3.2 Environmental Legislation, Standards and Guideline
3.3 Description of the Existing WENT Landfill and WENT Landfill Extension
3.5 Identification of Air Pollution Source and Environmental Impact
3.7 Prediction and Evaluation of Air Quality Impact
3.9 Residual Environmental Impact
Appendices
Appendix
3.1a Past Monitoring Record for the Removal
Efficiency of Flaring System
Appendix
3.1b Past 10-year Odour Complaint Records
Appendix
3.3
Detailed Calculations of Dust Emission Rate
Appendix
3.4 Detailed Calculations of
Vehicular Emission Rate
Appendix
3.6 Emission Inventory
Appendix 3.7
Odour Measurement Results
Appendix
3.9 Detailed Results of Construction
Dust Assessment
Appendix
3.10 Detailed Assessment Results of AQO
Pollutants
Appendix
3.11 Detailed Assessment Results of Non-AQO
Pollutants
Figures
Figure 3.1 Existing WENT Landfill Dust Monitoring
Locations ASR 4 & ASR 13
Figure 3.2 Existing WENT Landfill VOC Monitoring
Locations OM2 to OM5
Figure 3.3 Air Sensitive Receivers
Figure 3.4i Dust
Emission Source Locations (Contribution from WENT Landfill Extension – Scenario 1)
Figure 3.4k Dust
Emission Source Locations (Contribution from WENT Landfill Extension – Scenario 2)
Figure 3.4m Dust
Emission Source Locations (Contribution from WENT Landfill Extension – Scenario 3)
Figure 3.5a Locations of Potential Emission Sources
Figure 3.5b NO2 & SO2 Emission Sources Location
Figure 3.6 Locations
of Deodouriser Units
Figure 3.7a Locations
of Tipping Faces
Figure 3.7b Locations
of Tipping Faces (with Mitigation)
Figure 3.8a-1 Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 1A)
Figure 3.8a-2 Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 1A)
Figure 3.8a-3 Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 1B)
Figure 3.8a-4 Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 1B)
Figure 3.8a-5 Contours
of Annual TSP Concentration at 1.5m above Ground (Scenario 1)
Figure 3.8a Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 2A)
Figure 3.8b Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 2A)
Figure 3.8c Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 2B)
Figure 3.8d Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 2B)
Figure 3.8d-1 Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 2C)
Figure 3.8d-2 Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 2C)
Figure 3.8e Contours
of Annual TSP Concentration at 1.5m above Ground (Scenario 2)
Figure 3.8h Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 3A)
Figure 3.8i Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 3A)
Figure 3.8j Contours
of 1-hour TSP Concentration at 1.5m above Ground (Scenario 3B)
Figure 3.8k Contours
of 24-hour TSP Concentration at 1.5m above Ground (Scenario 3B)
Figure 3.8l Contours
of Annual TSP Concentration at 1.5m above Ground (Scenario 3)
Figure 3.9a Contours
of 1-hour NO2 Concentration at 1.5m above Ground
Figure 3.9b Contours
of 1-hour SO2 Concentration at 1.5m above Ground
Figure 3.9c Contours
of 24-hour NO2 Concentration at 1.5m above Ground
Figure 3.9d Contours
of 24-hour SO2 Concentration at 1.5m above Ground
Figure 3.9e Contours
of 24-hour RSP Concentration at 1.5m above Ground
Figure 3.9f Contours
of Annual NO2 Concentration at 1.5m above Ground
Figure 3.9g Contours
of Annual SO2 Concentration at 1.5m above Ground
Figure 3.9h Contours
of Annual RSP Concentration at 1.5m above Ground
Figure 3.10a Contours
of Odour Concentration at 1.5m above Ground (Scenario 1)
Figure 3.10b Contours
of Odour Concentration at 1.5m above Ground (Scenario 2 with Mitigation)
Figure 3.10c Contours
of Odour Concentration at 1.5m above Ground (Scenario 3)
Figure 3.10d Contours
of Odour Concentration at 1.5m above Ground (Scenario 4 with Mitigation)
Figure 3.10e Contours
of Odour Concentration at 1.5m above Ground (Scenario 5 with Mitigation)
3. AIR QUALITY IMPACT
This chapter presents the impact assessment on potential air quality aspects for the construction, operation, restoration and aftercare stages of the Project.
Control measures for construction related activities have been recommended, in accordance with the requirements specified in the Air Pollution Control (Construction Dust) Regulation. Proper emission control limits for stack emissions from ammonia stripping plant, flare and landfill gas (LFG) power generator will be in place for the WENT Landfill Extension, similar to the existing WENT Landfill operation. Together with the implementation of good site practice for the tipping operation, the air quality impact will be controlled to within Hong Kong Air Quality Objectives (HKAQOs).
The assessment has been conducted in accordance with the requirements of Annex 4 and Annex 12 of the TM-EIAO, as well as the requirements set out under Clause 3.4.1 of the EIA Study Brief.
The relevant legislation and associated guidance notes applicable to the study for the assessment of air quality implications include:
· Environmental Impact Assessment Ordinance (Cap. 499) and Technical Memorandum on Environmental Impact Assessment Process (TM-EIAO);
· Air Pollution Control Ordinance (APCO) (Cap. 311) Air Pollution Control (Construction Dust) Regulation (Cap. 311R);
·
· World Health Organisation (WHO); and
· United States Environmental Protection Agency (USEPA) references.
3.2.1 Air Quality Objectives
The principal legislation for controlling air pollutants is the Air Pollution Control Ordinance (Cap. 311) and its subsidiary regulations, which define statutory Air Quality Objectives (AQOs) for 7 common air pollutants. The AQOs for these air pollutants are tabulated in Table 3.1 below.
Table
3.1
|
Pollutant |
Concentration in micrograms per cubic metre (mg/m³) [1] (Parts per million, ppm in brackets) |
||||
|
1 Hour [2] |
8 Hour (3] |
24 Hours [3] |
3 Months [4] |
1 Year [4] |
|
|
Total Suspended Particulates (TSP) |
500 [7] |
|
260 |
|
80 |
|
Respirable Suspended Particulates (RSP) [5] |
|
|
180 |
|
55 |
|
Carbon Monoxide, CO |
30,000 (26.2) |
10,000 (8.7) |
|
|
|
|
|
800 (0.3) |
|
350 (0.13) |
|
80 (0.03) |
|
Nitrogen Dioxide, NO2 |
300 (0.16) |
|
150 (0.08) |
|
80 (0.04) |
|
Photochemical Oxidants (as Ozone, O3 ) [6] |
240 |
|
|
|
|
Notes:
[1] Measured at 298K (25°C) and 101.325 kPa (one atmosphere).
[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] Respirable suspended particulates means suspended particulates in air with a nominal aerodynamic diameter of 10 micrometres or smaller.
[6] Photochemical oxidants are determined by measurement of ozone only.
[7] Not an AQO. TM-EIAO suggested short-term averaging level for 1 hour is 500ug/m³. There is no exceedance allowance for 1-hour TSP guideline level.
3.2.2 Air Pollution Control (Construction Dust) Regulation
The Air Pollution Control (Construction Dust) Regulation identifies those processes that require special dust control. The DBO Contractor of the WENT Landfill Extension is required to inform EPD prior to carrying out such processes and to adopt dust reduction measures while carrying out "Notifiable Works" or “Regulatory Works”, as defined under the regulation. Works relevant to this Project are the site formation activities, for which TSP concentration shall not exceed 500 mg/m3.
3.2.3 Odour Criteria
In accordance with Annex 4 of TM-EIAO, the limit of 5 odour units (OU) based on an averaging time of 5 seconds for odour prediction assessment shall not be exceeded at any receivers.
3.2.4 Other Pollutants
Other pollutants that are not covered by the Hong Kong AQOs but may impose a health risk concern have also been considered. The criteria / guideline values related to carcinogenic and non-carcinogenic health risk evaluation are established from the following order of reference:
· World Health Organization (WHO);
· United States Environmental Protection Agency (USEPA); and
· California Environmental Protection Agency (CEPA).
The guidelines for the assessment of carcinogenic health risk from exposure to air toxics are based on the WHO and USEPA Integrated Risk Information System (IRIS)’s acceptable lifetime risk.
Long-term monitoring for 38 species of VOC relating to the landfilling operation is being conducted at the existing WENT Landfill. Nonetheless, emission for 18 species of these VOC is found to be insignificant and below the detection limit. Out of the remaining 20 species of VOC, only 8 species have documentary concern related to carcinogenic and non-carcinogenic health risk. The unit risk factor and reference dosage for the 8 related VOCs are tabulated in Table 3.2.
Table 3.2 Unit Risk factors and reference dosage from WHO/IRIS/CEPA database on related VOCs
|
Substance [1] |
Molecular Weight g/mol [4] |
Unit Risk Factor per μg/m3 [3] |
Reference dosage [2,4,5,6,7] |
|
Benzene (CASRN 71-43-2) |
78.11 |
6x10-6 |
Chronic Inhalation Exposure (RfC): 30 μg/m3 (9.4ppbv) (IRIS) Acute: 1.3 x 103 μg/m3 (406.9ppbv) (CEPA) |
|
1,4-Dichlorobenzene (CASRN 106-46-7) |
147.01 |
- |
Chronic Inhalation Exposure (RfC): 8x102 μg/m3 (133.1ppbv) (IRIS) |
|
Ethyl Benzene (CASRN 100-41-4) |
106.16 |
|
Chronic: 22,000 μg/m3 for 1 year averaged All based on WHO (Geneva) Chronic Inhalation Exposure (RfC): 1000 μg/m3 (230.3ppbv) (IRIS) |
|
Toluene (CASRN 108-88-3) |
92.14 |
- |
Acute: 1 x 103 μg/m3 for 30min averaged (odour threshold) (265.4ppbv), based on S5.14 of WHO Chronic: 260 μg/m3 (69ppbv) of 1 week, based on S5.14 of WHO |
|
Vinyl chloride (CASRN 75-01-4) |
62.5 |
1.0x10-6 |
Chronic Inhalation Exposure (RfC): 100 μg/m3 (IRIS) Acute: 1.8x105 μg/m3 (70,416ppbv) (CEPA) |
|
Xylenes (CASRN 1330-20-7) |
106.16 |
- |
Acute: 4800 μg/m3 for 24 hour averaged Chronic: 870 μg/m3 for 1 year averaged All based on WHO (Geneva) Chronic Inhalation Exposure (RfC): 100 μg/m3 (23.0ppbv) (IRIS) |
|
Tetrachloroethylene (CASRN 127-18-4) |
165.8 |
- |
Acute: 8000 μg/m3 for 30 min averaged; 250 μg/m3 for 24 hour averaged based on WHO (Geneva) |
|
Methylene Chloride / Dichloromethane (CASRN 75-09-2) |
84.93 |
4.7x10-7 [8] |
Acute: 3mg/m3 for 24 hour guideline; Chronic: 0.45mg/m3 for a weekly guideline All based on S5.7 of WHO |
Note: [1]. CASRN – Chemical Abstracts Service Registry Number
[2]. RfC – Reference Concentration
[3]. If WHO standard is available, it will be applied first
[4]. C ppbv = C ug/m3 x 24.45 / Molecular Weight
[5]. WHO represents Air Quality Guideline for Europe, WHO
[6]. WHO (Geneva) represents Guidelines for Air Quality, WHO, Geneva, 2000
[7]. CEPA represents California Environmental Protection Agency
[8]. As per Integrated Risk Information System (IRIS) (http://www.epa.gov/ncea/iris/subst/0070.htm)
3.2.4.1 Carcinogenic Health Risk Assessment
Emissions pertinent to this Project are benzene and vinyl chloride which are key control parameters from the Ammonia Stripping Plant (ASP), flares and LFG generators. Tables 3.3 and 3.4 show the unit risk factors for non-criteria key pollutants of benzene and vinyl chloride and the guidelines for assessment of individual risk.
Table 3.3 Unit risk factors guideline for non-criteria pollutants
|
Pollutant |
Unit Risk Factor ((μgm-3 ) -1 ) |
|
Benzene |
6x10-6 |
|
Vinyl Chloride |
1.0x10-6 |
Table 3.4 Risk guidelines for carcinogenic health risk assessment
|
Acceptability of Cancer Risk |
Estimated Individual Cancer Risk Level ((μgm-3 ) -1 ) |
|
|
Individual Lifetime Risk (A) |
Individual Risk Per Year (B) = (A)/70 |
|
|
Significant |
>10-4 |
>1.4x10-6 |
|
Risk should be reduced to As Low As Reasonably Practicable (ALARP) |
>10-6 & <= 10-4 |
>1.4x10-8 & <= 1.4x10-6 |
|
Insignificant |
£10-6 |
£1.4x10-8 |
3.2.4.2 Non-Carcinogenic Health Risk Assessment
Non-carcinogenic health risk guidelines apply to the assessment of chronic and acute health risks.
Chronic Health Risks
Using the chronic health risk assessment approach, the chronic reference concentrations for benzene and vinyl chloride are summarized in Table 3.5 and their acceptability criteria in Table 3.6.
Table 3.5 Chronic reference concentrations for benzene and vinyl chloride
|
Pollutant |
Chronic Reference Concentration (ACA ) (Annual Average) |
|
Benzene |
30 μg/m3 (9.4ppbv) (a) |
|
Vinyl Chloride |
100 μg/m3 (39.12ppbv) (a) |
Note: (a) Yr 2000 updated standard from Integrated Risk Information System (IRIS), USEPA
Table 3.6 Acceptability criteria for chronic non-cancer health risks
|
Acceptability |
Assessment Results (a) |
|
Chronic non-cancer risks are considered “Insignificant” |
ACA £ RCC |
|
Chronic non-cancer health risks are considered ‘Significant”. Detailed assessment of the control requirements and further mitigation measures are needed |
ACA > RCC |
Note: (a) ACA and RCC represent annual average concentration and chronic reference concentration respectively.
Acute Health Risks
Using the acute health risk assessment approach, the acute reference concentrations for benzene and vinyl chloride are summarized in Table 3.7 and their acceptability criteria in Table 3.8.
Table 3.7 Acute reference concentrations
|
Pollutant |
Acute Reference Concentration (ACHM) (1-hour average, μg m-3 ) |
|
Benzene |
1.3 x 103 (a) |
|
Vinyl Chloride |
1.8x105 (a) |
Note : (a) California Air Resources Board – Air Toxic Hot Spots Program Risk Assessment Guidelines, Part I – Technical Support Document for the Determination of Acute Reference Exposure Levels for Airborne Toxicants, May 2000.
Table 3.8 Acceptability criteria for acute non-cancer health risks
|
Acceptability |
Assessment Results (a) |
|
Acute non-cancer risks are considered “Insignificant”. |
ACHM £RCA |
|
Acute non-caner health risks are considered “Significant”. Detailed assessment of the control requirements, and further mitigation measures are needed. |
ACHM >RCA |
Note: (a) ACHM and RCA represent maximum hourly average concentration and acute reference concentration respectively.
3.3.1 Existing Vehicles Trips Generated from existing WENT Landfill
Based on the latest information from existing WENT Landfill, there is about 400 vehicles/day (or peak hourly flow of 43 vehicle/hour) travelling to and from the existing WENT Landfill site. These vehicles will generate some air pollutants. Most of the waste is however being transported by sea and the same method will be adopted for WENT Landfill Extension.
3.3.2 Existing Barges
Currently, there are 5 barging points at the existing WENT Landfill along the existing coastline to receive waste via barges from different transfer stations. These barges would inevitably generate air quality pollutants during both idling at the barging points and travelling along the marine route. According to the information provided by the operators, the current utilisation schedule of these barges is as follows. Also, according to the EIA Report of STF, the barge for STF is assumed to be berthed at the existing HATS barging point with idling period similar to that of WKTS (see Figure 3.5a for the locations of barges).
Table 3.8a Operation schedule for barges
|
|
Barging Points in Existing WENT Landfill |
|||||
|
IETS |
IWTS |
OITF |
WKTS |
NLTS |
STF |
|
|
Round Trips (nos / day) |
1 |
1 |
1 |
1 |
1 |
1 |
|
Idling period (Note) |
2130 - 1700 |
2100 -1800 |
1100 - 1430 |
0730 - 1930 |
0830 – 0920 |
0600 - 2000 |
|
Engine turned on during idling |
Aux |
Aux |
Aux |
No |
Only Generator |
No |
Note: Take IETS as an example, 2130 refers to the time when the barge arrives. When it arrives, it would wait until daytime period when the loading / unloading process starts. The process would be completed by 1700 and the barge would leave by 1700. This is the reason why manoeuvring would be before one hour before 2130 and one hour after 1700.
3.3.3 Existing Monitoring Location and Condition
3.3.3.1 Existing plants operation
During operation of existing WENT Landfill, gaseous emission from Ammonia Stripping Plant (ASP), flare system etc. would be generated. The flare system operates only when the ASP is not in use or when excessive LFG is pending for treatment. Yearly monitoring at the inlet and outlet of the flaring system is conducted to verify the destruction efficiency. Past monitoring results conclude that emission from flaring system has complied with the control limits. Appendix 3.1a presents the past monitoring results for the removal efficiency of the flaring system.
3.3.3.2 Existing Monitoring and Audit Findings
TSP / RSP
EM&A records for TSP/RSP monitoring over the last 10 years have been reviewed. TSP/RSP monitoring is conducted once every 6 days in two off-site locations (See Figure 3.1 for existing dust monitoring locations ASR4 & ASR13).
Key observations from the past monitoring records are summarised in Table 3.9 for TSP/RSP.
Table 3.9 Summary of Dust monitoring record for existing WENT Landfill operation
|
Monitoring ID |
Location |
Monitoring Parameters |
Frequency |
Observations |
Mitigation Measures |
|
ASR4 |
North-west part of Ha Pak Nai |
TSP/RSP (24-hour averaged) |
Once very 6 days. Increase frequency in case of exceedance event |
No exceedance since 2003 (only 2 x 24-hour average abnormalities detected from period 2002 to 2003.) |
Increase water spraying frequency in tipping area and haul road by water trucks and sweeper trucks Minimize the exposure duration of cut slopes and temporary capped areas by covering with plastic sheets. |
|
ASR13 |
South-west part of Ha Pak Nai |
No exceedance since 2003 (only 2 x 24-hour average abnormalities detected from period 2002 to 2003.) |
Remark : The established EM&A mechanism and good site practice in existing WENT Landfill effectively contains any dust problem on site in a timely manner.
An Independent Consultant (IC) had also reviewed all these monitoring results and the findings for the site inspection by Environmental Team. A summary of long-term TSP / RSP monitoring results are tabulated in Table 3.10.
Table 3.10 10-year averaged TSP/RSP concentration of the nearest ASRs (from Year 1996 to Year 2006)
|
Pollutants |
Parameter |
10-year monitoring data at off-site location, ug/m3 |
|
|
|
ASR 4 |
ASR 13 |
|
|
TSP (24-hr average) |
range |
25 - 300 |
15 - 360 |
|
average |
87 |
94 |
|
|
RSP (24-hr average) |
range |
3 - 290 |
1 - 300 |
|
average |
62 |
62 |
|
Remark: Only 4 x 24-hour average abnormalities detected in 10-year period, and the abnormalities were immediately rectified by standard mitigation measures.
VOC
EM&A records for VOCs monitoring over the last 10 years have been reviewed. VOC monitoring is conducted once every 3 months in four locations around the site boundary (See Figure 3.2 for existing VOC monitoring locations OM2 to OM5), and one at the gas well.
The sampling methodology was stipulated in Environmental Monitoring Monthly Reports. Equipment specified in Method T015 of USEPA and corresponding HOKLAS methods for the determination of Toxic Organic Compounds in ambient air were adopted for monitoring the existing WENT Landfill. VOC is collected in 6L stainless steel canisters coated internally with silica. Control practices have been exercised including one Field Blank sample with “Zero Air” for checking of potential contamination during the trip. There was another Field Sample which had been spiked with known VOCs and being analysed before and after the trip.
Key observations from the past monitoring records are summarised in Table 3.11 for VOC. In accordance with the long-term monitoring record, there were only 4 abnormality records on 24-hour averaged data found in a 10-year period (from Year 1996 to 2006).
Table 3.11 Summary of VOC monitoring information for existing WENT Landfill operation
|
Monitoring ID |
Location |
Monitoring Parameters |
Frequency |
Observations |
Mitigation Measures |
|
OM2
|
East of the landfill area |
44 VOCs including 8 prominent VOCs: · Benzene; · 1, 4 – Dichlorobenzenes; · Ethylbenzene; · Toluene; · Vinyl chloride; · Xylenes; · Tetrachloroethylene; · Methylene Chloride. |
Quarterly basis in March, June, September and December at four boundary locations and one gas well within the landfall. If the monitoring results show abnormality, site inspection and special monitoring will be conducted. |
No abnormality observed in the past 10 years
|
No exceedance was identified in the monitoring. In case of exceedance, site investigation to identify and pipe leakage (compare with gas composition) and to optimize extraction. The objectives are to determine radius of influence of abstraction wells and optimum suction pressure and extraction rates. |
|
OM3 |
North of the landfill area |
||||
|
OM4 |
West of the landfill area |
||||
|
OM5 |
South of the landfill area |
Remark: (1) VOC monitoring data and emission trend at source (within gas well) were compared with the results at the site boundary. Independent Consultant (IC) confirmed that the handful number of abnormal readings were not caused by / related to landfill operation.
(2) Trigger limit = OEL (on-site locations OM2, OM4 and OM5) and 1% OEL (off-site location OM3)
Trigger limits are available for a limited number of VOCs.
(3) OEL = Occupational Exposure Limit “UK Health and Safety (HSE) EH40/91 or EH40/93” – short term exposure unless otherwise specified.
An IC had also reviewed all these monitoring results and the findings for the site inspection by Environmental Team. It was concluded that no abnormality in the VOC monitoring was observed over the past 10 years. A summary of VOC monitoring results are tabulated in Table 3.12.
Table 3.12 10-year averaged VOC concentration at the site boundary of the existing WENT Landfill
|
Pollutants |
Parameter |
10-year monitoring data at the site boundary (in mg/m3 except methane) [1,2 and 3] |
|||
|
|
OM2 |
OM3 |
OM4 |
OM5 |
|
|
1,1,1-Trichloroethane (CASRN 71-55-6) |
range |
0.78 - 17 |
0.6 - 24 |
0.61 - 180 |
0.8 - 110 |
|
average |
1.4 |
1.7 |
4.6 |
3.5 |
|
|
1,2-Dibromoethane (CASRN 106-93-4) |
range |
1 - 1 |
1 - 1 |
1 - 1 |
1 - 1.5 |
|
average |
1.0 |
1.0 |
1.0 |
1.0 |
|
|
1,2-Dichloroethane |
range |
0.3 - 3.2 |
0.3 - 3.8 |
0.3 - 3.8 |
0.3 - 0.3 |
|
average |
0.4 |
0.4 |
0.4 |
0.3 |
|
|
a-Pinene |
range |
0.8 - 18 |
0.8 - 16 |
0.36 - 11 |
0.6 - 40 |
|
average |
1.4 |
1.3 |
1.4 |
2.9 |
|
|
Benzene (CASRN 71-43-2) |
range |
0.49 - 57 |
0.5 - 10 |
0.5 - 18 |
0.5 - 14 |
|
average |
5.9 |
3.3 |
3.6 |
3.0 |
|
|
b-Pinene |
range |
0 - 0.4 |
0 - 8.9 |
0 - 12 |
0 - 6.8 |
|
average |
0.3 |
0.5 |
0.7 |
0.4 |
|
|
Butan-2-ol (CASRN 71-36-2) |
range |
1.4 - 44 |
1.4 - 36 |
1.4 - 62 |
1.4 - 38 |
|
average |
2.3 |
2.2 |
2.6 |
3.5 |
|
|
Butanethiol |
range |
0 - 1.2 |
0 - 2 |
0 - 1.2 |
0 - 1.2 |
|
average |
1.1 |
1.2 |
1.1 |
1.1 |
|
|
Carbon Disulphide (CASRN 75-15-0) |
range |
0 - 12 |
0 - 0.9 |
0 - 7.5 |
0 - 0.5 |
|
average |
0.8 |
0.5 |
0.6 |
0.5 |
|
|
Carbon Tetrachloride |
range |
0.4 - 1.3 |
0.6 - 7.7 |
0.6 - 6.9 |
0.44 - 12 |
|
average |
0.7 |
0.9 |
0.8 |
0.9 |
|
|
Chloroform (CASRN 67-66-3) |
range |
0.8 - 18 |
0.8 - 11 |
0.8 - 11 |
0.8 - 13 |
|
average |
1.4 |
1.4 |
1.5 |
1.2 |
|
|
Dichlorodifluoro-methane (CASRN 75-71-8) |
range |
0.6 - 583.7 |
0.6 - 1296 |
0.6 - 947.6 |
0.6 - 700.3 |
|
average |
32.1 |
37.3 |
40.1 |
37.2 |
|
|
Dimethyl Sulphide |
range |
0.2 - 9.2 |
0.2 - 4 |
0 - 3 |
0.2 - 2.8 |
|
average |
0.5 |
0.3 |
0.3 |
0.3 |
|
|
Dipropyl Ether (CASRN 111-43-3) |
range |
0.9 - 0.9 |
0.9 - 0.9 |
0.9 - 0.9 |
0.9 - 1.3 |
|
average |
0.9 |
0.9 |
0.9 |
0.9 |
|
|
Limonene (CASRN 5989-27-5) |
range |
0.4 - 150 |
0.34 - 10 |
0.4 - 51 |
0.4 - 380 |
|
average |
9.6 |
0.9 |
4.4 |
28.0 |
|
|
Ethanethiol |
range |
0.6 - 19 |
0.6 - 17 |
0 - 0.6 |
0.6 - 81 |
|
average |
1.0 |
1.0 |
0.6 |
3.2 |
|
|
Ethanol |
range |
18 - 50 |
50 - 50 |
8.2 - 139 |
50 - 409 |
|
average |
49.3 |
50.0 |
51.0 |
66.6 |
|
|
Ethyl Butyrate |
range |
0.74 - 13 |
1.2 - 17 |
0.67 - 4.15 |
0.2 - 36 |
|
average |
1.9 |
1.8 |
1.5 |
2.6 |
|
|
Ethyl Propionate |
range |
1 - 2.1 |
1 - 7.3 |
1 - 1 |
1 - 1 |
|
average |
1.0 |
1.2 |
1.0 |
1.0 |
|
|
Ethyl Benzene (CASRN 100-41-4) |
range |
0.5 - 480 |
0.5 - 78 |
0.5 - 240 |
0.5 - 87 |
|
average |
27.5 |
6.3 |
16.9 |
11.5 |
|
|
m,p-Xylene |
range |
0.5 - 460 |
0.5 - 110 |
0 - 240 |
0.4 - 130 |
|
average |
40.6 |
13.2 |
29.3 |
21.0 |
|
|
m-Dichlorobenzene (CASRN 106-46-7) |
range |
1 - 48 |
1 - 17 |
0 - 58 |
1 - 23 |
|
average |
3.7 |
2.1 |
2.7 |
2.1 |
|
|
Methane (ppm) |
range |
45 - 100 |
14 - 100 |
0 - 100 |
3.3 - 100 |
|
average |
98.8 |
98.1 |
96.4 |
95.8 |
|
|
Methanethiol |
range |
0 - 0.4 |
0 - 0.4 |
0 - 60 |
0 - 0.4 |
|
average |
0.4 |
0.4 |
1.6 |
0.4 |
|
|
Methanol |
range |
0 - 30 |
0 - 30 |
0 - 36 |
0 - 30 |
|
average |
28.3 |
28.2 |
28.7 |
28.1 |
|
|
Methyl Butyrate |
range |
1 - 1.3 |
1 - 6.3 |
1 - 1 |
0.32 - 1 |
|
average |
1.0 |
1.2 |
1.0 |
1.0 |
|
|
Methyl Propionate |
range |
1.2 - 1.2 |
1.2 - 6.1 |
1.2 - 2.2 |
1.2 - 1.2 |
|
average |
1.2 |
1.3 |
1.2 |
1.2 |
|
|
Methylene Chloride |
range |
0 - 729 |
0 - 2740 |
0 - 942 |
0 - 1588 |
|
average |
57.1 |
122.3 |
93.7 |
103.1 |
|
|
n-Butyl Benzene |
range |
0.74 - 110 |
1 - 11 |
1 - 52 |
1 - 23 |
|
average |
3.5 |
1.6 |
2.1 |
1.9 |
|
|
n-Butyl Acetate |
range |
0.67 - 140 |
0.95 - 64 |
1.2 - 88 |
1 - 27 |
|
average |
4.7 |
3.0 |
3.9 |
3.3 |
|
|
n-Decane |
range |
0.55 - 47 |
0.56 - 11 |
0.7 - 20 |
0.7 - 11.3 |
|
average |
2.3 |
1.2 |
1.9 |
2.1 |
|
|
n-Heptane
|
range |
0.87 - 16 |
1 - 9.2 |
0.93 - 12 |
0.9 - 13.73 |
|
average |
2.4 |
1.8 |
2.3 |
2.8 |
|
|
n-Nonane |
range |
0.42 - 14 |
0.42 - 5.2 |
0.68 - 6.2 |
0.9 - 8.31 |
|
average |
1.6 |
1.2 |
1.3 |
1.9 |
|
|
n-Octane |
range |
1.2 - 6.1 |
0.34 - 5.5 |
0.63 - 8 |
0.85 - 7.3 |
|
average |
1.4 |
1.3 |
1.5 |
1.6 |
|
|
n-Propyl Benzene |
range |
0.48 - 62 |
0.8 - 27 |
0.8 - 130 |
0.34 - 320 |
|
average |
8.9 |
6.3 |
11.5 |
15.4 |
|
|
n-Undecane |
range |
0.39 - 2.6 |
0.34 - 3.42 |
0.67 - 5 |
0.6 - 12 |
|
average |
1.2 |
1.2 |
1.4 |
2.1 |
|
|
o-Dichlorobenzene |
range |
1 - 22 |
1 - 11 |
0.9 - 14 |
0.9 - 4.3 |
|
average |
1.9 |
1.7 |
1.5 |
1.1 |
|
|
Xylene (CASRN 1330-20-7) |
range |
0.48 - 150 |
0.5 - 59 |
0.41 - 110 |
0.2 - 67 |
|
average |
12.0 |
5.1 |
11.5 |
8.0 |
|
|
p-Dichlorobenzene |
range |
1 - 17 |
0.7 - 12 |
0 - 220 |
1 - 220 |
|
average |
2.8 |
2.9 |
10.1 |
9.1 |
|
|
Propyl Propionate |
range |
1 - 44 |
1 - 41 |
1 - 26 |
1 – 74 |
|
average |
2.5 |
3.0 |
1.7 |
3.4 |
|
|
Tetrachloroethylene (CASRN 127-18-4) |
range |
0.5 - 24 |
0.7 - 45 |
0.31 - 22 |
0.7 – 14 |
|
average |
1.7 |
3.1 |
2.6 |
2.1 |
|
|
Toluene (CASRN 108-88-3) |
range |
0.5 - 2200 |
0.5 - 950 |
0.5 - 400 |
0.2 – 1800 |
|
average |
120.2 |
67.6 |
65.3 |
110.5 |
|
|
Trichloroethylene (CASRN 79-01-6) |
range |
0.48 - 25 |
0.2 - 7.58 |
0.51 - 16 |
0.33 - 6.11 |
|
average |
2.8 |
1.7 |
2.4 |
1.8 |
|
|
Vinyl Chloride (CASRN 75-01-4) |
range |
0.3 - 19 |
0.3 - 9.7 |
0.3 - 318 |
0.3 - 0.7 |
|
average |
1.4 |
0.6 |
6.8 |
0.3 |
|
Remark (1) Assume to take the lowest detection limit as the monitoring result if the equipment record below detection limits
(2) Trigger limit = OEL (on-site locations OM2, OM4 and OM5) and 1% OEL (off-site location OM3)
Trigger limits are available for a limited number of VOCs.
(3) OEL = Occupational Exposure Limit “UK Health and Safety (HSE) EH40/91 or EH40/93” – short term exposure unless otherwise specified.
Odour
Odour complaint records from existing WENT Landfill site office and EPD Environmental Compliance Division have been checked. There were about 10 odour complaints in the past 2 years while most of the complaints occurred at Tuen Mun area at a separation distance of more than 2.5km. Detailed investigations were conducted by the Independent Consultant, Environmental Team of the existing WENT Landfill and EPD. According to the record of odour patrol conducted by existing WENT Landfill site staff, occasionally and intermittent slight malodour was only detected in the immediate area of about 50 m from the existing WENT Landfill. No malodour is detected in the area with distance of 1 km from the existing WENT Landfill. Thus, it was concluded that the existing WENT Landfill was not the source of the odour nuisance.
A summary of the odour complaints in the past 10 years (i.e. 1998-2008) is given in Appendix 3.1b.
Benzene, Vinly Chloride and NMOCr
Benzene, Vinyl Chloride and Non-methane Organic Carbon (NMOC) have also been monitored at the flare of the existing WENT Landfill, and the monitoring results (from Year 2002 to 2006) are summarised in Table 3.13.
Table 3.13 Monitoring data from flare system (from Year 2002 to Year 2006)
|
Pollutants |
NMOC |
Vinyl Chloride |
Benzene |
|||
|
5-year Monitoring Results |
Inlet |
Outlet |
Inlet |
Outlet |
Inlet |
Outlet |
|
Max (ppmv) |
1400 |
15 |
0.28 |
0.006 |
0.8 |
0.012 |
|
Min (ppmv) |
420 |
0.7 |
0.02 |
<0.002 |
0.05 |
<0.002 |
|
Average (ppmv) |
856 |
5.18 |
0.158 or 403.7 mg/m3 |
0.0032 or 8.2 mg/m3 |
0.414 or 1322.6 mg/m3 |
4.4 x10-3 or 14.1 mg/m³ |
|
Removal Efficiency [average value (inlet - outlet) pair_data /inlet] |
99.1% |
95.4% |
98.1% |
|||
Owing to the lack of monitoring data for ASP and power generator, reference has been made using typical control efficiency under Table 2.4-3, AP-42 of USEPA as the best estimate. The typical controlled efficiency of 99.6% and 99.8% are proposed for halogenated species and non-halogenated species for the modern type boiler/stream turbine. As compared to the controlled efficiency of 95.4% and 98.1% for halogenated species and non-halogenated species for flare in existing WENT Landfill, the efficiency in flare would be less effective than the USEPA database using more advance equipment. As a conservative assumption, the controlled efficiency for ASP and power generator is assumed to be the same as that for the flare in the existing WENT Landfill.
3.3.4 Ambient air quality from EPD monitoring station
The WENT Landfill Extension will be located adjacent to the existing WENT Landfill and close to the Black Point Power Station (BPPS). The local air quality is affected by the industrial emissions from the existing WENT Landfill, BPPS, and traffic emissions from existing roads and marine vessels.
There is no fixed air quality monitoring station near the existing WENT Landfill and its extension. The nearest EPD air monitoring station is Yuen Long. In accordance with the Guidelines in Assessing the ‘TOTAL’ Air Quality Impacts, the recent five years (2003-2007) average monitoring data are adopted as the background concentration. The background air pollutant concentrations adopted in this study are presented in Table 3.14a below.
Table 3.14a Background Major Air Pollutant Concentrations (5-year annual averaged)
|
Pollutant / Year |
2003 |
2004 |
2005 |
2006 |
2007 |
5-year Averaged Concentration (mg/m3) |
|
TSP |
98 |
113 |
104 |
101 |
97 |
103 |
|
RSP |
61 |
71 |
62 |
62 |
64 |
64 |
|
NO2 |
60 |
67 |
58 |
58 |
55 |
60 |
|
SO2 |
18 |
31 |
28 |
28 |
24 |
26 |
3.3.5 Contribution of Emission from Black Point Power Station and Castle Peak Power Station
Air quality in the vicinity of the WENT Landfill Extension will also be influenced by the two existing power stations namely Black Point Power Station (BPPS) and Castel Peak Power Station (CPPS). With reference to the approved EIA Study of Liquefied Natural Gas (LNG) Receiving Terminal and Associated Facilities (EIA-125/2006) and the Sludge Treatment Facilities (EIA-155/2008), the contribution from BPPS and CPPS are adjusted taking into account the updated ozone background concentration, the current generating capacity, and the effect of the low NOx burners installed in CPA unit and CPB units of CPPS. The same approach was adopted in this assessment.
The adjusted NO2 ,SO2 ,and RSP concentrations at different locations are summarized in Table 3.14b. Details of the calculations on the adjusted contribution from BPPS and CPPS are shown in Appendix 3.2.
Table 3.14b Adjust Maximum Hourly, 2nd Highest Daily and Annual NO2 ,SO2 and RSP Concentrations
|
Location |
Adjusted Concentration (μg/m3) |
|||||||
|
NO2 [1] |
SO2 |
RSP |
||||||
|
Max. Hourly |
Daily |
Annual |
Max. Hourly |
Daily |
Annual |
Daily |
Annual |
|
|
Ha Pak Nai |
94 |
19.2 |
0.5 |
171 |
60 |
1.5 |
3.9 |
0.1 |
|
Lung Kwu Tan |
50.5 |
20.4 |
0.5 |
- |
39 |
0.8 |
4.6 |
0.1 |
Note:
[1] Adjustment is based on the latest 5-year average (2003-2007) of the annual average of the daily hourly maximum ozone concentration (78.3 μg/m3) measured at Yuen Long Monitoring Station.
Air Sensitive Receivers (ASRs) have been identified in accordance with the guidelines in Annex 12 of the TM-EIAO. Existing ASRs were confirmed through site visits and review of survey maps. It is also noted that the latest Outline Zoning Plan does not cover the existing WENT Landfill and its extension, and hence no planned ASRs is identified in the vicinity area. Representative ASRs within a distance of 500m from the Project boundary have been selected for the assessment. Since some of the ASRs are located outside the 500m range, the nearest ASRs are also included in the assessment. Their respective locations are shown in Figure 3.3 and Table 3.15 below.
Table 3.15 Summary of representative air sensitive receivers
|
Assessment Point No. |
Assessment Point Description |
Use |
No. of Storey (max.) |
Shortest Horizontal Distance between ASR to boundary of WENT Landfill Extension, m |
|
A1-1 |
West Ha Pak Nai |
Residential |
3 |
1190 |
|
A1-2 |
West Ha Pak Nai |
Residential |
3 |
1240 |
|
A1-3 |
West Ha Pak Nai |
Residential |
3 |
1065 |
|
A1-4 |
East Ha Pak Nai |
Residential |
3 |
1765 |
|
A2-1 |
Black Point Power Station (Office) |
Industrial |
3 |
855 |
|
A3-1 |
STF Office |
Industrial |
3 |
165 |
|
A4-1 |
Lung Kwu Sheung Tan |
Place of Worship |
1 |
900 |
Note : For IWMF, there is no confirmed site for the development and there is no implementation programme. Hence, IWMF is not considered as a concurrent project and ASR will not be assigned for IWMF.
3.5.1 Source Identification
On-site and off-site air pollution sources during construction, operation, restoration and aftercare of the Project are summarised in Tables 3.16 and 3.17 below:
Table 3.16 Sources of air pollution from Construction and Restoration Phases
|
Sources of air pollution |
|
· Various construction activities during daytime · Wind erosion |
Table 3.17 Sources of air pollution from Operation Phase
|
Sources of air pollution |
|
· Road traffic (There is no increase in total flow between the existing WENT Landfill and its extension). · Potential dust emission arising from daily operations · Gases emission from flare, LFG power generator and ammonia stripping plants. · Odour emission from leachate treatment facilities. · Odour emission and surface gas emission from waste tipping operation. · Emission due to transportation of waste by barges (There is no increase in number of barges and no change under the operation mode). · Dust emission from phases being used due to wind erosion |
3.5.2 Construction Phase
Heavy construction activities during daytime include site clearance, ground excavation, cut and fill (i.e. earth moving) operations, construction of the associated facilities and temporary road access within the site. In addition, wind erosion of all open sites including stockpiling will have potential impact.
About 16.6Mm³ of excavated soil will also be generated during the site formation works. Some of which will be reused for on-site infrastructure or stockpiled on site for subsequent use as daily cover, intermediate cover and final capping.
Construction plants will be located across the site, depending on need. The nearest representative ASR, CLP Power Plant, is located at about 850 m away from the nearest construction site boundary (i.e. Phase 4 & 5 Development with a total area of 60ha). The total gaseous emissions generated by the plants over the two construction phases are small (only 10% of the site area, i.e. 6 ha) and it will disperse and be diluted by the ambient air very rapidly. Therefore, the potential air quality impact associated with operation of the construction plants on the identified ASR is envisaged to be limited and minor.
Throughout the construction period, good site practices and dust control measures stipulated in the Air Pollution Control (Construction Dust) Regulation will be implemented to reduce the dust emission as much as possible. The site-specific good site practices and dust control measures are recommended in Section 3.8.
According to the approved STF EIA Report, the construction of the proposed STF would commence by Mar 2010 and all the construction activities would be completed by Mar 2011. Since the construction of WENT Landfill Extension would only commence by mid 2010s, there would not be any cumulative construction impacts with STF.
For IWMF, the site selection process is still on-going and there is no implementation plan. Hence, it is not considered as a concurrent project and there would not be cumulative impacts.
A summary of the air pollutant sources for the construction phase of the
WENT Landfill Extension is given below:
|
Project |
Operation |
|
WENT
Landfill Extension |
o
Excavation and site formation for the phases under construction |
|
|
o
Waste filling for the phases under operation |
|
|
o
Slope work and other activities for Nim Wan Road Diversion |
|
Existing
WENT Landfill |
o
Waste filling |
|
|
o
Restoration |
|
|
o
Construction of ponds (as part of the ecological mitigation measures
for WENT Landfill Extension |
Figures 3.4a to 3.4m show the locations of all the construction phase air quality emission sources.
3.5.3 Operation Phase
During the operation phase, the air pollution source considered for cumulative air quality impacts included emissions from:
· Vehicular emissions from traffic associated with the WENT Landfill Extension (including the Nim Wan Road diversion);
· Marine vessels emissions during operation of WENT Landfill Extension;
· Gaseous emissions from operation plants including Ammonia Stripping Plant (ASP) of leachete treatment plant (LTP), LFG power generators and flare system;
· Fugitive emission from the active tipping area, construction plants and Castle Peak Power Plant, emissions of LFG / VOC from landfill surfaces;
· Emissions from other Industrial Plants, including existing WENT Landfill, Black Point Power Plant, Castle Peak Power Plant, the proposed Sludge Treatment Facilities (STF), Green Island Cement Plant, the proposed Eco-Park, and Shiu Wing Steel Mill.
· Odour Emissions from Waste Filling Activities, Operation of LTP and the proposed STF.
Figures 3.5a to 3.5b show the locations of all the operation phase air quality emission sources. The following sections describe the emission inventories identified.
3.5.3.1 Vehicular Emissions from Road Traffic
Current daily vehicular trip generation travelling to and from the existing WENT Landfill site is in the order of 400 vehicles per day (at about 43 veh/hr during peak hour). According to the information from the operator, there would not be any increase in the number of vehicles when the WENT Landfill Extension comes into operation since there would not be any overlap between the operation of the existing WENT Landfill and the WENT Landfill Extension. Traffic access through the existing WENT Landfill used by the villagers of nearby villages at Ha Pak Nai and Lung Kwu Tan (currently around 5 veh/day) would be maintained and not be affected by the Nim Wan Road diversion.
In general, most of the refuse collection vehicles (RCV) for Municipal Solid Waste (MSW) and sludge are of enclosed-type and odorous gases are well contained during transit under normal circumstances. Sludge vehicles / special vehicles that require admission tickets, and special condition can be imposed on the cleanliness of vehicle and disposal period to avoid adverse cumulative impact. With reference to the existing WENT Landfill experience, potential odour impact from RCVs can be adequately controlled and unlikely to be an issue. Quantitative assessment is therefore not required.
In addition, all vehicles will be cleansed by wheel washing facility before leaving landfill, and soil brought away from landfill is thus not anticipated. Vehicle containing dusty material will also be covered by sheet to avoid any potential nuisance. Any dusty discharge on road is a violation of the Public Health & Municipal Ordinance. Therefore adverse off site dust impact is not anticipated.
3.5.3.2 Marine Vessel Emission
Similar to the existing WENT Landfill, marine vessels will be used to transport waste from refuse transfer stations to WENT Landfill Extension, and marine emission would be a concern. These refuse transfer stations include Island East Transfer Station (IETS), Island West Transfer Station (IWTS), Outlying Island Transfer Station (OITS), West Kowloon Transfer Station (WKTS) and North Lantau Transfer Station (NLTS). Emission from a future marine vessel that may be operated to transport the sludge from Stonecutters Island Sewage Treatment Works (SCISTW) to existing WENT Landfill or STF for disposal is also considered in this study.
According to the information from the operation, the existing operation schedule in Section 3.3.2 would remain unchanged for the WENT Landfill Extension.
3.5.3.3 Gaseous Emissions from Operation Plants
As discussed in Section 3.3, there are air quality emission from the ASP and the LFG flaring system. Figure 5.6 illustrates the schematic arrangement of these plant (for both the WENT Landfill Extension and the existing WENT Landfill).
Emission from Ammonia Stripping Plant
As regards the ammonia stripping plant and leachate treatment plant for the WENT Landfill Extension, new plant will be built to the most updated international standard. For the existing restored WENT Landfill, new plant will also be provided with the most updated international standard. Treatment method such as Sequencing Batch Reactor could be adopted for biological treatment of leachate.
Leachate will be collected from the restored existing WENT Landfill and its extension and pumped to the new leachate treatment plant (LTP) in the new infrastructure area. Each LTP will consist of lecahate storage tanks, ammonia stripping plant, deodoriser, a stripped leachate storage tank, three SBR tanks and an effluent storage. All tanks will be enclosed and the air exhaust from the tanks will be diverted to the deodouriser for odour removal. Alternatively, ventilated cover with low wind speed immediately above the leachate surface will be provided with emissions extracted and diverted to suitable filters for an overall odour removal.
The raw leachate will be stripped in the ammonia stripping plant. The ammonia laden air and the exhaust air of the enclosed tanks will be oxidised and destroyed in the thermal destructor (which will operate at 850°C) prior to discharge to the atmosphere. Under this combustion temperature, the ammonia gas will be completely destroyed. Given particulate matter in the combustion process is negligible, emissions of ASP from the stacks are expected to be insignificant.
In accordance with US Environmental Protection Agency, AP-42 "Compilation of Air Pollutant Emission Factors" data, the thermal destructor is designed to destroy over 99% of VOCs (including methane, vinyl chloride, benzene and other non-methane hydrocarbons) in the landfill gas and exhaust from the ammonia stripping plant. Resulting discharge of benzene and vinyl chloride is reduced to a low limit. Similarly, all gaseous ammonia are completely oxidised to nitrogen and water.
According to USEPA AP 42, Fifth Edition, Volume I Chapter 2: Solid Waste Disposal, Section 2.4.3 “Municipal Solid Waste Landfills”, Table 2.4.3 (Nov 1998), the control efficiency of VOC of flaring system could achieve 99% (ref http://www.epa.gov/ttn/chief/ap42/ch02/index.html). This assumption has also been adopted in the approved EIA Reports for NENT Landfill Extension and SENT Landfill Extension.
NO2, SO2, Vinyl Chloride and Benzene are the key control parameters which will be quantitatively modelled to assess their potential impact.
The number of leachate storage tanks and sludge tanks are given below.
|
Type |
Number of Tanks |
|
|
WENT Landfill Extension |
Existing WENT Landfill |
|
|
SBR Tank |
3 |
3 |
|
Raw Leachate Storage |
1 |
1 |
|
Pre-treated Leachate Storage |
1 |
1 |
|
Effluent Storage |
1 |
1 |
|
Buffer Storage |
2 |
0 |
|
Sludge Dewatering & Storage |
4 |
2 |
|
Sludge Tanks |
0 |
2 |
Emission from LFG Power Generators and Flare System
A generator fuelled by LFG will be installed to provide power for on-site plant and equipment. Under normal operations, LFG collected from the WENT Landfill Extension will be primarily used as fuel for the LTP and generators. The remainder will be utilised or flared.
As it is still too early to formulate a LFG export scheme for the WENT Landfill Extension, the following assessment using similar flaring system as the existing landfill will be the worst-case scenario. In fact, the WENT Landfill Extension would generate a significant quantity of LFG over a sufficient long period. The energy associated with the methane in the LFG can be utilized as fuel for engines or, after purification, can be fed into the power supply and natural gas distribution system, where appropriate. The DBO Contractor is required to explore the LFG recovery and utilization system for the WENT Landfill Extension site with the latest technologies in the industry. Emission from LFG would thus be less than the current assessment.
NO2, SO2, RSP, Vinyl Chloride and Benzene are the key control parameters which will be quantitatively modelled to assess their potential impact.
3.5.3.4 Emissions from WENT Landfill Extension and existing WENT Landfill
Emissions from Active Tipping Face and Construction Plants
Based on long-term operation practice in existing WENT Landfill, active tipping during daily operation phase for the WENT Landfill Extension is estimated to be two cells with a rough dimension of 60m x 30m for MSW+LCW (Landfilled Construction Waste) + other special wastes. Most of the inactive areas in other phases are covered by impermeable sheets. Hence, for the active phase being implemented, the entire phase would be generating TSP which would be quantitatively included in the model.
Gaseous emissions such as nitrogen dioxide (NO2) and sulphur dioxide (SO2) will be generated from the operation of diesel-fuelled construction for the following activities.
· Deposition and compaction of waste – transportation, deposition and compaction of waste;
· Placement and removal of daily covered materials – by excavator, bulldozer, dump truck, vibratory roller and loader; and
· Capping and landscaping (progressive restoration) – by bulldozer, dump truck, vibratory roller, loader and mobile crane.
These plants will be located across the site, depending on need, in active and inactive areas. The nearest representative ASR, CLP Power Plant, is located at about 850 m away from the nearest construction site boundary. The total gaseous emissions generated by the plant over each tipping area are small (only two cells of 60m x 30m) and it will disperse and dilute with the ambient air very rapidly. Therefore, the potential air quality impact associated with operation of the construction plants on the identified ASR is envisaged to be limited and minor.
The management of fugitive dust at the WENT Landfill Extension will be similar to that being implemented at the existing WENT Landfill and will include immediate compaction of the fill area; regular damping down of the surface of the haul road; provision of vehicle washing facility for RCVs at the exit of the WENT Landfill Extension (to ensure no significant dust will be brought onto the public road); and regular cleaning of the main access road and waste reception area by road sweeper. With the implementation of good site practice, adverse dust emission in operating landfill is not anticipated.
Emissions of LFG / VOCs from Landfill Surfaces
Surface emission is controlled by extracting LFG from the waste mass to the flaring system for final destruction. Active extraction system by pumping will be applied and the inactive phase will be sealed and covered by impermeable plastic sheet cover. The edge of plastic sheet cover will be buried and covered underground.
For safety reason, the oxygen content in the LFG needs to be controlled to the minimum so as to reduce the risk of explosion at the flare. Therefore, the chance of oxygen infiltration or LFG migration at the edge of the covering sheet will be kept to the minimum. Periodic monitoring is being conducted at the site boundary to ensure the ambient VOCs concentration is within the health and safety limit. In accordance with the site investigation records for the past 10 years, there were no exceedance of VOCs limits at the site boundary.
When the existing WENT Landfill is restored, the landfill tipping areas will be capped with plastic sheet together with a thick layer of covering soil similar to other restored landfill sites and hence, the VOC emission will be insignificant.
By the time when the WENT Landfill Extension is in operation, the existing WENT Landfill will be capped with thick soil and equipped with active LFG extraction system. The surface emission from existing WENT Landfill will not be an issue based on the observation from other restored landfills in HK. In order words, the ambient VOC level would be significantly lower than the past monitoring data after restoration of existing WENT Landfill.
For the WENT Landfill Extension, after final levels of waste are reached, a protective soil layer will be placed over the waste before placing the final cap. The final cap comprises geotextile, geomembrane, HDPE liner, geonet, geotextile filer and a soil layer. The impermeable liner and cap will form a containment of void for waste so as to ensure that the waste is completely separated from the surrounding environment. Hence, this containment system will ensure minimal runoff and groundwater entering the waste and prevent off-site migration of leachate, odour and landfill gas. Figure 7.3 show the typical configuration of the liner system and the cap.
Surface emission from the existing restored WENT Landfill will not be an issue after capping. For WENT Landfill Extension, more strengthen requirements on LFG collection and LFG treatment efficiency will be provided, only a very small portion of VOC would be escaped from the active tipping phase.
Subject to future engineering design, the arrangement of the landfill gas collection system and surface covering material for inactive tipping area could be further improved by modern technology. Regular VOC monitoring will be conducted during the construction, operation, restoration and aftercare stages of the WENT Landfill Extension. Adverse impact on LFG emission is not anticipated.
3.5.3.5 Cumulative Impacts from Other Sources
The cumulative air quality assessment would need to take into account a number of concurrent sources as summarised below.
· WENT Landfill Extension
· Existing WENT Landfill;
· Marine Emission;
· Sludge Treatment Facilities (STF);
· EcoPark;
· Green Island Cement;
· Shiu Wing Steel Mill;
· Castle Peak Power Station; and
· Black Point Power Station.
As it is aware that the approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008) has assessed the cumulative impact from these sources, the emission rates presented in the STF EIA were therefore adopted in this assessment.
3.5.3.6 Odour Emission from Waste Filling Activities and Operation of LTP
Odour Emission from Refuse Disposal/Tipping Activities
The WENT Landfill Extension will be designed to receive municipal solid waste (MSW), construction waste and other special wastes. The WENT Landfill Extension is scheduled to start operation in end 2010s. By that time, sludge will be diverted to the proposed Sludge Treatment Facilities for treatment and disposal.
Based on our current assumption, upon the completion of the STF, all the sludge will be incinerated at STF and the ash will be disposed of at the WENT Landfill Extension. Thus, WENT Landfill Extension would not receive sludge during normal design condition. However, under special circumstances, sludge may be disposed of at the WENT Landfill Extension and the sludge will be immediatedly covered, as similar to the case of special waste to minimise the odour impact.
The operation life is expected to be about 10 years. WENT Landfill Extension will be developed in 6 phases (Phases 1 to 6) and open to receive waste from 8am to 8pm every day. The active tipping face is about 60m x 30m (maximum 2 numbers at the later stage of landfill development) and will be covered with 150mm of cover soil at the end of each working day.
|
Waste Reception Area : |
o All refuse collection vehicles (RCVs) visiting the WENT Landfill Extension are of enclosed-type and expected to comply with the relevant regulations and to be properly maintained; hence the potential odour emission from RCVs is anticipated to be minimal. |
|
Active Tipping Faces : |
o The RCVs delivering MSW and construction waste will be directed to the active tipping faces for unloading. The operation at the active tipping faces will be similar to that of the existing WENT Landfill. |
For the worst-case scenario, there will be 2 active tipping faces working simultaneously within the WENT Landfill Extension. The size of each tipping face will be about 60m x 30m. The wastes will be promptly spread by bulldozer and compacted by a landfill compactor to minimize the exposure time of MSW. At the end of the day, the WENT Landfill Extension will be closed and the compacted waste will be covered with 150mm of cover soil immediately. Therefore, odour emissions from the active tipping face are expected during the operating hours; however, the emissions will be much reduced thereafter.
Special waste will be disposed of at the special waste trench which will be immediately covered with soil. The reasons for not including the trench for special waste in the odour assessment are as follows:
· The use of special trench is on an as-needed basis, instead of on a regular basis.
· The size of the special trench is comparatively much small than the tipping face and depends on the quantity of the special waste to be disposed of. According to the current information, the special trench is about 5m x 3m under normal operation.
· The special waste trench will be immediately covered with soil after disposal.
Although the special trench is not expected to occur regularly, however, from the worst-case assessment principle, a special cell for animal carcasses with dimension of 3m x 3m is assumed in the model.
|
Daily Covered Area : |
o At the end of each working day (i.e. after 8pm), the active tipping faces (a total area of 60m x 30m x 2) will be covered with 150mm of soil and compacted. |
|
Intermediate Cover Area / Inactive tipping Phase: |
o Apart from the active tipping phase, all inactive phases of the WENT Landfill Extension will be covered with 300mm to 600mm of soil / impermeable liner on top in order to enhance landfill gas extraction, and to minimize rainwater infiltration into waste and odour emissions. It is therefore anticipated that no odour will be emitted from this area. |
|
Final Cover Area : |
o After waste filling reaches the final levels, a capping system will be installed. The capping system will comprise (from bottom to top) a soil layer, a non-woven geotextile, an HDPE liner (impermeable layer), a sub-soil drainage layer and a final cover soil layer. Permanent gas extraction system will be installed to extract LFG from the waste mass. Planting will also be provided for the final covered area. It is therefore anticipated that no odour will be emitted from this area. |
|
Main Haul Road to Active Tipping Faces : |
o The MSW will be delivered in RCVs with enclosed compactor body. It is therefore anticipated that the potential odour emission from RCVs will be minimal. |
|
Summary : |
o Only the active tipping faces (daytime) and daily covered area (night-time) will be the major odour sources from the operation phase. |
Odour Emission from Operation of Leachate Treatment Plant
To facilitate the development of WENT Landfill Extension, the existing leachate treatment plant of the existing WENT Landfill will be demolished. New on-site leachate treatment plants will be provided for the existing WENT Landfill and its extension. All the storage tanks and SBR tanks will be enclosed with ventilation and emissions will be extracted to suitable odour removal filters for treatment. An overall odour removal efficiency of 99% will be achieved.
According to the latest information, the odour removal efficiency would practically achieved 99%. In the approved EIA Report for NENT Landfill Extension, a 99% of odour removal efficiency was adopted. The locations of the deodouriser units are illustrated in Figure 3.6.
3.5.4 Restoration and Aftercare Phase
Fugitive Dust
In view of the nature and scale of the final capping operation, lesser plant will be employed for dusty operations during the restoration phase for final capping. During aftercare period, only a few numbers of plant will be required for regular maintenance.
Gaseous Emission
Nevertheless, emission from the flaring system, LFG power generation, leachate treatment plant and the ASP would still generate some gaseous emission.
In terms of gaseous emission, there will be very light activities within the capped area. Active control system for landfill gas and leachate will be operated without causing adverse environmental impact. In accordance with the observations from some restored landfills, detectable surface gas and odour emission are not anticipated.
As both the emission strength and scale of the operation will be less compared to the construction and operation phases, detailed assessment is not required since the impacts from construction and operation phases at the worse case have been assessed.
LFG
According to the latest design information, the maximum production rate of LFG for WENT Landfill Extension would occur during the operation phase. The LFG generation from the existing WENT Landfill at that time should be very small, probably < 5%. Hence, the assessment of the operation phase would have represented the worst case scenario as far as the LFG impacts are concerned.
Figures 3.5a to 3.5b show the locations of all the air quality emission sources during the restoration and the aftercare phases.
3.6.1 Construction Phase
3.6.1.1 Dust Emission Sources
The prediction of dust emissions is based on typical values and emission factors from USEPA, AP-42 "Compilation of Air Pollutant Emission Factors". References of the calculations of dust emission factors for different dust generating activities are listed in Table 3.18a.
Table 3.18a References of dust emission factors for different activities
|
Activities |
Reference |
Operating Sites |
Equations & Assumptions |
|
Heavy construction activities including land clearance, ground excavation, cut and fill operations, construction of the facilities, drill & blast, plant movement and hauling over the site areas |
S.13.2.3.3 |
All construction and excavation sites |
E = 1.2 tons/acre/month of activity or = 2.69 Mg/hectare/month of activity |
|
Wind Erosion
|
S.11.9, Table 11.9.4 |
All construction sites, and stockpile areas, (all open sites) |
E = 0.85 Mg/hectare/yr (24 hour emission) |
As all the inactive phases within the WENT Landfill Extension will be covered with impermeable sheets, wind erosion and general construction in the active phase are the major sources of dust generation from the site. The construction periods are assumed 26 days a month and 12 hours a day (from 0700 – 1900). Whereas, there will be a 24 hours emission for wind erosion.
Table 3.18b Summary of modeling of construction dust
|
Operation |
Locations of Emission |
Activities |
|
WENT Landfill Extension |
||
|
Excavation and site formation |
Active construction (~10% of the phase under construction for calculating the 1-hr and 24 hr concentration whilst 10% of active construction area is evenly distributed within the entire active construction area for calculating the annual concentration) |
Heavy construction |
|
Other areas of the phase under construction |
Wind erosion |
|
|
Waste filling |
Entire area of phase being used |
Wind erosion |
|
Slope work and other activities for Nim Wan Road Diversion |
Slope work |
Heavy construction |
|
Slope work |
Wind erosion
|
|
|
Existing WENT Landfill |
||
|
Waste filling |
Entire area of phase being used |
Wind erosion |
|
Restoration |
Existing WENT (~10% of entire Existing WENT area) |
Heavy construction |
|
|
Entire Existing WENT area |
Wind erosion |
|
Construction ponds (as part of the ecological mitigation measures for WENT Landfill Extension |
|
Heavy construction & Wind erosion |
3.6.1.2 Modelling Scenarios
The preliminary construction programme for the WENT Landfill Extension is given in Appendix 2.1. Also shown in the programme is the activities that are anticipated for the existing WENT Landfill.
A review of the preliminary construction programme has been conducted to identify the appropriate modelling scenarios for the purpose of identifying the worst case scenarios. Since the emission factors for heavy construction is much higher than that for the wind erosion, emphasis has been paid to identify any time slots at which different activities for heavy construction would overlap. A summary of the dust modelling scenarios is given below.
|
Scenarios |
Justifications |
|
1A & 1B |
o Early 2017 – 3rd Quarter of 2017 o Excavation works for Phase 1 o Overlap with the operation phase of the existing WENT Landfill (ie waste filling) o Before 2017, the construction of Phase 2 would not be in place and hence would not be as worse of after early 2017
|
|
2A, 2B & 2C |
o 4th Quarter of 2018 – Mid 2019 o Excavation works for Phases 2 & 3 overlap o Overlap with the Nim Wan Road diversion o Overlap with the restoration phase of the existing WENT Landfill o Overlap with the operation phase of Phase 1
|
|
3A & 3B |
o Early 2022 to mid 2022 o Excavation works for Phases 4 & 5 overlap o Overlap with the ponds construction o Overlap with the restoration phase of the existing WENT Landfill o Overlap with the operation phase of Phases 1, 2, & 3 In early 2023, the construction of Phases 5 & 6 would also overlap with the pond construction although most of the construction activities of the ponds would have been completed. Besides, the total area of the Phases 5 & 6 would be less than that of Phases 4 & 5. Furthermore, the restoration works for existing WENT Landfill would have been completed. Hence, it is considered that Scenarios 3A and 3B would have represented a more conservative case already. |
For each scenario, different sub-scenarios would be conducted to locate the 10% active construction area at closer distance to different ASRs so as to simulate the worst case impacts. Figures 3.4a to 3.4m show the locations of these dust emission sources for different modelling scenarios.
3.6.1.3 Dispersion Modelling
Dust impact assessment has been undertaken using the FDM model. Table 3.19 gives the list of modelling parameters. Details of the emission rates are listed in Appendix 3.3.
Table 3.19 Modeling parameters
|
Parameters |
Input |
Remark |
|
Particle size distribution |
1.25um = 3.06% 6.25um = 27.55% 20um = 69.39% |
Major dominant dust emission source in landfill is from unpaved road/working area. Owing to the lack of on-site monitoring data for particle distribution, it is the best estimate to assume the particle size distribution is the same as that for unpaved road. Table 13.2.2-2 of Section 13.2, USEPA AP-42, for unpaved road is adopted |
|
Particle density |
2.5g/m3 |
From Fugitive Dust Model (FDM) Manual |
|
Background Concentration |
5-year annual averaged value recorded at EPD’s Yuen Long monitoring station (Yuen Long) |
'TOTAL' Air Quality Guideline |
|
Modeling mode |
Rural with terrain effect Dry deposit mode activated |
- |
|
Meteorological data |
Lau Fau Shan weather station |
Mixing height of 500m adopted in accordance with EPD “Guidelines on Choice of Models and Model Parameters” |
|
Emission period |
General construction activities during daytime working hours (8 am to 8 pm) Site erosion over 24-hour period |
- |
|
ASR calculating levels |
1.5m, 5m and 10m above ASR level |
- |
|
Good Site Practice – Standard Precautionary Measures |
Assume a 94% efficiency for watering 8 times daily during the day-time period as in general practice based on AP-42 reference. |
Periodic watering and covering of inactive construction area with plastic sheet cover. The effectiveness will be monitored in the EM&A. |
3.6.1.4 Cumulative Impacts
As can be seen from Section 3.6.1.2, the modelling scenarios have included the cumulative impacts from the existing WENT Landfill. For STF, according to their approved STF EIA Report, the construction of the proposed STF would commence by Mar 2010 and all the construction activities would be completed by Mar 2011. Since the construction of WENT Landfill Extension would only commence by mid 2010s, there would not be any cumulative construction impacts with STF.
For IWMF, the site selection process is still on-going and there is no implementation plan. Hence, it is not considered as a concurrent project and there would not be cumulative impacts.
3.6.2 Operation Phase
Based on the traffic forecast, there will be insignificant increased in road traffic during the operation of WENT Landfill Extension (the waste catchment will remain the same and there is no overlapping of operation with the existing WENT Landfill).
Vehicular emission from Lung Kwu Tan Road and Nim Wan Road were incorporated into the assessment. The assessment is based on the projected peak hour flows for the worst year of 2028 within 15 years of commencement of operation. With reference to the approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008), the same emission factor – Fleet Average Emission Factors for Euro IV Model in Year 2011– had been adopted in this assessment, as shown in the following Table 3.20a.
Table 3.20a Fleet Average Emission Factors for Euro IV Model in Year 2011
|
Vehicle Type |
Yr 2011 Emission Factors (g/km-veh) |
||||
|
P/C |
Taxi |
SPB |
HGV |
PT |
|
|
NOx |
0.54 |
0.49 |
4.96 |
3.46 |
6.15 |
The composite emission factors for the road links were calculated as the weighted average of the emission factors of different types of vehicles. Details of the peak hour traffic flows and the calculation of emission rates are presented in Appendix 3.4.
Modelling approach and assumptions for vehicular emission are presented in Section 3.6.2.8.
3.6.2.2 Marine Vessel Emission
Similar to the existing WENT Landfill, marine vessels will be used to transport waste from refuse transfer stations to the WENT Landfill Extension, and marine emission would need to be addressed.
The latest information on the operation mode and schedule of marine vessels has been obtained from the operators of these transfer station and is incorporated in the assessment. Detailed calculations of marine emission are given in Appendix 3.5. A summary of the emission inventory is summarised in Appendix 3.6.
Modelling approach and assumptions for Marine emission are presented in Section 3.6.2.8.
For NO2 concentration, the predicted NOX from idling barges and travelling barges would be separately converted to NO2 by adopting the OLM method (with the Yuen Long Ozone concentration).
3.6.2.3 Emission from the Ammonia Stripping Plant and Landfill Engine and Flaring Systems
AQO-Pollutants
The assessment has assumed the maximum LFG generation of 58,000 m3/hr over the entire life of the WENT Landfill Extension. At that period, the LFG generation from the existing WENT Landfill would have largely diminished from its maximum value of 54,000 m3/hr during its operation phase to 3,940 m3/hr.
The emission rates of NOx, SO2, and RSP are calculated based on the available landfill gas utilization rates and the emission factors from Table 4-4 of USEPA’s “Air Emissions from Municipal Solid Waste Landfills – Background Information for Proposed Standards and Guidelines, March 1991 (EPA-450/3-90-011a)”. This approach was also quoted in the EIA report “Sludge Treatment Facilities – Feasibility Study” (EIA-155/2008).
The following Table 3.20b summaries the emission rates of NOx, SO2, and RSP. Detailed calculations are presented in Appendix 3.5 and a summary of the emission inventory is given in Appendix 3.6.
Table 3.20b Emission Rate for AQO Pollutants
|
Facilities |
Emission Rate (g/s)* |
||
|
NOx |
SO2 |
RSP |
|
|
Emissions from WENT Landfill Extension |
|||
|
Thermal Destructor |
0.6786 |
0.0291 |
Negligible |
|
LFG Flare System |
0.3712 |
0.2273 |
Negligible |
|
LFG Power Generator |
0.0427 |
0.0048 |
0.0598 |
|
Emissions from Existing WENT Landfill |
|||
|
Thermal Destructor |
0.3770 |
0.0162 |
Negligible |
|
LFG Flare System |
0.0049 |
0.0030 |
Negligible |
|
LFG Power Generator |
0.0427 |
0.0048 |
0.0598 |
Note*:
Emissions from each chimney (2 nos. for Thermal Destructor, 3 nos for LFG Flare System, 2 nos. for LFG Power Generator). There are no standby units.
Non-AQO Pollutants
For the assessment of non-AQO criteria pollutants, an air quality assessment for toxic and flaring emissions will adopt hazard to human life approach to evaluate plant emission from WENT Landfill Extension alone. Based on international references and observations from other landfills in Hong Kong, Vinyl Chloride and Benzene are the key controlling parameters. ISCST3 modelling will be conducted at heights 1.5m above ASR level. Historical meteorological data from Lau Fau Shan weather monitoring station for Year 2006 will be applied.
For the cancer risk assessment, the modelled annual average concentrations will be multiplied by the Unit Risk Factors to obtain the maximum individual lifetime cancer risk. The individual annual risk can be obtained from the individual lifetime risk by dividing by 70 years which is the assumed average lifetime. The calculated individual lifetime risk should be compared with assessment criteria to check the acceptability of the risks at the identified ASRs. The results will be compared with the guideline stipulated under item 2 of Annex 4 of TM-EIAO.
For the non-cancer risk assessment, the modelled annual average and maximum 1-hour average concentrations, together with the background pollutant concentrations, should be directly compared with the chronic reference concentration and the acute reference concentration.
The following Table 3.21a summaries the emission rates of Vinyl Chloride and Benzene. Detailed calculations are presented in Appendix 3.5, and a summary of the emission inventory is given in Appendix 3.6.
Table 3.21a Emission Rate for Non-criteria Pollutants
|
Facilities |
Emission Rate (g/s)* |
|
|
Vinyl Chloride |
Benzene |
|
|
Emissions from WENT Landfill Extension |
||
|
Thermal Destructor |
2.058 x 10-5 |
3.046 x 10-5 |
|
LFG Flare System |
1.608 x 10-4 |
2.381 x 10-4 |
|
LFG Power Generator |
3.430 x 10-6 |
5.077 x 10-6 |
|
Emissions from Existing WENT Landfill |
||
|
Thermal Destructor |
1.143 x 10-5 |
1.692 x 10-5 |
|
LFG Flare System |
2.013 x 10-6 |
3.114 x 10-6 |
|
LFG Power Generator |
3.430 x 10-6 |
5.077 x 10-6 |
Note*:
Emissions from each chimney (2 nos. for Thermal Destructor, 3 nos for LFG Flare System, 2 nos. for LFG Power Generator). There are no standby units
3.6.2.4 Emissions from Active Tipping Area
In view of the small size of the active tipping face, adverse gases emission impact is not anticipated. No detailed modelling is therefore required.
3.6.2.5 Emissions from Other Industrial Plants
Other than the emissions from existing WENT Landfill and WENT Landfill Extension, the assessment has also considered other concurrent emission sources. Since the parameters and assumptions of cumulative impact assessment has already made in the approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008), the emission rates and other details of the emissions presented in the STF EIA are therefore adopted directly in this assessment. The emission inventories are presented in Appendix 3.6. The corresponding references for the emission factors are listed in Table 3.21b below:
Table 3.21b References for various Emission Sources
|
Source |
Reference |
|
Proposed STF |
Approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008) |
|
Green Island Cement Plant |
Specified Process License |
|
Eco-Park |
Approved EIA Study “Development of an EcoPark in Tuen Mun Area 38” (EIA-104/2005) |
|
Shiu Wing Steel Mill |
Approved EIA Study “Shiu Wing Steel Mill Tuen Mun Area 38” (EIA-028/BC) |
Modelling approach and assumptions for these emissions are presented in Section 3.6.2.8. For NO2 concentration, the predicted NOX from each of the above sources would be separately converted to NO2 by adopting the OLM method (with the Lau Fau Shan Ozone concentration).
3.6.2.6 Odour Emissions from Open Tipping Area and Leachate Treatment Facilities
The operation of the WENT Landfill Extension will be divided into 6 phases starting from the east and filling progressively to the west. Five worst-case scenarios have been identified for the odour impact assessment, which have taken into account the worst case odour impact to existing ASRs in Ha Pak Nai, Pak Long and Black Point Power Station. The locations of the active tipping areas for these scenarios are selected in consideration of their shortest distances from the ASRs. These scenarios are summarised in Table 3.22a and the worst-affected ASRs are listed in Table 3.22b. Figure 3.7a illustrates the locations of tipping faces under different modelling scenarios. Modelling approach and assumptions are presented in Section 3.6.2.8.
Table 3.22a Identified Worst-case Scenario for Odour Impact Assessment
|
Worst-case Scenario |
Location |
Odour Source |
Area |
Operation Period |
|
Scenario 1 |
Eastern end of Phase 1 |
Daytime |
|
|
|
· Active Tipping Area (2 nos.) |
60m x 3m |
8am-8pm |
||
|
· Maneuvering Area (2 nos.) |
60m x 10m |
8am-8pm |
||
|
· Compacted Area (2 nos.) |
60m x 17m |
8am-8pm |
||
|
· Special Cell for Animal Carcasses |
3m x 3m |
8am-8pm |
||
|
Night-time |
|
|
||
|
· Daily cover area (2 nos.) |
60m x 30m |
8pm-8am on the next day |
||
|
24-hour |
|
|
||
|
· Deodouriser Unit for WENT Landfill Extension |
10m [1] |
24-hour |
||
|
· Deodouriser Unit for Existing WENT Landfill |
10m [1] |
24-hour |
||
|
· Deodourizing Unit 1 in STF [2] |
2m [1] |
24-hour |
||
|
· Deodourizing Unit 2 in STF [2] |
10m [1] |
24-hour |
||
|
Scenario 2 |
North-east end of Phase 1 |
Same as Scenario 1 |
Same as Scenario 1 |
Same as Scenario 1 |
|
Scenario 3 |
Northern end of Phase 1 |
Same as Scenario 1 |
Same as Scenario 1 |
Same as Scenario 1 |
|
Scenario 4 |
Southern end of Phase 3 |
Same as Scenario 1 |
Same as Scenario 1 |
Same as Scenario 1 |
|
Scenario 5 |
Western end of Phase 4 |
Same as Scenario 1 |
Same as Scenario 1 |
Same as Scenario 1 |
Note:
[1] Stack height in meters is presented
[2] Cumulative odour impact from the proposed STF is incorporated in this assessment.
Table 3.22b Worst-affected ASR under Different Odour modelling Scenarios
|
|
Worst-affect ASR |
Location |
|
Scenario 1 |
A1-1, A1-2, A1-4 |
West & East Ha Pak Nai |
|
Scenario 2 |
A1-3 |
West Ha Pak Nai |
|
Scenario 3 |
A3-1 |
STF office |
|
Scenario 4 |
A4-1 |
Lung Kwu Sheung Tan |
|
Scenario 5 |
A2-1 |
Black Point Power Station (Office) |
3.6.2.7 Determination of Odour Emission Rates
In-situ odour sampling was adopted to collect odour strength for landfill site in Hong Kong. It is also noted that there is only one accredited laboratory in HK that can conduct such In-situ odour measurement (i.e. Odour Research Laboratory of HKPU).
Odour samples were taken using the flux chamber method which is the method recommended by the USEPA[1] and is also the most commonly used odour sampling method for large surface emission source such as landfill sites. The flux chamber used is a circular chamber with a diameter of 0.41m and an area of 0.13 m2. It was tightly placed on the surface of the odour source and the air inside the chamber was purged with nitrogen gas at a sweeping rate of 5 litres per minute. The odour sample was collected in a Tedlar bag at a rate of 3 litres per minute. Before taking the next sample, the flux chamber was cleaned with distilled water and then flushed with nitrogen for about 10 minutes to remove residual odour in the chamber.
The odour sampling and subsequent olfactometry tests were conducted by qualified odour panellists from HKPU. The qualified odour panellists had their individual odour threshold of n-butanol in nitrogen gas in the range of 20 to 80 ppb/v as required by the European Standard Method (EN 13725). Odour samples from the active tipping areas, inactive areas and the leachate lagoons of the existing WENT Landfill were collected for the assessment. Measurements were taken between 0900 and 1700 on 27, 28, 30 and 31 August 2007. The ambient surface odour emission fluxes and pollutant concentrations were measured during the reasonable worst-case temperature (mostly above 30oC). Details of the measurement results are listed in Appendix 3.7.
Temperature is one of the factors which are thought to affect the strength of the odour emission. By reviewing the meteorological data recorded at the nearest weather station at Lau Fau Shan in 2006, the number of hours having the ambient temperature lower than 30oC was about 95%. However, the odour emission rates were measured at temperatures over 30oC in many instances. As a result, the measured odour emission rates were adopted directly to represent a reasonable worst case scenario. In addition, with reference to the approved EIA “South East new Territories (SENT) Landfill Extension” (EIA-143/2007), a reasonable worst case scenario was represented by the average of the measured odour emission rates to avoid overestimating the odour impact. The same approach is adopted in this assessment. The reasonable odour emission rates for area source and point source are presented in Table 3.23a and Table 3.23b respectively.
Table 3.23a Odour Emission Rates for Area Sources (Temperature under reasonable worst-case condition at 30°C)
|
Odour Source |
Odour Source Emission Rate, OU/m2s |
|
Day time: |
|
|
Active Tipping Area – MSW and CW |
3.30 |
|
Manoeuvring Area |
0.5 |
|
Compacted waste Area |
0.5 |
|
Special Cell for Animal Carcasses |
1.48 |
|
Night-time: |
|
|
Daily cover overlying waste |
0.35 |
Table 3.23b Odour Emission Rates for Point Sources (Temperature under reasonable worst-case condition at 30°C)
|
Odour Source |
Odour Source Emission Rate, OU/s |
|
24-hours: |
|
|
Deodourised Unit for WENT Landfill Extension |
115.42 [1] |
|
Deodourised Unit for Existing WENT Landfill |
90.78 [1] |
|
Deodourising Unit 1 for STF |
46.69 [2] |
|
Deodourising Unit 2 for STF |
85.61 [2] |
Note:
[1] Refer to Appendix 3.8 for the detailed breakdown
[2] Reference from the approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008)
3.6.2.8 Air Dispersion Model and Modelling Parameters
Vehicular Emission
The USEPA approved line source air dispersion model, CALINE4 developed by the California Department of Transport is used to assess vehicular emissions impact from existing and planned road network. In view of the limitation of the CALINE4 model in modelling elevated roads higher than 10m, the road heights of elevated road sections are set to 10m maximum in the CALINE4 model as the worst-case assumption. Modelling parameters adopted for the worst-case conditions were determined according to EPD’s “Guidelines on Choice of Models and Model Parameters “ as follows:
· Wind speed : 1 m/s
· Wind direction : worst angle
· Stability : F class
· Surface Roughness : 60cm
· Standard deviation : 5o
· Mixing height : 500m
· Temperature : 25 oC
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. The conversion of the NO2, and RSP (from vehicular emission using CALINE) from maximum 24-hour concerntration to annual concentration would be based on the contribution of vehicular emission to the cumulative impact at each ASR excluding background concentration and contribution from BPPS/CPPS, as described below:
where X is the contribution of vehicular
emission to the cumulative impact excluding background and contributions from
BPPS/CPPS:
Veh24-hour = Max. 24-hour contribution from vehicular emission
VehAnual = Annual contribution from vehicular emission
C24-hour = Max. 24-hour contributions from WENT Extension, Existing WENT Landfill, Marine Emission, STF, Green Island Cement Plant, Eco Park and Shiu Wing Steel Mill
CAnnual = Annual contributions from WENT Extension, Existing WENT Landfill, Marine Emission, STF, Green Island Cement Plant, Eco Park and Shiu Wing Steel Mill
Gaseous Emission
Gaseous emissions, including WENT Landfill Extension, existing WENT Landfill, Marine Emission, Proposed STF, Green Island Cement Plant, Eco-Park, and Shui Wing Steel Mill have been assessed by ISCST3 model. The modelling parameters are listed in Table 3.24.
Table 3.24 Modeling Parameters
|
Parameters |
Input |
Remark |
|
Background Concentration |
5-year annual averaged value recorded from existing WENT Landfill monitoring data and Yuen Long Monitoring Station |
Follow 'TOTAL' Air Quality Guideline and health risk approach |
|
Modeling mode |
Rural with terrain effect |
|
|
Meteorological data |
Lau Fau Shan weather station in Year 2006; in accordance with EPD Guidelines on Choice of Models and Model Parameters |
|
|
Emission period |
24-hour operation except Marine Emission |
|
|
ASR calculating levels |
1.5m, 5m and 10m above ASR level |
Modelling results are compared with the
respective criteria. A summary of the relevant criteria is listed in Table
3.25.
Table 3.25
Modeling Criteria
|
Parameters/
Pollutants |
Relevant Criteria/Remark |
|
·
NO2
·
SO2
·
RSP |
·
·
24-hour
averaged criteria ·
Annual
averaged criteria |
|
·
Benzene ·
Vinyl
Chloride |
WHO, USEPA, CEPA (Remarks: ·
Carcinogenic
Risk: Annual average concentrations have been multiplied by the Unit Risk
Factors to obtain the maximum individual lifetime risk. The individual annual
risk could be obtained from the individual lifetime risk divided by 70 years
which is the assumed average lifetime. The calculated individual lifetime
risk has been compared with assessment criteria to check the acceptability of
the risks at the identified ASRs. ·
Non-carcinogenic risk: Annual average and maximum
1-hour average concentrations together with the background pollutant
concentrations should be directly compared with the chronic reference
concentration and the acute reference concentration.) |
NO2/NOx Conversion
The NO2/NOx conversion for all emissions was estimated based on the Ozone Limiting Method (OLM). The 5-year average of the annual average of the daily hourly maximum ozone concentration recorded at EPD’s Yuen Long Air Quality Monitoring Station of 78.3 μg/m3 was adopted for the calculation. The NO2/NOx conversion was calculated as follows:
[NO2]pred = 0.1 x [NOx]pred + MIN {0.9 x [NOx]pred，or (46/48) x [O3]bkgd}
where
[NO2]pred = the predicted NO2 concentration
[NOx]pred = the predicted NOx concentration
MIN = the minimum of the two values within the brackets
[O3]bkgd = the representative O3 background concentration
(46/48) = the molecular weight of NO2 divided by the molecular weight of O3
The OLM were applied to the following sources individually for the estimation of NO2 concentrations:
· WENT Landfill Extension;
· Existing WENT Landfill;
· Marine Emission (manoeuvring);
· Marine Emission (idling)
· Proposed STF;
· Green Island Cement Plant;
· Eco-Park;
· Shui Wing Steel Mill; and
· Road Traffic Emission.
Odour Emission
The 5-second Odour Unit (OU) at the ASRs was assessed by AUSPLUME model. The use of AUSPLUME model has been approved by the EPD. It is based on the Gaussian dispersion equation and is similar to ISCST3. Other modelling parameters were determined according to EPD’s “Guidelines on Choice of Models and Model Parameters”.
Hourly meteorological data as recorded at the Lau Fau Shan Weather Station in 2006 was obtained from the Hong Kong Observatory for modelling the 1-hour average odour concentrations at the representative sensitive receivers.
Owing to the remote nature within 3km study radius, rural mode will be adopted in accordance with the USEPA Guideline for Air Quality Model. The modelling parameters will be determined in accordance with relevant international papers, such as “Workbook of Atmospheric Dispersion Estimates: An Introduction to Dispersion Modelling, Second Edition, D. Bruce Turner”. In accordance with the research, the Pasquill-Gifford parameters, and for rural mode dispersion can be estimated for a short averaging time period (3-minutes), which is equivalent to computer dispersion models set up to estimate conservative 1-hour average concentration. In other words, the predicted 1-hour average concentrations from AUSPLUME model will be equivalent to 3-minute average concentrations in rural condition.
To further convert these 3-minute average concentrations to 5-second averages, a Stability Class Conversion Factor of 10 will be employed for those hours with very unstable atmospheric Stability Classes A-B, and a factor of 5 will be used for those hours with Stability Classes C-F, in accordance with the “Odour Control – A concise Guide, Warren Spring Laboratory”. By taking both factors into account, the following Stability Class conversion factors would be applied. Table 3.26 shows the conversion factors applied to determine the 5-second value under different stability classes.
Table 3.26 Multiplying factors for averaging time correction for odour assessment (taking account of EPD’s Guideline on Choice of Models and Model Parameters)
|
Atmospheric Stability Class |
Conversion Factor from 1 hour to 15 min |
Conversion Factor from 15 min to 3 min |
Conversion Factor from 3 min to 5s |
Resultant Conversion Factor from 1 hour to 5s |
|
A |
1 |
1 |
10 |
10 |
|
B |
1 |
1 |
10 |
10 |
|
C |
1 |
1 |
5 |
5 |
|
D |
1 |
1 |
5 |
5 |
|
E |
1 |
1 |
5 |
5 |
|
F |
1 |
1 |
5 |
5 |
These conversion factors were applied to the emission rates input in the model run. The modelled results will therefore be the 5-second odour concentrations. Table 3.27 presents the corrected odour emission rates for the modelling run.
Table 3.27 Corrected Odour Emission Rates
|
Modeling Period |
Odour Source |
Odour Emission Rate, OU/m2s |
Corrected Odour Emission Rates, OU/m2s |
|
|
Stability Class A & B [3] |
Stability Class C – F [4] |
|||
|
Day-time (8am-8pm) |
Active Tipping Area |
3.30 |
33.0 |
16.5 |
|
Maneuvering Area |
0.50 |
5.0 |
2.5 |
|
|
Compacted Area |
0.50 |
5.0 |
2.5 |
|
|
Special Cell for Animal Carcasses |
1.48 |
14.8 |
7.4 |
|
|
Night-time (8pm-8am on the next day) |
Daily cover area |
0.35 |
3.5 |
1.75 |
|
24-hours |
Deodourised Unit for WENT Landfill Extension |
115.42 OU/s [1] |
1154.2 |
577.1 |
|
Deodourised Unit for Existing WENT Landfill |
90.78 OU/s [1] |
907.8 |
453.9 |
|
|
Deodourising Unit 1 for STF |
46.69 OU/s [2] |
466.9 |
233.45 |
|
|
Deodourising Unit 2 for STF |
85.61 OU/s [2] |
856.1 |
428.05 |
|
Notes:
[1] refer to Appendix 3.8 for the detailed breakdown
[2] Reference from the approved EIA Study “Sludge Treatment Facilities” (EIA-155/2008)
[3] A conversion factor of 10 is applied to convert the results from 3 minutes to 5 seconds.
[4] A conversion factor of 5 is applied to convert the results from 3 minutes to 5 seconds.
The overall modelling parameters are summarised in Table 3.28 for ease reference.
Table 3.28 Modeling parameters
|
Parameters |
Input |
Remark |
|
Background Concentration |
No (major source from landfill) |
In accordance with the preliminary design information, 5 scenarios have been assessed. |
|
Modeling mode |
Rural model with flatted terrain |
|
|
Meteorological data |
Lau Fau Shan weather station in Year 2006 |
|
|
Emission period |
· Daytime emission (8am-8pm) from tipping at active cell · Night time emission (8pm-8am) from daily cover overlying tipped waste · Whole day for emission from leachate treatment facilities · Effective temporary covers with impermeable plastic sheets will be applied at the inactive tipping areas, and no emission is anticipated. · Active LFG extraction system with an engineering cap will be applied at the restored WENT Landfill and no emission is anticipated. |
In accordance with the preliminary design information, 5 scenarios have been assessed. |
|
ASR calculating levels |
1.5m, 5m and 10m above local ground |
Notes: LFG extraction system would be provided for inactive tipping areas.
The locations of odour emission sources from existing WENT Landfill and its extension are shown in Figure 3.6 and Figure 3.7a.
3.7.1 Construction Phase
With the provision of 8 times / day of watering, the predicted maximum 1-hour and 24-hour average TSP concentration at the ASRs will be within the 500µg/m3 and 260 µg/m3 criterion, respectively. No adverse construction dust impact is anticipated. When the actual construction programme and methodology is finalised by the DBO Contractor, this measures can be further reviewed and verified by the EM&A monitoring.
Tables 3.29 and 3.30 show the 1-hour and 24-hour averaged TSP levels at the identified ASRs. Details of the assessment results are given in Appendix 3.9.
Table 3.29 Predicted highest 1-hr TSP Concentrations
|
ASR |
Max
1- hr TSP Concentration, ug/m3 [1] |
||
|
Scenario 1 (1A and 1B) |
Scenario 2 (2A, 2B and 2C) |
Scenario 3 (3A and 3B) |
|
|
Ha Pak Nai |
127 – 188 |
138 - 243 |
140 - 243 |
|
Black Point Power Station |
117 – 119 |
129 - 143 |
137 - 143 |
|
STF Office |
139 – 192 |
146 - 203 |
149 - 174 |
|
Lung Kwu Sheung Tan |
118 – 119 |
134 - 137 |
134 - 138 |
|
Criterion |
500 |
500 |
500 |
Notes:
[1] A background concentration of 103ug/m3 has been included and 8 times of watering per day (during daytime only) has been adopted.
Table 3.30 Predicted highest 24-hr TSP Concentrations
|
ASR |
Max
24- hr TSP Concentration, ug/m3 [1] |
||
|
Scenario 1 (1A and 1B) |
Scenario 2 (2A , 2B and 2C) |
Scenario 3 (3A and 3B) |
|
|
Ha Pak Nai |
108 - 123 |
111 - 139 |
112 - 140 |
|
Black Point Power Station |
107 |
114 - 118 |
114 - 115 |
|
STF Office |
119 - 128 |
120 - 133 |
123 - 128 |
|
Lung Kwu Sheung Tan |
106 - 107 |
110 - 112 |
110 - 111 |
|
Criterion |
260 |
260 |
260 |
Notes:
[1] A background concentration of 103ug/m3 has been included and 8 times of watering per day (during daytime only) has been adopted.
It can be seen from the above table that, after implementing 8 times of watering / day (during daytime only), both the 1-hr TSP and 24-hr TSP would be comply with the respective criterion at all the ASRs and there are no residual dust impacts for these parameters. The annual TSP concentrations have also been assessed for Scenario 1, Scenario 2 and Scenario 3 and the cumulative (i.e. WENT Landfill Extension and existing WENT Landfill) annual TSP concentrations are summarized in Table 3.30a. The project contributions to the annual TSP concentrations are summarized in Table 3.30b. Details of the assessment results are given in Appendix 3.9.
Table 3.30a Predicted Annual TSP Concentrations
|
ASR |
Annual TSP Concentration - Cumulative [1] |
||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
|
|
Ha Pak Nai |
103-105 |
104-106 |
104-106 |
|
Black Point Power Station |
104 |
107 |
107 |
|
STF Office |
111-113 |
113-115 |
114-116 |
|
Lung Kwu Sheung Tan |
103 |
104 |
104 |
|
Criterion |
80 |
80 |
80 |
Notes:
[1] A background concentration of 103ug/m3 has been included and 8 times of watering per day (during daytime only) has been adopted.
Table 3.30b Predicted Annual TSP Concentrations – Contribution from WENT Landfill Extension
|
ASR |
Annual TSP Concentration – Project Contribution [1] |
||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
|
|
Ha Pak Nai |
0.1-0.2 |
0.2-0.4 |
0.3-0.5 |
|
Black Point Power Station |
0.4-0.5 |
3.0-3.2 |
2.9-3.1 |
|
STF Office |
2.4-3.3 |
2.8-3.6 |
4.0-4.9 |
|
Lung Kwu Sheung Tan |
0.1-0.2 |
0.8-0.9 |
0.8-0.9 |
Notes:
[1] 8 times of watering per day (during daytime only) has been adopted.
It can be seen from the above table that the cumulative (i.e. WENT Landfill Extension and existing WENT Landfill) annual TSP concentrations are in the range 103 – 116ug/m3 which have exceeded the criterion of 80ug/m3. This is obviously due to the high background concentration of 103ug/m3. However, it can also be seen from the above that the contribution from the WENT Landfill Extension is less than 1 ug/m3 for all the residential developments and place of worship (Ha Pak Nai and Lung Kwu Sheung Tan) in the vicinity. This is less than 1% of the annual AQO (0.8 ug/m3). For the receivers in Black Point Power Station and STF, however, the contributions would be higher, in the range of 0.4 – 3.2 ug/m3 and 2.4 – 4.9 ug/m3 respectively, which would constitute about 0.5 - 4% and 3 - 6.1%of the annual AQO and 0.4 – 3.1% and 2.3 – 4.8% of the background concentration. However, it should be noted that the office areas of STF and the Black Point Power Station are central air-conditioned and hence any typical dust filters associated with the air-conditioning system would reduce at least 50% of the TSP level and hence would enable achieving the criterion. Hence, the cumulative annual TSP concentrations at Black Point Power Station and STF would be 52 - 54 and 56 - 58 ug/m3 respectively, which are within the annual AQO. The pollutant contours are given in Figures 3.8a to 3.8n.
3.7.1.1 “What if IWMF not proceed”
The feasibility of IWMF is still being conducted and there is no decision on the implementation programme and site selection. In case the IWMF is not located at the middle ash lagoon, the boundary of the WENT Landfill Extension would be further expanded to include the middle lagoon. The assessment so far has assumed that the pollutant sources are close to the waste boundary which is much closer to the sensitive receivers. Hence, even the middle ash lagoon is employed for the IWMF, the worst case environmental impacts have already been addressed in the current assessment and no additional impact on the sensitive receivers would be generated.
3.7.2 Operation Phase
3.7.2.1 AQO Criteria Pollutant
The maximum predicted 1-hour, 24-hour and annual NO2 ,SO2 and RSP concentrations at the identified ASRs were presented in Table 3.31, Table 3.32a and Table 3.32b respectively. Detailed assessment results are presented in Appendix 3.10.
Table 3.31 Predicted Cumulative 1-hr, 24-hr, and Annual Average NO2 Concentration at Various Heights
|
ASR ID |
Assessment Height (mAG) |
Predicted Cumulative NO2 Concentration in ug/m3 |
||
|
1-hour |
24-hour |
Annual |
||
|
A1-1 |
1.5 |
285 |
105 |
64 |
|
5 |
285 |
105 |
64 |
|
|
10 |
284 |
105 |
64 |
|
|
A1-2 |
1.5 |
258 |
102 |
64 |
|
5 |
257 |
102 |
64 |
|
|
10 |
254 |
102 |
64 |
|
|
A1-3 |
1.5 |
240 |
96 |
63 |
|
5 |
240 |
96 |
63 |
|
|
10 |
239 |
96 |
63 |
|
|
A1-4 |
1.5 |
263 |
98 |
63 |
|
5 |
263 |
98 |
63 |
|
|
10 |
264 |
99 |
63 |
|
|
A2-1 |
1.5 |
163 |
98 |
63 |
|
5 |
163 |
98 |
63 |
|
|
10 |
163 |
98 |
63 |
|
|
A3-1 |
1.5 |
275 |
106 |
65 |
|
5 |
275 |
106 |
65 |
|
|
10 |
275 |
105 |
66 |
|
|
A4-1 |
1.5 |
290 |
132 |
69 |
|
5 |
290 |
132 |
69 |
|
|
10 |
290 |
132 |
69 |
|
|
|
AQO Criteria |
300 |
150 |
80 |
Table 3.32a Predicted Cumulative 1-hr, 24-hr, and Annual Average SO2 Concentration at Various Heights
|
ASR ID |
Assessment Height (mAG) |
Predicted Cumulative SO2 Concentration in ug/m3 |
||
|
1-hour |
24-hour |
Annual |
||
|
A1-1 |
1.5 |
239 |
92 |
28 |
|
5 |
239 |
92 |
28 |
|
|
10 |
239 |
92 |
28 |
|
|
A1-2 |
1.5 |
232 |
91 |
28 |
|
5 |
232 |
91 |
28 |
|
|
10 |
232 |
91 |
28 |
|
|
A1-3 |
1.5 |
223 |
90 |
28 |
|
5 |
223 |
90 |
28 |
|
|
10 |
223 |
90 |
28 |
|
|
A1-4 |
1.5 |
232 |
91 |
28 |
|
5 |
232 |
91 |
28 |
|
|
10 |
232 |
91 |
28 |
|
|
A2-1 |
1.5 |
54 |
69 |
27 |
|
5 |
54 |
69 |
27 |
|
|
10 |
54 |
69 |
27 |
|
|
A3-1 |
1.5 |
220 |
90 |
28 |
|
5 |
220 |
90 |
28 |
|
|
10 |
220 |
90 |
28 |
|
|
A4-1 |
1.5 |
59 |
71 |
28 |
|
5 |
59 |
71 |
28 |
|
|
10 |
59 |
71 |
28 |
|
|
|
AQO Criteria |
800 |
350 |
80 |
Table 3.32b Predicted Cumulative 24-hr and Annual Average RSP Concentration at Various Heights
|
ASR ID |
Assessment Height (mAG) |
Predicted Cumulative RSP Concentration in ug/m3 |
|
|
24-hour |
Annual |
||
|
A1-1 |
1.5 |
73 |
65 |
|
5 |
73 |
65 |
|
|
10 |
73 |
65 |
|
|
A1-2 |
1.5 |
72 |
64 |
|
5 |
72 |
64 |
|
|
10 |
72 |
64 |
|
|
A1-3 |
1.5 |
73 |
64 |
|
5 |
73 |
64 |
|
|
10 |
73 |
64 |
|
|
A1-4 |
1.5 |
79 |
65 |
|
5 |
79 |
65 |
|
|
10 |
78 |
65 |
|
|
A2-1 |
1.5 |
92 |
66 |
|
5 |
92 |
66 |
|
|
10 |
92 |
66 |
|
|
A3-1 |
1.5 |
76 |
65 |
|
5 |
76 |
65 |
|
|
10 |
76 |
65 |
|
|
A4-1 |
1.5 |
84 |
65 |
|
5 |
83 |
65 |
|
|
10 |
83 |
65 |
|
|
|
AQO Criteria |
180 |
55 |
All the results are within the relevant AQO criteria, except the annual RSP concentrations at all the identified ASRs. According to the detailed assessment results presented in Appendix 3.10, it is found that the contribution from the Project (WENT Landfill Extension), Existing WENT Landfill and marine emissions, is less than 1% of the AQO. Moreover, the background RSP concentration of 64 μg/m3 adopted from Air Monitoring Station at Yuen Long has already exceeded the AQO criteria of 55 μg/m3, adverse air quality impact arisen from the Project is relatively insignificant, and therefore, mitigation measures are not required.
Apart from the identified ASRs, the hourly and/or daily contours plots for NO2, SO2 and RSP at 1.5m above ground are also produced to illustrate if there would be any area(s) within predicted exceedance of the AQO. Contours are plotted for the overall area (with a coarser grid size of 500m) and four focused area, including Ha Pak Nai Area, STF office, Black Point Power Station and Lung Kwu Tan Area (with a finer grid size of 100-200m). Figures 3.9a to 3.9h illustrate the hourly/daily/annual contour plots for NO2, SO2 and RSP. It is observed that there are no air sensitive uses within the exceedance area(s).
3.7.2.2 Non-criteria Pollutants
The maximum hourly and annual averaged concentrations of non-criteria pollutants (vinyl chloride and benzene) were predicted. The cumulative cancer risk for benzene and vinyl chloride (i.e. cancer risk of vinyl chloride plus that of benzene) is also within the cancer risk criteria. The contribution from the ASP, flare and generator plants are insignificant. Tables 3.33a and 3.33b show the non-criteria pollutant levels at the identified ASRs. Detailed results for non-criteria pollutants are given in Appendix 3.11. The emission impacts at the ASR are within the acute and chronic health risk criteria.
Table 3.33a Predicted health risk level for benzene and vinyl chloride at various heights (background included)
|
ASR ID |
Height (mAG) |
Predicted max vinyl chloride concentrations (µg/m3 ) |
Predicted max benzene concentrations (µg/m3 ) |
||||
|
max 1-hr and annual averaged vinyl chloride (1) |
Predicted Individual Risk Level per Year for Chronic Effect |
Within Acute and Chronic Reference Conc and Individual Risk Level |
max 1-hr and annual averaged benzene level (2) |
Predicted Individual Risk Level per Year Chronic Effect |
Within Acute and
Chronic Reference Conc and Individual Risk Level |
||
|
A1-1 |
1.5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
|
10 |
~2.275 |
2.857E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
|
A1-2 |
1.5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
10 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
A1-3 |
1.5 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
5 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
|
10 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
|
A1-4 |
1.5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
10 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
A2-1 |
1.5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
5 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
10 |
~2.275 |
2.857E-13 |
within |
~3.95 |
2.571E-12 |
within |
|
|
A3-1 |
1.5 |
~2.275 |
5.714E-13 |
within |
~3.95 |
5.143E-12 |
within |
|
5 |
~2.275 |
7.143E-13 |
within |
~3.95 |
6.857E-12 |
within |
|
|
10 |
~2.275 |
1.143E-12 |
within |
~3.95 |
1.114E-11 |
within |
|
|
A4-1 |
1.5 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
5 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
|
10 |
~2.275 |
1.429E-13 |
within |
~3.95 |
1.714E-12 |
within |
|
Remarks:
(1) Vinyl chloride background of 2.275µg/m3 has been incorporated; and
(2) Benzene background of 3.95µg/m3 has been incorporated
Table 3.33b Predicted cumulative health risk level from benzene and vinyl chloride at various heights (background included)
|
ASR ID |
Height (mAG) |
Predicted Individual Lifetime Risk Level per year (Benezene + Vinyl Chloride) |
Within Individual Risk Level |
|
A1-1 |
1.5 |
2.000E-12 |
within |
|
5 |
2.000E-12 |
within |
|
|
10 |
2.000E-12 |
within |
|
|
A1-2 |
1.5 |
2.857E-12 |
within |
|
5 |
2.857E-12 |
within |
|
|
10 |
2.857E-12 |
within |
|
|
A1-3 |
1.5 |
1.857E-12 |
within |
|
5 |
1.857E-12 |
within |
|
|
10 |
1.857E-12 |
within |
|
|
A1-4 |
1.5 |
2.857E-12 |
within |
|
5 |
2.857E-12 |
within |
|
|
10 |
2.857E-12 |
within |
|
|
A2-1 |
1.5 |
2.857E-12 |
within |
|
5 |
2.857E-12 |
within |
|
|
10 |
2.857E-12 |
within |
|
|
A3-1 |
1.5 |
5.714E-12 |
within |
|
5 |
7.571E-12 |
within |
|
|
10 |
1.229E-11 |
within |
|
|
A4-1 |
1.5 |
1.857E-12 |
within |
|
5 |
1.857E-12 |
within |
|
|
10 |
1.857E-12 |
within |
3.7.2.3 Odour Emission
The maximum 5-second averaged odour concentrations at the ASRs were predicted for 5 representative operating scenarios; namely Scenario 1 to Scenario 5, and the results are listed in Table 3.34. Exceedances of the odour criterion of 5 OU are expected at A1-3 (West Ha Pak Nai), A2-1 (Black Point Power Station), A3-1 (STF office) and A4-1 (Lung Kwu Sheung Tan). Mitigation measures are therefore required.
Table 3.34 Predicted Odour Concentration (OU, 5s averaging) under reasonably worst-case condition
|
ASR ID |
Height (m) |
Maximum Odour Concentration (OU) |
||||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
Scenario 4 |
Scenario 5 |
||
|
At 1.5m above Ground |
||||||
|
A1-1 |
1.5 |
3.1 |
3.9 |
4.3 |
1.5 |
1.6 |
|
A1-2 |
1.5 |
3.4 |
2.3 |
2.3 |
0.9 |
0.8 |
|
A1-3 |
1.5 |
3.8 |
5.2 |
2.9 |
1.4 |
0.9 |
|
A1-4 |
1.5 |
1.7 |
2.7 |
1.5 |
1.4 |
0.6 |
|
A2-1 |
1.5 |
1.7 |
1.4 |
2.4 |
4.8 |
5.6 |
|
A3-1 |
1.5 |
28.4 |
7.9 |
32.5 |
3.7 |
2.9 |
|
A4-1 |
1.5 |
2.0 |
2.1 |
1.0 |
6.3 |
1.1 |
|
At 5m above Ground |
||||||
|
A1-1 |
5 |
3.1 |
3.8 |
4.3 |
1.5 |
1.6 |
|
A1-2 |
5 |
3.4 |
2.2 |
2.3 |
0.9 |
0.7 |
|
A1-3 |
5 |
3.7 |
5.1 |
2.9 |
1.3 |
0.9 |
|
A1-4 |
5 |
1.7 |
2.6 |
1.5 |
1.4 |
0.6 |
|
A2-1 |
5 |
1.6 |
1.4 |
2.4 |
4.7 |
5.4 |
|
A3-1 |
5 |
25.0 |
7.6 |
26.3 |
3.6 |
2.9 |
|
A4-1 |
5 |
2.0 |
2.1 |
1.0 |
6.2 |
1.1 |
|
At 10m above Ground |
||||||
|
A1-1 |
10 |
2.9 |
3.6 |
4.1 |
1.5 |
1.5 |
|
A1-2 |
10 |
3.2 |
2.1 |
2.2 |
0.9 |
0.7 |
|
A1-3 |
10 |
3.5 |
4.7 |
2.7 |
1.3 |
0.9 |
|
A1-4 |
10 |
1.6 |
2.5 |
1.5 |
1.3 |
0.6 |
|
A2-1 |
10 |
1.6 |
1.3 |
2.3 |
4.4 |
5.0 |
|
A3-1 |
10 |
15.9 |
12.1 |
12.5 |
12.1 |
12.1 |
|
A4-1 |
10 |
2.0 |
2.0 |
1.0 |
5.7 |
1.0 |
Note: Bold value means exceedance of 5 OU odour limit
3.7.2.4 “What if IWMF not proceed”
Similar to the construction phase, the assessment so far has assumed that the pollutant sources are close to the waste boundary which is much closer to the sensitive receivers. Hence, even the middle ash lagoon is employed for the IWMF, the worst case environmental impacts have already been addressed in the current assessment and no additional impact on the sensitive receivers would be generated.
3.7.3 Restoration and Aftercare Phase
No potential odour impact is anticipated during the restoration and aftercare phases.
3.8.1 Construction Phase
Dust emission from construction vehicle movement is confined within the worksites area. Watering facilities will be provided at every designated vehicular exit point.
Watering should be implemented 8 times per day to suppress the dust generation. Periodic dust monitoring at the nearby ASRs should also be conducted and detailed in the EM&A manual.
In case of non-compliance, additional mitigation measures in accordance with the EM&A requirements will be implemented.
3.8.2 Operation Phase
3.8.2.1 Stack Discharge from ASP, Flare and LFG Power Generator
The emission factors assumed in this EIA would be included in the specification. Subject to the subsequent EPD’s requirement on chimney installation, regular stack monitoring of air pollutants, including NOx, SO2, RSP, NMOCs, vinyl chloride, and benzene shall be carried out at a quarterly interval (i.e. once every 3 months), and the operating conditions, including exhaust gas temperature and velocity shall be monitored continuously in order to demonstrate compliance during the operations.
3.8.2.2 Odour from Leachate Treatment Facilities
As mentioned in Section 3.5.3.6, it is noted that a new on-site leachate treatment plant has been planned. For the proposed leachate treatment plant in WENT Landfill Extension, the overall leachate treatment facilities include:
· Adopted updated treatment method such as Sequencing Batch Reactor for future leachate treatment. Provision of ventilated cover for the leachate storage lagoons / tanks and emissions extracted to suitable odour removal filters for odour removal.
· Ferric nitrate or sodium hypochlorite can be added to oxidise the odourous chemical in the leachate. The pH value of leachate can be controlled to a suitable value from future on-site experiment such that the generation of any odourous H2S and ammonia can be optimised.
· For the gaseous extraction system, the wind speed immediately above the leachate surface should be kept to minimal (in the order of 0.001m/s) such that the odour emission strength from lagoon can be minimised. Suitable treatment system should be provided for odour removal. The ventilated gaseous emission from lagoons should be provided with 5-10 air change per hour for further dilution before discharge. Together with all the above measures, an overall odour removal efficiency of 99% can be achieved.
· The locations of discharge points and discharge heights should be in accordance with the assumptions adopted in the EIA Report. If the future locations / heights of the stacks deviate from the assumptions adopted in the EIA Study, reassessment of the air quality impact should be conducted.
· The overall arrangement should be investigated in details by the DBO Contractor and agreed with IEC and EPD. As such, the odour emission from the future leachate treatment facilities will be insignificant.
3.8.2.3 Odour from Waste Transfer and Tipping Activities
Exceedances of the odour criterion of 5 OU are expected at A1-3 (West Ha Pak Nai), A2-1 (Black Point Power Station), A3-1 (STF office) and A4-1 (Lung Kwu Sheung Tan). In order to mitigate the adverse odour impact, the following mitigation measures are recommended:
(1) Setback of the Tipping Faces
In general operation, there are 2 numbers of 60m x 30m tipping faces. It is recommended that one of the tipping faces should only be located within 1100m from ASR A1-3, 1200m from ASR A2-1 and 1200m from ASR A4-1. The following Table 3.35a summarises the minimum setback distance required.
Table 3.35a Minimum Setback Distance Required
|
Phase |
Modelling Scenario (Affected ASRs) |
Setback Distance (m) |
|
Phase 1 |
Scenario 2 (A1-3) |
1100 |
|
Phase 3 |
Scenario 4 (A4-1) |
1200 |
|
Phase 4 |
Scenario 5 (A2-1) |
1200 |
In order to assess the worst-case for this mitigation option, the relocated tipping faces are assumed to site at the same wind direction to the worst-affected ASRs. Figure 3.7b illustrates the locations of tipping faces at various setback distances.
(2) On-site Odour Removal System
Adverse odour impact is expected at the planned ASR at the proposed STF office. As it is located adjacent to the odour sources, any setback of tipping face would not be capable of reducing the odour nuisance. As such, on-site odour removal system, such as activated carbon filter, is recommended. As a general practice, the odour removal system should achieve an odour removal efficiency of at least 90%. Therefore, 90% odour removal is assumed at the ASR A3-1.
The mitigated odour concentrations are therefore assessed and the results are summarised in the following Table 3.35b. Assessment results show that, with the implementation of the abovementioned mitigation measures, the odour concentration at all the ASRs would comply with the odour limit of 5 OU.
Table 3.35b Predicted Odour Concentration with Mitigated Measures
|
ASR ID |
Height (m) |
Maximum Odour Concentration (OU) |
||||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
Scenario 4 |
Scenario 5 |
||
|
At 1.5m above Ground |
||||||
|
A1-1 |
1.5 |
3.1 |
4.4 |
4.3 |
1.0 |
1.6 |
|
A1-2 |
1.5 |
3.4 |
3.1 |
2.3 |
1.6 |
1.2 |
|
A1-3 |
1.5 |
3.8 |
4.3 |
2.9 |
1.5 |
1.4 |
|
A1-4 |
1.5 |
1.7 |
2.5 |
1.5 |
1.3 |
0.9 |
|
A2-1 |
1.5 |
1.7 |
1.6 |
2.4 |
2.4 |
2.5 |
|
A3-1* |
1.5 |
2.8 |
0.7 |
3.2 |
0.4 |
0.3 |
|
A4-1 |
1.5 |
2.0 |
1.9 |
1.0 |
3.3 |
1.9 |
|
At 5m above Ground |
||||||
|
A1-1 |
5 |
3.1 |
4.3 |
4.3 |
1.0 |
1.5 |
|
A1-2 |
5 |
3.4 |
3.0 |
2.3 |
1.5 |
1.2 |
|
A1-3 |
5 |
3.7 |
4.2 |
2.9 |
1.4 |
1.4 |
|
A1-4 |
5 |
1.7 |
2.4 |
1.5 |
1.3 |
0.8 |
|
A2-1 |
5 |
1.6 |
1.6 |
2.4 |
2.4 |
2.4 |
|
A3-1* |
5 |
2.5 |
0.7 |
2.6 |
0.4 |
0.3 |
|
A4-1 |
5 |
2.0 |
1.9 |
1.0 |
3.2 |
1.9 |
|
At 10m above Ground |
||||||
|
A1-1 |
10 |
2.9 |
4.1 |
4.1 |
0.9 |
1.5 |
|
A1-2 |
10 |
3.2 |
2.9 |
2.2 |
1.5 |
1.2 |
|
A1-3 |
10 |
3.5 |
3.9 |
2.7 |
1.4 |
1.4 |
|
A1-4 |
10 |
1.6 |
2.3 |
1.5 |
1.2 |
0.8 |
|
A2-1 |
10 |
1.6 |
1.5 |
2.3 |
2.3 |
2.2 |
|
A3-1* |
10 |
1.6 |
1.2 |
1.2 |
1.2 |
1.2 |
|
A4-1 |
10 |
2.0 |
1.8 |
1.0 |
3.0 |
1.8 |
Note * On-site odour removal efficiency of 90% is adopted.
Contours for odour concentrations at 1.5m above ground under various modelling scenario with mitigation measures (setback only) implemented are illustrated in Figures 3.10a to 3.10e.
The followings are some odour precautionary measures that shall be considered by EPD and FEHD as environmental initiatives:
During Operation / Restoration Phases
· Planting
rows of trees along the northern side of WENT Landfill Extension (ie slope toe)
and along realigned
· Providing a vehicle washing facility before the exit of the landfill and providing sufficient signage to remind RCV drivers to pass through the facility before leaving the landfill.
· Reminding the RCV drivers to empty the liquor collection sump and close the valve before leaving the tipping face.
· Washing down the area where spillage of RCV liquor is discovered promptly.
· Reminding operators to maintain their RCVs properly and that liquor does not leak from the vehicles.
· Installation of vertical and/or horizontal LFG extraction system to enhance extraction of LFG from the waste mass and hence minimise odour associated with fugitive LFG emissions.
· Progressive / temporary restoration of the areas which reach the finished profile (a final capping system including an impermeable liner will be put in place) and installation of a permanent LFG extraction system.
· Maintaining the size of the active tipping face not greater than 2 x 60 m x 30 m. Active tipping face means the area where tipping activities are being carried out. Only one tipping face within 1100m from ASR A1-3, 1200m from ASR A2-1 & 1200m from ASR A4-1 is allowed.
· Daily cover the compacted waste with 150mm of soil.
· Covering the non-active tipping phase (ie the whole phase where no tipping activities are being carried out) with 300mm to 600mm of soil / an impermeable liner (on top of the intermediate cover), which will not only prevent odour emissions from landfilled waste but also enhance LFG extraction by the LFG extraction system.
· Providing deodoriser for the Leachate Treatment Plant (LTP).
· Enclosing all the leachate storage and treatment tanks and diverting the exhaust air from these tanks to a deodoriser to avoid potential odour emissions from the LTP.
· As an improvement measure to enhance to environmental standard for waste transfer, EPD could take the initiative to recommend others to use enclosed type RCVs (dominantly government vehicles and sludge vehicles).
· The trench for special waste shall be covered with soil immediately upon the disposal of special waste to reduce the odour emission.
· Cleaning / watering of the surface and clearing of the waste water receptor of government RCV is recommended before leaving refuse transfer station or government Refuse Collection Point (FEHD).
· The use of alternative daily cover (less permeable layer) instead of inert material should be considered under worst-case weather condition, subject to EM&A Programme.
· The use of immediate daily cover for odorous waste such as animal waste etc. under critical condition should also be considered, subject to EM&A Programme.
· In accordance with some reference from
· During stable and calm weather condition and subject to EM&A programme, tipping could be arranged to further increase the setback distance.
During Aftercare Phase
· Continue to maintain the integrity of the capping system.
· Provision of vertical and/or horizontal LFG extraction system to enhance extraction of LFG from the waste mass and hence minimise odour associated with fugitive LFG emissions.
· Enclosing all the leachate storage and treatment tanks and diverting the exhaust air from these tanks to a deodoriser to avoid potential odour emissions from the LTP.
3.8.2.4 VOC Surface Emission and Future Ambient Level
Similar to other restored landfill, the existing WENT Landfill will be capped by plastic covering sheet and a thick layer of soil during restoration period. Surface gas emission from existing restored landfill is insignificant. With the installation of permanent capping, together with the LFG management system, there are double preventive measures against surface emission. Odour and VOC emission from the restored WENT Landfill is not anticipated.
For the WENT Landfill Extension, with an effective temporary covers, together with LFG management system (active extraction to collect LFG within the landfill cells), natural escape of odourous VOC to the nearby ASRs is negligible.
EM&A will be conducted to review the future VOC ambient concentration and effectiveness of the extraction system. VOC monitoring at ASRs to be conducted once every 3 months is recommended before the commissioning of WENT Landfill Extension (as base-line) and in every year of tipping operation, during the period when the ASP and flare are not in operation. By comparing the monitoring data at the boundary and at ASR, the cause of VOC and the general downwind dispersion effect from the boundary to the ASR can be established.
Development of LFG Export Scheme / energy recovery scheme will be encouraged for the WENT Landfill Extension.
3.8.3 Restoration and Aftercare Phase
Similar measures as in construction and operation phases will be applied.
3.9.1 Residual Impact: Annual TSP and Annual RSP
As presented in the preceding sections, all the air quality criterion as stipulated in the Air Quality Objectives and in the EIAO-TM are met, with the exception of Annual TSP and Annual RSP.
Such exceedances constitute residual environmental impact, the significance of which needs to be addressed. In this regard, the following points are of vital relevance:
(a) As shown in Sections 3.7.1 and 3.7.2 the background Annual TSP & RSP concentrations already exceed their respective criteria. Hence, though this Project emits only a small amount of TSP & RSP, the Annual criteria are still exceeded after adding background concentrations. For ease of reference the relevant results are shown again in the summary below:
|
Data (µg/m³) |
Criterion |
Background |
Due to this Project |
Due to Existing WENT Landfill |
Other Sources |
Total |
|
Annual
TSP (Village Houses/Place of Worship) |
80
(AQO) |
103 |
< 1 |
< 2 |
- |
103 to 106 |
|
Annual
TSP (CLP Office) |
80
(AQO) |
103 |
0.4-3.2 |
<1 |
- |
104-107 |
|
Annual
TSP (STF Office) |
80
(AQO) |
103 |
2.4-4.9 |
< 8 |
- |
111-116 |
|
Annual
RSP |
55
(AQO) |
64 |
0.0 to 0.3 (Results are so small that these two need to
be added to show a reportable figure) |
< 66 |
64
to 66 |
|
These data summarise the range of
results at the 7 no. ASRs, i.e. showing the highest and lowest data.
(b) The Background figures (103/64 for Annual TSP/RSP respectively) are the average results of actual monitoring data obtained at EPD’s Air Monitoring Station at Yuen Long for the Years 2003 to 2007. These data have been confirmed by EPD as final. A summary is tabulated below:
|
Year |
2003 |
2004 |
2005 |
2006 |
2007 |
2008 |
|
Annual Average TSP (µg/m³) |
98 |
113 |
104 |
101 |
97 |
87 |
|
Annual Average RSP (µg/m³) |
61 |
71 |
62 |
62 |
64 |
60 |
|
Remarks |
· Average of 2003 - 2007 Annual TSP/RSP = 103/64 respectively; · Data of 2003 - 2007 already confirmed by EPD as final. |
Provisional |
||||
It can be seen that though the background TSP/RSP monitoring data at Yuen Long have exceeded the Annual criteria (80/55 for Annual TSP/RSP respectively), they are on a downward trend. And although the 2008 data are currently classified as provisional (pending EPD’s final confirmation), they do express the downward trend clearly. This downward trend is conceivably due to general reduction in emissions in the Pearl River Delta (PRD) area. In view of the Guangdong Province Government’s commitment on reduction of PRD emissions, the aforesaid downward trend will obviously continue in the years ahead. The assumption in this EIA that Background concentrations are equal to the average of 2003 - 2007 data at EPD’s Yuen Long Air Quality Monitoring Station is obviously conservative.
(c) RSP
The RSP generated by this Project is minor in comparison with the AQO Criteria and the background figures. In fact, the annual average RSP figures generated solely by this Project at the 7 no. ASRs are less than 0.3 µg/m³. As a comparison, the reporting tolerance of suspended particulates is generally of the order of 1 µg/m³. Thus, the effect due to the Annual RSP on the ASRs is unlikely to be significant.
TSP
The TSP generated by this Project is minor in comparison with the AQO Criteria and the background figures. Though the Project figures are not as minute as that of RSP, it should be noted that TSP is relatively less significant than RSP in terms of health consideration, because the particle size of RSP is much smaller than TSP and hence would have higher health implications especially in relation to respiratory system. In any case, the TSP figures generated by this Project are much less than both AQO criterion and the background figure anyway.
Details of the findings are presented below:
· For the calculation of the annual TSP concentration due to the construction of Nim Wan Road realignment, 10% of the works area (assume evenly distributed over the entire works area of Nim Wan Road realignment) has been adopted for the location of the emission over the whole 2-year construction period, which is on the conservative side as the construction works would not affect 10% of the area over the entire 2-year construction period.
· The TSP/RSP figures for each ASR are the figure at an outdoor point outside its premises. In the case of ASR A2-1 Black Point Power Station office and A3-1 STF office, the TSP inside the offices will be much lower, as an air-conditioner filter is generally capable of removing 50% dust. Hence, the mitigated cumulative annual TSP concentrations at ASR A2-1 and A3-1 would be within the annual AQO.
· Also worth noting is that ASR A4-1 is a place-of-worship. The actual receivers at this ASR are therefore generally the worshippers/descendants whose visits to the place are transient in nature. From the points of view of Annual TSP/RSP, their effect on the worshippers/visitors are unlikely to be significant, provided that the Hourly and Daily TSP/RSP figures do not exceed the AQO criteria (which is indeed the case here).
· As regards the other 4 ASRs A1-1 to A1-4, they are village houses at Ha Pak Nai, the contribution due to the construction of the WENT Landfill Extension is less than 1 µg/m³ out of the cumulative impact of up to 106 µg/m³. Hence, it can be concluded that the residual impact due to the Project itself (ie WENT Landfill Extension) is insignificant.
Notwithstanding the fact that the exceedances of Annual TSP & RSP criteria are by far predominantly due to existing high Background concentrations rather than this Project itself, the exceedances should still be considered as residual environmental impact. In this regard, the significance of this residual impact will be discussed below in the light of aspects stipulated in EIAO-TM Clause 4.4.3 and its Annex 20 Clause 7.
3.9.2 Factors in EIAO-TM Clause 4.4.3:
(i) effects on public health and health of biota or risk to life
TSP
As pointed
out in Section
3.9.1(a) above, this Project itself generates only up to 4.9 µg/m³ for Annual TSP. These are
already the highest figures amongst the various ASRs. As mentioned in 3.9.1(c) above, since the ASR
A2-1 and A3-1 are central air-conditioned, any typical dust filters associated
with the air-conditioning system would reduce at least 50% of the TSP level and
hence the annual TSP level would be within the annual AQO. For the other ASRs, the impact due to this
Project is insignigicant. Moreover, as
TSP is relatively less of a concern from health/life point of view as explained
in 3.9.1(c),
it is considered that the effects on public/biota health or risk-to-life should
not be significant. Also relevant is
that the TSP figures are likely to have been overestimated too, in view of
conservatism factor discussed in 3.9.1(c).
RSP
As pointed
out in Section
3.9.1(a) above, this Project itself generates only less than 0.3 µg/m³ for Annual RSP. These are already the highest figures amongst
the various ASRs. As the Project
figures for RSP are all-the-more minute, it is considered that the effects on
public/biota health or risk-to-life should not be significant.
(ii) the magnitude of the adverse environment impacts – As discussed above, even with conservatism factor, the assessed TSP/RSP figures due to this Project are still minute (especially for RSP). And although the Background figures are high, they are on a downward trend. Hence, the magnitude by which they exceed the Annual TSP/RSP criteria will diminish in the years ahead.
(iii) the geographic extent of the adverse environmental impacts – The residual impact is by far predominantly caused by the high Background Annual TSP/RSP figures. In terms of geographic extent, this is of course an area-wide issue. Nevertheless, the impact caused by this Project itself is minute, and the geographic extent of its own impact should be local, in a remote area between Lung Kwu Sheung Tan and Ha Pak Nai.
(iv) the duration and
frequency of the adverse environmental impacts – The construction works
near CLP office are the realignment works of
(v) the likely size of the community or the environment that may be affected by the adverse impacts – As discussed in 3.9.1 (c), the offices of ASRs A2-1 & A3-1 are unlikely to be affected, whereas the visits by worshippers/visitors to ASR A4-1 are transient in nature and therefore unlikely to be affected from the points of view of Annual TSP/RSP. As regards ASRs A1-1 to A1-4, 3.9.1(c) above has pointed out that the residual impact due to this Project itself is insignificant.
(vi) the degree to which the adverse environmental impacts are reversible or irreversible – As explained above, the impact due to this Project itself is minute. Upon completion of the WENT Landfill Extension, the project site will be restored to an area of substantial plantation, and will cease to emit TSP/RSP.
(vii) the ecological context – The exceedance does not involve ecological context.
(viii) the degree of disruption to sites of cultural heritage – The exceedance does not involve cultural heritage context.
(ix) international and regional importance – The exceedance does not involve international and regional importance.
(x) both the likelihood and degree of uncertainty of adverse environmental impacts – As explained in 3.9.1, the assessed TSP/RSP figures are likely to be on the conservative side i.e. high side.
3.9.3 Questions in Annex 20 Clause 7:
|
Have the available standards, assumptions and criteria which can be used to evaluate the impacts been discussed? |
Yes |
|
Have the predicted impacts been compared to the available standards and criteria? |
Yes |
|
Have the residual impacts, which are the net impacts with the mitigation measures in place, been described and evaluated against the available Government policies, standards and criteria? |
Yes |
|
Have the residual impacts been discussed and evaluated in terms of the impact on the health and welfare of the local community and on the protection of environmental resources? |
Yes |
|
Have the magnitude, location and duration of the residual impacts been discussed in conjunction with the value, sensitivity and rarity of the resource? |
Yes |
|
Where there are no generally accepted standards or criteria for the evaluation of residual impacts, have alternative approaches been discussed and, if so, is a clear distinction made between fact, assumption and professional judgment? |
Not applicable |
|
Have the residual impacts, if any, arising from the implementation of the proposed mitigation measures, been considered? |
Yes |
Clearly the residual impacts as regards Annual TSP & RSP are by far predominantly caused by existing Background concentrations unrelated to this Project, and that the impacts due to this Project itself are minute. The Annual TSP figures due to this Project itself are minor in magnitude, whereas the Annual RSP figures are even (much) smaller; yet both TSP and RSP figures are likely to have been overestimated, due to conservatism in the assessment. In view of the above, the residual impacts as regards Annual TSP & RSP ought not be considered as an issue of environmental concern in the context of this Project.
Nevertheless, the following measures would be taken to control the TSP figures due to this Project. These include:
(a) Shift some of the dust-generating tasks (e.g. excavation and site formation) further away from the affected ASR(s) in case weather condition such as wind direction is particularly adverse towards that ASR(s).
(b) Further increase the frequency of daily watering – In Section 3.7.1 above it has been put forward that watering will be carried out 8 times a day. This could be increased further if necessary.
The necessity for further measures as outlined above should be subjected to actual EM&A results, which will also determine the extent/details of the measures.
The potential air quality impacts during construction, operation, restoration and aftercare phases of the WENT Landfill Extension Project have been assessed.
3.10.1 Construction Phase
Construction dust modelling results show that the 1-hr and 24-hr average TSP concentrations at all the receivers would comply with the legislative requirements. The cumulative annual TSP concentration would however, due to the high background level, exceeds the respective criterion. Further analysis suggests that the contribution from the WENT Extension Project would nevertheless be insignificant, especially for the neighbouring village houses. For other areas that are provided with air-conditioning, it is anticipated typical dust filters would be able to reduce the dust level by 50% and hence would be sufficient to ensure acceptable air quality. Good site practice such as 8 times / day of watering should be carried out to control the dust problems. Requirements for regular monitoring of dust concentration are detailed in the EM&A Manual.
3.10.2 Operation Phase
3.10.2.1 Stack Gas and Surface Gas Emission
Dispersion modelling results show that gaseous emissions from ammonia stripping plant, LFG power generator and flaring system of the WENT Landfill Extension will have no adverse impact on the ASRs throughout the operation period of the WENT Landfill Extension, except the annual RSP concentration. However, further analysis revealed that the annual RSP contribution from the Project (WENT Landfill Extension), Existing WENT Landfill and marine emissions is less than 1% of the annual AQO. In addition, the background RSP concentration of 64 μg/m3 adopted from Air Monitoring Station at Yuen Long has already exceeded the AQO criteria of 55 μg/m3. Air quality impact arisen from the Project is therefore insignificant.
Subject to the subsequent EPD’s requirement on chimney installation, regular stack monitoring of air pollutants, including NOx, SO2, RSP, NMOCs, vinyl chloride, and benzene shall be carried out at a quarterly interval (i.e. once every 3 months), and the operating conditions, including exhaust gas temperature and velocity shall be monitored continuously in order to demonstrate compliance during the operations.
By adopting the best practice using effective active extraction system, plastic sheet cover at inactive tipping phase plus periodic EM&A monitoring, the surface gas emission can be significant reduced. With the provision of these measures, no adverse health risk impact is anticipated.
Regular emission monitoring of these facilities is recommended to ensure their proper functioning.
3.10.2.2 Odour
Odour assessment results show that some operational constraints on the locations of tipping faces (ie only one tipping face within certain distance from some sensitive receivers (1100m from West Ha Pak Nai, 1200m from office of Black Point Power Station & 1200m from Lung Kwu Sheung Tan)) are required to ensure compliance of the odour limits for the receivers. For the office at the STF office, some odour removal facilities would be installed to reduce the odour level accordingly. Other odour control measures (eg application of daily cover) would be implemented to minimise the odour impact.
Ventilated cover with emissions extracted to suitable odour removal filters for odour removal has been proposed for planned lagoons. Updated treatment method such as Sequencing Batch Reactor has been proposed for future lagoon. Ferric nitrate or sodium hypochlorite shall be added to oxidise the odourous chemical in the leachate. The pH value of leachate can be controlled to a suitable value from future on-site experiment such that the generation of any odourous H2S and ammonia can be optimised.
Suitable treatment system with overall odour removal efficiency of 99% should be provided for the leachate treatment plant for odour removal.
The locations of discharge points and discharge heights should be in accordance with the assumptions adopted in the EIA Report. If the future locations / heights of the stacks deviate from the assumptions adopted in the EIA Study, reassessment of the air quality impact should be conducted.
3.10.3 Restoration and Aftercare Phases
The scale of construction activities during the restoration and aftercare phases of the WENT Landfill Extension will be small when compared with the construction phase. Construction dust is therefore not anticipated to be an issue.
The impact of stack gas emissions from treatment facilities will be much reduced during these phases given the gradual reduction in leachate and LFG generation rates over time.
Odour in restored landfill will not be a concern.
Air quality conditions will not be worse than during the operation phase and hence no adverse impact is anticipated.