3.1.1.1 This section identifies potential impacts on air quality that may arise from the construction of the Project and the construction dust impact from the Project has been assessed. No operational phase air quality impacts are anticipated. Where necessary, appropriate mitigation measures have been recommended to reduce the impacts from the Project on the air sensitive receivers (ASRs) to satisfy the related environmental legislation and guidelines.
3.1.1.2 This air quality impact assessment has followed the criteria and guidelines stated in Section 1 of Annex 4 and Annex 12 respectively of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), together with the detailed technical requirements in Appendix A of the EIA Study Brief (Study Brief No. ESB-227/2011). The air pollutant concentrations have been assessed with reference to Appendices A-1 to A-3 in the EIA Study Brief.
3.1.1.3 The study area for the air quality impact assessment has been defined as a distance of 500 metres from the work boundary of the Project site. The assessment has included the existing, planned and committed sensitive receivers within the study area of the Ngong Ping drainage works and has been based on the best available information of the time of the assessment.
3.1.1.4 A description of the construction works sections and proposed construction works for the Project has been provided in Section 2.7 of this EIA report, including a summary of construction works in Table 2.7. The overall project is shown in Figure 1.1 with a more detailed layout of the proposed drainage alignment presented in Figure 2.9a.
3.2 Environmental Legislation, Standards and Guidelines
3.2.1.1 The establishment of the construction phase air quality impact assessment criteria for this Environmental Impact Assessment (EIA) study has make reference to the Hong Kong Planning Standards and Guidelines (HKPSG), Air Pollution Control Ordinance (APCO) (Cap 311), and Annex 4 of the EIAO-TM.
3.2.2.1 The APCO provides a regulatory framework for controlling air pollutants from a variety of stationary and mobile sources and encompasses a number of Air Quality Objectives (AQOs). Moreover, the Government’s overall policy objectives for air pollution are laid down in Chapter 9 of the HKPSG as follows:
·
Limit the contamination of the
air in
· Ensure that the AQOs for 7 common air pollutants are met as soon as possible.
3.2.2.2 The AQOs stipulate the compliance concentrations for a range of pollutants, namely sulphur dioxide (SO2), total suspended particulates (TSP), respirable suspended particulates (RSP), nitrogen dioxide, (NO2), carbon monoxide (CO), photochemical oxidants (as ozone) and lead (Pb). The AQOs are summarised in Table 3.1 below.
Table 3.1
|
Pollutant |
Concentration(i) mg
/m3 Averaging Time |
||||
|
1
Hour(ii) |
8
Hours(iii) |
24
Hours(iii) |
3
Months(iv) |
1
Year(iv) |
|
|
|
800 |
- |
350 |
- |
80 |
|
Total
Suspended Particulates (TSP) |
- |
- |
260 |
- |
80 |
|
Respirable
Suspended Particulates (RSP)(v) |
- |
- |
180 |
- |
55 |
|
Nitrogen
Dioxide (NO2) |
300 |
- |
150 |
- |
80 |
|
Carbon
Monoxide (CO) |
30,000 |
10,000 |
- |
- |
- |
|
Photochemical
Oxidants (as ozone) |
240 |
- |
- |
- |
- |
|
Lead
(PB) |
- |
- |
- |
1.5 |
- |
(i)
Measured
at 298K (25 oC) and 101.325 kPa (one atmosphere)
(ii)
Not to
be exceeded more than 3 times per year
(iii)
Not to
be exceeded more than once per year
(iv)
Arithmetic
means
(v)
RSP
means suspended particulates in air with a nominal aerodynamic diameter of 10mm and smaller
(vi)
Photochemical
oxidants are determined by measurements of ozone only
3.2.2.3 The EIAO-TM, also, stipulates that the hourly total suspended particulates (TSP) level should not exceed 500 mg/m3 (measured at 25oC and one atmosphere) for construction dust impact assessment. Standard mitigation measures for construction sites are specified in the Air Pollution Control (Construction Dust) Regulation. Notifiable and regulatory works are, also, under the control of the Air Pollution Control (Construction Dust) Regulation and requite the Environmental Protection Department (EPD) to be informed.
3.3.1.1 As shown in Figure 1.1, the existing environment of the study area is a rural area in Ngong Ping with an elevation of over 400 mPD. The proposed Project site is located close to, or passes through, an area occupied by the following major land uses:
·
village houses in the
· temples including the Po Lin Monastery and Buddha Statue and ancillary buildings in the Government, Institution or Community Zone;
· the Ngong Ping 360 cable car in the Other Specified Uses; and
·
the
3.3.1.2
Ngong Ping is a rural area which does not have heavy traffic flows. The
sources of dust are mainly from burning activities during worship at the
monasteries, the unpaved or non-vegetated open areas and emissions from the
3.3.2
Air Quality in Ngong Ping
3.3.2.1 There are no fixed air quality monitoring stations near the Project site. The nearest EPD Air Quality Monitoring Station (AQMS) is the Tung Chung AQMS and its latest 5 years of air quality statistics, i.e. 2007 to 2011, are summarised in Table 3.2 to depict the trend of the air quality. It should be noted that the AQMS at Tung Chung is not fully representative of the Ngong Ping area due to Tung Chung being a new development area which has higher road emissions. Notwithstanding, the vehicular emissions in Tung Chung are relatively low in comparison to main urban areas and this AQMS is closest to the Study Area.
Table 3.2 EPD Air Quality Monitoring Data at Tung Chung AQMS (2007 to 2011)
|
Pollutant |
Year |
Highest 1-hour Average (mg/m3) |
Highest 24-hour Average (mg/m3) |
Annual Average (mg/m3) |
|
NOx |
2007 |
414 |
210 |
71 |
|
2008 |
538 |
295 |
76 |
|
|
2009 |
368 |
194 |
68 |
|
|
2010 |
584 |
278 |
69 |
|
|
2011 |
498 |
294 |
75 |
|
|
AQO |
N/A |
N/A |
N/A |
|
|
Annual Average in the Latest 5 Years |
498 |
294 |
75 |
|
|
NO2 |
2007 |
248 |
127 |
46 |
|
2008 |
256 |
134 |
49 |
|
|
2009 |
221 |
119 |
45 |
|
|
2010 |
255 |
149 |
44 |
|
|
2011 |
228 |
137 |
51 |
|
|
AQO |
300 |
150 |
80 |
|
|
Annual
Average in the Latest 5 Years |
242 |
133 |
47 |
|
|
O3 |
2007 |
308 |
117 |
40 |
|
2008 |
310 |
146 |
41 |
|
|
2009 |
325 |
148 |
47 |
|
|
2010 |
341 |
115 |
44 |
|
|
2011 |
312 |
144 |
44 |
|
|
AQO |
240 |
N/A |
N/A |
|
|
Annual Average in the Latest 5 Years |
319 |
134 |
43 |
|
|
TSP |
2007 |
N/A |
240 |
70 |
|
2008 |
N/A |
198 |
69 |
|
|
2009 |
N/A |
133 |
60 |
|
|
2010 |
N/A |
231 |
59 |
|
|
2011 |
N/A |
141 |
65 |
|
|
AQO |
N/A |
260 |
80 |
|
|
Annual
Average in the Latest 5 Years |
-- |
189 |
65 |
|
|
RSP |
2007 |
314 |
199 |
54 |
|
2008 |
243 |
146 |
52 |
|
|
2009 |
210 |
162 |
46 |
|
|
2010 |
640* |
475* |
45 |
|
|
2011 |
250 |
142 |
47 |
|
|
AQO |
N/A |
180 |
55 |
|
|
Annual Average in the Latest 5 Years |
254 |
162 |
49 |
Note: Shaded
cell denotes exceedance of relevant AQO. The data of RSP marked with * were recorded
when Hong Kong was affected by a dust plume originating from the northern part
of China in March 2010 and the average values do not include these data.
3.3.2.2 The air quality data in Table 3.2 shows that the 1-hour, 24-hour and annual averages for NO2, 24-hour and annual averages for TSP and 1-hour and annual averages for RSP are all below the levels set by the AQO. However, the 1-hour average for O3 and 24-hour average for RSP exceed the AQO levels.
3.4 Identification of Air Sensitive Receivers
3.4.1.1 Air Sensitive Receivers (ASRs) have been identified in accordance with Annex 12 of the EIAO-TM, which includes domestic premises, hotels, hostels temporary housing accommodation, hospitals, medical clinics, educational institutions, offices, factories, shops, shopping centres, places of public worship, libraries, court of law or performing arts centre.
3.4.1.2 The existing ASRs are identified with reference to the latest information provided on the survey maps, topographic maps, aerial photos, land status plans and confirmed by various site surveys undertaken. The planned ASRs are also identified with reference to the latest published Ngong Ping Outline Zoning Plan (OZP) No. S/I-NP/6.
3.4.1.3 The relevant authorities have been approached as far as practicable so as to obtain the latest information on planning applications, layout and building height, etc. The major planned uses in the vicinity of the area include different land uses including Village Type, Development, Residential, Government, Institution or Community, Open Space, Recreation and Other Specified Uses.
3.4.1.4 With reference to Section 3.4.2.2 of EIA Study Brief, the study area for the air quality impact assessment has been defined as a distance of 500 metres from the boundary of the Project site and the assessment has included all relevant air sensitive receivers which may be potentially affected by the Project within this study area.
3.4.1.5
The existing ASRs are the
village houses, other specified uses such as
Table 3.3 Representative Air Sensitive Receivers
|
ASR |
Location |
Landuse [1] |
No.
of Storeys |
Assessment
Height (above ground level) |
Horizontal
Distance to the Proposed Drainage Works (m) |
|
ASR1 |
Columbarium of |
-- |
1 |
1.5m |
21 |
|
ASR2 |
|
OU |
2 |
1.5m |
23 |
|
ASR3 |
Village House No. 68 |
GB |
2 |
1.5m |
37 |
|
ASR4 |
Village House No. 65 |
GB |
2 |
1.5m |
31 |
|
ASR5 |
Village House No. 49A |
GB |
2 |
1.5m |
8 |
|
ASR6 |
Village House No. 40 |
V |
2 |
1.5m |
20 |
|
ASR7 |
Luen
Sin Tong |
V |
2 |
1.5m |
12 |
|
ASR8 |
Village House No. 34 |
V |
2 |
1.5m |
20 |
|
ASR9 |
Village House |
V |
2 |
1.5m |
4 |
|
ASR10 |
|
GIC |
2 |
1.5m |
15 |
Note: [1] -- – No zoning, OU – Other Specified Uses
(Cable Car Terminal), GB – Green Belt, V – Village Type Development, GIC –
Government, Institution or Community.
3.5 Identification of Potential Air Quality Impacts
3.5.1.1 Potential construction air quality impacts would mainly be related to dust nuisance from exposed site areas, including the excavation areas, movement of vehicles along unpaved roads, material handling and wind erosion of the site. Other air quality parameters are not considered key to the construction stage due to the relatively small number of plant that will be utilised on site. In addition, the dust generated during the construction works will not contain a significant proportion of fine particulates (less than 10 µm) which are deemed to the respirable and therefore, the 1-hr average and 24-hr average TSP concentrations, in addition to the annual average TSP concentrations have been evaluated to assess the short and long term dust impact from the Project on the ASRs, respectively and Respirable Suspended Particulates have not been assessed. The major sources of dust would be from the following construction activities for the Ngong Ping drainage improvement works as detailed in Section 2.6:
· Heavy construction activities such as site clearance, excavation and backfilling activities as a result of the use of the open cut-and-cover method for open trenches for the construction of the underground drainage pipelines (Sections 1 and 3, Figure 2.9a) and box culvert (Sections 4 and 5, Figure 2.9a);
· Heavy construction activities such as site clearance, excavation and backfilling activities for the construction and reinstatement of the jacking pits (JP1 and JP2, Figure 2.9a) and receiving pits (RP1, RP2, RP3 and RP4, Figure 2.9a) for the pipe-jacking process in Work Sections 2 and 6;
· Mucking-out activities at the jacking pits (JP1 and JP2) during the pipe-jacking process;
· Loading and unloading activities at the stockpile areas (SA1, SO, SA2, SA3 and SA4, Figure 2.9a); and
· Wind erosion at the above construction sites and stockpile areas.
3.5.1.2 In addition to the above major construction works, there would be some minor works such as erection of site office structures, open storage of equipment, etc. However, it would be anticipated that the dust impacts from these activities would be insignificant and, therefore, they have not been considered further.
3.6.1.1 There have been no concurrent projects identified in the Study Area that would be on-going in parallel to the proposed drainage improvement works and which would have the potential to result in cumulative dust impacts at the ASRs.
3.7.1.1 The emission factors for fugitive dust have been determined with reference to the Compilation of Air Pollution Emission Factors, USEPA AP-42, 5th Edition, January 1995 (AP-42). The Fugitive Dust Model (FDM) is proposed to be used for the simulation of the construction dust dispersion from the areas of emissions. It is assumed that dust emissions would be generated during the daytime working hours only, between 7:00am and 7:00pm. Any construction works outside this period and during weekends/holidays has been reviewed for the construction dust impact assessment as necessary.
3.7.2.1 Groups of PME have been assigned to various construction activities of the project. The Project Proponent has confirmed this emission inventory as being practical and adequate for completing the construction works within the scheduled timeframe (Appendix B1).
3.7.2.2 Dust emission factors for different construction activities have been extracted from the USEPA AP-42. The key assumptions for the calculation of dust emission factors are summarised in Table 3.4.
Table 3.4 Assumptions for Calculation of Dust Emission Factors
|
Activities |
Reference[1] |
Operating
Sites |
Equations
and Assumptions [1] |
|
Heavy
construction activities including land clearing, excavation, cut and fill
operations, equipment traffic, stockpile operations, mucking-out at jacking
pits and hauling over the site area. |
S.13.2.3.3 |
All
construction and excavation sites with open-cut and-cover methods, jacking
pits, receiving pits and stockpile areas. |
E
= 1.2
tons/acre/month of activity or 2.6Mg/hectare/month
of activity |
|
Wind
erosion |
S.11.9,
Table 11.9.4 |
All
construction and excavation sites with open-cut and-cover methods, jacking
pits, receiving pits and stockpile areas (all open sites) |
E
= 0.85 Mg/hectare/yr (24 hour emission) |
Note:
[1] USEPA Compilation of Air
Pollution Emission Factors (AP-42)
3.7.2.3 The assessment approach has been based on the requirements specified in the EIA Study Brief (ESB-227/2011) and the criteria and guidelines for assessing air quality impacts as stated in Annexes 4 and 12 of the EIAO-TM have been followed. The requirements as stipulated under the Air Pollution Control (Construction Dust) Regulation have, also, been followed to ensure that construction dust impacts are controlled to within the relevant standards as stipulated in the EIAO-TM.
3.7.2.4 The quantitative assessment of construction dust impacts has been conducted using the Fugitive Dust Model (FDM) as approved by EPD, which is a Gaussian Plume model designed for computing air dispersion model for fugitive dust sources. Modelling parameters, including the dust emission factors, particle size distribution, surface roughness, etc are specified in EPD’s Guidelines on Choice of Models and Model Parameters and USEPA AP-42.
3.7.2.5
The density of dust has been assumed
to be 2.5gm-3. According to
S13.2.4.3 of USEPA AP-42, the particle size distribution is assumed as 1.25mm, 3.75 mm, 7.5
mm, 12.5 mm and 22.5
mm with 7%, 20%, 20%, 18% and 35% size distribution, respectively. As the study area is categorised as “rural”,
the average monitoring data in the latest 5 years (i.e. 2007 to 2011) from the
EPD’s air quality monitoring station in Tung Chung which is shown in Table 3.5 has been adopted as the background concentration. Based on this, the
average TSP concentration has been calculated as 65 mg/m3.
Table 3.5 Air Quality Monitoring Data at Tung Chung AQMS Station (Years 2007 to 2011)
|
Pollutant |
Year
|
5
Year Average (mg/m3) |
||||
|
2007 |
2008 |
2009 |
2010 |
2011 |
||
|
Annual Average TSP Concentrations (mg/m3)
[1] |
70 |
69 |
60 |
59 |
65 |
65 |
Note [1]: AQO: 80mgm-3
3.7.2.6 Since the validity of the meteorological data at Ngong Ping Weather Station is less than 90%, the latest available sequential meteorological data recorded with at least 90% of valid data has been obtained for Nei Lak Shan Weather Station for the Year 2008 from the Hong Kong Observatory (HKO) for use in the prediction of 1-hour, 24-hour average and annual average TSP concentrations at representative ASRs. For the hourly meteorological data of wind speed, wind direction, stability class and temperature which are not available, the missing data has been replaced by the data from the previous hour. For the hourly meteorological data of mixing height, the missing data has been replaced by the minimum value of mixing height of the year.
3.7.2.7 The following meteorological conditions have been assumed in the assessment:
· Wind speed: hourly record of meteorological data from HKO;
· Wind direction: hourly record from meteorological data from HKO;
· Stability class: hourly record from meteorological data from HKO. It should be noted that the stability classes A-F have been applied;
· Mixing height: daily record from meteorological data at King’s Park Meteorological Station in Year 2008; and
· Temperature: hourly record of meteorological data from HKO;
· Anemometer height: 757m; and
· Surface roughness: 100cm.
3.7.2.8 Fugitive dust modelling has been conducted at heights 1.5m above local ground level as all of the drainage works are at grade or below ground level. The maximum cumulative 1-hour, 24-hour and annual averaged TSP concentrations at the selected ASRs have been determined and pollutant contours presented. A 50 x 50m grid contour has been used to investigate the pollutant distribution for the assessment.
3.7.2.9 According the construction programme detailed in Section 2.6, the Project will be constructed based upon two concurrent work fronts. However, in order to assess the worst case scenario, all the construction activities would be modelled at the same time to represent the worst case situation. The detailed calculations of emission rates and locations of dust sources assumed are presented in Appendix B2.
3.7.2.10 In respect of the short-term assessment of the 1-hour and 24-hour average TSP concentrations, it has been assumed that the construction work activities and equipment would not be concentrated in certain areas of the site closest to the ASRs at any time during the construction period. However, a “Tier 1” assessment has been carried out as a worst case scenario in which it has been assumed that all the active works site area would be 100% active.
3.7.2.11 After carrying out the Tier 1, the areas where construction dust impacts have been noted to exceed the AQO at specific ASRs could be subject to a “Tier 2” assessment. The Tier 2 assessment would identify the works areas closest to the ASR being affected and instead of assuming a 100% active area for this location, the actual construction programme would be reviewed and a percentage of active area determined based upon the scheduled works only. All other works areas along the drainage alignment would be assumed to remain at 100% active.
3.7.2.12 For the long-term assessment of the annual average TSP concentrations, there would be difficulty in identifying the exact locations of the individual dust emission sources of the construction works in the dust modelling. Therefore, the modelling has assumed that the dust emission sources are distributed across the whole work site area, that is, that 100% of the works areas are active, as a worst case, as per the short term assessment. However, in the actual situation, all the construction works would not be carried out at the same time.
3.7.3.1 The FDM model used for the modelling of the construction dust impact assessment is the accepted models for calculating the dust impact for the construction activities and which have made reference to the Guidelines on Choice of Models and Mode Parameters.
3.7.3.2 According to the construction programme, the construction works of each section of the drainage would not be carried out at the same time. However, for the purposes of the dust assessment, all the construction works areas have been assumed to be 100% active to present a worst case scenario in this assessment. Utilising this assumption has made the approach of the assessment more conservative.
3.7.3.3 Since the meteorological data at Ngong Ping Weather Station is less than 90%, the data at Nei Lak Shan Weather Station have been adopted for the modelling. Because of the similar height and meteorological characteristics, it is considered that using the data of Nei Lak Shan is appropriate.
3.7.3.4 Uncertainties in the assessment of impacts have been considered when drawing conclusions from the assessment and worst case scenarios have been adopted.
3.8 Construction Dust Impact Assessment
3.8.1.1 The maximum predicted unmitigated 1-hour, 24-hour and annual average cumulative TSP levels are presented in Table 3.6 below. The unmitigated annual cumulative contours at 1.5m above ground are provided in Figures 3.2 -3.10. The results show that the predicted 1-hour average cumulative TSP concentrations at all ASRs and the predicted 24-hour average cumulative TSP concentrations at ASR3, ASR4, ASR5 and ASR8 show exceedances of the AQOs based upon the worst case Tier 1 approach but with no dust mitigation measures applied. In addition, the predicted annual average cumulative TSP concentrations at ASR3, ASR4, ASR5, ASR8 and ASR9 have predicted exceedances of the relevant AQOs with no dust mitigation measures applied. Therefore, mitigation measures are required to control dust impacts.
Table 3.6 1-hour, 24-hour and Annual Average Maximum Cumulative Unmitigated TSP Concentrations (mg/m3) at ASRs (Including Background Level)
|
Receiver
Reference |
Predicted
Maximum 1-hour Concentration |
Predicted
Maximum 24-hour Concentration |
Predicted
Maximum Annual Concentration |
|
Criteria |
500mg-3 |
260mg-3 |
80mg-3 |
|
ASR1 |
515 |
121 |
71.4 |
|
ASR2 |
646 |
161 |
72.0 |
|
ASR3 |
1670 |
377 |
94.0 |
|
ASR4 |
1514 |
356 |
89.4 |
|
ASR5 |
1879 |
338 |
107.5 |
|
ASR6 |
719 |
156 |
70.3 |
|
ASR7 |
629 |
166 |
72.6 |
|
ASR8 |
1050 |
325 |
76.8 |
|
ASR9 |
1036 |
146 |
74.0 |
|
ASR10 |
550 |
113 |
72.2 |
|
|
Means the results exceed the AQOs. |
||
3.8.2.1 Specific mitigation measures (Appendix B2 and summarised in Section 11 of this EIA Report) have been assumed in the modelling to reduce the dust generation from the Project to within the 1-hour (500µgm-3), 24-hour (260µgm-3) and Annual (80µgm-3) criteria at ASRs, and have been applied for both the short-term Tier 1 and annual TSP predictions. The specific mitigation comprises watering of exposed soil areas in active works areas and paved haul roads once per hour for 12 hours a day to reduce dust emissions by 91.7%, with reference to the “Control of Open Fugitive Dust Sources” (USEPA AP-42). The amount of water to be applied would be 0.25L/m2 for the respective watering frequency (Appendix B3).
3.8.2.2 In addition to the mitigation mentioned above, under the auspices of the Air Pollution Control (Construction Dust) Regulation, the Contractor will be required to ensure that dust control measures stipulated in the Regulation should be implemented to control dust emissions. The dust control measures detailed below shall also be incorporated into the Contract Specification where practicable as an integral part of good construction practice:
(i) Use of regular watering to reduce dust emissions from exposed site surfaces and unpaved roads, particularly during dry weather;
(ii) Use of frequent watering for particularly dusty construction areas and areas close to ASRs;
(iii) 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 shall be applied to aggregate fines;
(iv) Open stockpiles shall be avoided or covered. Prevent placing dusty material storage piles near ASRs;
(v) Tarpaulin covering of all dusty vehicle loads transported to, from and between site locations;
(vi) Establishment and use of vehicle wheel and body washing facilities at the exit points of the site;
(vii) Imposition of speed controls for vehicles on unpaved site roads, 8 km per hour is the recommended limit;
(viii) Routing of vehicles and position of construction plant should be at the maximum possible distance from ASRs;
(ix) Every stock of more than 20 bags of cement or dry pulverised fuel ash (PFA) should be covered entirely by impervious sheeting or placed in an area sheltered on the top and the 3 sides;
(x) Cement or dry PFA delivered in bulk should be stored in a closed silo fitted with an audible high level alarm which is interlocked with the material filling line and no overfilling is allowed; and
(xi) Loading, unloading, transfer, handling or storage of bulk cement or dry PFA should be carried out in a totally enclosed system or facility, and any vent or exhaust should be fitted with an effective fabric filter or equivalent air pollution control system.
3.8.2.3
All these mitigation measures
are, also, summarised in the Environmental Mitigation Implementation Schedule
(EMIS) in Section 11.
Short Term Dust Predictions
3.8.3.1 The maximum predicted 1-hour and 24-hour results of the Tier 1 screening test at representative ASRs in the study area with mitigation measures applied are shown in Table 3.7 below. The mitigated Tier 1 screening test 1-hour and 24-hour cumulative contours at 1.5m above ground are shown in Figures 3.11 - 3.13 and Figures 3.14 - 3.16 respectively. The sample calculations for the results are shown in Appendix B4.
Table 3.7 Tier 1 Screening Test: 1-hour and 24-hour Average Maximum Cumulative Mitigated TSP Concentrations (mg/m3) at ASRs (Including Background Level)
|
Receiver Reference |
Predicted Maximum 1-hour Concentration |
Predicted Maximum 24-hour Concentration |
|
Criteria |
500 mg/m3 |
260 mg/m3 |
|
ASR1 |
102 |
70 |
|
ASR2 |
113 |
75 |
|
ASR3 |
189 |
95 |
|
ASR4 |
185 |
91 |
|
ASR5 |
209 |
89 |
|
ASR6 |
119 |
73 |
|
ASR7 |
112 |
74 |
|
ASR8 |
134 |
88 |
|
ASR9 |
146 |
72 |
|
ASR10 |
103 |
70 |
3.8.3.2 The results indicate that, for all of ASRs, no exceedances of the 1-hour and 24-hour TSP criteria are predicted to occur, even assuming the absolute worst case situation where 100% of every works site would be active and emitting dust. Since there are no exceedances at the ASRs, it is considered that a Tier 2 assessment is not required.
Annual Dust Predictions
3.8.3.3 The maximum predicted annual average TSP concentrations at representative ASRs in the study area with mitigation measures applied are shown in Table 3.8. The mitigated annual cumulative contours at 1.5m above ground are provided in Figures 3.17 - 3.19. The sample calculations for the results are shown in Appendix B4.
Table 3.8 Annual Average Maximum Cumulative Mitigated TSP Concentrations (mgm-3) at ASRs (Including Background Level)
|
Receiver Reference |
Predicted Maximum Annual Concentration |
|
Criteria |
80mg-3 |
|
ASR1 |
65.6 |
|
ASR2 |
65.7 |
|
ASR3 |
67.9 |
|
ASR4 |
67.5 |
|
ASR5 |
69.1 |
|
ASR6 |
65.5 |
|
ASR7 |
65.8 |
|
ASR8 |
66.2 |
|
ASR9 |
65.9 |
|
ASR10 |
65.7 |
3.8.3.4 The predicted annual average maximum cumulative TSP concentrations at representative ASRs detailed in Table 3.8 indicate that, for all of ASR, there would be no exceedances of the annual average TSP criterion are predicted to occur, even assuming the absolute worst case situation where 100% of every works site would be active and emitting dust, with all impacts being confined to the works area
3.8.3.5
Given that recommended measures
are tried and tested techniques used extensively throughout
3.10.1.1 The residual impacts refer to the net impacts after mitigation, taking into account the background environmental conditions and the impacts from existing, committed and planned projects.
3.10.1.2
Residual
air quality impacts associated with the project have been assessed. It is concluded that residual impacts would
be short in duration, occurring for the construction phase only. Although the whole period of construction for the Project will be 30 months, with
the exception of the work areas for the jacking pits and the stockpile areas,
the construction activities, overall, will be of short duration, localised and confined to small areas around the works
sites at a time, as each active cut and cover section under construction will
be about 40m long, which is programmed to take only about 2 months to complete. For the duration of the impacts at the
jacking pits and the stockpile areas, the periods of operation will be between
6 to 11 months. In addition, with the
proposed mitigation measures, the impacts from the construction activities will
not be significant, even though a worst case assessment assuming all the
construction works would be carried concurrently has been undertaken. . Therefore, construction dust is not predicted to affect the health and welfare of the local community or
local agricultural activities and no irreversible adverse environmental impacts
will be anticipated.
3.10.1.3 Adverse residual impacts during the construction or operational phases of the Project would not be anticipated, provided that the above mitigation measures are implemented.
3.11 Environmental Monitoring and Audit
3.11.1.1 The assessment
has concluded that mitigated construction dust impacts are within acceptable
levels and no adverse residual impacts will occur. However, it is recommended that, given the
close proximity of the ASRs to the works site, that construction phase environmental
monitoring and audit (EM&A), in the form of site audits, is undertaken to
ensure that there are no adverse impacts during the implementation of the
construction activities and ensure that recommended mitigation measures are
implemented. Further details of the
specific EM&A requirements are detailed in Section 10 of this report
and in the EM&A Manual under separate cover.
3.12.1.1 Potential air quality impacts from the construction works for the Ngong Ping drainage improvement works would mainly be related to construction dust from excavation, materials handling, spoil removal and wind erosion. With the implementation of hourly watering of all exposed areas and mitigation measures as defined in the Air Pollution Control (Construction Dust) Regulation and good site practices, adverse 1-hour, 24-hour or annual residual impacts would not occur. The predicted air impact would be unlikely to induce public health concern.