3.1
Noise
levels at three designated monitoring stations were monitored in the month in
accordance with the EM&A Manual. Appendix C shows the established Action
and Limit Levels for the environmental monitoring works.
3.2
The
monitoring schedule for the month is shown in Appendix D. Noise monitoring
stations are shown in Figure 3.1.
3.3
Integrating
Sound Level Meter was employed for noise monitoring. They were Type 1 sound level meters
capable of giving a continuous readout of the noise level readings including
equivalent continuous sound pressure level (Leq)
and percentile sound pressure level (Lx). They comply with
International Electrotechnical Commission
Publications 651:1979 (Type 1) and 804:1985 (Type 1). Portable electronic wind speed indicator
capable of measuring wind speed in m/s was employed to check the wind speed. Table 3.1 details the noise monitoring
equipment used.
Table 3.1 Noise Monitoring Equipment
Equipment |
Model |
Integrating Sound Level Meter |
Rion NL 18 |
Calibrator |
Rion NC-73 |
Monitoring Parameters, Frequency and
Duration
3.4
Table
3.2 summarised the monitoring parameters, period, frequency and duration of
impact noise monitoring.
Table 3.2 Noise Monitoring Parameters, Frequency and Duration
Time Period |
Parameters |
Duration (min) |
Frequency |
Daytime (0700
to 1900 on normal weekdays) |
Leq |
30 |
Once per week |
3.3
In
accordance with the EM&A Manual, three noise monitoring stations, as shown
in Figure 3.1 were selected for noise monitoring. Table 3.3 describes the
location of this monitoring station.
Table 3.3 Locations of Noise Monitoring Stations
Monitoring
Station |
Identity
/ Description |
NMC1 |
Correctional Services Department Married
Staff Quarters |
NMC2 |
Seamen’s Training Centre |
NMC3 |
|
Monitoring Procedures
·
The Sound Level Meter was set on a tripod at a height of
1.2 m above the ground.
·
Façade measurements were made at all three monitoring
locations.
·
The battery condition was checked to ensure the correct
functioning of the meter.
·
Parameters such as frequency weighting, the time
weighting and the measurement time were set as follows:
-
frequency weighting: A
-
time weighting: Fast
-
time measurement: Leq(30
minutes) during non-restricted hours i.e. between 07:00 and 19:00 on normal
weekdays
·
Prior to and after each noise measurement, the meter was
calibrated using a Calibrator for 94 dB at 1000 Hz. If the difference in the calibration
level before and after measurement was more than 1 dB(A),
the measurement would be considered invalid and repeat of noise measurement
would be required after re-calibration or repair of the equipment.
·
The wind speed was frequently checked with a portable
wind meter.
·
During the monitoring period, the Leq , L10 and
L90 were recorded. In
addition, site conditions and noise sources were recorded on a standard record
sheet.
·
Noise measurement was paused during periods of high
intrusive noise (e.g. dog barking, helicopter noise) if possible. Observations
were recorded when intrusive noise was unavoidable.
·
Noise monitoring was cancelled in the presence of fog,
rain, wind with a steady speed exceeding 5 m/s, or wind with gusts exceeding 10
m/s.
Maintenance and Calibration
·
The microphone head of the sound level meter and
calibrator is cleaned with soft cloth at quarterly intervals.
·
The
meter and calibrator are sent to the supplier or HOKLAS laboratory to check and
calibrate at yearly intervals.
·
Calibration
details for the sound level meter and calibrator are provided in Appendix E.
Results and Observations
3.4
Noise
monitoring was conducted at all designated monitoring stations as scheduled in
the month. Noise monitoring results and graphical presentations are provided in
Appendix G.
3.5
All
measured noise levels complied with the Action and Limit Levels in the month.
Table
3.4 Summary
of Impact Noise Monitoring Results during 07:00 – 19:00 on
Monitoring Station |
Measured
Noise Level, dB(A) Leq (30 min) |
Calculated Construction Noise Level, dB(A) |
Limit Level |
No. of Exceedance |
|
Average and Range |
Average and Range |
Action* |
Limit |
||
NMC1 |
64.7 (63.2
– 66.4) |
# (# - #) |
75 |
Nil |
Nil |
NMC2 |
65.1 (62.5
– 66.6) |
# (# - #) |
70 |
Nil |
Nil |
NMC3 |
64.8 (64.0
– 65.8) |
# (#
- #) |
70 |
Nil |
Nil |
* - Action Level is triggered by
receipt of a noise complaint
# - Measured noise level is less
than the baseline noise level