This Section of the EIA Report describes the
impacts on water quality associated with the construction and operation of a
600 – 850 kW wind turbine system supplying renewable energy to Lamma
Island. The purpose of the
assessment is to evaluate the acceptability of predicted impacts to water
quality from the construction and operation of the wind turbine with references
to the relevant environmental legislation and standards. Although the Study Area for the Project
covers a small portion of marine waters in the Southern WCZ, no discharge to
marine waters as a result of construction and operation of the turbine will
occur. Consequently, marine water
quality impacts are not expected to occur and hence are not discussed further.
The following relevant legislation and associated guidance are applicable to the evaluation of water quality impacts associated with the construction and operation of the Project.
· Water Pollution Control Ordinance (WPCO);
· Technical Memorandum – Standards for Effluents Discharged into Drainage and Sewerage Systems, Inland and Coastal Waters; and
· Environmental Impact Assessment Ordinance (Cap. 499. S.16), Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), Annexes 6 and 14.
Apart from the above 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.
The WPCO is the legislation for the control of water pollution and water quality in Hong Kong. Under the WPCO, Hong Kong waters are divided into 10 Water Control Zones (WCZs). Each WCZ has a designated set of statutory Water Quality Objectives (WQOs). The WQOs set limits for different parameters that should be achieved in order to maintain the water quality within the WCZs. The Project is wholly located within the Southern WCZ. The WQOs for the Southern WCZ, which are presented in Table 8.1, are applicable as evaluation criteria for assessing compliance of any effects from the construction and operation of the Project.
Table 8.1 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 per litre 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 1 metre below surface,
mid-depth and 1 metre above seabed).
In addition, the concentration of dissolved oxygen should not be less
than 2 mg per litre within 2 m 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 per litre 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 1 metre below surface, mid-depth and 1
metre above seabed). |
Fish Culture Subzones. |
|
c) Waste discharges shall not cause
the level of dissolved oxygen to be less than 4 mg per litre. |
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 per litre. |
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 per litre. |
Mui Wo (D)
Subzone and other inland waters. |
|
G. AMMONIA |
|
|
The unionised ammonia
nitrogen level should not be more than 0.021 mg per litre, 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 per litre, expressed as annual water column average (arithmetic mean of at
least 3 measurements at 1 metre below surface, mid-depth and 1 metre above
seabed). |
|
|
I. 5-DAY
BIOCHEMICAL OXYGEN DEMAND |
|
|
Waste discharges shall not
cause the 5-day biochemical oxygen demand to exceed 5 mg per litre. |
Inland waters of the Zone. |
|
J. CHEMICAL OXYGEN
DEMAND |
|
|
Waste discharges shall not
cause the 5-day chemical oxygen demand to exceed 30 mg per litre. |
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 |
All discharges during both the construction and the operational phases of the Project 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.
Annexes 6 and 14 of the EIAO-TM provide general guidelines and criteria to be used in assessing water quality issues.
In order to evaluate the water quality impacts resulting from the construction and operation of a 600-850 kW wind turbine on Lamma Island, the water sensitive receivers (WSR) have been identified in accordance with the Hong Kong Planning Standards and Guidelines, which provides criteria for identifying environmental factors influencing the proposed development.
The main inland water bodies within the Study Area (Figure 8.1) include:
· Service Reservoir (located north of Tai Ling Tsuen);
· A modified stream (Stream S1 passing through the northern part of Long Tsai Tsuen);
· A semi-natural stream (Stream S2 running from the service reservoir through Long Tsai Tsuen and terminated at Tai Wan To);
· A natural stream (Stream S3 locating north of the service reservoir); and
· A semi-natural stream (Stream S4 situated south of Lo Tik Wan).
During these construction activities the primary sources of water quality impacts will be from pollutants in site run-off. Pollutants, mainly suspended sediments, may also enter receiving waters if any pumped groundwater is not adequately controlled on-site.
The potential sources of impacts to water quality may be readily controlled by appropriate on-site measures to minimise potential impacts as described in Section 8.6. With the implementation of such measures adverse impacts to water quality are not expected to result from land based construction activities.
No EPD river water quality 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 low flow, particularly in the immediate vicinity of the works area. It is, therefore, expected that little or no water would be present in the dry season.
The turbine location is located reasonably far from the existing water bodies listed out in Section 8.3.1.
Table 8.2 Distance of the Wind Turbine from the Existing Water Bodies
|
Existing
Water Bodies |
Distance
from the Wind Turbine |
|
Service Reservoir |
170 m |
|
Modified stream S1 |
500 m |
|
Semi-natural stream S2 |
230 m |
|
Natural stream S3 |
270 m |
|
Semi-natural stream S4 |
500 m |
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.
The turbine and its operation will not create any waste waster emissions as it will be unmanned and hence there will be no adverse operational impacts to water quality.
Construction activities that may result in water quality impact directly or indirectly within and adjacent to the Study Area during the construction and operation of the proposed Project is described below.
The land-based construction activities that will be undertaken for the Project are listed as follows:
·
Site excavation by cutting and filling for
construction of a site platform (affected area approximately 3,100m2);
·
Construction of retaining wall around site
perimeter;
·
Site backfilling;
·
Erection of wind turbine by one heavy duty mobile
crane, one light duty mobile crane, and transformer pillars (hub height
approximately 45 m and rotor blade diameter of approximately 52 m, overall
height of the wind turbine approximately 71 m); and,
· Underground cable laying for connecting to the adjacent 275 kV Cable Route (approximately 50 m in length).
Stormwater runoff is considered to be the sole cause of impact to water quality through washing off sand/ suspended solids during excavation, backfilling and underground cable laying into any of the identified existing water bodies.
The Contractor shall implement the following on-site measures to minimise potential water quality impacts associated with land based construction.
· Surface run-off from the construction site should be directed into 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 should be provided on site to properly direct stormwater to such silt removal facilities.
· Silt removal facilities, channels and manholes should be maintained and the deposited silt and grit should 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 should be covered, eg by tarpaulin, and temporary access roads should be protected by crushed stone or gravel, as excavation proceeds. Intercepting channels should be provided (eg 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.
· Earthworks final surfaces should be well compacted and the subsequent permanent work or surface protection should be carried out as soon as practical after the final surface are formed to prevent erosion caused by rainstorms. Appropriate intercepting channels should be provided where necessary. Rainwater pumped out from trenches or foundation excavations should be discharged into storm drains via silt removal facilities.
· Open stockpiles of construction materials (eg aggregates and sand) on site should be covered with tarpaulin similar fabric during rainstorms. Measures should be taken to prevent the washing away of construction materials, soil, silt or debris into any drainage system.
· The use of chemical toilets will be necessary and these should be provided by a licensed contractor, who will be responsible for appropriate disposal and maintenance of these facilities.
No residual water quality impacts were predicted to occur due to construction of the wind turbine provided the above described mitigation measures are implemented.
No residual water quality impacts were predicted to occur in the Project.
No environmental monitoring and audit programme has been designed and specified as no adverse water quality impacts have been identified from either the construction or operation phases of the Project.
This Section has dealt with the assessment of the impacts on water quality of the construction and operation of the wind turbine on Lamma Island.
During the construction phase it was determined that minor impacts to water quality could arise directly from land-based construction works. These works relate to excavation and construction of the foundation for the wind turbine, and underground cable laying. No direct construction runoff is expected. However, stormwater runoff from the construction site could occur during rainstorms. Mitigation measures were described, which would provide a series of good site management options to minimise the impact of stormwater runoff.
No operational impacts to water quality are expected to occur. No mitigation measures are therefore necessary. Based on the impact assessment, no EM&A measures are required. The mitigation measures specified as well as good site management skills are considered sufficient to prevent impacts occurring.