7.1.1
This section presents an assessment of
potential noise impact pertinent to the construction and operation phase of the
proposed upgrading work for the Tai Po Sewage Treatment Works (hereinafter
referred to as “TPSTW”). Appropriate
mitigation measures have been recommended, where necessary, to alleviate the
potential noise impacts to acceptable levels.
7.2.1
Noise impacts were assessed in
accordance with the criteria and methodology given in the Technical Memoranda
made under the Noise Control Ordinance (NCO), and EIAO-TM.
7.2.2
The NCO provides the statutory
framework for noise control. This
defines statutory limits applicable to equipment used during the construction
and operation phases of the proposed works in the study area. The NCO invokes four Technical Memoranda,
which define the technical means for noise assessment:
·
Technical Memorandum on Noise from Places other than
Domestic Premises, Public Places or Construction Sites (IND-TM);
·
Technical Memorandum on Noise from Construction Work in
Designated Areas (DA-TM);
·
Technical Memorandum on Noise from Construction Work
other than Percussive Piling (GW-TM); and
·
Technical Memorandum on Noise from Percussive Piling
(PP-TM).
7.2.3
The NCO and the accompanying Technical
Memoranda provide a mechanism for assessing noise levels and provide the
statutory power to control noise.
7.2.4
With regard to the assessment of the
operational noise impacts, the NCO designates acceptable noise levels for Noise
Sensitive Receivers (NSRs) on the basis of an Area Sensitivity Rating (ASR),
based on the characteristics of the area within which they are located such as
rural, village, low-density residential, or urban. Within these areas, the
presence of "influencing factors" (such as the presence of industrial
activities or major roads) can further affect the ASR and hence the acceptable
noise level (see Table 7.1).
Table
7.1 Area Sensitivity Ratings
|
Type of Area Containing
NSR
|
Degree to which NSR is
affected by Influencing Factor
|
|
Not Affected
|
Indirectly Affected
|
Directly Affected
|
|
Rural Area
|
A
|
B
|
B
|
|
Urban Area
|
B
|
C
|
C
|
|
Low density residential
area consisting of low-rise or isolated high-rise developments
|
A
|
B
|
C
|
|
Area other than those
above
|
B
|
B
|
C
|
Construction Activities
7.2.5
Under the GW-TM, noise from
construction activity is not restricted during the period 0700 - 1900 hours on
weekdays, except Public Holidays. However, the EIAO-TM identifies a daytime
general construction noise limit of 75 dB(A) Leq (30 minutes) for
domestic premises. This standard was
used as the assessment criteria in the construction noise assessment.
7.2.6
Between 1900 and 0700 hours and all
day on Sundays and public holidays, activities involving the use of powered
mechanical equipment (PME) for the purpose of carrying out construction work
are prohibited unless a Construction Noise Permit (CNP) has been obtained. A
CNP may be granted provided that the Acceptable Noise Level (ANL) for the noise
sensitive receivers (NSRs) can be complied with. ANLs are assigned depending
upon the Area Sensitive Rating (ASRs). The corresponding basic noise levels
(BNLs) for evening and night-time periods are given in Table
7.2.
Table 7.2 Construction Noise Criteria for
Activity other than Percussive Piling
|
Time
Period
|
Basic
Noise Level (BNLs) (dB(A))
|
|
ASR A
|
ASR B
|
ASR C
|
|
Evening
(1900 to 2300 hours) (1)
|
60
|
65
|
70
|
|
Night
(2300 to 0700 hours)
|
45
|
50
|
55
|
Notes: (1) includes Sundays and Public Holidays during daytime and
evening
7.2.7
As the study area for TPSTW is located
inside Tai Po Industrial Estate as shown on Figure 7.1, the Area Sensitivity Rating (ASR) of “C” is determined. According
to the Table 7.2, the construction
noise criteria for the sensitive receiver would be 70 dB(A) in the evening and
55 dB(A) at night.
Operational
Activities
7.2.8
Operational noise emitted from the TPSTW
is controlled under the IND-TM.
According to the TM, the acceptable Noise Levels (ANLs) for different
Area Sensitivity Ratings (ASRs) are given in Table 7.3.
7.2.9
The ANL is a function of the type of
area within which the NSR is located, and the degree of the effect on the NSR
of influencing factors such as major roads and industrial areas. The ANLs for all ASRs are provided in Table
7.3.
Table 7.3 Acceptable Noise Levels (ANLs) (dB(A))
|
Time
Period
|
ASR A
|
ASR B
|
ASR C
|
|
Day
(0700 to 1900 hours)
|
60
|
65
|
70
|
|
Evening
(1900 to 2300 hours)
|
|
Night
(2300 to 0700 hours)
|
50
|
55
|
60
|
7.2.10
The EIAO-TM states that all fixed
noise sources should be so located and designed so that when assessed in
accordance with the IND-TM, the level of the intruding noise at the facade of
the nearest sensitive use should be at least 5 dB(A) below the appropriate ANL
shown in Table 2 of the IND-TM or, in the case of the background being 5 dB(A)
lower than the ANL, the predicted noise level should not exceed the background.
7.2.11
In any event, the ASR assumed in the
EIA is for indicative assessment only.
It should be noted that fixed noise sources are controlled under section
13 of the NCO. The Authority shall
assess the noise impacts based on the contemporary conditions/situations.
7.2.12
As mentioned in Section 7.2.7, the study
area is defined as ASR “C”, i.e. its planning criteria for NSRs would be 65
dB(A) for daytime operations and 55 dB(A) for night-time operations.
Noise
Criteria arising from the New Proposed Equipment
7.2.13
A noise survey was undertaken in March
2003 to determine the background noise levels.
Results indicated that the measured average daytime & evening time
noise level was 62.5 dB(A); and the measured average night-time noise level was
61.7 dB(A) at the selected station. As the background noise level for daytime
& evening time is 7.5 dB(A) lower than the relevant ANL, the background
noise level of 63 dB(A) (i.e. rounded to the nearest 1 dB(A)) would be adopted
as the daytime & evening time assessment criterion. On the other hand, as
the background noise level at night-time is higher than the relevant ANL, planning
criteria of 55 dB(A) would be adopted as the night-time assessment criterion. The
recommended assessment criteria for NSR are summarized in Table
7.4.
Table 7.4 Noise
Criteria for Operational Noise Levels– New Proposed Equipment
|
|
ANL
|
Planning Criteria
|
Measured Background Noise
Level
|
Recommended Noise Criteria
|
|
Day (0700 to 1900 hours)
|
70
|
65
|
62.5
|
63
|
|
Evening (1900 to 2300
hours)
|
|
|
|
|
|
Night (2300 to 0700 hours)
|
60
|
55
|
61.7
|
55
|
Cumulative Impact
7.2.14
Cumulative noise impacts arising from
all items of equipment including new equipment and existing equipment were also
calculated and compared against relevant ANL criteria. According to the Table
7.3, the ANL for the sensitive receiver would be 70
dB(A) in the daytime/evening and 60 dB(A) at night.
7.3.1
The Project site is located at the
south-eastern side of Tai Po Industrial Estate and away from the town centre of
Tai Po, overlooking Tai Po Shuen Wan Golf Centre to the east and Tai Po
Waterfront Park to the south. The site
is served by a local access road, Dai Kwai Street.
7.3.2
Baseline noise surveys were carried
out at one selected location (Figure 7.2) within
the study area on 2 and 3 March 2003.
The selected monitoring location is located near the TPSTW which is
representative to reflect the prevailing background noise level. All the noise
measurements were conducted in accordance with IND-TM. The detailed methodology and results were
presented in Appendix 7.1. The measured noise levels
at the selected location range from 60 to 66 Leq (30-min) dB(A).
Construction Phase
7.4.1
The assessment followed the procedures
given in the GW-TM. For the assessment
of noise from PME, the distance attenuation was estimated using the standard
formula:
Distance
Attenuation in dB(A) = 20 log D + 8 [where D is the distance in metres]
7.4.2
Sound Power Levels of the equipment
were taken from Table 3 of the GW-TM.
Where no SWL is supplied in the TM, reference was made to BS 5228,
previous similar studies or information from the contractors. Groups of powered
mechanical equipment (PME) likely to be employed for each construction task
(i.e. site clearance and set up site office, piling work, excavation,
demolition, concreting work and pipework or miscellaneous) are shown in Appendix
7.2.
7.4.3
The
construction noise assessment provided results for each month throughout the
construction period. As stated in paragraph
2.7.1, the Phase 1 of the Project is scheduled to commence in 20054 for
completion in 2009 whilst the Phase 2 works, being subject to actual flow
build-up, is scheduled to commission before 2016. In order to assess the noise impacts, a construction programme as
shown in Appendix 7.3, which assuming all works, including both Phase 1 and
Phase 2, to be carried out continuously and completed by December 2010, is
adopted for assessment.
7.4.4
Generally, the construction activities
of the Project would be carried out in non-restricted hours (0700-1900 hours)
with the exception of pipework/miscellaneous work which may be carried out in
restricted hours. In the event that the construction activities are undertaken
during restricted hours, it would be the responsibility of the Contractor to
ensure compliance with the NCO and the relevant TMs. In such cases, the
Contractor will be required to submit CNP application to the Noise Control
Authority and abide by any conditions stated in the CNP, should one be issued.
Therefore, the potential noise impacts of construction works within restricted
hours are not formally assessed in this EIA Report. In order to facilitate the
efforts of the project proponent to avoid any potentially adverse noise impact,
an indicative assessment for representative NSR has been undertaken and is
presented in Section 7.9below.
7.4.5
As the E&M works are mainly
installation work, limited number of PME would be used. Also most of the
E&M works would be carried out indoors. Thus, it is considered that E&M
works would not contribute to the cumulative impact at the NSR and are excluded
from this study.
7.4.6
Based on the construction programme
and the assigned PME groups, the construction noise levels from both individual
and all concurrent construction activities of the civil works which are
considered to be significant at the NSR have been assessed.
7.4.7
Noise impact was assessed on the basis
of the following three conservative assumptions:
·
All PME items required for a
particular construction activity would be located at the notional source
position, which is at a position mid-way between the appropriate geographical
centre of the construction site and its boundary nearest to the NSR.
·
A +3 dB(A) façade correction was added
to the predicted noise levels to account for the façade effect at each NSR.
·
Noise impacts at the nearest sensitive
façades of the residential buildings to the source positions were assessed.
7.4.8
Within 300m from the project boundary,
there are no other construction activities identified to be undertaken
concurrently with construction of this Project during the construction
period. Therefore, cumulative
construction noise impact is not expected.
Operational Phase
7.4.9
The assessment followed the procedures
given in the GW-TM. For the assessment
of noise from equipment, the distance attenuation was estimated using the
standard formula as mentioned in Section
7.4.1.
7.4.10
To provide more accurate and realistic
prediction, on-site noise measurement was carried out for some equipment (i.e.
mechanically raked bar screen and screw type grit classifier). However, on-site
noise measurement for other equipment (such as air blower, pumps and
ventilation fans etc) could not be carried out due to site constraint and high
background noise levels from other
noisy equipment nearby. On-site noise measurement would also affect the normal
operation of TPSTW if turning off the equipment. To avoid
overestimation/underestimation on the SWL of these equipment, the SWL of pump
and ventilation fans were derived from the Good
Practices on Pumping System Noise Control (GP-PS) and Good Practices on
Ventilation System Noise Control (GP-VS). The estimated SWLs of other
equipment were made reference to the specifications of similar items of equipment provided by contractor/plant
supplier and other similar projects.
7.4.11
Noise impact was assessed on the basis
of the following three conservative assumptions:
·
All items of operational plant required for operation
of the TPSTW / proposed facilities would be located at the actual source
position.
·
A +3 dB(A) façade correction was added to the predicted
noise levels to account for the façade effect at each NSR.
·
Noise impacts at the nearest sensitive façades of the
residential buildings to the source positions were assessed.
Potential Noise Impacts
7.5.1
Major potential noise impacts arising
from the Project would be:
·
Construction noise
·
Operation noise.
Noise Sensitive Receivers (NSRs)
7.5.2
Noise sensitive receivers (NSRs) were
identified according to the criteria set out in the EIAO-TM and through site inspection.
In accordance with Section 3 of Annex 13 of EIAO-TM, one NSR (Staff Quarters at
TPSTW) has been identified and is shown in Figure 7.3.
7.5.3
Apart from the Staff Quarters of
TPSTW, the nearest existing noise sensitive receivers (i.e. Marino Casa,
Richwood Park, Tycoon Place, Fortune Garden and Ha Hang) are located more than
600m away from the boundary of TPSTW. With reference to the Outline Zoning Plan
(Plan No. S/TP/14) issued in July 2002, no planned noise sensitive uses are
identified within 300m of the TPSTW. The area in the close vicinity of TPSTW
has been zoned for Other
Specified Uses (“OU”).
Construction Phase
7.6.1
As illustrated in the construction
programme, various construction activities would be carried out concurrently
during certain periods. Cumulative noise impacts arising from different
construction activities have been predicted and are shown in Appendix
7.4. As indicated in Appendix 7.2, the major noisy construction tasks would be site clearance and
excavation with total SWL of 124 dB(A).
7.6.2
The predicted noise levels at NSR TP1
were in the range 64 to 79 dB(A). The cumulative noise level at the NSR TP1 would
exceed the noise criteria of 75 dB(A) during certain periods. As a result, noise
mitigation measures would be required.
Operation Phase
7.6.3
The plant inventory and the SWL of the
TPSTW are summarised in Appendix 7.5. As
confirmed by the Project Proponent, the plant inventory used for prediction of
operation noise impact is practical and realistic. To represent the worst case
scenario, all items of equipment were assumed to operate concurrently 24 hours
a day and the directivity was not included in the calculation.
7.6.4
Facilities that would be housed /
enclosed in a concrete structure were assumed to have a 20 dB(A) reduction of
noise emitted from the sources due to transmission loss of the wall. Some items of equipment would be screened
from the line-of-sight of NSRs by building or the structures within the site. This allowed a reduction in the SWL of 10
dB(A) in accordance with the relevant Technical Memorandum. Due to the facade effect, a positive 3 dB(A)
has been added to predict noise levels at the NSRs. For determining the distance correction factors, the distances
between the probable source positions and the NSRs were considered.
Noise Impact Arising from The New
Equipment
7.6.5
According to the plant inventory of
the new proposed equipment as shown in Appendix 7.5, the predicted noise
levels at the NSR TP1 is 54 dB(A), which would meet both the daytime and
night-time criteria of 63 dB(A) and 55 dB(A) respectively. Thus, no mitigation
measures would be required for the new equipment. Details of the calculation are presented in Appendix
7.6.
Cumulative Impact
7.6.6
Assessment was also carried out based
on the SWLs of existing plant as well as new and replacement plant likely to be
installed under the works of the Project. Appendix 7.6 presents the results of the cumulative operational noise impacts of
TPSTW.
7.6.7
According to Appendix
7.6, the
predicted cumulative operational noise levels at the NSR TP1 would be 60 dB(A) ,
which would meet both the daytime and night-time criteria of 70 dB(A) and 60
dB(A) respectively. Thus, no mitigation measures would be required.
Table 7.5 The
Predicted Noise Levels at Representative NSR –Tai Po Sewage Treatment Plant
Staff Quarters (TP1)
|
|
Predicted Unmitigated Noise Levels, dB(A)
|
|
|
New Proposed Equipment
|
Cumulative
|
|
NSR: TP1
|
54
|
60
|
|
Noise Criteria
|
Daytime -63
Nighttime -55
|
Daytime-70
Nightttime-60
|
Construction Phase
Use of Quiet PME
7.7.1
To reduce construction noise impacts
on the affected NSRs, silenced types of PME, which are in accordance with BS
5228: Part 1, 1997, are recommended. The total Sound Power Level (SWL) of PME for each construction
activity were calculated and are summarised in Appendix 7.7.
7.7.2
With the use of quiet PME, a noise
reduction of up to 7 dB(A) could be achieved. A detailed calculation of
construction noise impact for the mitigated scenario is presented in Appendix
7.8. The results indicate that the cumulative
construction noise levels predicted at NSR TP1 would comply with the daytime
noise criteria of 75 dB(A).
Good Site Practice
7.7.3
In addition to quiet PME, good site
practices listed below should be adopted to further abate any residual impacts
during the construction phase of the Project and should be included in the
contract :
·
Only
well-maintained plant should be operated on-site and plant should be serviced
regularly during the construction program.
·
Silencers
or mufflers on construction equipment should be utilised and should be properly
maintained during the construction program.
·
Mobile
plant, if any, should be sited as far away from NSRs as possible.
·
Machines
and plant (such as trucks) that may be in intermittent use should be shut down
between work periods or should be throttled down to a minimum.
·
Plant
known to emit noise strongly in one direction should, wherever possible, be
orientated so that the noise is directed away from the nearby NSRs.
·
Material
stockpiles and other structures should be effectively utilised, wherever
practicable, in screening noise from on-site construction activities.
Operation Phase
7.8.1
No adverse construction noise impact
from the Project is expected with the use of silenced PME and implementation of
good site practices.
7.8.2
The assessment results indicated that
the relevant noise criteria would not be exceeded during the operation of the
TPSTW. The noise contribution from the operation of the new proposed equipment
for TPSTW would not increase the background noise levels (60-66 dB(A)) recorded
in the baseline noise survey) by more than 1 dB(A). The noise impact from the
operation of the TPSTW would therefore be negligible to the existing environment.
7.9.1
As most of the temporary flow
diversion works could only be carried out at night-time (during low flow
conditions), the pipework/miscellaneous work would be carried out during
restricted hours (1900-2300 and 2300-0700) at some working areas and therefore
would be under the control of the GW-TM. The locations of the works area,
namely Area A and Area B, are shown on Figure 7.4.
7.9.2
An indicative assessment was
undertaken to investigate the potential noise impact likely to arise from the
construction works. The construction criteria of 70 dB(A) in the evening and 55
dB(A) at night were adopted in this assessment.
7.9.3
As indicated in Appendix
7.10, the predicted noise levels at NSR TP1 with
adoption of Quiet PME are predicted to range from 56 to 60 dB(A), which would
comply with the evening noise criteria of 70 dB(A).
7.9.4
In order to reduce the construction
noise impact during the night-time period (2300-0700), use of quiet PME,
movable noise barrier and reduction in percentage on-time have been proposed
for particular plant. According to GW-TM, a movable noise barrier with a
cantilevered upper portion located above the noise generating part of the PME
could reduce noise by 5 dB(A) and 10 dB(A), depending on the line of sight that
could be blocked by the barrier when viewed from the NSR. The results are
summarised in Appendix 7.9.
7.9.5
With adoption of the above mitigation
measures, it is expected that the mitigated noise levels at NSR TP1 would
comply with the night-time noise criterion of 55 dB(A). Details of calculation
are presented in Appendix 7.10.
7.9.6
It should be noted that construction
noise impact assessment during restricted hours are carried out for indicative
purpose only. The Noise Control Authority will process any CNP application,
based on the NCO and the relevant TMs, in addition to considering the
contemporary situations/conditions.
7.10.1
It is recommended to establish an
Environmental Monitoring and Audit (EM&A) programme for control of construction
noise. The recommended mitigation measures should be incorporated into the
EM&A programme for implementation during construction period. Operational noise monitoring is not
required. Details of the programme are
provided in a stand-alone EM&A Manual.
Construction Phase
7.11.1
The potential noise impact arising
from construction activities on the representative NSR located in the vicinity
of the work sites were assessed. With the adoption of quiet PME and good site
practices, the predicted construction noise levels at representative NSR would
not exceed the relevant noise criteria.
7.11.2 An indicative assessment was
undertaken for pipework/miscellaneous work of the TPSTW during restricted hours
(1900 to 0700). With the adoption of quiet plant, the mitigated noise level at
the representative NSR TP1 would comply with the evening noise criterion but
exceedance of the night-time noise criterion was still predicted.
7.11.3 With adoption of the quiet PME, movable noise barrier and reduction
in percentage on-time for particular plant, the mitigated noise levels at NSR
TP1 would comply with the night-time noise criterion of 55dB(A). It should
be noted that the results of the construction noise impact assessment for
restricted hours (1900 to 0700) are for indicative purpose; the Noise Control
Authority will process any CNP application, based on the NCO and the relevant
technical memoranda in addition to considering the contemporary situations /
conditions.
Operation Phase
7.11.4
The noise impacts associated with the
operation of the Project were also assessed. The assessment result indicated
that the unmitigated operation noise levels predicted at representative NSR TP1
would comply with both the daytime and nighttime criteria. Thus, no adverse
noise impact arising from the Project would be expected.