3                        Summary of the Environmental Impacts

3.1                  Introduction

3.1.1            Potential environmental impacts associated with the construction and operation phases of the proposed Project have been assessed in the EIA Report and are summarized in the following sections.  


3.2                  Air Quality Impact

3.2.1           Impacts arising from the construction of the Project would primarily relate to dust nuisance from excavation works, material handling and gaseous emissions from the construction plant.  With the implementation of mitigation measures as stipulated in the Air Pollution Control (Construction Dust) Regulation, no adverse air quality impact arising from construction works of the Project would be expected.


3.3                 Noise Impact

3.3.1           Noise arising from the construction activities of the proposed Project would have potential impacts on the Noise Sensitive Receivers (NSRs) located in the vicinity of the proposed work areas.  Unmitigated construction noise levels at representative NSRs were predicted to exceed the EIAO-TM daytime construction noise criteria.

3.3.2           Sufficient noise control measures would be required to mitigate the potential construction noise impacts, such as adopting quiet construction plant, using movable/temporary noise barriers, and implementing good site practices.

3.3.3           With the recommended mitigation measures in place, the mitigated noise levels at most of the NSRs would comply with the EIAO-TM noise criteria.  A NSR located in very close proximity to the works site of the proposed retaining wall at Pak Ngau Heung River outlet would still be exposed to noise levels in exceedance of the EIAO-TM noise criterion, despite all practicable direct noise mitigation measures exhaustively employed.  However, it is expected that the residual impacts would be short-term and localized, and hence these residual impacts were considered surmountable.


3.4                 Water Quality Impact

3.4.1           The key issue in terms of water quality would be related to excavation works during the construction stage.  To minimize potential impacts on water quality during the channel construction, special working method controls and pollution control measures have been recommended.  In particular, excavation works at each river channel would be carried out in dry condition using containment measures within the channel.  The recommended water quality mitigation measures should be enforced by the provision of specifications of pollution control measures into works contracts.

3.4.2           Other potential sources of water quality impact would comprise construction site runoff and drainage; debris, refuse and liquid spillages from general construction activities; and sewage effluents from the construction workforce.  Minimization of water quality deterioration could be achieved through implementing adequate mitigation measures, such as control measures on the runoff and drainage from the works areas to minimize construction run-off.  Proper site management and good housekeeping practices would also be required to ensure that construction wastes and materials would not enter the adjacent waterbodies or stormwater drains.  Sewage effluent arising from the construction workforce would also require appropriate treatment through provision of portable toilets. 

3.4.3           With the implementation of these recommended mitigation measures, the construction works for the proposed drainage improvements to the river channels in Mui Wo would not be anticipated to result in unacceptable impacts on water quality.  Site inspections should be undertaken routinely to inspect the construction activities and works areas in order to ensure the recommended mitigation measures are properly implemented.  In addition, given that Pak Ngan Heung River, Tai Tei Tong River and Luk Tei Tong River discharge to the three-river confluence at the head of the Silver River, which ultimately discharges to Silver Mine Bay, monitoring of downstream water quality within the rivers was recommended during the construction phase. 


3.5                 Waste Management

3.5.1           The main waste arising during the construction phase would be excavated material from the river improvements works at Pak Ngan Heung River, Tai Tei Tong River, Luk Tei Tong River and Luk Tei Tong Bypass Channel. The excavated material would comprise soil, gravel and small rocks.  Excavated material with suitable characteristics should be be reused on-site as far as practicable, e.g. fill material for backfilling of temporary drainage channels or construction of river embankments.  Surplus excavated material would require disposal to a public filling area. 

3.5.2           Other wastes generated by the construction activities are likely to include general refuse from the workforce, chemical wastes from plant and vehicle maintenance, as well as construction and demolition material material from the demolition of existing structures and site clearance.  Provided that these identified waste arisings are to be handled, transported and disposed of using the recommended methods and good site practices are to be strictly followed, adverse environmental impacts would not be expected during the construction works.  The recommended mitigation measures should form the basis of the Waste Management Plan to be developed by the Contractor.


3.6                 Ecological Impact

3.6.1           A literature review and ecological surveys covering the wet and dry seasons were undertaken to establish the ecological profile of the assessment area.

3.6.2           Habitats considered of low-moderate/moderate/moderate-high ecological value included Pak Ngan Heung River, Tai Tei Tong River, Luk Tei Tong River and Luk Tei Tong (2) River. Secondary woodland was found on the hillsides surrounding Mui Wo Valley and Butterfly Hill, and Luk Tei Tong Marsh. Other habitats recorded such as active agricultural land and villages were considered of lower ecological value.

3.6.3           Several faunal species of conservation interest were recorded in the assessment area, comprising two fishes, one amphibian, and 16 birds. Of particular interest were the fish species Flagtail (Kuhlia marginata) and Predaceous Chub (Parazacco spilurus). Avifauna of conservation interest included White-shouldered Starling (Sturnus sinensis), which have been recorded breeding adjacent to the proposed Luk Tei Tong works area near the confluence, and various species of avifauna recorded feeding at the lower reaches of the three rivers, and to a lesser extent, Luk Tei Tong Marsh. The locally uncommon and declining Chinese Bullfrog (Rana rugulosa) has been recorded from the Mui Wo area during previous surveys, and was again recorded from the Assessment Area during surveys conducted for this Study. Previous records of the locally protected Romer’s Tree Frog (Philautus romeri) have also been noted in the Mui Wo Area. Although not recorded during recent surveys, it is possible this species still occurs in the assessment area.

3.6.4           The key ecological impact resulting from the Project would be the direct impacts to 175m of Pak Ngan Heung River, 160m of Tai Tei Tong River, and 225m of Luk Tei Tong River. The Project would also directly impact approximately 0.13ha of moderate-high value secondary woodland, and 0.8ha of Luk Tei Tong Marsh. Although the Marsh as a whole was considered of moderate-high ecological value, areas directly affected by the proposed works were observed to be relatively dry, dominated by weedy species, and not to be of particular conservation interest.

3.6.5           Measures to avoid, minimise and compensate for identified ecological impacts have been recommended. These included measures to control sedimentation, the adoption of ecological design for the drainage channels (such as the use of natural lining for channel beds, rock-filled gabion to line the channel banks, and compensatory planting along the channel banks), the provision of compensatory marsh habitat in the design of Luk Tei Tong By-pass Channel, avoidance of works close to White-shouldered Starlings (Sternus sinensis) during the main breeding season of the Starling, and translocation of fish and amphibian species of conservation interest

3.6.6           With the implementation of the recommended mitigation measures, residual impacts from the proposed drainage improvement works are expected to be ecologically acceptable.


3.7                 Cultural Heritage

3.7.1           Based on cultural heritage field surveys undertaken, key potential archaeological impacts would be limited to small areas of minor excavation works associated with the proposed 0.75m U-channel at Ling Tsui Tau Tsuen within the Chung Hau Archaeological Site. Further investigation and a watching brief are recommended before the construction work takes place.

3.7.2           There may be potential vibration impact to the existing retaining wall and associated structures of the Yuen Compound during the construction of rubble seawall and retaining wall at the Luk Tei Tong River, requiring careful construction and vibration monitoring.


3.8                  Environmental Monitoring and Audit

3.8.1            An environmental monitoring and audit programme for the Project will be implemented to monitor construction noise, water quality, ecology and cultural heritage.  Details of the programme are presented in a separate Environmental Monitoring and Audit Manual.