4. WATER QUALITY

Introduction

4.1 As identified in the EIA Report, construction of the seawall and reclamation at Tai Lam Kok and seawall between Ka Loon Tsuen and Tai Lam Kok would involve dredging activities which would cause disturbance to the marine sediments and release of fine sediments into suspension. Marine water quality monitoring shall be carried out during the construction phase to ensure that any unacceptable increase in suspended solids/turbidity and decrease in dissolved oxygen due to dredging activities could be readily detected and timely action be taken to rectify the situation.

4.2 The water quality impact assessment undertaken in the EIA study concluded that adverse impacts on water quality arising from the release of heavy metals in contaminated sediment are not anticipated during the dredging works. A quantification of the release of heavy metals from the sediment pore water indicated that the predicted instantaneous concentrations in the marine waters surrounding the dredging site would not exceed the UK Water Quality Standards. The monitoring of heavy metals in the water column is therefore not considered necessary during the dredging work.

4.3 Filling works of the project will only commence when the seawall construction has been completed and would taken place behind the seawalls. Any losses of fine sediment to suspension during filling would thus be retained by the seawalls and are not expected to affect the receiving waters beyond the reclamation areas.

Water Quality Parameter

4.4 Dissolved oxygen (DO), turbidity in NTU and suspended solids (SS) levels shall be monitored by ET to ensure that any deteriorating water quality is readily detected and timely action taken to rectify the situation. DO and turbidity should be measured in-situ whereas SS should be determined by an approved laboratory.

4.5 In association with the water quality parameters, other relevant data shall also be recorded, such as monitoring location/position, time, water depth, water temperature, salinity, DO saturation, sea conditions, tidal stages, weather conditions and any special phenomena and work underway at the construction site.

4.6 A sample monitoring record sheet is shown in Appendix 6.

Monitoring Equipment

Dissolved Oxygen and Temperature Measuring Equipment

4.7 The instrument should be a portable, weatherproof dissolved oxygen (DO) measuring instrument complete with cable and sensor, and use a DC power source. The equipment should be capable of measuring:

· a DO level in the range of 0‑20 mg/l and 0‑200% saturation; and

· a temperature of 0‑45 degree Celsius.

4.8 It should have a membrane electrode with automatic temperature compensation complete with a cable. Sufficient stocks of spare electrodes and cables shall 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).

4.9 Should salinity compensation not be built-in in the DO equipment, in-situ salinity should be measured to calibrate the DO equipment prior to each DO measurement.

Turbidity Measurement Instrument

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

Water Sampler

4.11 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).

Water Depth Detector

4.12 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 hand held or affixed to the bottom of the work boat, if the same vessel is to be used throughout the monitoring programme.

Salinity

4.13 A portable salinometer capable of measuring salinity in the range of 0-40 mg/l (i.e. ppt-part per thousand) should be provided for measuring salinity of the water at each monitoring location.

Sample Containers and Storage

4.14 Water samples for SS measurement should be stored in high density polythene bottles with no preservative added, packed in ice (cooled to 4°C without being frozen) and delivered to the laboratory and analyzed as soon as possible after collection.

Monitoring Position Equipment

4.15 A hand-held or boat-fixed type digital Differential Global Positioning System (DGPS) with way point bearing indication or other equivalent instrument of similar accuracy should be provided and used during marine water monitoring to ensure the monitoring vessel is at the correct location before taking measurements.

Calibration of In-Situ Instruments

4.16 The DO meter and turbidimeter shall 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 shall be carried out before measurement at each monitoring location.

4.17 For the on site calibration of field equipment, the BS 127:1993, "Guide to Field and on-site test methods for the analysis of waters" should be observed.

4.18 Sufficient stocks of spare parts shall 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.

Laboratory Measurement / Analysis

4.19 Analysis of suspended solids in marine water shall be carried out in a HOKLAS or other international accredited laboratory. Water samples of about 1000 ml shall be collected at the monitoring stations for carrying out the laboratory SS determination. The detection limit shall be 1 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 EPD.

4.20 Additional duplicate samples may be required by EPD for inter laboratory calibration. A minimum of 15% of duplicate samples should be collected and analysed for QA/QC purposes. Remaining samples after analysis shall be kept by the laboratory for 3 months in case repeat analysis is required. In any circumstance, the sample testing shall have comprehensive quality assurance and quality control programmes. The laboratory shall prepare to demonstrate the programmes to EPD or his representatives when requested.

Monitoring Locations

4.21 The marine water quality monitoring stations during the construction works are shown in Figure 4.1 and the co-ordinates of the proposed monitoring stations are listed in Table 4.1.

4.22 The status and location of water quality sensitive receivers and marine activity sites may change after issuing this Manual. If such cases exist, the ET leader shall propose updated monitoring locations and seek approval from DEP. When alternative monitoring locations are proposed, they should be chosen based on the following criteria:

(i) locations close to the boundary of the mixing zone of the major site activities as indicated in the EIA Report, i.e. to just outside the sediment plume generated by dredging and filling works (as indicated in the EIA Report);

(ii) close to the sensitive receptors which are directly or likely to be affected;

(iii) 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 downstream of the works area.

Table 4.1 Proposed Marine Water Quality Monitoring Stations

Station	Easting	Northing
Impact Monitoring Station
M1	819649	824284
M2	720315	823874
M3	820838	823800
Control Station
C1	819051	824772
C2	821736	823874

4.23 Control stations are 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 should be outside the area of influence of the works and, as far as practicable, not affected by any other works.

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

Baseline Monitoring

4.25 Baseline conditions for marine water quality shall be established and agreed with EPD prior to the commencement of works. The purpose of the baseline monitoring is to establish ambient conditions prior to the commencement of the works and to demonstrate the suitability of the proposed impact and control monitoring stations. The baseline conditions shall normally be established by measuring the water quality parameters specified in Sections 4.4 – 4.5. The measurements shall be taken at all designated monitoring stations including control stations, three days per week, at mid-flood and mid-ebb tides, for at least four weeks prior to the commencement of marine works.

4.26 There shall not be any marine construction activities in the vicinity of the stations during the baseline monitoring.

4.27 Other relevant data shall also be recorded, such as: monitoring location/position, time, water depth, tidal stages, weather conditions and any special phenomena underway near the monitoring station. There shall not be any marine construction activities in the vicinity of the stations during the baseline monitoring.

4.28 In exceptional cases when insufficient baseline monitoring data or questionable results are obtained, the ET Leader shall seek approval from the IC(E) and EPD on an appropriate set of data to be used as baseline reference.

4.29 Baseline monitoring schedule and a tide table shall be faxed to EPD one week prior to the commencement of baseline monitoring. The interval between two sets of monitoring shall not be less than thirty-six hours.

Impact Monitoring

4.30 During the dredging works for the seawall foundation and reclamation construction, monitoring shall be undertaken three days per week, at mid-flood and mid-ebb tides, with sampling/measurement at the designated monitoring stations. The interval between two sets of monitoring shall not be less than thirty-six hours except where there are exceedances of Action and/or Limit levels, in which case the monitoring frequency will be increased.

4.31 The proposed water quality monitoring schedule shall be faxed to EPD on or before the first day of the monitoring month. EPD and IC(E) shall also be notified immediately for any changes in schedule by fax.

Post-construction Monitoring

4.32 Upon completion of all marine-based construction activities, a post-project monitoring exercise on water quality shall be carried out for four weeks in the same manner as the impact monitoring.

Environmental Quality Performance Limits

4.33 Marine water quality criteria, namely Action and Limit levels, are shown in Table 4.2. These criteria should be applied to ensure that any deteriorating water quality could be readily detected. When the monitoring results of the water quality parameters at any designated monitoring stations exceed the water quality criteria, the actions in accordance with the Event and Action Plan in Table 4.3 shall be carried out.

4.34 The ET Leader should assess the effectiveness and efficiency of the proposed mitigation measures and/or remedial actions for the on-going construction activities. The performance of the environmental management system (i.e. of the overall EM&A programme) should be reviewed by the ET Leader on a quarterly basis. The findings of this review should be included in the quarterly EM&A summary reports, together with any recommendations to improve the performance of the EM&A programme.

Table 4.2 Action and Limit Levels for Marine Water Quality

Parameters	Action	Limit
DO in mg/l (Surface, Middle & Bottom)	Surface & Middle 5%-ile of baseline data for surface and middle layer Bottom 5%-ile of baseline data for bottom layer	Surface & Middle 4 mg/l or 1%-ile of baseline data for surface and middle layer Bottom 2 mg/l or 1%-ile of baseline data for bottom layer
SS in mg/l (depth-averaged)	95%-ile of baseline data or 120% of upstream control station's SS at the same tide of the same day	99%-ile of baseline or 130% of upstream control station's SS at the same tide of the same day
Turbidity in NTU (depth-averaged)	95%-ile of baseline data or 120% of upstream control station's Turbidity at the same tide of the same day	99%-ile of baseline or 130% of upstream control station's Turbidity at the same tide of the same day

Notes: 1 "depth-averaged" is calculated by taking the arithmetic means of reading of all three depths.

2 For DO, non-compliance of the water quality limits occurs when monitoring result is lower than the limits.

3 For turbidity and SS, non-compliance of the water quality limits occurs when monitoring result is higher than the limits.

4 All the figures given in the table are used for reference only and the EPD may amend the figures whenever it is considered as necessary.

Table 4.3 Event and Action Plan for Marine Water Quality

Event	ET Leader	IC(E)	ER	Contractor
Action level being exceeded by one sampling day	Repeat measurement on next day of exceedance to confirm findings; Identify source(s) of impact; Inform IC(E), contractor and ER; Check monitoring data, all plant, equipment and Contractor's working methods; Discuss mitigation measures with IC(E), Contractor and ER.	Discuss with Contractor’s ET leader, ER and Contractor on the mitigation measures; Review proposals on mitigation measures submitted by Contractor and advise the ER accordingly; Assess the effectiveness of the implemented mitigation measures.	Discuss with IC(E) on the proposed mitigation measures; Make agreement on the mitigation measures to be implemented.	Inform the ER and confirm notification of the non-compliance in writing; Rectify unacceptable practice; Check all plant and equipment and amend working methods if appropriate. Discuss with Contractor’s ET leader and IC(E) and propose mitigation measures to IC(E) and ER; Implement the agreed mitigation measures.
Action level being exceeded by two or more consecutive sampling days	Repeat measurement on next day of exceedance to confirm findings; Identify source(s) of impact; Inform IC(E), contractor and ER; Check monitoring data, all plant, equipment and Contractor's working methods; Discuss mitigation measures with IC(E), ER and Contractor; Ensure mitigation measures are implemented; Increase the monitoring frequency to daily until no exceedance of Action level.	Discuss with ET leader and Contractor on the mitigation measures; Review proposals on mitigation measures submitted by Contractor and advise the ER accordingly; Assess the effectiveness of the implemented of mitigation measures.	Discuss with IC(E) on the proposed mitigation measures; Ensure mitigation measures are properly implemented; Assess the effectiveness of the implemented mitigation measures.	Inform the Engineer and confirm notification of the non-compliance in writing; Rectify unacceptable practice; Check all plant and equipment and consider changes of working methods; Submit proposal of additional mitigation measures to ER within 3 working days of notification and discuss with ET, IC(E) and ER; Implement the agreed mitigation measures.
Limit level being exceeded by one sampling day	Repeat measurement on next day of exceedance to confirm findings; Identify source(s) of impact; Inform IC(E), contractor, ER and EPD; Check monitoring data, all plant, equipment and Contractor's working methods; Discuss mitigation measures with IC(E), ER and Contractor; Ensure mitigation measures are implemented; Increase the monitoring frequency to daily until no exceedance of Limit level.	Discuss with ET and Contractor on the mitigation measures; Review the proposed mitigation measures submitted by Contractor and advise the ER accordingly; Assess the effectiveness of the implemented mitigation measures.	Discuss with IC(E), ET and Contractor on the proposed mitigation measures; Request Contractor to critically review the working methods; Ensure mitigation measures are properly implemented; Assess the effectiveness of the implemented mitigation measures.	Inform the ER and confirm notification of the non-compliance in writing; Rectify unacceptable practice; Check all plant and equipment and consider changes of working methods; Submit proposal of mitigation measures to ER within 3 working days of notification and discuss with ET, IC(E) and ER; Implement the agreed mitigation measures.
Limit level being exceeded by two or more consecutive sampling days	Repeat measurement on next day of exceedance to confirm findings; Identify source(s) of impact; Inform IC(E), contractor, ER and EPD; Check monitoring data, all plant, equipment and Contractor's working methods; Discuss mitigation measures with IC(E), ER and Contractor; Ensure mitigation measures are implemented; Increase the monitoring frequency to daily until no exceedance of Limit level for two consecutive days.	Discuss with ET and Contractor on possible remedial actions; Review the Contractor’s mitigation measures whenever necessary to assure their effectiveness and advise the ER accordingly; Assess the effectiveness of the implemented mitigation measures.	Discuss with IC(E), ET and Contractor on the proposed mitigation measures; Request Contractor to critically review the working methods; Make agreement on the mitigation measures to be implemented; Assess the effectiveness of the implemented mitigation measures; Consider and instruct, if necessary, the Contractor to slow down or to stop all or part of the marine work until no exceedance of Limit level.	Inform the ER and confirm notification of the non-compliance in writing; Rectify unacceptable practice; Check all plant and equipment and amend working methods if appropriate; Submit proposal of mitigation measures to ER within 3 working days of notification and discuss with ET, IC(E) and ER; Implement the agreed mitigation measures; As directed by the Engineer, to slow down or to stop all or part of the marine work or construction activities until no exceedance of Limit level.

Water Quality Mitigation Measures

4.35 The EIA report has recommended water quality control and mitigation measures. The Contractor shall be responsible for the design and implementation of these measures. The recommended measures for the construction works are summarised below.

Construction Phase

Dredging

4.36 In order to minimize the potential water quality impact arising from dredging and filling works, the following constraints shall be followed during the construction of the seawalls and reclamation:

· Dredging should be undertaken using closed grab dredgers with a maximum total production rate of 3,000 m³ day^-1;

· Deployment of silt curtain around the immediate dredging area while dredging works are in progress;

· Filling should commence only after the completion of seawall construction and should be undertaken behind the seawalls;

· Mechanical grabs should be designed and maintained to avoid spillage and seal tightly while being lifted;

· All vessels should be sized so that adequate clearance is maintained between vessels and the seabed in all tide conditions, to ensure that undue turbidity is not generated by turbulence from vessel movement or propeller wash;

· All hopper barges and dredgers should be fitted with tight fitting seals to their bottom openings to prevent leakage of material;

· Construction activities should not cause foam, oil, grease, scum, litter or other objectionable matter to be present on the water within the site or dumping grounds; and

· Loading of barges and hoppers should be controlled to prevent splashing of dredged material into the surrounding water. Barges or hoppers should not be filled to a level that will cause the overflow of materials or polluted water during loading or transportation.

Construction Runoff and Drainage

4.37 The Contractor shall observe and comply with the Water Pollution Control Ordinance and its subsidiary regulations. The Contractor shall carry out the Works in such a manner as to minimise adverse impacts on the water quality during the road improvement works.

4.38 Proper site management measures shall be implemented to control site runoff and drainage, and thereby prevent high sediment loadings from entering the nearby coastal waters and stormwater drains. The Contractor shall follow the practices, and be responsible for the design, construction, operation and maintenance of all the mitigation measures as specified in ProPECC PN 1/94 “Construction Site Drainage”. The design of the mitigation measures shall be submitted by the Contractor to the Engineer for approval. These mitigation measures shall include the following practices to minimise site surface runoff and the chance of erosion, and also to retain and reduce any suspended solids prior to discharge:

i) Before commencing any site formation work, all sewer and drainage connections shall be sealed to prevent debris, soil, sand etc. from entering public sewers/drains;

ii) Provision of perimeter channels to intercept storm-runoff from outside the site. These shall be constructed in advance of site formation works and earthworks;

iii) Temporary ditches such as channels, earth bunds or sand bag barriers shall be included to facilitate runoff discharge into the stormwater drain, via a sand/silt basin/trap;

iv) Works programmes shall be designed to minimise works areas at any one time, thus minimising exposed soil areas and reducing the potential for increased siltation and runoff;

v) Sand/silt removal facilities such as sand traps, silt traps and sediment basins shall be provided to remove the sand/silt particles from run-off. These facilities shall be properly and regularly cleaned and maintained. These facilities shall be carefully planned to ensure that they would be installed at appropriate locations to capture all surface water generated on site;

vi) Careful programming of the works to minimise excavation works during the rainy season;

vii) Temporary access roads shall be protected by crushed gravel and exposed slope surfaces shall be protected when rainstorms are likely; and

viii) Open stockpiles of construction materials on-site shall be covered with tarpaulin or similar fabric during rainstorms to prevent erosion.

General Construction Activities

4.39 Debris and rubbish generated on-site should be collected, handled and disposed of properly to avoid entering the nearby coastal waters and stormwater drains. All fuel tanks and storage areas should be provided with locks and be sited on sealed areas, within bunds of a capacity equal to 110% of the storage capacity of the largest tank. Open drainage channels and culverts near the works areas should be covered to block the entrance of large debris and refuse.

Sewage Effluent

4.40 Portable toilets shall be provided by the Contractors, where necessary, to handle sewage from the workforce. The Contractor shall also be responsible for waste disposal and maintenance practices.

Operation Phase

4.41 A surface water drainage system will be provided to collect road runoff. The following measures are recommended to ensure road runoff will comply with the standards stipulated in the Technical Memorandum on Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters for discharges into storm water drains:

· The road drainage should be directed through silt traps in the gully inlets to remove silt and grit before entering the public storm water drainage system; and

· The silt traps should be regularly cleaned and maintained in good working condition.

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4.42 If the above measures are not sufficient to restore the water quality to an acceptable levels upon the advice of the ET Leader, the Contractor shall liaise with the ET Leader on some other mitigation measures, propose to ER for approval, and carry out the mitigation measures. The implementation schedule of the recommended mitigation measures is presented in Appendix 2c.

Site Inspection

4.43 The site inspections and the document review procedures are mentioned in Section 8 of this manual, the ET Leader shall pay special attention to the issues relating to water quality, and check whether the Contractor has followed the recommended mitigation measures and the relevant legislation and guidelines.