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 monitoring programme is recommended for baseline
conditions and during the construction phase to assess and ensure the
performance of the proposed 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 up to date
requirements for baseline and construction phase water quality monitoring.
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) |
|
|
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, weather conditions
and any special phenomena and work 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.
Turbidity Measurement Instrument
4.3.3 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
4.3.4
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
4.3.5 pH meter (e.g. Hanna – HI 9024 or equivalent) should be used to measure pH value of the water samples in situ.
Positioning Device
4.3.6 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
4.3.7 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
4.3.8 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.
4.3.9 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.
4.3.10 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.
4.3.11 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
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. 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 Figures 4.1 – 4.3. 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
|
Monitoring Station |
Description |
Purpose of Placing Sampling Station |
|
MUP-W1 |
Upstream of MUP01 works |
Establish background levels of parameters to be
monitored, control station |
|
MUP-W2 |
Upstream of MUP02 works |
Establish background levels of parameters to be
monitored, control station |
|
MUP-W3 |
Upstream of MUP04A works |
Establish background levels of parameters to be
monitored, control station |
|
MUP-W4 |
Downstream of MUP05 works immediately at the
discharge point to River Indus |
Monitor and audit potential impacts from all MUP
channels works, check water quality discharging to River Indus |
|
MUP-W5 |
Within MUP05, downstream of the discharge point of
MUP01/02 and upstream of the discharge point of MUP04A |
Temporary / mobile station to monitor and audit
potential impacts from individual MUP channels works |
|
MUP-W6 |
Within MUP05, downstream of the discharge point of
MUP01/02 and MUP04A |
Temporary / mobile station to monitor and audit
potential impacts from individual MUP channels works |
|
LMH-W1 |
Upstream of LMH01 works |
Establish background levels of parameters to be
monitored, control station |
|
LMH-W2 |
Upstream of LMH01 works |
Establish background levels of parameters to be
monitored, control station |
|
LMH-W3 |
Downstream of all LMH01 works immediately at the
discharge point to |
Monitor and audit potential impacts from all LMH01
works |
|
LMH-W4 |
Upstream and downstream of particular group of LMH01
works |
Temporary / mobile station to monitor and audit
potential impacts from individual works |
|
LMH-W5 |
Upstream and downstream of particular group of LMH01
works |
Temporary / mobile station to monitor and audit
potential impacts from individual works |
|
LMH-W6 |
Upstream and downstream of particular group of LMH01
works |
Temporary / mobile station to monitor and audit
potential impacts from individual works |
Notes:
-
Channels
MUP01, MUP02 are non-DPs.
-
Temporary
/ mobile station to be proposed by the ET Leader with reference to the
contractor’s working programme.
-
All
monitoring stations shall be proposed by the ET Leader and verified by the IEC
before submitting to EPD for approval 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 including control stations for 3 days per
week for 4 consecutive weeks prior to commencement of the works.
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. The interval between 2 sets of monitoring shall not be
less than 36 hours.
Water Quality
Monitoring Locations, Parameter, Frequency
and Duration
for Baseline
|
Locations |
Parameters |
Frequency |
Duration |
|
All
locations |
DO,
pH, turbidity, and temperature |
3
days per week |
Four
weeks |
4.7.1
During
the course of the construction works, impact monitoring shall be undertaken
according to the parameters, frequencies, and duration 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
|
Parameter |
Locations |
Frequency |
|
DO,
pH, turbidity, and temperature |
All
locations |
3 days per week 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
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 (depth-averaged) |
5%-ile of
baseline data |
1%-ile of
baseline data |
|
SS in mg/L (depth-averaged) |
95%-ile of baseline data or 120% of
upstream control station of the same day |
99%-ile of baseline data or 130% of
upstream control station of the same day |
|
Turbidity in NTU (depth-averaged) |
95%-ile of baseline data or 120% of
upstream control station of the same day |
99%-ile of baseline data or 130% of
upstream control station of the same day |
|
pH |
95%-ile of baseline data or 120% of
upstream control station of the same day |
99%-ile of baseline data or 130% of
upstream control station of the same day |
Notes:
-
For DO, non-compliance of the water quality limits
occurs when monitoring result is lower than the limits.
-
For SS and Turbidity, non-compliance of the water
quality limits occurs when monitoring result is higher than the limits.
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 an 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 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 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 stage 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. In particular, the contractor shall submit and implement an Erosion Control Plan (as part of the Environmental Management Plan) which shall incorporate details of the mitigation measures recommended below to reduce water quality impacts arising from construction works. The design of the mitigation measures and the Plan shall be submitted by the contractor to the Engineer for approval.
Site Surface Runoff
4.9.4 Proper construction site drainage management measures shall be implemented to control site runoff and drainage, and thereby prevent high sediment loadings from reaching downstream sections of the river and adjacent agricultural land.
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 waterbodies via adequately designed sand/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, channels should be maintained and the deposited silt and grit should be removed regularly, 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 waterbodies. 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 Streams and Removal of Sediment
4.9.9 The use of containment structures such as earth bund or sand bag barriers wrapped with goetextile fabric or similar material or diversion channels is recommended to facilitate a dry or at least confined excavation within watercourses.
4.9.10 Excavation works at the existing stream section of MUP05 should be programmed to be carried out during periods of low flow (dry season from 1st October to 31st March) to minimise impacts on downstream water quality and sensitive receivers. For the ecologically sensitive stream of LMH01, the restriction period should be further extended for an additional month (i.e. excavation works allowed from 1st November to 31st March) to protect the aquatic fauna from silty runoff due to possible heavy rain during the transitional period of the wet / dry seasons.
4.9.11 In addition, the excavation works should be carried out in sections to reduce the area of exposed surfaces as described below. For MUP05, the first 300m upstream portion will have no restriction as the works involve small scale reconstruction of existing concrete drains/channel. The associated area of excavation is expected to be small. For the remaining sections of MUP05 (within existing stream course), the length of excavation would be restricted to 300m at any one time. For MUP04A, a 100m restriction should be imposed for the entire stream works area to cater for potential cumulative impact on MUP05.
4.9.12 As for LMH01, given its relatively small scale works but sensitive nature of the stream, it is recommended that only either one portion of bank improvement works or one vehicular crossing reconstruction should be carried out at any one time.
4.9.13 No restriction is necessary for MUP03 and MUP04B as works involve small scale reconstruction of existing culvert and roadside concrete drains.
4.9.14 After dewatering of the streams, 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 watercourses. Given its small quantity, all excavated sediment should be reused on-site as backfilling material.
4.9.15 Excavated sediment will likely be temporarily stored on-site before reuse as backfilling material. This should be stored in a bunded area and covered during wet season or when rainstorm is forecasted to avoid inadvertent release of silts and suspended solids to nearby water bodies.
4.9.16 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
4.9.17 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. Re-use of the supernatant from the sediment pits for washing out of concrete lorries should be practised.
4.9.18 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.
4.9.19 To protect the sensitive stream of Lin Ma Hang, no concrete should be used during bank improvement works at LMH01.
Site
Workshop or Depot
4.9.20 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.
4.9.21 All compounds in works areas should be located on areas of hard standing with provision of drainage channels and settlement ponds where necessary to allow interception and controlled release of settled/treated water; and provision of bunding for all potentially hazardous materials on site including fuels. 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 done 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.
4.9.22 The contractor should prepare an emergency contingency plan (spill action plan) for the Project to contain and remove all 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 entering the stream water and affecting the 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 response procedures
(v) list of emergency telephone hotlines
(vi) locations and types of emergency response equipment
(vii) training plan & testing for effectiveness.
General Guidance for
Handling of Spillage / Leakage
4.9.23 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 and the contractor should propose other response procedures in the emergency contingency plan based on the particular types and quantities of chemicals or hazardous substances used, handled and stored on-site.
· 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)
4.9.24 Sewage arising from the additional population of 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. The collected wastewater from sewage facilities and also from eating areas or washing facilities must be disposed of properly, in accordance with the WPCO requirements. Wastewater collected should be discharged into foul sewers and collected by licensed collectors.
4.9.25 Either chemical toilets or other types of sewage treatment facilities without local discharge of wastewater shall be used to handle the foul water effluent arising from the project sites.
Summary of Mitigation
Measures for Construction Phase
4.9.26 The potential impacts on water quality during the construction phase of the Project and the associated recommendation of mitigation measures are summarised in Table 4.7.
Summary of
Mitigation Measures for Construction Impacts
|
Impacts
from Construction |
Mitigation
Measures |
|
Increase of suspended solids and
turbidity from silty site run-off. |
Reduction of site run-off by
diversion into temporary sedimentation or other silt removal facilities. Site management practices in
accordance with ProPECC PN 1/94. Carry out works in dry season. Construction of bunds or barriers
where there is potential for runoff to enter watercourses. |
|
Release of nutrients/ silts into
runoff during excavation of stream sediment. |
Carry out works in sections and
during dry season. Drying of sediment before
excavation. Careful handling of sediment being
excavated. Storage of sediment in bunded area
and properly covered. Sediments to be reuse on-site as
backfilling material to minimize off-site disposal. Avoid stockpiling, if unavoidable
stockpile for the shortest duration possible. Ability to confine flow of water
(using bunds, diversion channels, etc). Monitor suspended solids and turbidity
in water courses. |
|
Elevation of pH in water courses
from concrete washings. |
Close monitoring of pH in
watercourses. Construction of bunds around the
concreting work to collect spilt cement and concrete washings. Adjustment of pH in any water which
has become contaminated with concrete. Restrict the use of concrete for
bank improvement works at LMH01. |
|
Release of waste oil or other
chemicals used in the site workshop or depot. |
Registration of contractor as a
chemical waste producer. Provide a safe designated storage area for chemicals
on-site. Removal of waste oil by licensed
collectors. Siting the workshop away from water
bodies. Installation and maintenance of oil
interceptor in hard standing compound. Oil interceptor should have a bypass
installed and be regularly maintained. Good housekeeping practices to minimise
careless spillage. Prepare an emergency contingency
plan to contain and remove all accidental spillage. Appropriate training given to the
personnel to handle chemicals. |
|
Increase of sewage and other
wastewater from additional workers. |
Provision of portable chemical
toilets and proper collection and disposal of sewage and wastewater. |
Operational Phase Mitigation Measures
4.9.27 The most important feature of the proposed channels is the prospect of suitable re-vegetation of the gabion side slopes replicating existing riparian vegetation. The vegetation is not expected to be detrimental in any way to the structure. However, seasonal cutting and clearance of vegetation, particularly in advance of the wet season will be required. This mitigation measure has additional benefits of aesthetic and ecological value.
4.9.28 In addition, the use of gabion or rock fill base for the bed of the channel has the benefit of providing uneven surfaces and cavities for sediment to accumulate. Ultimately a sediment layer will build up on the gabion floor, 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 75 mm thick sediment would be allowed to accumulate at the channel bed to permit recolonizing of benthic communities. Growth of vegetation within the gabion sections 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.
4.9.29 The main disadvantage in the use of gabions in the channel is the increase of hydraulic resistance. This will cause a slightly wider hydraulic section to be adopted in the channel design to maintain the same capacity for flood control.
4.9.30 Certain wetland plant species such as ‘sedges’ which have high flexibility and are easily deformed during flood conditions and present minimum drag to flow can be used without significantly compromising the flood capacity of the channel. Species such as vetiver are well documented as being hardy and able to grow under seasonally flooded conditions and are ideally suited for channel bank stabilisation and re-vegetation.
4.9.31 Maintenance of grass species in the channel bottoms is relatively simple and they can be cut prior to the rainy season to prevent washing into River Indus. The recommended vegetation will take up both nutrients and pollutants and should be disposed to landfill. At the same time as grass cutting, excessive sediment may be removed to prevent this being washed into River Indus. As the volume of excess sediment is expected to be minimal, this can be disposed to landfill along with the excess vegetation. The excess sediment should be allowed to drained and dried before disposal.
4.9.32 Odour reduction can be achieved through regular sediment removal during low flow (dry season).
Environmental Considerations for Maintenance of the
Proposed Channels
4.9.33 Maintenance may be necessary for the proposed gabion channel at regular intervals to remove excessive silts, vegetation, debris and obstruction. Little or no maintenance will be necessary for the natural streams (e.g. Lin Ma Hang and ‘two-stage’ channel of MUP05). Good practice guides for the planning and execution of desilting and maintenance works on environmentally sensitive watercourses are recommended in the following sections.
4.9.34
Before proceeding with any desilting or maintenance works,
except for emergency works, the maintenance engineer should check to ascertain
if any of the proposed works will be located in or near an environmentally
sensitive and/or ecologically important watercourses. In case of doubt, advice
from
4.9.35
If the proposed works will be located inside or near one of
the environmentally sensitive and/or ecologically important watercourses,
careful consideration should be given to the proposed method of implementation
so as to minimise any adverse environmental impact. Depending on the extent of
the maintenance works,
4.9.36 The following considerations should be included in planning for the maintenance works for the proposed gabion channels:
(a)
Maintenance of the channels should be restricted to annual
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)
A minimum of 75mm thick sediment should be allowed to
accumulate on the channel bed to permit recolonization of benthic communities.
(d)
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 watercourse
in short sections. A free passage along the watercourse is necessary to avoid
forming stagnant water in any phase of the works and to maintain the integrity
of aquatic communities.
(e)
Containment structures (such as sand bags barrier) should be
provided for the active desilting works area to facilitate a dry or at least
confined working area within the watercourses.
(f)
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 watercourse, adjacent vegetation and nearby sensitive
receivers by construction plants.
(g)
The use of lesser or smaller construction plants should be
considered to reduce disturbance to the channel bed where fish habitats are
located and to the nearby sensitive receivers. Quiet construction plants should
be used.
(h)
The use of concrete or the like should be avoided or
minimized.
(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.
4.9.37 A summary of the mitigation measures proposed is shown in Table 4.8.
Summary of
Mitigation Measures for Operational Impacts
|
Impacts
from Operation |
Mitigation
Measures |
|
Reduction in water quality of
downstream water courses from introduction of pollutants upstream. |
Pollutants present in run-off
during operation can be reduced through an increase in permeable areas in
sections where the run-off occurs to reduce the volume of pollutants entering
the channels. Grasscrete and gabions can be used to achieve this. |
|
Removal of permeable area presently
covered in vegetation. |
Use of gabions in sections of the
channels mitigates this impact through allowing vegetative growth.
Infiltration of water into the ground and passage through vegetation will
provide partial treatment of the water in terms of trapping suspended solids
and removal of BOD through aeration. |
|
Increased sediment transport to
River Indus and ultimately to |
Sediment will be carried to River
Indus and ultimately to |
|
Temporary release of odour from
polluted water and sediments in the channel during low flow condition. |
Odour reduction can be achieved
through regular sediment removal during dry season. |
|
Temporary release of suspended
solids and waste during maintenance process, minor disturbance from
maintenance equipment. |
Implement good practice guides for
the planning and execution of desilting and maintenance works such as works during
dry season, phasing of the works, use of containment structures, sensitive
use of construction plant to reduce disturbance, minimise the use of
concrete, and proper storage and disposal of waste. |
4.9.38 If the above 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.
4.9.39 The implementation schedule for the recommended mitigation measures is presented in Appendix A.