3.                NOISE MONITORING

 

Monitoring Requirements

 

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.

 

Monitoring Equipment

 

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.

 [INCLUDE CALIBRATION RECORD SUMMARY IN APPENDIX D]

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

 

Monitoring Locations

 

3.5              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

Customs & Excise Training School

 

Monitoring Methodology

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

 

3.6              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.

 

3.7              All measured noise levels complied with the Action and Limit Levels in the month. [INCLUDE DATA TABLES FOR REPORTING PERIOD & THREE-MONTH GRAPHS IN APPENDIX F] A summary of noise monitoring results is presented in Table 3.4.

 

Table 3.4          Summary of Impact Noise Monitoring Results during 07:00 – 19:00 on Normal Weekdays

 

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

64.2

(64.0 – 65.7)

#

(# - #)

75

Nil

Nil

NMC2

62.8

(62.5 – 63.4)

#

(# - #)

70

Nil

Nil

NMC3

63.0

(62.8 – 63.4)

#

(# - #)

70

Nil

Nil

* - Action Level is triggered by receipt of a noise complaint

# - Measured noise level is less than the baseline noise level