7.1 Potential air quality impacts associated with the construction phase of the Project are presented in this section. Representative Air Sensitive Receivers (ASRs) have been identified. The potential air quality impacts on these receivers likely to result from the construction of the Project have been identified and evaluated. Potential impacts have been avoided wherever possible and appropriate mitigation measures have been proposed to minimise the potential air quality impact.
Environmental Legislation, Standards and Guidelines
7.2 The criteria for evaluating air quality impacts and the guidelines for air quality assessment are set out in Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM).
Air Quality Objective & EIAO-TMs
7.3 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 must be satisfied, stipulate the maximum allowable concentrations over specific periods for typical pollutants. The relevant AQOs are listed in Table 7.1.
Table 7.1
|
|
Maximum Concentration (µg/m-3) (1) |
|||
|
Pollutant |
Averaging Time |
|||
|
|
1 hour (2) |
8 hour (3) |
24 hour (3) |
Annual (4) |
|
- |
- |
260 |
80 |
|
|
Respirable Suspended Particulates (RSP) (5) |
- |
- |
180 |
55 |
|
|
800 |
- |
350 |
80 |
|
Nitrogen Dioxide (NO2) |
300 |
- |
150 |
80 |
|
Carbon Monoxide (CO) |
30,000 |
10,000 |
- |
- |
|
Photochemical Oxidants (as Ozone, O3) (6) |
240 |
- |
- |
- |
Note:
(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.
7.4 The EIAO-TM stipulates that the hourly TSP level should not exceed 500 mg/m3 (measured at 25°C and one atmosphere) for construction dust impact assessment. Standard mitigation measures for construction sites are specified in the Air Pollution Control (Construction Dust) Regulations.
Air Pollution Control (Construction Dust) Regulation
7.5 Notifiable and regulatory works are under the control of Air Pollution Control (Construction Dust) Regulation. Notifiable works are site formation, reclamation, demolition, foundation and superstructure construction for buildings and road construction. Regulatory works are building renovation, road opening and resurfacing slope stabilisation, and other activities including stockpiling, dusty material handling, excavation, concrete production, etc. This Project is expected to include regulatory works. Contractors and site agents are required to adopt construction dust suppression measures to reduce dust emission to the acceptable level.
Description of the Environment
7.6 The existing air quality near the proposed project site would be mainly contributed by emissions from vehicular traffic on nearby road works. In the absence of in-situ monitoring data, reference is made to the annual average concentrations of major air pollutants measured at EPD’s nearest monitoring stations (i.e. Central/Western Station) for the last 5 years. The latest 5-year annual average TSP levels at Central/Western station is 77µg/m3 according to Air Quality 1999-2005 (annual averages of year 2001 and 2002 do not meet the minimum data requirement).
7.7 However the Central/Western Air Quality Monitoring Station is located in an urban area at a lower level (the sampling point is about +80 mPD) than the subject site (the level of Po Shan Road close to the subject site is about +180 mPD) and the traffic of the surrounding roads are more busy in compare with that of Po Shan Road. Hence it is expected that the annual average TSP level in the area of the subject site should be lower than 77µg/m3.
7.8 Based on the criteria set out in Annex 12 of the EIAO-TM, representative air receivers (ASRs) have been identified close to the Project site. A brief description of the representatives ASRs is summarized in Table 7.2 and the ASR locations are shown on Figure 7.1.
Table 7.2 Summary of Representative Air Sensitive Receivers
|
ASR |
Description |
Horizontal Separation from Closest Works Area Boundary (m) |
Height of ASR (storeys) |
Land Use |
|
A1 |
Block A, Po Shan Mansions |
7 |
20 |
Residential |
|
A2 |
Hamilton Court |
145 |
20 |
Residential |
|
A3 |
Piccadilly Mansion |
165 |
20 |
Residential |
|
A4 |
Ching Yuen Garden |
320 |
1 |
Residential |
|
A5 |
No. 21 Po Shan Road |
45 |
2 |
Residential |
|
A6 |
No. 53 Conduit Ro ad |
55 |
3 |
Residential |
|
A7 |
No. 23 Po Shan Road |
80 |
8 |
Residential |
|
A8 |
No. 24 Po Shan Road |
95 |
3 |
Residential |
|
A9 |
No. 30 Po Shan Road |
225 |
3 |
Residential |
|
A10 |
Pok Fu Lam Country Park |
-(1) |
n/a |
Country Park |
Note: (1) The landslide preventive works fall partially within the Pok Fu Lam Country Park
Identification of Pollutant Sources
7.9 Potential impacts arising from the construction of the proposed landslide preventive work would include dust nuisance and gaseous emissions from the construction plant and vehicles. The major construction activities would generate potential sources of construction dust in the Study Area include soil nail installation, rock slope stabilization and raking drain installation. It is anticipated that dust would be generated from excavation, materials handling and wind erosion from the site.
7.10 The construction of the Project would induce additional traffic to the existing Po Shan Road. Based on the preliminary construction programme, it is envisaged that only about two construction vehicles per day (on average) would be induced by the proposed Project. Air quality impact due to project induced traffic emissions would be expected to be minor.
7.11 As discussed in Sections 2.9 to 2.16, the proposed construction method of this Project is optimized with both engineering practicability and minimal environmental impacts.
7.12 As the scale of works including excavation would be minor, it is expected that, with implementation of dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation and proposed mitigation measures, significant dust impact would not arise. A qualitative approach to evaluate the air quality impact pertinent to the construction of the Project is therefore adopted.
7.13 Construction activities would be carried out in Works Areas E and F with no more than 6 drill rigs. The quantity of dust generated by the soil nail installation, soil nail and raking drain installation would be limited. In view of the limited number of equipment operating on site and the scale of the works to be carried out, air quality impact during construction phase is not expected. With the implementation of standard dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation and recommended measures in Section 7.16, there would be no adverse dust impacts on the ASRs in the vicinity of the construction sites. Additionally, an environmental monitoring and audit programme will be implemented during construction to ensure all the proposed mitigation measures would be properly in place.
7.14 There is another designated project “Agreement No. CE 28/2004 (GE) Landslide Preventive Works at Po Shan, Mid-levels – Design and Construction” (under Environmental Permit EP-235/2005/A) on-going during the construction period of the Project. As the majority of the construction works of this concurrent project is carried out inside tunnel and the scale of other proposed works is small with limited number of plants, it is concluded in the Project Profile of this concurrent project that adverse air quality impacts would not be expected. Standard dust suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation are also recommended to be implemented for the concurrent project.
7.15 In the light of the above, adverse cumulative air quality impacts on the ASRs in the vicinity of the construction sites would not be envisaged.
Mitigation of Adverse Environmental Impacts
7.16 To ensure compliance with the guideline level and AQO, the Air Pollution Control (Construction Dust) Regulation should be implemented and good site practices should be incorporated into the contract clauses to minimize construction dust impact. A number of practical measures are listed below:
· Covering of any aggregate or dusty material storage piles to reduce emissions. Where this is not practicable owing to frequent usage, watering shall be applied to aggregate fines.
· Open stockpiles shall be avoided or covered. Where possible, prevent placing dusty material storage piles near ASRs.
· Tarpaulin covering of all dusty vehicle loads transported to, from and between site locations.
· Use of vehicle wheel and body washing facilities at the exit points of the site.
· Dusty activities should be re-scheduled where possible if high-wind conditions are encountered.
· Instigation of an environmental monitoring and auditing program to monitor the construction process in order to enforce controls and modify method of work if dusty conditions arise.
Evaluation of Residual Impacts
7.17 With the implementation of the Air Pollution Control (Construction Dust) Regulation and proposed mitigation measures, adverse residual impact is not expected.
Environmental Monitoring and Audit
7.18 An Environmental Monitoring and Audit (EM&A) programme is recommended to be established to check compliance with legislative requirements. All the recommended mitigation measures should be incorporated into the EM&A programme for implementation during construction. Details are provided in a stand-alone EM&A Manual.
7.19 With the implementation of effective dust suppression measures, no adverse construction dust impact would be expected in the vicinity of the project.