Table 10.1 Summary of Key Environmental Outcomes / Benefits

10. conclusions & summary of environmental outcomes

10.1 Introduction

10.1.1.1 This EIA study has provided an assessment of the potential environmental impacts associated with the construction and operation phases of the proposed upgrading works at Pillar Point STW. The environmental issues below have been assessed in the EIA Study, in accordance with the EIA Study Brief (No. ESB-122/2004) registered under the EIA Ordinance for the Project.

n Air Quality Impact

n Water Quality Impact

n Ecological Impact

n Waste Management Implications

n Landscape and Visual Impact

10.1.1.2 Specific mitigation measures necessary for avoiding or reducing impacts from the Project to acceptable levels, as well as environmental monitoring and auditing procedures to ensure full implementation of all mitigation measures and compliance with relevant standards and guidelines, have been developed during the detailed assessments. The Implementation Schedules listing the recommended mitigation measures are presented in Section 11. The principal findings of this EIA Report are summarized below.

10.2 Air Quality Impact

10.2.1.1 Air quality impact during the construction phase of the Project has been assessed. With the implementation of mitigation measures specified in the Air Pollution Control (Construction Dust) Regulation, dust nuisance at ASRs would not be expected. An EM&A programme is recommended for the construction phase to ensure that the dust criteria would be satisfied at the ASRs.

10.2.1.2 Odour emission from the Upgraded PPSTW would be the main concern during the operation phase. Air dispersion modelling was conducted to simulate the potential odour impacts of the preliminary layout of the Upgraded PPSTW on the ASRs. With reference to the modelling results as shown in Table 3.8, it is noted that only providing deodourizing units for the treatment of vented air from the covered sewage/sludge treatment facilities (as mentioned in Table 3.4 and Table 3.5) of the upgraded PPSTW except the quiescent zone of sedimentation tanks is not sufficient to make all the ASRs below the odour criterion of 5 odour units. Highest odour concentration of 8.5 odour units is predicted at A1 under the worst-case scenario. With the implementing the recommended mitigation measure, covering the quiescent zone of sedimentation tanks and providing an additional deodourizing units for the treatment of vented air as stated in Section 3.7.2.3, the predicted odour level at representative ASRs would comply with the EPD criterion of 5 odour units.

10.2.1.3 Based on the preliminary design with implementing the mitigation measure, all the exposed areas ^([1]) with sewage or sludge of the upgraded PPSTW would be covered (See Figure 3.3). The vented air from the inlet pumping station, coarse screens, aerated grit channels, fine screens, common flow channels, outfall pumping station, flash mixing tanks, flocculation tanks, low lift and returns pumping station, weir area and effluent channel of the sedimentation tanks, quiescent zone of the sedimentation tanks and the solids handling building (SHB) would be treated at the three deodourizing units (OD1, OD2 & OD5) next to low lift and returns pumping station before discharging into the atmosphere. While the vented air from the sludge pumping station, raw sludge holding tanks, sludge dewatering building, return liquor pumping station, septic waste reception area, exposed area with sewage or sludge of UV contact tanks and fine screens (including all influent & effluent channels) of UV disinfection facilities would be treated in the two deodourizing units (OD3 & OD4). All the deodourizing units are with 90% odour removal efficiency, which is considered common and practically achievable. Operational odour monitoring is proposed to monitor the effectiveness of recommended mitigation measures.

10.3 Water Quality Impact

Construction Phase

10.3.1.1 Minor water quality impact would be associated with land-based construction. Impacts may result from the surface runoff and sewage from on-site construction workers. Impacts could be controlled to comply with the WPCO standards by implementing the recommended mitigation measures. Unacceptable residual impacts on water quality would not be expected.

Operation Phase

10.3.1.2 An assessment of water quality impact due to the operation of the Project was made using the Delft3D model. The water quality modelling results showed that the discharge of effluent from the upgraded PPSTW after CEPT and UV disinfection would not cause adverse water quality impacts. A sensitivity test was carried out to investigate the water quality effect due to the change from CEPT with disinfection to a higher treatment level (i.e. secondary treatment with nitrogen removal and disinfection). The sensitivity test indicated that there would be no substantial differences in the water quality impacts due to this change. Based on the impact assessment results, the selection of CEPT with disinfection is considered the most effective option for PPSTW in minimizing the water quality impacts.

10.3.1.3 The model predicted that the bacteria levels in the Tuen Mun and Tsuen Wan coastal waters would be elevated due to the emergency release of untreated effluent at the PPSTW. Mitigation measures, including dual power supply, standby pumps, back-up treatment units and equipment, would be provided to avoid the occurrence of any emergency discharge. A frame work of the emergency response procedures has been formulated to minimise the impact due to any temporary discharge of untreated effluent from the PPSTW. A detailed EM&A programme are also recommended to collect water quality information and to mitigate the potential impact. The monitoring results shall be employed to identify areas for any further necessary mitigation measures to avoid, rectify and eliminate environmental damage associated with the emergency release of untreated effluent from the PPSTW. No insurmountable water quality impact would be expected from these temporary discharges under emergency situation provided all the recommended mitigation measures are properly implemented.

10.4 Ecological Impact

10.4.1.1 A literature review has been conducted to establish the ecological baseline condition of the Assessment Area and assessment of potential impacts conducted in accordance with the EIAO TM requirements.

10.4.1.2 The water quality modeling results indicated that there would be a reduction of E. coli, BOD₅, SS and sedimentation rate in the Northwestern and Western Buffer WCZs and a slight increase in DO level localized at the PPSTW outfall after the Project completion. Therefore, the Project would have a positive impact on the identified marine ecological resources. On the other hand, the model predicted that the Project would cause an increase in the TIN level in the receiving waters. The key issue in relation to the TIN would be the possible enhancemeng of algal bloom. As the model predicted that the change of TIN would be minor and localized at the PPSTW outfall, no adverse ecological impacts are anticipated from the Project.

10.5 Waste Management Implications

10.5.1.1 Waste types generated by the construction activities are likely to include C&D material from excavation works, general refuse from the work force, and chemical waste from the maintenance of construction plant and equipment. Wastes generated by the operational activities would include sludge and spent UV lamps. Provided that these wastes are handled, transported and disposed of using approved methods and that the recommended good site practices are strictly followed, adverse environmental impacts are not anticipated during the construction and operation phases.

10.6 Landscape and Visual Impact

10.6.1.1 There are a total of approximately 343 trees within the existing PPSTW. Of these, 253 trees are proposed to be retained, 90 trees will be affected. The species of all the affected trees are listed in Figure 8.9.3 and none of them are classified as the Old and Valuable (OVT) trees. Apart from the 18 numbers of “Leucaena leucocephala”, all the affected trees are proposed to be transplanted. The 18 numbers of “Leucaena leucocephala” are proposed to be felled in accordance with ETWB TCW No. 3/2006. There will be mitigation through the transplanting of some existing trees and the planting of new stock. The felled trees will be compensated by Heavy Standard Sized new trees at one to one ratios. Moreover, 81 numbers of “Cassia surattensis” will be provided as the additional compensatory planting for loss of greenery in the area due to removal of the affected trees.

10.6.1.2 There is expected to be moderate impacts on the existing institutional areas (LCA4) during construction phase to the landscape character of the Government utilities area.

10.6.1.3 Workers on River Trade Terminal & Cargo Handling Area (OU1) would have moderate adverse visual impact during construction phase. Impact would be lessen as slight in operational stage when landscape and visual mitigation measures are fully implemented. The visual impact would be insubstantial significance as most of the tree planting would provide proper screening effect in maturity of 10 years.

10.6.1.4 Day 1 after the implementation of mitigation measures during operation there would still be some slight negative visual impact on the VSRs close to the Project on OU1. 10 years after the implementation of mitigation measures during operation, the residual impacts on all VSRs are insubstantial.

10.6.1.5 After the proposed mitigation measures have been implemented and the proposed tree planting has matured over 10 years, it is anticipated that all residual adverse landscape and visual impacts in the operational phase will be of insubstantial significance.

10.7 Overall Conclusion

10.7.1.1 The findings of this EIA Study have determined the likely nature and extent of environmental impacts predicted to arise from the construction and operation phases of the Project. The EIA has, where appropriate, identified mitigation measures to ensure compliance with environmental legislation and standards.

10.7.1.2 Overall, the EIA Study for the proposed upgrading works at Pillar Point STW has predicted that the Project, with the implementation of the proposed mitigation measures for construction and operation phases, would comply with all applicable environmental standards and legislation. This EIA has also demonstrated the acceptability of the residual impacts from the Project and the protection of the population and environmentally sensitive resources. Table 10.1 summarises the environmental outcomes/benefits from the implementation of the Project and the recommended mitigation measures. Environmental monitoring and audit mechanisms have been recommended, where necessary, to verify the accuracy of the EIA predictions and the effectiveness of recommended mitigation measures.

Table 10.1 Summary of Key Environmental Outcomes / Benefits

Area/Issue	Environmental Outcomes / Benefits and Mitigation Measures
Purpose and Scope of the Project	Under the Review of the Tuen Mun and Tsing Yi Sewerage Master Plan (RTMTYSMP) commissioned in February 1999, the existing Pillar Point STW was recommended to be upgraded from preliminary treatment to chemical treatment with disinfection. The aim of the PPSTW upgrading works is to improve the effluent quality, and to meet the demand of future population and pollutant loads at ultimate development scenario (UDS). The RTMYSMP recommended the viability of the upgrading works to the STW, which comprised the following: · expanding the treatment capacity of the existing STW to cope with the increased peak wet weather sewage flow under the UDS to cater for the increase in population arising from the planned development in Tuen Mun area; · upgrading the sewage treatment level of the existing STW to incorporate chemical treatment (subject to EIA Study under the Assignment) with disinfection at minimum removal rates of 70%, 55% and 99.9% for suspended solids, biochemical oxygen demand and E. coli respectively; · upgrading existing septic waste reception facilities at PPSTW; and · providing and upgrading ancillary facilities including the administration building, workshop, laboratory, odour control facilities, sludge handling and dewatering facilities, access roads and minor landscaping works within the STW for the operation and maintenance of the upgraded STW. A preliminary design taking into account all the Project requirements is carried out. In the preparation of the preliminary design, the sewage flows and loads are to be estimated in order to determine the treatment capacity and effluent standards of the upgraded PPSTW. Moreover, an appropriate treatment process is to be selected for the upgraded PPSTW. The EIA Study is conducted based on the preliminary design is to provide information on the nature and extent of environmental impacts arising from the construction and operation of the Project and related activities that take place concurrently.
Selection of Preferred Treatment Processes	The technical review and evaluation of different treatment processes conducted for the Project recommended the following processes and these recommendations were adopted for development of the preliminary design : · CEPT with conventional single-deck clarifier · UV irradiation for disinfection · Compact septic waste reception station and discharging septic waste into sludge holding tanks · Sludge dewatering by using centrifuges
Key Environmental friendly designs recommended	· All the exposed areas of the upgraded PPSTW would be covered with providing deodourizing facility. All vented air would be treated in the deodourizing units with 90% odour removal efficiency, which is considered common and practically achievable, before discharging into the atmosphere. · Dual power supply should be provided to prevent the occurrence of power failure. The main treatment units include the sedimentation tanks, sludge treatment facilities including the sludge holding tanks and sludge dewatering building and the UV disinfection facility. There are in total 9 nos. of sedimentation tanks in which 8 nos. are duty, which are capable for the treatment during peak design flow and 1 no. of sedimentation tank is reserved for standby. There are in total 3 nos. of sludge holding tanks in which one tank is in use normally and the second tank is for in use over weekend due to weekend stopage and the third tank retained for emergency storage. There are in total 4 nos. of centrifuges installed in the sludge dewatering building, with 3 in duty and 1 in standby mode for sludge dewatering. There are spare UV lamps and accessories, like ballasts etc., for the UV disinfection facility. They will be stored in the spares storage areas as shown in Figure 2.3 for replacement of worn parts/accessories in the UV tanks during non-peak period. At least one standby pump will be provided for each pumping station for maintenance purpose. · Trees affected by the upgrading works will be mitigated through the transplanting of existing trees and planting of new stock. All excavated area and disturbed area for utilities diversion, temporary road diversion, and pipeline woks will be reinstated to former conditions, subject to applicable Government Standards. Existing topsoil shall be re-used where possible for new planting areas within the project. The construction program shall consider using the soil removed from one phase for backfilling another. Suitable storage ground, gathering ground and mixing ground may be set up on-site as necessary. · Compatible design, construction materials and surface finishes of the proposed structure should match with the nearby existing external appearance of PPSTW buildings for achieving visual uniformity. Finishing materials shall have due consideration to form, basic color, color/tone variation, micro- and macro-texture, and reflectivity/light absorbance to avoid glare. Planting, such as turf, low groundcovers and climbers, may also be planted on top of these elements to provide greening and aesthetic effect.
Key environmental problems avoided	The aim of the upgrading works is to expand the sewage treatment capacity and to upgrade the treatment level of the PPSTW in order to cater for the projected ultimate population and planned developments in the Tuen Mun area.
Air Quality Impact	Population and environmental sensitive receivers protected: (Refer to Figure 3.1) · River Trade Terminal Office (Commercial) · Chu Kong Warehouse 1 (Factory) · Chu Kong Warehouse 2 (Factory) · Sawmill (Factory) · Sunhing Hung Kai Tuen Mun Godown (Factory) · Tuen Mun EMSD Servicing Vehicle Station · Pillar Point Fire Station Compensation areas included: Not required (no adverse air impact is predicted from the Project after implementation of the mitigation measures). Environmental benefits of environmental protection measures recommended: The odour level predicted at the air sensitive receivers would be reduced to an acceptable level.
Water Quality Impact	Population and environmental sensitive receivers protected: (Refer to Figure 4.1) · Cooling Water Intakes · Fish Culture Zone · Beaches · Secondary Contact Recreation Subzones · Site of Special Scientific Interest (SSSIs) · Ramsar Site · Marine Park · WSD Flushing Water Intakes · Corals · Artificial Reefs · Horseshoe Crab · Seagrass · Mangrove Communities · Chinese White Dolphins · Mai Po Nature Reserve Area Compensation areas included: Not required (no adverse water impact would be resulted from this upgrading project). Environmental benefits of environmental protection measures recommended: With dual power supply and standby facilities as proposed, occurrence of emergency discharge and the associated water quality impact would be minimized.
Ecological Impact	Population and environmental sensitive receivers protected: Ecological resources at and near the Project site (refer to Figure 6.1) Compensation areas included: Not required (no adverse ecological impact would be resulted from this upgrading project). Environmental benefits of environmental protection measures recommended: With dual power supply and standby facilities as proposed, occurrence of emergency discharge and the associated ecological impact would be minimized.
Waste Management Implications	Population and environmental sensitive receivers protected: Water quality and air sensitive receivers at or near the Project site, the waste transportation routes and the waste disposal site. Compensation areas included: Not required (no adverse waste impact is predicted after implementation of the mitigation measure). Environmental benefits of environmental protection measures recommended: Implementation of the proposed waste control and mitigation measures (refer to Section 7.5 for details) would avoid the potential water quality, dust and odour impacts associated with handling, transportation and disposal of the identified wastes arising from the Project.
Landscape and Visual Impact	Population and environmental sensitive receivers protected: Landscape resources and visual sensitive receivers near the Project site. Compensation areas included: Trees affected by the upgrading works will be mitigated through the transplanting of existing trees and planting of new stock. 81 numbers of “Cassia surattensis” will be provided as the additional compensatory planting for loss of greenery in the area due to removal of the affected trees. Environmental benefits of environmental protection measures recommended: After the proposed mitigation measures have been implemented and the proposed tree planting has matured over 10 years, it is anticipated that all residual adverse landscape and visual impacts will be of insubstantial significance.

Area/Issue

Environmental Outcomes / Benefits and Mitigation Measures

Purpose and Scope of the Project

Under the Review of the Tuen Mun and Tsing Yi Sewerage Master Plan (RTMTYSMP) commissioned in February 1999, the existing Pillar Point STW was recommended to be upgraded from preliminary treatment to chemical treatment with disinfection. The aim of the PPSTW upgrading works is to improve the effluent quality, and to meet the demand of future population and pollutant loads at ultimate development scenario (UDS).

The RTMYSMP recommended the viability of the upgrading works to the STW, which comprised the following:

· expanding the treatment capacity of the existing STW to cope with the increased peak wet weather sewage flow under the UDS to cater for the increase in population arising from the planned development in Tuen Mun area;

· upgrading the sewage treatment level of the existing STW to incorporate chemical treatment (subject to EIA Study under the Assignment) with disinfection at minimum removal rates of 70%, 55% and 99.9% for suspended solids, biochemical oxygen demand and E. coli respectively;

· upgrading existing septic waste reception facilities at PPSTW; and

· providing and upgrading ancillary facilities including the administration building, workshop, laboratory, odour control facilities, sludge handling and dewatering facilities, access roads and minor landscaping works within the STW for the operation and maintenance of the upgraded STW.

A preliminary design taking into account all the Project requirements is carried out. In the preparation of the preliminary design, the sewage flows and loads are to be estimated in order to determine the treatment capacity and effluent standards of the upgraded PPSTW. Moreover, an appropriate treatment process is to be selected for the upgraded PPSTW. The EIA Study is conducted based on the preliminary design is to provide information on the nature and extent of environmental impacts arising from the construction and operation of the Project and related activities that take place concurrently.

Selection of Preferred Treatment Processes

The technical review and evaluation of different treatment processes conducted for the Project recommended the following processes and these recommendations were adopted for development of the preliminary design :

· CEPT with conventional single-deck clarifier

· UV irradiation for disinfection

· Compact septic waste reception station and discharging septic waste into sludge holding tanks

· Sludge dewatering by using centrifuges

Key Environmental friendly designs recommended

· All the exposed areas of the upgraded PPSTW would be covered with providing deodourizing facility. All vented air would be treated in the deodourizing units with 90% odour removal efficiency, which is considered common and practically achievable, before discharging into the atmosphere.

· Dual power supply should be provided to prevent the occurrence of power failure. The main treatment units include the sedimentation tanks, sludge treatment facilities including the sludge holding tanks and sludge dewatering building and the UV disinfection facility. There are in total 9 nos. of sedimentation tanks in which 8 nos. are duty, which are capable for the treatment during peak design flow and 1 no. of sedimentation tank is reserved for standby. There are in total 3 nos. of sludge holding tanks in which one tank is in use normally and the second tank is for in use over weekend due to weekend stopage and the third tank retained for emergency storage. There are in total 4 nos. of centrifuges installed in the sludge dewatering building, with 3 in duty and 1 in standby mode for sludge dewatering. There are spare UV lamps and accessories, like ballasts etc., for the UV disinfection facility. They will be stored in the spares storage areas as shown in Figure 2.3 for replacement of worn parts/accessories in the UV tanks during non-peak period. At least one standby pump will be provided for each pumping station for maintenance purpose.

· Trees affected by the upgrading works will be mitigated through the transplanting of existing trees and planting of new stock. All excavated area and disturbed area for utilities diversion, temporary road diversion, and pipeline woks will be reinstated to former conditions, subject to applicable Government Standards. Existing topsoil shall be re-used where possible for new planting areas within the project. The construction program shall consider using the soil removed from one phase for backfilling another. Suitable storage ground, gathering ground and mixing ground may be set up on-site as necessary.

· Compatible design, construction materials and surface finishes of the proposed structure should match with the nearby existing external appearance of PPSTW buildings for achieving visual uniformity. Finishing materials shall have due consideration to form, basic color, color/tone variation, micro- and macro-texture, and reflectivity/light absorbance to avoid glare. Planting, such as turf, low groundcovers and climbers, may also be planted on top of these elements to provide greening and aesthetic effect.

Key environmental problems avoided

The aim of the upgrading works is to expand the sewage treatment capacity and to upgrade the treatment level of the PPSTW in order to cater for the projected ultimate population and planned developments in the Tuen Mun area.

Air Quality Impact

Population and environmental sensitive receivers protected:

(Refer to Figure 3.1)

· River Trade Terminal Office (Commercial)

· Chu Kong Warehouse 1 (Factory)

· Chu Kong Warehouse 2 (Factory)

· Sawmill (Factory)

· Sunhing Hung Kai Tuen Mun Godown (Factory)

· Tuen Mun EMSD Servicing Vehicle Station

· Pillar Point Fire Station

Compensation areas included:

Not required (no adverse air impact is predicted from the Project after implementation of the mitigation measures).

Environmental benefits of environmental protection measures recommended:

The odour level predicted at the air sensitive receivers would be reduced to an acceptable level.

Water Quality Impact

Population and environmental sensitive receivers protected:

(Refer to Figure 4.1)

· Cooling Water Intakes

· Fish Culture Zone

· Beaches

· Secondary Contact Recreation Subzones

· Site of Special Scientific Interest (SSSIs)

· Ramsar Site

· Marine Park

· WSD Flushing Water Intakes

· Corals

· Artificial Reefs

· Horseshoe Crab

· Seagrass

· Mangrove Communities

· Chinese White Dolphins

· Mai Po Nature Reserve Area

Compensation areas included:

Not required (no adverse water impact would be resulted from this upgrading project).

Environmental benefits of environmental protection measures recommended:

With dual power supply and standby facilities as proposed, occurrence of emergency discharge and the associated water quality impact would be minimized.

Ecological Impact

Population and environmental sensitive receivers protected:

Ecological resources at and near the Project site (refer to Figure 6.1)

Compensation areas included:

Not required (no adverse ecological impact would be resulted from this upgrading project).

Environmental benefits of environmental protection measures recommended:

With dual power supply and standby facilities as proposed, occurrence of emergency discharge and the associated ecological impact would be minimized.

Waste Management Implications

Population and environmental sensitive receivers protected:

Water quality and air sensitive receivers at or near the Project site, the waste transportation routes and the waste disposal site.

Compensation areas included:

Not required (no adverse waste impact is predicted after implementation of the mitigation measure).

Environmental benefits of environmental protection measures recommended:

Implementation of the proposed waste control and mitigation measures (refer to Section 7.5 for details) would avoid the potential water quality, dust and odour impacts associated with handling, transportation and disposal of the identified wastes arising from the Project.

Landscape and Visual Impact

Population and environmental sensitive receivers protected:

Landscape resources and visual sensitive receivers near the Project site.

Compensation areas included:

Trees affected by the upgrading works will be mitigated through the transplanting of existing trees and planting of new stock. 81 numbers of “Cassia surattensis” will be provided as the additional compensatory planting for loss of greenery in the area due to removal of the affected trees.

Environmental benefits of environmental protection measures recommended:

After the proposed mitigation measures have been implemented and the proposed tree planting has matured over 10 years, it is anticipated that all residual adverse landscape and visual impacts will be of insubstantial significance.

^([1]) The exposed areas of sewage treatment facilities include inlet chambers/influent channel of the inlet pumping station, coarse screens, aerated grit channels, fine screens, common flow channels, solid handling house, wet well of the low lift and returns pumping station, rapid mixing tanks, flocculation tanks, weir zone of sedimentation tanks, sedimentation tanks (quiescent zone), sedimentation tank effluent channel, fine screens of UV disinfection facilities, UV contact tanks, UV contact tank influent and effluent channels, sludge holding tanks, sludge dewatering building, sludge/septic waste reception area, sludge pumping station, return liquor pumping station and inlet chamber of the outfall pumping station of the upgraded PPSTW.