3                                      Air Quality

3.1                                Introduction

3.1.1.1                     This section presents the methodology for assessment of the potential air quality impacts associated with the construction and operation phases of the proposed Sludge Treatment Facilities (STF).  A key environmental issue would be the cumulative aerial emission impacts in the vicinity of the proposed STF.  Other potential air quality impacts arising from construction dust emissions and odour emissions are also assessed.

3.2                                Environmental Legislation, Policies, Plans, Standards and Criteria

3.2.1.1                     The criteria for evaluating air quality impacts and the guidelines for air quality assessment are laid down in Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), respectively.

3.2.1.2                     The Air Pollution Control Ordinance (APCO) provides a statutory framework for establishing the Air Quality Objectives (AQOs) and stipulating the anti-pollution requirements for air pollution sources.  The AQOs, which must be satisfied, stipulate the maximum allowable concentrations over specific period for a number of criteria pollutants.  The relevant AQOs are listed in Table 3.1.

Table 3.1         Hong Kong Air Quality Objectives

Pollutant

Maximum Concentration (mg/m3)

Averaging Time

1 hour(2)

8 hour(3)

24 hour(3)

Annual(4)

Total Suspended Particulates (TSP)

-

-

260

80

Respirable Suspended Particulates (RSP) (5)

-

-

180

55

Sulphur Dioxide (SO2)

800

-

350

80

Nitrogen Dioxide (NO2)

300

-

150

80

Carbon Monoxide (CO)

30,000

10,000

-

-

Photochemical Oxidants

(as Ozone, O3) (6)

240

-

-

-

Notes:

(1)         Measured at 298 K and 101.325 kPa.

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

(3)         Not to be exceeded more than once per year.

(4)         Arithmetic mean.

(5)         Suspended particulates in air with a nominal aerodynamic diameter of 10 mm or smaller.

(6)         Photochemical oxidants are determined by measurement of ozone only.

 

3.2.1.3                     The EIAO-TM stipulates that the hourly TSP level should not exceed 500 mgm-3 (measured at 25°C and one atmosphere) for construction dust impact assessment.  Mitigation measures for construction sites are specified in the Air Pollution Control (Construction Dust) Regulation.

3.2.1.4                     In accordance with the EIAO-TM, odour at an air sensitive receiver should not exceed 5 odour units based on an averaging time of 5 seconds for odour prediction assessment.

3.3                                Description of the Environment

3.3.1                          Environs

3.3.1.1                     The STF is proposed to be located in pulverized fuel ash lagoon area in Tsang Tsui near Nim Wan.  The site is located in the northern part of the East Lagoon, adjacent to the West New Territories (WENT) Landfill and to the northeast of the Black Point Power Station (BPPS).  The local air quality is affected by the industrial emissions from the existing BPPS, Castle Peak Power Station (CPPS) and WENT Landfill, and traffic emissions from existing roads and marine vessels.

3.3.1.2                     The proposed project site is in a predominantly rural area with a very low population density.  The study area is located in the Deep Bay Airshed where dispersion is inhibited by the surrounding hills, ridges and valleys.  According to the Hong Kong Observatory’s Summary of Meteorological Observations in Hong Kong, the prevailing wind direction of the area is mostly easterly wind (wind data monitored at Lau Fau Shan Station).

3.3.2                          Background Air Quality

3.3.2.1                     There is no fixed air quality monitoring station near the proposed STF site.  The nearest EPD air monitoring station is Yuen Long.  In accordance with the Guidelines in Assessing the ‘TOTAL’ Air Quality Impacts, the recent five years (2002-2006) average monitoring data are adopted as the background concentration.  The background air pollutant concentrations adopted in this study are presented in Table 3.2.

Table 3.2         Background Air Pollutant Concentrations adopted in this Study

Pollutant

Background Concentration (mg/m3)

Total Suspended Particulates (TSP)

100(2)

Respirable Suspended Particulate (RSP)

62(2)

Nitrogen Dioxide (NO2)

60

Sulphur Dioxide (SO2)

24

Ozone (O3)

74(1)

Note:

(1)      The O3 concentration is 5-year average of the annual average of daily hourly maximum concentration recorded at Yuen Long Air Quality Monitoring Station in Year 2002-2006.

(2)      Monitoring results that exceeded AQO are shown in bold characters.

 

3.3.3                          Contribution of Emissions from BPPS and CPPS

3.3.3.1                     Air quality in the vicinity of the proposed STF will also be influenced by the two existing power stations namely BPPS and CPPS.  With reference to the approved EIA Study of Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities, the contribution from BPPS and CPPS are adjusted taking into account the revised ozone background concentration, the current generating capacity, and the effect of the low NOX burners installed in CPA unit and CPB unit of the CPPS.  The same approach was adopted in this assessment.

3.3.3.2                     The adjusted NO2, SO2 and RSP concentrations for different locations are summarized in Table 3.3.  Details of the calculations on the adjusted contribution from BPPS and CPPS are presented in Appendix 3.1.

Table 3.3         Adjusted Maximum Hourly, 2nd Highest Daily and Annual NO2, SO2 and RSP Concentrations

Location

Adjusted Concentration (mg/m3)

NO2(a)

SO2(g)

RSP

Maximum Hourly

Daily (d)

Annual (d)

Maximum Hourly

Daily (e)

Annual (e)

Daily (d)(j)

Annual (d)(j)

Sheung Pak Nai

84(b)

17(f)

0.4(f)

171(e)

60(f)

1.5(f)

3.9(f)

0.09(f)

Ha Pak Nai

92(b)

17

0.4

171

60

1.5

3.9

0.09

Lung Kwu Tan

45(c)

18

0.5

_(h)

39

0.8

4.6

0.12

Tin Shui Wai Park

84(b)

22

0.5

112

56

1.1

2.7

0.06

Tuen Mun Valley & Butterfly Beach Area

23(c)

14

0.6

_(h)

34

1.0

2.7

0.11

Tuen Mun Area 38

30(c)

18(g)

0.7(g)

_(h)

34(i)

1.0 (i)

4.6(k)

0.19(k)

Notes:

(a)    Adjustment is based on the latest 5-year average of the annual average of the daily hourly maximum ozone concentration (74 mg/m3) measures at Yuen Long Monitoring Station in Year 2002-2006.

(b)    BPPS and CPPS contributions are included.  Current power generating capacity of BPPS (2,500 MW) has been accounted for.  NOX reduction has been considered for CPA and CPB, respectively.

(c)    Since CPPS is located at different upwind direction of BPPS and STF, therefore only the BPPS contribution is considered.  A factor of 0.5 is applied to adjust for the current power generating capacity of BPPS.

(d)    Both BPPS and CPPS contributions are considered.  No adjustment has been made to account for the reduced power generation capacity of BPPS and the future NOX reduction at CPB due to the implementation of the Emission Control Project.

(e)    Only CPPS contributions are considered.  Adjustment has been made to the future SO2 reduction at CPB due to the implementation of the Emission Control Project and no adjustment has been made to account for the reduced power generation capacity of BPPS.

(f)     Sheung Pak Nai is not included in the wind tunnel testing in EIA for the Proposed 6000MW Thermal Power Station at Black Point (BPPS EIA Study); however, the worst wind angle for Sheung Pak Nai is similar to that for Ha Pak Nai.  As it is located further away from the BPPS and CPPS than Ha Pak Nai, the Ha Pak Nai predictions were adopted as the worst case assumption.        

(g)    The daily and annual average NO2 concentrations are contributed by both BPPS and CPPS.  For BPPS contribution, as indicated by the maximum hourly concentrations (due to BPPS only), the worst-case impacts at Tuen Mun Area 38 is about 30% higher than that at Butterfly Beach Area.  For CPPS contribution, as no wind tunnel testing was performed at Tuen Mun Area 38 in the BPPS EIA Study, reference was made to the Emission Control Project to CPPS "B" Units EIA Study with regards to the CPPS contribution.  The maximum concentration ratio predicted at Tuen Mun Area 38 is lower than the maximum concentration ratio predicted at Butterfly Beach Area as presented in the CPPS "B" Units EIA Study.  Overall on conservative side, we assume that the total daily and annual BPPS and CPPS contribution at Tuen Mun Area 38 would be 30% higher than the total daily and annual BPPS and CPPS contribution at Butterfly Beach Area.

(h)    No SO2 contribution from BPPS due to negligible SO2 emissions from gas-fired units.

(i)     The daily and annual average SO2 concentrations are mainly contributed by CPPS.  For CPPS contribution, as no wind tunnel testing was performed at Tuen Mun Area 38 in the BPPS EIA Study, reference was made to the Emission Control Project to CPPS "B" Units EIA Study with regards to the CPPS contribution.  The maximum concentration ratio predicted at Tuen Mun Area 38 is lower than the maximum concentration ratio predicted at Butterfly Beach Area as presented in the CPPS "B" Units EIA Study.  Overall on conservative side, we assume that the total daily and annual BPPS and CPPS contribution at Tuen Mun Area 38 would be same as the total daily and annual BPPS and CPPS contribution at Butterfly Beach Area.

(j)     As the RSP concentrations were not assessed in the BPPS EIA Study, the ratio of maximum RSP to NOX concentration stated in the Specified Process Licence for BPPS and CPPS were applied to adjust RSP concentration contribution from the power plants.

(k)    As no wind tunnel testing was performed at Tuen Mun Area 38 in the BPPS EIA Study, the highest RSP/NO2 ratio among all the assessed ASRs in this study is used as worst case estimate.

 

3.4                                Air Sensitive Receivers

3.4.1.1                     In accordance with Annex 12 of the EIAO-TM, any domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, place of public worship, library, court of law, sports stadium or performing arts centre are considered as air sensitive receivers (ASRs).  A total of 32 representative ASRs were identified for this assessment in accordance with the criteria set out in the EIAO-TM.  The details of the representative ASRs are summarised in Table 3.4 and locations of the ASRs are shown in Figure 3.1.

3.4.1.2                     The air quality impact at 1.5m above local ground level of representative ASRs, which is the average height of the human breathing zone, was assessed in the study.  Higher assessment levels were also selected for elevated ASRs to show the vertical variation of the pollutant concentrations.

Table 3.4         Identified Air Sensitive Receivers

ASR

Description

Land Use

Near Field/

Far Field

Horizontal Separation from STF (m)

Assessment Height (mAG)

A1

Ngau Hom Sha

Residential

Near Field

5000

1.5, 5, 10

A2

West Ha Pak Nai

Residential

Near Field

1170

1.5, 5, 10

A3

West Ha Pak Nai

Residential

Near Field

1270

1.5, 5, 10

A4

West Ha Pak Nai

Residential

Near Field

1190

1.5, 5, 10

A5

East Ha Pak Nai

Residential

Near Field

1770

1.5, 5, 10

A6

Black Point Power Station (Office)

Industrial

Near Field

1935

1.5, 5, 10

A7

EPD WENT Landfill Site Office

Industrial

Near Field

230

1.5

A8

Lung Kwu Sheung Tan

Residential

Near Field

2330

1.5, 5, 10

A9

Sheung Pak Nai

Residential

Near Field

4380

1.5

A10

Tin Shui Wai Park

Recreational

Far Field

8420

1.5

A11

Pak Long

Residential

Far Field

3360

1.5, 5

A12

Leung King Estate

Residential

Far Field

3930

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A13

Tsing Shan Monastery

GIC

Far Field

4570

1.5

A14

Siu Shan Court

Residential

Far Field

6080

1.5, 5, 10, 20, 40, 60

A15

Butterfly Beach Park

Recreational

Far Field

6120

1.5

A16

San Shek Wan

Residential

Far Field

5380

1.5, 5, 10

A17

Tuen Mun Area 38

Residential

Far Field

5410

1.5

A18

Green Island Cement (Office)

Industrial

Far Field

5475

1.5, 5, 10

A19

Site Office of Castle Peak Power Company Limited

Commercial

Far Field

5070

1.5, 5, 10

A20

Site Office of Eco Park

Commercial

Far Field

5740

1.5, 5, 10

A21

Lung Kwu Tan

Residential

Far Field

3985

1.5, 5, 10

A22

Temple near the Tsang Tsui Ash Lagoons

Place of public worship

Near Field

560

1.5

A23

Site Office of Shiu Wing Steel Mill

Commercial

Far Field

5550

1.5, 5, 10, 20

A24

Siu Lung Court

Residential

Far Field

6335

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A25

On Ting Estate

Residential

Far Field

6110

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A26

Yau Oi Estate

Residential

Far Field

5800

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A27

Tuen Mun Town Plaza

Residential

Far Field

5845

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A28

S.K.H. St. Simon’s Lui Ming Choi Secondary School

Education Institution

Far Field

5390

1.5, 5, 10, 20

A29

Hong Lai Garden

Residential

Far Field

5400

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A30

Tai Hing Garden

Residential

Far Field

5080

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A31

Chelsea Heights

Residential

Far Field

5160

1.5, 5, 10, 20, 40, 60, 80, 100, 120

A32

Melody Garden

Residential

Far Field

6025

1.5, 5, 10, 20, 40, 60, 80, 90

 

3.5                                Identification of Pollution Sources

3.5.1                          Construction Phase

3.5.1.1                     The major construction works of the Project would be the decommissioning of part of the Ash Lagoon at Tsang Tsui, construction of proposed STF and construction of the access road.  The major potential air quality impact during construction phase of the Project would be dust arising from the following activities:-

l        Excavation and materials handling;

l        Filling activities;

l        Haul roads; and

l        Wind erosion of open sites and stockpiling areas.

3.5.1.2                     As part of this Project, apart from some localized cut and fill operations at the ash lagoon, the majority of the ash stored at the ash lagoon would be left in-situ.  The construction dust generating activities would be those associated with site formation and building construction.  Extensive excavation and transportation of the ash would not be required as part of this Project.  Based on the preliminary design, the construction works would generate about 62,800m3 excavated material in total, out of which, 25,000m3 would be required to be disposed offsite.  The number of trucks hauling on site depends on the schedule of construction activities.  In accordance with the tentative construction programme, the excavation and construction activities would be completed within 300 days.  The volume of excavated material per day during the construction period would be approximately 200m3.  The average number of trucks (carrying 5m3 excavated material) required on-site would be about 5 trucks per hour.

3.5.1.3                     With the implementation of practicable dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation, adverse construction dust impact at the ASR is not expected during construction of the Project.

3.5.1.4                     Based on the latest available information, the construction of the proposed WENT Landfill Extension would not overlap with the major construction activities of STF and thus cumulative dust impact from these two projects are not expected.

3.5.2                          Operation Phase

3.5.2.1                     Air pollution control and stack monitoring system will be installed for the STF to ensure that the emissions from the STF stacks will meet the stringent target emission limits equivalent to those stipulated in Hong Kong (namely A Guidance Note on the Best Practicable Means for Incinerators (Municipal Waste Incineration), BPM 12/1, EPD/AMP, February 2008) and the European Commission for waste incineration.  Further details are given in Section 3.6.2.5 to Section 3.6.2.7 below.  Major criteria air pollutants of concern include nitrogen dioxide, sulphide dioxide, and respirable suspended particulate.

3.5.2.2                     Cumulative air quality impacts at ASRs would also be expected due to the other major pollution sources in the Tuen Mun area including Black Point Power Station, Castle Peak Power Station, Green Island Cement Plant, existing WENT Landfill and its proposed extension, EcoPark, Shiu Wing Steel Mill, industrial chimney emissions near Tuen Mun town centre area, road traffic emissions and marine vessel emission in close proximity to the Project site.  The locations of these cumulative air pollution sources are shown in Figure 3.2.

3.5.2.3                     Apart from the incineration emission, odour nuisance generated from the proposed on-site wastewater treatment plant and the handling and storage of sewage sludge within the STF site would also be expected during the operation phase. ku

3.6                                Assessment Methodology

3.6.1                          Construction Phase

3.6.1.1                     Under the APCO, dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation should be implemented.  With effective implementation of these mitigation measures, adverse construction dust impacts are not expected at the nearby ASRs.  Quantitative assessment is considered not necessary.

3.6.2                          Operation Phase

3.6.2.1                     The proposed STF would comprise six incineration units, with a maximum design capacity of 2,000 tpd of sewage sludge.  Based on the outline design of the STF, the exhaust flue gases would be discharged via a multi-flue chimney.

3.6.2.2                     The proposed STF is bounded by the surrounding hills, ridges and valleys.  The far field ASRs near the Tuen Mun town centre area are located at another side of the hills.  The dispersion of the STF emissions is inhibited by the surrounding topography.  The impact of the STF emissions on the far field ASRs is expected to be far less than that on the near field ASRs.  It is expected that the near field ASRs would be the worst-affected ASRs with regards to the STF emissions.

Gaseous Pollutants
Emission Inventory

3.6.2.3                     During the operational phase, the air pollution sources considered for cumulative air quality impacts include emissions from:

l        Proposed Sludge Treatment Facilities;

l        Black Point and Castle Peak Power Plants;

l        Green Island Cement;

l        Existing WENT Landfill and Proposed WENT Landfill Extension;

l        EcoPark;

l        Shiu Wing Steel Mill;

l        Marine Emissions (along the navigation channel outside the WENT Landfill);

l        Industrial Chimney Emissions near Tuen Mun Town Centre Area; and

l        Vehicle Emissions from Open Roads (Lung Kwu Tan Road – from CPPS to BPPS and Nim Wan Road – from BPPS to Tsang Tsui).

3.6.2.4                     An emission inventory of all emission sources (except vehicle emissions) is summarized in Appendix 3.2 and the locations of the emission sources other than STF are shown in Figure 3.2.  The emission inventory is prepared based on the best available information collected at the time of preparation of this assessment.  For those chimneys identified as part of a specified process, the emission data are referred to the information presented in the corresponding Specified Process License and adopted in this assessment.  For other chimneys, the emission information was either retrieved from the relevant EIA reports or validated by survey in the form of visual inspection outside the premises of concern.

(i)             Chimney Emission from Sludge Treatment Facilities

3.6.2.5                     The target emission levels proposed for STF are listed in Table 3.5 and are compared with the concentration limits stipulated in “A Guidance Note on the Best Practicable Means for Incinerator (Municipal Waste Incineration) BPM 12/1” published by EPD and also with other relevant overseas standards.

3.6.2.6                     Based on the comparison, the proposed target emission limits are equivalent to those stipulated in the Hong Kong BPM for Municipal Waste Incineration and the EC’s Waste Incineration Directive (which is also applicable to sewage sludge incineration).  With regards to the US emission limits for sewage sludge incineration, only four air pollutants namely carbon monoxide, total hydrocarbons, mercury, and beryllium are specified.  Beryllium is not specified in both the Hong Kong BPM and the EC’s Waste Incineration Directive, whereas the emission limits of the other three air pollutants are less stringent than those specified in the Hong Kong BPM and the EC’s Waste Incineration Directive.

3.6.2.7                     The target emission limits will be specified in the contract documents of the proposed STF.  The future operator of the proposed STF will be required to design and operate the proposed STF to comply with the said target emission limits.

3.6.2.8                     The target emission levels of STF were adopted in this air quality assessment as conservative assumptions.  It is assumed that the size of particulate matter emitted from the chimney is less than 10 mm (i.e. within the RSP category), and daily emission limit of particulate matter, 10 mg/m3, is assumed for RSP.

 

Table 3.5         Target Emission Limits of STF

Air Pollutant

Target Emission Limits (mg/m3) (a)

Hong Kong’s Emission Limits in BPM for Municipal Waste Incineration (mg/m3) (a)

European’s Emission Limits in EC’s Waste Incineration Directive (mg/m3) (a)

US’s Emission Limits in Title 40 Part 503 of CFR on Sewage Sludge Incineration

(mg/m3) (a)

Daily

Half - Hourly

Daily

Half - Hourly

Daily

Half - Hourly

Particulates (d)

10

30

10

30

10

30

-

Organic Compounds

10

20

10

20

10

20

50.9 (e)(i) (calculated as methane, monthly average)

Hydrogen Chloride (HCl)

10

60

10

60

10

60

-

Hydrogen Fluoride (HF)

1

4

1

4

1

4

-

Sulphur Dioxide (SO2)

50

200

50

200

50

200

-

Carbon Monoxide (CO)

50

100

50

100

50

100

89.0 (i)

(monthly average)

Nitrogen Oxides (NOX) as Nitrogen Dioxide (NO2)

200

400

200

400

200

400

-

Mercury

0.05 (b)

-

0.05 (b)

-

0.05 (b)

-

0.87 (f)(j)

(daily average)

Total Cadmium & Thallium

0.05 (b)

-

0.05 (b)

-

0.05 (b)

-

-

Total Heavy Metals

0.5 (b)

-

0.5 (b)

-

0.5 (b)

-

-

Dioxins & Furans (c)

1´10-7

-

1´10-7

-

1´10-7

-

-

Beryllium

-

-

-

-

-

-

0.0027 (g)(j)

(daily average)

Notes:

(a)         Emission limits are reference to 0oC and 101.325 kPa, dry and 11% oxygen content conditions.

(b)         Average values over a sampling period of a minimum of 30 minutes and a maximum of 8 hours. Including Sb, As, Pb, Co, Cr, Cu, Mn, V and Ni.

(c)         The unit is I-TEQ (The emission limit is equal to 0.1 ng I-TEQ m-3), according to the BPM 12/1, the averaging time for dioxin is 6 to 8 hours.

(d)         The particulate emission limit is assumed to be RSP.

(e)         The US emission limit is for total hydrocarbons.

(f)         Calculated based on the total exit volume flow of STF emission under standard conditions and the US emission limit of 3.2kg over 24 hours period.

(g)         Calculated based on the total exit volume flow of STF emission under standard conditions and the US emission limit of 10g over 24 hours period.

(h)         In accordance with the US’s Emission Limits in Title 40 Part 503 of CFR on Sewage Sludge Incineration, the pollutant limits for lead, arsenic, cadmium, chromium and nickel are controlled by limiting the concentrations of these metals in sewage sludge to be incinerated.

(i)          Conversion from ppm to mg/m3 for CO and total hydrocarbons,

 

Emission limit in mg/m3, at 7% oxygen = US emission limit in ppm´ molecular weight / (gas constant ´ standard temperature/standard pressure) x 10-3

 

Therefore,

Emission limit for CO = 100 x 28 / (8.314N-m/(mol-K) ´ 273K / 101325N/m2) x 10-3 = 125.0 mg/m3

Emission limit for total hydrocarbon (calculated as methane) = 100 x 16 / (8.314N-m/(mol-K) ´ 273K / 101325N/m2) x 10-3 = 71.4 mg/m3

 

In accordance with Annex VI of EU Directive 200/76/EC,

Ca, dry, Oa = Ca, dry, Os ´ (20.9-Oa) / (20.9-Os)

 

where    Ca, dry, Oa is flue gas concentration, dry gas, at 11% oxygen,

Ca, dry, Os is flue gas concentration, dry gas, at 7% oxygen

 

Then,

Emission limit for CO in mg/m3, at 11% oxygen = 125.0 mg/m3 ´ (20.9-11) / (20.9-7) = 89.0 mg/m3

Emission limit for total hydrocarbons in mg/m3, at 11% oxygen = 71.4 mg/m3 ´ (20.9-11) / (20.9-7) = 50.9 mg/m3

 

(j)          Conversion from mass to concentration for mercury and beryllium,

In accordance with Annex VI of EU Directive 200/76/EC,

Ca, dry, Oa = Ca, dry, Os x (20.9 - Oa) / (20.9 - Os)                                                            (eqn. 1)

Ca, dry, Oa                   = M / Va, dry                                                                                                    (eqn. 2)

= M / [Va, wet x (1 - %H2O)]                                                                           (eqn. 3)

Ca, wet, Oa = M / Va, wet = Ca, dry, Oa x (1 - %H2O)                                                         (from eqn. 3)

= Ca, dry, Os x (1 - % H2O) x (20.9 –Oa) / (20.9 –Os)                                        (from eqn. 1) (eqn. 4)

Cs = M / Vs                                                                                                                   (eqn. 5)

 

By standard gas law, Pa x Va, dry / Ta = Ps x Vs / Ts

Since Pa = Ps, therefore, Va, dry / Ta = Vs / Ts

From eqn. 2 and eqn. 5, (M / Ca, dry, Oa) / Ta = (M / Cs) / Ts

Therefore, Ca, dry, Oa = Cs x Ts / Ta

From eqn. 4, Ca, wet, Oa = Cs x (Ts / Ta) x (1 - %H2O) x (20.9 – Oa) / (20.9 – Os)

 

where,

Oa:                     Oxygen concentration of flue gas, dry gas

Os:                      Standard oxygen concentration, dry gas

Ca, dry, Oa:            Actual flue gas concentration, dry gas, Oa

Ca, dry, Os:            Actual flue gas concentration, dry gas, Os

Ca, wet, Oa:            Actual flue gas concentration, wet gas, Oa

Cs:                      Flue gas concentration at standard conditions

Va, dry:                Volume of flue gas at emission point, dry gas

Va, wet:                Volume of flue gas at emission point, wet gas

Vs:                      Volume of flue gas under standard condition, dry gas

M:                      Mass of pollutant in flue gas

%H2O:               % of moisture in flue gas

Pa:                      Pressure of flue gas at emission point

Ps:                      Standard pressure

Ta:                      Temperature of flue gas at emission point

Ts:                      Standard temperature

 

For STF, for any pollutant,

Oa = 11%, Os= 11%, %H2O= 39.76%, Ta= 463K, and Ts= 273K;

Cs = 432,411 m3/hr

Therefore,

Ca, wet, Oa = Cs x (273K / 463K) x (1 – 0.3976) x (20.9 – 11) / (20.9 – 11) = 0.355 Cs

 

Therefore,

Emission limit for mercury in mg/m3

= US emission limit for mercury in kg/24hr ´ actual flow rate at the emission source (m3/hr)

= 3.2kg/24hr ´ 432411m3/hr ´ 0.355 = 0.87mg/m3

 

Emission limit for beryllium in mg/m3

= US emission limit for beryllium in g/24hr ´ actual flow rate at the emission source (m3/hr)

= 10g/24hr ´ 432411m3/hr ´ 0.355 = 0.0027mg/m3

 

3.6.2.9                     The half-hourly average emission limits were used to model the hourly average concentrations at the representative ASRs and the daily average emission limits were used to model the daily and annual average concentrations at the representative ASRs.  For heavy metals, cadmium & thallium, and mercury, the 30 min. to 8 hours average emission limits were used to model the hourly and longer-term average concentration at the ASRs.  For dioxins & furans, there is no guideline on acute exposure.  For chronic exposure, the 6-hour to 8-hours average emission limits were used to predict the longer-term average concentrations at the ASRs.  The calculation of emission factors for the STF stack emission is presented in Appendix 3.3.

3.6.2.10                 Based on the preliminary design, the STF chimney height would be 65m above ground level with six flues each with a diameter of 1.3m.  The discharge temperature of flue gas is 463K and the efflux velocity is 15m/s.

3.6.2.11                 NO2, SO2 and RSP are the common criteria air pollutants of concern for the STF and the two major air pollution sources in the Tuen Mun area namely the BPPS and CPPS.  These 3 air pollutants are therefore selected as the most critical criteria air pollutants of concern for the cumulative air quality impact assessment.

3.6.2.12                 The other potential air pollutants (individual chemicals) covered in Annex 1 of EPD’s “A Guidance Note on the Best Practicable Means for Incinerator (Municipal Waste Incineration) BPM 12/1” are identified as contaminants of concern (COCs).  BPM 12/1 aims to prevent the emissions of air pollutants of incinerators from harming the environment and human health or creating nuisance.  As a result, Annex 1 of BPM 12/1 should cover an adequate range of pollutants, which their emission levels need to be controlled to achieve the above aim.  It is considered appropriate to adopt the pollutant list in BPM 12/1 as COCs and their cumulative health impacts are further assessed in Section 4 of this EIA Report.

(ii)            Emission from Green Island Cement Plant

3.6.2.13                 With regards to the Green Island Cement Plant which is located at more than 5km from the proposed STF site, the potential emissions assessed under this study include the major stack emissions from fuel combustion together with the fugitive emissions as listed in its Specified Process License.

3.6.2.14                 The potential emissions from the Green Island Cement in accordance with the information stated in its Specified Process License were included in the cumulative air quality assessment.  The detail calculation of the emission factor is presented in Appendix 3.4.

(iii)          Emission from Existing WENT Landfill and Proposed WENT Landfill Extension

3.6.2.15                 Flaring emissions from the landfill gas flaring plant and the thermal oxidizer at the existing WENT Landfill and proposed WENT Landfill Extension were also included in this assessment.  Based on the review of the available WENT Landfill gas utilization data and relevant technical reports, the peak landfill gas generation from the existing WENT Landfill and its Extension would be about 54,000 m3/hr and 58,000 m3/hr, respectively.  These peak landfill gas generation rates are expected for the existing WENT Landfill at Year 2019 and for its Extension at Year 2045.  Out of these, about 750m3/hr is used in the gas engines to meet the landfill site load and 4,500m3/h is used in the leachate recovery plant boilers.  The remaining landfill gas will be flared.  The emission rates are calculated based on these landfill gas utilization rates and the emission factors from Table 4-4 of USEPA’s ”Air Emissions from Municipal Solid Waste Landfills - Background Information for Proposed Standards and Guidelines, March 1991 ((EPA-450/3-90-011a)”.

3.6.2.16                 With reference to the 10 years VOC monitoring data recorded at the site boundary of the existing WENT landfill provided by the operator of WENT Landfill, the concentrations of the 2 most critical VOCs namely benzene and vinyl chloride recorded at the site boundary of the WENT Landfill are 3.96µgm-3 and 2.29 µgm-3 respectively.  These are far below the relevant health risk criteria and are similar to the background concentration of 3.9µgm-3 and 3 µgm-3 for benzene and vinyl chloride as presented in the NENT Landfill Extension EIA Report.  This confirms that the LFG extraction system in the existing WENT Landfill is operating effectively and surface emission from the existing WENT Landfill should not be an issue.  For the future WENT Landfill extension, similar or more effective LFG extraction system should be installed to prevent any VOC surface emission.

3.6.2.17                 Besides, with reference to the 5 years flare removal efficiency data of the existing WENT Landfill provided by the operator of WENT Landfill, the average flare removal efficiencies of VOCs are high and in the range of 95.37% to 99.99% and the maximum VOC concentrations at the outlet is comparable to the case of the existing NENT Landfill as presented in the NENT Landfill Extension EIA Report.  It is therefore expected that the VOC emissions from the WENT Landfill would only result in tiny amount and far lower than the background concentration for the area of 3.96µgm-3 benzene and 2.29 µgm-3 vinyl chloride as described above.  Thus, it is assumed that the VOC emission from the WENT Landfill would be negligible with the proper operation of the flaring system.

3.6.2.18                 The VOC monitoring data and flare removal efficiency data of the existing WENT Landfill, as well as the detailed calculation of landfill gas emission is shown in Appendix 3.5.

(iv)          Emissions from EcoPark

3.6.2.19                 The EcoPark is located at more than 5km from the proposed STF site.  The potential emissions of EcoPark assessed under this study include the major stack emissions from fuel combustion together with the fugitive emissions as listed in the Eco Park EIA Report.  With reference to the EcoPark EIA Study, there are total nine possible locations of the discharge chimney.  With regards to stack emissions, as shown in Table 3.25 of the EcoPark EIA Report, source location A2 would result in the highest NO2 concentration at nearby ASRs.  Since NO2 is the most critical criteria pollutant in this study, source location A2 was therefore adopted as the worst-case emission location of EcoPark for the purpose of this assessment.  The detailed calculation of emissions from EcoPark is shown in Appendix 3.6.

(v)           Emissions from Shiu Wing Steel Mill

3.6.2.20                 For Shiu Wing Steel Mill which is located at about 5km from the proposed STF site, the potential emissions assessed under this study were made reference to the Shiu Wing Steel Mill (Tuen Mun) Final EIA.  The principal emissions from the mill are particulate matter containing a proportion of heavy metals, sulphur dioxide and nitrogen dioxide and the major emission sources are the two major stacks within the mill namely the arc furnace stack and the reheat furnace stack as well as some fugitive emission sources described in the EIA report.  The detailed calculation of emissions from Shiu Wing Steel Mill is shown in Appendix 3.7.

(vi)          Marine Emissions

3.6.2.21                 Emissions from the marine vessels for transportation of wastes / sludge from Island East Transfer Station (IETS), Island West Transfer Station (IWTS), Outlying Islands Transfer Station (OITS), West Kowloon Transfer Station (WKTS) and North Lantau Transfer Station (NLTS) to the STF travelling along the navigation channel outside the WENT Landfill were also considered in this assessment.  With reference to the information provided by operators of these transfer stations (summarized in Appendix 3.8), emission rates for the marine vessel of each transfer station were calculated.  The schedule of the marine vessels was also referring to the provided information.  With reference to the information for the marine vessel serving both Island East Transfer Station & Island West Transfer Station, the vessel operated the main propulsion engine and generator engine on marine gas oil with sulphur content of 0.3%.  In the absence of the fuel sulphur content for other transfer stations, fuel sulphur content of 0.3% were also applied for all vessels as they were all regulated under the same EPD contract condition.

3.6.2.22                 Emission from a future marine vessel that may be operated to transport the sludge from Stonecutters Island Sewage Treatment Works (SCISTW) to WENT Landfill or STF for disposal is also considered in this study.  In absence of information for this additional marine vessel, it is assumed that this additional marine vessel will be of similar size as the WKTS vessel and that on-shore power will be provided for this additional vessel at the berth of the WENT Landfill.  It is also assumed that the hours for manoeuvring of this additional marine vessel along the navigation channel outside the WENT Landfill would be different from the WKTS vessel.

3.6.2.23                 The emission rates of air pollutants from the operation of the main propulsion engine and generator engine were estimated based on the approach stipulated in the Current Methodologies and Best Practices in Preparing Port Emission Inventories, Final Report, January 2006 prepared by ICF Consulting for USEPA.  Detailed emission calculation is presented in Appendix 3.8.

(vii)        Industrial Chimney Emissions near Tuen Mun Town Centre Area

3.6.2.24                 According to the site surveys taken in January 2008 and August 2008, industrial chimneys near Tuen Mun Town Centre were found within 7km radius of the Project.  Air quality impacts due to these industrial chimneys were considered in this assessment

3.6.2.25                 An inventory of the industrial chimneys was prepared based on the best available information, including the information provided by the owners/operators of the chimneys and the findings of the site surveys.  In order to demonstrate the reasonable worst-case scenario, the emissions were calculated pro-rata to the cross-sectional area of the chimney discharge point.  The exit velocity and temperature were assumed to be 8m/s and 473k, respectively, with reference to the nominal values described in EPD’s Guidelines on Estimating Height Restriction and Position of Fresh Air Intake Using Gaussian Plume Models, B.2.

3.6.2.26                 The chimney emission factors for NO2 and SO2 were estimated based on AP-42 (USEPA 1998: Table 1-3-1 Criteria Pollutant Emission Factors for Fuel Oil Combustion).  The locations of the industrial chimneys included in this assessment are shown in Figure 3.2.  The calculation of chimney emission factor is shown in Appendix 3.9.

(viii)       Vehicle Emissions from Open Roads

3.6.2.27                 Vehicle emissions from Lung Kwu Tan Road (from CPPS to BPPS) and Nim Wan Road (from BPPS to Tsang Tsui) were incorporated into the assessment.  The assessment is based on the projected peak hour flows for the worst year (in Year 2027) within 15 years of commencement of operation.  The Fleet Average Emission Factors – EURO4 Model were used in the assessment.  The composite emission factors for the road links were calculated as the weighted average of the emission factors of different types of vehicles.  A sensitivity test was conducted for the projected 2027 traffic flows in morning peak hour and afternoon peak hour, and it indicated that the worst scenario in terms of air pollution from vehicle emission is found in afternoon peak hour traffic flows.  Projected 2027 afternoon peak hour traffic flows and vehicle composition of the roads are shown in Appendix 3.10.  A comparison of the combined effects of the traffic flow and emission factors for morning peak hour and afternoon peak hour are shown in Appendix 3.11.

NO2/NOX Conversion

3.6.2.28                 The NO2/NOx conversion for all emissions from STF, cement plant, landfills, marine vessels and traffic emission sources for all averaging periods were estimated individually based on the Ozone Limiting Method.  The 5-year average of the annual average of the daily hourly maximum ozone concentrations recorded at EPD’s Yuen Long Air Quality Monitoring Station of 74 µg/m3 was adopted for the calculation.  The NO2/NOx conversion was calculated as follows:

[NO2]pred = 0.1 ´ [NOX]pred + MIN {0.9 ´ [NOX]pred, or (46/48) ´ [O3]bkgd}

where

[NO2]pred      is the predicted NO2 concentration

[NOX]pred      is the predicted NOX concentration

MIN            means the minimum of the two values within the brackets

[O3]bkgd        is the representative O3 background concentration

(46/48)         is the molecular weight of NO2 divided by the molecular weight of O3

 

Air Dispersion Model

3.6.2.29                 The dispersion of the stack emissions from the proposed STF is inhibited by the surrounding terrain to the south and to the east.  Therefore, a 3-dimensional mathematical model namely CALPUFF which can take into account the topographical effect of the intervening terrain was adopted to predict the potential air quality impacts from the STF emission at those far field ASRs.

3.6.2.30                 CALMET model, which generates 3-dimensional meteorological fields, was used to provide hourly 3-dimensional meteorological data (wind speed, wind direction and temperature), and hourly 2-dimensional mixing height and surface layer data in the computational domain for the CALPUFF model.

3.6.2.31                 The 3-dimensional meteorological fields generated by the CALMET meteorological model (from hourly meteorological data of 2006 and hourly mesoscale model of MM5 with resolution of 1.5km) were taken in this assessment for the CALPUFF model.  The meteorological model was applied on a domain covering the western part of Hong Kong.  The horizontal grids in both the x- and y- directions were spaced at 500m intervals to provide the required meteorological fields.

3.6.2.32                 The terrain in the vicinity of the STF site is fairly complex with hills, ridges and valleys.  The influence of the terrain features was modelled by the CALMET model and the CALPUFF dispersion model.  The CALPUFF dispersion model is capable of accounting for the transport and dispersion phenomena in rugged terrain environments by assessing plume dispersion near individual features such as hills and ridges.

3.6.2.33                 For the potential air quality impacts due to other emission sources (except BPPS, CPPS, and road traffic emissions) and the near field impacts due to the STF emissions, an air dispersion model namely Industrial Source Complex Short Term (ISCST3) was used to simulate their respective dispersion to produce more conservative predictions but with better spatial resolution as compared with the CALPUFF model.  For road traffic emissions, a traffic emission dispersion model CALINE4 was used to predict the contribution due to road traffic emissions in the vicinity of the STF site.

3.6.2.34                 The proposed STF is sited within the Ash Lagoon at Tsang Tsui.  Hills are located to the south of the proposed STF.  A few village houses are scattered in the Ha Pak Nai / Nim Wan area according to the findings of site visit and the latest Outline Zoning Plan.  For the purpose of air quality modelling, the study area would be classified as “Rural” in accordance with EPD’s Guideline on Assessing the ‘TOTAL’ Air Quality Impacts and therefore “Rural” mode was adopted in the model run.

3.6.2.35                 Hourly meteorological data including wind speed, wind direction, air temperature, Pasquill stability class and mixing height from the nearest Hong Kong Observatory weather station, Lau Fau Shan Station, for the year 2006, were employed for the model run.

3.6.2.36                 The focus of this study is to examine the air quality impact from the STF on the ASRs.  Therefore, the wind condition for the worst cumulative impact with STF contribution at each ASR was applied to predict the hourly and daily cumulative impacts with the wind data in Year 2006.

3.6.2.37                 For road traffic impact, the predicted worst-case impacts under worst wind direction, wind speed of 1m/s and stability class D or F at each ASR is taken to predict the hourly average.  This approach would result in conservative cumulative estimates as compared to the predictions using hourly historical wind data.  In the production of the worst-case cumulative hourly average NO2 concentration contour plots (Figures A.15a and A.15b of Appendix 3.17), more refined predictions of the cumulative impact along Lung Kwu Tan Road using hourly historical wind data for road traffic impact were adopted.  A 0.4 daily traffic profile adjustment factor was applied to the hourly prediction to estimate the daily average prediction.  It is also assumed that the annual contribution of traffic emissions to the cumulative impact at each ASR would be the same as the corresponding daily contribution.

3.6.2.38                 The proposed STF would be operated continuously twenty-four hours per day.  It was assumed in the air dispersion model that the chimney would be operated in full capacity with maximum load during the operation hours, as a worst case scenario.

3.6.2.39                 The dispersion model as well as the NO2/NOX conversion adopted for each potential emission source considered in this study is summarized in the following Table 3.6 for easy reference.

Table 3.6         Model Assumptions for the Potential Emission Sources

Emission Sources

Dispersion Model to be Employed

NO2/NOX Conversion

Sludge Treatment Facilities

ISCST3 (for near field ASRs);

CALPUFF (for far field ASRs)

 

 

 

 

 

OLM conversion equation

(see S.3.6.2.29)

Green Island Cement

 

 

 

ISCST3

Existing WENT Landfill and Proposed WENT Landfill Extension

EcoPark

Shiu Wing Steel Mill

Marine Emissions

Industrial Emissions

Vehicle Emissions from Open Roads

CALINE4

Black Point Power Station

Wind tunnel test results from BPPS EIA Study

Predicted NO2 concentration from BPPS EIA Study

Castle Peak Power Station

 

3.6.2.40                 As mentioned in Section 3.4.1.2 above, elevated ASRs were also examined in this study.  With regards to the air quality impacts associated with BPPS, in accordance with Table 3.3a of the BPPS EIA Study, the wind speed for worst impacts at the ASRs in Tuen Mun Valley is 8m/s.  With reference to the result table in the forth last page of Annex C of the BPPS EIA Report, the predicted NO2 concentration (under Option 3) at Butterfly Estate at 0m and 60m above ground at 8m/s is 37.3 and 35.6 respectively.  Therefore an adjustment factor of 0.95 was applied to impacts at high level ASRs due to BPPS emissions.  As stated in Table 3.3, for the ASRs at Tuen Mun Valley and Butterfly Beach Area, since CPPS is located at different upwind direction of BPPS and STF, therefore only the BPPS contribution was considered in the hourly impact assessment.

Concentration Calculation

3.6.2.41                 The hourly, daily and annual average NO2, and SO2 concentrations at each ASR due to each source group were predicted.  As mentioned in Section 3.6.2.28, ozone limiting method was applied to each source group individually in estimating the NO2 concentrations.  The cumulative NO2 concentrations were then calculated by summing up the predicted NO2 concentrations at each ASR due to each source group.  The background air quality (as presented in Table 3.2) together with the emissions from the two existing power stations (as presented in Table 3.3) were then added to predict the cumulative impact at each ASR.

Odour Impacts
Emission Inventory
(i)          Odour Emissions from On-site Wastewater Treatment Plant

3.6.2.42                 The on-site wastewater treatment plant is designed for treating the wastewater generated from on-site activities, such as toilet flushing.  The sewage is mainly domestic in nature which is similar as other municipal sewage treatment plant such as SCISTW but in a much smaller scale.

3.6.2.43                 As the on-site wastewater treatment plant is a planned facility, no odour measurement can be carried out, and there is also no measurement conducted at other similar small scale sewage treatment plant.  Therefore, as a conservative assumption, the results of the odour measurement carried at SCISTW were adopted in this assessment.

3.6.2.44                 Odorous facilities comprise untreated sewage holding tank, equalization tank, membrane bioreactor tank, chlorination tank, effluent storage tank and sludge holding tank.  All odorous facilities will be enclosed and maintained at a negative pressure by extracting the odorous air to the deodorizing unit.  The odour removal efficiency of the deodorizing unit would be 95%.  With reference to the “Code of Practice on Assessment and Control of Odour Nuisance from Waste Water Treatment Works, April 2005” published by the Scottish Executive, odour removal efficiency of 95% or more is achievable by common odour abatement systems available in the market.

3.6.2.45                 SCISTW is a primary sewage treatment works, hence no odour measurement data is available for secondary treatment facilities.  As a conservative assumption, the maximum specific odour emission rate of 6.93ou/m2.s for sewage measured at SCISTW was adopted for all sewage treatment facilities in STF including untreated sewage holding tank, equalization tank, membrane bioreactor tank, chlorination tank, effluent storage tank.  However, for sludge holding tank, which is considered as an intensive odorous source, the specific odour emission rate calculated using the odour concentration of the fresh dewatered sludge measured at SCISTW of 20.17 ou/m2.s was adopted, this is the maximum value measured in a four-day odour measurement exercise at SCISTW.

3.6.2.46                 The average daytime temperature in the odour surveys at SCISTW was 29°C.  In accordance with Year 2005 to 2007 meteorological data from the Hong Kong Observatory, the mean daily maximum ambient temperatures in the summer (June – September) were in the range of 29 to 33°C.  With reference to the Hydrogen Sulphide Control Manual (Technological Standing Committee on Hydrogen Sulphide Corrosion in Sewage Works, 1989), the equation below presented by Pomeroy and Parkurst was taken to estimate the variation of odour emissions due to temperature changes:

G = M[BOD5]1.07T-20

where         G                 =        sulphide flux

                [BOD5]       =        5-day biochemical oxygen demand

                T                  =        Temperature °C

                M                 =        coefficient, m/h

 

3.6.2.47                 Based on the above equation, the sulphide flux increased by about 31% when temperature increased from 29 to 33°C.  Therefore, 31% increase or a 1.31 correction factor was applied in the odour emission rate which was calculated based on the measurement data from the SCISTW to estimate the worst case odour emission.  Detailed emission calculation is presented in Appendix 3.12.

(ii)        Odour Emissions from Sludge Treatment Facilities

3.6.2.48                 The sewage sludge would be delivered to the proposed STF in ISO-containers and skips by heavy load trucks from different sewage treatment works.  After entering the sludge reception hall, sludge would be discharged into the sludge hopper systems through intake openings by gravity of drag out mechanisms.  The reception hall and the sludge hopper systems are enclosed and separated by a door, the entrance of the reception hall is also installed with a door.  Refer to the plant design, the sludge hopper systems would be maintained at a negative pressure by extracting the odorous air as combustion air to the incinerators.  Odorous compounds will be destroyed under the high operating temperature of the incinerators.  Odour impacts from the incinerators facilities would therefore be negligible.  Besides, all dewatered sludge transfer tanks for the STF operation would be properly designed to avoid odour leakage during transportation.  Odour impact arising from the transportation of dewatered sludge is therefore not expected.

3.6.2.49                 The reception hall would also be maintained at a negative pressure by extracting the odorous air to the deodorizing unit and STF chimney.  The odour removal efficiency of the deodorizing unit for reception hall would be 95%.  As the sewage sludge is collected from various sewage treatment plants, the sewage nature would be the same as the sewage sludge at other sewage treatment works such as SCISTW.  Therefore, the odour concentration of the fresh dewatered sludge measured at SCISTW of 20.17 ou/m2.s was adopted to estimate the potential odour emissions from sludge tankers/trucks within the reception hall.  Temperature correction factor mentioned in Section 3.6.2.47 was also applied.  Detailed emission calculation is presented in Appendix 3.12.

Dispersion Modelling

3.6.2.50                 Air quality impacts of odour on ASRs were modelled with the air dispersion model Industrial Source Complex Short Term (ISCST3).  Hourly meteorological data for the year 2006 (including wind speed, wind direction, air temperature, Pasquill stability class and mixing height) of the Lau Fau Shan Weather Station were employed for the model run.

3.6.2.51                 In accordance with EPD’s Guideline on Assessing the “Total” Air Quality Impacts, the surrounding area of proposed project site is classified as ‘Rural’ area and ‘Rural’ mode was adopted in the dispersion model.

3.6.2.52                 The modelled hourly odour concentrations at the ASRs were converted to 5-second average odour concentration by the methodology proposed by Duffee et al.[1] and Keddie[2].  In addition, Turner[3]has identified that the Pasquill-Gifford vertical dispersion parameter used in the ISC3 model is around 3 to 10 minutes.  As a conservative assumption, the hourly average estimated by ISCST3 model is assumed as 15 minutes, and the conversion factors for the predicted 1-hour averaged concentration of odour at the receivers is adjusted to 5-second averaging time by the values shown in Table 3.7.

Table 3.7         Conversion Factors to 5 second Average Concentration

Pasquill Stability Class

Conversion Factor

15 min to 3 min

3 min to 5 sec

Overall

A

2.23

10

22.3

B

2.23

10

22.3

C

1.7

5

8.5

D

1.38

5

6.9

E

1.31

5

6.55

F

1.31

5

6.55

 

3.6.2.53                 With the installation of the proper deodorization units, the odour emissions from the proposed STF would be limited and hence the potential odour impacts would also be confined to the immediate vicinity of the STF site.  The only ASR identified within 500m from the STF site boundary is the site office of the WENT Landfill.  Since the WENT Landfill is itself an odour source, thus its site office is not considered as an ASR for odour impact.  In order to demonstrate the extent of the potential odour impact from STF to the receptors in its vicinity, the nearest ASR for odour impact, namely the temple near the Tsang Tsui Ash Lagoons, is identified for the odour impact assessment. 

3.7                                Identification, Prediction and Evaluation of Air Quality Impacts

3.7.1                          Gaseous Pollutants

3.7.1.1                     The predicted cumulative NO2, SO2 and RSP concentrations at the representative ASRs are summarized in Table 3.8 to Table 3.10 and the detailed assessment results are presented in Appendix 3.13 to Appendix 3.15. The other potential air pollutants (individual chemicals) covered in Annex 1 of EPD’s “A Guidance Note on the Best Practicable Means for Incinerator (Municipal Waste Incineration) BPM 12/1” are identified as contaminants of concern (COCs).  The predicted short-term and long-term concentrations of these COCs are presented in Appendix 3.16 and their health impacts are assessed in Section 4 of this EIA Report.

 

Table 3.8         Predicted Cumulative Hourly, Daily and Annual Average NO2 Concentration at Various Assessment Height Level

Near Field/ Far Field

ASR

Assessment Height (mAG)

Predicted Cumulative NO2 Concentration in mg/m3(a)(b)

Hourly

Daily

Annual

Near Field

A1

1.5

187

90

61

 

5

187

90

61

 

10

187

90

61

 

A2

1.5

293

106

64

 

5

293

106

64

 

10

293

106

64

 

A3

1.5

261

98

63

 

5

261

98

63

 

10

260

97

63

 

A4

1.5

245

90

62

 

5

244

91

62

 

10

244

91

62

 

A5

1.5

259

97

63

 

5

262

98

63

 

10

270

98

63

 

A6

1.5

170

96

64

 

5

170

96

64

 

10

170

96

64

 

A7

1.5

209

104

66

 

A8

1.5

240

123

67

 

5

239

123

67

 

10

239

123

67

 

A9

1.5

200

88

62

 

A22

1.5

198

112

67

Far Field

A10

1.5

195

91

61

 

A11

1.5

251

106

66

 

5

251

105

66

 

A12

1.5

133

83

62

 

5

133

83

62

 

10

133

83

62

 

20

132

83

62

 

40

131

83

62

 

60

129

83

63

 

80

137

84

63

 

100

142

84

63

 

120

141

85

63

 

A13

1.5

260

133

69

 

A14

1.5

179

89

63

 

5

179

89

63

 

10

179

89

63

 

20

178

88

63

 

40

178

88

63

 

60

176

88

63

 

A15

1.5

160

95

63

 

A16

1.5

258

120

66

 

5

258

120

66

 

10

261

120

66

 

A17

1.5

221

128

68

 

A18

1.5

215

101

65

 

5

215

101

65

 

10

215

101

65

Far Field

A19

1.5

250

117

66

 

5

250

117

66

 

10

250

117

66

 

A20

1.5

199

96

64

 

5

199

96

64

 

10

199

97

64

 

A21

1.5

286

119

66

 

5

286

119

66

 

10

285

118

66

 

A23

1.5

209

102

64

 

5

208

102

64

 

10

208

102

64

 

20

207

101

65

 

A24

1.5

157

87

63

 

5

157

87

63

 

10

157

87

63

 

20

156

87

63

 

40

168

88

63

 

60

207

89

63

 

80

238

90

63

 

100

226

92

63

 

120

205

94

63

 

A25

1.5

174

87

62

 

5

174

87

62

 

10

174

87

62

 

20

173

87

62

 

40

172

89

62

 

60

170

91

63

 

80

180

106

65

 

100

213

102

63

 

120

249

111

63

 

A26

1.5

178

87

63

 

5

178

87

63

 

10

178

87

63

 

20

178

87

63

 

40

177

87

63

 

60

174

89

63

 

80

173

93

64

 

100

181

99

64

 

120

204

109

63

 

A27

 

1.5

143

85

62

 

5

143

85

62

 

10

143

85

62

 

20

143

85

62

 

40

142

85

62

 

60

140

84

63

 

80

138

85

63

 

100

137

86

63

 

120

137

88

62

 

A28

1.5

153

85

62

 

5

153

85

62

 

10

153

85

62

 

20

152

85

62

Far Field

A29

1.5

151

85

62

 

5

151

85

62

 

10

151

85

62

 

20

151

85

62

 

40

151

85

62

 

60

149

85

63

 

80

158

88

63

 

100

219

129

71

 

120

257

114

64

 

A30

1.5

170

83

62

 

5

170

83

62

 

10

170

84

62

 

20

172

84

62

 

40

175

86

62

 

60

175

86

63

 

80

173

94

63

 

100

188

91

63

 

120

209

91

63

 

A31

1.5

136

83

62

 

5

136

83

62

 

10

136

83

62

 

20

145

83

62

 

40

171

83

62

 

60

175

83

62

 

80

179

84

63

 

100

178

87

63

 

120

153

84

62

 

A32

1.5

178

91

63

 

5

178

91

63

 

10

178

91

63

 

20

177

91

63

 

40

177

91

63

 

60

175

89

63

 

80

175

96

63

 

90

179

101

63

 

Notes:

(a)      Background NO2 concentration of 60 mg/m3 is included.

(b)     Adjusted hourly, daily and annual NO2 concentration due to the contribution of BPPS and CPPS is added (refer to Table 3.3).

Table 3.9         Predicted Cumulative Hourly, Daily and Annual Average SO2 Concentration at Various Assessment Height Level

Near Field/ Far Field

ASR

Assessment Height (mAG)

Predicted Cumulative SO2 Concentration in mg/m3(a)(b)

Hourly

Daily

Annual

Near Field

A1

1.5

207

88

26

 

5

207

88

26

 

10

207

88

26

 

A2

1.5

221

88

26

 

5

221

88

26

 

10

221

88

27

 

A3

1.5

217

88

27

 

5

217

88

27

 

10

217

88

27

 

A4

1.5

233

86

26

 

5

233

86

26

 

10

234

86

26

 

A5

1.5

220

87

26

 

5

220

87

26

 

10

220

87

26

 

A6

1.5

52

67

26

 

5

52

67

26

 

10

52

67

26

 

A7

1.5

204

87

26

 

A8

1.5

49

68

26

 

5

49

68

26

 

10

49

68

26

 

A9

1.5

209

88

26

 

A22

1.5

57

67

26

Far Field

A10

1.5

163

85

25

 

A11

1.5

65

67

26

 

5

65

67

26

 

A12

1.5

58

62

26

 

5

58

62

26

 

10

58

62

27

 

20

58

63

27

 

40

80

67

28

 

60

117

71

29

 

80

154

74

29

 

100

170

77

29

 

120

200

79

29

 

A13

1.5

195

94

37

 

A14

1.5

67

64

27

 

5

67

64

27

 

10

67

64

27

 

20

67

64

27

 

40

67

64

27

 

60

76

63

27

 

A15

1.5

52

65

26

 

A16

1.5

162

79

30

 

5

161

79

30

 

10

159

79

30

 

A17

1.5

151

74

28

 

A18

 

1.5

48

61

26

 

5

48

61

26

 

10

51

61

26

Far Field

A19

1.5

53

62

26

 

5

53

62

26

 

10

53

62

26

 

A20

1.5

48

60

26

 

5

48

60

26

 

10

48

61

26

 

A21

1.5

76

69

26

 

5

76

69

26

 

10

76

69

26

 

A23

1.5

51

61

26

 

5

51

61

26

 

10

51

61

26

 

20

55

61

26

 

A24

1.5

63

64

26

 

5

63

64

26

 

10

63

64

26

 

20

64

64

26

 

40

69

66

27

 

60

106

65

27

 

80

149

71

27

 

100

183

78

27

 

120

195

73

27

 

A25

1.5

65

64

26

 

5

65

64

26

 

10

65

64

26

 

20

66

64

26

 

40

67

65

26

 

60

103

72

27

 

80

719

150

35

 

100

331

77

28

 

120

115

69

27

 

A26

1.5

75

65

27

 

5

75

65

27

 

10

76

65

27

 

20

77

65

27

 

40

84

70

28

 

60

110

71

29

 

80

179

76

31

 

100

195

81

30

 

120

156

78

28

 

 

A27

1.5

53

63

26

 

5

53

64

26

 

10

53

64

26

 

20

54

64

26

 

40

59

66

27

 

60

84

68

27

 

80

143

74

28

 

100

147

71

28

 

120

108

70

27

 

A28

1.5

56

63

26

 

5

56

63

26

 

10

56

63

26

 

20

57

63

26

Far Field

A29

1.5

54

63

26

 

5

54

63

26

 

10

54

63

26

 

20

54

63

26

 

40

59

67

27

 

60

88

73

28

 

80

151

87

30

 

100

658

252

58

 

120

407

98

30

 

A30

1.5

54

63

26

 

5

54

63

26

 

10

54

63

26

 

20

57

63

26

 

40

111

71

27

 

60

216

82

29

 

80

404

115

31

 

100

382

104

31

 

120

422

95

30

 

A31

1.5

57

62

26

 

5

57

62

26

 

10

57

62

26

 

20

58

63

26

 

40

131

71

27

 

60

87

69

28

 

80

191

81

29

 

100

318

89

29

 

120

163

81

28

 

A32

1.5

62

63

26

 

5

62

63

26

 

10

62

63

26

 

20

62

63

26

 

40

62

63

27

 

60

71

63

27

 

80

86

66

27

 

90

89

68

27

 

Notes:

(a)      Background SO2 concentration of 24 mg/m3 is included.

(b)     Adjusted hourly, daily and annual SO2 concentration due to the contribution of BPPS and CPPS is added (refer to Table 3.3).

Table 3.10     Predicted Cumulative Daily Average RSP Concentration at Various Assessment Height Level

Near Field/ Far Field

ASR

Assessment Height (mAG)

Predicted Cumulative RSP Concentration in mg/m3(a)(b)

Daily

Near Field

A1

1.5

69

5

69

10

69

A2

1.5

70

5

70

10

70

A3

1.5

68

5

68

10

68

A4

1.5

69

5

69

10

69

A5

1.5

75

5

75

10

75

A6

1.5

82

5

82

10

82

A7

1.5

69

A8

1.5

74

5

74

10

74

A9

1.5

67

A22

1.5

69

Far Field

A10

1.5

70

 

A11

1.5

86

 

5

86

 

A12

1.5

66

 

5

66

 

10

66

 

20

66

 

40

66

 

60

66

 

80

66

 

100

66

 

120

66

 

A13

1.5

76

 

A14

1.5

81

 

5

81

 

10

81

 

20

80

 

40

78

 

60

74

 

A15

1.5

73

 

A16

1.5

80

 

5

80

 

10

80

 

A17

1.5

97

 

A18

1.5

87

 

5

90

 

10

108

Far Field

A19

1.5

105

 

5

110

 

10

123

 

A20

1.5

93

 

5

95

 

10

99

 

A21

1.5

86

 

5

86

 

10

87

 

A23

1.5

91

 

5

94

 

10

103

 

20

156

 

A24

1.5

68

 

5

68

 

10

68

 

20

68

 

40

68

 

60

68

 

80

68

 

100

67

 

120

67

 

A25

1.5

75

 

5

75

 

10

75

 

20

75

 

40

73

 

60

71

 

80

71

 

100

69

 

120

69

 

A26

1.5

75

 

5

75

 

10

75

 

20

75

 

40

73

 

60

71

 

80

69

 

100

69

 

120

69

 

 

A27

1.5

67

 

5

67

 

10

67

 

20

67

 

40

67

 

60

67

 

80

67

 

100

66

 

120

66

 

A28

1.5

80

 

5

80

 

10

80

 

20

79

Far Field

A29

1.5

80

 

5

80

 

10

80

 

20

79

 

40

77

 

60

73

 

80

71

 

100

70

 

120

70

 

A30

1.5

68

 

5

68

 

10

68

 

20

68

 

40

67

 

60

67

 

80

67

 

100

66

 

120

66

 

A31

1.5

66

 

5

66

 

10

66

 

20

66

 

40

66

 

60

66

 

80

66

 

100

66

 

120

66

 

A32

1.5

81

 

5

81

 

10

81

 

20

80

 

40

77

 

60

73

 

80

71

 

90

71

 

Notes:

(a)      Background RSP concentration of 62 mg/m3 is included.

(b)     Adjusted daily RSP concentration due to the contribution of BPPS and CPPS is added (refer to Table 3.3).

 

3.7.1.2                     The results indicated that the predicted cumulative hourly, daily and annual average NO2 & SO2 and daily RSP concentrations at all representative ASRs would comply with the respective AQO.

3.7.1.3                     Apart from the representative ASRs, the hourly and/or daily contour plots for NO­2, SO2 and RSP at the worst-affected elevations are produced and included in Appendix 3.17 to illustrate if there would be any area(s) with predicted exceedance of the AQO.  The pollutant contour plots are produced for both a larger study area (namely the Overall Area) covering more than 5km from the Project site (with a coarser grid size of 500m) and four focused areas namely the Ha Pak Nai Area, Lung Kwu Tan Area, Butterfly Beach Area, and the Tuen Mun Town Centre Area (with a finer grid size of 50m).  For the Overall Area, contour plots are produced at two selected worst-affected heights of 10mPD and 130mPD.  For the Ha Pak Nai Area and Lung Kwu Tan Area, contour plots are produced at 10mPD, whereas for the Butterfly Beach Area and Tuen Mun Town Centre Area, contour plots are produced at 100mPD and 130mPD respectively.

3.7.1.4                     With reference to the modelling results predicted at the representative ASRs, only the highest values predicted for hourly average NO2 exceeded 90% of the corresponding AQO at some of the Ha Pak Nai Area and Lung Kwu Tan Area, additional contour plots are therefore produced at 10mAG level of Ha Pak Nai Area and 1.5mAG of Lung Kwu Tan Area to confirm that no AQO exceedances would be expected at air sensitive areas (see Figures A.10b and A.15b of Appendix 3.17).  Besides, since the hourly average NO2 is also the most critical parameter among the examined parameters, contour plots of hourly average NO2 are produced for the Overall Area at a number of additional elevations namely 20mPD, 30mPD, 40mPD, 70mPD and 100mPD (see Figure A5 of Appendix 3.17).

3.7.1.5                     As shown in the contour plots in Appendix 3.17, exceedances of AQO are predicted at some areas at different elevations.  For the Overall Area, exceedances of AQO for SO2 (hourly average) and NO2 (hourly and daily average) are observed at upper elevations from 70mPD to 130mPD around some of the major stack emission sources (see Figures A.3b, A.4b, A.5e, A.5f, and A.5g of Appendix 3.17).  However, no air sensitive uses at the affected elevations are identified within the exceedance area(s).

3.7.1.6                     For the Ha Pak Nai Area, exceedances of hourly average AQO for NO2 are predicted along the coast (see Figures A.10a and A.10b of Appendix 3.17) with major contribution of the exceedances is the emission from marine vessels manoeuvring along the coast.  No air sensitive uses at the affected elevations are identified within the exceedance area(s).

3.7.1.7                     For the Lung Kwu Tan Area, exceedances of hourly average AQO for NO2 are predicted at 1.5mAG in close proximity to Lung Kwu Tan Road (see Figure A.15b of Appendix 3.17) due largely to the traffic emissions along the road.  No air sensitive uses at the affected elevations are identified within the exceedance area(s).

3.7.1.8                     No AQO exceedances are predicted at the Butterfly Beach Area.  For the Tuen Mun Town Centre Area, exceedances of AQO for SO2 (hourly and daily average) and NO2 (hourly and daily average) are observed at the 130mPD level in the immediate proximity of some major industrial stacks in the area (see Figures A.22 to A.25 of Appendix 3.17).  However, no air sensitive uses at the affected elevations are identified within the exceedance area(s).

3.7.2                          Odour Impacts

3.7.2.1                     Odour level at the nearest representative ASR for odour impact, namely the temple near the Tsang Tsui Ash Lagoons, is predicted and the assessment result is shown in Table 3.11.

Table 3.11       Predicted Odour Levels at ASRs

ASR

Description

Odour Level (5 seconds average) (OU) at 1.5m above ground

A22

Temple near the Tsang Tsui Ash Lagoons

0.1

 

3.7.2.2                     The modelling results indicated that the predicted odour impact at the nearest ASR for odour impact would be well below EPD’s odour criteria of 5 OU.  The predicted odour level of 0.1 OU at the nearest ASR due to STF emissions is well below 1 OU, i.e. not detectable by most of the population.  Cumulative odour impacts with other potential odour sources further away from STF including the WENT Landfill and its Extension is therefore not expected.

3.8                                Mitigation Measures

3.8.1                          Construction Phase

3.8.1.1                     To ensure compliance with the guideline level and AQO at the ASRs, the Air Pollution Control (Construction Dust) Regulation should be implemented and good site practices should be incorporated in the contract clauses to minimize construction dust impact.  A number of practicable measures are listed below:-

l        Use of regular watering, with complete coverage, to reduce dust emissions from exposed site surfaces and unpaved roads, particularly during dry weather.

l        Use of frequent watering for particularly dusty construction areas and areas close to ASRs.

l        Side enclosure and covering of any aggregate or dusty material storage piles to reduce emissions.  Where this is not practicable owing to frequent usage, watering should be applied to aggregate fines.

l        Open stockpiles should be avoided or covered.  Where possible, prevent placing dusty material storage piles near ASRs.

l        Tarpaulin covering of all dusty vehicle loads transported to, from and between site locations.

l        Establishment and use of vehicle wheel and body washing facilities at the exit points of the site.

l        Provision of wind shield and dust extraction units or similar dust mitigation measures at the loading points, and use of water sprinklers at the loading area where dust generation is likely during the loading process of loose material, particularly in dry seasons/ periods.

l        Imposition of speed controls for vehicles on unpaved site roads.  Ten kilometres per hour is the recommended limit.

l        Where possible, routing of vehicles and positioning of construction plant should be at the maximum possible distance from ASRs.

l        Instigation of an environmental auditing program to monitor the construction process in order to enforce controls and modify method of work if dusty conditions arise.

3.8.2                          Operation Phase

3.8.2.1                     Air pollution control and stack monitoring system will be installed for the STF to ensure that the emissions from the STF stacks will meet the stringent target emission limits equivalent to those stipulated in Hong Kong and the European Commission for waste incineration.  According to the assessment results, the STF would not cause adverse cumulative air quality impact at all the representative ASRs.

3.8.2.2                     To ensure the compliance of odour criteria at the sensitive receptors in the vicinity of the STF, all the potential odour emissions associated with the operation of the STF namely those from the sludge reception hall and the on-site wastewater treatment plant should be collected and destroyed by the incineration process or ventilated to deodorizer before discharge to the atmosphere.

3.9                                Residual Environmental Impact

3.9.1                          Construction Phase

3.9.1.1                     With the implementation of the mitigation measures as stipulated in the Air Pollution Control (Construction Dust) Regulation, and with the adoption of good site practices and audit, no adverse residual dust impact is expected.

3.9.2                          Operation Phase

3.9.2.1                     With the implementation of practicable air pollution control and stack monitoring system for the STF, emissions from the STF stacks will meet the stringent target emission limits equivalent to those stipulated in Hong Kong and the European Commission for waste incineration and no adverse residual air quality impact due to STF stack emission is expected.

3.9.2.2                     With the implementation of recommended odour mitigation measures, no adverse residual odour impact would be expected at the nearby ASRs.

3.10                            Environmental Monitoring and Audit Requirements

3.10.1                      Construction Phase

3.10.1.1                 With the implementation of practicable dust suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation, adverse construction dust impact is not expected during construction of the Project.  Yet, regular site environmental audits during the construction phase of the Project as specified in the EM&A Manual should be conducted to ensure that the recommended dust suppression measures are implemented properly.

3.10.2                      Operation Phase

3.10.2.1                 During the operation of the STF, the potential sources of air quality impacts would be the air emissions from the stacks of incineration process and the odour nuisance from the on-site wastewater treatment plant and the sludge reception hall.  Air pollution control and stack monitoring system will be installed for the STF to ensure that the emissions from the STF stacks will meet the stringent target emission limits and all the potential odour emissions associated with the operation of the STF will be collected and destroyed by the incineration process or ventilated to deodorizer before discharge to the atmosphere.  Monitoring of air quality parameters of concern due to stack emissions has to be conducted in accordance with the requirements similar to those stipulated in the “A Guidance Note on the Best Practicable Means for Incinerator (Municipal Waste Incineration) BPM 12/1”.  Besides, odour monitoring should be carried out by odour patrol to demonstrate the effectiveness of the proposed odour mitigation measures and to ensure the odour impact can be minimized to meet the air pollution control requirements.

3.11                            Conclusion

3.11.1                      Construction Phase

3.11.1.1                 Air quality impacts from the construction works for the Project would mainly be related to construction dust from excavation, materials handling, filling activities and wind erosion.  With the implementation of mitigation measures specified in the Air Pollution Control (Construction Dust) Regulation, dust impact on air sensitive receivers would be minimal.

3.11.2                      Operation Phase

3.11.2.1                 During the operation of the STF, the potential sources of air quality impacts would be the air emissions from the stacks of incineration process and the odour nuisance from the on-site wastewater treatment plant and the sludge reception hall.

3.11.2.2                 There would also be cumulative air quality impacts contributed from other existing and planned emission sources in Tuen Mun, including the Black Point Power Station, Castle Peak Power Station, Green Island Cement Plant, WENT landfill and the proposed WENT landfill extension, EcoPark, Shiu Wing Steel Mill, etc.

3.11.2.3                 Air pollution control and stack monitoring system will be installed for the STF to ensure that the emissions from the STF stacks will meet the stringent target emission limits equivalent to those stipulated in Hong Kong and the European Commission for waste incineration.  Besides, all the potential odour emissions associated with the operation of the STF will be collected and destroyed by the incineration process or ventilated to deodorizer before discharge to the atmosphere.

3.11.2.4                 With the implementation of practicable air pollution control, the STF would not cause adverse cumulative air quality impact at all the air sensitive receivers in the vicinity of the Project site and those further away in the Tuen Mun new town area.

 


[1]    Richard A. Duffee, Martha A. O”Brien and Ned Ostojic (1991).  Odor Modeling – Why and How, Recent Developments and Current Practices in Odor Regulation, Controls and Technology, Air & Waste Management Association.

[2]   Keddie, A. W. C (1980).  Dispersion of Odours, Odour Control – A Concise Guide, Warren Spring Laboratory.

[3]    Turner, D. (1994).  Workbook of Atmosphere Dispersion Estimates, 2nd Edition, Lewis Publishers.