3               Noise

Monitoring Requirement

 

3.1               According to the EM&A Documents for HKLR listed in Table 1.1, baseline noise monitoring shall be carried out for a period of fourteen days at all the monitoring locations.

 

3.2               The noise levels shall be measured in terms of the A-weighted equivalent continuous sound pressure level (Leq).

 

3.3               Logger function check and calibration was carried out according to manufacturer’s recommendations.  The equipment was checked and inspected not less than once every two days after the set up at each monitoring station.

Monitoring Locations

 

3.4               Baseline noise monitoring was conducted at the two monitoring stations under the Contract, as shown in Figure 2.  Table 3.1 describes the locations of the noise monitoring stations.

 

Table 3.1        Location for Noise Monitoring Stations

Monitoring Stations

Location

NMS 1

Sha Lo Wan

NMS 4

San Tau

Monitoring Equipment

 

3.5               Integrating Sound Level Meter was used for noise monitoring.  The meter is a Type 1 sound level meter capable of giving a continuous readout of the noise level readings including equivalent continuous sound pressure level (Leq) and percentile sound pressure level (Lx) and also complied with International Electrotechnical Commission Publications 651:1979 (Type 1) and 804:1985 (Type 1) specifications.  The noise monitoring equipment being used and copies of the calibration certificates for the sound level meter and calibrator can be referred to the Baseline Environmental Monitoring Report for HKBCF..

 


 

Monitoring Parameters, Frequency and Duration

 

3.6               In accordance with the EM&A Documents, baseline noise for the A-weighted levels Leq, L10 and L90 was recorded.  Data obtained from the baseline noise monitoring was processed and presented according to the following periods:

 

Ÿ  Daytime: 0700-1900 hrs on normal weekdays

Ÿ  Evening-time: 1900-2300 hrs

Ÿ  Holiday-time: 0700-1900 hrs on holidays

Ÿ  Night-time: 2300-0700 hrs of next day

 

3.7               The frequency and parameters of noise measurement are presented in Table 3.2.

 

Table 3.2        Frequency and Parameters of Noise Monitoring

Monitoring Stations

Location for Measurement

Time Period

Duration, min

Parameter

 

NMS 1

Area in front of No. 12

Sha Lo Wan

Daytime on normal weekdays

(0700-1900 hrs)

30 min

Leq, L10 & L90

 

Evening time on all days (1900-2300 hrs) and Holidays (including Sundays) during daytime and evening (0700-1900 hrs)

All days during the night-time

(2300-0700 hrs)

5 min

NMS 4

San Tau

(Rooftop of Village Office)

Monitoring Methodology and QA/QC Procedures

 

3.8               Table 3.3 summarizes the types of measurement undertaken in the two monitoring stations.

Table 3.3        Type of Measurement

Monitoring Station

Measurement

NMS 1

Free Field measurement

NMS 4

Free Field measurement

 

3.9               Weather data was recorded during the baseline period and is presented in Appendix B.  The air temperature, precipitation and the relative humidity data was obtained from Hong Kong Observatory where the wind speed and wind direction were recorded by the installed Wind Anemometer. The general weather conditions (i.e. sunny, cloudy or rainy) were recorded by the field staff’s observation on the monitoring days.

Field Monitoring

 

3.10           The monitoring procedures are as follows:

·       The microphone head of the head level meter was normally positioned 1m exterior of the noise sensitive facade and lowered sufficiently so that the building’s external wall acts as a reflecting surface. 

·       For free field measurement, the meter was positioned away from any nearby reflective surfaces. All records for free field noise levels will be adjusted with a correction of +3 dB(A).

·       The battery condition was checked to ensure good 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

- measurement time       : 5 minutes (Leq (30-min) would be determined for daytime noise by calculating the logarithmic average of six Leq (5min) data.)

 

·       Prior to and after noise measurement, the meter was calibrated using the calibrator for 94.0 dB at 1000 Hz.  If the difference in the calibration level before and after measurement is more than 1.0 dB, the measurement was considered invalid and repeat of noise measurement was required after re-calibration or repair of the equipment.

·       Noise monitoring was carried out continuously for 24 hours during the 14 days baseline monitoring period.  Monitoring data was recorded and stored automatically within the sound level meter system.  At the end of the monitoring period, noise levels in term of Leq, L90 and L10 were recorded.  In addition, site conditions and noise sources were recorded when the equipment were checked and inspected every two days.

·       All the monitoring data within the sound level meter system was downloaded through the computer software, and all these data was checked and reviewed within the computer.

Maintenance and Calibration

 

3.11           Maintenance and Calibration procedures were as follows:

·       The microphone head of the sound level meter and calibrator were cleaned with a soft cloth at quarterly intervals.

·       The sound level meter and calibrator were checked and calibrated at yearly intervals.

·       Immediately prior to and following each noise measurement the accuracy of the sound level meter shall be checked using an acoustic calibrator generating a known sound pressure level at a known frequency. Measurements may be accepted as valid only if the calibration levels from before and after the noise measurement agree to within 1.0 dB.

Results and Observations

Results

3.12           Baseline noise monitoring was conducted at the six monitoring station in the period between 18th October 2011 and 1st November 2011.  The monitoring schedule is shown in Appendix A.

 

3.13           The baseline noise monitoring results are summarized in Table 3.4 to 3.6.  All baseline noise monitoring results and graphical presentations of the data can be referred to Appendix G and the Baseline Environmental Monitoring Report for HKBCF respectively.  Weather conditions recorded during the baseline monitoring period are shown in Appendix B.

Table  3.4       Summary of Daytime Noise Monitoring Results (Normal Weekdays)

Daytime

0700-1900 hrs on

normal weekdays

Range of Noise Level, dB(A)

Leq (30 min)

L10 (5 min)

L90 (5 min)

Mean

Max

Min

Mean

Max

Min

Mean

Max

Min

NMS 1

66.9

77.2

48.9

69.6

85.0

46.6

52.7

77.2

38.3

NMS 4

56.0

70.9

49.1

57.7

82.1

47.1

52.1

57.1

42.9

Table 3.5        Summary of Evening-Time & Daytime (Holidays) Noise Monitoring Results

Evening-time

1900-2300 hrs on

all days & Daytime

0700-1900 hrs on

holidays

Range of Noise Level, dB(A)

Leq (5 min)

L10 (5 min)

L90 (5 min)

Mean

Max

Min

Mean

Max

Min

Mean

Max

Min

NMS 1

67.1

79.2

42.0

70.6

84.0

44.8

52.9

76.2

35.5

NMS 4

56.2

66.5

48.0

58.2

70.4

50.3

52.9

56.4

44.3

Table 3.6        Summary of Night-Time Noise Monitoring Results

Night-time

2300-0700 hrs of the next day

Range of Noise Level, dB(A)

Leq (5 min)

L10 (5 min)

L90 (5 min)

Mean

Max

Min

Mean

Max

Min

Mean

Max

Min

NMS 1

59.3

82.7

40.5

62.2

89.4

42.4

49.3

71.7

37.0

NMS 4

54.6

66.8

42.7

56.0

65.3

44.3

52.4

56.8

41.0

Observations

3.14           The weather was generally sunny and fine during the baseline monitoring periods.  

 

3.15           During the baseline noise monitoring period, the influencing factors which may affect the results are summarized in Table 3.7:

 

Table 3.7        Influencing Factors at Noise Monitoring Stations

Monitoring Station

Influencing Factors

NMS 1

Air traffic noise

NMS 4

Insect and bird calling

 

 

Action and Limit Levels

3.16           The Action and Limit Levels were established in accordance with the EM&A Documents for HKLR.  The baseline noise level shall be referenced during the compliance check in the impact noise monitoring period.  Table 3.8 presents the Action and Limit Levels for construction noise.

Table 3.8        Action Limit Levels for Noise during Construction Period

Time Period

Action Level

Limit Level

0700-1900 hrs on normal weekdays

When one documented complaint is received

75 dB(A) *

 Noted: If works are to be carried during restricted hours, the conditions stipulated in the construction noise permit issued by the Noise Control Authority have to be followed.

(*)           reduce to 70 dB(A) for schools and 65 dB(A) during school examination periods.