This Section presents
the water quality impact assessment for the construction phase of the
Project. As the construction works will
be land-based, direct impacts on water quality will not arise. The purpose of the assessment is to evaluate the acceptability of predicted
impacts to water quality from the construction of the wind turbine with
reference to the relevant environmental legislation and standards.
The enabling works along the long and short access routes and the
construction of the wind turbine at the Project Site would generate surface
run-off and wastewater which has the potential to cause adverse water quality
impacts if not properly controlled or mitigated.
7.2
Relevant
Legislation and Guidelines
The following relevant legislation and associated guidelines are
applicable to the evaluation of water quality impacts associated with the
construction of the Project.
• Water
Pollution Control Ordinance (WPCO);
• Technical
Memorandum on Standards for Effluents Discharged into Drainage and Sewerage
Systems, Inland and Coastal Waters (TM);
• Environmental
Impact Assessment Ordinance (Cap. 499. S.16), Technical Memorandum on
Environmental Impact Assessment Process (EIAO-TM), Annexes 6 and 14;
Apart from these statutory requirements, the Practice Note for
Professional Persons, Construction Site
Drainage (ProPECC PN 1/94), issued by ProPECC
in 1994, also provides useful guidelines on the management of construction site
drainage and prevention of water pollution associated with construction
activities.
7.2.1
Water Pollution Control Ordinance
The WPCO is the principal
legislation for the control of water pollution and water quality in
Table 7.2a Water
Quality Objectives for the Southern Water Control Zone
|
Water Quality Objectives |
Part or Parts of Zone |
|
A. AESTHETIC APPEARANCE |
|
|
a) Waste discharges
shall cause no objectionable odours or discolouration of the water. |
Whole zone |
|
b) Tarry residues,
floating wood, articles made of glass, plastic, rubber or of any other
substances should be absent. |
Whole zone |
|
c) Mineral oil
should not be visible on the surface.
Surfactants should not give rise to a lasting
foam. |
Whole zone |
|
d) There should be no
recognisable sewage-derived debris. |
Whole zone |
|
e) Floating,
submerged and semi-submerged objects of a size likely to interfere with the
free movement of vessels, or cause damage to vessels, should be absent. |
Whole zone |
|
f) Waste discharges
shall not cause the water to contain substances which settle to form
objectionable deposits. |
Whole zone |
|
B. DISSOLVED
OXYGEN |
|
|
a) Waste
discharges shall not cause the level of dissolved oxygen to fall below 4 mg L-1
for 90% of the sampling occasions during the year; values should be
calculated as the water column average (arithmetic mean of at least 3
measurements at 1m below surface, mid-depth and 1m above seabed). In addition, the concentration of dissolved
oxygen should not be less than 2 mg L-1 within 2m of the seabed
for 90% of the sampling occasions during the year. |
Marine waters excepting Fish
Culture Subzones. |
|
b) The
dissolved oxygen level should not be less than 5 mg L-1 for 90% of
the sampling occasions during the year; values should be calculated as the
water column average (arithmetic mean of at least 3 measurements at 1m below
surface, mid-depth and 1m above seabed). |
Fish Culture Subzones. |
|
c) Waste discharges shall not cause the level of dissolved
oxygen to be less than 4 mg L-1. |
Inland waters of the Zone |
|
C. pH |
|
|
a) The pH of the
water should be within the range of 6.5 - 8.5 units. In addition, waste discharges shall not
cause the natural pH range to be extended by more than 0.2 units. |
Marine waters excepting Bathing
Beach Subzones; Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and Mui Wo (F) Subzones. |
|
b) The pH of the
water should be within the range of 6.0 - 9.0 units. |
Mui Wo
(D) and other inland waters. |
|
c) The pH of the
water should be within the range of 6.0 - 9.0 units for 95% of samples. In addition, waste discharges shall not
cause the natural pH range to be extended by more than 0.5 units. |
Bathing Beach Subzones. |
|
D. TEMPERATURE |
|
|
Waste discharges shall not cause
the natural daily temperature range to change by more than 2.0 oC. |
Whole zone |
|
E. SALINITY |
|
|
Waste discharges shall not cause
the natural ambient salinity level to change by more than 10%. |
Whole zone |
|
F. SUSPENDED
SOLIDS |
|
|
a) Waste discharges shall
neither cause the natural ambient level to be raised by 30% nor give rise to
accumulation of suspended solids which may adversely affect aquatic
communities. |
Marine waters. |
|
b) Waste
discharges shall not cause the annual median of suspended solids to exceed 20
mg L-1. |
Mui Wo (A), Mui Wo
(B), Mui Wo (C), Mui Wo
(E) and Mui Wo (F) Subzones. |
|
c) Waste
discharges shall not cause the annual median of suspended solids to exceed 25
mg L-1. |
Mui Wo (D) Subzone
and other inland waters. |
|
G. AMMONIA |
|
|
The unionised ammonia nitrogen
level should not be more than 0.021 mg L-1, calculated as the annual
average (arithmetic mean). |
Whole zone |
|
H. NUTRIENTS |
|
|
a) Nutrients shall not be
present in quantities sufficient to cause excessive or nuisance growth of
algae or other aquatic plants. |
Marine Waters |
|
b) Without
limiting the generality of objective (a) above, the level of inorganic
nitrogen should not exceed 0.1 mg L-1, expressed as annual water
column average (arithmetic mean of at least 3 measurements at 1m below
surface, mid-depth and 1m above seabed). |
|
|
|
|
|
Waste discharges shall not cause
the 5-day biochemical oxygen demand to exceed 5 mg L-1. |
Inland waters of the Zone. |
|
J. CHEMICAL
OXYGEN DEMAND |
|
|
Waste discharges shall not cause
the 5-day chemical oxygen demand to exceed 30 mg L-1. |
Inland waters of the Zone. |
|
K. TOXINS |
|
|
a) Waste discharges shall not
cause the concentrations of dangerous substances in marine waters to attain such
levels as to produce significant toxic, 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. |
Whole zone |
|
b) Waste discharges of
dangerous substances shall not cause a risk to any beneficial uses of the
aquatic environment. |
Whole zone |
7.2.2
Technical Memorandum for Effluent
Discharges
All discharges during the construction
phase are required to comply with the Technical
Memorandum – Standards for Effluents Discharged into Drainage and Sewerage
Systems, Inland and Coastal Waters (TM)
issued under Section 21 of the WPCO. The TM
defines discharge limits to different types of receiving waters. Under the TM,
effluents discharged into the drainage and sewerage systems, inshore and
coastal waters of the WCZs are subject to pollutant
concentration standards for particular discharge volumes. Any new discharges within a WCZ are subject
to licence conditions and the TM acts
as a guideline for setting discharge standards for the licence. In accordance with TM, new effluent will not
be allowed to discharge in any typhoon shelter.
With regard to inland waters ([1]), the beneficial use of the inland waters
is the only factor governing the quality and quantity of the effluent that may
be discharged met. Under the TM, inland waters are classified into
four groups, which are presented in Table
7.2b.
Table 7.2b Different
Groups of Inland Waters Specified in the TM
|
Group of Inland Waters |
Beneficial Use |
|
Group A |
Abstraction for Portable Water Supply |
|
Group B |
Irrigation |
|
Group C |
Pond Fish Culture |
|
Group D |
General Amenity and Secondary Contact
Recreation |
For this Project only Group D waters prevail, as the Project encroaches
on the inland waters which are within the Study Area. The effluent discharge from the Project
should comply with Table 6 of
the TM.
Annexes 6 and 14 of the EIAO-TM provide general guidelines and criteria to be used in
assessing water quality issues.
The assessment of the potential impact of land based construction
activities on water quality has been undertaken in a qualitative manner. Consideration has been given to controlling
potentially harmful impacts from the site works and to the use of ‘best
practice’ measures to minimise the potential for discharges of pollutants to
nearby receiving waters.
7.4
Baseline
Conditions and Water Quality Sensitive Receivers
7.4.1
Baseline Conditions
The Project Site is located inland at southern Hei Ling Chau.
One existing road (the long access route) and a temporary access road (the
short access route), will be allowed accessing the Project Site (see details in
Section 3 – Project Description). The long access route is along the northern
edge of the island followed by a southward road down to the Project Site, while
the short access route starts at the new temporary unloading steel platform and
a steel bridge at south-west of the island going eastwards to the Project
Site.
The locations of the Project site, the two access routes and the
associated enabling work sites are shown in Figure 7.4a. For easy reference, bundles of works in close
proximity to each other are regarded as a “Zone”. There are five Zones (A to E) for this
Project and details of each are illustrated in Figure 7.4a.
During the construction phase, the primary potential source of water
quality impacts will be pollutants in site run-off. Pollutants, mainly suspended sediments, may
also enter receiving waters if any stormwater is not
adequately controlled on-site. These
potential impacts may be readily controlled by standard measures, as described
in Section 7.6. With the
implementation of these measures adverse impacts to water quality are not
expected to result from land based construction activities.
No EPD river water quality monitoring data are available for the
identified streams within the Study Area.
Site visits during the wet season revealed that the majority of the
streams had a low flow, particularly in the immediate vicinity of the works
areas. It is, therefore, expected that
little or no water would be present in the streams in the dry season.
EPD routinely carries out water quality monitoring at Hei Ling Chau
typhoon shelters (notated as ST3).
Referring to the most recently published data in 2004 ([2]), the water quality at ST3 was considered
to be fairly good, with the highest dissolved oxygen (DO) (depth-averaged of
7.2 mg L-1), low suspended solids (SS) (< 10.0 mg L-1)
and low E.Coli
(<20 coliform cfu 100mL-1)
among the others. The nutrients were
also in low level, including ammonia nitrogen and total inorganic nitrogen.
7.4.2
Water Sensitive Receivers
In order to evaluate the water quality impacts resulting from the
construction of Project, the proximity of Water Sensitive Receivers (WSRs) must be considered.
WSRs have been identified in accordance with Hong
Kong Planning Standards and Guidelines (HKPSG) as well as the EIAO-TM, which provide criteria for
identifying environmental factors influencing development planning. The identified WSRs
are illustrated in Figure
7.4a.
There is an enclosed reservoir to the north of the Project Site located
in the middle of the island. The
reservoir collects the water from the hillside on the western side, no Project
– related construction activities are proposed in the reservoir catchment.
In addition, there are three natural streams but none of them are in
close to the works areas. The lengths of
the three identifiable streams and their characteristics are shown in Table 7.4a.
Five locations at inshore waters in the vicinity of Hei Ling Chau have
been identified for the assessment.
There is a possibility of impacts at these locations due to site
run-off.
Table 7.4a Identified
Water Sensitive Receivers
|
Water
Sensitive Receivers |
Area (ha)/ Length (m) |
Shortest Distance
(m) from Works Area |
Characteristics |
|||||
|
Project Site |
Zone A |
Zone B |
Zone C |
Zone D |
Zone E |
|||
|
Streams |
|
|
|
|
|
|
|
|
|
Stream 1 (S1) |
55m |
259 |
1,429 |
1,161 |
1,259 |
732 |
170 |
Stream S1 is a drainage channel running through
abandoned wet agricultural land. The
lower course of stream S1 was cemented while the upper course was an
underground channel. The closest sites
to Stream S1 are the Project Site and Zone E but neither are
in the stream catchment area. Only limited water
flow was recorded in Stream S1 during the survey. |
|
Stream 2 (S2) |
81m |
911 |
1,009 |
777 |
786 |
80 |
723 |
Stream S2 was partially channelised in the lower
courses and running under the existing |
|
Stream 3 (S3) |
263m |
446 |
1,116 |
857 |
929 |
482 |
134 |
Stream S3 was partially channelised in the upper
and lower courses, which were connected to the reservoir located in the
middle of the |
|
Reservoir (R1) |
0.2 ha |
580 |
1,089 |
830 |
893 |
375 |
366 |
A reservoir is present in the middle of the |
|
Inshore Water
|
|
|
|
|
|
|
|
|
|
Inshore Water (W1) |
- |
420 |
2,063 |
1,813 |
1,920 |
1,339 |
598 |
W1 is located to the south-east of the island and
is potentially affected by run-off from the Project Site. |
|
Inshore Water (W2) |
- |
1,188 |
1,313 |
1,098 |
1,071 |
179 |
1,036 |
W2 is located to the north-east of the island and
is potentially influenced by run-off from Zone D. |
|
Inshore Water (W3) |
- |
1,652 |
45 |
143 |
63 |
938 |
1,250 |
W3 is located to the north-west of the island and
potentially influenced by run-off from Zones A, B and/or C. |
|
Inshore Water / Typhoon Shelter (W4) |
- |
473 |
1,143 |
902 |
1,000 |
875 |
27 |
W4 is inside the Hei Ling Chau typhoon shelter
located to the west of the island and receives natural surface run-offs from
the catchment on the western side of the island. |
|
Inshore Water / Typhoon Shelter (W5) |
- |
277 |
1,518 |
1,286 |
1,429 |
1,179 |
134 |
W5 is inside the Hei Ling Chau typhoon shelter located
to the south-west of the island and receives natural surface run-offs from
the catchment on the south-western side of the
island. |
7.5.1
Construction Runoff and Drainage
Construction activities that may result in direct or indirect water
quality impacts within and adjacent to the Study Area are summarised below
(refer to Section 3 – Project Description
for details). No marine works will be carried for this
Project.
·
Site Preparation Works at All Zones:
The works include road widening and associated slope excavation, rock
cut and filling works.
·
Site Preparation Works at the Project Site: The works include excavation,
filling and construction of a site office.
The equipment will be transported from the existing jetty at north-west
of Hei Ling Chau to the Project Site via the long access route.
·
Construction of Perimeter Drainage Channel: An intercepting open-type
U-drainage channel will be constructed for the entire perimeter of the Project
Site.
·
Construction of a Temporary Platform at Zone E: The works include a rock cut at
the bottom of the slope.
·
Construction of a
·
Transportation of the Wind Turbine Components: The blades, nacelle and steel
tower segments will be delivered to the temporary platform, lifted up to the
bridge and transported to the Project Site via the short access route.
·
Erection of the Wind Turbine: The steel tower, nacelle and
the blades will be erected in stages using mobile cranes.
·
Underground Cable Laying: The power cable which is
located to the west of the Project Site will be connected to the adjacent
overhead 11kV cable (located at approximately 50m from the Project Site).
Stormwater runoff is considered to be the only potential source
of impact to water quality during the site works. Runoff and drainage from construction sites
may contain considerable loads of suspended solids and contaminants. Potential sources of water pollution from
site runoff include:
·
Runoff
and erosion of exposed bare soil, slopes and earth, and stockpiles;
·
Release
of cement materials with rain wash;
·
Washwater from dust suppression sprays and vehicle wheel
washing facilities; and
·
Fuel,
oil, and lubricant from maintenance of construction vehicles and mechanical
equipment.
Local and coastal water pollution will be substantial if the
construction site runoff is allowed to drain into the stormwater
drains or natural drainage without mitigation.
A drainage system, as shown in Figure 7.5a, will be
constructed prior to site formation and other earthworks and will be comprised
two intercepting open-type drains along the entire perimeter of the Project
Site. Surface runoff generated within
the site will be collected by the proposed U-channel drain along the east side
of the site and discharged, via a catchpit with silt
trap and oil interceptor to the existing watercourse to the east of the
site. A U-channel drain along the north,
west and south sides of the site is proposed to maintain the existing flow of
surface runoff from the site-adjacent hills to the stream to the west of the
site, to maintain the existing drainage flow conditions and avoid these surface
flows from entering the site. They will
be of an adequate size and capacity to capture all surface runoff from the
Project Site for storms of up to 1 in 50-year return periods and convey
collected flows to a temporary silt and grease treatment facility (comprised a
silt trap and a petrol/oil interceptor) that will remove construction generated
silt, debris, oil and grease. The silt
and debris will be disposed together with general refuse to the HLC Refuse
Transfer Station. The oil and grease
will be collected and transported off-site by a licensed chemical waste
collector to a licensed treatment facility (ie the Chemical Waste Treatment
Centre at Tsing Yi) for treatment and disposal.
During construction, a wheel washing facility will also be provided at
the Project Site entrance. Flows from
the facility will be contained and conveyed to the temporary silt and grease
trap.
Treated stormwater and washwater
from the silt and grease trap will gravitate to the nearest watercourse. A drainage management plan will be devised at
the outset of the construction stage to ensure discharges from the Project Site
drainage system in compliance with the WPCO. Hence, the works of the Project Site is
unlikely to adversely affect the water quality of the respective WSR, ie,
Inshore Water W5 and W1.
For other sites of works, ie, Zones A to E, the earth/slope works are of
a small scale and very short duration (less than 1 month). In Zone E, the enabling works consist of a
temporary steel platform on spread foundations and a temporary steel bridge on
spread and mini-pile foundations as detailed on Figure 3.3f in the
report. These will be in place for less
than a year and removed on completion of the works. Minor trimming / extension of existing slope
works as indicated on Figure
3.3g are required to facilitate transportation. No polluted flows will arise as a result of
the mini-piling works or spread foundation works for the temporary structures
during construction. The deck surface
will only be used for occasional transportation.
During construction of the slopes at Zones A to E, there will not be any
construction wastewater generated by the sloping works under normal weather
conditions. On heavy rainy days, surface
run-off will be controlled by appropriate measure(s). Figures 7.5a to
7.5g illustrate the proposed drainage arrangements at each
zone during construction. Above and
across the top perimeter of the slopes will be modified to an intercepting
channel in the form of a half-round U-channel to order to prevent uphill stormwater runoff from flowing down across the exposed
slope surface. In addition, sandbags
will be placed in a line beside the existing drains to guide the slope surface
water to a temporary/permanent catch pit with a sand trap. Details of the intercepting channel and the
sandbag line are shown on Figure 7.5h. For the small scaled footing excavation (of
about 5m x 5m x 2m in size) at Zone E, it is proposed to put a line of sandbags
on slope above the footing excavation to avoid stormwater
runoff washing through the excavation area to the typhoon shelter (see Figure 7.5g). After the slopes have been constructed, the
slope runoff will connect to the existing access route network as is the case
with the existing slopes. Details will
be presented in the drainage management plan which will be devised at the early
construction stage.
Any wastewater will be discharged into a temporary silt and grease
trap. The treated water will be
discharged into the existing stormwater drains. It is thus not expected that the works will
cause any adverse impacts to the related WSRs, ie,
Inshore Water W1 to W5.
In accordance with the TM, new
effluent will not be allowed to discharge into the Hei Ling Chau typhoon
shelter (W4 and W5). There is no project
related effluent piped directly into the typhoon shelter and hence this will
comply with the TM.
As discussed in Section 7.4.2,
none of the works areas are within the catchments of the streams or the
reservoir and hence no unacceptable impacts on Streams S1 to S3 and Reservoir
R1 are expected.
In addition, with the proper implementation of the good construction
site practices and housekeeping, as discussed in Section 7.6, unacceptable water quality impacts due to construction
run-off and drainage are not expected.
7.5.2
General Construction Site Activities
On-site construction activates may cause water pollution due to the
follows:
·
Uncontrolled
discharge of debris and rubbish such as packaging, construction waste and
refuse etc; and
·
Spillages
of liquid stored on-site, such as oil, diesel and solvents etc.
The debris and rubbish would probably enter the open drainage channels
and cause blockage. The spillage of
liquid may also result in water quality impacts if they enter stormwater drains or open drainage channels.
However, the effects on water quality from the construction activities
are likely to be minimal, provided that site boundaries are well maintained and
good construction site practices are implemented to ensure that litter, fuel
and solvents are managed, stored and handled properly.
7.5.3
Sewage Effluent
The maximum number of on-site workers is estimated to
be 40 during the delivery and erection of the wind turbine, split between the
two sites (temporary bridge and Project Site).
In view of small number of worker on site, portable chemical toilets
will be provided for the site workers. A
licensed contractor will be responsible for appropriate disposal and
maintenance of these facilities.
Therefore, no adverse water quality impacts are anticipated.
The following mitigation measures should be implemented during the
construction of the wind turbine:
7.6.1
Construction Runoff and Drainage
Construction site runoff and drainage will be prevented or reduced in
accordance with the guidelines stipulated in the EPD Practice Note for
Professional Persons, Construction Site Drainage (ProPECC PN 1/94). The good
practices include:
·
Provision
of construction drainage will be implemented prior to commencement of the site
formation works and/or other earthworks at each working site.
·
Exposed
soil surfaces will be covered by a tarpaulin as soon as possible to reduce the
potential for soil erosion.
·
Open
stockpiles of construction materials on site will be covered with tarpaulin or
similar fabric during rainstorms.
·
Surface
run-off from the construction site will be directed into an existing stream
channel via adequately designed sand/silt removal facilities such as sand
traps, silt traps and sediment basins.
Channels, earth bunds or sand bag barriers will be provided on site to
properly direct stormwater to such silt removal
facilities.
·
Silt
removal facilities, channels and manholes will be maintained and the deposited
silt and grit will be removed regularly, at the onset of and after each
rainstorm to ensure that these facilities are functioning properly at all
times.
·
During
excavation in the wet season, temporarily exposed soil surfaces will be
covered, eg by tarpaulin, and temporary access roads
will be protected by crushed stone or gravel, as excavation proceeds. Intercepting channels will be provided (eg along the crest/edge of the excavation) to prevent storm
runoff from washing across exposed soil surfaces. Arrangements will always be in place to
ensure that adequate surface protection measures can be safely carried out well
before the arrival of a rainstorm.
·
Earthworks
final surfaces will be well compacted and the subsequent permanent work or
surface protection will be carried out as soon as practical after the final
surface are formed to prevent erosion caused by rainstorms. Appropriate intercepting channels will be
provided, where necessary. Rainwater
pumped out from trenches or foundation excavations will be discharged into
storm drains via silt removal facilities.
·
The
contractor(s) concerned will apply for and obtain all the necessary discharge
licences.
7.6.2
General Construction Activities
Debris and rubbish generated on-site will be collected, handled and
disposed of properly to avoid entering the nearby stormwater
drains and open drainage channels. All
fuel tanks and storage areas will be provided with locks and be sited on sealed
areas, within bunds of a capacity equal to 110% of the storage capacity of the
largest tank. Open stormwater
drains and culverts near the works area will be covered to block the entrance
of large items of debris and refuse.
7.6.3
Sewage from Workforce
Temporary sanitary facilities, such as portable chemical toilets, will
be employed. A licensed contractor would
be responsible for appropriate disposal and maintenance of these facilities.
General construction activities could lead to site runoff containing
sand/silt and associated contaminants that may enter the nearby
watercourses. With the full
implementation of the recommended mitigation measures for the works, no
residual impacts on water quality are expected.
7.8
Environmental
Monitoring and Audit Requirements
No water quality monitoring is required as no unacceptable water quality
impact is expected. However, it is
considered necessary to carry out regular site (ie at monthly intervals) audits
to check the environmental performance of the Project and carry out ad-hoc
visit to the impacted sites in response to any complaints or reported
non-compliance on water quality aspects in order to enable prompt actions to
rectify any malpractice which may give rise to water pollution problem.
Due to the absence of marine works, the small scale of the land-based
construction works and the short duration of construction period, water quality
impacts are negligible during the construction phase of the Project, provided
that good site practices and housekeeping.
No water quality monitoring will be necessary during the construction
phase. However, it is recommended that
monthly site audits be conducted to check the performance of the Project. It is not anticipated there will be any
residual impacts on water quality with full implementation of mitigation
measures. Furthermore, no future
activities associated with the Project, which will affect the water systems and
water sensitive receivers, are anticipated.
([1])
In accordance with Technical Memorandum – Standards for Effluents Discharged into Drainage
and Sewerage Systems, Inland and Coastal Waters, inland waters means all
coastal waters where the water depth is less than 6 m at mean low tide, or that
are within 200 m of the mean low water mark, whichever position is further from
the shore.