3.                     air quality impact

 

3.1                   Introduction

 

3.1.1             In this section, air quality impacts associated with the construction and operation phases of the proposed Roads D1, D8, D10 and the extended Road P2 are assessed.  Dust is likely to be the major potential impact during construction phase, and vehicle emission is likely to be the key air quality concern during operation phase. 

 

3.1.2             As mentioned in Section 1.3, two separate assessments (with and without the possible future development to the south of Road D1) were done with respect to air quality impacts.  Since for Assessment 1, it is assumed that there will be possible further development to the south of Road D1, in terms of the number of concurrent construction activities, this should be the worst case situation during the construction phase.  Therefore, only the assessment with the possible future development to the south of Road D1 during the construction phase was studied.

 

3.1.3             During operation phase, since the proposed noise mitigation measures under the assumptions of the two assessments are different, the air quality impact for the two assessments was studied accordingly.

 

3.2                   Environmental Legislation, Policies, Plans, Standards and Criteria

 

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

 

3.2.2             The Air Pollution Control Ordinance (APCO) provides the statutory authority for controlling air pollutants from a variety of sources.  The ordinance encompasses a number of Air Quality Objectives (AQOs) which stipulate maximum concentrations for a range of pollutants, of which nitrogen dioxide (NO2), respirable and total suspended particulates (RSP & TSP) are relevant to this study.  The relevant AQOs are listed in the following table.

 

Table 3.1         Hong Kong Air Quality Objectives

 

Parameter

Maximum Average Concentration (µgm-3)1

 

 

1-Hour2

 

24-Hour3

Annual4

NO2

300

150

80

RSP

-----

180

55

TSP

-----

260

80

 

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.

 

3.2.3             The EIAO-TM also stipulated that the hourly TSP level should not exceed 500 µgm-3 TSP (measured at 25°C and one atmosphere) for construction dust impact assessment.  Mitigation measures from construction sites have been specified in the Air Pollution Control (Construction Dust) Regulations.

 

3.2.4             In addition, according to the EPD’s Practice Note on Control of Air Pollution in Vehicle Tunnels 1995, the criteria for tunnel quality are presented in Table 3.2.

 

Table 3.2         Tunnel Air Quality Criteria

 

Parameter

Maximum Concentration1, 2

CO

115,000 µgm-3

100 ppm

NO2

1,800 µgm-3

1 ppm

SO2

1,000 µgm-3

0.4ppm

1           Averaging time is 5 minutes

2           Measured at 298 K and 101.325 kPa.

 

3.3                   Description of the Environment

 

Baseline Condition

 

3.3.1             Existing air quality in the vicinity of Roads D1, D8, D10 and the extended Road P2 is affected by emissions from existing road traffic.

 

3.3.2             According to the separate EA study for Area 86[1], emission levels of air pollutants (including copper, lead, particulate, SO2, NO2, CO, HF, HCl and VOCs) arising from the metal works in Area 85, flares in TKO Stage I and Stage II / III landfills, and fossil fuel consuming stacks in Tseung Kwan O Industrial Estate (TKOIE) and the nearby areas were predicted to be well below the acceptable levels.  Table 3.3 summarizes the relevant maximum predicted SO2, NO2 and TSP concentrations at the worst affected locations.  If the predicted SO2, NO2 and TSP concentrations in this EIA report (where most of the ASRs are further away from the industrial sources) are also well below the acceptable levels, no adverse cumulative air quality impact arising from the industrial emissions is anticipated.

 

Table 3.3         Maximum Predicted SO2, NO2 and TSP Concentrations from the Separate EA Study for Area 86

 

Pollutants

Modelled Concentration (with background), mgm-3

Assessment Criteria, mgm-3

SO2

Highest 1-hr

345.7 at southeast of Area 86

800

NO2

Highest 1-hr

52.5 at north of Area 86

300

TSP

Daily

184 at east of Area 86

260

 

3.3.3             The EPD’s TKO air quality monitoring station ceased operation in 1993.  Background air quality of TKO was not available for this study.  Indeed, in the past few years, TKO has been transformed into a new development area.  The air quality monitoring data before 1993 therefore could not reflect the existing background air quality of TKO for this study. 

 

3.1.1The nearest EPD’s air quality monitoring station to the study area is located at Kwun Tong.  However, Kwun Tong is an industrial area and its air quality would not represent that of the TKO new town.

 

3.3.4             According to the EPD’s “Guideline on Assessing the ‘TOTAL’ Air Quality Impacts”, TKO is classified as a rural/new development area.  Tai Po is also specified in the Guideline as a rural/new development area indicating that the background air pollutant levels for Tai Po and TKO are compatible.  For the purpose of this assessment, Tai Po air quality data were therefore taken as the background offor TKO forin this study.

 

3.3.5             Moreover, the background pollutant levels measured at Tai Po station in 2000 was lower than those in 1997 (Table 3.4).  In such, the background pollutants levels (Tai Po station, 1997) used in this assessment represent a worst-case scenario.

 

Table 3.4         Air Pollutant Levels Recorded at EPD Air Quality Monitoring Stations

 

Pollutants

Annual Average Concentrations (mgm-3)

 

TKO (1993)

Tai Po (1997)

Tai Po (2000)

NO2

21

50

47

RSP

39

55

48

TSP

77

80

63

 

 

Air sensitive receivers

 

3.3.6             Existing and planned Air Sensitive Receivers (ASRs) including domestic premises, industrial and commercial buildings, educational institutions, and recreational and leisure facilities have been identified for air quality impact assessment.

 

3.3.7             Two heights were used for the assessment: 1.5 metres above local ground level (which is the average height of the human breathing zone) and 10.0 metres above local ground level.

 

Construction Phase

 

3.3.8             The work packages and the construction period for the road project comprise the following:

 

·          Road D1 (2003-2006)

·          Road D8 (2003-2006)

·          Town Centre Link, Road D10 (2003-2007)

·          Minor road junction improvement works at road junction of Road D10 / Wan Po Road, and road junctions along Roads D1 and D8 (2002-2009)

·          Extended Road P2 (2003-2010)

 

3.3.9             The nearby concurrent construction sites which are expected to involve major dusty activities in between the construction period of the work packages of the road project are:

 

·          Cross Bay Link, Road D9 (2003-2011)

·          Road D6 (2003-2008)

·          Minor road junction improvement works at road junctions of Road D9 / Wan Po Road, Road D6 / Wan Po Road, and road junctions along D4 and P2 (2002-2009)

·          Water Supply Infrastructure (2003-2007/08)

·          Area 86 (2000-2010)

·          Area 65D and 67 (indicative and may be completed before 2007)

 

3.3.10         As a worst case, the following possible future development were also included in the construction phase air quality impact assessment:

 

·          Site formation work for the possible future development of Pak Shing Kok (Area 78) (2003-2008)

·          Possible future development to the south of Road D1 and the associated roads and drains in the development (indicative and may be constructed in 2005-2013)

 

3.3.11         Since the construction of Western Coast Road will be farther than 500m from the study boundary, the cumulative construction impact will not be addressed.

 

3.3.12         Taking into account the construction period of the work packages of the road project, and the concurrent construction activities in close proximity and the intake of nearby ASRs,  Year 2005 is identified to be the worse year throughout the construction period.

 

3.3.13         For the construction of Road D1, the nearest ASRs would be in Areas 51, 55A, 65B, 65C and 72.  For the construction of Road D8, the nearest ASRs would be in Area 72, 73 and 74.  And for the construction of Road D10, the nearest ASRs would be in Areas 65C, 77, 85 and 104106.  For the construction of extended Road P2, the nearest ASRs would be in Areas 57B, 72 and 74.

 

3.3.14         A description of the representative ASRs during the construction of Roads D1, D8, D10 and the extended Road P2 are summarized in Table 3.5.  Locations of the ASRs are shown in Figure 3.1.

 

Table 3.5         Description of Air Sensitive Receivers (ASRs) during Construction Phase in Year 2005

 

 

ASR ID

 

Description

 

Area No.

Population

Intake

Contributions among D1, D8, D10 and extended P2

A21

Planned Residential, R2

72

2000-2004

D1, D8

A24

Planned Residential, R2

72

2000-2004

D8

A25

Planned School

72

2000-2004*

D8

A26

Planned School

72

2000-2004*

Extended P2

A29

Planned Residential

65B

2005

D1

A30

Planned School

65C

2006*

D1, D10

A31

Planned Residential, R1

51

2000

D1

A37

Planned Residential

85

2005-2006*

D10

A39

Planned Film Studio

106

2003*

D10

A43

Planned Residential

73

2002

D8

A44

Planned Residential

74

2006

D8

A45

Planned Residential

55A

2002

D1

A46

Existing Soccer Pitch

77

-

D10

A48

Planned Residential

74

2006

Extended P2

A49

Planned Residential

57B

2002

Extended P2

*  Represents the commissioning date

 


Operation Phase

 

3.3.15         As mentioned in Section 3.1, two separate assessments (with and without the possible future development to the south of Road D1) were conducted.  According to the criteria stipulated in the EIAO-TM, the nearest existing and planned ASRs have been identified and indicated in Table 3.6.  Figures 3.2 and 3.3 show the locations of the ASRs for Assessments 1 and 2, respectively.

 

Table 3.6      Description of Air Sensitive Receivers (ASRs) during Operation Phase

 

 

ASR

ID

 

Description

 

Area

No.

 

Population

Intake

Horizontal distance from the kerb of its closest road (m)

 

Assess-ment 1

 

Assess-ment 2

A07

 

Possible future development to the south of Road D1

 

 

N/A

 

 

 

 

 

N/A

97

Ö

´

A10

35

Ö

´

A11

23

Ö

´

A12

70

Ö

´

A13

167

Ö

´

A14

53

Ö

´

A21

Planned Residential, R2

72

2000-2004

20

Ö

Ö

A22

Planned Residential, R1

67B

2007

23

Ö

Ö

A23

Planned Residential, R1

65D

2008

16

Ö

Ö

A24

Planned Residential, R2

72

2000-2004

60

Ö

Ö

A25

Planned School

72

2000-2004*

15

Ö

Ö

A26

Planned School

72

2000-2004*

23

Ö

Ö

A29

Planned Residential

65B

2005

53

Ö

Ö

A30

Planned School

65C

2006*

11

Ö

Ö

A31

Planned Residential, R1

51

2000

180

Ö

Ö

A37

Planned Residential

85

2005-2006*

23

Ö

Ö

A39

Planned Film Studio

106

2003*

71

Ö

Ö

A42

Planned Residential

86

2004-2012

4

Ö

Ö

A43

Planned Residential

73

2002

14

Ö

Ö

A44

Planned Residential

74

2006

23

Ö

Ö

A45

Planned Residential

55A

2002

15

Ö

Ö

A46

Existing Soccer Pitch

77

-

56

Ö

Ö

A47

Planned School

67

2007

26

Ö

Ö

A48

Planned Residential

74

2006

32

Ö

Ö

A49

Planned Residential

57B

2002

60

Ö

Ö

* Represents the commissioning date

 


3.4                   Assessment Methodologies

 

Construction Phase

 

3.4.1             Cumulative construction dust impact owing to the construction of the road project and the other nearby concurrent construction sites has been assessed.

 

3.4.2             As discussed in Section 3.3, taking into account the different construction periods and the intake of population, Year 2005 has been identified as the worst year throughout the construction period.

 

3.4.3             In 2005, the major dusty activities in and around the road projects will be:

 

·          Roadworks for Road D1

·          Roadworks for Road D8

·          Roadworks and bridge foundations for Town Centre Link (Road D10)

·          Roadworks for extended Road P2

·          Construction activities for Cross Bay Link (Road D9)

·          Site formation work for possible future development of Pak Shing Kok (Area 78)

·          Possible future development to the south of Road D1 and the associated roads and drains in the development

·          Water supply infrastructure

·          Construction activities for Area 86

·          Construction activities in Area 65D and Area 67

·          Minor road junction improvement works at the junctions of Road D9 / Wan Po Road, Road D10 / Wan Po Road, Road D6 / Wan Po Road, and road junctions along D1, D4, D8 and P2

 

3.4.4             Prediction of dust emissions was based on emission factors from USEPA Compilation of Air Pollution Emission Factors (AP-42), 5th Edition.  For a conservative simulation, general construction activities and wind erosion of open sites were considered to be the major dust emission sources from the construction works in this study.

 

3.4.5             The dust emission factors adopted in this assessment are given in Table 3.7

 

Table 3.7         Dust Emission Factors used in this Assessment

 

Activities

References (AP-42, 5th Edition)

General construction activities

2,690 kg/hectare/month (Section 13.2.3)

Wind erosion of open site

850 kg/hectare/year (Table 11.9.4)

 

3.4.6             For conservatism, construction activity was assumed to be continuous (although night time and evening work is not actually planned).  The sites to be developed cover large areas, but only parts of the site will be actively worked at any one time.  Taking into account the horizontal extent of a general construction site, it was assumed that a maximum of 30 percent of the construction site area would be actively operated at any one time during the construction periods.  Wind erosion would also occur from all open construction areas.

 

3.4.7             Detailed calculations of the emission factors are given in Appendix 3.1.

 

3.4.8             Fugitive Dust Model (FDM) was used to assess potential dust impacts from construction activities.  1-hour average and 24-hour average of TSP concentrations were predicted at the selected air sensitive receivers.

 

3.4.9             One year’s sequential meteorological data for the year 1994 from Hong Kong Observatory (TKO Bay Station) were used in the FDM to predict the 1-hour and 24-hour average TSP concentrations.  The data include wind speed, wind direction, stability class, ambient temperature and mixing height.

 

3.4.10         Surface roughness of the terrain in the study area was taken as 1 metre in the FDM model, a height that is generally applied to relatively flat construction areas in Hong Kong.  The mixing height was assumed to be 500 metres above local ground level.

 

3.4.11         As discussed in Section 3.3, a background TSP concentration of 80 mgm-3 has been added to the maximum 1-hour average and maximum 24-hour average results.

 

3.4.12         A sample output file of the FDM model run, which includes all the input information and model parameters for this assessment, is presented in Appendix 3.2 of this report for reference.

 

Operation Phase

 

Vehicle Emissions

 

3.4.13         Potential air quality impact during the operation phase of Roads D1, D8, D10 and the extended Road P2 would be dominated by vehicle emissions arising from road traffic.  Air quality impacts associated with road traffic are caused mostly by Nitrogen Dioxide (NO2) and Respirable Suspended Particulates (RSP).  The 1-hour and 24-hour concentrations of NO2 and RSP were calculated and compared with the AQO limits.

 

3.4.14         All the major roads within 500m of the project development were incorporated into the assessment.  Roads include:

 

·          Roads D1, D4, D6, D8, D9 and D10

·          Roads P1, P2, Wan Po Road, Chiu Shun Road, Po Ning Road and Hang Hau Road

·          Local roads in and around Areas 55, 56, 57, 65, 66, 67, 72 and 74

·          Local roads in possible further development to the south of Road D1

 

3.4.15         The assessment should be based on projected peak hour flows for the worst year within 15 years of commencement of operation.  According to the traffic forecast, 2030 is assumed to be the worst year within 15 years of commencement of the operation.

 

3.4.16         The AM peak hour traffic flow and vehicle mix predicted by the traffic consultant for the road network for the year 2030 was used for the assessment.  With reference to the Annual Traffic Census 1997, the lowest PM hour traffic flow is generally around 20% of AM peak hour traffic flow.  For a conservative simulation, 1/3 of the AM peak hour traffic flow was applied during the modelling of nighttime periods.

 

3.4.17         The most up-to-date vehicular emission factors (Fleet Average Emission Factors – EURO3 Model) available from EPD are for the year 2011 and these were adopted for 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.  Preliminary calculations show that the combination of projected traffic flow in 2030 and emission factor in 2011 represent the worst scenario in terms of air pollution from the road as the emission factor in 2011 is higher than that in 2030.  The vehicular emissions for different vehicle categories are listed in the following table.  Details for the calculations of the composite emission factors for each road link are given in Appendix 3.3a.

 

Table 3.8         Emission Factors for Year 2011 for Different Vehicle Category

 

Pollutant

Emission Factors (gm/km)

 

Bus

HGV

LGV

Private Car

Taxi

NOx

6.80

3.84

1.23

0.71

0.73

RSP

0.69

0.53

0.11

0.03

0.01

 

3.4.18         The CALINE4 dispersion model was used to determine of the hourly NO2, 24-hour NO2 and 24-hour RSP concentrations.  For the calculation of the NO2 concentrations, the vehicular emission factor of NOx was adopted and the conversion factor from NOx to NO2 was assumed to be 20%.

 

3.4.19         The CALINE4 model calculates hourly concentrations only.  The highest predicted hourly concentration between daytime and nighttime is assumed to be the maximum 1-hour average concentration.  With reference to the Screening Procedures for Estimating the Air Quality Impact of Stationary Source (EPA-454/R-92-019), a conversion factor of 0.4 is used to convert the 1-hour average concentrations to 24-hour average concentrations.

 

3.4.20         Worst case scenario was adopted in the modelling.  The following summarises the meteorological conditions adopted in the air quality modelling using the CALINE4 model:

 

·          Wind speed                      :           1 m/s

·          Wind direction                  :           worst case

·          Wind variability                :           18° (day time) or 6° (night time)

·          Stability class                    :           D (day time) or F (night time)

·          Surface roughness            :           1 m

·          Mixing height                    :           500 m

 

3.4.21         Potential air quality impacts from implementation of proposed roadside noise mitigation measures in and around the Study Area were also incorporated into the air quality model.

 

3.4.22         According to the results of the noise impact assessment, two sets of noise mitigation measures have been proposed for Assessments 1 and 2.  Details of the noise mitigation measures are given in Section 4 and the locations of the barriers are shown in Figures 4.3 - 4.7. 

 

3.4.23         The major differences between the two sets of noise mitigation measures are that two sections of deckover spanning the entire width of Road D1 are proposed for Assessment 1 whilst two sets of semi-enclosure is proposed for Road D1 for Assessment 2 when it is assumed that there will be no further development to the south of Road D1.

 

3.4.24         In addition, deckovers proposed for Road D4 in the EIA report of “Tseung Kwan O Town Centre Central” were also incorporated into the air quality model.

 

3.4.25         It was assumed that with the installation of noise barriers, all the traffic pollutants generated from that road section would be emitted from the top of the noise barriers.  In addition, for the cantilever barrier, the source of the emissions was adjusted by shifting the road section by a distance equal to the width of the road section covered by the cantilever.  In the air quality model, the road type was set to ‘fill’ and the relative height was set to the effective height of the barrier.  No correction or adjustment to the receiver heights was made in the model.  Similar methodology was adopted in the EIA study for “Tseung Kwan O Development Contract F – Grade Separated Interchange T1/P1/P2”.

 

3.4.26         Portal emissions from the deckovers were modelled in accordance with the Permanent International Association of Road Congress Report (PIARC, 1991).  The volume of pollutants was assumed to eject from the portal as a portal jet such that 2/3 of the total emissions was dispersed within the first 50m of the portal and 1/3 of the total emissions within the second 50m.  Detailed calculations of the emission rates at the portals are shown in Appendices 3.3b and 3.3c.

 

3.4.27         As mentioned in Section 3.3, the background concentrations for NO2 and RSP were taken as 50 mgm-3 and 55 mgm-3 respectively, which were added to the corresponding predicted concentrations.

 

3.4.28         Appendix 3.4 provides sample computer outputs from the CALINE4 model used for the vehicle emissions impact assessment.

 

Air Quality inside Deckovers of Road D1 for Assessment 1

 

3.4.29         According to the findings in Chapter 4, two sections of about 190m and 115m long deckovers are proposed on Road D1 for Assessment 1, i.e. assuming that there will be further development to the south of Road D1.  The air quality inside the two sections of the deckover was assessed using the theory developed by Ohashi and Koso[2].

 

3.4.30         Two scenarios were considered for the deckover, i.e. normal traffic flow condition and congested traffic flow condition.  It was assumed that under normal traffic condition the vehicles travel at a speed of 50 kph, whereas under congested conditions, the separation between vehicles is assumed to be 1 m. 

 

3.4.31         Appendix 3.5 shows the detailed calculation of the inside tunnel air quality assessments for the two sections of the deckover.

 

3.5                   Environmental Impact Identification, Prediction and Evaluation

 

Construction phase

 

3.5.1             The predicted cumulative maximum 1-hour average and maximum 24-hour average TSP concentrations at the representative ASRs in 2005 are tabulated in Table 3.9.  These results are for the unmitigated scenario, that is without any dust suppression measures.

 

Table 3.9         Predicted Cumulative TSP Concentrations at the Representative ASRs in Year 2005 (Unmitigated)

 

 

TSP Concentration (mgm-3)*

ASRs

Receiver height = 1.5m

Receiver height = 10m

 

1-hr Average

24-hr Average

1-hr Average

24-hr Average

A21

1230

583

688

333

A24

890

399

698

331

A25

930

421

753

358

A26

1508

696

769

397

A29

640

286

557

276

A30

1192

564

737

412

A31

751

293

635

274

A37

1028

420

476

293

A39

760

342

501

287

A43

806

385

702

330

A44

822

379

706

336

A45

527

243

479

241

A46

885

327

589

263

A48

1168

503

747

377

A49

1178

480

684

350

                   Value in bold type indicates that the TSP concentration exceeds the HKAQO or the guideline level of 500 mgm-3.

                   * Background TSP concentration of 80 mgm-3 is included.

 

3.5.2             From the results, all representative ASRs exceeded the 1-hour TSP guideline limit of 500 mgm-3 at a receiver height of 1.5m.  The highest predicted 1-hour average TSP concentration is 1508 mgm-3 predicted at ASR A26 (Area 72).  There would also be exceedances of the 24-hour average AQO for TSP at both receiver heights.

 

3.5.3             Figures 3.4 and 3.5 show contours of cumulative hourly average and 24-hour average TSP concentrations at 1.5 m above ground.

 

3.5.4             Since most of the representative ASRs would suffer exceedance of both TSP guideline level and AQO, mitigation measures will be required to suppress the dust.

 


operation phase

 

Assessment 1 – Worst case situation (with possible further development)

 

Vehicle Emissions

 

3.5.5             With the proposed noise mitigation measures for Assessment 1, the predicted maximum 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations for the representative ASRs are tabulated in Table 3.10.

 

Table 3.10     Predicted 1-hour Average NO2, 24-hour average NO2 and 24-hour Average RSP Concentrations at the Representative ASRs (Assessment 1)

 

 

1-hour Average

24-hour Average

24-hour Average

 

ASRs

NO2 Concentration (mgm-3)*

NO2 Concentration (mgm-3)*

RSP Concentration (mgm-3)*

 

 

 

Receiver height

Receiver height

Receiver height

Receiver height

Receiver height

Receiver height

 

 

= 1.5m

= 10m

= 1.5m

= 10m

= 1.5m

= 10m

 

A07

113

108

75

73

68

66

 

A10

194

128

108

81

83

69

 

A11

130

118

82

77

71

68

 

A12

111

97

74

69

67

64

 

A13

93

87

67

65

64

62

 

A14

112

105

75

72

67

66

 

A21

170

149

98

90

79

74

 

A22

124

115

80

76

70

67

 

A23

157

124

93

80

76

69

 

A24

124

119

80

78

70

68

 

A25

109

104

73

72

67

66

 

A26

143

138

87

85

74

73

 

A29

147

127

89

81

74

70

 

A30

105

92

72

67

65

63

 

A31

84

83

64

63

62

62

 

A37

107

97

73

69

67

65

 

A39

80

79

62

62

62

61

 

A42

96

82

68

63

64

61

 

A43

147

120

89

78

74

68

 

A44

111

103

74

71

67

66

 

A45

153

102

91

71

75

65

 

A46

88

81

65

62

62

61

 

A47

156

143

92

87

77

74

 

A48

152

126

91

80

75

70

 

A49

164

144

96

88

77

73

 * Background NO2 concentration of 50 mgm-3 and RSP concentration of 55 mgm-3 are included.

 

3.5.6             From the results, the predicted 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations at 1.5m high range between 80-194 mgm-3 (27-65% of AQO),, 62-108 mgm-3 (41-72% of AQO) and 62-83 mgm-3, respectively. (34-46% of AQO) respectively.  No exceedance of the AQO limit is expected as the predicted pollutant concentrations are well below the AQOsand  and itherefore it would not be necessary to impose any mitigation measures.

 

3.5.7             From the results, fluctuation in baseline with 84% of NO2 and 176% of RSP increases can be allowed.  However, as the baseline adopted for this assessment is considered as a representative worst-case scenario, no adverse air quality impact is anticipated.

 

3.5.8             The predicted 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations contour plots at 1.5m and 10m above local ground are shown in Figures 3.6 - 3.11.

 

Air Quality inside Deckover

 

3.5.9             For the air quality assessment inside the deckover, two scenarios have been considered.  Results of the predicted maximum NO2 concentrations inside the two sections of the deckover during normal traffic condition and congested traffic condition are presented in Table 3.11.  The implementation of the proposed noise mitigation measures has also been considered.

 

Table 3.11       Predicted Maximum NO2 Concentrations inside the Two Sections of the Deckover

 

Deckover

Maximum NO2 Concentration (mgm-3)*

 

Normal Condition

Worst Condition

Section of 190m

430

477

Section of 115m

295

325

* Background concentration is included.

 

3.5.10         As shown in Table 3.11, the maximum NO2 concentration inside the two sections of the deckover is below the guideline level of 1,800 mgm-3.  Hence, no adverse air quality is expected inside the deckover.

 

Assessment 2 – Committed development

 

Vehicle Emissions

 

3.5.11         With the proposed noise mitigation measures for Assessment 2, the predicted maximum 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations for the representative ASRs are tabulated in Table 3.12.

 

Table 3.12       Predicted 1-hour Average NO2, 24-hour average NO2 and 24-hour Average RSP Concentrations at the Representative ASRs (Assessment 2)

 

 

1-hour Average

24-hour Average

24-hour Average

 

ASRs

NO2 Concentration (mgm-3)*

NO2 Concentration (mgm-3)*

RSP Concentration (mgm-3)*

 

 

 

Receiver height

Receiver height

Receiver height

Receiver height

Receiver height

Receiver height

 

 

= 1.5m

= 10m

= 1.5m

= 10m

= 1.5m

= 10m

 

A21

164

142

95

87

78

73

 

A22

154

117

92

77

76

68

 

A23

134

106

84

73

72

66

 

A24

119

114

78

76

69

68

 

A25

109

104

73

72

67

66

 

A26

137

132

85

83

73

72

 

A29

147

127

89

81

74

70

 

A30

105

92

72

67

65

63

 

A31

84

83

64

63

62

62

 

A37

107

97

73

69

67

65

 

A39

80

79

62

62

62

61

 

A42

89

90

66

66

63

63

 

A43

144

118

88

77

73

68

 

A44

111

103

74

71

67

66

 

A45

153

102

91

71

75

65

 

A46

88

81

65

62

62

61

 

A47

144

132

88

83

74

72

 

A48

150

122

90

79

75

70

 

A49

163

142

95

87

77

73

 

 * Background NO2 concentration of 50 mgm-3 and RSP concentration of 55 mgm-3 are included.

 

3.5.12         From the results, the predicted 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations at 1.5m high range between 80-164 mgm-3 (27-55% of AQO),, 62-95 mgm-3  (41-63% of AQO) and 62-78 mgm-3 (34-43% of AQO),,  respectively.  No exceedance of the AQO limit is expected as the predicted pollutant concentrations are well below the AQOs and therefore it would not be necessary to impose any mitigation measures.

 

3.5.13         From the results, fluctuation in baseline with 110% of NO2 and 185% of RSP increases can be allowed.  However, as the baseline adopted for this assessment is considered as a representative worst-case scenario, no adverse air quality impact is anticipated.

 

3.5.14         The predicted 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP concentrations contour plots at 1.5m and 10m above local ground are shown in Figures 3.12 - 3.17.

 

3.6                   Mitigation of Adverse Environmental Impacts

 

CONSTRUCTION PHASE

 

3.6.1             According to AP-42, a 50 percent reduction of the dust generated from wind erosion and general construction activities could be achieved with watering of the site areas with complete coverage twice a day.  Watering of the site areas once every 1.5 hours of the site areas would increase the dust suppression efficiency to 75 percent.

 

3.6.2             In addition, with reference to the Control Techniques for Particulate Emissions from Stationary Sources (EPA 450381005A), the efficiencies of other dust suppression measures, such as road paving, vehicle speed control and street cleaning, have been estimated at about 85%, 80% and 80%, respectively.  During the transfer of dusty materials, conveyor belt, telescoping chutes, lowering well or other device can be used to shorten the fall distance.  Estimated control efficiencies of 80% are possible.  Covering of dusty material storage piles from wind action can also reduce the dust emissions effectively. 

 

3.6.3             Indeed, dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation are more extensive.  Therefore, it is expected that with watering the construction site twice a day together with strict implementation of dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation can achieve at a 75% dust reduction level.

 

3.6.4             Since the predicted 1-hour and 24-hour TSP concentrations are very high, watering twice a day over the whole construction area is not expected to be sufficient.  However, watering once every 1.5 hours on the working areas may not be practicable.  Therefore, it is recommended to water the site twice a day together with strict implementation of other dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation.  As mentioned in Section 3.6.3, with the combination of these mitigation measures in place, the dust levels are expected to be reduced by over 75%.

 

3.6.5             According to the Air Pollution Control (Construction Dust) Regulation, practical dust suppression measures include:

 

·          use of regular watering to reduce dust emissions from exposed site surfaces and unpaved roads, at least twice daily with complete coverage, particularly during dry weather;

·          use of frequent watering for particularly dusty static construction areas and areas close to air quality sensitive receivers;

·          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 shall be applied to aggregate fines;

·          open stockpiles shouldall be avoided or covered.  Where possible, prevent placing dusty material storage piles near air quality sensitive receivers;

·          provision of barriers, which may be the temporary noise barrier, between the site and nearby air quality sensitive receivers to act as dust barriers;

·          tarpaulin covering of all dusty vehicle loads transported to, from and between site locations;

·          establishment and use of vehicle wheel and body washing facilities at the exit points of the site, combined with cleaning of public roads where necessary;

·          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;

·          imposition of speed controls for vehicles on unpaved site roads.  Eight kilometres per hour is the recommended limit;

·          where feasible, routing of vehicles and positioning of construction plant should shall be at the maximum possible distance from air quality sensitive receivers;

·          instigation of an environmental monitoring and auditing program to monitor the construction process in order to enforce controls and modify methods of work if dusty conditions arise; and

·          good site practices.

 

3.6.6             Calculations of the dust emissions after implementation of recommended dust suppression measures are given in Appendix 3.1.  The following table lists the predicted TSP concentrations after implementation of the above mentioned dust suppression measures.

 

Table 3.13       Predicted TSP Concentrations at the Representative ASRs in Year 2005 (Mitigated)

 

 

TSP Concentration (mgm-3)*

ASRs

Receiver height = 1.5m

Receiver height = 10m

 

1-hr Average

24-hr Average

1-hr Average

24-hr Average

A21

367

206

232

143

A24

282

160

235

143

A25

293

165

248

149

A26

437

234

252

159

A29

220

131

199

129

A30

358

201

244

163

A31

248

133

219

129

A37

317

165

179

133

A39

250

145

185

132

A43

262

156

235

143

A44

265

155

237

144

A45

192

121

180

120

A46

281

142

207

126

A48

352

186

247

154

A49

355

180

231

148

 

                   * Background TSP concentration of 80 mgm-3 is included.

 

3.6.7             The maximum 1-hour average and 24-hour average TSP concentrations were predicted at the worst affected ASR, A26, with concentrations of 437 mgm-3 (87% of guideline level) and 234 mgm-3 (90% of AQO), respectively. 

 

3.6.8             From the results, fluctuation in baseline with 33% of TSP increase can be allowed.  However, as the baseline adopted for this assessment is considered as a representative worst-case scenario, no adverse air quality impact is anticipated.

 

3.6.9             Figures 3.18 and 3.19 show contours of cumulative hourly average and 24-hour average TSP concentrations in 2005 in units of mgm-3 at 1.5 m above ground.  With implementation of the proposed mitigation measures, dust emission would be suppressed and dust levels at ASRs are expected to be within the 1-hour and 24-hour average TSP guideline level and AQO limit.

 

3.6.10         It is concluded that in conducting the major dusty activities as described in Section 3.3, implementation of the proposed mitigation measures will be required in order to avoid the adverse dust nuisance to the nearest ASRs.

 

3.6.11         Apart from the dust suppression measures mentioned above, the inclusion of good site practices in the contract clauses to minimize cumulative dust impacts is also recommended.  In addition, a comprehensive dust monitoring and audit programme will be required to ensure proper implementation of mitigation measures.  Details of the monitoring and audit requirements will be provided in the separate EM&A Manual.

 


operation phase

 

Assessment 1 – Worst case situation (with possible further development)

 

Vehicle Emissions

 

3.6.12         As mentioned in Section 3.5, no exceedance of 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP AQOs would be expected at any representative ASRs.  Thus, it would not be necessary to impose any mitigation measures.

 

Air Quality inside Deckover

 

3.6.13         Under the worst case scenario, no adverse air quality is predicted inside the proposed two sections of the deckover.  Thus, it would be unnecessary to impose any mitigation measures.

 

Assessment 2 – Committed development

 

Vehicle Emissions

 

3.6.14         As mentioned in Section 3.5, no exceedance of 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP AQOs would be expected at any representative ASRs.  Thus, it would not be necessary to impose any mitigation measures.

 

3.7                   Definition and Evaluation of Residual Environmental Impacts

 

construction phase

 

3.7.1             With the implementation of 75% dust suppression measure and good site practices, there would be no residual exceedances of AQO at any representative ASRs.

 

Operation phase

 

3.7.2             In both Assessments 1 and 2, exceedance of 1-hour average NO2, 24-hour average NO2 and 24-hour average RSP AQOs is not expected at any representative ASRs.  Thus, no adverse residual impact at any representative ASRs would occur.

 

3.7.3             For the air quality inside the proposed two sections of the deckover for Assessment 1, adverse air quality impact is not expected.

 


 



[1]     MTR Tseung Kwan O Line Tseung Kwan O Area 86 Comprehensive Development Area Submission under Section 16/4A Town Planning Ordinance Environmental Assessment, January 1999

[2]       Ohashi H. and T. Koso, Longitudinal Diffusion of Exhaust Pollutants in Two-way Automobile Tunnels, International Symposium on the Aerodynamics & Ventilation of Vehicle Tunnels, 1995