Water Pollution Control Ordinance (WPCO)
5.2.1
The
Water Pollution Control Ordinance (Cap. 358), in existence since 1980, is the
major legislation relating to the protection and control of water quality in
Hong Kong. According to the Ordinance
and its subsidiary legislation, Hong Kong waters are divided into ten water
control zones (WCZ). Corresponding
statements of Water Quality Objectives (WQO) are stipulated for different water
regimes (marine waters, inland waters, bathing beaches subzones, secondary
contact recreation subzones and fish culture subzones) in the WCZ based on
their beneficial uses. The study area
is located within the North Western and Southern WCZs. The WQOs for the North Western and Southern
WCZs are shown in Tables 5.1 and 5.2, respectively.
Table 5.1 Water Quality Objectives for North Western Water Control Zone
|
Parameter |
Objective |
Part(s)
of Zone |
|
Aesthetic Appearance |
(a) discharge shall not cause objectionable odour or
discoloration (b) no tarry
residue, floating wood, articles made of grass, plastic, rubber or any other substance (c) Mineral oil not visible on the surface. Surfactants
shall not give rise to a lasting foam. (d) no recognizable sewage-derived debris (e) no floating, submerged or semi-submerged subjects
likely to interfere with the free movement or damage of material (f) not to contain substances which settle to form
objectionable deposits |
Whole Zone Whole Zone Whole Zone Whole Zone Whole Zone Whole Zone |
|
E. coli |
annual geometric
mean not to exceed 610/100 mL geometric mean not
to exceed 180/100 mL during March to October inclusive in 1 year; sample
should be taken at least 3 times in 1 calendar month at intervals of between
3 to 14 days geometric mean of
the most recent 5 consecutive samples taken at intervals of between 7 and 21
days not to be less than 1/100 mL geometric mean of the most recent 5 consecutive samples
taken at intervals of between 7 and 21 days not to exceed 1000/100 mL |
secondary contact recreation subzones Bathing beach subzones Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering
Ground Subzones Tuen Mun (C) and other Inland Waters |
|
Colour |
Not to exceed 30
Hazen units Not to exceed 50
Hazen units |
Tuen Mun (A) and Tuen Mun (B) Subzones and Water Gathering
Ground Subzones Tuen Mun (C) and
other Inland Waters |
|
Dissolved Oxygen
within 2 m of bottom |
not less than 2 mg/L
for 90% samples |
marine waters |
|
Depth averaged
Dissolved Oxygen |
not less than 4 mg/L
for 90% samples not less than 4mg/L
at any point within the water column |
marine waters fish culture subzones Tuen Mun (A) and Tuen Mun (B) Tuen Mun (C) Subzones, Water Gathering Ground
Subzones and other Inland waters |
|
pH value |
within the range 6.5
to 8.5; change due to waste discharge not to exceed 0.2 within the range 6.5
- 8.5 within the range 6.0
- 9.0 within the range 6.0
- 9.0; change due to waste discharge not to extend by 0.5 |
marine waters except bathing beach subzones Tuen Mun (A) and Tuen Mun (B) Tuen Mun (C) Subzones and water gathering ground
subzones other inland waters Beach Bathing
Subzones |
|
Salinity |
change due to waste discharge not to exceed 10% of natural
ambient level |
whole zone |
|
Temperature |
change due to waste discharge not to exceed 2oC |
whole zone |
|
Suspended solids |
waste discharge not
to raise the natural ambient level by 30%, nor cause the accumulation of
suspended solids which may adversely affect aquatic communities annual median not to
exceed 20 mg/L annual median not to exceed 25 mg/L |
marine waters Tuen Mun (A) and
Tuen Mun (B) Tuen Mun (C) Subzones
and water gathering ground subzones other inland waters |
|
5-Day Biochemical
Oxygen Demand |
not to exceed 3 mg/L not to exceed 5 mg/L |
Tuen Mun (A) and
Tuen Mun (B) Tuen Mun (C) Subzones
and water gathering ground subzones other inland waters |
|
Chemical Oxygen
Demand |
not to exceed 15
mg/L not to exceed 30
mg/L |
Tuen Mun (A) and
Tuen Mun (B) Tuen Mun (C) Subzones
and water gathering ground subzones other inland waters |
|
Un-ionized ammonia |
annual mean not to exceed 0.021 mg/L |
whole zone |
|
Nutrients |
not to be present in
quantities that cause excessive growth of
algae or other aquatic plants annual mean depth average inorganic nitrogen not to exceed
0.3 mg/L annual mean depth average inorganic nitrogen not to exceed
0.5 mg/L |
marine waters Castle Peak Bay
Subzone marine waters except Castle Peak Bay Subzone |
|
Toxins |
not to be present at
levels producing significant toxic effect, carcinogenic, mutagenic or
teratogenic effects in humans, fish or any other aquatic organisms, with due
regard to biologically cumulative effects in food chains and to interactions
of toxic substances with each other not to cause a risk to any beneficial use of the aquatic
environment |
whole zone whole zone |
|
Phenol |
not to produce a specific odour or concentrations greater
than 0.05 mg/L as C6H5 OH |
Bathing Beach
Subzones |
|
Turbidity |
No changes in turbidity or any other factors shall reduce
light transmission substantially from the normal level |
Bathing Beach
Subzones |
Table 5.2 Water Quality Objectives for Southern Water Control Zone
|
Parameter |
Objective |
Part(s)
of Zone |
E. coli
|
annual geometric
mean not to exceed 610/100 mL geometric mean not to exceed 180/100 mL during March to
October inclusive in 1 year; sample should be taken at least 3 times in 1
calendar month at intervals of between 3 to 14 days |
secondary contact recreation subzones; fish culture
subzones bathing beach subzones |
|
Dissolved Oxygen
within 2 m of bottom |
not less than 2 mg/L
for 90% samples not less than 2 mg/L
for 90% samples |
marine waters except fish culture subzones fish culture
subzones |
|
Depth averaged
Dissolved Oxygen |
not less than 4 mg/L
for 90% samples not less than 5 mg/L
for 90% samples not less than 4mg/L
at any point within the water column |
i) marine waters ii) Inland waters of the zone fish culture subzones Inland waters of the zone |
|
pH value |
within the range 6.5
to 8.5; change due to waste discharge not to extend by 0.2 within the range 6.0
- 9.0; change due to waste discharge not to extend by 0.5 within the range 6.0
– 9.0 |
marine waters except bathing beach subzones; Mui Wo (A),
Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) Subzones Bathing beach zones Mui Wo (D) Subzones
and other inland waters |
|
Salinity |
change due to waste discharge not to exceed 10% of natural
ambient level |
whole zone |
|
Temperature |
change due to waste discharge not to exceed 2oC |
whole zone |
|
Suspended solids |
waste discharge not
to raise the natural ambient level by 30%, nor cause the accumulation of
suspended solids which may adversely affect aquatic communities annual median not to
exceed 20 mg/L annual median not to
exceed 25 mg/L |
marine waters Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo
(F) Subzones Mui Wo (D) Subzones
and other inland waters |
|
Chemical Oxygen
Demand |
not to exceed 30 mg/L |
Inland waters of the Zone |
|
Aesthetic Appearance |
(a) discharge shall not cause objectionable odour or
discoloration (b) no tarry
residue, floating wood, articles made of grass, plastic, rubber or any other substance (c) Mineral oil not visible on the surface. Surfactants
shall not give rise to a lasting foam. (d) no recognizable sewage-derived debris (e) no floating, submerged or semi-submerged subjects
likely to interfere with the free movement or damage of material (f) not to contain substances which settle to form
objectionable deposits |
Whole Zone Whole Zone Whole Zone Whole Zone Whole Zone Whole Zone |
|
Nutrients |
not to be present in
quantities that cause excessive growth of
algae or other aquatic plants annual mean depth average inorganic nitrogen not to exceed
0.1 mg/L |
marine waters marine waters |
|
5-Day Biochemical
Oxygen Demand |
not to exceed 5 mg/L |
Inland waters of the
Zone |
|
Unionized Ammonia |
annual level shall not exceed 0.021 mg/L |
Whole Zone |
|
Dangerous Substances |
not to be present at levels producing significant toxic
effect in humans, fish or any other aquatic organisms, with due regard to
biologically cumulative effects in food chains and to toxicant interactions
with each other not to cause a risk to any beneficial use of the aquatic
environment |
whole zone whole zone |
Technical Memorandum
5.2.2
Besides
setting the WQOs, the WPCO controls effluent discharging into the WCZs through
a licensing system. A Technical Memorandum (TM) on Standards for
Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal
Waters was issued under the WPCO which gives guidance on the 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 effluents.
Under the TM, effluents discharged into inland waters are subject to
standards for particular volumes of discharge.
The discharge standard will vary with the use of downstream water. The majority of the inland water bodies
within the study area at Pui O are used for agricultural purposes, which are
classified as Group B inland waters.
Any new effluent discharge during the construction phase would be required
to comply with the terms and conditions of a discharge licence, issued by EPD,
under the WPCO. No new effluent will be
allowed within 100m of the boundaries of Pui O beach in any direction,
including rivers, streams and storm water drains.
Practice Notes
5.2.3
A
practice note (PN) for professional persons was issued by the 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. Practices outlined
in the PN should be followed as far as possible during construction to minimize
the water quality impact due to construction site drainage.
5.3.1
There
are three permanent streams at Pui O (labelled Streams 1 to 3 on Figures 6.2a
to 6.2c). River water quality data are
not available for these streams in the Pui O area from the EPD routine river
water quality monitoring programme. The
three streams drain agricultural, plantation and village areas. A description of the physical
characteristics of these streams as observed during the ecological surveys
conducted for the Project is described below.
5.3.2
The
largest stream, Stream 1, drained the southern slopes of Yi Tung Shan. The
stream course was largely natural to the north of South Lantau Road, with good
water quality and a substrate consisting of cobbles and large boulders. In the lower reaches below the South Lantau
Road, the stream channel was modified with rock-filled gabion and
concrete. Stream 2 flowed through the
centre of Pui O village, and formed a tributary of the larger Stream 1. Though relatively natural in its upper
reaches to the north of South Lantau Road, this stream was affected by domestic
inputs from village housing within Pui O village. South of the road, the stream
was obviously polluted with organic wastes, being malodorous. Stream 3 was a relatively small watercourse
and appeared to have good water quality.
5.4.1
There
are twohree streams at Pui O which would fall
partially within the proposed works area for the raw water mains along South
Lantau Road (see Figure 5.1). Stream 1
is located in close proximity of the proposed demolition and reprovisioning
works for Pui O Raw Water Pumping Station and uprating works for Pui O No. 2
Raw Water Pumping Station. The streams
discharge to Pui O Wan, where there is a gazetted beach. There are concrete drainage channels to the
north and south of the Siu Ho Wan WTW which collect the surface runoff in the
area, including the runoff from the small seasonal streams on the hillslopes
above the Siu Ho Wan WTW (see Figure
5.2).
5.5.1
The
water sensitive receivers that may be affected by the construction works for
the Project were identified. Potential
sources of water quality impact that may arise during the construction and
operation phases were described. This
task included identifying pollutants from point discharges and non-point
sources to surface run-off. 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. No cumulative water quality impact would be expected within the
study areas at Siu Ho Wan and Pui O as no concurrent activities of other
committed projects within 300m of the Project boundaries have been identified.
Construction Phase
5.6.1
Potential
sources of water quality impact associated with the construction phase of the
Project have been identified and include:
·
construction
site runoff and drainage;
·
general
construction activities; and
·
sewage
effluent produced by on-site workforce.
5.6.2
The
above impacts are common to the proposed extension works at the Siu Ho Wan WTW,
the construction of the proposed Siu Ho Wan Raw Water Booster Pumping Station,
the demolition and reprovisioning works for Pui O Raw Water Pumping Station and
uprating works for Pui O No. 2 Raw Water Pumping Station, and the proposed raw
water mains along South Lantau Road at Pui O.
Construction Site Runoff and Drainage
5.6.3
Runoff
from the construction works areas at Siu Ho Wan and Pui O during earthworks and
demolition works (for the Pui O Raw Water Pumping Station only) may contain
increased loads of sediments, other suspended solids and contaminants. Potential sources of pollution from site
drainage include:
·
runoff
and erosion from exposed soil surfaces, earth working areas and stockpiles;
·
release
of cement materials with rain wash;
·
wash
water from dust suppression sprays; and
·
fuel
and lubricants from maintenance of construction vehicles and mechanical
equipment.
5.6.4
Sediment
laden runoff may carry pollutants (adsorbed onto the particle surfaces) into
the nearby streams at Pui O and the drainage channels at Siu Ho Wan. Associated effects which may arise include
increased suspended solids concentrations in receiving waters and blockage of
storm water drains. Mitigation measures should be implemented to control
construction site runoff and drainage from the works areas, and to prevent
runoff and drainage water with high levels of suspended solids from entering
the nearby streams or local storm water drainage system. With the implementation of adequate
construction site drainage and provision of sediment removal facilities as
described in Section 5.7.2, it is anticipated that unacceptable water quality
impacts would not arise. The demolition
and reprovisioning works for Pui O Raw Water Pumping Station and uprating works
for Pui O No. 2 Raw Water Pumping Station and the extension to the Siu Ho Wan
WTW would take place within the existing site boundaries, with a small works
area.
5.6.5
The
streams at Pui O discharge into Pui O Wan and therefore the implementation of
mitigation measures would also be required to prevent polluted discharges of
site runoff and drainage water from entering the bay. With the implementation of the recommended mitigation measures,
it is not anticipated that adverse water quality impacts would arise at Pui O
beach.
General
Construction Activities
5.6.6
On-site
construction activities may cause water pollution from the following:
·
uncontrolled
discharge of debris and rubbish such as packaging, construction materials and
refuse; and
·
spillages
of liquids stored on-site, such as oil, diesel and solvents etc, are likely to
result in water quality impacts if they enter the nearby streams at Pui O, the
drainage channel at Siu Ho Wan, or local storm water drainage system.
5.6.7
Good
construction and site management practices should be observed to ensure that
litter, fuels and solvents do not enter the nearby watercourses or storm water
drains.
Sewage
Effluents
5.6.8
Domestic
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. It is unlikely that sewage generated from the site
would have a significant water quality impact, provided that sewage is not
discharged directly to the nearby streams or drainage channels, and chemical
toilets are used and properly maintained.
Operation Phase
5.6.9
During
the operation of the Project, the process wastewater generated from the
extended Siu Ho Wan WTW would normally be recycled back to the raw water
inlet. No wastewater discharge would
therefore be expected. Domestic
wastewater generated from the office of the extended Siu Ho Wan WTW would be
limited and would be discharged to the sewer and treated in the sewage
treatment plant. Hence, no adverse
water quality impact arising from the operation of the Project would be
anticipated.
5.7.1
Proposed
mitigation measures for containing and minimizing water quality impacts are
summarized below.
Construction Site Run-off and Drainage
5.7.2
Proper
site management measures should be implemented to control site runoff and
drainage, and thereby minimize potential adverse impacts on water quality. The site practices outlined in ProPECC PN
1/94 Construction Site Drainage should be followed as far as practicable in
order to minimize surface runoff and the chance of erosion, and also to retain
and reduce any suspended solids prior to discharge. These practices include the following
measures:
·
Before
commencing any site formation work, all sewer and drainage connections should
be sealed to prevent debris, soil, sand etc. from entering public
sewers/drains.
·
Sand/silt
removal facilities such as sand traps, silt traps and sediment basins should be
provided to remove sand/silt particles from runoff to meet the requirements of
the Technical Memorandum standard under the Water Pollution Control
Ordinance. The design of silt removal
facilities should be based on the guidelines provided in ProPECC PN 1/94. All drainage facilities and erosion and
sediment control structures should be inspected monthly and maintained to
ensure proper and efficient operation at all times and particularly during
rainstorms.
·
Water
pumped out from foundation excavations should be discharged into silt removal
facilities.
·
Open
trench excavation for the mainlaying works at Pui O near the stream courses
should be avoided in the wet season as far as practicable (i.e. during April to
October), and the trench should be excavated and backfilled in short sections.
·
Exposed
soil surfaces should be protected by paving or fill material as soon as
possible to reduce the potential of soil erosion.
·
Open
stockpiles of construction materials or construction wastes on-site of more
than 50m3 should be covered with tarpaulin or similar fabric during
rainstorms.
General Construction Activities
5.7.3
Debris
and refuse generated on-site should be collected, handled and disposed of
properly to avoid entering the nearby watercourses and storm water drains. Stockpiles of cement and other construction
materials should be kept covered when not being used. In particular, care should be exercised during the mainlaying
works at Pui O at the locations where the proposed raw water mains would be
constructed over the top of the streams.
5.7.4
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 provided with locks and be sited on
sealed areas, within bunds of a capacity equal to 110% of the storage capacity
of the largest tank. The bund should be
drained of rainwater after a rain event.
Sewage from Construction Workforce
5.7.5
Temporary
sanitary facilities, such as portable chemical toilets, should be employed
on-site. A licensed contractor would be
responsible for appropriate disposal and maintenance of these facilities.
5.8.1
Aside
from auditing the implementation of the recommended mitigation measures, a
specific water quality monitoring programme is deemed unnecessary.
5.9.1
With
the full implementation of the recommended mitigation measures for the
construction phase of the proposed Project, no unacceptable residual impacts on
water quality are anticipated. It is
recommended that regular audit of the implementation of the recommended
mitigation measures be carried out during the construction phase.