13. SUMMARY OF ENVIRONMENTAL OUTCOME
13.1.1.1 Major potential air quality impacts during the construction phase of the project would result from dust arising from site clearance and preparation, excavation and filling, open site erosion, construction of foundation and superstructure, and handling and transportation of construction and demolition material. There may also be cumulative dust impacts due to the concurrent construction activities of the proposed Deep Bay Link and HSKNDA in the area.
13.1.1.2 Practicable and effective dust suppression measures should be implemented to minimise the dust nuisance arising from the construction activities. Specific measures recommended in the EIA include twice daily watering with complete coverage of active construction sites and limit the vehicle travel speed on unpaved site areas to no more than 10 km per hour. Besides, relevant dust control requirements set out in Parts I, III and IV of Schedule 1 of the Air Pollution Control (Construction Dust) Regulation should be adopted by the site agent while carrying out construction works.
13.1.1.3 With the implementation of effective dust control measures, adverse dust impacts from the construction works of the project is not expected. The highest predicted cumulative dust levels at the air sensitive receivers near the San Wai STW and Ha Tsuen Pumping Station are all below 87% of the Air Quality Objectives for total suspended particulates under the mitigated scenario.
13.1.1.4 During the operational phase, major air quality impact would be related to the potential odour emissions from the expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station. Odour mitigation measures have been recommended in the EIA. For the San Wai STW, the odour sources namely the fine screen, the detritors, the sludge holding tanks, the solid handling house, the sludge dewatering house, the rapid mix and flocculation tank, and the primary sedimentation tanks should all be contained within either building structures or enclosure to minimise direct emission of odour to the atmosphere. All odour emissions from the odour sources should be ventilated to a deodorization unit with a hydrogen sulphide removal efficiency of 96% or better before discharging to the atmosphere.
13.1.1.5 For the Ha Tsuen Pumping Station, it is recommended that the air ventilated from the existing and the new wet wells should be treated by deodorisers with a hydrogen sulphide removal efficiency of 97% or better before discharge to the atmosphere.
13.1.1.6 The computer dispersion modelling results showed that the odour levels at the air sensitive receivers around the San Wai STW and Ha Tsuen Pumping Station could be reduced to below the EPD odour criteria of 5 odour unit with the implementation of the recommended odour control measures.
13.2.1.1 The construction noise impacts of this project will be associated with the expansion and upgrading of the existing San Wai STW, the expansion of the existing Ha Tsuen Pumping Station, and the construction of the emergency bypass culvert. There may also be cumulative construction noise impacts due to the concurrent construction activities of the proposed Deep Bay Link and HSKNDA in the area.
13.2.1.2 The identified existing and future noise sensitive receivers are located at considerable distance from the construction sites of the San Wai STW and Ha Tsuen Pumping Station. The predicted construction noise levels at the noise sensitive receivers are all within the construction noise criteria with the use of quiet plant and/or temporary noise barriers. Adverse residual noise impacts are not expected.
13.2.1.3 During the operational phase of the expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station, it is recommended to house all noisy equipment underground or within building structure made of material with a sound transmission loss of 30 dB(A) or better (e.g. concrete with thickness of 300mm) to enclose all noise emissions. Adverse residual noise impacts at nearby noise sensitive receivers are not expected.
13.3.1.1 Construction activities related to this project namely excavation, filling, and construction of superstructure would generate site runoff. The nature of site runoff is usually characterised by high concentration of suspended solids. Suitable mitigation measures as recommended in ProPECC PN 1/94 Construction Site Drainage need to be undertaken. Site drainage systems and treatment facilities would be required to minimise water pollution. A discharge licence issued by the Environmental Protection Department (EPD) would be required for discharging effluent from the construction sites.
13.3.1.2 Through effective implementation of the practicable mitigation measures, the water quality impacts associated with the construction activities of this project would be reduced to acceptable levels.
13.3.1.3 The upgrading and expansion of San Wai STW would enhance the treatment efficiency and increase the capacity of the existing facilities. Irrespective of the final selection of the treatment option, the effluent quality from the upgraded treatment works would be improved as compared with the current preliminary treatment process. The residual impacts are expected to the low.
13.3.1.4 As discussed in Section 5, CEPT with disinfection is identified as the preferred treatment option for the expanded and upgraded San Wai STW. Due to the dispersive characteristics of tidal flows in the vicinity of the NWNT Outfall, the water quality modelling results showed that discharge of effluent after CEPT treatment is not likely to cause adverse water quality impacts in the North Western and Deep Bay Water Control Zones. In addition, the selection of CEPT with disinfection rather than biological treatment options would not jeopardise the compliance of the relevant WQOs for DO, UIA and TIN. The disinfection process would also minimise the impact to the aquatic environment in terms of spreading of faecal coliform and satisfy the precautionary requirement for protection of dolphins.
13.3.1.5 The EIA has also assessed the water quality impacts
for the following emergency discharge scenarios:
Ø Discharge of treated effluent via Tin Shui Wai Drainage Channel into Deep Bay
if NWNT Outfall/Tunnel is not in operation;
Ø Discharge of raw sewage into Deep Bay via Tin Shui Wai Drainage Channel when
both San Wai STW and NWNT Outfall/Tunnel are not in operation or during the
breakdown of Ha Tsuen Pumping Station; and
Ø Discharge of raw sewage via the NWNT Outfall in case the San Wai STW is not
functioning.
13.3.1.6 For the first and the second emergency discharge scenarios, the modelling results showed that the increases in E.coli, total inorganic nitrogen (TIN) and unionised ammonia (UIA) would cause a short-term deterioration of the water quality conditions in the inner part of Deep Bay during the emergency discharge period. The impacts are apparently related to the duration of emergency discharge period. The water quality conditions would quickly recover after the termination of emergency discharge. The potential impacts to the water quality sensitive receivers located further away from the discharge location would be less significant.
13.3.1.7 The emergency discharge at NWNT Outfall under the third emergency discharge scenario would cause lower water quality impacts when compared to the discharge through Tin Shui Wai Drainage Channel into Deep Bay.
13.4 Waste Management Implications
13.4.1.1 The construction activities of this project including the site formation and foundation works at the proposed expanded and upgraded San Wai STW and the expanded Ha Tsuen Pumping Station will generate construction and demolition (C&D) material. The construction of the proposed emergency bypass culvert will be carried out by traditional open trench method and will also results in a certain amount of C&D material. It is estimated that there will be a total of about 57,000m3 of excavated spoil and most of them are soft clayey materials which are not suitable for the foundation of the expanded and upgraded STW. About 10,600m3 of the excavated spoil will be reused onsite and 46,400m3 will be disposed off site. About 123,400m3 of suitable filling material will be imported for the construction of the expanded and upgraded STW foundation.
13.4.1.2 If appropriate mitigation measures are implemented during the handling, collection, and disposal of construction waste material, the residual environmental impacts would be reduced to acceptable levels. These mitigation measures can be enforced by incorporating them into a waste management plan as part of the contract document. Environmental monitoring and audit will be necessary to ensure the implementation of correct disposal requirements for the various wastes generated from construction works.
13.4.1.3 The sludge generated during the operation of the expanded and upgraded San Wai STW should be dewatered to more than 30% dry solids and transported to the landfills. The operators of future UV disinfection facility should work with the supplier/manufacturer on recycling and reuse of the defective UV lamps as far as possible. In handling the UV lamps, cautions should be exerted to avoid breakage of lamps and release of contaminants.
13.4.1.4 The handling, storage and disposal of spent UV lamps and spent odour scrubbing fluids should follow the requirements under the Waste Disposal (Chemical Waste) (General) Regulation. Unless the spent fluids are treated to meet discharge standards as stipulated in the Technical Memorandum under Water Pollution Control Ordinance, direct discharge into local sewerage systems should not be allowed.
13.5 Land Contamination Impact
13.5.1.1 In the current design, the expanded Ha Tsuen Pumping Station will be entirely located within the currently site boundary of the Ha Tsuen Pumping Station and no additional land will be required. The potential of land contamination impacts is considered minimal.
13.5.1.2 For the expanded site of San Wai STW, most part of site, other than the existing San Wai STW, is occupied by the two fishponds to the north and the container yard to the east. Based on the review of the past and present land uses, land contamination issue related to the area of the two fishponds is not anticipated.
13.5.1.3 The area of the container yard was previously agricultural land and fishpond and was then converted to container yard since early 1990s. Localised land contamination issues within this area would be related to vehicle and plant maintenance and repairing activities. Similar land contamination concern also applies to the open storage area to the west outside but adjacent to the proposed expanded site.
13.5.1.4 In order to verify the low potential of land contamination impact prior to the commencement of the construction of the San Wai STW expansion, a land contamination assessment includes intrusive sampling and testing will be carried out during the detailed design stage of the project when access to the concerned areas is gained. A Contamination Assessment Report (CAR) will be prepared and submitted to the Environmental Protection Department (EPD) for approved. If the findings confirmed the potential of land contamination, a Remediation Action Plan (RAP) will be formulated and implemented prior to the construction stage of the project.
13.6.1.1 Deep Bay is facing long-term pollution problems which threaten the sensitive ecosystem in Deep Bay. HKSAR Government is planning to substantially reduce pollution loadings in Deep Bay. Under the Yuen Long/Kam Tin Sewerage Master Plan, sewage networks will be provided to unsewered villages and new developments, and sewage effluents from Yuen Long and Kam Tin will be transported out of Deep Bay to the better flushed water in Urmston Road for disposal (EPD 2001). The proposed project is an important component of the Plan.
13.6.1.2 Flora and fauna recorded in the Study Area during field surveys covering wet and dry seasons are generally of low conservation importance and disturbance tolerant. Habitats within the Study Area are mostly man-made, highly fragmented and disturbed. The project will mainly cause permanent loss of habitats of low ecological importance, hence ecological impact is considered minor. The project will greatly improve water quality in Deep Bay, a site of recognised international importance. Tiny increases of UIA (1%) would be expected near the outfall location and in the Sha Chau and Lung Kwu Chau Marine Park. The changes, however, would be very small and would be outweighed by the significant drop of E. coli count there. Therefore, the overall impact of the project will be positive.
13.6.1.3 An emergency bypass culvert, in the form of box culvert, will be constructed from San Wai STW to nearby drainage channel as part of this project. This culvert will largely reduce the chance of discharging raw sewage into Deep Bay. Under the current emergency situation, raw sewage will be discharged directly from the Ha Tsuen Pumping Station into the Tin Shui Wai Drainage Channel and then to Deep Bay when the NWNT effluent tunnel or the Urmston Road outfall is out of operation. The proposed project will provide an alternative pathway for San Wai STW to dispose treated effluent. With this enhancement measure, the effluent discharged to Tin Shui Wai Drainage Channel and Deep Bay under the emergency event when the NWNT effluent tunnel or the Urmston Road outfall is out of operation will be treated effluent instead of raw sewage. The associated environmental impacts would certainly be lower when compared with the current arrangement.
13.7.1.1 A review of existing information supplemented by the results of recent field surveys on commercial fisheries resources confirmed that the area of concern supports fisheries resources that are neither abundant nor of high value in comparison to resources in other fishing areas of Hong Kong.
13.7.1.2 Potential impacts to fisheries resources and operations may arise from permanent loss of fishponds, and changes in water quality. Due to the small percentage compared to the overall resources in Hong Kong, permanent losses of fisheries resources due to the project are predicted to cause minor impacts to Hong Kong fisheries. As changes in water quality would be mostly positive, adverse impacts to fisheries resources are not predicted. In the North Western Water Control Zone, the much higher tidal flushing rate would effectively dilute and disperse the pollutant concentrations that would occur at higher levels in the effluent discharged from the upgraded San Wai STW.
13.8 Cultural and Heritage Impact
13.8.1.1 The cultural heritage impact assessment has identified significant remains of cultural heritage in the San Wai and Ha Tsuen areas, including historic buildings at San Sang Tsuen and an archaeological site with Neolithic deposit and late historical ruins at Tseung Kong Wai. Besides, two graves with a possible pre-war dating have been identified at So Kwun Tsai and Hau Tsz Shan.
13.8.1.2 The Tseung Kong Wai potential site of cultural heritage with archaeological significance will be encroached upon by the Alternative 3 alignment of the proposed emergency bypass culvert. The Alternative 3 alignment is thus not preferable from a cultural heritage preservation point of view.
13.8.1.3 The historic buildings and pre-war graves identified in the San Wai and Ha Tsuen areas will not be affected directly by this project. It is recommended that appropriate mitigation measures should be taken by the project proponent to protect the potential sites of cultural heritage from any indirect impact potentially caused by the proposed construction.
13.9 Landscape and Visual Impact
13.9.1.1 In both the expanded sites of San Wai STW and Ha Tsuen pumping station, this project is anticipated to result in a temporary loss of vegetation during construction. In the Ha Tsuen pumping station compound approximately 30 trees comprising a mix of Acacia and Eucalyptus species planted as amenity planting will need to be removed to accommodate the new extension works. Subject to a detailed tree survey it may be possible to transplant some of the better specimens to the perimeter to reinforce the existing screen planting. In addition, upon completion of the construction works, it is proposed to provide compensatory tree planting to create denser and more effective boundary screen planting. The net landscape impact will be a loss of 0.19 ha. of mixed woodland and 0.33 ha. of lawn and shrubs.
13.9.1.2 At San Wai STW, an area of fishpond will need to be backfilled and approximately 50 trees comprising a mix of Acacia, Celtis, Mallotus and Macaranga species established on the pond bunds will need to be removed to accommodate the new extension works. Subject to a detailed tree survey it may be possible to transplant some of the better specimens to the proposed 5m wide planting reserve around the perimeter of the existing STW works to establish an effective visual screen to the site. The peripheral planting will also create a beneficial impact by replacing a portion of the unsightly container yards adjacent to the site. The net landscape impact will be a gain of 0.55 ha. of mixed woodland and a loss of 0.01 ha. of grassland and 1.75 ha. of fishpond.
13.9.1.3 In addition to the proposed compensatory planting the
EIA also recommended the following mitigation measures to ameliorate the
landscape and visual impacts.
Ø Align new utilities clear of existing trees and boundary line of project
sites
Ø Erect protective hoarding around existing trees to be retained to prevent
damage during construction
Ø Store any good excavated topsoil on site for reuse in screen planting and
hydroseeding works
Ø Select recessive colour scheme for the new buildings to help blend them into
the surrounding landscape.
13.9.1.4 With the implementation of the recommended mitigation measures the residual landscape and visual impacts are considered acceptable during the construction and operational phases of this project.
13.10 Summary of Options Review
13.10.1 Options Considered in this EIA
13.10.1.1 Design issues with possible options considered in
this EIA study include:
Ø Chemicals for CEPT in the expanded and upgraded San Wai STW
Ø Disinfection options for the expanded and upgraded San Wai STW
Ø Sewage treatment levels for the expanded and upgraded San Wai STW
Ø Alignments of emergency bypass culvert
13.10.1.2 Environmental aspects that are most relevant to the above design issues were discussed and assessed in different sections of this EIA report. A summary of the comparisons and assessments are presented in the following paragraphs.
13.10.2 Chemicals for CEPT in the Expanded and Upgraded San Wai STW
13.10.2.1 The review in Section 2 of this report concluded that various chemicals namely ferric chloride, ferric sulphate, alum, and cationic polymeric coagulants can readily achieve the required effluent quality of <100mg BOD/L and <55 mg SS/L for the proposed expanded San Wai STW.
13.10.2.2 Sludge dewatering has been demonstrated to be without major technical difficulties for both the ferric chloride and alum. Nevertheless, there appears difference in the UV transmittance by using difference chemicals and hence the performance of UV disinfection. The final choice of chemical is likely to depend on the results of UV transmittance tests and review of chemical costs to be undertaken during the detailed design stage of the project.
13.10.3 Disinfection Options for the Expanded and Upgraded San Wai STW
13.10.3.1 A number of potential disinfection options namely chlorination, UV irradiation, ozonation, and microfiltration have been reviewed for the proposed expanded and upgraded San Wai STW. Among the reviewed disinfection options, UV irradiation is considered as a technically feasible option suitable for the proposed expanded and upgraded San Wai STW. This option imposes minimal environmental impacts and lack of by-products in the effluent, and also require the lowest landtake among the reviewed options.
13.10.4 Sewage Treatment Levels for the Expanded and Upgraded San Wai STW
13.10.4.1 Four options of treatment levels were considered in this EIA namely Option 1 (CEPT), Option 2 (CEPT with disinfection), Option 3 (secondary treatment with disinfection), and Option 4 (secondary treatment with nitrogen removal and disinfection).
13.10.4.2 Based on the water quality impact assessment results, there are no substantial differences of Option 2 from Options 3 and 4. Options 3 and 4 would further reduce BOD5 and nutrient levels in the receiving water. However, the model results showed that the improvement of the water quality would be small.
13.10.4.3 Option 2 has an advantage over Option 1 due to the reduction in E. coli in the receiving water body. The model predictions indicated that there would be no adverse water quality impacts for the adoption of Option 2 as a preferred treatment option at San Wai STW.
13.10.4.4 The ecological and fisheries impact assessments indicate that with the adoption of Option 2, it will greatly improve water quality in Deep Bay, which in turn will enhance species richness of benthic fauna and the food base of migratory birds. Besides, the significant improvement in water quality with the adoption of Option 2 would have positive effects on the health of marine organisms including capture fisheries species and marine culture fish species.
13.10.4.5 Option 2, CEPT with disinfection, is thus identified as the preferred treatment option for the expanded and upgraded San Wai STW.
13.10.5 Alignments of Emergency Bypass Culvert
13.10.5.1 Four alternative alignments of the emergency bypass culvert have been proposed and are shown in Figure 1.3. Some sections of the proposed emergency bypass culvert will cross over the proposed HSKNDA and will laid under the local roads of the proposed HSKNDA. The exact alignment of the proposed emergency bypass culvert will thus be subject to modifications as per the road alignment of the proposed HSKNDA. In order to minimise the impact associated with the construction of the emergency bypass culvert, the proposed emergency bypass culvert will be constructed at the same time as the infrastructure works of the proposed HSKNDA.
13.10.5.2 In term of construction phase impacts, Alternative 4 would involve the shortest length and the smallest works area. Therefore, the dust, noise, water quality, ecology as well as visual and landscape impacts associated with the construction of Alternative 4 would be the lowest among the four alternatives. Whereas Alternative 3 alignment would encroach upon the Tseung Kong Wai potential site of cultural heritage with archaeological significance and thus is not preferable from a cultural heritage preservation point of view.
13.10.5.3 All the four alternatives will be constructed in the form of box culvert up to the connection point with the existing Tin Shui Wai Drainage Channel for Alternatives 1, 2, and 3, and with the existing Lo Uk Tsuen Drainage Channel for Alternative 4. The proposed emergency bypass culvert will only be used for discharging treated effluent from the proposed expanded and upgraded San Wai STW under emergency and maintenance situations. The residual sulphide content in the treated effluent would be minimal if any and thus odorous hydrogen sulphide emissions from the treated effluent flowing along the emergency bypass culvert would not be expected. Environmental impacts associated with the operation of the proposed emergency bypass culvert would be minimal if any.
13.10.5.4 Taking into account the potential construction and operational phases impacts of the four alternative alignments, Alternative 4 is identified as the preferred alignment option for the proposed emergency bypass culvert.