7.1 In connection with the development
of constructing an international theme park and associated infrastructures at
North Lantau, the former shipyard, Cheoy Lee Shipyard (CLS), at the inner part
of Penny’s Bay will be decommissioned.
Potential environmental impacts arising from the CLS decommissioning
were only broadly discussed under the Northshore Lantau Development Feasibility
Study (NLDFS) EIA (Schedule 3).
7.2 This section presents
the potential water quality impacts associated with the shipyard
decommissioning and associated decontamination works. Key concerns relate to the potential release of the contaminated
groundwater to the nearby marine waters, and the effluent discharges from land
based demolition/ construction and soil remediation activities.
7.3 As explained in the
precedent chapter, contaminated soils found within the CLS site will be
excavated and treated in on-site and off-site facilities. Land transportation
of contaminated soil to the off-site treatment facility would be proposed and
therefore no marine water quality impact in association with the marine
transportation is envisaged. The
Project is of land based and will not involve any dredging of sediment or
sediment transportation, no impacts associated with the sediment quality issue
are expected.
7.4 The impacts of filling
works have been addressed in the Theme Park EIA Report and will not be
addressed in this EIA Report.
Environmental Legislations, Standards and
Evaluation Criteria
7.5 The criteria for
evaluating water quality impacts in this EIA Study include:
·
Technical
Memorandum on Environmental Impact Assessment Process (Environmental Impact
Assessment Ordinance) (EIAO-TM);
·
Water
Pollution Control Ordinance (WPCO);
·
Hong
Kong Planning Standards and Guidelines (HKPSG);
·
Practice
Note for Professional Persons (ProPECC), Construction Site Drainage
(PN 1/94);
·
Technical
Memorandum on Standards for Effluents Discharged into Drainage and Sewerage
Systems, Inland and Coastal Waters (TM-ES); and
·
Heavy
Metals Standards as stipulated in UK Water Quality Standards for Coastal
Surface Water([1]).
Environmental Impact Assessment Ordinance (EIAO), Cap.
499, S.16
7.6 This Project comprises
two Designated Projects under Schedule 2 of the EIAO. The EIAO-TM was issued by the EPD under Section 16 of the
EIAO. It specified the assessment
method and criteria that were followed in this Study. Reference sections in the EIAO-TM provide the details of
assessment criteria and guidelines that are relevant to the water quality
assessment, including:
·
Annex 6 – Criteria for Evaluating
Water Pollution;
·
Annex 14 – Guidelines for Assessment
of Water Pollution.
Water Quality Objectives
7.7 The Water Pollution
Control Ordinance (Cap. 358) provides the major statutory framework for 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 (WCZs). Corresponding statements of Water Quality
Objectives (WQOs) are stipulated for different water regimes (marine waters,
inland waters, bathing beaches subzones, secondary contact recreation subzones
and fish culture subzones) in the WCZs based on their beneficial uses. The CLS site and To Kau Wan site are located
within the Southern and North Western WCZs, respectively. The corresponding WQOs are summarised in Tables 7.1 and 7.2.
Table 7.1 Summary of Water Quality Objectives for the Southern WCZ
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive Odour, Tints |
Not to be present |
Whole zone |
|
Visible foam,
oil scum, litter |
Not to be present |
Whole zone |
|
E. coli |
Not to exceed 610 per
1000mL, calculated as the geometric mean of all samples collected in one
calendar year |
Secondary contact
recreation subzones, fish culture subzones and bathing beach subzones |
|
Not to exceed 180 per
100mL, calculated as the geometric mean of all samples taken at least 3 times
in a calendar month at intervals of between 3 and 14 days from March to
October inclusive in one calendar year |
(L.N. 453 of 1991) |
|
|
Dissolved
Oxygen (DO) within 2 m of the seabed |
Not less than 2.0mg/L for
90% of samples |
Marine waters |
|
Depth-averaged
DO |
Not to fall below 4.0 mg/L
for 90% of samples caused by waste discharges |
Marine water excepting fish
culture subzones |
|
Not less than 5.0 mg/L for
90% of samples |
Fish culture subzones |
|
|
Dissolved
Oxygen |
Not less than 4.0 mg/L for
90% of samples |
Inland waters |
|
pH |
To be in the range of 6.5 –
8.5, change due to waste discharges not to exceed 0.2. |
Marine waters excepting
bathing beach subzones; Mui Wo (A), Mui Wo (B), Mui Wo (C), Mui Wo (E) and
Mui Wo (F) subzones. |
|
To be in the range of 6.0 –
9.0. |
Mui Wo (D) subzone and
other inland waters |
|
|
To be in the range of 6.0 –
9.0 for 95% of samples, change due to waste discharges not to exceed 0.5. |
Bathing beach subzones |
|
|
Salinity |
Change due to waste
discharges not to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to waste
discharge not to exceed 2°C |
Whole zone |
|
Suspended
solids |
Not to raise the ambient
level by 30% caused by waste discharges |
Marine waters |
|
Annual median not to exceed
20 mg/L due to waste discharges |
Mui Wo (A), Mui Wo (B), Mui
Wo (C), Mui Wo (E) and Mui Wo (F) subzones. |
|
|
Annual median not to exceed
25 mg/L due to waste discharges |
Mui Wo (D) subzone and
other inland waters |
|
|
Ammonia |
Annual mean not to exceed
0.021 mg/L as unionised form |
Whole zone |
|
Nutrients |
Not to cause excessive
growth of algae or other aquatic plants |
Marine waters |
|
Annual mean depth-averaged
inorganic nitrogen not to exceed 0.1 mg/L |
Marine waters |
|
|
BOD5 |
Not to exceed 5 mg/L due to
waste discharges |
Inland waters |
|
Chemical Oxygen
Demand |
Not to exceed 30 mg/L due
to waste discharges |
Inland waters |
|
Dangerous
substances |
Not to attain such levels
as to produce significant toxic effects in humans, fish or any other aquatic
organisms due to waste discharges |
Whole zone |
|
Not to put a risk to any
beneficial uses of the aquatic environment due to waste discharges |
Whole zone |
Table 7.2 Summary of Water Quality Objectives for the North Western WCZ
|
Parameters |
Objectives |
Sub-Zone |
|
Offensive
Odour, Tints |
Not to be present |
Whole zone |
|
Colour |
Not to exceed 30 Hazen
units, due to waste discharges |
Tuen Mun (A) and Tuen Mun
(B) subzones and water gathering ground subzones |
|
Not to exceed 50 Hazen
units, due to waste discharges |
Tuen Mun (C) subzone and
other inland waters |
|
|
Visible foam,
oil scum, litter |
Not to be present |
Whole zone |
|
E. coli |
Not to exceed 610 per
1000mL, calculated as the geometric mean of all samples collected in one
calendar year |
Secondary contact
recreation subzones |
|
To be less than 1 per
100mL, calculated as the running median of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days. |
Tuen Mun (A) and Tuen Mun
(B) subzones and water gathering ground subzones |
|
|
Not to exceed 1000 per
100mL, calculated as the running median of the most recent 5 consecutive
samples taken at intervals of between 7 and 21 days. |
Tuen Mun (C) subzone and
other inland waters |
|
|
Not to exceed 180 per
100mL, calculated as the geometric mean of all samples taken at least 3 times
in a calendar month at intervals of between 3 and 14 days from March to
October inclusive in one calendar year |
Bathing beach subzones |
|
|
Dissolved
Oxygen (DO) within 2 m of the seabed |
Not less than 2.0mg/L for
90% of samples |
Marine waters |
|
Depth-averaged
DO |
Not to fall below 4.0 mg/L
for 90% of samples caused by waste discharges |
Marine water |
|
Dissolved
Oxygen |
Not less than 4.0 mg/L for
90% of samples |
Tuen Mun (A) and Tuen Mun
(B) and Tuen Mun (C) subzones, water gathering ground subzones and other
inland waters |
|
pH |
To be in the range of 6.5 –
8.5, change due to waste discharges not to exceed 0.2. |
Marine waters excepting
bathing beach subzones |
|
Not to exceed the range of
6.5 – 8.5 due to waste discharges. |
Tuen Mun (A) and Tuen Mun
(B) and Tuen Mun (C) subzones, 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% of samples, change due to waste discharges not to exceed 0.5. |
Bathing beach subzones |
|
|
Salinity |
Change due to waste
discharges not to exceed 10% of ambient |
Whole zone |
|
Temperature |
Change due to waste
discharge not to exceed 2°C |
Whole zone |
|
Suspended
solids |
Not to raise the ambient
level by 30% caused by waste discharges |
Marine waters |
|
Annual median not to exceed
20 mg/L due to waste discharges |
Tuen Mun (A) and Tuen Mun
(B) and Tuen Mun (C) subzones, water gathering ground subzones |
|
|
Annual median not to exceed
25 mg/L due to waste discharges |
Other inland waters |
|
|
Ammonia |
Annual mean not to exceed
0.021 mg/L as unionised form |
Whole zone |
|
Nutrients |
Not to cause excessive
growth of algae or other aquatic plants |
Marine waters |
|
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 |
|
|
BOD5 |
Not to exceed 3 mg/L due to
waste discharges |
Tuen Mun (A) and Tuen Mun
(B) and Tuen Mun (C) subzones, water gathering ground subzones |
|
Not to exceed 5 mg/L due to
waste discharges |
Inland waters |
|
|
Chemical Oxygen
Demand |
Not to exceed 15 mg/L due
to waste discharges |
Tuen Mun (A) and Tuen Mun
(B) and Tuen Mun (C) subzones, water gathering ground subzones |
|
Not to exceed 30 mg/L due
to waste discharges |
Inland waters |
|
|
Toxin |
Not to cause the toxins in
water to attain such levels as to produce significant toxic, carcinogenic,
mutagenic or teratogenic effects in
humans, fish or any other aquatic organisms due to waste discharges |
Whole zone |
|
Not to cause a risk to any
beneficial uses of the aquatic environment due to waste discharges |
Whole zone |
|
|
Phenol |
Not to present in such
quantities as to produce a specific odour, nor to exceed 0.05mg/L as C6H5OH |
Bathing beach subzones |
|
Turbidity |
Not to reduce light
transmission substantially from the normal level due to waste discharges |
Bathing beach subzones |
Hong Kong Planning Standards and Guidelines (HKPSG)
7.8 The Hong Kong Planning Standards and Guidelines (HKPSG),
Chapter 9 (Environment), provides additional
information on regulatory guidelines against water pollution for sensitive uses
such as aquaculture and fisheries zones, bathing waters and other contact
recreational waters.
Practice Note
7.9 A practice note for
professional persons was issued by the EPD to provide guidelines for handling
and disposal of construction site discharges.
The ProPECC PN 1/94 “Construction
Site Drainage” provides good practice guidelines for dealing with ten 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 constructions, acid
cleaning, etching and pickling wastewater, and wastewater from site
facilities. Practices given in the
ProPECC PN 1/94 should be followed as far as possible during construction to
minimise the water quality impact due to construction site drainage.
Technical Memorandum
7.10
Besides setting the WQOs, the WPCO
controls effluent discharging into the WCZ through a licensing system. The Technical
Memorandum on Standards for Effluents Discharged into Drainage and Sewerage
Systems, Inland and Coastal Waters (TM-ES) was issued under Section 21
of the WPCO that 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. Wastewater and sewage from the shipyard
decommissioning and decontamination activities should comply with the standards
for effluents discharged into the foul sewers, inshore waters or marine waters
of the Southern, North Western and Western Buffer WCZs, as shown in Table 10b
of the TM-ES.
Heavy Metal Standards
7.11
Since there is no existing legislative
standard or guideline for individual heavy metal contents in marine waters, the
UK Water Quality Standards for Coastal
Surface Water is adopted as assessment criteria. The standards of the relevant heavy metals (such as arsenic,
cadmium, chromium, copper, lead, nickel and zinc) are listed in the following
table.
Table 7.3 UK Water Quality
Standards
|
Heavy Metals |
Water Quality Standards (mg/L) |
|
Arsenic |
65 |
|
Cadmium |
2.5 |
|
Chromium |
15 |
|
Copper |
5 |
|
Lead |
25 |
|
Nickel |
30 |
|
Zinc |
40 |
Description of the Environment
Existing Marine Water Quality
7.12
There are two routine EPD water
quality monitoring stations located in the vicinity of the CLS site (Southern
WCZ) and the To Kau Wan site (North Western WCZ). In addition, water quality data of three routine monitoring
stations as included in the monitoring programme for Penny’s Bay Reclamation
Phase 1 are also made reference. The locations of the reference routine monitoring
stations are shown in Figure 7.1. A summary of water quality data for each of
the stations is presented in Table 7.4.
Table 7.4 Routine Water
Quality Monitoring Data in the Vicinity of the Project Area
|
WQ Parameter |
CLS Site |
To Kau Wan Site |
|||
|
SM10 |
G2 |
G4 |
NM1 |
G6 |
|
|
Temperature (°C) |
23.4 (16.3 - 27.2) |
23.6 (17.4 – 29.1) |
23.6 (17.2 – 29.9) |
23.6 (18.2 - 26.8) |
23.6 (17.6 – 30.0) |
|
Salinity (ppt) |
30.2 (26.9 - 33.4) |
31.0 (13.1 – 37.3) |
30.8 (18.6 – 37.3) |
29.3 (21.9 - 32.5) |
30.4 (6.0 – 38.3) |
|
Dissolved Oxygen (mg L-1) |
4.0 (3.2 - 7.2) |
6.4 (3.5 - 9.2) |
6.7 (3.5 – 12.6) |
3.5 (3.2 - 8.4) |
6.5 (3.6 – 10.5) |
|
Dissolved Oxygen Bottom
(mg L-1) |
4.3 (3.9 - 7.2) |
6.0 (2.8 – 9.3) |
6.3 (3.7 – 11.1) |
2.9 (2.7 - 8.3) |
5.9 (2.9 – 10.0) |
|
5-Day Biochemical Oxygen
Demand (mg L-1) |
0.9 (0.1 - 1.8) |
-- |
-- |
0.9 (0.2 - 2.0) |
-- |
|
Suspended Solids (mg L-1) |
6.9 (4.1 - 9.9) |
13.8 (3.7 – 47.8) |
21.4 (2.7 – 115.9) |
4.0 (1.1 - 6.7) |
14.0 (3.2 – 51.0) |
|
Total Inorganic Nitrogen
(mg L-1) |
0.27 (0.14 - 0.43) |
-- |
-- |
0.43 (0.24 - 0.66) |
-- |
|
Unionised Ammonia (mg L-1) |
0.003 (0.001 - 0.009) |
-- |
-- |
0.005 (0.002 - 0.007) |
-- |
|
E.coli (cfu 100mL-1) |
9 (2 - 300) |
-- |
-- |
110 (6 - 570) |
-- |
Notes:
1. Data from EPD (1999) Marine Water
Quality in Hong Kong in 1998 and Penny’s Bay Reclamation Phase 1 EM&A data
from September 2000 to August 2001.
2. Data presented are depth
averaged, except as specified.
3. Data presented are annual
arithmetic means except for E. coli
which are geometric means.
4. Data enclosed in brackets
indicate the ranges.
5. Boldface type indicates
non-compliance with the WQOs.
7.13
The data indicated that there were
non-compliances with the WQO for depth averaged dissolved oxygen at stations
SM10 and NM1, despite the compliance with the bottom dissolved oxygen WQO. This revealed a deterioration from the data
collected in 1997, which showed compliance with both depth averaged and bottom
dissolved oxygen WQOs. However it might
not be the case that the DO levels measured in G2, G4 & G6 show the
compliance with WQO. Therefore, it is
premature to conclude that the dissolved oxygen concentrations in the study
area are deteriorating based on the 1998 data alone.
7.14
The total inorganic nitrogen WQO is
exceeded at Station SM10. The
exceedance of the total inorganic nitrogen WQO at Station SM10 has been
recorded for the last ten years. It is
worth noting that the WQO for total inorganic nitrogen is not exceeded at
Station WM4, even though the average concentration is higher than that at
Station SM10. This is because of the different
WQO for total inorganic nitrogen in the Western Buffer WCZ, which is higher
compared with that of the Southern WCZ.
7.15
The WQO for E. coli at Station SM10, which is in a Secondary Contact Recreation
Subzone, was achieved and also satisfied the WQO for bathing beaches. Station NM1 is somewhat influenced by sewage
effluent discharges, as shown by higher E.
coli concentrations. This is
possibly because this station is in one of the main flow paths between the
waters of Victoria Harbour and will therefore receive dilute discharges of
sewage from this areas.
7.16
The data for temperature, salinity and
dissolved oxygen show a wide variation, which indicates seasonal changes. These are most pronounced at Station NM1,
which is the station most influenced by the discharges from the Pearl River
estuary.
Groundwater Quality at Cheoy Lee Shipyard
7.17
As part of this EIA study, contaminant
testing of groundwater samples collected within the CLS site was undertaken. The groundwater samples were collected
between July and October 2001, which is a wet season in Hong Kong. Most of the contaminated soils were found to
be at top 2m layer and the water table in wet season is generally high (1-3m
below grade). It means the groundwater system will have more contacts with the
contaminated soil and the contaminant concentration in the groundwater can be
expected to be higher in the wet season.
Therefore, the testing results can represent a worst-case scenario.
7.18
A risk assessment has been carried out
to assess whether the groundwater concentrations pose any risk to the site
future users. The details of the
assessment are presented in the Land Contamination Section of the EIA report. It was found that the observed groundwater
concentrations are below risk-based standards. The following discussion focuses on the potential impact of groundwater
migration/ discharge to the marine environment.
7.19
From the testing results, it is noted
that heavy metals and total petroleum hydrocarbons (TPH) are the dominant
chemicals identified in the groundwater samples. Table 7.5 shows the comparison of the
identified heavy metals in the groundwater samples with the UK surface water
quality standards. Figures 7.2a to 7.2c give locations of groundwater samples
having exceedances of metal levels.
Table 7.5 Comparison of Identified Heavy Metals in the
Groundwater Samples with the UK Water Quality Standards
|
|
Concentration in groundwater
(mg/L) |
No. of groundwater |
UK Surface Water |
||
|
Heavy Metals |
Range |
Average |
Median |
samples exceeded UK |
Quality Standards |
|
|
|
|
|
standard / Total No. |
(mg/L) |
|
Arsenic |
<10
– 38 |
11 |
10 |
0
/ 63 |
65 |
|
Cadmium |
<0.2 - 17.8 |
1.0 |
0.2 |
4 / 63 |
2.5 |
|
Chromium |
<0.1
– 67 |
2.0 |
0.1 |
1
/ 63 |
15 |
|
Copper |
<1
– 1187 |
27 |
1 |
17
/ 63 |
5 |
|
Lead |
<1
- 2254 |
49 |
1 |
2
/ 63 |
25 |
|
Nickel |
<1
- 7200 |
120 |
2 |
4
/ 63 |
30 |
|
Zinc |
<10
- 1200 |
105 |
31 |
25/
63 |
40 |
Note
: Boldface type indicates non-compliance with the UK Surface WQ Standard.*
7.20
Although high levels of heavy metal
were found in the groundwater samples, they are regarded as isolated events
given the much lower median levels. Therefore
for the purpose of this assessment, the average levels have been used for
comparison. The average copper, lead,
nickel and zinc levels in groundwater is found to exceed the corresponding UK Surface
Water Quality Standards by 5.4, 2.0, 4.0 and 2.6 times respectively. However,
such direct comparisons between groundwater concentration and surface water quality
standards are used for screening purpose only.
This is because as groundwater slowly seeps into the marine environment
via drainage channels, it is subject to dilution processes in the channel where
the metal concentration will be reduced by 88 times (refer Section 7.56 for the
calculation of the dilution factor) before entering to the marine water.
7.21
Maximum TPH concentration of 0.4 mg/L
was determined in the groundwater samples.
Risk-based approach has been adopted to evaluate the groundwater
contamination to confirm the acceptable risk level for the future site users. It
is noted that there are no statutory marine water quality standards for TPH,
BTEX and other toxic parameters. Their insignificant impacts on the marine
water quality can be inferred by the
fact that their concentrations in marine water would be well below the analytical
detection limits (25mg/L for
TPH and 6mg/L for BTEX) once the dilution effect (dilution
by 88 times) is taken into account. (Refer
Section 7.56 for the calculation of the dilution factor of 88).
7.22
Apart from the detectable level of heavy
metals and TPH in the groundwater samples, the pH of the groundwater samples is
in a range of 6.1-8.1 pH units, which comply with the pH standard of 6-10 pH
units as stipulated in the TM-ES.
7.23
The shipyard decommissioning and
decontamination activities at CLS site and To Kau Wan site may potentially
affect water quality in Penny’s Bay and the neighbouring waters. The Theme Park
EIA report has assessed several water sensitive receivers of the potential
impact, which include the broad designations of gazetted and non-gazetted
bathing beaches, water intakes, fish culture zones, sites of ecological
interest and recreational areas. Figure 7.3 gives locations of existing
sensitive receivers. In addition, an
artificial lake at the Water Recreation Centre at Penny’s Bay (Figure 7.4), which is located immediate
adjacent to the CLS site, will be built after the CLS decommissioning, the
potential water quality impact on the operation of the planned Water Recreation
Centre is a concern in this study. For
the purpose of this assessment, the following water sensitive receivers have
been identified.
·
Gazetted Bathing Beaches: Gemini, Hoi
Mei Wan, Casam, Lido, Ting Kau, Approach, Tung Wan (Ma Wan), Silvermine Bay;
·
Non-Gazetted Beaches: Dragon and
Discovery Bay;
·
Fish Culture Zones: Ma Wan (South and North); and
·
Recreational Uses: Discovery centre at Sze Pak Wan and the artificial
lake of the future Water Recreation Centre at Penny’s Bay.
7.24
It is known that the temporary
drainage channel immediately adjacent to the southern boundary (seawall) of the
CLS will have been filled up at the time of CLS decommissioning. Potential impact will be on future drainage
channel to the north of the CLS site.
During the decommissioning work, there will be no direct discharge from
site drainage or groundwater drawn from CLS into the marine water. In concluding insignificant impact to the nearby
marine water via the drainage channel, water quality in the drainage channel has
to be compared and complied with the relevant marine water quality standard.
7.25
The objective of the water quality
impact assessment is to identify and evaluate the potential source of water
pollution associated with the decommissioning and decontamination of the
shipyard. Criteria and guidelines for
evaluating and assessing water pollution as stated in Annexes 6 and 14 of the
EIA-TM have been adopted for the present study in order to address all
assessment objectives specified in the section 3.5.3 of EIA Study Brief.
Identification of Water Quality Impacts
Building Demolition
7.26
Surface runoff and site discharges are
the only sources that pose potential water quality impact during the building
demolition.
7.27
Precipitation that falls on unpaved
lands and areas with the topsoil exposed during the demolition will wash away soil
particles. Such surface runoff and stormwater
overflows with high levels of suspended solids if directly discharged into water
bodies or via the drainage channel would lead to a water quality impact. Wastewater resulting from wheel washing of
site vehicles at site entrances would also pose a potential water quality
impact if not adequately controlled.
7.28
Effluent discharge from temporary site
facilities shall be controlled to prevent direct discharge to the neighbouring
marine waters and storm drains. Such
wastewater may include sewage effluent from toilets.
Slope Improvement
7.29
There will be improvement works on the
slope behind CLS. Earthworks from slope cutting and soil nailing may impact the
adjacent stream course by introducing debris and suspended solids. Surface runoff primarily laden with sediments
may also enter into the stream.
Soil Remediation
7.30
Upon recommendations in the chapter of
the “Land Contamination Assessment”, contaminated soil at CLS will be excavated
and treated either on-site or in an off-site facility at TKW dependent on the
contaminant of concern.
At Cheoy Lee Site
7.31
The remediation works involved in CLS
will be the soil excavation work and treatment of metal contaminated soil by
solidification. Potential water quality impacts will be expected from the
following sources.
Excavation and Dewatering
7.32
Excavations of contaminated soil will
be required for the decontamination works.
Where such excavation takes place below the water table in the
contaminated areas within the shipyard, dewatering may be required in order to
facilitate excavation. Groundwater pumped
out if discharged directly into local drains or drainage channels may impose adverse
water quality impact to the marine water.
7.33
The subsequent construction works for
the foundations of the Chok Ko Wan Link Road (CKWLR), Road P2 and the Penny’s
Bay Rail Link (PBRL) may however require dewatering. However, these are beyond the scope of this EIA which focus on
the decommissioning work.
Groundwater Seepage
7.34
Potential water quality impact may
arise from groundwater seeping directly into the marine water, indirectly via drainage
channels adjacent to CLS site into the marine water and into the artificial
lake of the future water recreation centre.
Operation of the Solidification Facility
7.35
Cement solidification is a remediation
method for the treatment of metal-contaminated soil. During the cement solidification process, cement, water and other
additive(s) (such as fly ash, lime, soluble silicates, and clays) are added to
the contaminated soils to form solid block.
Mixing of contaminated soils and cement/water/other additive(s) would
introduce potential leaching of contaminants, if water addition is not well
controlled. There will be temporary
stockpiles of metal contaminated soils with quantity up to 24,000m3 at
CLS site pending the construction of solidification facility. The temporary stockpiling that lasts for approximately
seven months is unavoidable because excavation works will advance before the
commencement of the solidification facility for making room for the facility
and gauging with the Project programme. Runoff from the stockpile may impact
the nearby water course if not controlled.
Decontamination Water and Wastewater from Wheel Washing
7.36
After excavating and handling the
dioxin-contaminated soil at CLS, excavators/ backhoes and dump trucks are to be
decontaminated by steam cleaning. Such decontamination water that may carry
dioxin poses water quality impact if discharged without prior treatment. Wastewater from the wheel washing bay at the
site entrance is also potentially contaminated and may pose the similar water
quality impact.
At To Kau Wan Site
7.37
Potential water quality impacts are
associated with the construction and operation of the remediation plant at To
Kau Wan.
Construction of Soil Remediation Plants
7.38
Possible sources of water quality
impact during construction of the remediation plant include;
·
Surface runoff of elevated levels of
suspended solids as a result of precipitation and wheel washing water,
·
Wastewater from temporary site
facilities, such as toilets and site canteens, and
·
Uncontained spillage water from plant
servicing facilities being contaminated with oil and other petroleum products.
Operation of Soil Remediation Plants
7.39
Decontamination processes, viz. biopiling,
thermal desorption and cement solidification will be carried out in the To Kau
Wan decontamination site.
7.40
Biopiling is a bioremediation method
for the restoration of the contaminated soils with organic compounds. By using microorganisms to degrade the
contaminants in soil, biopiles transform hazardous/toxic materials into
harmless elements such as water, carbon dioxide, and other innocuous products. On
forming the biopile, trucks holding the TPH contaminated soil from CLS would
directly unload at the biopile area, therefore there will be no temporary
stockpiles nor associated water quality impacts. Leachate resulting from rain
percolation in case that the biopiles are not fully covered and from biodegradation
product would be a concern to the underlying soil, groundwater system and water
bodies if not properly controlled.
7.41
Thermal desorption process employs
high temperature to volatilise or vaporise, but not to destroy, dioxin from the
contaminated soils. On commencing the Project, dioxin-contaminated soils at CLS
will be transported to and temporarily stored at TKW in a purpose-built
concrete bin pending the construction and commissioning of the thermal
desorption facility. Leachates and runoff from the storage bin if not properly
drained and controlled may result in a potential water quality impact to the
underlying soil, groundwater system and adjacent water bodies. Soil loading and
unloading activities for the thermal desorber and the transport operations
within site may pose a source of spilled soil, which in contact with rainwater may
lead to contaminated runoff. This
contaminated runoff may impact the water bodies adjacent to TKW if not properly
drained and treated. Thermal desorption process would create condensate, which
will be concentrated and contained for disposal. The condensate drums will be
stored in accordance with the Waste Disposal
(Chemical Waste)(General) Regulation with proper spill containment
measures. Should there be any
accidental spillage, the soil of the affected area will be excavated and treated
on-site as CLS soil. Water quality
impacts arising from the operation of the thermal desorption is therefore not
expected.
7.42
Cement solidification will be the last
treatment procedure for mixed contaminated soils after treated by biopiling or
thermal desorption. During the cement
solidification process, cement, water and other additive(s) (such as fly ash,
lime, soluble silicates, and clays) are added to the contaminated soils to form
solid block. Mixing of contaminated
soils and cement/water/other additive(s) would introduce potential leaching of
contaminants, if water addition is not well controlled.
Decontamination Water and Wastewater from Wheel Washing
7.43
Dump trucks after unloading are to be
decontaminated and wheel washed before exiting TKW site. Such decontamination
water that may carry dioxin poses water quality impact if discharged without
prior treatment. Wastewater from the
wheel washing bay at the site entrance is also potentially contaminated and may
pose the similar water quality impact.
To Kau Wan Decommissioning
7.44
Upon completion of the soil
remediation, the soil treatment facility at TKW will be decommissioned and
removed off the site. As of a
demolition site, surface runoff will be the only source that poses potential
water quality impact during the TKW decommissioning.
Evaluation of Water Quality Impacts
Building Demolition
7.45
The potential impacts arising from surface
runoff and site discharges can be readily controlled by appropriate on-site
measures. The ProPECC PN 1/94 “Construction Site Drainage” recommends good site
practices for dealing with various discharges from a construction site. With the
implementation of recommended site practices, no adverse impacts on the surface
waters are expected. Given that all
buildings have been provided with temporary roofing, generation of contaminated
surface runoff as a result of precipitation is not possible.
Slope Improvement
7.46
The potential sources of water quality
impacts arising from the slope works can be readily mitigated by implementation
of appropriate on-site measures as recommended in the ProPECC PN 1/94 “Construction Site Drainage”, no adverse water
quality impact is expected on the identified water quality sensitive receivers.
Soil Remediation
At Cheoy Lee Site
Excavation and Dewatering
7.47
During excavation, all exposed pits
shall be whenever possible backfilled immediately or covered. Direct soil loading
from the excavator onto the dump truck shall be the priority practice. Where it is unavoidable to have transient soil
piles pending collection by dump trucks, the transient piles shall be bottom-lined,
bunded and covered during rain events with impervious membrane. As such, it is unlikely that the surface
runoff is contaminated. Therefore, the surface runoff after sedimentation can
be safely discharged into the local drainage.
7.48
As contaminants with levels higher
than the screening levels for risk assessment are found in the groundwater,
direct discharge of groundwater collected from the dewatering process during
excavation of contaminated soil shall not be practised. It is recommended that the groundwater be
recharged back into the ground in the vicinity of the extraction point as per
the scheme proposed in the section “Land Contamination Assessment”. The
recharge scheme has taken into account of avoiding the migration of
contaminants caused by the locally high groundwater level at the recharge location.
Furthermore the recharge locations
shall be distant from the culvert or the shore. Therefore adverse water quality
impacts are not expected.
Groundwater Seepage
7.49
There are essentially three main
concerns with regard to the seepage of CLS groundwater, i.e. seepage of
groundwater to the artificial lake of the future water recreation centre;
direct seepage of groundwater to the marine water and seepage of groundwater to
the marine water indirectly via the nearby surface channels.
Impact on the Artificial Lake
7.50
As mentioned in the NLDFS EIA report,
potential migration of any residual contamination or impact to the proposed
artificial lake at the Water Recreation Centre is a concern. However, no adverse water quality impact is
expected on the artificial lake of the planned Water Recreation Centre because:
·
the artificial lake (planned water
surface at about +7.35 mPD) will have a hydraulic head above that of CLS site
(average water table level at about +2.50mPD measured from the SI boreholes),
migration of the contaminated groundwater from the CLS site (lower level) to
the artificial lake (higher level) is therefore not expected;
·
the artificial lake will be
constructed offshore and away from the CLS site, by first dredging the sediment
from the relevant part of Penny’s Bay, followed by placement of a impermeable
HDPE liner. This liner, whilst designed
to hold the freshwater in, will also prevent against subsurface contaminant
infiltration provided that the liner integrity is maintained; and
·
under the present EIA study,
appropriate remediation actions are recommended in the Land Contamination
Assessment section and shall be implemented to clean up the contamination to
acceptable levels, hence removing a source of contaminating water.
Direct Impact to the Marine Water
7.51
The contaminated site in CLS is an
inland site and will be approximately 1.5km from the nearest future seawall at
the Penny’s Bay reclamation. This makes
it highly unlikely for any groundwater to directly leach to the marine water.
Indirectly impact to the Marine Water via
Surface Channels
7.52
The groundwater from the CLS site seeping
via the nearby surface channels into the marine water is a concern in this
study. The temporary drainage channel located immediately adjacent to the existing
southern seawall of CLS site will no longer be a receiver because it will have
been filled at the time of CLS decommissioning.
7.53
No seepage of CLS groundwater into the
future drainage channel to the north of the site is expected. It is because after the decommissioning, CLS
site will be filled to a level at about 7 to 8 m above the existing ground
level before constructing the future drainage channel. This increase of ground
level would effectively isolate the CLS groundwater (at about 3m below the
existing ground level) from the bottom of the future drainage channel (at 4m
above the existing ground level given 3m depth of the channel).
7.54
In an unexpected case that the CLS groundwater
can reach the future drainage channel, the very slow seepage rate of groundwater
and subsequent dilution of the groundwater in the channel confer no adverse
impact to the marine water.
7.55
According to the Darcy’s empirical
law([2]), the seepage velocity (v) of the groundwater within the site can
be expressed as follows:
v
= k i / n,
where k is the coefficient of permeability, i is hydraulic gradient and n
is the porosity of soil.
7.56
With reference to the groundwater
sampling data collected in wet season, the maximum hydraulic gradient was
determined to be about 10-2 and the averaged porosity of soil within
the site was about 40%. Silty and
clayey sand were found to be dominant within the CLS site, and therefore the
coefficient of permeability was assumed to be about 10-5 m/s. Based on the above equation, the calculated
seepage velocity of the groundwater within the site was 2.5x10-7 m/s, which is extremely slow to transport the
contaminants into the marine waters.
7.57
Assuming that the seepage velocity of
the groundwater from the CLS site to the drainage channel is same as that
within the CLS site, and that the total contact area of the future drainage
channel with respect of the groundwater seepage is 3,180 m2 (i.e. ~1,060m
long by ~3m deep), the calculated seepage rate of the contaminated groundwater
is 7.95x10-4m3/s.
As the flow rate of the waters in the drainage channel is assumed 0.07 m3/s,
there is a dilution effect of about 88 on the contaminants in the water column
in the drainage channel.
7.58
As discussed in Section 7.20, the average
heavy metal concentration in the groundwater exceeds the UK Water Quality
Standards by no more than 5.4 times. Taking
into account of the dilution effect, the heavy metal concentrations in the
waters of the drainage channel as a result of groundwater seepage would comply
with the UK Water Quality Standards. Considering
that the contribution of heavy metal level from seeped groundwater is at least 22
times (for nickel) less than the UK Water Quality Standards , which are
insignificant, associated adverse impacts to the coastal sensitive receivers and
the marine biota including Chinese White Dolphin and fish are not envisaged.
7.59
In summary, the water quality of the waters
in the drainage channel complies with the water quality standards and thus no
adverse water quality impact associated with the discharge of the waters from
the drainage channel to the marine waters is anticipated. The water quality of the identified water
sensitive receivers in the vicinity of the CLS site would also comply with the
relevant water quality guidelines.
Operation of the Solidification
Facility
7.60
It would be recommended that temporary
stockpiles of metal contaminated soil be lined with impervious sheet, bunded and
covered by impermeable sheeting pending receipt by the solidification
facility. With the implementation of these
mitigation measures, contaminated runoff and leachate would be minimised in
quantity. During the solidification process, excessive addition of water is avoided. This would eventually eliminate the
possibility of leachate generation from the facility. Further, taking into account of the dust reduction measures, the
solidification facility will be housed in a shed that prevents contaminated
runoff. All contaminated runoff and
leachate shall be treated together with the decontamination water and wheel
wash water in the centralised wastewater treatment unit before being
discharged. Taking the above considerations, no adverse water quality impact is
expected during the solidification process.
Decontamination Water and
Wastewater from Wheel Washing
7.61
It would be the required site practice
not to directly discharge the decontamination water and the potentially
contaminated wheel washing water into the surface channel or nearby water
bodies. All decontamination water and
wheel washing water would be regarded contaminated and diverged to a centralised
wastewater treatment unit where flocculation/ sediment and activated carbon
filtering processes would be deployed. Metal
contaminants would be flocculated out with the aid of precipitating agents and
TPH would be removed by activated carbons. Dioxin at large is hydrophobic and will
remain adhering to soil particles that would be settled out during
sedimentation while the last bit of aqueous phase dioxin would be removed in
the polishing activated carbon filter. Any contaminants and pollutants are in
the effluent shall be treated before discharged into local drainage channel. Therefore significant water quality impact is
not expected.
At To Kau Wan Site
Construction of Soil Remediation
Plants
7.62
The potential sources of water quality
impacts arising from the construction of remediation plant at TKW can be
readily mitigated by implementation of appropriate on-site measures as
recommended in the ProPECC PN 1/94
“Construction Site Drainage”, no adverse water quality impact is expected
on the identified water quality sensitive receivers.
Operation of Soil Remediation
Plants
Biopiling
7.63
As recommended in the chapter of “Land
Contamination Assessment”, concrete perimeter bund and impermeable floor
sheeting shall be constructed respectively around and underneath the biopile. With the floor sheeting and bund in place, any
biopile leachate would be contained and migration of leachate out of the
biopiling area is not likely. In operation,
low impermeability sheeting shall be employed to cover the biopile after
formation and during rains. This avoids
contaminated runoff as a result of the rainwater washing over the biopile and leaching
of the biopile by the rainwater. It is
also proposed that a centralised wastewater treatment unit employing
flocculation/ sedimentation and activated carbon filtering processes be
constructed to treat all biopile leachate before being discharged into local
sewers or drainage channels. With the implementation of mitigation measures, adverse
water quality impacts on the nearby water quality sensitive receivers are not expected.
Thermal
Desorption
7.64
Pending the construction and
commissioning of the thermal desorption plant, dioxin-contaminated soils from
CLS will be temporarily stored in a purpose-built concrete bin. The storage bin
shall be sheltered and bottom-lined. No rainwater washing over the soil is
expected. A sump shall be in place to
diverge and collect any leachate from the soil stack and subsequently the
leachate will be treated in the centralised wastewater treatment unit before
discharging. To prevent contaminated runoff from migrating out of the thermal
desorption plant, the boundary of the plant shall be bunded and runoff collected
for treatment at the centralised wastewater treatment unit. It is proposed that
the runoff from the first 30 minutes of a rainstorm be regarded as contaminated
and collected (rainwater in the first 30 minutes would have sufficiently washed
away the soil remains and any runoff after first 30 minutes will be considered
as uncontaminated). Given maximum hourly rainfall to the record of Hong Kong
Observatory of 109.9mm and plant area of 3,280m2, the maximum volume
of contaminated runoff collected during the first 30 minutes of a rainstorm will
be 180m3. Aqueous product resulting from the thermal desorption is
to be recharged into the process to quench and rehumidify the thermally-treated
soil. Non-aqueous condensate
(containing dioxin and TPH) being the end product of the thermal desorption, shall
be properly stored in sealable leak-proof containers subject to transporting to
CWTC for treatment. With the implementation of the mitigation measure and
process practice, no adverse water quality impact arising from the soil storage
and thermal desorption plant is envisaged.
Solidification
7.65
Any metal contaminant left over in soil
after biopiling and thermal desorption treatment will be dealt with by
solidification. During the process, excessive addition of water is
avoided. This would eventually
eliminate the possibility of leachate generation from the facility. Further, taking also the dust reduction
consideration, the solidification facility will be housed in a shed that
prevents contaminated runoff. As such,
no adverse water quality impact is expected during the solidification process.
Decontamination Water and
Wastewater from Wheel Washing
7.66
It would be site practice not to
directly discharge the decontamination water and the potentially contaminated
wheel washing water into the surface channel or nearby water bodies. All decontamination water and wheel washing
water shall be diverged to a centralised wastewater treatment unit where the
contaminants and pollutants in the effluent shall be treated before discharged
into local drainage channel. Therefore
significant water quality impact is not expected.
To Kau Wan
Decommissioning
7.67
The potential sources of water quality
impacts arising from the TKW decommissioning can be readily mitigated by
implementation of appropriate on-site measures as recommended in the ProPECC PN 1/94 “Construction Site Drainage”,
no adverse water quality impact is expected on the identified water quality
sensitive receivers.
Summary of Potential Water Quality Impacts
7.68
In summary, the likely water quality
impacts arising from the different stages of the Project is tabulated below.
Table 7.6 Potential
Water Quality Impacts Arising from the Project
|
Project Stage |
Source of water quality impacts |
Pollutants/ Contaminants of Concern |
|
Building Demolition at CLS |
1.
Surface runoff & stormwater overflow |
1.
Sand and Silt |
|
Slope Improvement |
1.
Surface runoff & stormwater overflow |
1.
Sand and Silt |
|
Soil Remediation at CLS |
1.
Runoff during building demolition phase 2.
Groundwater from dewatering during excavation 3.
Groundwater seepage 4.
Decontamination water and wheel washing water |
1.
Sand and Silt 2.
Silt, metals, TPH and other contaminants found in CLS soil 3.
metals, TPH and other contaminants found in CLS soil 4.
Sand/ silt, TPH and dioxin found in CLS soil |
|
Soil Remediation at TKW |
1.
Surface runoff & stormwater during construction phase 2.
Runoff from thermal desorption plant, leachate from biopiles/ storage
bins and decontamination/ wheel washing water during operation phase |
1.
Sand and silt 2.
Metals, TPH and dioxin found in CLS soil |
|
TKW decommissioning |
1.
Surface runoff & stormwater overflow |
1.
Sand and Silt |
Mitigation of Environmental Impacts
Building Demolition
7.69
Mitigation measures are required to
prevent and minimise the adverse water quality impacts from the surface runoff
and site discharge during the CLS decommissioning. The details of the recommended mitigation measures are summarised
in the following sections.
Surface Runoff
7.70
Catchpits and perimeter channels shall
be constructed in advance of site formation works and earthworks. Surface runoff from the construction sites shall
be directed into storm drains via adequately designed wastewater treatment facilities
such as sand traps, silt traps and sediment basins. Channels, earth berms or sand bag barriers shall be provided on
site to properly direct stormwater to such facilities.
7.71
Silt removal facilities, channels and
manholes shall be maintained and the deposited silt and grit shall be removed regularly,
at the onset of and after each rainstorm to ensure that these facilities are
functioning properly at all times.
7.72
Open stockpiles of demolition materials
on site shall be avoided or where unavoidable covered with tarpaulin or similar
fabric during rainstorms. Measures shall
be taken to prevent the washing away of construction materials, soil, silt or
debris into any drainage system.
7.73
Manholes (including any newly
constructed ones) shall always be adequately covered and temporarily sealed so
as to prevent silt, construction materials or debris from getting into the
drainage system.
Wheel Washing Water
7.74
All vehicles and plant shall be
cleaned before they leave the construction site to ensure that no earth, mud or
debris is deposited by them on roads. A
wheel washing bay shall be provided at every site exit and wash-water shall
have sand and silt settled out or removed before being discharged into storm
drains. In any case, discharge of wheel wash water shall be minimised and
recycled where possible. The section of
construction road between the wheel washing bay and the public road shall be
paved with backfill to reduce vehicle tracking of soil and to prevent surface
runoff from entering public road drains.
Wastewater from Site Facilities
7.75
Should the use of chemical toilets be
necessary then these shall be provided by a licensed contractor, who will be
responsible for appropriate disposal and maintenance of these facilities.
Storage and Handling of Oil, Other Petroleum Products and Chemicals
7.76
All fuel tanks and chemical storage
areas shall be provided with locks and be sited on sealed areas. The storage areas shall be surrounded by
bunds with a capacity equal to 110% of the storage capacity of the largest tank
to prevent spilled oil, fuel and chemicals from reaching the receiving waters. The Contractors shall prepare guidelines and
procedures for immediate clean-up actions following any spillages of oil, fuel
or chemicals.
Wastewater Treatment Facilities
7.77
Sufficient wastewater treatment facilities
shall be provided to treat the surface runoff and wheel wash water to the
discharge standards as stipulated in the Technical
Memorandum on Standards for Effluents Discharged into Drainage and Sewerage
Systems, Inland and Coastal Waters.
In addition, discharge licence under the Water Pollution Control Ordinance shall be obtained for any
discharge of treated runoff and wheel wash water to the environment.
Slope Improvement
7.78
Mitigation measures as recommended in
sections 7.70 to 7.77 shall be implemented.
Soil Remediation
At Cheoy Lee Site
Excavation and Dewatering
7.79
During excavation, all exposed pits
shall be whenever possible backfilled immediately or covered and bunded.
Further, all excavated soils shall be loaded into dump truck directly but where
it is unavoidable to transiently pile up soils next to the excavation pit, the
transient pile shall be bottom-lined and covered with impervious membrane
during rain event in order to avoid generation of the contaminated runoff.
7.80
Final surfaces after excavation shall be
well compacted and the subsequent permanent work or surface protection shall be
carried out as soon as practical after the final surfaces are formed to prevent
erosion caused by rainstorms.
Appropriate intercepting channels and partial shelters shall be provided
where necessary to prevent rainwater from collecting within the trenches or
footing excavations. The contractor
shall develop contingency plans for capture and control of any runoff prior to
backfill during runoff-producing rainfall events.
7.81
Groundwater drawn from the dewatering process
during excavation and rainwater collected within the trenches or excavation
pits shall be pumped out and recharged back the ground in the vicinity. The recharge scheme as recommended in the
chapter of “Land Contamination Assessment” shall be followed.
Groundwater Seepage
7.82
Given that the water quality impact
arising from the seepage of contaminated groundwater into the adjacent drainage
channel is insignificant, no mitigation measure is considered necessary in this
respect.
Operation of the
Solidification Facility
7.83
The designated stockpiling area before
incepting contaminated soils shall be concrete-paved or lined with impervious
floor membrane and shall have its perimeter constructed of a concrete bund in
order to avoid any contaminated leachate from migrating out of the area. Temporary stockpiles upon formation shall be
immediately covered with impermeable cover to stop precipitation from washing
the contaminated soil thus generating contaminated runoff. The contractor shall
formulate contingency plans for the runoff collection and control.
7.84
The solidification facility shall be
sheltered and area of soil unloading/ loading shall be provided with shed to
avoid contaminated runoff. Excessive addition
of water during the process shall be avoided during the process.
7.85
As an additional measure, Any pit used
for solidification area shall be shallower than the water table to minimize the
leaching of the contaminated soils. And
a impermeable membrane/sheet shall be placed at the bottom of any
solidification pit during the solidification process.
Decontamination Water and Wastewater from Wheel
Washing
7.86
During soil excavation, dump trucks or
excavators shall be decontaminated before they leave the site to ensure that no
contaminated earth, mud or debris is deposited by them on roads. A wheel washing bay shall be provided at
every site exit that equipped with an adequately sized centralised wastewater
treatment unit. The wastewater treatment unit shall deploy flocculation/
sedimentation and activated carbon filtering by which processes sands/ silts with
dioxin cohered are to be settled out and other soil contaminants in wheel
washes and decontamination water removed.
The polluting parameters in effluent shall be with compliance of TM
discharge standards and dioxin in effluent shall be cleared of to an
undetectable range before the effluent being discharged into the storm
drains. The installation and operation
of the wastewater treatment unit shall be licensed and subject to the effluent
monitoring as required under the Waste
Disposal Ordinance. In any case, discharge of wheel wash water shall be
minimised and recycled where possible.
The section of construction road between the wheel washing bay and the
public road should be paved with backfill to reduce vehicle tracking of soil
and to prevent surface runoff from entering public road drains.
At To Kau Wan
Construction of Soil Remediation Plants
7.87
Mitigation measures as recommended in
sections 7.70 to 7.77 shall be implemented.
Operation of Soil Remediation Plants
7.88
Mitigation measures are required at
the To Kau Wan site to minimize the potential water quality impacts during the
decontamination process. The
dioxin-contaminated soils and the liquid end products shall be properly stored . Non-dioxin
contaminated soils shall be stored in earth bunds and covered by impermeable
membranes to prevent wind erosion and exposure to rain. An impermeable base and drainage system shall
also be required to collect the contaminated leachate.
Biopiling
7.89
Impermeable liner shall be placed at
the bottom of the biopiles and leachate collection sump shall be constructed
along the perimeter of the biopiles to prevent leachate from contaminating the
underlying soil/groundwater. Concrete bund shall be constructed along the
perimeter of biopiles to prevent the runoff coming out from the contaminated
soil. All leachate collected shall be
treated in a centralised wastewater treatment unit. The wastewater treatment
unit shall deploy flocculation/ sedimentation and activated carbon filtering by
which processes sands/ silts and other soil contaminants in wheel washes and
decontamination water removed. The
polluting parameters in effluent shall be with compliance of TM discharge
standards before the effluent being discharged into the storm drains. The installation and operation of the wastewater
treatment unit shall be licensed and subject to the effluent monitoring as
required under the Waste Disposal Ordinance.
7.90
Biopiles after formation and during
rain shall be covered by anchored low permeability geotextiles to prevent
contaminated runoff. It is proposed
that the exposed biopile section at any time shall not be more than 5m in
length.
Thermal Desorption
7.91
The storage bin for the
dioxin-contaminated soils shall be sheltered and bottom lined to prevent
generation of contaminated runoff. The
storage bin shall be equipped with leachate sump to collect any leachate from
the soil stack and subsequently the leachate will be treated in the centralised
wastewater treatment unit before discharging. Concrete bund and adequately sized sump shall be constructed at
the perimeter of thermal desorption plant to collect any runoff within the
plant to cater occasionally very heavy downpour during the remediation period. The
runoff from the desorption plant during the first 30 minutes of a rainstorm shall
be considered to be contaminated. The
contaminated runoff shall be collected and treated in the centralised wastewater
treatment unit. The wastewater treatment work shall contain sedimentation, filters,
coagulation/ flocculation unit and activated carbon adsorption. The treatment
plant will be subject to the effluent monitoring requirement under the Waste Disposal Ordinance. All non-aqueous condensates from the thermal
desorption processes shall be stored in sealable, leak-proof containers for
off-site disposal. The aqueous phase of
the condensate shall be used to quench the thermally-treated soil and
rehumidify it to reach a specified moisture content. Excessive aqueous product shall be treated in the wastewater
treatment unit before discharged. No direct discharge of excessive aqueous
product into the local drains or drainage channel shall be allowed.
Solidification
7.92
The solidification facility shall be
sheltered and area of soil unloading/ loading shall be provided with shed to
avoid contaminated runoff. Excessive
addition of water during the process shall be avoided during the process.
7.93
As an additional measure, any pit used
for solidification area shall be shallower than the water table to minimize the
leaching of the contaminated soils. And
an impermeable membrane/sheet shall be placed at the bottom of any
solidification pit during the solidification process.
To Kau Wan Decommissioning
7.94
Mitigation measures as recommended in
sections 7.70 to 7.77 shall be implemented.
Cumulative Environmental Impacts
7.95
During the demolition and excavation
at CLS that will take around 6-7 months, the period is comparatively short and also
no major impacts were found in the assessment, cumulative water quality impact added
on the Penny’s Bay area is considered insignificant.
7.96
Yam O reclamation will be on-going
during the remediation work at TKW. Since all possible effluents, viz the leachate and contaminated
runoff from the TKW site, shall be treated and their quality be monitored
before discharged, no significant cumulative water quality impact imposed by
the setting up and operation of TKW soil remediation plants is expected.
Residual Environmental Impacts
7.97
No adverse residual environmental
impacts were predicted to occur during the demolition and decommissioning of
the CLS and decontamination works conducted at the To Kau Wan site provided that the recommended mitigation
measures, including those detailed in the remediation action plan, are
implemented. The mitigation measures
were specified as a series of ‘best practice’ methods of working and
appropriate treatment/remediation methods for the contaminated soil found
within the shipyard site.
Demolition and Excavation at Cheoy Lee Shipyard
7.98
Potential adverse water quality
impacts from the shipyard demolition and excavation would primarily be from the
contaminated groundwater (including seepage and dewatering), potentially
contaminated surface runoff and from and sewage effluent generated by the
construction workforce. However, no
unacceptable water quality impact on the nearby sensitive receivers was
identified.
7.99
A number of mitigation measures during
demolition and excavation were specified to reduce the potential adverse
impacts to acceptable levels and no residual impact was anticipated. No water quality monitoring of any
potentially contaminated surface runoff to be discharged during demolition and
excavation at CLS is recommended. Furthermore,
site audit is recommended to ensure that the recommended mitigation/remediation
measures and ‘best practice’ site procedures are being implemented.
Slope Works behind Cheoy Lee Shipyard
7.100
As part of the slope work, slope
cutting and soil nailing may impact the water quality of the nearby watercourses.
Same for the demolition and excavation work at CLS, site mitigation measures
were specified to reduce the potential adverse impacts to acceptable levels and
no residual impact was anticipated. No water quality monitoring was recommended
but site audit is recommended to ensure that the recommended mitigation/remediation
measures and ‘best practice’ site procedures are being implemented.
Soil Remediation at To Kau Wan
7.101
Biopile, solidification and thermal
desorption are the processes conducted at the To Kau Wan decontamination site. Potential water quality impact would be
arising from the leachate from contaminating the underlying soil/groundwater,
surface runoff and the leakage of contaminated waters to surroundings. Significant
impact is not envisaged where the leachate shall be treated before discharged.
7.102
As a number of mitigation/remediation
measures and ‘best practice’ site procedures are being undertaken, water
quality impacts associated with the decontamination works is expected to be
insignificant and no residual impact is anticipated.
Potential Impact on the Planned Water Recreation Centre
7.103
As the artificial lake at the Water
Recreation Centre is located at an elevation higher than the CLS site, and
there is an impermeable liner at the bottom of the lake and most of the
contaminants in the CLS site have been clean up, migration of the contaminated
groundwater from the CLS site to the artificial lake is not expected. Therefore, no adverse water quality impact
or residual impact is anticipated.
