5.1
The
Project is to construct and operate a biological treatment facility to convert
source-separated organic waste into compost and biogas. A process flow diagram is illustrated in
Figure 2.3.
5.2
During
construction phase, the key concerns would include the potential water quality
impacts from site run-off, sewage from workforce, and discharge of wastewater
from various construction activities. During operational phase, wastewater
would be generated from organic waste treatment processes, which might have
potential water quality impacts on the water environment, if uncontrolled.
5.3
This
section identifies and assesses potential water quality impacts associated with
the construction and operation of the Project. Recommendations for mitigation measures
have been provided to minimise potential adverse water quality impacts and to
ensure the acceptability of any residual impacts.
Environmental
Legislation, Policies, Plans, Standards and Criteria
Water
Pollution Control Ordinance (WPCO)
Ÿ Annex 6 Criteria for Evaluating
Water Pollution
Ÿ Annex 14 Guidelines for Assessment
of Water Pollution.
Marine Water Quality Objectives
5.5
The
Water Pollution Control Ordinance (WPCO) provides the major statutory framework
for the protection and control of water quality in
Table 5.1 Summary
of Water Quality Objectives for the North
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive
Odour, Tints |
Not
to be present |
Whole
zone |
|
Visible
foam, oil scum, litter |
Not
to be present |
Whole
zone |
|
Dissolved
Oxygen (DO) within 2 m of the seabed |
Not
less than 2.0 mg/L for 90% of samples |
Marine
waters |
|
Depth-averaged
DO |
Not
less than 4.0 mg/L |
Tuen
Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones, Water Gathering Ground
Subzones and other inland waters |
|
Not
less than 4.0 mg/L for 90 % sample |
Marine
waters |
|
|
pH |
To
be in the range of 6.5 - 8.5, change due to human activity not to exceed 0.2 |
Marine
waters excepting Bathing Beach Subzones |
|
To
be in the range of 6.5 – 8.5 |
Tuen
Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground
Subzones |
|
|
To
be in the range of 6.0 –9.0 |
Other
inland waters |
|
|
To
be in the range of 6.0 –9.0 for 95% samples |
Bathing
Beach Subzones |
|
|
Salinity |
Change
due to human activity not to exceed 10% of ambient |
Whole
zone |
|
Temperature |
Change
due to human activity not to exceed 2 oC |
Whole
zone |
|
Suspended
solids (SS) |
Not
to raise the ambient level by 30% caused by human activity |
Marine
waters |
|
Not
to cause the annual med |
Tuen
Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground
Subzones |
|
|
Not
to cause the annual med |
Inland
waters |
|
|
Unionized
Ammonia (UIA) |
Annual
mean not to exceed 0.021 mg/L as unionized form |
Whole
zone |
|
Nutrients |
Shall
not cause excessive algal growth |
Marine
waters |
|
Total
Inorganic Nitrogen (TIN) |
Annual
mean depth-averaged inorganic nitrogen not to exceed 0.3 mg/L |
Castle
Peak Bay Subzone |
|
Annual
mean depth-averaged inorganic nitrogen not to exceed 0.5 mg/L |
Marine
waters excepting Castle Peak Bay Subzone |
|
|
Bacteria |
Not
exceed 610 per 100ml, calculated as the geometric mean of all samples
collected in one calendar year |
Secondary
Contact Recreation Subzones |
|
Should
be less than 1 per 100 ml, calculated as the running med |
Tuen
Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones |
|
|
Not
exceed 1000 per 100 ml, calculated as the running med |
Tuen
Mun (C) Subzone and other inland waters |
|
|
Not
exceed 180 per 100 ml, calculated as the geometric mean of all samples
collected from March to October inclusive. Samples should be taken at least 3
times in one calendar month at intervals of between 3 and 14 days. |
Bathing
Beach Subzones |
|
|
Colour |
Not
to exceed 30 Hazen units |
Tuen
Mun (A) and Tuen Mun (B) Subzones and Water Gathering Ground Subzones |
|
Not
to exceed 50 Hazen units |
Tuen
Mun (C) Subzone and other inland waters |
|
|
5-Day
Biochemical Oxygen Demand (BOD5) |
Not
to exceed 3 mg/L |
Tuen
Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground
Subzones |
|
Not
to exceed 5 mg/L |
Inland
waters |
|
|
Chemical
Oxygen Demand (COD) |
Not
to exceed 15 mg/L |
Tuen
Mun (A), Tuen Mun (B) and Tuen Mun (C) Subzones and Water Gathering Ground
Subzones |
|
Not
to exceed 30 mg/L |
Inland
waters |
|
|
Toxins |
Should
not cause a risk to any beneficial uses of the aquatic environment |
Whole
zone |
|
Waste
discharge shall not cause the toxins in water significant to produce toxic
carcinogenic, mutagenic or teratogenic effects in humans, fish or any other
aquatic organisms. |
Whole
zone |
|
|
Phenol |
Quantities
shall not sufficient to produce a specific odour or more than 0.05 mg/L as C6
H5OH |
Bathing
Beach Subzones |
|
Turbidity |
Shall
not reduce light transmission substantially from the normal level |
Bathing
Beach Subzones |
Source: Statement of Water Quality
Objectives (North Western Water Control Zone).
Technical
Memorandum
5.6
Discharges
of effluents are subject to control under WPCO. The Technical Memorandum on Standards
for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters (TM-DSS), issued under Section 21 of WPCO, gives guidance on permissible
effluent discharges based on the type of receiving waters (foul sewers, storm
water drains, inland and coastal waters).
The limits control the physical, chemical and microbial quality of
effluent. Any sewage from the
proposed construction and operation activities must comply with the standards
for effluent discharged into the foul sewers, inshore waters and marine waters
of the North Western WCZ provided in TM-DSS.
Practice
Notes
5.7
A
practice note (PN) for professional persons was issued by EPD to provide
environmental guidelines for handling and disposal of construction site
discharges. The ProPECC PN 1/94
“Construction Site Drainage” provides good practice guidelines for dealing with
various types of discharge from a construction site. These include surface runoff, groundwater,
boring and drilling water, bentonite slurry, water for testing and
sterilisation of water retaining structures and water pipes, wastewater from
building construction, acid cleaning, etching and pickling wastewater, and
wastewater from site facilities. Practices outlined in the ProPECC PN 1/94
should be followed as far as possible during construction to minimize the water
quality impact due to construction site drainage.
Description of the
Environment
5.8
There
is no EPD marine water quality monitoring station in vicinity of the Project Site. The EPD monitoring stations NM1 and NM2
in North Western WCZ are the nearest monitoring stations to the Project Site. EPD monitoring data collected at these
two monitoring stations in 2007 were summarized in Table 5.2.
5.9
According
to the “2007 Marine Water Quality in Hong Kong”, which is the latest available
information from EPD at the moment of preparing this EIA Report, compl
Table 5.2 Baseline
Marine Water Quality Condition for North
|
Parameter |
Lantau Island (North) |
Pearl Island |
WPCO WQO (in marine waters) |
|
|
NM1 |
NM2 |
|||
|
Temperature (oC) |
23.0 |
23.4 |
Not more than 2oC in daily temperature range |
|
|
Salinity |
30.9 |
29.5 |
Not to cause more than 10% change |
|
|
Dissolved Oxygen (DO)
(mg/L) |
Depth average |
5.7 |
6.0 |
Not less than 4 mg/L for 90% of the samples |
|
Bottom |
5.4 |
5.7 |
Not less than 2 mg/L for 90% of the samples |
|
|
Dissolved Oxygen (DO) (% Saturation) |
Depth average |
79 |
83 |
Not Available |
|
Bottom |
75 |
79 |
Not Available |
|
|
pH |
8.0 |
8.0 |
6.5 - 8.5 (± 0.2 from natural range) |
|
|
Secchi disc Depth (m) |
1.8 |
1.6 |
Not Available |
|
|
Turbidity (NTU) |
14.9 |
12.5 |
Not Available |
|
|
Suspended Solids (SS)
(mg/L) |
8.2 |
5.8 |
Not more than 30%
increase |
|
|
5-day Biochemical Oxygen
Demand (BOD5) (mg/L) |
1.0 |
1.0 |
Not Available |
|
|
Ammonia Nitrogen (NH3-N)
(mg/L) |
0.13 |
0.13 |
Not Available |
|
|
Unionised Ammonia (UIA)
(mg/L) |
0.005 |
0.006 |
Not more than 0.021 mg/L
for annual mean |
|
|
Nitrite Nitrogen (NO2-N) (mg/L) |
0.05 |
0.063 |
Not Available |
|
|
Nitrate Nitrogen (NO3-N)
(mg/L) |
0.207 |
0.281 |
Not Available |
|
|
Total Inorganic Nitrogen
(TIN) (mg/L) |
0.39 |
0.48 |
Not more than 0.5 mg/L
for annual mean |
|
|
Total Kjeldahl Nitrogen
(mg/L) |
0.30 |
0.31 |
Not Available |
|
|
Total Nitrogen (TN)
(mg/L) |
0.56 |
0.657 |
Not Available |
|
|
Orthophosphate Phosphorus
(OrthoP) (mg/L) |
0.025 |
0.024 |
Not Available |
|
|
Total Phosphorus (TP)
(mg/L) |
0.05 |
0.05 |
Not Available |
|
|
Silica (as SiO2)
(mg/L) |
1.3 |
1.5 |
Not Available |
|
|
Chlorophyll-a (µg/L) |
5.4 |
6 |
Not Available |
|
|
E coli (cfu/100 mL) |
670 |
360 |
Not Available |
|
|
Faecal Coliforms (cfu/100 mL) |
1500 |
820 |
Not Available |
|
Notes:
1. Data source: Marine Water Quality In Hong Kong
in 2007.
2. Except as specified, data presented are depth-averaged values calculated
by taking the means of three depths: surface, mid-depth, bottom.
3. Data presented are annual arithmetic means of depth-averaged results
except for E. coli and faecal coliforms that are annual geometric means.
4. Data in brackets indicate the ranges.
5.10
The
Project Site is located at Siu Ho Wan and it is bounded northeast by North
Lantau Highway and southeast by a disturbed headland where the Siu Ho Wan Water
Treatment Works (SHWWTW) are located. There are no particular areas of
conservation value, ecological importance or mariculture activities in the
vicinity of the Project Site. No
marine water sensitive receivers are identified. The closest water sensitive receiver
would be an open nullah located in the north-western part of the Project area.
No water quality monitoring data are available for the nullah.
5.11
Potential
sources of water quality impact that may arise during the Project works were
described. All the identified
sources of potential water quality impact were then evaluated and their impact
significance determined. The need
for mitigation measures to reduce any identified adverse impacts on water
quality to acceptable levels was determined.
Identification of
Environmental Impacts
5.12
Potential
sources of water quality impact associated with the construction activities for
the Project would include:
Ÿ construction site runoff;
Ÿ general construction activities;
Ÿ excavation of soil materials;
Ÿ accidental spillage;
Ÿ sewage effluent;
Ÿ nullah reconstruction activities
Construction Site Runoff
5.13
Soil
surfaces would be exposed during construction phase of the Project. Site runoff generated during a rainstorm
would wash away the soil particles on unpaved lands and areas with exposed
topsoil. This runoff is generally
characterized by high concentrations of suspended solids. Directly release of uncontrolled site
runoff would increase SS levels and turbidity in the nearby environment. Site runoff may also wash away
contaminated soil particles and therefore cause water pollution.
5.14
Wind
blown dust would be generated from exposed soil surfaces in the works areas. It
is possible that wind blown dust would fall directly onto the nearby water
bodies when a strong wind occurs.
Dispersion of dust within the works areas may increase the SS levels in
surface runoff causing a potential impact to the nearby sensitive receivers.
General Construction
Activities
5.15
Land-based
construction works may have the potential to cause water pollution. Various types of construction activities
would generate wastewater. These
include general cleaning and polishing, wheel washing, dust suppression and
utility installation. These types
of wastewater would contain high concentrations of suspended solids. Wastewater would also be generated from
the accumulation of solid waste such as plastic package and construction
materials. If uncontrolled, these
would lead to deterioration in water quality. Increased nutrient level from
contaminated discharges and sewage effluent could also lead to a number of
secondary water quality impacts including decreases in DO concentration and
localised increase in ammonia nitrogen concentrations which could stimulate
algal growth.
Excavation of Soil
Materials
5.16
The
construction of the Project includes excavation of soil materials. Excavated soil may have to be stored
on-site before being sorted, reused or transported to disposal sites. If stored as open air stockpiles with no
cover during rainfall, excavated soils would have a potential risk to be washed
away and back into the nearby water environment, thereby causing sudden
increase of SS and oxygen demand.
Accidental Spillage and
Accumulation of Solid Wastes
5.17
Variety
of chemicals would be used for carrying out construction activities. These chemicals may include petroleum
products, spent lubrication oil, grease, mineral oil, solvent and other chemicals. Accidental spillages of chemicals in the
works area may contaminate the surface soils. The contaminated soil particles may be
washed away by construction site runoff causing water pollution. Accumulation of solid waste (such as
debris, rubbish and demolition materials) could also lead to deterioration in
water quality, if not well controlled.
Sewage Effluent
5.18
Sewage
effluent might be generated from the workforce during the construction phase. However, this temporary sewage can be
adequately treated by interim sewage treatment facilities, such as portable
chemical toilets, which can be installed within construction site.
Nullah Decking
5.19
There
is an open nullah located within the Project Site boundary at the
northwest. In the reference design
of OWTF, it is proposed to deck over the nullah car parking purposes.for use as
open space / carpark. The
construction of proposed nullah decking, which would involve demolition of existing nullah, excavation
activities, and construction of box culvert, may pollute storm water in the
existing open nullah due to potential release of construction wastes, if
uncontrolled.
Operational
Phase
5.20
The
potential operational phase pollution sources include:
Ÿ domestic sewage effluent from
workforce;
Ÿ wastewater generated from the organic
waste treatment processes;
Ÿ contaminated surface runoff and accidental
spillage.
Domestic Sewage Effluent
from Workforce
5.21
Sewage
effluent generated from workforce is characterized by high levels of
nutrients. Directly discharge of
sewage effluent into the water environment would cause excessive algal growth
and reduce dissolved oxygen in water bodies.
Organic Waste Treatment
Processes
5.22
The
organic waste treatment facilities (OWTF) are to convert the source-separated
organic waste into compost and biogas.
Wastewater would be generated during the treatment processes.
Wastewater from Dewatering Process
5.23
According
to the reference design of OWTF, digestate from the digesters would be pumped
to the dewatering units where solids are separated from liquid (i.e. filtrate)
and wastewater, resulting in a nominal flow of 143 m3/day and a
maximum flow of 172 m3/day. Major composition would include chemical
oxygen demand (COD), biological oxygen demand (BOD), kjeldahl nitrogen (TKN),
ammonia-nitrogen (NH3-N) and suspended solid (SS). If uncontrolled, the wastewater
generated would deteriorate water quality and adversely affect aquatic life in
the nearby water environment.
Leachate from Waste Reception Area
5.24
Organic
waste would be collected and transported to the Site by waste vehicles. On arrival at the Site, the incoming
waste will be unloaded to unloading bays in a reception area. As the wet nature of organic waste,
occasional formation of leachate will be expected in the reception area.
Condensate from Biogas Handling and Scrubber of the
Air Treatment System
5.25
As
biogas from digestion would be saturated with moisture, removal of condensate
from biogas will be required before entering to Cogen Units. A small amount of wastewater would then
be generated from the process of condensate removal.
5.26
In
addition, air pollution emission would be occurred during the course of solid
treatment processes. Thus, air
treatment facilities such as scrubber and biofilter would be provided to
control air pollution emission. In the
scrubber, air would be treated by spraying water in countercurrent and a small
amount of wastewater would then be generated.
Surplus Water from the Truck Washing Facility
5.27
A
truck washing facility would be equipped at the Project Site to thoroughly wash
the entire exterior of waste collection vehicles leaving the Site. Water from the truck washing facility
would be reused on site. Surplus
water may have potential to be discharged into nearby water environment and
cause adverse water quality impact, if uncontrolled.
Contaminated Surface
Runoff
5.28
Surface
or rainwater runoff generated during the operational phase is also potentially
contaminated and may pose similar water quality impact, if not well controlled.
Cumulative Water Quality Impact
5.29
Relevant
concurrent projects in the vicinity of OWTF are shown in Table 2.4 under Section
2. As all the construction
works proposed under this Project would be land-based and with implementation
of the recommended mitigation measures, any potential water quality impact
generated during construction phase of the Project would be localized and
minor. No marine construction works would be required under this Project, and
hence no significant cumulative water quality impact with other possible
concurrent projects would be expected.
5.30
Since
all possible effluents, leachate and contaminated
runoff from the Project operation shall be treated and their quality be
monitored before discharged, no significant cumulative water quality impact imposed
by the Project is expected during the operational phase.
Prediction and
Evaluation of Environmental Impacts
Construction
Phase
Construction Site Runoff
5.31
It
is important that proper site practice and good site management are observed to
prevent site runoff entering the surrounding waters in particular the open nullah
at the northwestern part of the Project Site, avoid disturbance of water bodies
and minimise deterioration in water quality. Recommended mitigation measures are
detailed in Section 5.44.
Provided that the recommended mitigation measures are properly
implemented, unacceptable impacts on water quality are not anticipated.
General Construction
Activities
5.32
Land-based
construction activities may generate wastewater and cause water pollution. These impacts are likely to be minimal,
provided that good constructions and proper site managements would be
observed. It is anticipated that
water quality impacts caused by general construction activities would be insignificant
with adequate implementations of recommended mitigations as mentioned in Section 5.44.
Excavation of Soil
Materials
5.33
There
is a potential that excavated soil material is washed away from the
construction site to the nearby watercourses during rain event, and hence
increases SS concentration and oxygen demand in water bodies. Mitigation measures are recommended in Section 5.45 to minimise the potential water quality
impacts.
Accidental Spillage and
Accumulation of Solid Waste
5.34
Site
drainage should be well maintained and good construction practices should be
observed to ensure that litter, fuels and solvents are managed, stored and
handled properly and do not enter the nearby water streams. No adverse water quality impacts are
expected with proper implementation of the recommended mitigation measures.
Sewage Effluent
5.35
Sewage
would be generated from the workforce during the construction phase. However, this temporary sewage can be
adequately treated by interim sewage treatment facilities, such as portable
chemical toilets, which can be installed within the construction site. Provided that sewage would not discharge
directly to water streams, and chemical toilets are used and properly
maintained, it is unlikely that sewage generated from the site would cause
significant water impact.
Nullah Decking
5.36
Adoption
of good house keeping and mitigation measures would reduce the generation of
construction wastes and potential water pollution due to the proposed nullah decking
works. With the implementation of
adequate construction site drainage and the provision of mitigation measures as
described in Section 5.53, it is anticipated that unacceptable water
quality impacts would not arise.
Operational
Phase
Sewage Effluent from
Workforce
5.37
During
the operation of the Project, sewage effluent will be generated from
workforce. Generated sewage should
be connected to the foul sewerage system.
No adverse water quality impact is anticipated.
Wastewater from Dewatering
Process
5.38
It
is expected that dewatering of digestate and filtrate production would result
in daily nominal flow of 143 m3 and a maximum flow of 172 m3/day. The on-site wastewater treatment plant
shall deploy suitable treatment processes to reduce the pollution level to an
acceptable standard (refer to Section 5.54). Treated
effluent would be stored temporarily in order to be used as process water
within the plant. The storage
volume would be around 20 m3.
The effluent to be discharged to foul sewers could be taken as an
overflow from the tank. Levels of
contaminants and pollutants in the effluent of the on-site wastewater treatment
plant to be discharged to foul sewers shall satisfy the requirements specified
in the TM-DSS. Thus, adverse water
quality is not expected.
Leachate from Waste
Reception Area
5.39
Because
of the wet nature of organic waste, occasional formation of leachate is
expected. The reception area will
be provided with a drainage system on the floor connecting to the wastewater
treatment plant (refer to Section 5.54). No
direct discharge of leachate would be adopted. Adverse water quality impact would not be
anticipated.
Condensate from Biogas
Handling and Scrubber of the Air Treatment System
5.40
Condensate
from biogas handling and spraying water from scrubber will be collected and
transferred to the wastewater treatment plant (refer to Section 5.54). No
direct discharge of such wastewater would be adopted and therefore adverse
water quality impact would not be anticipated.
Surplus Water from the
Truck Washing Facility
5.41
A
truck washing facility will be equipped and thoroughly wash the entire exterior
of waste collection vehicles leaving the Site. Generated wastewater would be collected
and delivered to the wastewater treatment plant (refer to Section 5.54).
No adverse water quality impact would therefore be anticipated.
Contaminated Surface
Runoff
5.42
It
would be a required site practice not to directly discharge contaminated
surface runoff into the surface channel or nearby water bodies. Based on the reference design of OWTF, the
waste reception, treatment facilities and compost storages of OWTF would be
located in enclosed buildings to prevent generation of contaminated rain
runoff. All surface runoff such as
washed water generated in the treatment processes areas would be properly
collected and diverted to the on-site wastewater treatment plant (refer to Section 5.54). Adverse
water quality impact from contaminated surface runoff is not expected.
5.43
Site
drainage should be well maintained and good management practices should be
observed to ensure that wastes and chemicals are managed, stored and handled
properly and do not enter the nearby water streams. No adverse water quality impacts are
expected with proper implementation of the recommended mitigation measures.
Mitigation Measures of Adverse
Environmental Impacts
Construction Site Runoff
and General Construction Activities
Ÿ Sand/silt removal facilities such as
sand/silt traps and sediment basins should be provided to remove sand/silt
particles from runoff to meet the requirements of the TM-DSS. The design of efficient silt removal
facilities should be based on the guidelines in Appendix A1 of ProPECC PN 1/94,
which states that the retention time for silt/sand traps should be 5 minutes
under maximum flow conditions. The
detailed design of the sand/silt traps shall be undertaken by the contractor prior
to the commencement of construction.
Ÿ All drainage facilities and erosion
and sediment control structures should be regularly inspected and maintained to
ensure proper and efficient operation at all times and particularly during
rainstorms. Deposited silt and grit
should be regularly removed, at the onset of and after each rainstorm to ensure
that these facilities are functioning properly at all times.
Ÿ Measures should be taken to minimize
the ingress of site run-off and drainage into excavations. Drainage water pumped out from
excavations should be discharged into storm drains via silt removal facilities.
Ÿ If surface excavation works cannot
be avoided during the wet season (April to September), temporarily exposed
slope/soil surfaces should be covered by a tarpaulin or other means, as far as
practicable. Interception channels
should be provided (e.g. along the crest/edge of the excavation) to prevent
storm runoff from washing across exposed soil surfaces. Arrangements should always be in place
to ensure that adequate surface protection measures can be safely carried out
well before the arrival of a rainstorm.
Other measures that need to be implemented before, during and after
rainstorms are summarized in ProPECC PN 1/94.
Ÿ All vehicles and plant should be
cleaned before leaving the site to ensure no earth, mud, debris and the like is
deposited by them on roads. An
adequately designed and sited wheel washing facility should be provided at
every site exit where practicable.
Wash-water should have sand and silt settled out and removed at least on
a weekly basis to ensure the continued efficiency of the process. The section of access road leading to,
and exiting from, the wheel-wash bay to the public road should be paved with
sufficient backfall toward the wheel-wash bay to prevent vehicle tracking of
soil and silty water to public roads and drains.
Ÿ Open
stockpiles of construction materials or construction wastes on-site of more
than 50m3 should be covered with tarpaulin or similar fabric during
rainstorms.
Ÿ Water used in ground boring and
drilling should only be discharged into storm drains via silt removal
facilities.
Excavation of Soil
Materials
Accidental Spillage and
Accumulation of Solid Waste
5.46
Contractor
must register as a chemical waste producer if chemical wastes would be produced
from construction activities. The
Waste Disposal Ordinance (Cap 354) and its subsidiary regulations in particular
the Waste Disposal (Chemical Waste) (General) Regulation should be observed and
complied with for control of chemical wastes.
5.47
Maintenance
of vehicles and equipments involving activities with potential for leakage and
spillage should only be undertaken within the areas which appropriately
equipped to control these discharges.
5.48
Oils
and fuels should only be used and stored in designated areas which have
pollution prevention facilities.
All fuel tanks and storage areas should be sited on sealed areas in
order to prevent spillage of fuels and solvents to the nearby
watercourses. All waste oils and
fuels should be collected in designated tanks prior to disposal.
5.49
Disposal
of chemical wastes should be carried out in compl
Ÿ Suitable containers should be used
to hold the chemical wastes to avoid leakage or spillage during storage,
handling and transport.
Ÿ Chemical waste containers should be
suitably labelled, to notify and warn the personnel who are handling the wastes,
to avoid accidents.
Ÿ Storage area should be selected at a
safe location on site and adequate space should be allocated to the storage
area.
5.50
Construction
solid waste, debris and rubbish on site should be collected, handled and
disposed of properly to avoid entering to the nearby watercourses. Stockpiles of cement and other
construction materials should be kept covered when not being used. Rubbish and litter from construction
sites should also be collected to prevent spreading of rubbish and litter from
the site area. It is recommended to
clean the construction sites on a regular basis.
Sewage Effluent
5.51
The
presence of construction workers generates sewage. It is recommended to provide sufficient
chemical toilets in the works areas.
The toilet facilities should be more than 30m from any watercourse. A licensed waste collector should be
deployed to clean the chemical toilets on a regular basis.
5.52
Notices
should be posted at conspicuous locations to remind the workers not to
discharge any sewage or wastewater into the nearby environment during the
construction phase of the project.
Regular environmental audit on the construction site can provide an
effective control of any malpractices and can achieve continual improvement of
environmental performance on site.
Nullah Decking
Ÿ The proposed works should be carried out
within the dry season between October and March when the flow in the open
nullah is low.
Ÿ The use of less or smaller
construction plants may be specified to reduce the disturbance to the nullah
bed.
Ÿ Temporary storage of materials (e.g.
equipment, filling materials, chemicals and fuel) and temporary stockpile of
construction materials should be located well away from the nullah and any
water courses during carrying out of the construction works.
Ÿ Stockpiling of construction
materials and dusty materials should be covered and located away from the
nullah any water courses.
Ÿ Construction debris and spoil should
be covered up and/or disposed of as soon as possible to avoid being washed into
the nullah and nearby water receivers.
Ÿ Construction activities, which
generate large amount of wastewater, should be carried out in a distance away
from the nullah, where practicable.
Ÿ Construction effluent, site run-off
and sewage should be properly collected and/or treated.
Ÿ Any works site inside the nullah
should be temporarily isolated, such as by placing of
sandbags or silt curtains with lead edge at bottom and properly supported props
to prevent adverse impact on the water quality.
Ÿ Proper shoring may need to be
erected in order to prevent soil/mud from slipping into the nullah and nearby
watercourse.
Ÿ Supervisory staff should be assigned
to station on site to closely supervise and monitor the works.
Operational
Phase
5.54
The
Project Site will be equipped with an adequately sized wastewater treatment
plant. A high rate type of active
sludge system specifically designed for the removal of nitrogen components from
the wastewater in combination with conversion of residual BOD and COD would be
deployed. The wastewater treatment
plant would also be incorporated with
Ÿ Cleaning and maintenance of
treatment facilities should be conducted on a regular basis to ensure that
removal rate of each treatment facility would not be reduced.
Ÿ Cleaning and maintenance of
pipelines should be carried out on a regular basis to prevent block of pipeline
and leaching of wastewater, and therefore prevent overflowed or leached
wastewater discharging into nearby drainages and water streams.
Ÿ Regular site inspection should be
conducted to ensure that no wastewater can be directly discharged into nearby
water streams.
5.55
In
the scrubber, spraying water should be re-circulated to minimize the need for
external water. The spraying water
would be collected at the bottom of the scrubber. Excess water should be properly diverted
and discharged to the on-site wastewater treatment plant as described in Section 5.54.
5.56
The
waste reception, treatment facilities and compost storages of OWTF should be
located in enclosed buildings to prevent generation of contaminated rain
runoff. All surface runoff such as
washed water generated in the treatment processes areas should be properly
collected and diverted to the on-site wastewater treatment plant as described
in Section 5.54.
5.57
All
drainage system for collection and transferring wastewater generated in OWTF to
the on-site wastewater treatment plant as described in Section 5.54 should be capable of preventing clogging and
easy maintenance and cleaning.
Evaluation of Residual
Impacts
Construction
Phase
5.58
The
construction phase water quality impact would generally be temporary and
localised during construction. No
unacceptable residual water quality impacts would be expected during the
construction phase of the Project, provided that all the recommended mitigation
measures are properly implemented.
Operational
Phase
5.59
All
sewage or wastewater generated from the operation of the Project will be
adequately treated in the on-site wastewater treatment plant before reused
on-site or discharged to the public sewerage system. No residual water quality impacts would
be anticipated.
Environmental Monitoring
and Audit
5.60
With
the implementation of recommended mitigation measures, no unacceptable water
quality impact would be expected from the Project. Water quality monitoring is not
considered necessary. However, it
is recommended that regular site inspections should be undertaken to ensure
that the recommended mitigation measures are properly implemented during the
construction phase of the Project.
5.61
During
construction phase, potential water quality impact would be generated from site
run-off, sewage from workforce, and discharge of wastewater from various
construction activities. Provided
that all the recommended mitigation measures are properly implemented, no
adverse water quality impacts would be expected during the construction phase
of the Project. To avoid any potential water quality impact,
the nullah decking work would be carried out during the dry season, between
October and March.
5.62
The
operation of OWTF is to convert organic waste into compost and biogas. All sewage or wastewater generated from
the operation of the Project will be adequately treated in the on-site
wastewater treatment plant before reused on-site or discharged to the public
sewerage system. No adverse water
quality impacts would be anticipated.