12.1
The
Assessment Area for this project included Northwestern Water Control Zone
(WCZ), Western Buffer WCZ,
l
Establish the importance of the
fisheries habitats that may be affected by construction and operation of the
Project.
l
Identify fisheries sensitive
receivers.
l
Assess the scale of possible impacts
on fisheries resources arising from the proposed works.
l
Identify any necessary mitigation
measures and evaluate residual impacts.
l
Assess the need for a fisheries
monitoring and audit programme.
12.2
As
the upgrade of existing Preliminary Treatment Works (PTWs) at North Point, Wan
Chai East, Central,
12.3
Impacts
on fisheries from disinfection processes (E.
coli levels, Dissolved oxygen depletion) and the potentially harmful
products associated with disinfection such as Total Residual Chlorine and
Chlorination By-products have been assessed in Agreement No. CE
7/2005 (EP) “Harbour Area Treatment Scheme Environmental Impact Assessment
Study for the Provision of Disinfection Facilities at
12.4
The
ADF EIA concluded that no adverse fisheries impact associated with disinfection
processes and subsequent discharge of disinfected effluent would be anticipated
during operation of the Project because:
· Disinfection of sewage would improve the water quality in Western Buffer Water Control Zone and western Victoria Harbour Water Control Zone by reducing E. coli levels.
· The levels of total residual chlorine (TRC) and chlorination by-products (CBP) in the disinfected sewage effluent would only cause highly localised changes in water quality at the Stonecutters Island Sewage Treatment Works (SCISTW) outfall and thus there would be no unacceptable ecological risk on fisheries resources in relation to toxicity of TRC and CBP.
· As no adverse impacts on fisheries resources were predicted, no fisheries specific mitigation measures would be required.
12.5
Fisheries impacts were evaluated according to criteria
set out in the Technical Memorandum on Environmental Impact Assessment Process
(EIAO TM). EIAO TM Annex 17 sets out the methodology for assessment of
fisheries impacts and Annex 9 provides the evaluation criteria.
12.6
Other legislations which apply
to fisheries and are relevant to fisheries impact assessment include:
l The Fisheries Protection Ordinance (Cap. 171), which protects fisheries resources and regulates fishing practices
l The Marine Fish Culture Ordinance (Cap. 353), which regulates and protects marine fish culture and related activities
l Water Pollution Ordinance (Cap. 358) – which sets limits to water quality parameters in various Water Control Zones.
12.7 Baseline information on fisheries resources in the Assessment Area was elucidated via a desktop review of current literature. This review included relevant fisheries baseline data presented in Agricultural, Fisheries and Conservation Department’s (AFCD)’s Port Survey 2006 and incorporated the most recent information available in other reports and publications. The information available was extensive and no data gap was identified. Therefore field surveys were not deemed necessary. The impact assessment followed the criteria and guidelines for evaluating and assessing fisheries impacts as stated in Annexes 9 and 17 of the EIAO TM.
12.8
The Assessment Criteria used
for the evaluation of fisheries impact included the following:
·
Nature
of the impact: whether the impacts would be permanent,
irreversible or long term.
·
Size
of affected area: this included fisheries habitats,
fishing grounds, or mariculture zones and took into consideration whether the
area constituted a high proportion of the total area of fishing grounds or
aquaculture sites.
·
Loss
of fisheries resources/ production: included
capture fisheries and aquaculture production in relation to overall resources
or production in
·
Destruction
and disturbance of nursery and spawning grounds:
disturbance or destruction of nursery and spawning grounds of commercially
important species.
·
Impact
on fishing activity: numbers of fishermen or fishing
vessels with a high dependence on the affected area
·
Impact
on aquaculture activity: numbers of aquaculturists or
mariculture (fisheries culture) zones that would be affected.
12.9
12.10 Over the past 60 years, there has been a decline in reported landings of large-sized and high value food species in commercial catches, such as groupers, wrasses and mackerels and an increase in catches of lower value species, e.g. Rockfish (Sebastiscus marmoratus), Rabbitfish (Siganus fuscescens) and the Chocolate Hind (Cephalopholis boenak) (ERM, 1998).
12.11
In
12.12
According to AFCD (2006),
12.13
Some recent data on the local
capture fisheries industry against the background of heavy exploitation and
over-fishing of inshore fisheries resources are shown in Table 12.1. Since 1999, Mainland authorities have implemented a
fishing moratorium for two months during midsummer in
Table
12.1 Industry Figures for Capture
Fisheries
|
Parameter |
2006 |
2005 |
2004 |
2003 |
2002 |
2001 |
2000 |
1999 |
|
Fishing fleet
size (No. of
vessels) |
3,940 |
4,150 |
4,300 |
4,600 |
4,470 |
5,100 |
5,250 |
5,170 |
|
Local
fishers engaged in capture fisheries |
8,500 |
9,170 |
9,700 |
10,100 |
10,860 |
11,560 |
11,900 |
12,900 |
|
Mainland
deckhands employed |
No data |
No data |
No data |
3,908 |
4,100 |
4,560 |
5,200 |
6,300 |
|
Production (tonnes) |
155,000 |
162,000 |
167,500 |
157,400 |
169,790 |
174,000 |
157,010 |
127,780 |
|
Value of
production (HK$ million) |
1,600 |
1,600 |
1,600 |
1,500 |
1,600 |
1,700 |
1,600 |
1,500 |
Note: no data = data were unavailable at time of
reporting
Source: AFCD
Annual Reports, 1999 - 2006
12.14 Culture fisheries activities included 26 Fish Culture Zones (FCZs) located in various sheltered embayments across the HKSAR which occupy about 209 ha of sea area. Typically, fish farms were relatively small scale, family-run operations consisting of one or two rafts with an average size of about 270 m2. In the AFCD Annual Report (2005), 1,080 licensed operators were reported and annual production by the marine fish culture industry was estimated to be about 1,488 tonnes of fish valued at HK$89 million. Culture fisheries activities catered for about 7.9% of local demand for live marine fish (AFCD, 2006).
Capture
Fisheries
12.15
With regard to the capture fisheries operations and
resources, the Assessment Area comprised the following WCZs as designated under
the Water Pollution Control Ordinance:
l
Eastern Buffer WCZ
l
l
l
Junk Bay WCZ
l
Western Buffer WCZ
l
North Western WCZ
12.16
The latest AFCD Port Survey
undertaken in 2006 (AFCD, 2006) indicated that the highest fishing yields were
obtained in eastern waters (e.g.
12.17
The fishable areas of Victoria Harbour,
away from shipping lanes, produced
moderate yields from small vessels, less than 15 m in length (AFCD, 2006). The
fishing grounds of
12.18 The capture fisheries yields of the top 10 families in the area surrounding the SCI outfall are tabulated below.
Table 12.2 Production of the Top 10 Fish Families in the Area Surrounding SCI Outfall
|
Fish
Family |
Fish
Production – adult weight (kg/ha) |
|
Siganidae |
<
5 |
|
Clupeidae |
<
5 |
|
Sciaenidae |
<
5 |
|
Carangidae |
<
5 |
|
Squid
(All Families) |
<
5 |
|
Shrimp
(All Families) |
<
5 |
|
Engraulidae |
0 |
|
Crab
(All Families) |
<
5 ( |
|
Sparidae |
<
5 |
|
Mugilidae |
<
5 |
Source: AFCD, 2006
12.19
The
Western Buffer WCZ around Stonecutters Island (SCI) and the north-western part
of
12.20
Surveys
undertaken on the western side of
12.21
With reference to AFCD (2006),
the most common catches in the Assessment Area included:
·
Low (<5-20 kg/ha) catches of
sardine
· Croaker catch generally ranged from 10-40 kg/ha, but was high south west Lamma and Kau Yi Chau.
·
Generally low-moderate catches
of Rabbit fish at Tsing Yi
·
Scad catch generally ranged
from low to moderate but was high (40->60 kg/ha) in southern waters around
·
The catches of shrimp ranged
from low to moderate
· The catches of anchovy were generally low in the Assessment Area, but moderate at Tung Lung Chau and east Po Toi.
·
Crab catches were generally low
in the assessment area except Chung Chau, south Lamma, south Po Toi,
· Seabream catches were low throughout the assessment area except at Kai Tak and south west Junk Bay where they were moderate..
·
Mullet catches were low except
at
·
Squid catches generally ranged
from low-moderate but were high in Ap Lei Chau, east Po Toi and Waglan south.
12.22
The Study of “Fisheries
Resources and Fishing Operations in Hong Kong Waters” (ERM, 1998), stated that for areas which were
considered important spawning grounds at certain times of the year for
commercial fish and crustacean species, increased protection from
over-exploitation in order to safeguard future stocks was recommended.
Important spawning grounds identified by the ERM (1998) study included
12.23 ERM (1998) also identified northern and southern Lantau waters as fisheries spawning grounds for high value commercial species. The key fish and crustacean species recorded in the south Lantau spawning ground were Leiognathus brevirostris (ponyfish), Johnius belengeri (croaker), Nibea diacanthus (croaker) and Metapenaeus joyneri (prawn). The main commercial fish species reported in the north Lantau spawning area included Leiognathus brevirostris (ponyfish), Lateolabrax japonicus (sea bass/ perch) and Clupanodon punctatus (gizzard shad).
12.24
The
majority of commercial species recorded in
12.25
Caranx kalla (shrimp scad)
was found to spawn in the early summer (around June) whilst Leiognathus
brevirostris (ponyfish)
and croakers were found to be reproductive from May to December. The spawning
period of most of the crustacean species, including Metapenaeus
joyneri was found to be from April to November
(ERM, 1998
12.26
ERM (1998) identified important nursery grounds
in south Lantau for a number of commercial juvenile fish
and crustacean species including Oratosquilla
anomala, Siganus
oramin and Collichthys
lucida (ERM, 1998
12.27
Important
nursery grounds were also identified from the main areas of fry collection for
the mariculture industry. However fry collection in recent years has been much
reduced in scale and the latest interview studies (AFCD,
2006) reported that fry collection has become very limited throughout
Aquaculture Production
12.28
AFCD
(2006b) reported 26 Fish Culture Zones, or FCZs, in
12.29
In
the past, grow out operations were common practice where fish fry of
commercially valuable species were caught from the wild, then reared in sea
cages until the fish attained a marketable size. Consequently, there used to be
intensive seasonal collection of wild fry from local waters for mariculture and
export to the Japanese and
12.30
Since
most fry were imported, the species cultured in
12.31
Another
practice that has become popular in
12.32
Water
quality within Marine FCZs is regulated under the Water Pollution Control
Ordinance (WPCO) and its supporting regulations and statements. Within FCZs,
the dissolved oxygen level should not be less than 5 mg/l for 90% of the sampling
occasions during the year; values should be calculated as 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/l within 2 metres of the seabed for 90% of the
sampling occasions during the year, and the annual geometric mean of E. coli
should not exceed 610 counts/100 ml.
12.33 The sewage conveyance system connecting the PTWs to SCISTW will be constructed by deep tunneling below the sea bed and therefore there would be no adverse impacts on fisheries resources.
12.34
During the upgrading works to
existing PTWs at North Point, Wan Chai East, Central,
12.35 At Aberdeen PTW, a small area of seawall would be demolished and re-constructed. The construction is not expected to adversely affect fisheries resources as no dredging is required. There is, however, potential for release of suspended sediment during construction, into the water column. This can be avoided by the use of standard good site practices, silt/sediment traps and silt curtains. With these methods in place, no significant adverse impact is expected during the construction works at Aberdeen PTW.
12.36 Planned temporary bypass of sewage effluent via seawall or submarine outfalls of SCISTW and individual PTW would be required during the construction stage, and immediately prior to and/or during the early phase of the commissioning of the upgraded SCISTW and PTW. The temporary sewage bypass would cause transient increase of pollution levels in the receiving marine water. Fish culture zones would be particularly susceptible to infection by sewage derived microorganisms, such as E. coli, as the fish are enclosed in cages and therefore can not move away from deteriorating water quality conditions. The planned temporary sewage bypass will be scheduled in the dry season or low flow period (November to February) to minimize the potential impact.
12.37 The existing outfall diffuser at SCISTW has led to a permanent loss of seafloor area for fishing activities such as demersal trawling. However, this diffuser has been in place since HATS Stage 1 was completed in 2001, so this impact is not discussed further.
12.38 Impacts associated with the HATS Stage 2A operational phase mainly involve changes in water quality due to effluent discharge. These impacts are long term and the severity depends largely on existing and future hydrographical parameters of the water bodies surrounding SCISTW diffuser.
12.39
Key
parameters of concern relating specifically to the disinfection process would
include total residual chlorine (TRC) and chlorination by-products (CBPs)
12.40
There
may be direct impacts from TRC and CBPs which are toxic
and persistent in nature and could cause formation of mutagenic/carcinogenic
and toxic by products within organisms which would pose ecological risks to
fisheries resources (Monarca et al., 2000). Other potential direct impacts
may be mortality or sub-lethal toxicity in fish. The potential impacts of acute
and chronic toxicity to fisheries resources from the disinfected effluent were
assessed and found to be acceptable in the ADF EIA.
12.41 Other factors of concern include Total Inorganic Nitrogen, (Nitrate, Nitrite and Ammonia), and Phosphorous in the effluent, and reduction in levels of dissolved oxygen as a result of effluent discharge.
12.42 In the immediate vicinity of the SCISTW diffuser, DO concentration may decrease as a result of changes in water quality during the operational phase. Lowered dissolved oxygen concentrations may cause some species of fish to avoid this area, although this is countered by the tendency of some fish to aggregate near sewage outfalls.
12.43 If dissolved oxygen reaches critically low levels, marine organisms may suffocate and die. If levels of DO are reduced to a low but sub-lethal level, many organisms can survive by increasing their ventilation rate and volume. However, the increase in oxygen consumption rate is metabolically demanding and would reduce the energy available for other vital processes (Valverde et al., 2006). DO depletion would cause an adverse effect on the eggs and larvae of fish and crustaceans, as at these stages of development high levels of oxygen in the water are required for growth to support high metabolic growth rates.
12.44 Fish grown in aquaculture practices are particularly susceptible to changes in water quality such as decreasing DO. As fish are enclosed in cages, so they can’t move away if conditions deteriorate. They would also be particularly susceptible to infection by sewage derived micro-organisms.
12.45 Ammonia present in sewage effluent can be toxic to fish. In water, ammonia exists in two forms, un-ionised ammonia (NH3) and ammonium (NH4+). Un-ionized ammonia is the form of ammonia that is toxic to aquatic life because it can most readily gain entry to aquatic organisms. In fish, ammonia can disrupt electrochemical gradients, deplete cerebral energy and damage gill structures affecting osmoregulation (Boardman, 2004). Toxicity of ammonia depends largely on other water quality parameters (pH, temperature, salinity) which control the ratio of ionized to un-ionised ammonia in the water. Not much information is available on the chronic toxicity of ammonia in marine environments, but fish are generally more sensitive to ammonia than invertebrates.
12.46 High levels of Total Inorganic Nitrogen (TIN) and phosphorus could result in high rates of primary production and potentially lead to Harmful Algal Blooms (HABs) when other favorable conditions such as turbulence, vertical mixing and sunlight occur concurrently. Current scientific knowledge on the growth of HAB species and the conditions leading to their development, is insufficient to be able to predict when and where such events will occur (Landsberg, 2002). HABs can have a significant effect of fisheries resources but this is difficult to quantify as wild fish are likely to move away from blooms as conditions deteriorate. However, fish in mariculture operations are confined to their cages so are particularly vulnerable to HABs. Fish kills may occur from toxins produced by toxic phytoplankton, through mechanical damage to the gills by non-toxic algae, or as a result of hypoxia when dense blooms use up DO in the water column (Landsberg, 2002). As discussed above, reduced levels of DO can impact the eggs and larvae of fish and crustaceans which require high levels of oxygen for development.
12.47 Emergency discharge of preliminarily treated effluent may be required during heavy rainfall events or during equipment/power failure. Heavy rain would potentially result in the need for emergency discharge via seawall bypass at SCISTW and all PTWs when inflow exceeds the capacity of the system.
12.48 Emergency discharge would also occur during equipment/power failure at PTWs or SCISTW. If equipment/power failure occurs at SCISTW then preliminary treated sewage effluent would be discharged from all PTWs. If power/equipment failure occurred at an individual PTW then raw sewage would be discharged into the receiving water body via the seawall bypass of the same PTW. Emergency discharge of raw sewage or preliminarily treated sewage would cause a temporary deterioration in water quality in the receiving water body and have potential adverse impacts on fisheries resources as described above.
12.49
Fisheries sensitive receivers considered in this
impact assessment for the construction and operational phases of HATS Stage 2A included
the following (in accordance with the general criteria set out in Annex 9 of
the EIAO TM:
·
Important fishing grounds – defined as those areas
where the fisheries resources/production constitute a high proportion of the
total fisheries resources/production in Hong Kong waters, or the fisheries
resources are of high value. As there are no marine works involved in the
upgrade of PTWs at North
Point, Wan Chai East, Central,
·
Spawning and nursery grounds of commercial fish
species –
12.50
Although the area surrounding SCISTW was ruled out as
an important nursery/spawning ground, it is important to consider potential impacts
to areas in close proximity to the outfall. Southern Lamma Island was
previously identified as a significant spawning/nursery ground (ERM, 1998) but
at present only very low levels of fry collection were reported around central
Lamma Island (AFCD, 2006). Fry collection used to take place in the Sandy Bay
fishing area (ERM, 1998); but the most recent AFCD Port Survey 2006 reported no
current fry collection off the entire north western coast of Hong Kong. It is
therefore concluded that currently there are no significant spawning and
nursery grounds at or nearby the SCISTW outfall.
12.51 Indirect impacts on water quality would potentially arise from land based construction activities at all PTWs. Sediment/ pollution laden site run-off, sewage from workforce, accidental spillage and discharges of wastewater entering the marine environment would potentially cause a deterioration in water quality which may have subsequent adverse impacts on fisheries resources. Standard good site practice and the implementation of mitigation measures, proposed in Water Quality Section 6, such as the use of silt/sediment and grease traps, effective site drainage, and provision of chemical toilets would minimise any adverse impacts to fisheries resources resulting from land based construction activities. Thus no significant adverse impact is expected.
12.52 Planned temporary bypass of sewage via seawall or submarine outfalls of SCISTW and individual PTW would be required during the construction stage, and immediately prior to and/or during the early phase of the commissioning of the upgraded SCISTW and PTW. This would lead to an increased level of E, coli and other sewage derived microorganisms in the receiving water body. It should be noted that the planned discharge would last 2 weeks in dry season. Water quality modelling has shown that the level of E. coli in the receiving water bodies would fluctuate highly on a daily basis during this period. Only minor impact on capture fisheries resources is expected, as increased levels of E. coli would be transient and fish have the ability to avoid areas of low water quality. However culture fisheries resources would be particularly susceptible to raised levels of E. coli, as fish are trapped in cages and can therefore not escape deteriorating water quality conditions. Water quality modelling however predicted that if planned temporary bypass of sewage is carried out during the dry season, no exceedance of the WQO would occur at all the FCZ, Therefore, no significant adverse impact on culture fisheries resources would be expected.
12.53 Potential changes in the concentrations of TRC, CBPs, DO and E coli. have been predicted by water quality modeling in Section 5 of the ADF EIA and summarised in Section 6 of this report.. The results showed small increases in TRC, CBPs and small decrease in DO, which would be highly localized around the existing SCISTW outfall. Please see the ADF EIA for an in-depth discussion of the results presented below.
12.54 As discussed in Section 6, the dispersion of TRC and CBPs in the disinfected effluent would be localized at the existing SCISTW sewage outfalls. At the edge of the ZID the level of TRC would be lower than 0.001 mg/l, within the assessment criteria of 0.008 mg/l (See Section 6, para. 6.167-6.170). The acute and chronic effects of TRC and CBPs on fish are assessed in Section 8 (para. 8.50-8.55 and Appendix 8.2) and no adverse impact is anticipated.
12.55 With the implementation of the Project, the levels of E. coli would be significantly reduced and there would be improvement to water quality in the Western Buffer WCZ and western Victoria Harbour WCZ. In the intermediate operation stage of HATS (in year 2013), the south of Tsing Yi Island and western Victoria Harbour WCZ would have E coli levels reduced from over 50000 numbers per 100ml (without disinfection facilities) to 1000-5000 number per 100ml (with disinfection facilities). In the ultimate year operation stage of HATS, the south of Tsing Yi Island and Western Victoria Harbour E. coli levels would be reduced from over 500-5000 number per 100ml (without disinfection facilities) to less than 180 number per 100ml (with disinfection facilities) (See Section 6, para. 6.196-6.197). The reduction in E. coli levels by the Project would have a positive impact on fisheries resources.
12.56
Literature on the effects
of residual chlorine discharges on fisheries resources was reviewed to provide
data for potential impact evaluation. Studies on the toxic effects of residual
chlorine on fish eggs and larvae indicated that abnormal development might
occur if residual chlorine was present at concentrations of 0.31 to 0.38 mg/l
(Morgan and Prince, 1977). However, behavioural studies indicated that adult
fish would avoid areas where concentrations of residual chlorine in the water
exceeded 0.035 mg/l (Grieve et. al, 1978).
12.57
The discharge standard for Total
Residual Chlorine (TRC) in the chlorinated/dechlorinated (C/D) HATS effluent
would be 0.2mg/l, which means the TRC concentration in the C/D HATS effluent
before initial dilution would already be lower than the TRC concentration that may induce toxic
effects on fish eggs and larvae (0.31 to 0.38 mg/l). Near
field water quality modelling predicted the minimum dilution of effluent at the
ZID to be 34 to 47 times in various project scenarios (See Appendix 6.1), which
would further reduce the TRC concentration in seawater.
12.58
Furthermore,
concentrations of residual chlorine have been shown to
diminish rapidly with time and distance from the discharge point (Mattice and Zittel, 1976
12.59
Toxicity data of
chlorination by-products (CBPs) on fish larvae and eggs were limited to date.
Chemical analysis conducted under this EIA Study revealed that only 8 and 5 of the 34 documented potential
CBPs were detected in the C/D CEPT effluent and secondary treated effluent
respectively. According to the
water quality impact assessment, the presence of the detected CBPs in the
seawater would be very low, with concentrations of less than 1 mg/l which would comply with the
available marine water quality standards that were developed to protect aquatic
biota.
12.60
In
view of the predicted low concentration increase of CBPs in only a small
localized area at SCISTW and compliance with available marine water quality
standards, it was considered that fish larvae and eggs would not be affected by
CBPs in diluted C/D HATS effluent. Juvenile fish were also not expected to be
affected as the nearest nursery/spawning grounds (
12.61
It
was concluded that residual chlorine and CBPs in discharged C/D HATS effluent
would not adversely impact fisheries resources.
12.62
Other
environmental Impacts associated with the HATS Stage 2A operational phase
mainly involved changes in water quality from the effluent discharged. These
impacts are long term and their severity depends largely on existing and future
hydrographical parameters of the water bodies surrounding SCISTW outfall
diffuser.
12.63 Water quality modelling predicted that the Hong Kong Water Quality Objective (WQO) for un-ionised ammonia (annual mean < 0.021 mg/l) would be met in all of the assessment areas except a small localized area surrounding the SCISTW outfall diffuser. As the WQO would be met in the majority of the Assessment Area, no significant adverse impact on fisheries resources was expected (See Section 6, para.6.232-6.235).
12.64 Water quality modelling predicted oxygen depletion levels at the SCISTW outfall to be highest in the wet season at 0.028 mg/l, in the initial and intermediate operation years of HATS Stage 2A. The actual levels were expected to be smaller as the prediction represented the worst case scenario. Besides, this depletion of oxygen was measured in a 120 m x 140 m grid cell. The oxygen depletion in the adjacent cell would be less than half this figure, so oxygen depletion should be considered acceptable. Such slight decrease in DO level localized at the SCISTW outfall would not pose adverse impacts to fisheries in Western Buffer and Victoria Harbour WCZs or at Ma Wan FCZ (See Section 6, para., 6.193-6.195).
12.65
Water quality models for HATS
Stage 2A indicated that there would be exceedances of TIN and Orthophosphate
(PO4) in the Assessment Area, in western
12.66 While elevated nutrient levels would not have a direct impact on fisheries resources, they may result in higher levels of primary production, which increases chances of HAB events. Indirect effects include fish kills caused by toxins produced by toxic phytoplankton, through mechanical damage to the gills by non-toxic algae, or as a result of hypoxia when dense blooms use up DO in the water column (Landsberg, 2002). As discussed above, reduced levels of DO can impact the eggs and larvae of fish and crustaceans which require high levels of oxygen for development.
12.67
Little
is known about the specific conditions leading to HABs
as they have been documented in polluted and unpolluted waters. Current levels
of TIN and Orthophosphate already exceeded the WQOs, but since the
commissioning of HATS Stage 1 in 2001, there has been no obvious rise in the
number of HAB events in
12.68
Emergency
discharge of sewage effluent at PTW and SCISTW may occur during periods of
heavy rain when inflow exceeds the capacity of the system. This would cause
deterioration in water quality and would potentially cause adverse impacts to
fisheries resources as described above. Based on historical records of high
rainfall events the worst case scenario for emergency discharge is predicted to
last for 8 hours. Water quality modelling predicted the the peak E.coli level to
reach 700 per 100ml during the
overflow period. Although the peak E.coli
level predicted at Tung Lung Chau FCZ (F1) marginally breached the criteria
value of 610 no. per 100 mL during the overflow period, the impact would be
short term (for a few hours). Non-compliance with the WQO/WQC (which is an
annual geometric mean) was not predicted.(For
a detailed discussion of the modelling results, see Water Quality Section 6,
Para. 6.280-6.291).
12.69
Emergency
discharge due to power/equipment failure would cause E. coli levels to rise to a peak level of 738 per 100ml at Tung Lung Chau FCZ which marginally exceeds the criteria value
of 610 per 100ml. As the exceedance occurred only for a
very short period (about three hours), non-compliance with the WQO/WQC (which
is an annual geometric mean value) was not predicted. Water quality modelling predicted that water
quality would return to normal conditions within 2 days of the emergency discharge.
With the implementation of precautionary measures such as the use of back up
pumps and generators the risk of emergency overflow would be greatly reduced (For a detailed discussion of the
modelling results, see Water Quality Section 6, Para.6.292-6.311).
12.70
No
insurmountable impact is expected on culture fisheries resources under these
emergency discharge scenarios because in both cases, emergency discharge would
be highly transient in nature, historical records indicate that emergency
discharges due to heavy rain and power/equipment failure are rare, emergency
discharge volume is insignificant when compared with the total sewage from HATS
and overall the project would result in decrease in E. coli levels in Eastern Buffer WCZ where Tung Lung Chau FCZ is situated.
12.71
Impacts
potentially arising during the construction and operational phase of the HATS
Stage 2A project were evaluated against the criteria stipulated in Annex 9 of
the EIAO TM and summarised below.
Nature of impact and size of affected area
12.72
The
operation of SCISTW would have a permanent effect on a small localized area
surrounding the outfall (approx. 300-400 m), corresponding to the ZID. No far
field water quality impacts are expected. TIN and Orthophosphate levels are
expected to exceed WQOs in western
Loss of Fisheries Resources/Production
12.73 As only a localised area surrounding the SCISTW outfall diffuser would be affected by the operation of the project and fisheries production and resources in this area were considered low, no adverse impact is expected.
Destruction and Disturbance of Spawning/Nursery Grounds
12.74 No important fish spawning or nursery ground was identified around SCISTW and no fry collection was reported to operate in the area. No significant adverse impact is expected.
Impact on Fishing Activity
12.75 No adverse impact on fishing activities is expected.
Impact on Aquaculture Activity
12.76 The nearest FCZ to SCISTW is at Ma Wan, over 7 km away. Near field affects of discharged effluent were not expected to affect Ma Wan FCZ as WQOs were not exceeded. Far field water quality would not deteriorate compared to existing conditions. If planned temporary bypass of sewage, necessary during the construction phase of the project is carried out during the dry season then no exceedances of WQO at FCZs are predicted. Thus no impact on aquaculture activity is anticipated.
12.77 Following EIAOTM Annex 16 and EIAO Guidance Note No. 3/2002, mitigation measures are discussed in this section in the order of priority, to avoid, minimize and compensate for the identified impacts on fisheries resources.
Construction Phase
Avoidance
12.78 The planned temporary bypass of sewage during construction will be carried out during the dry season or low flow period (November to October) to avoid adverse impacts on culture fisheries resources. The modelling predicted that the planned temporary sewage bypass would not cause any exceedance of the WQO for E. coli at all the FCZ..
Minimisation
12.79
To minimize the potential
indirect impacts on water quality from construction site runoff and various
construction activities, the practices outlined in ProPECC PN 1/94
Construction Site Drainage should be adopted. Detailed mitigation measures
to minimise the impacts on water quality associated with all construction
activities are discussed in Water Quality Section 6,
Operational Phase
12.80 The current location of SCISTW and outfall diffuser was chosen from multiple options to be situated in an area where fisheries resources and production were considered of low value, thus minimizing adverse impacts on key fisheries resources. As WQOs would only be exceeded in a small localised area (surrounding the SCISTW outfall diffuser), no fisheries specific mitigation measures would be required during the normal operation of the project.
12.81
Based
on the above assessment
Emergency Discharges
12.82
It was predicted that the E.coli level would exceed the criteria value
of 610 no. per 100 mL at Tung Lung Chau FCZ due to the emergency discharge
scenarios during power/equipment failure. However, the predicted peak increases
of E. coli would only marginally
exceeded the criteria value. As the exceedances would only occur for a very
short period, non-compliance with the WQO/WQC (which is an annual geometric
mean value) was not predicted. No insurmountable water quality impact would be
expected on the Tung Lung Chau FCZ due to the emergency discharge scenarios.
(See also Water Quality Section 6,
12.83 Environmental monitoring and auditing requirements relevant to protection of fisheries are covered in the water quality assessment and ecological risk assessment in Section 6 and Section 8 of this report, respectively.
12.84
A
literature review was conducted to establish the fisheries baseline conditions
of the Assessment Area and assessment of potential impacts was conducted in
accordance with the EIAO TM requirements.
12.85
The
existing SCISTW outfall location was chosen in the area where fisheries
resources were considered to be of low value. No significant adverse fisheries impact
is anticipated
·
Improvement in water quality with
reduction in E. coli levels in
Western Buffer WCZ and western Victoria Harbour WCZ
·
Only localized and small changes
in TRC
·
No exceedance of unionized ammonia
levels, which can be toxic to fish
·
Oxygen depletion would be minimal
and highly localized
·
There is no documented data on the
specific conditions leading to HABs and they have been documented in polluted
and un-polluted water. Increases in nutrient levels would be unlikely to
trigger HAB events
·
TIN and Orthophosphate levels have
increased in the Assessment Area since the implementation of HATS Stage 1, but
no increase in the number of HAB events has been observed
·
Water quality modeling predicted
little difference in levels of TIN and Orthophosphate with or without the
implementation of the project
·
Water quality objectives would be
met at Ma Wan FCZ
·
Planned temporary bypass of sewage
during construction will be carried out during the dry season to avoid adverse
impacts on culture fisheries resources
·
Emergency discharges of sewage
effluent at SCISTW or PTW seawall bypass due to heavy rainfall or
power/equipment failure would only cause marginal exceedance of criteria value
for E. coli. However,
as the exceedances would only occur for a very short period (a few hours only),
non-compliance with the WQO/WQC for E.coli
(which is an annual geometric mean value) was not predicted. The emergency
discharge would be rare and very
short term, thus no insurmountable impact is expected on fisheries resources.
12.86 As there would be no significant adverse impacts on fisheries resources from the proposed disinfection or discharge of effluent during normal operation of the project, no fisheries specific mitigation measure would be required. Environmental monitoring and auditing requirements relevant to fisheries protection during emergency discharge of planned bypass of sewage are covered in the water quality assessment, Section 6, ecological risk assessment, Section 8 and the stand alone EM&A Manual.
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