4.
WATER QUALITY
4.1.1
The EIA identified activities
and locations during the construction of the Project that may have potential
impacts on water quality. The EIA recommended a number of mitigation measures
that should be implemented to control the potential impacts to within
acceptable limits. A water quality monitoring programme is recommended for
baseline conditions and during the construction phase to monitor the
effectiveness and efficiency of the proposed mitigation measures.
4.1.2
This section of the Manual
lists all the recommended mitigative and preventive measures in the EIA for the
protection of water quality during construction phase, and the requirements for
baseline and construction phase water quality monitoring.
3.1.1
No
adverse water quality impact is expected during operation phase, hence water
quality monitoring during operation phase is considered not necessary.
4.2.1
The
ET shall be responsible for monitoring the parameters, as shown in Table
4.1, to ensure that any deteriorating water quality can be readily
detected and action be taken in time to rectify the situation.
Water Quality Parameters
|
Parameter |
Type of Analysis |
|
Dissolved Oxygen (DO) (mg/L
and % saturation) |
In situ measurement |
|
Temperature (oC) |
|
|
pH value |
|
|
Turbidity (NTU) |
|
|
Salinity (ppt) |
|
|
Water depth |
|
|
Suspended Solids (SS) (mg/L) |
Laboratory analysis |
4.2.2
These
parameters are selected for monitoring on the following basis:
·
to
reflect the background water quality near and within the working area; and
·
to
reflect the nature of the construction activities.
4.2.3
In
addition to the water quality parameters, relevant data shall also be measured,
such as monitoring location / position, time, saturation, tidal condition, weather
conditions and any special phenomena and works underway at the construction
site.
4.2.4
The
data format of the water quality monitoring record and a sample monitoring
record sheet are shown in Appendix B for reference.
4.3.1
Water
quality monitoring equipment with the following specifications shall be
supplied and maintained by the ET.
Dissolved Oxygen and Temperature Measuring
Equipment
4.3.2
The
equipment shall have the following characteristics and functions.
(a)
The
instrument shall be a portable, weatherproof dissolved oxygen measuring
instrument complete with cable, sensor, comprehensive operation manuals, and
with the use of a DC power source. (e.g. YSI model 59 meter, YSI 5739 probe,
YSI 5795A submersible stirrer with reel and cable or an approved similar
instrument). It shall be capable of measuring:
-
a
dissolved oxygen level in the range of 0-20 mg/L and 0-200% saturation; and
-
a
temperature of 0-45 oC.
(b)
It
shall have a membrane electrode with automatic temperature compensation connected
with a cable. Sufficient stocks of spare electrodes and cables shall be
available for replacement where necessary.
(c)
Should
salinity compensation not be built-in in the equipment, in-situ salinity shall be measured to calibrate the DO equipment
prior to each DO measurement.
Salinity
4.3.3 A portable salinometer capable of measuring salinity in the range of 0 – 40 parts per thousand (ppt) shall be provided for measuring salinity of the water at each monitoring location..
Turbidity Measurement Instrument
4.3.4 The instrument shall be a portable, weatherproof turbidity-measuring instrument complete with comprehensive operation manual. The equipment shall use a DC power source. It shall have a photoelectric sensor capable of measuring turbidity between 0-1000 NTU (e.g. Hach model 2100P or an approved similar instrument).
Suspended Solids
4.3.5
The
equipment shall have the following characteristics and functions.
(a)
Sampling
shall be carried out using a water sampler which 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 shall 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).
(b)
Water
samples for suspended solids measurement shall be collected in high density
polythene bottles, packed in ice (chilled to 4°C without being frozen), and
delivered to the laboratory as soon as possible after collection.
pH
4.3.6 pH meter (e.g. Hanna – HI 9024 or an approved similar instrument) should be used to measure pH value of the water samples in situ.
Positioning Device
4.3.7 The locations of water monitoring points should be located using a hand-held or boat fixed digital Global Positioning System (GPS) 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
4.3.8 A portable, battery-operated echo sounder shall 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
4.3.9 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.
Calibration of Equipment
4.3.10 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.
4.3.11 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.
4.3.12 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 in under maintenance, calibration, etc.
4.4
Laboratory Measurement / Analysis
4.4.1
Analysis
of suspended solids shall be carried out in a HOKLAS or other international
accredited laboratory. Water samples of about 1000ml shall be collected at the
monitoring stations for carrying out the laboratory SS determination. The SS
determination work shall start within 24 hours after collection of the water
samples. The detection limit shall be 1 mg/L or better. The SS determination
shall follow APHA 17ed 2540D or equivalent methods subject to approval of EPD.
4.4.2
If
a site laboratory is set up or a non-HOKLAS and non-international accredited
laboratory is hired for carrying out the laboratory analysis, the laboratory
equipment, analytical procedures, and quality control shall be approved by the
EPD. All the analysis shall be witnessed by the ER. The ET Leader shall provide
the ER with one copy of the relevant chapters of the “Standard Methods for the
Examination of Water and Wastewater” updated edition and any other relevant
document for his reference.
4.4.3
For
the testing methods of other parameters as recommended by EIA or required by
EPD, detailed testing methods, pre-treatment procedures, instrument use,
Quality Assurance/Quality Control (QA/QC) details (such as blank, spike
recovery, number of duplicate samples per batch, etc.), detection limits and
accuracy shall be submitted to EPD for approval prior to the commencement of
monitoring programme. The QA/QC shall be in accordance with the requirement of
HOKLAS or international accredited scheme. The QA/QC results shall be reported.
EPD may also request the laboratory to carry out analysis of known standards
provided by EPD for quality assurance. Additional duplicate samples may be
required by EPD for inter laboratory calibration. Remaining samples after
analysis shall be kept by the laboratory for 3 months in case repeat analysis
is required. If in-house or non-standard methods are proposed, details of the
method verification may also be required to submit to EPD. 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.
4.5.1
The
proposed monitoring locations are shown in Table 4.2 and Figure 4.1. The
monitoring locations could be adjusted by the ET Leader to suit the location of
the construction works but prior agreement must be obtained from the IEC and
the EPD.
Proposed Monitoring Locations for Water Quality
|
Water Quality Monitoring Station |
Description |
Purpose of Placing Sampling Station |
Coordinates E = Easting |
|
W1 |
Downstream of the works immediately at the discharge
point to |
Monitor and audit potential impacts from the works,
check water quality discharging to |
E: 816023 N: 836095 |
|
W2 |
Near the oyster bed in |
Monitor and audit potential impacts from the works,
check water quality discharging to |
E: 815791 N: 836276 |
|
W3 |
Near the oyster bed in |
Monitor and audit potential impacts from the works,
check water quality discharging to |
E: 815673 N: 836076 |
|
W4 |
Immediate downstream of any specific works within
Hang Hau Tsuen channel |
Temporary / mobile station to monitor and audit
potential impacts from any specific works, check water quality discharging to
Deep Bay, impact station |
See notes below |
|
W5 |
Upstream of the works at
the confluence of San Hing Tsuen Channel and Fung Kong Tsuen Channel |
Establish background water quality levels entering
Hang Hau Tsuen stream, control station |
E: 816390 N: 836039 |
|
W6 |
Waters of |
Establish background water quality levels in |
E: 815496 N: 836713 |
|
W7 |
Waters of |
Establish background water quality levels in |
E: 815174 N: 835484 |
Notes:
-
Temporary
/ mobile station to be proposed by the Environmental Team Leader with reference
to the contractor’s working programme and works location.
-
All
monitoring stations shall be proposed by the Environmental Team Leader and
verified by the Independent Environmental Checker before submitting to EPD
prior to commencement of any monitoring.
4.5.2
When
alternative monitoring locations are proposed, they shall 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 as indicated in the EIA final report, 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
shall be taken to cause minimal disturbance during monitoring; and
(d)
two
or more control stations which shall be at locations representative of the
project site in its undisturbed condition. Control station shall be located, as
far as is practicable, both upstream and downstream of the works area.
4.5.3
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 shall be outside
the area of influence of the works and, as far as practicable, not affected by
any other works.
4.5.4
Measurements
shall be taken at 3 water depths, namely, 1m below water surface, mid-depth and
1m above stream or 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.
4.5.5
Duplicates
in-situ measurements and sample collected from each independent monitoring
event are required for all parameters to ensure a robust statistically
interpretable dataset.
4.6.1
Baseline
conditions for 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, control monitoring
stations. The baseline conditions shall be established by measuring the water
quality parameters specified in Table 4.3. The measurement shall be
taken at all designated monitoring stations for 3 days per week, at mid-flood
and mid-ebb tides, for at least 4 weeks prior to commencement of the works. The
interval between 2 sets of monitoring shall not be less than 36 hours.
4.6.2
There
shall not be any construction activities in the vicinity of the stations during
the baseline monitoring.
4.6.3
In
exceptional cases when insufficient baseline monitoring data or questionable
results are obtained, the ET Leader shall seek approval from the IEC and EPD on
an appropriate set of data to be used as baseline reference.
4.6.4
Baseline
monitoring schedule shall be send to EPD 1 week prior to the commencement of
baseline monitoring.
Water Quality
Monitoring Locations, Parameter, Frequency
and Duration
for Baseline
|
Locations |
Parameters |
Frequency |
Duration |
|
All
designated water quality monitoring stations |
DO,
pH, SS, turbidity, salinity and temperature |
3
days per week at mid-flood and mid-ebb tides |
Four
weeks |
4.7.1
During
the course of the construction works, impact monitoring shall be undertaken at
the designated monitoring locations 3 days per week, at mid-flood and mid-ebb
tides, according to the parameters, locations and frequencies described in Table
4.4. The interval between two sets of monitoring shall not be less than
36 hours except where there are exceedances of Action and Limit levels, in
which case the monitoring frequency will be increased.
Locations, Parameters, Frequencies
and Durations during Construction Phase
|
Parameters |
Locations |
Frequency |
|
DO,
pH, SS, turbidity, salinity and temperature |
All
designated water quality monitoring stations |
3 days per week at mid-flood and
mid-ebb tides throughout construction phase. |
4.7.2
All
monitoring information including date and time, weather conditions, operator,
identification and description of monitoring locations, works progress and
construction activities, sample ID, method, analytical data and calculation
etc., shall be recorded in the monitoring data sheet.
4.7.3
Upon
completion of all activities in the channel, a post project monitoring exercise
on water quality shall be carried out for 4 weeks in the same manner as the
impact monitoring.
4.7.4
The
proposed water quality monitoring schedule shall be send to ER, IEC and EPD on
or before the first day of the monitoring month. They shall also be notified
immediately for any changes in schedule.
4.8
Event and Action Plan for Water
Quality
4.8.1
The
Action and Limit levels for water quality are shown in Table 4.5. Should the
monitoring results at any designated monitoring stations indicate that the
Action and Limit levels are exceeded, the actions specified in Table
4.6 shall be carried out.
Action
and Limit Levels for Water Quality
|
Parameters |
Action |
Limit |
|
DO in mg/L (surface, middle and 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 data 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 data 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 SS and Turbidity, 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 4.6 Event and Action Plan for Water Quality
|
Event |
ET Leader |
IEC |
ER |
Contractor |
|
Action Level
being exceeded by one sampling day |
1. Repeat in-site measurement to confirm findings. 2. Identify source(s) of impact. 3. Inform IEC and Contractor. 4. Check monitoring data, all plant, equipment and
Contractor’s working methods. 5. Discuss mitigation measures with IEC and Contractor. 6. Repeat measurement on next day of exceedance. |
1. Discuss with ET and Contractor on the mitigation
measures. 2. Review proposals on mitigation measures. submitted
by Contractor and advise the ER accordingly. 3. Assess the effectiveness of the implemented
mitigation measures. |
1.
Discuss
with IEC on the proposed mitigation measures. 2.
Make
agreement on the mitigation measures to be implemented. 3.
Assess
effectiveness of the implemented mitigation measures. |
1.
Inform the
ER and confirm notification of the non-compliance in writing. 2.
Rectify
unacceptable practice. 3.
Check all
plant and equipment. 4.
Consider
changes of working methods. 5.
Discuss
with ET and IEC and propose mitigation measures to IEC and ER. 6.
Implement
the agreed mitigation measures. |
|
Action Level
being exceeded by more than one consecutive sampling days |
1. Repeat in-situ measurement to confirm findings; 2. Identify source(s) of impact. 3. Inform IEC and Contractor. 4. Check monitoring data, all plant, equipment and
Contractor’s working methods. 5. Discuss mitigation measures with IEC and Contractor. 6. Ensure mitigation measures are implemented. 7. Prepare to increase the monitoring frequency to
daily. 8. Repeat measurement on next day of exceedance. |
1. Discuss with ET and Contractor on the mitigation
measures. 2. Review proposals on mitigation measures submitted by
Contractor and advise the ER accordingly. 3. Assess the effectiveness of the implemented
mitigation measures. |
1. Discuss with IEC on the proposed mitigation
measures. 2. Make agreement on the mitigation measures to be
implemented. 3. Assess the effectiveness of the implemented
mitigation measures. |
1. Inform the ER and confirm notification of the
non-compliance in writing. 2. Rectify unacceptable practice. 3. Check all plant and equipment. 4. Consider changes of working methods. 5. Discuss with ET and IEC and propose mitigation
measures to IEC and ER within 3 working days. 6. Implement the agreed mitigation measures. |
|
Limit Level
being exceeded by one sampling day |
1. Repeat in-situ measurement to confirm findings. 2. Identify source(s) of impact. 3. Inform IEC, contractor, AFCD and EPD. 4. Check monitoring data, all plant, equipment and
Contractor’s working methods. 5. Discuss mitigation measures with IEC, ER and
Contractor. 6. Ensure mitigation measures are implemented; 7. Increase the monitoring frequency to daily until no
exceedance of Limit Level. |
1. Discuss with ET and Contractor on the mitigation
measures. 2. Review proposals on mitigation measures submitted by
Contractor and advise the ER accordingly. 3. Assess the effectiveness of the implemented
mitigation measures. |
1. Discuss with IEC, ET and Contractor on the proposed
mitigation measures. 2. Request Contract to critically review the working
methods. 3. Make agreement on the mitigation measures to be
implemented. 4. Assess the effectiveness of the implemented
mitigation measures. |
1. Inform the ER and confirm notification of the
non-compliance in writing. 2. Rectify unacceptable practice. 3. Check all plant and equipment. 4. Consider changes of working methods. 5. Discuss with ET, IEC and ER and propose mitigation
measures to IEC and ER within 3 working days. 6. Implement the agreed mitigation measures. |
|
Limit Level
being exceeded by more than one consecutive sampling days |
1. Repeat in-situ measurement to confirm findings. 2. Identify source(s) of impact. 3. Inform IEC, contractor, AFCD and EPD. 4. Check monitoring data, all plant, equipment and
Contractor’s working methods. 5. Discuss mitigation measures with IEC, ER and
Contractor. 6. Ensure mitigation measures are implemented. 7. Increase the monitoring frequency to daily until no
exceedance of Limit Level for two consecutive days. |
1. Discuss with ET and Contractor on the mitigation
measures. 2. Review proposals on mitigation measures submitted by
Contractor and advise the ER accordingly. 3. Assess the effectiveness of the implemented
mitigation measures. |
1. Discuss with IEC, ET and Contractor on the proposed
mitigation measures. 2. Request Contractor to critically review the working
methods. 3. Make agreement on the mitigation measures to be
implemented. 4. Assess the effectiveness of the implemented
mitigation measures. 5. Consider and instruct, if necessary, the Contractor
to slow down or to stop all or part of the work until no exceedance of Limit Level. |
1. Inform the ER and confirm notification of the
non-compliance in writing. 2. Rectify unacceptable practice. 3. Check all plant and equipment. 4. Consider changes of working methods. 5. Discuss with ET, IEC and ER and propose mitigation
measures to IEC and ER within 3 working days. 6. Implement the agreed mitigation measures. 7. As directed by the ER, to slow down or to stop all
or part of the work or construction activities. |
4.9
Water Quality Mitigation Measures
Construction
Phase Mitigation Measures
4.9.1 The main potential impacts from the construction phase of the Project include an increase in suspended solids, pH value, oil & grease and general site effluent entering adjacent water bodies. The following sections discuss the proposed mitigation measures for the potential water quality impacts identified above.
General
4.9.2 The Contractor shall observe and comply with the Water Pollution Control Ordinance (WPCO) 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 execution of the works. In particular the Contractor shall arrange his method of working to minimise the effects on the water quality within and outside the site and on the transport routes.
4.9.3 The Contractor shall follow the practices, and be responsible for the design, construction, operation and maintenance of all the mitigation measures below and 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.
Site
Preparation / Clearance
4.9.4
Proper construction site drainage management measures should
be implemented to control site runoff and drainage, and thereby prevent high
sediment loadings from reaching
4.9.5 Turbid water from construction sites must be treated to minimise the solids content before being discharged. Advice on the handling and disposal of site discharge is given in the ProPECC Note PN 1/94 – “Construction Site Drainage”.
4.9.6 In general, surface run-off from construction sites should be discharged into water bodies via adequately designed silt removal facilities such as sand traps, silt traps and sediment basins. Channels or earth bunds or sand bag barriers should be provided on site to properly direct stormwater to such silt removal facilities. Perimeter channels at site boundaries should be provided to intercept storm run-off from outside the site so that it will not wash across the site (or into the proposed channel works area). Catchpits and perimeter channels should be constructed in advance of earthworks.
4.9.7 Silt removal facilities and diversion channels should be maintained and the deposited silt and grit should be removed regularly, especially at the onset of and after each rainstorm to ensure proper functioning of these facilities at all times.
4.9.8 Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into the nearby water bodies. Open stockpiles susceptible to erosion should be covered with tarpaulin or similar fabric and provided with containment such as bunds, sand bag barriers or equivalent measures, especially during the wet season (April – September) or when heavy rainstorm is predicted. Runoff to watercourses should be reduced by minimising flat exposed areas of permeable soil, and by forming pits or diversion channels into which runoff can flow to suitable treatment facilities before discharge.
De-watering / Excavation of Stream / Pond and Removal
of Sediment
4.9.9 Excavation works within the existing stream section and pond should be programmed to be carried out during dry season from 1st October to 31st March as far as practicable to minimise impacts on downstream water quality and nearby sensitive receivers.
4.9.10 The use of containment structure such as sheet pile barriers, earth bunds, sand bag barriers wrapped with geotextile fabric or similar material, diversion channels or other similar techniques should be installed surrounding the excavation area to facilitate a dry or at least confined excavation within the stream. Schematic diagram of typical drainage measures during excavation of the stream is shown in Figure 5.3 (of the EIA). The Contractor should submit details of the temporary drainage measures along with the proposed measures to ameliorate the potential water quality impacts to the Environmental Team (ET) for verification and to the Engineer for approval before commencement of the construction works.
4.9.11 The excavation area should be limited to section of half width of the stream in order to maintain continuous water flow within the stream during the construction phase.
4.9.12 After dewatering of the stream and pond, the sediments should be allowed to dry before excavation (yet still maintain a moist state to avoid dust nuisance). This will facilitate excavation of the sediments and also minimise the risk of drained water flowing back into watercourses as the sediment is handled. Where time or weather constraints require handling of wet sediment, care should be taken in the removal of sediment and the storage area should be bunded to prevent silty runoff entering water bodies.
4.9.13 Tightly sealed closed grab excavators should be employed to minimize leakage and loss of sediments during excavation works within the stream.
4.9.14 Excavated sediment material from stream should be stored in covered impermeable skips and disposed within 2 days, to avoid inadvertent release of silty runoff and contaminants to nearby water bodies. If sediment material is identified to be suitable for reuse as stream bed material, it should be properly stockpiled, adequately covered and provided with containment to prevent runoff during wet season.
4.9.15 Regular monitoring of suspended solids and turbidity should be conducted during excavation works. Any exceedance of water quality in the nearby water bodies caused by inadvertent release of site runoff should be rectified in accordance with EM&A programme for this Project.
Concreting
Work
4.9.16 Runoff should be carefully channelled to prevent concrete-contaminated water from entering watercourses. Adjustment of pH can be achieved by adding a suitable neutralising reagent to wastewater prior to discharge. Reuse of the supernatant from the sediment pits for washing out of concrete lorries should be practised.
4.9.17 Any exceedance of acceptable range of pH levels in the nearby water bodies caused by inadvertent release of site runoff containing concrete should be monitored and rectified under the EM&A programme for this Project.
Site
Workshop or Depot
General
Construction Works
4.9.18 Any Contractor generating waste oil or other chemicals as a result of his activities should register as a chemical waste producer and provide a safe designated storage area for chemicals on site. The storage site should be located away from existing water courses.
4.9.19 All compounds in works areas should be located on areas of hard standing surface with provision of diversion channels and settlement ponds where necessary to allow interception and controlled release of settled / treated water. Hard standing compounds should drain via an oil interceptor. The oil interceptor should be regularly inspected and cleaned to avoid wash-out of oil during storm conditions. A bypass should be provided to avoid overload of the interceptor's capacity. To prevent spillage of fuels or other chemicals to water courses, all fuel tanks and storage areas should be sited on sealed areas within a bund of a capacity equal to 110% of the storage capacity of the largest tank. Where temporary storage of chemicals or fuel drums outside the storage area is necessary, drip tray should be provided. Disposal of the waste oil should be carried out by a licensed collector. Good housekeeping practices should be implemented to minimise careless spillage and to keep the storage and the work space in a tidy and clean condition. Appropriate training including safety codes and relevant manuals should be given to the personnel who regularly handle the chemicals on site.
Emergency
Contingency Plan
4.9.20 The Contractor should prepare an emergency contingency plan (spill response plan) for the Project to contain and remove accidental spillage of chemicals and all hazardous materials on-site including fuels at short notice and to prevent or to minimize the quantities of contaminants from entering the stream water and affecting the sensitive habitats. The Contractor should submit the emergency contingency plan to the ET for review & comment and the Engineer for approval. The Plan should include, but not limited to, the following:
(i)
potential emergency situations
(ii)
chemicals or hazardous materials used on-site (and their
location)
(iii)
emergency response team
(iv)
emergency action plans and procedures
(v)
list of emergency telephone hotlines
(vi)
locations and types of emergency response equipment
(vii)
training plan and emergency drill
(viii)
schedules for review and audit.
General Guidance
for Handling of Spillage / Leakage
4.9.21 In the event that accidental spillage or leakage of hazardous substances / chemical wastes takes place, the response procedures as listed below should be followed. It should be noted that the procedures below are not exhaustive. The Contractor should propose other response procedures in the emergency contingency plan based on actual site conditions as well as the particular types and quantities of chemicals or hazardous substances used, handled and stored on-site.
·
Contact person in charge or nominated person immediately and
initiate action plans based on the emergency contingency plan.
·
Oil leakage or spillage should be contained and cleaned up
immediately. Waste oil should be collected and stored for recycling or disposal
in accordance with the Waste Disposal Ordinance.
·
Instruct untrained personnel to keep at a safe distance well
away from the spillage area.
·
If the spillage / leakage involves high toxic, volatile or
hazardous waste, initiate emergency evacuation and call the emergency service.
·
Only trained persons equipped with suitable protective
clothing and equipment should be allowed to enter and clean up the waste
spillage / leakage area.
·
Where the spillage / leakage is contained in the enclosed
storage area, the waste can be transferred back into suitable containers by
suitable handheld equipment, such as hand operated pumps, scoops or shovels. If
the spillage / leakage quantity is small, it can be covered and mixed with
suitable absorbing materials such as tissue paper, dry soft sand or
vermiculite. The resultant slurry should be treated as chemical waste and transferred
to suitable containers for disposal.
·
For spillage / leakage in other areas, immediate action is
required to contain the spillage / leakage. Suitable liquid absorbing materials
such as tissue paper, dry soft sand or vermiculite should be used to cover the
spill. The resultant slurry should be treated as chemical waste and transferred
to suitable containers for disposal.
·
Areas that have been contaminated by chemical waste spillage
/ leakage should be cleaned. While water is a soluble solvent for aqueous
chemical wastes and water soluble organic waste, kerosene or turpentine should
be used for organic chemical wastes that are not soluble in water. The waste
from the cleanup operation should be treated and disposed of as chemical waste.
·
In incidents where the spillage / leakage may result in significant
contamination of an area or risk of pollution, the Environmental Protection
Department should be informed immediately.
Presence of Additional Population (Workers)
4.9.22 Sewage arising from construction workers on site should be collected in a suitable storage facility, such as portable chemical toilets. An adequate number of portable toilets should be provided for the construction workforce. The portable toilets should be maintained in a state that will not deter the workers from using them. Wastewater collected should be discharged into foul sewers and collected by licensed collectors.
4.9.23 The collected wastewater from sewage facilities and also from eating areas or washing facilities of site offices should be disposed to foul sewer. If there is no foul sewer in the vicinity, a septic tank and soakaway system or for larger flow, a sewage treatment plant should be provided. All domestic sewage discharges (except into foul sewer) are controlled under the WPCO. The Contractor must apply for a discharge licence from EPD and must comply with the terms and conditions of a valid WPCO licence.
Operational Phase Mitigation Measures
Measures to Reduce Pollution Loadings entering the
Channel
4.9.24 Appropriate location along the toe zone of the channel will be filled with about 200 mm thick original stream bed materials. The upstream dry weather flow channel will also be filled with a layer of about 100 mm thick original stream bed materials on top of the rip-rap lining. The most important feature of such measure is the prospect of natural re-colonization of benthic communities and re-establishment of vegetation along the toe zone of the channel replicating riparian vegetation. The vegetation is not expected to be detrimental in any way to the channel structure or to the conveyance of flood flow. Specific planting is considered not necessary as vegetation will recolonized and established itself naturally similar to current condition. Non-woody species (such as sedges) is preferred for ease of maintenance and pruning as they are easier to be pruned and will impede the flow of water to lesser extent during large flow as the vegetation will just collapse and spring back. However, seasonal cutting and clearance of vegetation, particularly in advance of the wet season may be required. This mitigation measure has additional benefits of aesthetic and ecological value.
4.9.25 In addition, the use of rock fill base or original stream bed materials for the channel bed has the benefit of providing uneven surfaces and cavities for sediment to accumulate. Ultimately a sediment layer will build up on the channel bed, forming a natural layer for development of the benthic community. Removal of the upper layer of this sediment will only be necessary once the layer thickness has built up to around 300 mm thick, and sediment is likely to be washed downstream in heavy storms. A minimum of 100 mm thick sediment should be allowed to accumulate at the channel bed to permit recolonizing of benthic communities. Growth of vegetation will inhibit washout of sediment and sediment removal can be carried out at the same time as vegetation harvesting during the dry season when flows are minimal.
4.9.26
Catchpits with sand traps will
be provided in the drainage system to trap sands, grits and rubbish in the Hang
Hau Tsuen surface runoff prior to discharge to
Environmental Considerations for Maintenance of the
Proposed Channel
4.9.27 Maintenance may be necessary for the proposed channel at regular intervals to remove excessive silts, vegetation, rubbish, debris and obstruction. Little or no maintenance will be necessary for the natural stream bed section of the channel. Likewise, the retained and compensated mangroves within the mangrove zone (Figure 2.7 of the EIA) will not require any long term maintenance. Good practice guides for the planning and execution of desilting and maintenance works are recommended in the following sections.
4.9.28 The following considerations should be included in planning for the maintenance works of the proposed channel:
(a)
Maintenance of the channel should be restricted to silt
removal when the accumulated silt will adversely affect the hydraulic capacity
of the channel (except during emergency situations where flooding risk is
imminent). Desilting should be carried out by hand or light machinery during
the dry season (October to March) when water flow is low.
(b)
The management of woody / emergent vegetation should be
limited to manual cutting, to be carried out during dry season and only when
unchecked growth of such vegetation is very likely to impede channel flow.
(c)
Mangroves within the mangrove zone should be retained if the
hydraulic capacity of the channel is adequate. Mangroves found outside the
mangrove zone but within the proposed channel should be remove as they will
affect the hydraulic capacity of the channel. Rip-rap that are used to
delineate the mangrove zone should be replaced if found damaged.
(d)
A minimum of 100 mm thick sediment should be allowed to
accumulate on the channel bed to permit recolonization of benthic communities.
(e)
Phasing of the works should be considered to better control
and minimize any impacts caused, and to provide refuges for aquatic organisms.
Where possible, works should be carried out along half width of the channel in
short sections. A free passage along the channel is necessary to avoid forming
stagnant water in any phase of the works and to maintain the integrity of
aquatic communities.
(f)
Containment structures (such as sand bags barrier or similar
method) should be provided for the active desilting works area to facilitate a
dry or at least confined working area within the channel.
(g)
Where no maintenance access is available for the channel, temporary
access to the works site should be carefully planned and located to minimize
disturbance caused to the channel, adjacent vegetation (especially mangroves) and
nearby sensitive receivers by construction plants.
(h)
The use of lesser or smaller construction plants should be
considered to reduce disturbance to the channel bed. Quiet construction plants
should be used.
(i)
The locations for the disposal of the removed materials
should be identified and agreement sought with the relevant departments before
commencement of the maintenance works. Temporary stockpile of waste materials
should be located away from the channel and properly covered. These waste materials
should be disposed of in a timely and appropriate manner.
Mitigation Measures for the Proposed Access Road,
Viewing Point and Carpark
4.9.29 The following measures should be implemented to ensure no adverse water quality impacts during the operation of the access road, viewing point and carpark.
4.9.30
Highways Department (HyD) standard road drainage system
should be provided along the proposed access road and viewing point and carpark
to collect the road runoff. The road drainage design should incorporate gullies
and silt / grit traps to trap any pollutants in the road surface runoff prior
to discharge into
4.9.31 Regular cleansing of the access road and viewing point and carpark following normal established practices should be carried out to remove any accumulated silts, grits and litters. The gullies and silt / grit traps should also be regularly cleaned and maintained in good working condition.
4.9.32 If the above construction mitigation measures are not sufficient to restore the impacts to acceptable levels upon the advice of ET Leader, the Contractor shall liaise with the ET Leader on some other mitigation measures, endorsed by IEC and propose to ER for approval, and implement the mitigation measures.
4.9.33 The implementation schedule for the recommended mitigation measures is presented in Appendix A.