for RCVs at the exit of the Extension (to ensure no significant dust will be brought onto the public road); and regular cleaning of the main access road and waste reception area by road sweeper.

Although the lining of side slopes will be carried out concurrently with the waste tipping operation, no earthworks will be required for the slope lining works.  Hence, there will be no cumulative dust impacts for these activities.

At the existing SENT Landfill, the average ambient daily TSP concentration record at the ambient TSP monitoring stations located at the site boundary ([5]) over the past five years (2002-2006) was 89 µg m-3.  There were no exceedances of the daily dust criterion of 260 µg m-3 due to the operation of the landfill.

As the majority of the Extension site will be covered with impermeable liner, the potential areas from which dust can be generated will be much lower when compared with the existing SENT Landfill operation.  Hence, it is anticipated that the potential dust to be generated due to the operation of the Extension will be much lower than that from the operation of the existing SENT Landfill.  With the implementation of the dust control measures recommended in Section 4.8.2, it is expected that the TSP concentrations at the Extension site boundary during the operation/restoration phase will be well below the daily dust criterion and there will be no adverse dust impacts to the identified ASRs.

Gaseous Emissions from Construction Plant:  Gaseous emissions such as nitrogen dioxide (NO2) and sulphur dioxide (SO2) will be generated from the operation of diesel-fuelled construction for the following activities. 

·           Construction of drainage channels and sumps – transportation of materials, bar bending and cutting as well as concreting;

·           Road construction – transportation of materials, grading, road rolling;

·           Deposition and compaction of waste – transportation, deposition and compaction of waste;

·           Placement and removal of daily covered materials – by excavator, bulldozer, dump truck, vibratory roller and loader; and

·           Capping and landscaping (progressive restoration) – by bulldozer, dump truck, vibratory roller, loader and mobile crane.

These plants will be located across the site, depending on need.  The nearest representative ASR, TVB City, is located at about 110 m away from the nearest construction site boundary.  The total gaseous emissions generated by the plant over the construction site area (ie, 20ha) are small and it will disperse and diluted with the ambient air very rapidly.  Therefore, the potential air quality impact associated with operation of the construction plant on the identified ASRs is envisaged to be limited and minor.

Emissions of LFG including VOCs from Landfill Surfaces:  The predicted LFG generation rates have been discussed in Section 8.5.1.  The LFG management system is designed to collect LFG generated from the Extension as early as possible.  Except the active tipping face and the special waste trench, all the areas will be covered by 600mm of soil and an impermeable liner.  In addition to the vertical LFG collection wells, a number of horizontal LFG collection wells will be installed above the leachate drainage layer and within the waste mass.  The majority of LFG will be captured by the collection system.

The composition of LFG is anticipated to be similar to that from the existing SENT landfill, given that the waste types accepted will be similar.

Samples obtained from the LFG abstraction wells of the existing SENT Landfill contain about 40 to 60% methane, 30 to 45% carbon dioxide and a trace amount of VOCs ([6]).  In 2005 and 2006, out of the 39 VOCs ([7]) analysed, only dichlorodifluoromethane, vinyl chloride, dimethyle sulphide, methylene chloride, benzene, heptanes, trichloroethylene, toluene, octanes, tetrachloroethylene, ethylbenzene, xylenes, propyl benzene and dichlorobenzene were detected.  For most of these, the measured concentrations were in the range 0.01 and 39.7 µg m-3.

The ambient concentrations of the 39 VOCs were also monitored on a quarterly basis at the ambient air quality monitoring stations at the site boundary.  A summary of the measured concentrations of these 39 VOCs from 2002 to 2006 is presented in Table 4.5f.  Benzene, chloroform, dichlorodifluoromethane, ethylbenzene, methylene chloride, propyl benzene, toluene and xylene were measured in most of the samples.  However, the concentrations were well below the respective trigger levels.  Other VOCs were not detected or measured.  Exceedances of the trigger levels for chloroform and propyl benzene were detected in one occasion at the ambient VOC monitoring stations.  Investigations were conducted and it was considered that the abnormal readings were caused by off-site sources such as vehicle exhaust.


Table 4.5f       VOC Concentrations at Site Boundary and On-site of the Existing SENT Landfill (2002 - 2006)

Pollutant

Trigger Level

Monitored VOC Concentration (µgm-3)

VOC/1

VOC/4

VOC/6

VOC/8

On-site

Min

Max

Average

Min

Max

Average

Min

Max

Average

Min

Max

Average

Min

Max

Average

1,1,1-Trichloroethane

19,000

ND

2.3

1.2

ND

2.9

1.5

ND

5.8

1.7

ND

4.1

1.2

ND

4.1

1.4

1,2-Dibromoethane

40

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

4.4

4.4

ND

ND

ND

1,2-Dichloroethane

400

ND

0.6

0.4

ND

2.1

0.9

ND

1.3

0.7

ND

2.5

1.2

ND

4.4

1.7

Benzene

160

ND

4.4

1.0

<0.5

10.1

1.5

<0.5

25.1

2.1

<0.5

13.1

1.5

<0.5

4

1.2

Butan-2-ol

3,000

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Buthanethiol

4

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Butyl Benzene

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Carbon Disulphide

255

ND

0.9

0.9

ND

41.2

26.0

ND

5.5

5.1

ND

6.7

6.7

ND

6.8

6.3

Carbon Tetrachloride

126

ND

3.5

1.1

ND

0.9

0.7

ND

1.3

0.8

ND

5

1.2

ND

3.8

1.6

Chloroform

98

ND

67

9.5

ND

409.2

36.1

ND

19.1

3.4

ND

30.2

11.0

ND

67

17.2

Decane

1,000

ND

ND

ND

ND

<1

<1

ND

ND

ND

ND

ND

ND

ND

ND

ND

Dichlorobenzene

1500

ND

29

4.1

ND

95

19.3

ND

65

5.6

ND

137

13.8

ND

4

1.5

Dichlorodifluoromethane

49,500

1

37.1

3.7

ND

450

27.1

ND

159.4

11.0

ND

490

25.9

ND

8.1

1.9

Dimethyl Sulphide

11

ND

ND

ND

ND

9.4

5.0

ND

0.7

0.7

ND

ND

0.4

ND

0.2

0.2

Di-n-Propyl Ether

2700

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Ethanethiol

1

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Ethanol

1,900

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Ethyl Butyrate

-

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Ethyl Propionate

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Ethylbenzene

1,000

ND

160

14.1

ND

268

28.3

ND

562

32.3

ND

182

17.8

ND

160

16.7

Heptane

16,000

ND

21.9

7.2

ND

<1

0.8

ND

34

17.8

ND

49

17.0

ND

47.9

21.6

Limonene

57

ND

5.2

5.2

ND

ND

ND

ND

3.5

3.5

ND

2

2.0

ND

ND

ND

Methane

-

<1

480

31.2

<1

250

48.7

<1

97.9

21.1

<1

436.7

34.4

<1

130

10.2

Methanethiol

-

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Methanol

2,600

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Methyl Butyrate

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Methyl Propionate

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Methylene Chloride

3,500

<0.4

557.3

49.5

<0.4

174

28.9

<0.4

104.2

17.1

ND

680.6

97.9

<0.4

2885

197.5

n-Butyl Acetate

1,500

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Nonane

24,000

ND

5

1.8

ND

29

7.9

ND

<0.9

<0.9

ND

<0.9

<0.9

ND

26

16.0

Octane

14500

ND

13

4.5

ND

3

1.8

ND

37

25.9

ND

30

12.2

ND

14.5

6.2

Propyl Benzene

196

ND

74.9

11.1

<0.8

605.1

42.3

ND

340

31.0

ND

280

24.0

ND

282

21.9

Propyl Propionate

56,000

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Terpenes

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Tetrachloroethylene

3,350

ND

94.5

10.1

ND

19.5

6.3

ND

24.5

3.8

ND

11.5

6.1

ND

7.5

2.7

Toluene

1,880

4

124

24.2

<0.5

463

89.6

<0.5

1003

74.2

<0.5

423

55.0

<0.5

264

50.4

Trichloroethylene

5,350

ND

2.2

1.4

ND

6

3.1

ND

4.8

2.8

ND

4.4

2.0

ND

<1.2

<1.2

Undecane

1,300

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

ND

Vinyl Chloride

78

0.4

0.4

0.4

ND

9.5

4.2

ND

36.5

5.1

ND

4.9

3.5

ND

<0.3

0.3

Xylene

4,350

ND

200

16.7

<0.5

479

50.1

<0.5

941

54.4

<0.5

271

29.8

<0.5

200

22.8

Notes:

(a)     “ND” means Not Detectable.

(b)     Bold and underlined figure indicates the exceedance of the trigger level.


As the majority of the Extension site will be covered with an impermeable liner and LFG will be extracted via a comprehensive LFG collection system during the operation phase, it is anticipated that the fugitive LFG emission from the Extension due to waste tipping activities will be significantly reduced relative to the existing SENT Landfill.  Taking account of the ambient VOC monitoring results at the existing SENT Landfill, it is expected that the ambient VOC concentrations at the Extension Site boundary will be well below the trigger levels for individual compounds.  Further dilution of the VOC concentration is expected due to dispersion off-site.  The anticipated VOC concentrations at the identified ASRs will be minimal and will not cause adverse impacts.

Odour Emissions from Waste Filling Activities and Operation of LTP

The restoration of the landfill will take place progressively, whilst operations are ongoing on other parts of the site, therefore, these two phases have been considered together in the assessment.

Potential sources of odour impact during operation/restoration phase included:

·           Waste filling area; and

·           Operation of the LTP and the LFG treatment facility.

In order to minimize the potential odour emissions during the operational phase of the Extension, a number of odour management and control measures have been incorporated into the outline design.  These measures are summarized in Table 4.8a.

Odour Emissions from Waste Filling Area

The Extension is scheduled to commence operation in 2013 and will be designed to receive MSW, special waste ([8]) and construction waste.  By that time, the Sludge Treatment Facilities (STF) are scheduled to be in operation ([9]) and sludge from sewage treatment works (STWs) will be diverted to the STF for treatment and disposal. 

The operational life of the Extension is expected to be about 6 years.  The Extension will be developed in 6 phases (Phases 1 to 6) and each phase will be in operation for approximately 1 year.  The ground level of the first phase will be at about +6mPD and the highest level will be at +150 mPD.  The Extension will open to receive wastes from 8 am to 11 pm every day. 

Waste Reception Area:  All incoming and outgoing refuse collection vehicles (RCVs) will be weighed at the enclosed weighbridge office at the waste reception area.  All RCVs visiting the Extension are of enclosed-type and expected to comply with relevant regulations and to be properly maintained, therefore, the potential odour emission from RCVs and at the waste reception area are assumed to be minimal.

Active Tipping Face:  After weighing, the RCVs will be directed to the active tipping face for unloading.  The operation at the active tipping face will be similar to that of the existing SENT Landfill.  Two platforms (ie lower and upper platforms) will be used for separate unloading of MSW (at the lower platform) and construction waste (at the upper platform).  The construction waste will overlay the MSW.  The wastes will be promptly spread by bulldozer and compacted by a landfill compactor to minimize the exposure time of MSW thus minimise the opportunity of odour emission to the atmosphere.  The tipping face area will be 30m x 40m ([10]).  After 11 pm, the Extension will be closed and the compacted waste will be covered with 300mm of cover soil immediately.  Therefore, odour emissions from the active tipping face are expected during the operating hours; however, the emissions will be much reduced thereafter.

Special Waste Trench:  A trench will be excavated into the landfill mass for the disposal of waste that needs special handling.  The trench will be located at least 50 m from the active tipping face and the waste boundary.  The trench will only operate when the waste depth is at least 10m above the base to avoid damage to the leachate collection system.  The size of the trench will vary in accordance with the volume of special waste that has been pre-registered for disposal by the special waste producers.  With reference to the operational experience at the existing SENT Landfill and the quantity of special waste received, it is expected that the maximum size of the trench will be about 6m x 2.5m.  The trench will be open to receive special waste from 9 am to 5 pm everyday.  After 5 pm, the trench will be backfilled with inert waste and covered by 600 mm of soil and an impermeable liner to minimise odour emissions.  Special waste for trench disposal is normally required to be delivered in sealed bags and no odour will be generated from the bagged waste.  However, odour will potentially be emitted from the side walls and the base of the trench itself during operating hours.  In order to reduce the odour emission from the trench, the trench will be covered by a movable cover with retractable or suitable opening so that the trench is covered at all times except during waste deposition.  The air trapped inside the trench will be extracted and scrubbed by a mobile odour removal unit prior to discharge to the atmosphere.  Therefore, the odour emitted from the trench will be minimal.  However, for the worst-case assessment in this Study, it is assumed that the trench is open to atmosphere without any odour removal.
Main Haul Road to Active Tipping Face:  The MSW will be delivered in RCVs with enclosed compactor body.  It is therefore anticipated that the potential odour emission from the RCVs along the haul road of the Extension will be minimal.
Daily Covered Area:  At the end of each working day (ie after 11 pm), the active tipping face will be covered with 300 mm of soil and compacted.

Intermediate Cover Area:  Except for the active tipping face and the final cover area (see below for details), all other areas of the Extension will be covered with 600mm of soil ([11]) and an impermeable liner in order to minimize rainwater infiltration into the waste and odour emission as well as to enhance LFG extraction.  It is therefore anticipated that no odour will be emitted from this area ([12]).

Final Cover Areas:  After waste tipping reaches the final levels, a capping system will be installed.  The capping system will comprise (from bottom to top) a soil layer, a non-woven geotextile, an HDPE liner (impermeable layer), a sub-soil drainage layer and a final cover soil layer.  Permanent gas extraction system will be installed to extract LFG from the waste mass.  Planting will also be provided for the final covered area.  It is therefore anticipated that no odour will be emitted from this area ([13]).

Operation of Leachate Treatment Plant (LTP)

Leachate collected from the Extension and the existing SENT Landfill will be pumped to the LTP in the new infrastructure area.  The LTP will consist of four buffer storage tanks, two ammonia stripping towers, two thermal oxidisers (i.e., one in operation and one standby), a stripped leachate storage tank, two SBR tanks and a sludge holding tank.  Except for the SBR tanks, all tanks will be enclosed and the air exhaust from the tanks will be diverted to the thermal oxidiser.  The operation temperature of the thermal oxidizer is about 850°C.  Odorous gas in the exhaust air (such as ammonia) will be oxidised and destroyed at such high temperature ([14]) in the thermal oxidiser prior to discharge to the atmosphere.  The SBR tanks will therefore be the only odour emission source in the LTP. 

The dimension of each of the SBR tanks is 20m (width) x 35m (length).  The tank height is about 5m.  The leachate temperature in the SBR will be maintained at about 40°C throughout the year.  The LTP will operate on a 24-hours per day basis.

Operation of LFG Treatment Facility

The LFG treatment facility will be operated on a 24-hours per day basis.  The LFG collected from the LFG extraction system will be either diverted to other utilization scheme for beneficial use or flared at the treatment facility.  The flaring temperature is about 850°C and odorous compounds such as VOCs or H2S in the LFG will be oxidised and destroyed at such temperatures.  Therefore, no odour emission is expected from the LFG treatment facility.

Summary of Potential Odour Emission Sources

As discussed above, the major potential odour sources will include waste tipping activities at the active tipping face and at the special waste trench as well as the operation of the LTP.

The odour emission sources during the operation/ restoration phase are summarized in Table 4.5g.

Table 4.5g      Summary of Odour Emission Sources

Odour Emission Source

Area

Remarks

During Operation Hour (8am – 12 midnight)

Active tipping face for MSW + construction waste

30m x 20m

·       From 8am to 11pm.  Covering the active tipping face after operation at 11pm to 12 midnight

Active tipping face for construction waste

30m x 20m

·       From 8am to 11pm.  Covering the active tipping face after operation at 11pm to 12 midnight

Special waste trench

6m x 2.5m (plan area exposed to air) (a)

·       From 9am to 5pm.  Covering the trench at 5pm – 6pm

After Operation Hour (12 midnight – 8am on the next day)

Daily cover area

30m x 40m

12 midnight – 8am (on the next day)

24-hour Operation

SBR tanks of the LTP

20m x 35m
(2 nos.)

24 hours

Note:

(a)     Longer side : 6m (l) x 2m (H); shorter side: 2.5m (l) x 2m (H); bottom: 6m x 2.5m

4.5.3                                Aftercare Phase

Upon completion of final filling and capping, the aftercare phase will commence and is estimated to last for up to 30 years.  The LFG and leachate management systems as well as the LFG generator will continue to operate during the aftercare phase.

Operation of LTP

It should be noted that once the landfill is restored, the leachate generation rate from the Extension will be significantly reduced and hence the average daily volume of leachate to be treated will be reduced from about 350 m3 d-1 to 23 m3 d-1, ie approximately an 93% reduction).  With respect to the small volume of leachate generated, it will be able to reduce the nitrogen levels in the leachate using biological treatment (ie, nitrification and denitrification) so that the effluent will comply with the discharge standards.  The operation of the ammonia strippers and thermal oxidisers will not be necessary.

The vent gas from the enclosed leachate storage and treatment tanks will be diverted to an air scrubber or the flares prior to discharge to the atmosphere.  The designed odour (including ammonia gas) removal efficiency of the air scrubber will be at least 95%.  Therefore, majority of the odorous gas in the vent gas from enclosed tanks will be removed.  The scrubbed vent gas will be used as part of the air intake for the aeration system of the SBR tank.  If the vent is diverted to the flare(s) as part of the air intake, the odorous gas will be destroyed at high combustion temperature (at 850oC).

The potential source of odour emission during the aftercare phase will only be the open SBR tanks (please refer to Table 4.6e for the odour emission rate of the SBR tanks).

Operation of LFG Treatment Facility

Together with the final capping system, the permanent LFG extraction system will prevent fugitive emission of LFG from the restored landfill.  The LFG abstracted will be utilised or flared.  Under a high combustion temperature (850oC) at the flare, the odorous VOCs in the LFG will be completely oxidised and destroyed.

Conversely, the total LFG generated from the restored SENT Landfill and the Extension will increase (maximum yield of about 17,000 m3 hr-1).  A worst case scenario has been assumed where the two flares will be operated at full load (20,000 m3 hr-1).  The emission inventory of flares is summarized in Table 4.5h.  The detailed calculation is summarized in Annex A1.

LFG Generator

LFG generator will continue to provide power supply for the operation of LFG Treatment Facility, LTP and other facilities at the infrastructure area.  The emission inventory of the LFG generator is summarized in Table 4.5h and detailed calculations are presented in Annex A1.

Table 4.5h      Summary of Gaseous Emission Inventory for the Flares and Generator During Aftercare Phase (a) (b)

Parameter

Flare

LFG Generator

No. of emission points

2

1 (one duty and one standby)

Stack height (m)

25

28

Stack diameter (m)

3.8

0.305

Exhaust gas velocity (m s-1)

12.24

48.6

Exhaust gas flowrate (m3 s-1)

499,582

12,780

Exit temperature (°C)

850

454

Emission limit for NOx (c)

11.28 mg m-3

0.14 lb mmBTU-1

Emission limit for CO (c)

28.19 mg m-3

0.44 lb mmBTU-1

Emission limit for SO2 (c)

1.55 mg m-3

0.045 lb mmBTU-1

Emission limit for benzene (c)

2.98x10-3 mg m-3

2.1x10-5 lb mmBTU-1

Emission limit for vinyl chloride (c)

1.88x10-3 mg m-3

1.6x10-6 lb mmBTU-1

Emission rate for NO2 (g s-1) (d)

0.31

0.11

Emission rate for CO (g s-1)

3.91

1.721

Emission rate for SO2 (g s-1)

0.22

0.176

Emission rate for vinyl chloride (g s-1)

4.14x10-4

8.22x10-5

Emission rate for benzene (g s-1)

2.61x10-4

6.26x10-6

Notes:

(a)       Detailed calculations are summarized in Annex A1.

(b)       Reference to Table 4.5d

(c)       All emission limits are under exhaust gas condition.

(d)       Assuming 20% of NOx is NO2

4.5.4                               Cumulative Impacts

According to the EIA Study Brief requirement, major emission sources in the vicinity should be included to assess the cumulative air quality impact.

Construction Phase

The operation of the existing SENT Landfill (last year of operation) and the C&DM Handling Facility in TKO Area 137 are identified as potential concurrent projects during the construction phase of the Extension.

During the last year of the operation of the existing SENT Landfill, most of the landfill area will be capped and restored.  Dust will be emitted from the placement of cover materials, traffic movements on the unpaved haul roads and traffic movements at the waste reception area (please refer to Figure 4.5a).  As discussed in Section 4.5.3, due generation will be minimised by implementation of dust control measures, including immediate compaction of the fill area; regular damping down of the surface of the haul road; provision of vehicle washing facility for RCVs at the exit of the existing SENT Landfill (to ensure no significant dust will be brought onto the public road); and regular cleaning of the main access road and waste reception area by road sweeper. 

The separation distance between the active tipping area of the existing SENT Landfill and the dusty construction work area of the Extension site is about 850m (refer to Figure 4.5a).  As the worse wind angles which carry the dust from dusty activity area of Extension and that for dust generated from the active tipping area of the existing SENT Landfill are different, no cumulative dust impacts are anticipated due to the operation of the existing SENT Landfill and the construction of the Extension.

TKO Area 137 is currently planned for Deep Water Front Industrial uses.  A Construction and Demolition Material (C&DM) Handling Facility is scheduled to be commissioned in phases in TKO Area 137 (see Figure 3.9b) in 2009.  The capacity of the C&DM Handling Facility is about 20,000 tonnes per day.  However, the detailed design information is not available at this stage but it is understood that the potential dust impacts associated with the operation of the C&DM Handling Facility will be assessed as part of the feasibility and engineering design of the facility.  It is recommended that the cumulative dust impact in the vicinity should be addressed in the environmental study under that study.  It is anticipated that the facility will incorporate necessary dust control measures (as stipulated in the Air Pollution Control (Construction Dust) Regulations) in the design of the facility (which may include enclosure of the dusty operations) and good site practices to control dust emissions from the facility. It is expected that no adverse dust impact will result from the operation of the facility.

As of the existing fill bank at TKO Area 137 will be decommissioned by the end of 2008, no cumulative dust impact will be anticipated.

In summary, no cumulative dust impact is anticipated during the construction of the Extension.

Operation/Restoration and Aftercare Phases

Odour Impact

When the Extension commences operation, the existing SENT Landfill will be closed and will not generate odour.  No other similar concurrent type of odour source is identified within 500m of the Extension site boundary during the operation/restoration and aftercare phases.  Hence, no cumulative landfill odour impact is expected.

Gaseous Emissions from the existing TKO Industrial Estate

Within 500m from the Extension site boundary, emissions from TVB City and HAESL may cause cumulative air quality impact.  On-site chimney survey within the 500m area from the Extension site boundary was conducted in January 2008.  Interviews were also conducted to validate the stack operation and its emission inventory.

According to the information provided by TVB City and the public information obtained from the EPD Regional Office (East), the major gaseous emission sources identified at TVB City are the emergency generators.  As the emergency generators will only operate when CLP’s grid is suspended, the operating time of these generators is very limited and it will not expected to cause cumulative air quality impact within the Study Area.

With reference to the EIA Report of HAECO Aircraft Engine Test Cell Facility at TKO, NO2, CO and SO2 are the key air pollutants to be emitted during engine testing.  These emission rates and stack characteristics are summarized in Table 4.5i.

Table 4.5i       Stack and Emission Characteristics in Study Area (a)

Stack ID

No. of Stacks

Efflux Velocity (m s-1)

Stack Diameter (m)

Stack Height Above Ground (m)

Exit Temp. (°C)

Emission Rate (g s-1)

 

 

 

 

 

 

NO2

CO

SO2

HAECO / HAESL (c)

1

16.4 for NO2 and SO2;
12 for CO

14.7

40

52

21.2

23.9

1.92

Notes:

(a)       Reference to the EIA Report of HAECO Aircraft Engine Test Cell Facility at TKO.

(b)       It is the equivalent diameter.  The stack is in square shape with an area of 13m x 13m.

The above stack characteristic, emission inventory and engine type being tested at HAESL have been confirmed by HAESL.

The emissions of NO2, CO and SO2 from HAESL are included to assess the cumulative air quality impact during both the operation/restoration and aftercare phases.

4.6                                      Assessment Methodology

4.6.1                                Construction Phase

Dust will be generated from blasting, materials handling, wind erosion, rock crushing and truck movements on paved haul roads within the site.  It should be noted that no construction works will be carried out during blasting due to the site constraint and safety reason.  The dust impact from blasting will be assessed individually.

TSP levels at the identified ASRs were predicted using the Fugitive Dust Model (FDM).  The 2006 meteorological data obtained from the existing SENT Landfill weather station and TKO weather station operated by the Hong Kong Observatory (HKO) were used for the model runs.  Dust emission rates and associated particle size distributions for the assessment were determined in accordance with the Compilation of Air Pollutant Emission Factors, AP-42, 5th Edition.  One blast will be made each day and the construction works would be carried out for 12 hours (from 7am to 7pm) per day and 24 days per month.  During night-time (7pm to 7am on next day), only wind erosion of open fill area was considered.  Mitigation measures recommended in Section 4.8.1 have been considered in the dust emission rate estimation.

The mitigated TSP emission rates during blasting, rock crushing, materials handling, wind erosion and truck movement on unpaved haul road within the construction site are estimated and summarized in Table 4.6a and detailed calculations are presented in Annex A2.

Table 4.6a      Mitigated Dust Emission Rates (a) (b) (c)

Construction Works

Dust Generating Activities

Dust Emission Rate

Remarks

Slope Cutting

Blasting

1.93 gs-1

·     Blasting area = 1,000 m2 (estimated by the engineer)

·     1 blast per day during daytime

·     Total no. of day = 107 days

·     Emission height = 0,5m

Excavation

Materials Handling

0.0103 gs-1

·     Excavation period = 1.5 year

·     Total volume of soil excavated = 770,000 m3

·     Hourly soil generation rate = 148.5 m3/hr

·     50% dust removal efficiency by watering

·     Working time: between 7am and 7pm

·     Emission height: 0.5m

 

Rock crushing

·   Crushing = 0.0098 gs-1

·   Screening = 0.018 gs-1

·     Rock to be crushed per day = 400m3 per day (max.)

·     Working time: between 7am and 7pm

·     Emission height = 5m

 

Truck movement on unpaved haul road

0.00435 gm-2s-1

·     Total no. of vehicle trip per hour = 70 (including return trip)

·     Average truck weight = 21.5 tonnes

·     90% dust removal efficiency by watering of main haul road, limiting vehicle speed and paving with aggregate/gravel

·     Working time: between 7am and 7pm

·     Emission height: 0.5m

Filling

Materials Handling

0.0054 gs-1

·     Filling period = 1.5 year

·     Total volume of fill materials = 407,200 m3

·     Hourly filling rate = 78.5 m3/hr

·     50% dust removal efficiency by watering

·     Working time: between 7am and 7pm

·     Emission height: 0.5m

 

Truck movement unpaved haul road

0.00156 gm-1s-1

·     Total no. of vehicle trip per hour = 26 (including return trip)

·     Average truck weight = 20 tonnes

·     90% dust removal efficiency by watering of main haul road, limiting vehicle speed and paving with aggregate/gravel

·     Only carried out during daytime between 7am and 7pm

 

Wind erosion

§   Daytime : 1.35x10-6 gm-2s-1

§   Night-time : 2.7x10-6 gm-2s-1

·     Total area = about 15 hectare

·     50% dust removal efficiency by watering during daytime and no dust reduction at night-time

·     24-hour

Notes:

(a)       Detailed calculations and location of the dust emission sources are presented in Annex A2.

(b)       Dust emission factors in Compilation of Air Pollutant Emission factors, (AP-42), 5th Edition by USEPA is used.

(c)       Dust control measures recommended in Section 4.8.2 have been adopted.

Hourly and daily TSP concentrations were predicted at 1.5m and 10m above ground of the representative ASRs A1 to A4, A7 and A8 which are located within 500m of the Extension site boundary as the dust impact is localized.  Daily TSP concentrations predicted from blasting, construction works and night-time wind erosion activities will be directly added to obtain an overall daily TSP concentration at the ASRs.  The background TSP concentration, as presented in Table 4.3a, was also used to assess the cumulative TSP concentrations.

4.6.2                                Cumulative Gaseous Emissions During Operation/Restoration and Aftercare Phases

An EPD approved air dispersion model, ISCST3, was employed for the assessment.  The 2006 meteorological data obtained from the existing SENT Landfill weather station and TKO weather station operated by the Hong Kong Observatory (HKO) were used for the model runs.  The “rural” mode was used.  Terrain effects within 500m of the Extension site boundary have been included.

The emission rates of NO2, CO, SO2, benzene and vinyl chloride from the operation of the LFG treatment facility, LTP and LFG generator during operation/restoration and aftercare phases, presented in Tables 4.5d and 4.5h, respectively, were used for the prediction.  The thermal oxidiser, LFG flares and LFG generator will be operated 24 hours per day.  It is conservatively assumed that the engine testing at HASEL will be carried on a 24-hour basis.  The locations of the LFG treatment facility, LTP, LFG generator and the emission points at HASEL are shown in Figure 4.5b.

The hourly, daily and annual average concentrations of the key air pollutants were predicted at 1.5m to 30m above ground at the representative ASRs A1 to A4, A7 and A8 as the maximum height of these ASRs is 30 m above ground.  The worst affected height was identified and isopleths showing the levels of these key air pollutants at 1.5m above ground and the worst affected height were plotted.

Background concentrations presented in Table 4.3a were included in the assessment of the cumulative air quality impact. 

4.6.3                                Odour Emissions from Waste Filling Activities and Operation of LTP During Operation/Restoration Phase

Selection of Emission Source Locations for Worst Cases

The operation/restoration of the Extension will be divided into six phases starting from the south and filling progressively to the north (see Figures 4.6a-1 and 4.6a-2) in general.  Three worst-cases (Cases 1 – 3) in each phase (except Phase 6) have been identified for the odour impact assessment, which have taken into account the worst case odour impacts to existing ASRs in TKOIE (eg TVB City), planned ASRs in the TKO Area 137, and ASRs at higher elevations (eg LOHAS Park (ASR A20)).  Odour emission inventory including type of source, source area, source height, duration and the temperature of each worst-case are summarized in Table 4.6b.

Table 4.6b      Odour Emission Inventory in Each Worst Case

Source Height

Worst-case Scenario (b)

Odour Source

Area

Air Temperature of Odour Emission (a)

Phase 1

·       10m above ground

Phase 2

·       30m above ground

Phase 3

·       50m above ground

Phase 4

·       70m above ground

Phase 5

·       100m above ground

Phase 6

·       130m above ground

In each phase, there will be 3 worst cases (b):

·   Case 1
(southern end of Extension)

·   Case 2
(western side of Extension close to A1-1)

·   Case 3
(northern side of the Extension)

During Extension Opening Hours (8am – 12 midnight)

Active tipping face for MSW + construction waste

·     30m x 20m

 

30°C

Active tipping face for construction waste

·     30m x 20m

30°C

Special waste trench

·     6m x 2.5m (plan area exposed to air)

30°C

After Extension Opening Hours (12 midnight – 8am on the next day)

Daily cover area

·     30m x 40m

30°C

24-hour Operation

SBR tanks

·     35m x 20m
(2 nos.)

30°C

Notes:

(a)     Reference to the sensitivity analysis summarized in Annex A3.

(b)     For Phase 6, since the waste tipping area is small, therefore, 2 worst cases are assumed.

Reasonable Worst-case Odour Modelling Parameter

Odour Sampling at SENT Landfill

Odour generated from landfill operation varies from landfill site to landfill site; no general odour emission rates for landfilling activities are available.  Odour samples were taken from the existing SENT Landfill for olfactometry analysis by the Odour Research Laboratory of the Hong Kong Polytechnic University to establish a set of odour emission rates for this study.

Sampling Time and Locations: Measurements were taken between 9:00 am and 9:30 pm at four locations (see Table 4.6c).  The sampling locations and the ambient temperature during sampling are presented in Table 4.6c.

Table 4.6c      Odour Sampling Regime

Location

Sampling ID

Ambient Temperature (°C)

MSW + Construction Waste (S1)

S1-1

30.83

 

S1-2

31.45

 

S1-3

26.01

 

S1-4

23.03

 

S1-5

20.85

 

S1-6

30.05

MSW + Construction Waste + 300mm Soil Cover (S2)

S2-1

30.97

 

S2-2

31.58

 

S2-3

26.16

 

S2-4

29.55

Special Waste Trench (S3)

S3-1

27.00

 

S3-2

26.47

SBR of LTP (S4)

S4-1

26.90

As the existing SENT Landfill receives MSW, construction waste, special wastes as well as dewatered sludge from sewage treatment works (STWs), the sampling locations for S1 and S2 were therefore selected away the existing active tipping face and at the upwind location to avoid potential odour contamination.  A new tipping platform was formed at the sampling location and MSW and construction waste were disposed of using the normal practices.  The ratio of MSW to construction waste disposed was the same as that predicted for the Extension (ie the ratio of MSW to construction waste is about 1 : 2).  For S2, the compacted MSW and construction waste was covered with 300mm of cover soil.  The odour samples for S3 and S4 were taken at the base of the special waste trench and at the water surface of the SBR tank of the SENT Bioplant, respectively.

The odour emission from construction waste is very low and on a conservative basis, it is assumed that the odour emission rate from construction waste tipping is the same as that for S2.

It should be noted that the existing SENT Landfill also receives sewage sludge; therefore, the odour emission rate measured at the trench will be much higher than that expected for the Extension.  Adopting the measured odour emission rates measured at the existing special waste trench in the assessment is a conservative approach.

Odour Sampling and Analysis Methods:  Odour samples were taken using the flux chamber method which is the method recommended by the USEPA ([15]) and is also the most commonly used odour sampling method for large surface emission source such as landfill sites.  The flux chamber used is a circular chamber with a diameter of 0.41m and an area of 0.13 m2.  It was tightly placed on the surface of the odour source and the air inside the chamber was purged with nitrogen gas at a sweeping rate of 5 litres per minute.  The odour sample was collected in a Tedlar bag at a rate of 3 litres per minute.  Before taking the next sample, the flux chamber was cleaned with distilled water and then flushed with nitrogen for about 10 minutes to remove residual odour in the chamber.  The sampling system and the flux chamber are shown in Figure 4.6b.

The odour samples were analysed within 24 hours of the sampling using the olfactometry method by the Odour Research Laboratory of the Hong Kong Polytechnic University.  The odour concentration of the samples, measured in Odour Units (OU) per m3, was determined by a Forced-choice Dynamic Olfactometer in accordance with the European Standard Method EN 13725.

 

 

Odour emission rate was then calculated using the following equation:

Odour Sampling Results:  The measured odour concentrations and calculated odour emission rates of each odour source are summarized in Table 4.6d.

Table 4.6d      Odour Sampling Results

Location

Sampling ID

Onsite Ambient Temperature  During Sampling (°C)

Measured Odour Concentration (OU/m3)

Odour Emission Rate (OU/m2/s)

MSW + Construction Waste (S1)

S1-1

30.83

1,092

0.70

S1-2

31.45

1,738

1.11

S1-3

26.01

1,521

0.98

S1-4

23.03

1,296

0.83

S1-5

20.85

264

0.17

S1-6

30.05

1,579

1.01

MSW + Construction Waste + 300mm Soil Cover (S2)

S2-1

30.97

80

0.051

S2-2

31.58

160

0.10

S2-3

26.16

169

0.11

S2-4

29.55

193

0.12

Special Waste Trench (S3)

S3-1

27.00

10,768

6.90

S3-2

26.47

16,830

10.79

SBR of LTP (S4)

S4-1

26.90

76

0.049

Definition of a Reasonable Worst-case Odour Modelling Parameters

A sensitivity analysis was undertaken to determine a reasonable worst-case scenario for the odour assessment.  Details of the sensitivity analysis can be found in Annex A3.  The analysis shows that the reasonable worst-case ambient temperature for estimating the odour emission rate is 30°C.  Therefore, the reasonable worst-case odour emission rates at this temperature are summarized in Table 4.6e.

Table 4.6e      Reasonable Worst-case Odour Emission Rates Adopted in Odour Impact Assessment

Odour Source

Source Area

Odour Emission Rates at 30°C (OU/m2/s) (a)

Total Odour Emission (OU/s)

During Extension Opening Hours (8am – 12 midnight)

Active tipping face for MSW + Construction Waste

30m x 20m

0.94

564

Active tipping face for construction waste

30m x 20m

0.12

72

Special waste trench

6m x 2.5m (plan area exposed to air)

31.74 (c)

476

After Extension Opening Hours (12 midnight – 8am on the next day)

Daily cover area (b)

30m x 40m

0.12

144

24-hour Operation

 

 

 

SBR tanks

2 number of
35m x 20m

0.049

69

Notes:

(a)     Reference to Annex A3.

(b)     Total area of active tipping face.

(c)     Reference to Annex A3 for the adjustment of the odour emission rate at 30°C.

Air Dispersion Model and Worst-case Odour Modelling Parameters

The AUSPLUME model, developed by the Australian Government (Environmental Protection Agency, Victoria), was employed for the odour impact assessment.  The use of the AUSPLUME model has been approved by the EPD.

As discussed in Annex A3, the modelling parameters are summarized in Table 4.6f.

Table 4.6f       Worst-case Odour Modelling Parameters

Modelling Parameter

Setting

Surface roughness

·        120 cm

Meteorological data

·        2006 hourly SENT landfill weather data : wind speed, wind direction and air temperature

·        2006 HKO TKO weather data : stability class

·        2006 HKO King’s Park weather data : mixing height

·        90% of data are valid

Terrain effect

·        Terrain data within 500m from the Extension site boundary have been included in model

·        “Egan half height” option is selected

Type of odour source in model

·        Area source : active tipping faces for MSW and construction waste, daily cover area at night-time and special waste trench

·        Point source : SBR tanks (with very low exit velocity of 0.001 m s-1) as the leachate temperature is slightly higher than ambient

Also, odour management and control measures summarized in Table 4.8a have been considered in the worst-case assessment.

Assessment Height and Presentation of Predicted Results

5-second odour concentrations were modelled at 1.5m, 10m, 20m, 30m, 50m, 70m and 90m ([16]) above ground level at the identified ASRs and the worst affected heights under different worst-case scenarios are also identified in the assessment.  Contours of the predicted odour concentrations at the worst affected height within the Study Area (500m from the Extension site boundary) under different scenarios were plotted.

Conversion of Modelled Results From 3-minute Averaging Time to 5-second Averaging Time

Under the EIAO-TM, the odour assessment criterion is defined as 5 OU under a 5-second averaging time.  To convert the AUSPLUME output (presented as the maximum 3-minute mean concentration) to a maximum 5-second mean concentration, the approach suggested by the Warren Spring Laboratory (WSL) ([17]) was adopted:

Typical maximum or peak 5-second average concentrations within any 3-minute period appear to be of the order of 5 times the 3-minute average.  During very unstable conditions larger ratios, perhaps 10:1, are more appropriate…..

It should be noted that the ratios provided in the WSL report refer to peak to mean concentrations for emissions from stacks.  Emissions from low-level area sources will fluctuate less and therefore the peak to mean ratios will be lower.  The use of the peak to mean ratios provided in the WSL report therefore provides a conservative estimate for the 5-second mean concentrations for area sources.

For stable conditions (stability classes C to F), a factor of 5 was applied whilst for unstable conditions (stability classes A and B) a factor of 10 was applied to the emission rates input in the model run.  The modelled results will be the 5-second odour concentrations.

The factored odour emission rates are presented in Table 4.6g.  These odour emission rates applied to the three worst-cases described in Table 4.6b.  An example showing hourly emission rate file adopted in AUSPLUME model is presented in Annex A4.

Table 4.6g      Odour Emission Rates for AUSPLUME Model Run

Modelling Period

Odour Emission Source

Area Size in Model

Air Temperature of Odour Emission

Factored Odour Emission Rate to be used in Model Run to obtain 5-second Results
(OU m-2 s-1) (b)

 

 

 

Stability Class A & B (c)

Stability Class C to F (d)

During Operation (8am – 12 midnight)

Active tipping face for MSW + Construction Waste

30m x 20m

30°C

9.4

4.7

Active tipping face for construction Waste (a)

30m x 20m

30°C

1.2

0.6

Special Waste Trench

6m x 2.5m (plan area exposed to air)

30°C

317.41

158.7

Night-time (Midnight to 8am on the next day)

Daily Cover Area (a)

30m x 40m

30°C

1.2

0.6

24-hour Operation

2 numbers of SBR tanks

20m x 35m (each)

30°C

343 (OU s-1)

171.5 (OU s-1)

Notes:

(a)     The odour emission rates of daily cover area at night and the active tipping face for construction waste during operation are similar due to the odour nature of the ground is the same.

(b)     Reference to Tables 4.6b and 4.6e for original odour emission at 30°C.

(c)