6 Noise

6.1 Introduction

This Section provides an evaluation of the potential noise impacts associated with the activities at the proposed Contaminated Mud Disposal Facilities at South Brothers. Mitigation measures will be recommended, if necessary, to ensure that the legislative criteria will be satisfied.

6.2 Identification of Sources of Noise Impacts

The principal noise sources associated with the disposal facility are dredging, backfilling and capping works within the Site. The works programme presented in Section 1 indicates that concurrent undertakings of dredging, backfilling and capping are possible at several time intervals.

For dredging, it is assumed that two grab dredgers will be operating within the Site, but a barge will be only operated at any one time for either backfilling or capping operations. The assumed construction plant list and the corresponding sound power levels are presented in

Table 6.1

~~Table 6.1Table 6.1Table 6.1~~.

Table 6.1 Construction Plant List and Sound Power Levels (SWLs)

Activity	PME	CNP	Quantity	SWL/Unit	Sub-Total SWL
Dredging	Dredger, Grab	CNP063	2	112	115
Backfilling	Derrick barge	CNP061	1	104	104
Capping	Derrick barge	CNP061	1	104	104

6.3 Noise Assessment Methodology

The assessment of potential noise impacts has been undertaken in accordance with the Technical Memorandum On Noise From Construction Work Other Than Percussive Piling (GW-TM) and Annex 13 of the EIAO-TM. The general methodology is summarised as follows:

· identify the sequence and duration of noise generating activities (i.e. dredging, backfilling and capping) required for the implementation of the CMP Project;

· identify the required type and number of Power Mechanical Equipment (PME) likely to be deployed for the dredging, backfilling and capping activities;

· calculate the maximum total Sound Power Level (SWL) for each activity using the PME list and SWL data given for each plant in the GW-TM (as presented in Table 6.1);

· identify representative NSRs with closest proximity to the CMP Site to represent the potential impact for the area (as shown in Table 6.2);

· identify representative NSRs around the CMP Site as defined by the EIAO-TM based on existing and planned landuses that may be affected by the CMP Project. In view of the widespread and spacious extent of sites, only the representative NSRs with closest proximity to the CMP Site will be identified to represent the potential impact for the area;

· measure the distance and calculate the distance attenuation to the NSRs from worksite notional noise source point at each pit;

· apply correction for façade reflection; and

· predict noise levels at the NSRs in the absence of any mitigation measures.

As the distances between most of the NSRs and the CMP Site are over 1 km, sound absorption by the atmosphere (assumed at 500 Hz, 20°C, RH 70%) has been accounted for in accordance with ISO 9613-1 Acoustics – Attenuation of Sound During Propagation Outdoors – Part 1: Calculation of the Absorption of Sound by the Atmosphere.

If the noise assessment criteria are exceeded at the representative NSRs, mitigation measures will be explored. A re-evaluation of the total SWL for each construction activity will be undertaken.

6.4 Assessment of Noise Impacts

Noise assessments at the five representative NSRs were made based on the tentative construction program, PME list, distances attenuation, atmospheric absorption, façade reflection and corresponding Sound Power Level. The results are summarised in Table 6.2 and detailed calculations are presented in Table 1 of Annex D.

Table 6.2 Noise Assessment Results

NSR	Description	Area Sensitivity Rating	Noise Criteria ⁽¹⁾	Predicted Noise Levels
N1	Regal Airport Hotel	C ⁽²⁾	75 ⁽³⁾/70 ⁽⁴⁾/55 ⁽⁴⁾	19 to 33 dB(A)
N2	Seaview Crescent in Tung Chung	B ⁽²⁾	75/65/50	15 to 32 dB(A)
N3	Monterey Cove in Tung Chung	B ⁽²⁾	75/65/50	15 to 36 dB(A)
N4	Planned R(B)6 Residential Area at Area 77b (in future Kei Tau Kok reclamation area)	B ⁽²⁾	75/65/50	18 to 42 dB(A)
N5	Ho Yu School	B ⁽²⁾	70/65 ⁽⁵⁾	15 to 38 dB(A)
N6	Planned Residential Area at Area 77 (in future Kei Tau Kok reclamation area)	B ⁽²⁾	75/65/50	18 to 53 dB(A)
Notes: (1) Criteria for daytime/ all days during the evening (1900-2300) and general holidays including Sunday during the day and evening (0700-2300) / all days during the night-time (2300-0700) (2) Area Sensitive Rating is assumed in accordance with the GW-TM (3) L_{eq, 30min} 75 dB(A) is the EIAO recommended daytime non-restricted hours criterion (4) Noise criteria for restricted hours are prescribed under the NCO in L_{Aeq 5min} (5) Noise criteria for normal school days / examination period

As indicated in Table 6.2, the predicted noise levels at the six representative NSRs would comply with the daytime (i.e. 0700 – 1900, non-restricted hours) and evening hours (i.e. 1900 – 2300, restricted hours) noise criteria. The highest noise level of 53 dB(A) has been predicted at NSR N6, which is a planned residential development. Ho Yu School (N5) will not be affected by the dredging, backfilling and capping works during normal school days and examination period.

Should dredging work be required during the night-time period (i.e. 2300 – 0700 hours) within pit C, an exceedance of the night-time criterion by 3 dB(A) in 2008 has been predicted at N6 due to its close proximity. Therefore, the feasibility of the night-time dredging works within Pit C shall be evaluated in the context of the construction programme~~Therefore, mitigation measures~~ ~~will~~ ~~be required for night-time dredging works within Pit C~~.

6.5 Mitigation of Adverse Noise Impact

The above assessment indicates that no exceedance of the day and evening criteria is anticipated at the identified NSRs. However, exceedance of the night-time criterion has been predicted for NSR 6 during dredging activities at Pit C.

The use of mitigation measures such as quieter PME and noise barriers are commonly adopted at land-based construction sites. However, these measures are regarded infeasible and ineffective taking into account the nature of work. ~~Therefore, mitigation in the form of reducing the number of dredgers from 2 to 1 is considered. This measure would reduce the night-time noise level by 3 dB(A) to 50 dB(A).~~

~~As reduction in the number of grab dredgers can reduce the noise level at N6 to comply with the L~~_{eq, 5min} ~~50 dB(A) night-time criterion, this is regarded as a feasible option.~~To enable dredging works to be conducted at night-time, it would be necessary to operate only one grab dredger at any one time. The predicted noise level at N6 under this scenario would be 50dB(A) and would comply with the night-time criterion. It is therefore recommended that dredging work by 2 dredgers operating simultaneously shall be avoided at Pit C during the night-time. This restriction will be imposed for night-time dredging only if given the planned housing developments (N6) are occupied prior to the dredging activities within Pit C in 2011 to 2012.

Nevertheless, the EPD shall not be bound by the results presented in this report when assessing any application for a Construction Noise Permit (CNP) for works planned during restricted hours.

6.6 Residual Environmental Impacts

No residual environmental impacts, in terms of exceedances of applicable noise criteria, were predicted to occur during the day and evening time. At night-time the noise exceedance for Pit C can be avoided provided that the programming arrangement~~can be mitigated provided that the measure~~ described in Section 6.5 is implemented.

6.7 Environmental Monitoring & Audit

Given the compliance with the noise criteria, noise monitoring is not required during the construction or operation of the South Brothers facility.

6.8 Conclusion

Noise impact associated with the dredging, backfilling and capping works at the South Brothers Facility have been assessed. It has been assumed that 2 grab dredgers will be deployed on-site for dredging work and 1 barge for the backfilling or capping activity. Since restricted hours construction activities may be required, the prediction results were compared against the EIAO-TM daytime (non-restricted hours) and the evening (1900 – 2300) and night-time (2300 – 0700) restricted hours criteria.

The results indicated that the criteria for daytime and evening works will comply with the criteria at all representative NSRs. To enable dredging works to be conducted at night-time, it would be necessary to operate only one grab dredger at any one time. The predicted noise level at N6 under this scenario would be 50dB(A) and would comply with the night-time criterionHowever, exceedance of the night-time noise criterion has been predicted at NSR 6 (3 dB(A)) during dredging work at Pit C. By reducing the number of grab dredgers from two to one, the noise level at NSR N6 is reduced by 3 dB(A) to 50 dB(A), which complies with the night-time criterion.

It is recommended that night-time dredging by 2 dredgers at Pit C shall be avoided if the planned residential developments at Kei Tau Kok reclamation area are occupied in the years 2011 to 2012. If the planned developments are not occupied prior to the dredging activities within Pit C, no restriction will be imposed for night-time dredging.