3.                  air quality IMPACT

3.1              Introduction

3.1.1        This section presents the potential air quality impacts associated with the construction and operation of the Project.  Dust impact from the construction activities of the proposed raw water mains was identified as the potential key environmental issues of concern during construction phases of the Project.  Air sensitive receivers (ASRs) were identified for this study and the potential air quality impacts on these receivers were predicted.  Mitigation measures required to protect the ASRs were recommended, where necessary, to meet the air quality criteria.

 

3.2              Environmental Legislation and Standards

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 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 Hong Kong Air Quality Objectives (AQOs), which stipulate the maximum allowable concentrations over specific periods for typical pollutants, should be met. The relevant AQOs are listed in Table 3.1.

 

Table 3.1                 Hong Kong Air Quality Objectives

 

Pollutant

Maximum Average Concentration (µg m-3) (1)

 

1-Hour (2)

8-Hour (3)

24-Hour (3)

Annual (4)

Total Suspended Particulates

-

-

260

80

Respirable Suspended Particulates (5)

-

-

180

55

Sulphur Dioxide

800

-

350

80

Nitrogen Dioxide

300

-

150

80

Carbon Monoxide

30,000

10,000

-

-

(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.

 

3.2.3        The EIAO-TM also stipulates that the hourly total suspended particulates (TSP) level at sensitive receivers should not exceed 500 µg m-3 (measured at 25°C and one atmosphere) for construction dust impact assessment.

 

3.2.4        The Air Pollution Control (Construction Dust) Regulation specifies site formation is one of the controlled processes.  Contractors and site agents are required to inform EPD and adopt dust reduction measures to minimize dust emission, while carrying out construction works, to the acceptable level.

 

 

3.3              Description of the Environment

Siu Ho Wan

 

3.3.1        The Siu Ho Wan WTW is located near North Lantau Highway and adjacent to the Siu Ho Wan Bus Depots of the Long Win Bus Co. Ltd. and City Bus Ltd, and Siu Ho Wan Sewage Treatment Works (Siu Ho Wan STW).

 

3.3.2        Traffic emission from North Lantau Highway and odour from Siu Ho Wan STW are expected to be major air pollutants on the site.  Two concrete batching plants located at Siu Ho Wan adjacent to Siu Ho Wan WTW were also identified as pollutant source within the Study Area.

 

Pui O

 

3.3.3        Pui O Raw Water Pumping Station was located at about 50m from Pui O Lo Wai Tsuen and facing South Lantau Road. Surrounding development and facilities included 2 to 3-storey high village houses, Bui O Pubic School, sitting out area, playground, etc.  Traffic emission from South Lantau Road is major air pollutant source in the study area.

 

3.4              Air Sensitive Receivers

3.4.1        Representative air sensitive receivers (ASRs), which are in the vicinity of the sites, were identified for assessment, in accordance with the criteria stipulated in the EIAO-TM. Domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, home for the aged and active recreational activity areas are classified as ASRs. The locations of the representative ASRs for the air quality assessment are listed in Table 3.2 and are shown in Figure 3.1a & 3.1b. Distances between the closest ASRs and the site are also presented in Table 3.2.

 

Table 3.2                 Summary of Representative Air Sensitive Receivers

 

ASR

Description

Closest Distance between ASR and site boundary (m)

Siu Ho Wan Study Area

 

 

A1

Siu Ho Wan Sewage Treatment Works

76

A2

Siu Ho Wan Bus Depot (City Bus)

132

A3

Hong Kong Siu Ho Wan Police Vehicle Pound Vehicle Examination Centre and Weigh Station

116

A4

Siu Ho Wan Bus Depot (Long Win Bus Co. Ltd.)

220

A5

Siu Ho Wan Water Treatment Works (Admin Building)

11

Pui O Study Area

 

Proposed

Option

LUT

Lo Uk Tsuen

10

PG1

Children’s Playground next to Chi Ma Wan Road

2.5

PG2

Sitting Out Area next to South Lantau Road

2

LWT2

Pui O Lo Wai Tsuen facing South Lantau Road

22

LWT3

Pui O Lo Wai Tsuen facing the Pumping Station

16

ALWT2

Pui O Au Lo Wai Tsuen facing South Lantau Road

28

 

3.5              Assessment Methodology

3.5.1        Fugitive Dust Model (FDM) (1993 version) was adopted to assess potential dust impact from the construction works.  One year sequential meteorological data for the year 2002 from the Hong Kong Observatory Cheung Chau Station was used to predict the 1-hour and 24-hour average TSP concentrations at representative discrete ASRs close to the construction works.  Since the construction activities would be undertaken at ground level and underground level, the worst dust impact on the ASRs would be at the ground floor of the ASRs.  The height of 1.5m above ground, which is the breathing level of human, was adopted for the construction dust impact assessment.

 

3.5.2        Predicted dust emissions wasPredicted dust emissions were based on emission factors from USEPA Compilation of Air Pollution Emission Factors (AP-42), 5th Edition.  The major construction activities for the Project, which would be potential sources of construction dust in the Study Area, include earthworks and backfilling for the raw water mains construction at Pui O, and demolition and construction of Pui O Raw Water Pumping Station. It is anticipated that dust would be generated from ground excavation, aggregate handling and wind erosion of the opened sites.  Detailed calculations of the emission factors are given in Appendix 3.1.

 

Table 3.3                 Emission Factors for Dusty Construction Activities

 

Activity

Emission Rate

Remarks

Works Area along the raw water mains

Aggregate Handling

E = 1.0634 g/Mg

=6.65 x 10-3 g/s

·         Volume of material: 225 m3/day per drilling location

·         Moisture content: 4.8 %

·         Average wind speed: 5.2 m/s

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 13.2.4

Wet Drilling

E = 8.4 x 10-5 g/Mg

= 5.25 x 10-7 g/s

·         Volume of material: 225 m3/day per drilling location

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 11.19.2

Wind Erosion

E = 0.85 Mg/hectare/year

= 1.35 x 10-6 g/m2/s

·        50% reduction by water suppression.

·         AP42, Section 11.9

Connection point (Works Area between the existing raw water main and proposed raw water main – about 10m in length)

Aggregate Handling

E = 1.0634 g/Mg

=8.86 x 10-3 g/s

·         Volume of material: 300 m3/day per drilling location

·         Moisture content: 4.8 %

·         Average wind speed: 5.2 m/s

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 13.2.4

Wet Drilling

E = 8.4 x 10-5 g/Mg

= 7.0 x 10-7 g/s

·         Volume of material: 300 m3/day per drilling location

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 11.19.2

Wind Erosion

E = 0.85 Mg/hectare/year

= 1.35 x 10-6 g/m2/s

·        50% reduction by water suppression.

·         AP42, Section 11.9

Pui O Raw Water Pumping Station

Aggregate Handling

E = 1.0634 g/Mg

=2.95 x 10-3 g/s

·         Volume of material: 100 m3/day per drilling location

·         Moisture content: 4.8 %

·         Average wind speed: 5.2 m/s

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 13.2.4

Wet Drilling

E = 8.4 x 10-5 g/Mg

= 2.33 x 10-7 g/s

·         Volume of material: 100 m3/day per drilling location

·         Density of spoil: 2 Mg/m3

·         50% reduction by water suppression.

·         AP42, Section 11.19.2

Wind Erosion

E = 0.85 Mg/hectare/year

= 1.35 x 10-6 g/m2/s

·        50% reduction by water suppression.

·         AP42, Section 11.9

 

3.5.3        The Air Pollution Control (Construction Dust) Regulation specified that dust depression measures such as watering should be applied for the construction site.  Dust emission from the site would be reduced by 50% if watering with complete coverage of active construction area twice a day.  This assumption was considered in the construction dust impact assessment.

 

3.5.4        Activities such as the installation of aboveground raw water mains at discrete locations would not be expected to general significant dust emission.  Therefore, construction of aboveground raw water mains was not considered necessary to be included in the construction dust impact assessment.

 

3.5.5        10-hour working day (08:00-18:00) was assumed for the construction works in the assessment.  Wind erosion of open sites would take place over the whole day.  It is expected that the pipe laying works at Pui O would be carried out section by section and each section was about 30 meters in length.  As a worst-case scenario, laying of whole raw water mains would be considered in the assessment, in addition to construction work for Pui O Raw Water Pumping Station.

 

3.5.6        With reference to the Guidelines on Assessing the Total Air Quality Impacts, the background TSP (87 mg/m3) for rural/new development was adopted as an indication of the future TSP background concentration.

 

3.6              Identification of Environmental Impacts

Construction Phase

 

3.6.1        The construction activities within the boundary of the existing Siu Ho Wan WTW and proposed Siu Ho Wan Raw Water Booster Pumping Station would include excavation, raw water mains laying, erection of concrete structures and installation of E&M equipment.  As the active work site area within the WTW would be limited and the representative ASRs are located far away from the work sites, the potential dust impacts at the nearby ASRs and the operation of existing Siu Ho Wan WTW would be insignificant after implementation of the dust control measures stipulated in the Air Pollution Control (Construction Dust) Regulation.  Quantitative assessment for Siu Ho Wan study area is considered unnecessary.

 

3.6.2        The construction activities for the proposed duplication of raw water mains at Pui O would include earthworks and backfilling.  The major activities for Pui O raw water pumping stations would be removal of old E&M equipment, installation of new E&M equipment, demolition of existing concrete structure (for Pui O Raw Water Pumping Station only), concrete structure works and raw water mains laying.   It was expected that dust would be generated from excavation, demolition, material handling and wind erosion from the sites.  As some ASRs at Pui O located so close to the site boundary of the work areas, quantitative assessment would be carried out for the work area at Pui O.

 

Operational Phase

 

3.6.3        Potential air quality impacts such as dust and odour would not be expected from the operation of the Siu Ho Wan WTW extension, the Siu Ho Wan Raw Water Booster Pumping Station, Pui O Raw Water Pumping Station, Pui O No. 2 Raw Water Pumping Station and the proposed raw water mains at Pui O.

 

3.7              Prediction and Evaluation of Environmental Impacts

3.7.1        Construction dust impacts were modelled using the FDM model.  The hourly and daily TSP concentrations at the ASRs were predicted and shown in Table 3.4 below.  Dust mitigation measures, watering on the work area twice a day, stipulated in the Air Pollution Control (Construction Dust) Regulation were included in the prediction .prediction.

Table 3.4                 Predicted TSP Concentration at the Representative ASRs at 1.5m above Ground Level

 

ASR

TSP Concentration (mg/m3)

1 hr average

24 hr average

LUT

285

174

PG1

403

224

PG2

228

148

LWT2

397

220

LWT3

228

147

ALWT2

190

132

Criteria

500

260

(1)    Background TSP concentration included in the figure.

 

 

 

3.7.2        The predicted hourly TSP concentration at 1.5m above ground level would range from 190 mg/m3 to 403 mg/m3, and the daily concentration between 132 mg/m3 and 224 mg/m3 were predicted at ground level receivers. It was predicted that the dust level at all representative ASRs would comply with AQO.

 

3.8              Mitigation of Adverse Environmental Impacts

3.8.1        With adoption of watering on the work site at Pui O twice a day, the assessment results showed that the closest representative ASRs at Pui O would comply with the dust criteria.  This mitigation measures is also applied to For the work site at Siu Ho Wan WTW, it is recommended to apply watering twice a day so as to prevent the contamination on the sedimentation tanks and filters.

 

3.8.2        The other dust mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation should also be incorporated to further control dust emission from the sites at Siu Ho Wan and Pui O.  Major control measures relevant to this Project are listed below:

·         skip hoist for material transport should be totally enclosed by impervious sheeting;

·         vehicle washing facilities should be provided at every vehicle exit point;

·         the area where vehicle washing takes place and the section of the road between the washing facilities and the exit point should be paved with concrete, bituminous materials or hardcores;

·         every main haul road should be scaled with concrete and kept clear of dusty materials or sprayed with water so as to maintain the entire road surface wet;

·         every stock of more than 20 bags of cement should be covered entirely by impervious sheeting placed in an area sheltered on the top and the 3 sides;

·         all dusty materials should be sprayed with water prior to any loading, unloading or transfer operation so as to maintain the dusty materials wet;

·         every vehicle should be washed to remove any dusty materials from its body and wheels before leaving the construction sites;

·         the dusty materials stockpiled on site should be covered;

·         the load of dusty materials carried by vehicle leaving a construction site should be covered entirely by clean impervious sheeting to ensure dust materials do not leak from the vehicle.

 

3.9              Evaluation of Residual Impacts

Construction Phase

 

3.9.1        With the incorporation of Air Pollution Control (Construction Dust) Regulation, adverse residual impact would not be expected.

 

Operational Phase

 

3.9.2        No adverse residual impact would be expected during operation phase.

 

3.10          Environmental Monitoring and Audit

3.10.1    With the implementation of mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation, dust levels at all closest representative ASRs would comply with the dust criteria. Environmental monitoring and audit is recommended to be conducted during construction phase of the Project so as to check whether it is in compliance with legislative requirement. Details of the monitoring and audit programme would be mentioned in a stand-alone EM&A Manual.