3.
AIR QUALITY IMPACT ASSESSMENT
3.1.1
This Section presents the
assessment of potential air quality impacts arising from the construction and
operation of the proposed Project. The
Study Area is generally defined by a distance of 500 m from the boundary of the
Project site (Figure 3.1). Representative Air Sensitive Receivers (ASRs)
and emission inventories have been identified and an assessment of air quality
impacts has been conducted. Mitigation
measures and environmental monitoring and audit (EM&A) programme have been
proposed if deemed necessary.
3.2.1
The principal legislation for
the management of air quality in Hong Kong is
the Air Pollution Control Ordinance (APCO) (Cap. 311). The prevalent AQOs, as presented in Table 3.1, stipulate the statutory
limits for air pollutants and the maximum allowable number of exceedances over
specific periods. This set of AQOs was
used as the evaluation criteria for this assessment.
Table 3.1 – Hong Kong
Air Quality Objectives
|
Air Pollutant
|
Averaging Time
|
Concentration (mgm-3)(a)
|
No. of Exceedances
Allowed Per Year
|
|
Sulphur
Dioxide (SO2)
|
10-minute
|
500
|
3
|
|
|
24-hour
|
125
|
3
|
|
Respirable
Suspended Particulates (RSP) (b)
|
24-hour
|
100
|
9
|
|
Annual
|
50
|
-
|
|
Fine
Suspended Particulates (FSP) (c)
|
24-hour
|
75
|
9
|
|
Annual
|
35
|
-
|
|
Nitrogen
Dioxide (NO2)
|
1-hour
|
200
|
18
|
|
|
Annual
|
40
|
-
|
|
Ozone
(O3)
|
8-hour
|
160
|
9
|
|
Carbon
Monoxide (CO)
|
1-hour
|
30,000
|
-
|
|
|
8-hour
|
10,000
|
-
|
|
Lead
|
Annual
|
0.5
|
-
|
|
Notes:
(a)
All measurements of the concentration of gaseous air pollutants,
i.e., SO2, NO2, O3 and CO, are to be adjusted to a reference temperature of
293 Kelvin and a reference pressure of 101.325 kilopascal.
(b)
RSP means suspended particles in air with a nominal aerodynamic
diameter of 10 μm or less.
(c)
FSP means suspended particles in air with a nominal aerodynamic
diameter of 2.5 μm or less.
|
3.2.2
In addition to the APCO, a
maximum hourly average of Total Suspended Particulates (TSP) level of 500 mgm-3
at ASR is stipulated in Annex 4 of the
Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM)
to address potential construction dust impacts.
3.2.3
The criterion of 5 odour units
based on an averaging time of 5 seconds is also stipulated in the EIAO-TM for
odour assessment.
3.2.4
The measures stipulated in the Air Pollution Control (Construction Dust)
Regulation should be followed to ensure that any dust impacts are reduced.
3.2.5
Requirements stipulated in the Air Pollution Control (Non-road Mobile Machinery)
(Emission) Regulation will be followed to control potential emissions from
non-road mobile machinery during construction phase.
In
accordance with the EIA Study Brief, the Study Area for the air quality
assessment is defined by a distance of 500 m from the boundary of the Project
site. The Study Area is shown in Figure 3.1.
The
proposed Project is located in Sha Tau Kok Town. The area has a relatively low population
density and the local air quality is mainly influenced by vehicle emissions
from road network within Sha Tau Kok Chuen.
No major odour emission sources have been identified in the Study
Area. Within the Study Area, there are
several major low-rise residential developments, recreational facilities and
governmental or institutional uses.
3.3.1
Existing Air Quality
Existing air quality of the Study Area has been
determined through a review of EPD’s routine air
quality monitoring data collected between 2011 and 2015. The nearest EPD’s Air Quality Monitoring
Station (AQMS) is located in Tai Po. The
latest 5 years annual averaged concentrations (2011 - 2015) of nitrogen dioxide (NO2),
sulphur dioxide (SO2), respirable suspended particulates (RSP) and
fine suspended particulates (FSP) recorded at this AQMS are presented in Table 3.2. The 5-year annual averaged concentrations
(2011-2015) of these air pollutants give an indication of the existing air
quality of the Study Area.
Table 3.2 – Summary of
Background Air Quality at Tai Po AQMS (2011-2015)
|
Air Pollutant
|
Annual Averaged
Concentration (mg m-3)
in the Recent 5 Years
|
|
|
2015
|
2014
|
2013
|
2012
|
2011
|
5-year average
|
Annual AQOs
|
|
SO2
|
6
|
4
|
9
|
7
|
8
|
6.8
|
- (b)
|
|
NO2
|
37
|
45
|
53
|
51
|
45
|
46.2
|
40
|
|
RSP
|
36
|
41
|
-- (d)
|
41
|
46
|
41.0
|
50
|
|
FSP (c)
|
23
|
27
|
-- (d)
|
28
|
--
|
26.0
|
35
|
|
Notes:
(a)
5 years annual average
concentrations (2011 - 2015) of air pollutants measured at EPD’s AQMS in Tai
Po.
(http://www.aqhi.gov.hk/en/download/air-quality-reportse469.html?showall=&start=1)
(b) No annual
AQO for SO2 Concentration.
(c) FSP monitoring
data at the EPD Tai Po AQMS are publicly available since 2012.
(d) Annual
average is not published for non-compliance with the representative
requirement of no less than 2/3 representative period in a quarter.
|
The
monitoring results as presented in Table 3.2 are indicative of the prevailing
background air quality at the Project Site.
The 5-year averages of RSP and FSP concentrations in 2011 - 2015 are
below their respective AQOs (ie 50 mg m-3 and 35 mg m-3, respectively), while the 5-year average of NO2
concentration (46.2 mg m-3) has exceeded the AQO (i.e. 40 µg m-3).
Air Sensitive
Receivers (ASRs) were identified within the Study Area in accordance with Annex 12 of EIAO-TM. Latest Outline
Zoning Plans (OZP), Outline Development Plan (ODP) and relevant land use plans
published by Lands Department were also reviewed to identify future or
committed ASRs. Representative
ASRs within the Study Area are summarized in Table 3.3 and shown in Figure 3.1. The representative ASRs have been identified
on the basis that they are close to the Project site and are likely to receive
the worst possible impact arising from the Project. Assessment undertaken at these representative
ASRs are considered representative of the 500m Study Area from the Project.
Table
3.3 –
Representative Air Sensitive Receivers
|
ASR
|
Location
|
Type of
Use
|
Approximate Separation
Distance from the Nearest Site Boundary (m)
|
Status (existing/
planned)
|
Approximate
Maximum Height
(m above ground)
|
|
A1
|
Sha Tau Kok Playground
|
Residential
|
75
|
Existing
|
-
|
|
A2
|
Tin Hau Temple
|
Temple
|
60
|
Existing
|
3
|
|
A3 (b)
|
Sha Tau Kok Chuen Block 42 – 44
|
Residential
|
160
|
Existing
|
12
|
|
A4
|
Sun Yin Lau
|
Residential
|
180
|
Existing
|
9
|
|
A5
|
Operation Base – Sha Tau Kok Division
Border District
|
G/IC
|
130
|
Existing
|
6
|
|
A6
|
Sha Tau Kok Fire Station
|
G/IC
|
170
|
Existing
|
12
|
|
A7 (c)
|
Ha Tam Shui Hang
|
Residential
|
190
|
Existing
|
9
|
|
A8
|
Police Operation Base
|
G/IC
|
20
|
Existing
|
12
|
|
Notes:
(a)
G/IC – Government,
Institution or Community
(b)
A3 has been
identified as the representative ASR of Shau Tau Kok Chuen.
(c)
A7 has been identified as representative ASR as it is more
representative of the actual location of Ha Tam Shui Hang.
|
3.5.1
Construction Phase
The
key construction activities for the Project are listed below:
(a)
Construction of a temporary sewage treatment plant (TSTP) to cope with
the sewage flow during the expansion works of the STKSTW;
(b)
Expansion works for the upgrading of the STKSTW to increase its treatment
capacity to 10,000m3/day at ADWF;
(c)
Decommissioning of the existing Sha Tau Kok Sewage Pumping Station
(STKSPS), the rising main between STKSPS and STKSTW, and the existing submarine
outfall;
(d)
Construction of gravity sewer;
(e)
Construction of a new submarine outfall; and
(f)
Associated ancillary works.
No
major earthworks or site formation works associated with the construction of
the Project will be required.
Soil
excavation, materials handling, truck movements on unpaved roads and wind
erosion from open stockpiling of dusty materials within the Project Site are
identified to be the potential dust generating activities.
Dust
in terms of TSP, RSP and FSP and odour are the key air pollutants during
construction and decommissioning works.
Tentatively,
the construction of the Project will last for about 49 months and is scheduled
to commence in 3rd quarter of 2017. The
normal working hours will be between 0700 and 1900 hrs from Monday to Saturday
(except public holidays).
3.5.2
Operation Phase
Potential
odour emission is expected from the exhaust pipe of the TSTP and the STKSTW
during operation. Potential odour
nuisance may also result from the transportation, storage and handling of
sludge produced during the sewage treatment process. The potential odour nuisance during transportation
of sludge is considered to be minor as the sludge will be transported by
enclosed type tankers.
3.6
Impact Assessment
3.6.1
Construction Phase
(a) Construction
of TSTP and Expanded STKSTW
Construction
of the TSTP and the expanded STKSTW, which will take approximately 15 and 32
months, respectively, would primarily involve site clearance, excavation,
backfilling, construction of substructure and superstructure and other civil
works.
Vegetation
if any and debris will be removed during site clearance and fugitive dust
emission is considered to be limited.
Only
small-scale excavation works are expected during site formation as the site has
been formed and no major site formation work is required. It is estimated that a total of about 400 m3
and 40,500 m3 of excavated soils will be generated from the
construction of the TSTP and the expanded STKSTW, respectively throughout the
construction period. The excavated
materials will be disposed of at fill bank as public fill. In view of such small amount of excavated
materials generated throughout the construction period, the potential fugitive
dust emission is expected to be minimal with the implementation of dust
control/ suppression measures stipulated under the Air Pollution Control
(Construction Dust) Regulation and those recommended in Section 3.7.1 during
excavation and backfilling, together with proper site management and good
housekeeping.
No
fugitive dust emission is expected from construction of substructure and
superstructure as they will involve mainly concreting and steel-reinforcement
works.
Due
to small construction works area and scale of construction works, the number of
construction plants employed in the construction of TSTP and STW would be very
limited. Also, requirements as
stipulated in the Air Pollution Control
(Non-road Mobile Machinery) (Emission) Regulation will be followed to
control potential emissions from non-road mobile machinery. Therefore, gaseous emission from
diesel-fuelled construction equipment would be minor and would not cause any
adverse air quality impact.
(b) Construction
of Sewerage
A
sewerage scheme has been proposed which involves the decommissioning of the
STKSPS after the expansion of STKSTW.
The scheme includes the removal of existing rising main and construction
of new sewer such that sewage from Sha Tau Kok town will be conveyed via new
sewer to the expanded STKSTW by gravity.
The construction of the gravity sewer will be carried out for about 12
months. The gravity sewer will be
constructed in small sections using open cut methods and trenchless method
using pipe jacking. The open cut method involves soil excavation
works and backfilling, which may have the potential to cause fugitive dust
emissions, and negligible dust emissions are expected from the trenchless
method. As the gravity sewer is
constructed in small sections, the excavated materials generated will be
limited (about 4,620 m3) and potential dust impact due to open cut
method is expected to be low. Also,
there will be limited number of construction plant to be deployed in the works
since the construction works areas would be small. With the implementation of dust control
measures recommended in Section 3.7.1,
potential dust emissions from the decommissioning of
the STKSPS and
associated rising main and the construction of new gravity sewer are expected
to be minimal. Hence, no adverse dust
impact associated with the aforementioned works on nearby ASRs is anticipated.
(c) Construction
of Submarine Outfall
Trenchless
construction technique by Horizontal Direction Drilling (HDD) is proposed for
the construction of the new submarine outfall beneath Starling Inlet. The construction of the new submarine outfall
will take approximately 39 months.
Cofferdam will be constructed and dried, followed by the removal of
sediments for the installation of diffuser at the outfall location. Any sediment removed will be disposed of
properly at off-site locations. In view
of high moisture of the sediment, no fugitive dust emission is expected.
(d) Odour
Impact from Decommissioning Works
The
existing sewage pumping station and rising mains will be clean and flushed out
properly to clear away any remaining potential sources of odour emission, such
as sewage sludge from the facilities.
The decommissioning including removal of the pumping station and rising
mains will take place after the cleaning and flushing out. No unacceptable odour emission is
anticipated during the construction phase.
Hence, no adverse odour impact is anticipated from the decommissioning
of the STKSTW.
3.6.2
Operation Phase
As
discussed in Section 3.5.2, odour
impact associated with the operation of TSTP and STKSTW may potentially affect
the nearby ASRs and hence a quantitative assessment using computational
modelling has been carried out to evaluate the potential odour impact. No other major odour emission sources have
been identified nearby.
(a) Design
of Exhaust and Odour Emission Rate Estimation
The
exhausts of the TSTP and STKSTW will be located at the side of roof top of the
structure which is located away from the nearby ASRs as far as possible. Before the STKSTW expansion, the TSTP will be
in operation, therefore, both TSTP and STKSTW will not be in operation
concurrently. The design parameters of
exhaust stacks and the odour emission rates of the TSTP and STW are summarized
in Table 3.4. Detailed calculations of odour emission rates,
which have made reference to the approved EIA report of Upgrading Cheung Chau
Sewage Collection, Treatment and Disposal Facilities project and Harbour Area
Treatment project, are presented in Annex 3A.
Table
3.4 – Design
Parameter of Exhaust Stack and Odour Emission Rates of TSTP and STKSTW
|
Design Parameter
|
Unit
|
STKSTW
|
TSTP
|
|
Location
|
-
|
STKSTW No.1
|
STKSTW
No.2
|
TSTP
No.1
|
TSTP No.2
|
|
No. of emission points
|
-
|
1
(a)
|
2
|
|
Building height
|
m above ground
|
15.65
|
14.3
|
14.3
|
|
Stack height
|
m above ground
|
17.65
|
16.3
|
16.3
|
|
Equivalent stack diameter
|
m
|
1.69
|
0.15
|
0.25
|
|
Exit temperature
|
-
|
ambient
|
ambient
|
ambient
|
|
Total flowrate @ exit temp.
|
m3hr-1
|
70,279
|
46,722
|
3,952
|
9,293
|
|
|
m3s-1
|
19.52
|
12.98
|
1.10
|
2.58
|
|
Exit velocity
|
ms-1
|
14.44
|
15.53
|
13.15
|
|
Odour emission rate at inlet
|
OUs-1
|
17600
|
16300
|
3500
|
160
|
|
% of odour removal
|
%
|
99.5
|
99.5
|
99.5
|
99.5
|
|
Odour emission rate at exhaust
|
OUs-1
|
169.5 (b)
|
17.5
|
0.8
|
|
Notes:
(a)
Same emission point for STKSTW No.1 and STKSTW No.2.
(b)
Combined emission rate for STKSTW No.1 and STKSTW No.2.
|
|
|
|
|
|
|
|
(b) Assessment
Methodology and Assumptions
The
Industrial Sources Complex Short Term 3 (ISCST3) model, which is an EPD’s
accepted air dispersion model, has been employed for the prediction of the
odour impact at the ASRs and in the vicinity.
The TSTP and STKSTW are assumed to be operating 24 hours a day, 7 days a
week. As described above, the TSTP and
STKSTW will not be in operation concurrently at any time, two modelling
scenarios have been setup, ie, (a) one scenario considering odour emission from
STKSTW only, and (b) the other scenario considering odour emission from TSTP
only. The design parameters of exhaust
stack and the odour emission rates, as presented in Table 3.4, have been inputted for the model run. 0 degree K for stack exit temperature was
inputted for the model run to represent ambient exit temperature.
As
the site area is classified as “rural” in accordance with the EPD’s Guidelines on Choice of Models and Model
Parameter, a “rural” dispersion mode was used in the model. In addition, the local terrain within Study
Area has been incorporated into the model to account for terrain-induced
impacts to dispersion.
Depending
on the actual heights of the ASRs as identified in Table 3.3, assessment heights were selected at 1.5m, 4.5m, 7.5m and
10.5m above ground to assess the odour impact at relevant levels at the ASRs.
Hourly
MM5 data predicted by the PATH (Pollutants in the Atmosphere and their
Transport over Hong Kong) model in 2010 have been adopted for meteorological
data in this assessment. The Study Area
covers four PATH grids, (31,45), (31,46), (32,45) and (32,46). All identified representative ASRs falls
within the PATH grid (32,46). Stability
class of the PATH MM5 data was calculated by PCRAMMET (version 99169). Mixing heights in MM5 which are lower than
the lowest recorded mixing height by the Hong Kong Observatory (HKO) (i.e.
121m) in 2010 were adjusted to 121m.
The
assessment has been conducted based on the assumed reasonably worst case
scenario under normal operating condition of the Project. The modelled hourly averaged odour
concentrations at the ASRs by the ISCST3 were converted into 5-second averaged
odour concentrations for comparison with the odour assessment’s criterion
stipulated in the EIAO-TM. A set of conversion factors stipulated in “Approved Methods for Modelling and
Assessment of Air Pollutants in New South Wales” published by the
Department of Environment and Conservation, New South Wales, Australia were
adopted in this assessment. As the
stacks (i.e. about 2 m high) will be located at the roof top of the structure
of the STKSTW or TSTP which is less than 2.5 times of building height of STKSTW
or TSTP, building wake effect is expected.
Building dimensions and locations obtained from latest site layout were
inputted into the model to take into account the building wake effect. The conversion factors stated in this
method are for converting 1-hour averaged concentrations to 1-second averaged
concentration for near field regions. In
this assessment, the conversion factors were directly adopted for converting 1-hour
averaged concentrations to 5-second averaged concentration as a conservative
approach. The conversion factors adopted
in this assessment for different stability classes are shown in Table 3.5.
Table
3.5 – Conversion Factors from 1-hour to 5-second Mean Concentrations for
Wake-affected Point Source (a)
|
Pasquill Stability Class
|
Conversion Factors (1-hour to
5-second averages)
|
|
A
|
2.3
|
|
B
|
2.3
|
|
C
|
2.3
|
|
D
|
2.3
|
|
E
|
2.3
|
|
F
|
2.3
|
|
Note:
(a) Reference to Approved Methods for Modelling and Assessment of Air Pollutants in
New South Wales published by the Department of Environment and
Conservation, New South Wales, Australia.
The derivation of the peak-to-mean ratios stated in the method was
based on experimental and theoretical analyses and had assumed a 0.1%
exceedance level (With reference to “Statistical
Elements of Predicting Water Science and Technology, Australia, 44:0 pp
157-164, 2001”).
|
(c) Assessment
Results
The
predicted maximum 5-second odour concentrations at relevant levels above ground
at the representative ASRs during the operation of TSTP or STKSTW are presented
in Table 3.6 and Table 3.7, respectively.
Contours at ground level and height above ground where the highest
predicted odour concentrations occur were plotted.
Table
3.6 – Predicted Maximum 5-second Odour Level at ASRs during the Operation of
TSTP
|
ASR
|
Predicted Maximum 5-second Odour Level (OU/m3)
|
|
|
1.5m above ground
|
4.5 m above ground
|
7.5m above ground
|
10.5 m above
ground
|
|
A1
|
0.06
|
-
|
-
|
-
|
|
A2
|
0.06
|
-
|
-
|
-
|
|
A3
|
0.03
|
0.03
|
0.03
|
0.03
|
|
A4
|
0.04
|
0.04
|
0.04
|
-
|
|
A5
|
0.05
|
0.05
|
-
|
-
|
|
A6
|
0.04
|
0.04
|
0.04
|
0.04
|
|
A7
|
0.03
|
0.03
|
0.03
|
-
|
|
A8
|
0.06
|
0.07
|
0.09
|
0.12
|
|
Odour Criterion
|
5
|
5
|
5
|
5
|
Table
3.7 – Predicted Maximum 5-second Odour Level at ASRs during the Operation of
STKSTW
|
ASR
|
Predicted Maximum 5-second Odour Level (OU/m3)
|
|
|
1.5m above ground
|
4.5 m above ground
|
7.5m above ground
|
10.5 m above
ground
|
|
A1
|
0.04
|
-
|
-
|
-
|
|
A2
|
0.04
|
-
|
-
|
-
|
|
A3
|
0.03
|
0.03
|
0.04
|
0.05
|
|
A4
|
0.03
|
0.03
|
0.04
|
-
|
|
A5
|
0.04
|
0.04
|
-
|
-
|
|
A6
|
0.04
|
0.04
|
0.04
|
0.05
|
|
A7
|
0.04
|
0.04
|
0.06
|
-
|
|
A8
|
0.03
|
0.04
|
0.08
|
0.13
|
|
Odour Criterion
|
5
|
5
|
5
|
5
|
The
predicted maximum 5-second averaged odour levels at relevant heights at the
identified ASRs are very low and comply with the odour criterion (i.e. 5 OU/m3
in 5-second averaging time). During the
operation of TSTP, the highest predicted odour concentration (i.e. 0.12 OU/m3)
is predicted at ASR 8 (Police Operation Base) at 10.5 m above ground. During the operation of STKSTW, the highest
predicted odour concentration (i.e. 0.13 OU/m3) is also predicted at
ASR 8 at 10.5 m above ground. Contour
plots of the predicted maximum 5-second averaged odour concentrations at 1.5 m
and 10.5 m above ground, for the operation of TSTP and STKSTW are shown in Figure
3.2 to Figure 3.5. A7 has been selected as representative ASR of
Ha Tam Shui Hang as it is more representative of the actual location of Ha Tam
Shui Hang. As shown in Figure
3.2 to Figure 3.5, the odour
impact at other village houses in Ha Tam Shui Hang (NSR1 and NSR2) (see Figure
4.1) are well within the odour criterion. The potential worst odour impact has been
addressed at A8 which is the closest to the Project.
A3
has been selected as the representative ASR of Sha Tau Kok Chuen. The odour impact at other locations in Shau
Tau Kok Chuen (NSR4 and NSR6) (see Figure 4.1) is very minor as shown in Figure
3.2 to Figure 3.5.
Sha
Tau Kok Central Primary School (NSR3) and building along Shun Lung Street (NSR
8) (see Figure
4.1) are relatively distant from the Project site. The odour impact at the locations of NSR3 and
NSR8 is very minor. Higher odour impact
in the similar direction has been addressed at the identified representative
ASR A1 to A6, which are closer to the Project site and well comply with the
odour criterion. Similarly, the
location of NSR7 (see Figure 4.1) is relatively distant from
the Project site. The odour impact at
the location of NSR7 is very minor.
Higher odour impact has been addressed at the identified representative
ASR A1 to A4, which are closer to the Project site and well comply with the
odour criterion.
Therefore,
for operation of TSTP or STKSTW, isopleths show that the predicted maximum
5-second odour concentrations at both 1.5 m and 10.5 m above ground within the
Study Area are in compliance with the odour criterion. Thus, adverse odour impact due to the
operation of TSTP or STKSTW is not anticipated.
3.7.1
Construction Phase
Dust
control measures stipulated in the Air
Pollution Control (Construction Dust) Regulation will be implemented during
the construction of the Project to control potential fugitive dust
emissions. Standard construction
practices for dust minimisation, including a number of practical measures such
as regular water spraying, provision of vehicle wheel-washing and body washing
facilities and shielding or covering with impervious sheet of stockpiled
materials or exposed area when it is not use, will be implemented to reduce
dust nuisance. For open trench
construction of the gravity sewers, each work front should be around 20m to 30m
in length to control potential dust emission.
In
order to avoid potential odour emissions from the decommissioning activities,
the existing sewage pumping station and rising main will be flushed out and
sludge will be pumped away before the start of decommissioning works.
Site
practices such as regular maintenance and checking of the diesel-driven PMEs
will be adopted to avoid any black smoke emissions and to reduce gaseous
emissions.
3.7.2
Operation Phase
The
major process equipment of the TSTP and STKSTW will be confined inside the
substructure/superstructure as far as possible to minimize odour nuisance to
the surrounding air sensitive receivers.
Hydrogen sulphide (H2S) in the exhaust air is the major odour
source. Deodourizing facility using
activated carbon filters and/or bio-trickling filters will be equipped for both
TSTP and STKSTW, attaining the required odour removal efficiency at exhaust, as
presented in Table 3.4. The deodorization system would undergo maintenance annually or when
the average odour removal efficiency of deodorization facility is smaller than
the required odour removal efficiency. Ventilation system will also be provided inside the TSTP and STKSTW
to ensure adequate air exchange within the plants. In accordance with the Waste
Disposal Ordinance (WDO), the sludge produced will be thickened and
dewatered to 30% dry solids prior to disposal at the landfill. The sludge produced should be removed
off-site regularly to avoid accumulation of odourous materials on site. Trucks transporting the sludge to landfill
would be fully enclosed to minimise any potential odour impact during the
transportation process. With the implementation of these mitigation measures, adverse odour
impact associated with the operation of the TSTP or STKSTW is not expected.
3.8
Residual Impacts
3.8.1
Construction Phase
No residual air quality impact is
anticipated from the construction of the Project with the implementation of the
recommended mitigation measures and good construction site practices.
3.8.2
Operation Phase
With
the implementation of the recommended odour control measures and proper site
management practices, no residual air quality impact is envisaged at all
identified ASRs.
No residual impact
is identified in the EIA report. Hence,
no additional study is required.
3.9.1
Construction Phase
No adverse fugitive dust impact or
odour impact is anticipated during the construction period, dust monitoring and
odour monitoring are considered not necessary.
However, it is recommended to conduct regular environmental site audit,
for example, on weekly basis, to ensure the implementation of the dust control
measures and good site practices throughout the construction period.
3.9.2
Operation Phase
During the operation phase, a
commissioning test for the TSTP is recommended to be performed prior to the
operation of the TSTP to ascertain the effectiveness of the deodorization
systems at the TSTP.
Similarly, a commissioning test for the STKSTW should also be performed
prior to the operation of the STKSTW. Exhaust
air flow rate, temperature of exhaust, odour emission rate of the deodorization
systems should be monitored during the commissioning test. The exhaust air flow rate, temperature of
exhaust, odour emission rate presented in Table
3.4 should be maintained. Weekly
monitoring of odour emission at the exhausts at TSTP
and STKSTW by
taking odour samples is recommended to be conducted in the first two months of
the first year of the operation. The
monitoring parameter will include exhaust flow rate, temperature of exhaust and
odour emission rate and the monitoring results should be compared with that
presented in Table 3.4. Provided that the monitoring results show no
non-compliance on a weekly basis during the first two months, it is recommended
to reduce the frequency to monthly in the subsequent four months and further
reduce to quarterly in the remaining six months of the first year if no
non-compliance is found. If there is any
non-compliance, the operator should inspect the deodorization unit. Frequency of odour monitoring should not be
reduced unless no non-compliance is found.
Quarterly odour monitoring is also recommended to continue in the second
year of the operation. If monitoring in
the first two years of operation shows that compliance can be achieved consistently,
the Project Proponent may propose and seek approval with EPD to reduce
monitoring frequency to every six-month or yearly basis for subsequent years of
operation.
Odour patrol is proposed during the period of maintenance or cleaning of
the deodorization system for TSTP or STKSTW.
It is generally defined as Level 0 to Level 4 in which Level 0 means no
odour and Level 4 means unacceptable odour.
If Level 3 – 4 is reported and the source of odour is confirmed to be
originated from the exhaust of TSTP or STKSTW, the operator should be notified
immediately and should investigate and rectify the problem of the cleaning or
maintenance works within 24 hours in order to restore the level to below Level
2.
3.10
Conclusions
This
Section of the EIA has described the potential air quality impacts associated
with the construction and operation of the proposed expansion of the Sha Tau
Kok Sewage Treatment Works. The purpose
of the assessment is to evaluate the acceptability of predicted impacts to air
quality.
Potential
air quality impacts arising from construction activities have been
considered. With implementation of
standard construction practices and mitigation measures, no unacceptable impact
on ASRs during the construction phase is anticipated.
Potential
odour impacts from the operation of the TSTP or STKSTW have been quantitatively
assessed. With the proper implementation
of the proposed plant design, provision of adequate ventilation and appropriate
deodorization systems, the predicted maximum 5-second odour concentrations at
the identified ASRs would comply with the odour criterion stipulated in the EIAO-TM.
Hence, adverse air quality impact arising from the operation phase of
the Project is not anticipated.
Notwithstanding
the above, regular site inspections will be carried out during the construction
phase in order to confirm that the mitigation and control measures are properly
implemented and are working effectively. During the operation phase, commissioning test for the TSTP and STKSTW is
recommended to be conducted prior to their operation to ascertain the
effectiveness of the odour control measures at the TSTP and STKSTW during their
operation. Odour patrol is also proposed
during the period of maintenance of the deodorization system for TSTP or STKSTW.