4. WATER QUALITY

4.1 Introduction

4.1.1 Water quality impacts arising from the construction and operation of the SWC would be minimised by implementation of suitable mitigation measures and through good management practices. Contractual documents for the SWC project should incorporate the recommended mitigation measures for water pollution control.

4.1.2 Discharges of wastewater generated from the construction activities are subject to control under the Water Pollution Control Ordinance (WPCO). Wastewater should be adequately treated prior to the final discharge. The site management is responsible for applying a discharge licence from EPD for effluent discharges. Monitoring of effluent quality is required to make sure that a full compliance with the licence conditions is achievable. The pollutants should be controlled at source so as to minimise the potential water quality impacts from the construction sites.

4.1.3 Water quality monitoring shall be included in the EM&A programme to ensure that there would be no deterioration of water quality during the construction and operational phases of the Project. Site audits shall also be implemented to ensure that the mitigation measures recommended in the EIA are fully implemented.

4.1.4 Pollutants generated from vehicles, which use the Shenzhen Western Corridor, would enter the Deep Bay waters and the mudflats through road drainage systems when a rainstorm occurs. Pollutants that are harmful to birds and the other organisms living on the mudflats would have detrimental effects to the environment in Deep Bay.

4.1.5 It has been recommended in the EIA that HyD should undertake the task to clean the road twice a week (each of the cleaning events should not be separated by more than four days) using a vacuum air sweeper/truck to remove the pollutants at source and to prevent build-up of the pollutants on the road surface. In order to ensure that the bridge runoff after the cleaning operation would not be heavily polluted, monitoring of bridge runoff during the operational phase of the SWC project is included as part of the environmental monitoring and audit programme.

4.1.6 The purposes of the monitoring are to determine the characteristics of bridge runoff in particular the first flush flow from the SWC bridge during rainstorm events and to review the frequency of road cleaning.

4.2 Water Quality Parameters

Construction Phase Monitoring - Marine Water

4.2.1 The monitoring shall be carried out by the ET to ensure that any deterioration of water quality could be readily detected and action be taken in time to rectify the situation.

4.2.2 To check compliance with relevant Water Quality Objectives (WQOs), monitoring of suspended solids (SS) and tributyltin (TBT) shall be included in the water quality monitoring. Measurement of TBT is included as the release potential of TBT at the sediment sampling locations D1, D2, D3 and D5 (see Figure EM4.1) was high as indicated in the EIA Report.

4.2.3 In association with the water quality parameters, some relevant data should also be measured/recorded, such as monitoring location/position, sampling time, water depth, water temperature, salinity, dissolved oxygen saturation, turbidity, pH, dissolved oxygen, weather conditions, sea conditions, tidal stage, and any special phenomena and work being carried out at the construction site.

4.2.4 A sample monitoring record sheet is shown in Appendix B-3 for reference.

Operational Phase Monitoring - Bridge Runoff

4.2.5 The monitoring shall be carried out by the ET to ensure that any deterioration of bridge runoff quality could be readily detected and action be taken in time to rectify the situation.

4.2.6 Water samples shall be collected and analysed for the following most commonly found pollutants in highway runoff:

· Total suspended solids
· Total organic carbon
· Chemical oxygen demand
· Nitrate
· Nitrite
· Total Kjeldahl Nitrogen
· Total phosphorus
· Copper
· Lead
· Zinc

4.2.7 The average flow rate of runoff passing through the drainage down pipe shall either be measured using a flow measurement device or estimated based on the Rational Method (Stormwater Drainage Manual by Drainage Services Department) and hydraulic calculations. Rainfall intensity and duration of each rainstorm event based on the information collected from relevant monitoring station of the Hong Kong Observatory shall be reported. All this information shall be used to review the effectiveness of the mitigation measure.

4.3 Monitoring Equipment

Dissolved Oxygen and Temperature Measuring Equipment

4.3.1 The instrument should be a portable, weatherproof dissolved oxygen-measuring instrument equipped with cable, sensor, comprehensive operation manuals, and use a DC power source. It should be capable of measuring:

	dissolved oxygen level in the range of 0-20 mg/l and 0-200% saturation; and
	temperature of 0-45 oC.

4.3.2 It should have a membrane electrode with automatic temperature compensation complete with a cable. Sufficient stocks of spare electrodes and cables should be available for replacement where necessary (e.g. YSI model 59 meter, YSI 5739 probe, YSI 5795A submersible stirrer with reel and cable or an approved similar instrument).

4.3.3 Should salinity compensation not be built-in in the DO equipment, in-situ salinity shall be measured to calibrate the DO equipment prior to each DO measurement.
Turbidity Measurement Instrument

4.3.4 The instrument should be a portable, weatherproof turbidity-measuring instrument complete with comprehensive operation manual. The equipment should use a DC power source. It should have a photoelectric sensor capable of measuring turbidity between 0?1000 NTU and be complete with a cable (e.g. Hach model 2100P or an approved similar instrument).

Suspended Solids

4.3.5 A water sampler comprises a transparent PVC cylinder, with a capacity of not less than 2 litres, and can be effectively sealed with latex cups at both ends. The sampler should have a positive latching system to keep it open and prevent premature closure until released by a messenger when the sampler is at the selected water depth (e.g. Kahlsico Water Sampler or an approved similar instrument).

4.3.6 Water samples for suspended solids measurement should be collected in high density polythene bottles, packed in ice (cooled to 4 oC without being frozen), and delivered to the laboratory as soon as possible after collection.

Salinity

4.3.7 A portable salinometer capable of measuring salinity in the range of 0-40 mg/l should be provided for measuring salinity of the water at each monitoring location.

Positioning Device

4.3.8 The locations of water monitoring points should be located using a hand-held or boat-fixed type digital Global Positioning System (GPS) with way point bearing indication or other equivalent instrument of similar accuracy. This is to ensure that the water sampling locations are correct during the water quality monitoring work.

Water Depth Detector

4.3.9 A portable, battery-operated echo sounder should be used for the determination of water depth at each designated monitoring station. This unit can either be handheld or affixed to the bottom of the work boat, if the same vessel is to be used throughout the monitoring programme.

Water Sampling Equipment

4.3.10 A transparent PVC or glass cylinder, which has a volume of not less than 2 litres and can be sealed at both ends with cups, should be used for collection of water samples at various depths. The water sampler should be equipped with a positive latching system. During water sampling, a messenger is released to trigger the closure of the water sampler at suitable water depth.

4.3.11 All in-situ monitoring instruments should be checked, calibrated and certified by a laboratory accredited under HOKLAS or any other international accreditation scheme before use, and subsequently re-calibrated at 3 monthly intervals throughout all stages of the water quality monitoring. Responses of sensors and electrodes should be checked with certified standard solutions before each use. Wet bulb calibration for a DO meter should be carried out before measurement at each monitoring location.

4.3.12 For the on site calibration of field equipment, the BS 127:1993, Guide to Field and On-Site Test Methods for the Analysis of Water should be observed.

4.3.13 Sufficient stocks of spare parts should be maintained for replacements when necessary. Backup monitoring equipment shall also be made available so that monitoring can proceed uninterrupted even when some equipment is under maintenance, calibration, etc.

Runoff Sampling Equipment

4.3.14 Water samples shall be collected using automatic samplers. The sampling tube of the automatic sampler should be connected to the outlet of the selected drainage down pipe to collect water sample. Installation of a control device is required to switch on the automatic sampler when bridge runoff is detected. The control device is triggered by the existence of flow. Alternatively, the sampling tube and the control device should be placed inside the selected road gully on the bridge deck to collect water samples. Gully grating should be removable so as to facilitate the installation of the equipment.

4.3.15 Based on the findings in the University of New South Wales (UNSW) Research Report No. 204 , pollutant concentrations in runoff were negligible after 20 to 30 minutes. The automatic sampler shall therefore be programmed to collect the first 20 to 30 minutes of bridge runoff. The automatic sampler shall contain 24 individual sampling bottles.

4.4 Laboratory Measurement / Analysis

Construction Phase Monitoring - Marine Water

4.4.2 Analysis of suspended solids shall be carried out in a HOKLAS or other international accredited laboratory. Water samples of a bout 1000 ml shall be collected at the monitoring stations for carrying out the laboratory SS determination. The detection limit shall be 0.5 mg/L or better. The SS determination work shall start within 24 hours after collection of the water samples. The SS determination shall follow APHA 17ed 2540D or equivalent methods subject to approval of DEP.
4.4.3 There are no assessment criteria for defining allowable concentrations of organic

micro-pollutants in the receiving water. USEPA Standards and the European Community Standards were used in the EIA as the assessment criteria for TBT. In order to compare with the assessment criteria, the recommended detection limit for TBT is 0.002 mg/L. Water samples of at least 1000 ml shall be collected at the monitoring stations for laboratory analysis of TBT. The TBT determination shall follow Krone et al. (1989) - GC/MS or equivalent methods subject to approval of DEP.

Operational Phase Monitoring - Bridge Runoff

4.4.4 Each water sample collected shall be one litre in volume and a total of 24 individual samples shall be collected per each rainstorm event. For a rainstorm event with less than 24 samples collected, the water samples need not to be analyzed and the monitoring event will not be counted. 4 composite samples shall be prepared from the 24 individual water samples for laboratory analysis. The first composite sample is a mix of the first to sixth water samples collected in the automatic sampler. Similar approach shall be used to prepare the other composite samples. After each rainstorm event, the water samples collected in the automatic sampler shall be delivered to laboratory for analysis within as short a time as possible. The water samples shall be cooled to 4°C without being frozen. The analysis shall commence within 24 hours after collection of the water samples. The water samples shall be analysed in a HOKLAS or other international accredited laboratory.

4.4.5 The detection limits for the bridge runoff parameters are shown in Table EM 4.1.

Notes:

1. APHA: American Public Health Association. Standard Methods for the Examination of Water and Wastewater Ed 19

2. ASTM: Annual Book of American Society for Testing and Materials Standards, Vol 11.01 & 11.02.

4.5.3 Tidal flows in Deep Bay move from the Deep Bay mouth to the inner part of the bay during flood tides. The tidal flow direction reverses during ebb tides. Impact on water quality should be monitored in accordance with the direction of flow. For example, when the tidal current moves towards the Inner Deep Bay during flood tides, W2 station is used as a control station, whereas W1 station is used for impact monitoring. When the tidal current direction is reversed, W1 station is used as a control, whereas W2 station is for impact monitoring.

4.5.4 The SWC will be connected to Deep Bay Link (DBL) at Ngau Hom Shek. Any discharges from the works area for SWC and from the section of DBL near Ngau Hom Shek may cause water quality impacts to Deep Bay. Construction wastewater and site runoff generated from the SWC works area and the DBL project near Ngau Hom Shek would be properly treated before discharging into Deep Bay. The discharge location is shown in Figure EM4.2. Monitoring stations W1 and W2 are therefore also used to monitor the water quality conditions in the region near the discharge location.

4.5.5 The locations of W1 and W2 are within inter-tidal zone and monitoring at these two locations may be affected by the tidal conditions. When the water depth at these locations is too shallow, monitoring may not be feasible. The ET Leader shall propose updated monitoring locations for these two monitoring stations and seek approval from the IEC, DAFC and DEP.

4.5.6 The status and locations of water quality sensitive receivers and the marine activities sites may change after issuing this manual. If such cases exist, the ET Leader shall propose updated monitoring locations and seek approval from the IEC, DAFC and DEP.

4.5.7 When alternative monitoring locations are proposed, they should be chosen based on the following criteria:
(a) at locations close to and preferably at the boundary of the mixing zone of the major site activities, which are likely to have water quality impacts;
(b) close to the sensitive receptors which are directly or likely to be affected;
(c) for monitoring locations located in the vicinity of the sensitive receptors, care should be taken to cause minimal disturbance during monitoring;
(d) two or more control stations which shall be at locations representative of the project site in its undisturbed condition. Control stations should be located, as far as is practicable, both upstream and down stream of the works area.

4.5.8 Control stations area necessary to compare the water quality from potentially impacted sites with the ambient water quality. Control stations shall be located within the same body of water as the impact monitoring stations but shall be outside the area of influence of the works and, as far as practicable, not affected by any other works.

4.5.9 Measurements shall be taken at 3 water depths, namely, 1m below water surface, mid-depth and 1m above sea bed, except where the water depth less than 6m, the mid-depth station may be omitted. Should the water depth be less than 3m, only the mid-depth station will be monitored. The ET Leader shall seek approval from the IEC, DAFC and DEP on all the monitoring stations.

4.5.10 Replicates in-situ measurements and samples collected from each independent sampling event are required for all parameters to ensure a robust statistically interpretable dataset.

Operational Phase Monitoring - Bridge Runoff

4.5.11 Water samples shall be collected during rainstorm events at the outlets of the drainage down pipes or from the road gullies. Since the types of fuel used by the vehicles travelling on the southbound carriageway and the northbound carriageway of the SWC bridge may not be the same, three sampling points shall be allocated at each side of the carriageways. The exact locations of the sampling points shall be determined based on the final road drainage layout plan to be prepared at the detailed design stage.

4.6 Baseline Monitoring

Marine Water

4.6.1 Baseline conditions for water quality shall be established and agreed with DEP prior to the commencement of works. The purposes of the baseline monitoring are to establish ambient conditions prior to the commencement of the works and to demonstrate the suitability of the proposed impact, control and reference monitoring stations. The baseline conditions shall normally be established by measuring the water quality parameters specified in Section 4.2.

4.6.2 Seasonal variations and human activities in the vicinity of monitoring area may change the water quality conditions. The water quality data collected during baseline monitoring may not be able to fully represent the ambient water quality conditions during the construction period of the SWC project. Concurrent monitoring of water quality at the control stations and impact monitoring stations could minimise any influence from seasonal and local variations of water quality conditions in the region where monitoring is carried out.

4.6.3 In view of the above, it is therefore suggested to review the trend of water quality conditions at the project site using EPD's data measured at DM2, DM3 and DM4 for the past 10 years. Measurements at all the designated monitoring stations including control stations at mid-flood and mid-ebb tides should also be conducted for at least 4 weeks (3 days per week) prior to the commencement of marine works to provide data to establish the baseline conditions. There shall not be any marine construction activities in the vicinity of the stations during the baseline monitoring. The water quality parameters specified in Section 4.2 should be measured during the baseline monitoring. However, the TBT measurement can be monitored once a week at three water depths during flood and ebb tides at W1, W2, W3, W4, W5 and W6. In the event that questionable baseline monitoring data are obtained or the baseline monitoring data are significantly different from the EPD's data, the ET Leader shall seek approval from the IEC and DEP on the final data set to be used as baseline reference.

4.6.4 Baseline monitoring schedule shall be faxed to EPD 1 week prior to the commencement of baseline monitoring. The interval between 2 sets of monitoring shall not be less than 36 hours.

4.7 Construction Phase Impact Monitoring

Marine Water

4.7.1 During the course of the marine works, monitoring shall be undertaken three days per week, at mid-flood and mid-ebb tides, with sampling/measurement at the designated monitoring stations. The monitoring frequency for TBT can be limited to two days per week. The interval between two sets of monitoring shall not be less than 36 hours except where there are exceedances of Action and/or Limit levels, in which case the monitoring frequency will be increased.

4.7.2 The release potential of TBT at the sediment sampling locations D1, D2, D3 and D5 (see Figure EM4.2) was high as indicated in the EIA Report. Measurements of TBT at W1, W2, W3, W4, W5 and W6 are included to detect the increase in TBT levels when sediment dredging is carried out at pier sites. However, the need for monitoring TBT should be reviewed every 2 months based on the monitoring results. The review period should cover dredging being carried out at D1, D2, D3 and D5. If the measured TBT levels at the control and impact monitoring stations during dredging are consistently lower than the reference criteria of the European Community Standard of 0.002 mg/L or are consistent with the baseline TBT results, it would not be necessary to include this parameter in the subsequent monitoring programme. Approval from the IEC, AFCD and DEP on this arrangement is required.

4.7.3 Upon completion of all marine activities, a post marine works monitoring exercise on water quality shall be carried out for four week in the same manner as the impact monitoring.

4.7.4 Proposed water quality monitoring schedule should be faxed to AFCD and EPD on or before the first day of the monitoring month, AFCD and EPD should also be notified immediately for any changes in schedule by fax.

4.8 Operational Phase Impact Monitoring

Bridge Runoff

4.8.1 The road cleaning frequency proposed in the SWC EIA is twice a week. Each of the cleaning events should not be separated by more than four days. For bridge runoff monitoring, the minimum interval between two sampling events shall not be less than 4 days. Since the initial traffic flow in SWC would be low and may not truly reflect the normal conditions of the bridge usage at the beginning of the bridge opening, two periods of monitoring during the first 3 months and after 6 months of the opening of the SWC bridge should be considered. The monitoring should include in total 12 sampling/rainstorm events (12 sets of data) and cover the dry season period. A total of 6 sets of sampling data should be collected during the first 3 months after the opening of the SWC bridge. The other 6 sets of sampling data should be collected in month 7 to month 9 after the opening of the SWC bridge. The monitoring results of each sampling event shall be submitted to EPD for information once the data is available. If the monitoring results trigger the proposed action level, the cleaning frequency shall be increased to remove the vehicle-generated pollutants from the SWC bridge. In case that the effective rainstorm events are less than 6 for each of the monitoring periods, the ET Team Leader shall seek approval from IEC and DEP for extending the monitoring period to collect enough bridge runoff data.

4.8.2 A review report shall be prepared by the ET after each monitoring period that includes 6 sets of data to evaluate the road runoff quality and to determine if the proposed cleaning frequency is adequate to remove pollutants from the road section. The average daily number of vehicles using the northbound and southbound carriageways based on the traffic data published in the "Transport Monthly Digest" by Transport Department or to be obtained directly from relevant government departments should be reported to give an indication of the effectiveness of road cleaning to different levels of traffic flows. All the monitoring results shall also be included in the EM&A report. The bridge runoff monitoring programme will also be reviewed after the completion of the 12 sampling/rainstorm events for the two periods to determine whether the monitoring programme needs to be extended.
4.9 Event and Action Plan for Water Quality

Construction Phase Monitoring - Marine Water

4.9.1 The water quality assessment criteria, namely Action and Limit levels are based on EPD's data, the results of baseline monitoring and WQO of the relevant water control zone (Table EM4.3). Should the monitoring results of the water quality parameters at any designated monitoring stations indicate that the water quality assessment criteria are exceeded, the actions in accordance with the Action Plan in Table EM4.4 should be carried out. For TBT, Action and Limit levels should be agreed with AFCD and EPD after completing the baseline monitoring. The time for TBT analysis would be longer than the other monitored parameters, a separate Event and Action Plan for exceedance of TBT level is included in Table EM4.5.

Table EM4.4 Event and Action Plan for Water Quality

Table EM4.5 Event and Action Plan for Exceedance of TBT

Operational Phase Monitoring - Bridge Runoff

4.9.2 There are no existing guidelines for controlling the discharge of road runoff into the Hong Kong waters. Since the main objective of implementing frequent cleaning of vehicle-generated pollutants from the SWC bridge is to prevent the pollutants from entering the Deep Bay waters and the mudflats, the pollution level of the bridge runoff with frequent cleaning should be lower than that of the normal road runoff from highways and expressways. With the implementation of road cleaning twice a week on the SWC bridge, it is expected that the pollutant concentrations of the bridge runoff would be low.

4.9.3 There is no information to establish the baseline pollutant concentrations of the bridge runoff for the case without road cleaning. It is difficult to know whether the pollution levels of the bridge runoff with road cleaning have been reduced. A stormwater study would soon be carried out by EPD. Relevant information on the quality of highway runoff would be available by the time of the operational phase monitoring for the SWC. At present, it is proposed to use relevant overseas highway runoff data to form a set of reference criteria for comparison with the future monitoring data and to determine whether the runoff generated from the SWC bridge is within acceptable levels. The reference criteria shall be reviewed before the commencement of the operational phase monitoring to incorporate the latest findings from EPD's stormwater study.

4.9.4 Table EM4.6 shows the general characteristics of highway runoff collected from various overseas studies. The ranges of pollutant concentrations are included in the last column of the table.

4.9.5 In Table EM4.6, the value in bracket represents the average of the lowest value and the highest value of the parameter. At present, there is no information to establish the baseline pollutant concentrations of the road runoff for the case without cleaning. The average pollutant concentrations for highway runoff shown in the table are used as reference criteria to compare with the pollutant concentrations for the future bridge runoff. Table EM4.7 summarises the proposed criteria. The proposed action level and required action are also included in the table. The criteria should be reviewed and updated prior to the commencement of the monitoring based on the latest findings from EPD's stormwater study.

Table EM4.7 Proposed Criteria to be Used for Determination of Cleaning Frequency, Action Level and Action

4.10 Site Audits

4.10.1 Implementation of regular site audits is to ensure that the recommended mitigation measures shall be properly undertaken during the construction and operational phases of the SWC project. It could also provide an effective control of any malpractices and achieve continual improvement of environmental performance on site.

4.10.2 The ET is responsible for carrying out the regular site audits. Site audits would include site inspections, compliance and conformance audits and environmental complaints.

Site Inspections

4.10.3 A programme for site inspections should be established defining the frequency, procedures and actions to be undertaken during the carrying out of site inspections. Site inspections should be based on the mitigation measures for water pollution control recommended in the EIA Report. In the event that the recommended mitigation measures are not fully or properly implemented, deficiency should be recorded and reported to the site management. Suitable actions are to be carried out to:
· Investigate the problems and the causes;
· Issue action notes to the Contractor which is responsible for the works;
· Implement remedial and corrective actions immediately;
· Re-inspect the site conditions upon completion of the remedial and corrective actions; and
· Record the event and discuss with the Contractor for preventive actions.

4.10.4 The ET should liaise closely with the Contractor to obtain information on the adopted working methods. Submission of method statements for the construction and operation activities by the Contractor could help the ET to accurately address the potential water quality impacts that may arise. Alternative working methods could be suggested to the Contractor in order to avoid adverse water quality impacts.

Compliance and Conformance Audits

4.10.5 Monitoring of effluent quality is required during the construction and operational phases of the Project. The monitoring should be carried out at the pre-determined discharge point. Compliance audits are to be undertaken to ensure that a valid discharge licence has been issued by EPD prior to the discharge of effluent from the project site. In addition, the monitoring frequency and parameters specified in the discharge licence should be fully considered during the monitoring. The audit results reflect whether the effluent quality is in compliance with the discharge licence requirements. In case of non-compliance, suitable actions should be undertaken to:

· Notify the site management for the non-compliance;
· Identify the sources of pollution;
· Check the implementation status of the recommended mitigation measures;
· Investigate the operating conditions of the sedimentation systems;
· Implement corrective and remedial actions to improve the effluent quality;
· Increase monitoring frequency until the effluent quality is in compliance with the discharge licence requirements; and
· Record the non-compliance and propose preventive measures.

4.10.6 Conformance audits are to ensure that the works carried out by the Contractor meet the statutory regulations and water pollution control requirements specified in the contractual documents. The Contractor should be responsible for design and implementation of the recommended mitigation measures. The ET should:

· Check the contractual documents which define the roles of the Contractor in water pollution control;
· Recommend necessary improvement works to the mitigation measures designed and undertaken by the Contractor;
· Evaluate the effectiveness of mitigation measures performed by the Contractor;
· Carry out ad hoc inspections of the Contractor's performance on water pollution control;
· Report to the site management for any non-conformance works; and
· Initiate actions to remedy any non-conformance works.

4.10.7 Good housekeeping on site is essential to the protection of water pollution. It is recommended to conduct audits to ensure that all the recommended elements are fully incorporated in the management system. It is recommended that pre-set checklists could be used to check the overall performance.

Environmental Complaints

4.10.8 A complaint hotline may be provided to the public for reporting of any unsatisfactory environmental conditions that could be created by the SWC project. Procedures for complaint investigation should be developed in advance of commencement of the construction works. When a complaint on water pollution is received, the ET should:
· Record the date and time of receipt, and name and contact telephone number of the complainant;
· Report the complaint to the site management and initiate the investigation according to the information provided by the complainant;
· Discuss with the Contractor to verify the complaint and to identify the possible sources of pollution;
· Check the effectiveness and adequacy of relevant mitigation measures if the complaint is valid;
· Implement necessary corrective and remedial actions;
· Monitor the situation and take necessary follow-up action; and
· Inform the complainant the investigation results and actions taken for remedial works.

Continual Improvement

4.10.9 Implementation of mitigation measures safeguards the aquatic environments in the vicinity of the SWC alignment and is one of the important components for improvement of water pollution control. This component needs to be integrated with other components to form an integral system for achieving water pollution control. These include:

· commitment to control water pollution;
· good planning;
· staff training;
· checking and corrective actions; and
· management review.

4.10.10 The integral system should be implemented in a systematic manner. Continual improvement of water pollution control would be achieved through the implementation of the integral system.

4.11 Water Quality Mitigation Measures

4.11.1 Mitigation measures for control of water pollution have been recommended in the EIA Report on Shenzhen Western Corridor. The Contractor should be responsible for the design and implementation of these measures. The recommended mitigation measures and guidelines to reduce the potential water quality impacts during the construction and operational phases of the SWC project are summarised as follows:

During Construction Phase

Construction Site Runoff and Wastewater from Construction Activities

4.11.2 Good site practices should be adopted in order to handle and treat the excavated soils and fill materials on site.

4.11.3 Wastewater generated from washing of concrete lorry on site should be properly treated.
4.11.4 Practices outlined in ProPECC PN 1/94 Construction Site Drainage should be adopted in order to minimise the potential water quality impacts from construction site runoff and various construction activities.

4.11.5 Perimeter channels in the works areas should be installed to intercept runoff at site boundary where practicable.

4.11.6 Drainage channels are required to collect site runoff and convey site runoff to sand/silt traps for removal of soil particles.

4.11.7 Provision of regular cleaning and maintenance to ensure the normal operation of the facilities throughout the construction period.

4.11.8 Sand bags should be provided in areas where a large amount of exposed soils exist to control site runoff before a rainstorm occurs.

4.11.9 The construction programme should be properly planned to minimise soil excavation, if any, in rainy seasons, so as to prevent soil erosion from exposed soil surfaces.

4.11.10 Exposed stockpiles should be covered with tarpaulin or impervious sheets before a rainstorm occurs.

4.11.11 The exposed soil surfaces should be properly protected to minimise dust emission.

4.11.12 Hydroseeding should be applied to protect exposed slope surfaces.

4.11.13 The stockpiles of materials should be placed in the locations away from the shore and stream courses so as to avoid releasing materials into these water bodies.

4.11.14 Final surfaces of earthworks should be compacted and protected by permanent work.

4.11.15 Haul roads should be paved with concrete and the temporary access roads should be protected using crushed stone or gravel, wherever practicable.

4.11.16 Wheel washing facilities should be provided at all site exits to ensure that earth, mud and debris in the works areas would not be taken away by vehicles.

4.11.17 A discharge licence should be applied from EPD for discharging effluent from the construction site. The discharge quality is required to meet the requirements specified in the discharge licence.

4.11.18 All the runoff and wastewater generated from the works areas should be collected and diverted to a wastewater treatment system for removal of suspended solids and to adjust pH prior to final discharge.

4.11.19 Suitable coagulants and neutralising chemicals should be used to enhance the efficiency of the treatment system.

4.11.20 Treated effluent should be reused and recycled so as to minimise water consumption and reduce the effluent discharge volume.

4.11.21 During the installation of the SWC bridge sections, good site practices should be adopted to clean the rubbish and litter on the bridge sections so as to prevent the rubbish and litter from dropping into the Deep Bay waters.

4.11.22 Road sections should be cleaned on a regular basis.

Sewage from Workforce

4.11.23 Chemical toilets should be provided in the works areas. In view of the length of the SWC bridge, chemical toilets may also be required to provide on the some of the completed bridge sections at the later stage of the construction works for collection of sewage from workforce.

4.11.24 Wastewater generated from kitchens, if any, should be collected in a temporary storage tank.
4.11.25 A licensed waste collector should be deployed to clean the chemical toilets and temporary storage tank on a regular basis. The collected sewage and wastewater should then be transported to the sewage treatment plants for disposal.

4.11.26 Notices should be posted at conspicuous locations to remind the workers not to discharge any sewage or wastewater into the Deep Bay waters during the construction phase of the project.
Accidental Spillage of Chemicals

4.11.27 An emergency plan should be developed by the contractor in order to deal with accidental spillage of chemicals.

4.11.28 A chemical waste producer should be registered if chemical wastes would be produced from the construction activities. The Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular the Waste Disposal (Chemical Waste) (General) Regulation should be observed and complied with for control of chemical wastes.

4.11.29 Areas for chemical storage should be securely locked and kept as far from the drainage systems or stream courses as possible.

4.11.30 Retention structure, which can contain the content of the largest container or 20% of the total chemical waste volume in the storage area should be provided to minimise release of chemicals during accidents.

4.11.31 Disposal of chemical wastes should be carried out in compliance with the Waste Disposal Ordinance. The Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes published under the Waste Disposal Ordinance details the requirements to deal with chemical wastes. General requirements are given as follows:

· Suitable containers should be used to hold the chemical wastes to avoid leakage or spillage during storage, handling and transport.
· Chemical waster containers should be suitably labelled to notify and warn the personnel who are handling the wastes to avoid accidents.
· Storage area should be selected at a safe location on site and adequate space should be allocated to the storage area.

Sediment Dredging

4.11.32 Mitigation measures are:

· Cofferdams should be installed prior to dredging of sediment for pile cap construction. One of the purposes of installing the cofferdams is to provide a confined environment that can be isolated from the surrounding water during dredging, hence water pollution would be minimised.
· Closed grabs or sealed grabs should be used for sediment dredging and the mechanical grabs need to be tightly sealed.
· The dredging operation should be carefully controlled to avoid splashing sediment into the surrounding water during the transfer of sediment from the dredging point to the barge.
· Cleaning of excess material from decks and exposed fittings of barge before the barge moves away from the dredging point.
· The distance between the barge for sediment dredging and the cofferdam should be shortened as far as possible to avoid sediment loss from the closed grab to the surrounding water.
· Transport of dredged sediment along the temporary access bridge in shallow water region should be carefully controlled to avoid splashing sediment into the temporary access bridge and the surrounding water.

4.11.33 Silt curtains should be installed at each pier site throughout the period with dredging activities. Provision of silt curtains surrounding the pier site would reduce the spreading of sediment in the water. Water quality monitoring should be implemented during the construction period to ensure the surrounding water quality is within acceptable levels. Routine water monitoring is required and shall be included as part of the EM&A programme.

4.11.34 Proposed mitigation measures for sediment dredging at Mai Po:

1. Access Route
· install sheet piles at both end of the access route to isolate the dredging area as a dry area
· stockpiling of the dredged material should be avoided
· suspend the dredging work and cover the dredged material with tarpaulin or impervious sheets when a rainstorm occurs
2. Inlet Water Channel
· use a floating pontoon equipped with closed grab to carry out the dredging work during flood tides
· install silt curtains or sheet piles to confine the dredging area so as to avoid spreading of sediment plume
· employ a licensed waste collector to collect and dispose the dredged material in compliance with the Dumping at Sea Ordinance

Changes in Hydrodynamic Conditions during the Bridge Pier Construction

4.11.35 Mitigation measures to minimise the effect on tidal flows during the bridge pier construction are:
· To avoid the install and removal of cofferdam during high tidal current conditions, i.e. mid-flood and mid-ebb;
· Remove the cofferdam immediately after the completion of bridge pier construction at each pier site; and
· Remove a strip of oyster beds along the bridge alignment to restore tidal flows prior to the commencement of construction work.

During Operational Phase

Road Runoff from SWC Bridge

4.11.36 A road drainage system should be provided to collect road runoff from the road surface of the SWC bridge. The collected road runoff would either be discharged into the Deep Bay waters or be released to the mudflat depending on the location of the drainage pipe.

4.11.37 Standard design and cleaning should be adopted for treating the road runoff. Standard HyD road gullies incorporate silt traps that collect sediment should be provided on SWC bridge.

4.11.38 Vehicle-generated pollutants should be removed from the road surface prior to the occurrence of a rainstorm to prevent them from entering the Deep Bay waters and to Deep Bay mudflat. HyD should undertake the task to clean the road twice a week (each of the cleaning events should not be separated by more than four days) during low traffic flow period using vacuum air sweeper/truck equipped with side broom, which is to sweep road sludge and debris into the suction nozzle to increase the removal efficiency of pollutants. Vacuum air sweeper/truck is commercially available. One of the types of vehicles available is Johnston Vacuum Suction Sweeper. This operation would prevent build-up of the pollutant load on the road surface. After the removal of the pollutants, the pollution levels in storm runoff would be much reduced. The collected pollutants would be tankered away for off site disposal at landfill sites. There is a need to monitor the bridge runoff quality during the operational phase of the Project.

4.11.39 Monitoring of bridge runoff during the operational phase of the SWC project is recommended to determine the effectiveness of the vacuum cleaning operation. If required, the cleaning frequency would be increased.

4.11.40 An energy dissipator would be installed in the drainage down pipe at the bottom of the pier to reduce exit flow velocity and to minimise the disturbance to mudflat.

Accidental Spillage of Chemicals During Accidents

4.11.41 For general vehicle accidents, emergency response actions should be undertaken by relevant government depart ments to control the spreading of oil spill on the road surface and release of spill into Deep Bay; and clean up the spill.

4.11.42 For vehicle accidents involving chemical spillage, the risk is minimized through:

· Implementation of the revised regulations of FSD to minimise the risk of accidental spillage of chemicals as a result of vehicle accidents on SWC.
· Development of a detailed Emergency Response Plan to enhance the established response actions in order to take due consideration of the need to protect the ecologically sensitive Deep Bay environment;
· Implementation of the detailed Emergency Response Plan with the support from relevant government departments to deal with any spill incident;
· Quick response to vehicle accident, which involves chemical spillage, on SWC;
· Storage of clean up materials at HKPF's weigh-station near Ha Tsuen Interchange for use in controlling the spreading of spill; and
· Assessment of the viability of incorporating the drainage interceptor in the bridge drainage system at the detailed design stage of the SWC project.