8.1
With reference to Clause
8.2 The Ecological Risk Assessment (ERA), which covers the assessment of risk to ecological resources, and compliance assessment on water quality criteria in terms of acute and chronic toxicity are presented in this section of the EIA Report. Risk assessment for human health is presented in Section 7 of the EIA Report.
8.3 The objective of the assessments are described as follows:
· ERA – Aquatic Life – to assess the adverse chronic effects to aquatic life associated with the exposure to toxic substances from effluent discharges of the Project
· ERA – Marine Mammals - to assess the adverse chronic effects to marine mammals associated with the exposure to toxic substances from effluent discharges of the Project
· Compliance Assessment on Water Quality Criteria – Acute and Chronic Toxicity
- To assess whether the water quality criteria in terms of acute and chronic toxicity would be complied in the presence of Project effluent discharge. This assessment could provide additional information concerning the potential ecological risks
8.4
The study area of this
assessment is in line with the one for water quality assessment according to
Clause
8.5 The risk assessment will focus on assessing the potential risks/impacts to ecological resources due to chronic exposure to the contaminants present in the HATS effluent discharge including potential contaminants produced in the disinfection process.
8.6 Under Agreement No. CE 7/2005 (EP) “Harbour Area Treatment Scheme Environmental Impact Assessment Study for the Provision of Disinfection Facilities at Stonecutters Island” (ADF EIA), a multi-tiered, multi-criteria evaluation exercise was conducted to select the disinfection option for the Stonecutters Island Sewage Treatment Works (SCISTW). Chlorination with dechlorination was selected to be the disinfection method. Therefore, the risk due to potential by-products produced in the chlorination / dechlorination process, together with the contaminants present in CEPT / secondary treated effluent will be assessed.
8.7 The approach and methodology of this ERA will follow those adopted in the ADF EIA.
8.8 Three project scenarios are considered in the assessments:
·
Late Stage
·
Before commissioning of HATS
Stage 2B with disinfection, HATS discharges
·
HATS Stage 2B with disinfection
(ultimate year), HATS discharges
8.9 It should be noted that the year 2020 completion date for Stage 2B is an assumption made for the purpose of risk assessment in the current EIA Study. Also note that scenarios 2 and 3 would use design flows whereas scenario 1 would use a lower flow rate based on calculated effluent flow generated in 2020.
8.10 The detailed risk assessment methodologies for ERA – Aquatic Life and ERA – Marine Mammals are presented in Appendix 8.1. The framework of the risk assessments is presented below:
· Contaminant of Potential Concern (COPC) Identification and Contaminant of Concern (COC) Selection
· Exposure and Ecological Effects Characterization
8.11 A brief overview of the risk assessment methodology is presented below:
8.12 This stage of the risk assessment establishes objective, scope and focus of the assessment, constructs the Site Conceptual Model (SCM) and defines assessment endpoint. SCM presents an overview of the chemical sources, exposure pathways and receptors of the risk assessment. The SCMs adopted in the risk assessments are presented graphically in Figure 8.1. More detailed discussion is presented in Appendix 8.1.
8.13 A total number of 35 chemicals are identified as COPCs from the chlorination/dechlorination process. The COPCs includes 9 chlorination by-products (CBPs) regulated by USEPA National Primary Drinking Water Standards; 25 priority pollutants[1] (which may contain potential CBPs) regulated by the USA National Pollutant Discharge Elimination System (NPDES)[2]; and total residual chlorine (as disinfectant residue). Chemical analysis is conducted to determine the COPC concentrations in chlorinated/dechlorinated (C/D) CEPT effluent and ambient seawater for the subsequent tasks of the risk assessment.
8.14 Unlike other conventional human health risk assessments for air pollution source (e.g. incinerator) and contaminated land/groundwater, a look-up table of contaminants/list of possible COPC for CBPs risk assessment in effluent is not identified from local and overseas authorities. Moreover, according to the review of local and overseas practice, list of “regulated CBPs in sewage effluent” is not identified.
8.15 Hence, a conservative approach is adopted in this Study to include all the regulated CBPs in drinking water plus the 25 priority pollutants (may contain potential CBPs) regulated by NPDES as COPCs, although these pollutants are not regulated due to the concern of generation during chlorination process.
8.16
The NPDES practice is adopted
because it contains the most comprehensive list of regulated pollutants for
effluent discharge, based on the review of practice in the
8.17 Therefore, the 35 COPCs identified from the chlorination/dechlorination process include all documented potential CBPs/disinfectant residue which are regulated due to their potential to cause impact to human health and/or ecological resources. The list of identified COPCs (which the COCs for risk calculation are selected from the list) is considered sufficiently comprehensive to assess the potential risk to ecological resources due to chronic exposure to the contaminants produced in the disinfection process in the effluent discharges.
8.18
A comprehensive chemical
analysis was conducted under the Environmental and Engineering Feasibility
Assessment Studies in relation to the Way Forward of the HATS (HATS EEFS)
(2004) to determine the pollutant concentrations in HATS CEPT effluent (Stage 1
and Stage
8.19 The COCs are selected from the COPCs based on a number of selection rules and their risks are determined in the risk assessment.
8.20 COC exposure by aquatic life is characterized as the COC concentrations in seawater, which are determined by using dilution factors estimated in water quality modelling.
8.21 This stage of the assessment involves water quality modelling, characterization of potential marine mammals receptors and calculation of COC exposure. COC bioconcentration and bioaccumulation along the food chain have been considered in the determination of COC concentration of preys. As such, the risks associated with COC bioconcentration and bioaccumulation have been considered and evaluated in the risk assessment.
8.22 This stage of the assessment characterizes the ecological effects of COC exposure to aquatic life by comparing the COC concentrations in the seawater at the receptor points to the Toxicity Reference Value (TRV) for aquatic life. TRVs for COCs are derived from water quality criteria/standards for protection of aquatic life when available; for COCs without such criteria/standards, toxicity values obtained from the scientific literature are used to derive TRVs.
8.23 This stage of the ERA characterizes the ecological effects of COC exposure to marine mammals by comparing the COC daily dose to the toxicity reference doses for the marine mammals, which are derived by reviewing the toxicological effects data from various scientific literature, database and guidelines.
8.24 In this stage of the assessment, the risk associated with the COCs to the ecological resources is characterized by COC-specific hazard quotients (HQs) and hazard index (HI).
8.25 The assessment results need to compare against the established assessment criteria to evaluate the environmental acceptability of the chlorination disinfection technology option, which are presented below.
8.26 Hazard Quotient (HQ) and Hazard Index (HI)[3] are used as the measure for the risk to aquatic life and marine mammals. At present USEPA has taken 1.0 as the screening value for HQ and HI. A HQ and/or HI below the screening value (i.e. 1) would indicate that the risk of the proposed action does not present an unacceptable risk and no further investigation would be required.
8.27 When the calculated HQ and HI are above the screening value, it does not immediately indicate that the proposed action would present an unacceptable risk. Rather, it triggers further investigation to examine whether the assumptions for the concerned chemicals are too conservative and whether the severities of the effect of the chemicals are of great concern.
8.28 The adoption of 1 as the screening value is consistent with the interpretation of HQ and HI in the approved “EIA for New Contaminated Mud Marine Disposal Facility at Airport East / East Sha Chau Area”.
8.29 Acute Toxicity Unit (TUa) and Chronic Toxicity Unit (TUc) are the endpoints for acute and chronic toxicity criteria respectively. For acute toxicity due to the project effluent, 1-hour average limit of 0.3 TUa should be met at the edge of initial dilution zone. While for chronic toxicity due to the project effluent, 4-day average limit of 1.0 TUc should be met at the edge of mixing zone.
8.30 In the ADF EIA, chemical analysis and whole effluent toxicity tests (WETT) are conducted for the C/D CEPT effluent from SCISTW and secondary treated effluent from Tai Po/Shatin Sewage Treatment Works to obtain the data for the risk assessments. The chemical analysis aimed to determine the concentrations of identified 35 COPCs (from chlorination/dechlorination process) in the C/D effluents and ambient seawater for COC selection and calculation of human health and ecological risk; whereas the WETT aimed to determine the toxicity of C/D effluent in order to assess the compliance of acute and chronic toxicity criteria.
8.31
A comprehensive chemical
analysis was conducted under the HATS EEFS (2004) to determine the pollutant
concentrations in HATS CEPT effluent (Stage 1 and Stage
8.32 Under the ADF EIA, WETT was conducted to determine the whole effluent toxicity of C/D CEPT effluent from SCISTW and C/D secondary treated effluent from Tai Po/Shatin Sewage Treatment Works for the following five species:
· Amphipod (Melita longidactyla), with 48-hour survival test
· Barnacle larvae (Balanus amphitrite), with 48-hour survival test
· Fish (Lutjanus malabaricus), with 48-hour survival test
· Shrimp (Metapenaeus ensis), with 48-hour survival test
· Diatom (Skeletonema costatum), with 7-day growth inhibition test
8.33 The WETT followed the protocol agreed and adopted in previous study which aimed at establishing fisheries and marine ecological criteria appropriate to local marine biota and fisheries resources (Centre for Coastal Pollution and Conservation, 2001). The species used in the WETT are same to those used in the previous study, which are considered as the “representative local species” of great ecological and fisheries significance.
8.34 The test conditions of the WETT are shown as follows:
· Temperature: 22 ± 1oC
· Salinity: 30 ± 1ppt
· Illuminance: 500 – 1000 lux (2500 – 3000 lux for diatom)
· Photoperiod: 12h light : 12h dark
8.35
The toxicity tests for amphipod,
barnacle larvae, fish and shrimp are to determine the acute toxicity of the
effluents to the 4 animal species while the toxicity tests for diatom are to
determine the chronic toxicity of the effluents to the plant species. Tables
Table
|
48-hr LC |
NOECb |
48-hr LC50 |
||
Note: a 48-hr LC50, the lethal concentration of effluent to 50% of test animals after 48 hours of exposure.
b No-Observable-Effect-Concentration, the highest concentration of effluent producing effects not significantly different from responses to controls
N.D = Not Determined, due to less than 50% mortality was recorded when animal species were exposed to the highest concentration of effluent
Table 8.1b Summary of WETT Result for CEPT Effluent (Chronic Toxicity)
|
Test Species |
Composite CEPT
Effluent |
Chlorinated/Dechlorinated
CEPT Effluent |
||
|
7-day IC |
NOECb |
7-day IC50 |
NOEC |
|
|
Diatom |
34.9% |
27.2% |
39.7% |
27.2% |
Note: a 7-day IC50, the inhibition concentration to 50% of organisms after 7 days of exposure.
b No-Observable-Effect-Concentration, the highest concentration of effluent producing effects not significantly different from responses to controls
8.36
Statistical analysis is
conducted for the toxicity test data of barnacle larvae and diatom to determine
whether C/D process induced additional toxicity in the CEPT effluent. The analysis showed that the C/D process
did not induce statistically significant difference to the toxicity effect in
CEPT effluent to barnacle larvae and diatom, i.e. C/D process did not induce
additional toxicity.
Table
|
48-hr LC50 |
48-hr LC50 |
|||
|
N.D1 |
N.D2 |
N.D1 |
N.D2 |
|
|
N.D1 |
N.D2 |
N.D1 |
N.D2 |
|
|
N.D1 |
N.D2 |
N.D1 |
N.D2 |
|
|
N.D1 |
N.D2 |
N.D1 |
N.D2 |
|
N.D = Not Determined,
1 LC50 could not be determined due to less than 50% mortality was recorded when animal species were exposed to the highest concentration of effluent
2 NOEC could not be determined; the highest concentration of effluent did not produce effects significantly different from controls
Table 8.1d Summary of WETT Result for Secondary Treated Effluent (Chronic Toxicity)
|
Treated Effluent |
||||
|
7-day IC50 |
7-day IC50 |
|||
|
N.D1 |
N.D2 |
N.D1 |
N.D2 |
|
N.D = Not Determined,
1 IC50 could not be determined due to less than 50% growth inhibition was recorded when plant species were exposed to the highest concentration of effluent
2 NOEC could not be determined; the highest concentration of effluent did not produce effects significantly different from controls
8.37 Acute toxicity unit (TUa) and chronic toxicity unit (TUc) of the C/D effluent are calculated using the 48-hr LC50 and 7-day IC50 obtained in the WETT. TUa and TUc can be calculated using the following equations, as documented in “Technical Support Document for Water Quality-based Toxics Control” (USEPA 1991):
TUa = 100/LC50 Equation 1
Where
LC50 = % of effluent which gives 50% survival of the most sensitive of the range of species tested for acute toxicity effect
TUc = 100/NOEC (chronic) Equation 2
Where
NOEC (chronic) = No-Observable-Effect-Concentration, based on the most sensitive of the range of species tested for chronic toxicity effect
8.38 Apart from using Equation 2, by applying “acute-to-chronic ratio” (ACR)[4], available acute toxicity data of a barnacle larvae can be used to extrapolate to the chronic toxicity to the species. According to USEPA (1991), a value of 10 for ACR would be appropriate.
8.39 For TUa of C/D CEPT effluent, it is calculated based on the test result for barnacle larvae, because mortality of amphipod, shrimp and fish is insufficient to determine the LC50 values. By applying Equation 1, TUa of C/D CEPT effluent = 100 / 40.2 = 2.49.
8.40 For TUc of C/D CEPT effluent, it can be calculated based on the test result for diatom. By applying Equation 2, TUc of C/D CEPT effluent = 100 / 27.2 = 3.68. TUc can also be determined by applying ACR to the TUa calculated from acute toxicity data to barnacle larvae, which is:
TUc = TUa x ACR = 2.49 x 10 = 24.9.
Since the TUc determined by extrapolation from acute toxicity data is found to be greater than that calculated from chronic toxicity data, the former (i.e. 24.9) is used to determine the compliance of chronic toxicity criteria.
8.41 C/D secondary treated effluent generally does not exert acute and chronic toxicity effect to the species used in the WETT; no 48-hr LC50 for animal species and no NOEC for diatom could be determined and therefore no TUa and TUc could be calculated for C/D secondary treated effluent.
8.42
From the identified COPCs, COCs
are selected and their effluent concentrations are determined for calculation
of risks. The COC selection and
effluent concentrations are based on the chemical analysis results and a number
of established rules. The detailed
COC selection and effluent concentration determination process are presented in
Appendix 8.1; the selected COCs in risk assessments and their determined
effluent and ambient seawater concentrations are summarized in Tables
Table
|
COC |
Effluent Conc. (mg/L) |
Ambient Seawater Conca. (mg/L) |
|
From chlorination/dechlorination
process |
||
|
Total
residual chloride |
100 |
0 |
|
Chloroform |
7 |
0 |
|
Chloroacetic acid |
4 |
0 |
|
Dibromoacetic acid |
4 |
0 |
|
Dichloroacetic acid |
45.9 |
0 |
|
Trichloroacetic acid |
22 |
0 |
|
Tetrachloroethylene |
1.3 |
0 |
|
Trichloroethylene |
2 |
0 |
|
2,4,6-trichlorophenol |
2 |
0 |
|
Hexachlorobenzene |
0.25b |
0 |
|
Beta-benzene hexachloride |
0.5b |
0 |
|
Gamma-benzene hexachloride |
0.5b |
0 |
|
From CEPT effluent |
||
|
Aluminium |
15.9 |
15.6 |
|
Antimonyc |
0.721 |
0.258 |
|
Bariumc |
23.2 |
6.65 |
|
Chromium IIIc |
9.58 |
0.28 |
|
Copperc |
8.59 |
0.02 |
|
Leadc |
0.128 |
0.055 |
|
Nickelc |
26.2 |
0.77 |
|
Seleniumc |
0.31 |
0.07 |
|
Silverc |
0.182 |
0.006 |
|
Tinc |
0.844 |
0.14 |
|
Vanadiumc |
29.5 |
1.73 |
|
Zincc |
14.1 |
2.37 |
|
Ammonia |
22,000 |
230 |
|
Sulphide |
4,900 |
48 |
|
TCDD (I-TEQ) |
0.1pg/L |
0.039pg/L |
|
Toluene |
12 |
0 |
|
Diazinon |
0.048 |
0 |
|
Malathion |
0.031 |
0 |
c Dissolved concentration for metals was adopted for ecological risk assessment
Table 8.2b Selected COCs and Effluent Concentrations for ERA (Project Scenario 3)
|
COC |
Effluent Conc. (mg/L) |
Ambient Seawater Conca. (mg/L) |
|
From chlorination/dechlorination process |
||
|
Total
residual chlorine |
10b |
0 |
|
Bromoform |
49 |
0 |
|
Dibromochloromethane |
8 |
0 |
|
Dibromoacetic
acid |
10 |
0 |
|
Dichloroacetic
acid |
3 |
0 |
|
Trichloroacetic
acid |
7 |
0 |
|
Hexachlorobenzene |
0.25b |
0 |
|
Beta-benzene
hexachloride |
0.5b |
0 |
|
Gamma-benzene
hexachloride |
0.5b |
0 |
|
From Secondary Treated Effluent |
||
|
Antimonyc |
0.782 |
0.258 |
|
Bariumc |
23.7 |
6.65 |
|
Chromium IIIc |
8.44 |
0.28 |
|
Copperc |
6.63 |
0.02 |
|
Nickelc |
22.3 |
0.77 |
|
Seleniumc |
0.13 |
0.07 |
|
Silverc |
0.099 |
0.006 |
|
Tinc |
0.457 |
0.14 |
|
Vanadiumc |
31.3 |
1.73 |
|
Zincc |
9.79 |
2.37 |
|
Ammonia |
4,200 |
230 |
|
Sulphide |
53 |
48 |
|
TCDD (I-TEQ) |
0.062pg/L |
0.039pg/L |
|
Diazinon |
0.058 |
0 |
|
Malathion |
0.015 |
0 |
Note: a For COCs that are not detected in the ambient seawater samples, the ambient seawater concentration is set as zero.
b Selected COCs with concentration below detection limit in C/D effluent, their effluent concentrations were assumed to be one-half of the detection limit. This is a standard approach accepted by USEPA.
c Dissolved concentration for metals was adopted for ecological risk assessment
8.43 As discussed in Section 6 and shown in Figure 6.43 and Figure 6.44, the effluent plume from SCISTW, Tai Po/Shatin STW and Pillar Point STW would not overlap each other. This means the contaminants discharged from Tai Po/Shatin STW and Pillar Point STW would not significantly contribute to the contaminant concentrations at the edge of ZID, edge of mixing zone (of the effluent plume from SCISTW) and the Tsuen Wan beaches, which would be due to the C/D effluent from SCISTW.
8.44 Therefore, it is appropriate to apply the dilution factors calculated by water quality modelling at different exposure points (i.e. edge of ZID, edge of mixing zone and the nearest beach from SCISTW outfall) to calculate the contamination concentration.
8.45 In ERA – Aquatic Life, the risk of individual COCs is characterized by hazard quotient which is composed of COC concentration at exposure point as numerator and the derived COC-specific toxicity reference value (TRV) as denominator. The averaging time of COC concentration at exposure point used for hazard quotient calculation should match the averaging time of the TRV of the corresponding COC. Table 8.3 summarizes the averaging time of different TRVs and the corresponding dilution factor for COC concentration calculation. Calculations of hazard quotient and derivation of COC-specific TRV are presented in Appendix 8.1 and Appendix 8.4 respectively.
Table 8.3 Averaging Time of TRVs and Corresponding Dilution Factor
|
The lower value of weight average dilution factor estimated for dry season and that of wet season |
The lower value of weight average dilution factor estimated for dry season and that of wet season |
Note:
a
Minimum dilution factor was adopted as a conservative estimate
b Dilution factor exceeded 90% of the time (i.e. 10% of values are below this value)
c For COC without water quality standard/criteria, which TRV was derived from toxicity data
8.46 10 %tile dilution factors (dry and wet season combined) achieved at the ZID are adopted for calculation of risk imposed to marine mammals, such approach has been adopted in the previous relevant ADF EIA. Since COC exposure by marine mammals occurs in both wet and dry season, dry and wet season combined dilution factors are adopted. Adopting 10 %tile dilution factor for risk calculation is an approach consistent with previous studies, which results in a more realistic yet conservative range of risk calculations.
8.47
Table
Table
|
38b |
|||||
|
54d |
82e |
||||
|
172h |
|||||
|
209h |
|||||
Note: *The edge of mixing zone of dichloroacetic acid (the COC with the largest mixing zone)
Table 8.4b Estimated Dilution Factors (Project Scenarios 2 and 3)
|
Cannot be determined as no mixing zone determined for dry season |
|||||
|
43d |
77e |
128h |
|||
Note: *The edge of mixing zone of bromoform (the COC with the largest mixing zone)
a Dilution factor exceeded 90% of the time (i.e. 10% of values are below this value)
b Applied to (1) assess the compliance of criteria for acute toxicity
c Applied to (1) determine COC conc. at edge of ZID (for calculation in ERA – Marine Mammals)
d Applied to determine COC conc. at edge of mixing zone (COCs with established water quality criteria having daily averaging time, for calculation in ERA – Aquatic Life)
e Applied to determine COC conc. at edge of mixing zone (COCs with established water quality criteria that need to be complied at least 90% of occasions, for calculation in ERA – Aquatic Life)
f Applied to determine COC conc. at edge of mixing zone (COC with established water quality criteria having annual averaging time, for calculation in ERA – Aquatic Life)
g Applied to determine COC conc. at
edge of mixing zone (COC with toxicity reference value derived from toxicity
data, for calculation in ERA – Aquatic Life)
h Applied to (1) assess the compliance of criteria for chronic toxicity, (2) determine COC conc. at edge of mixing zone (COCs with established water quality criteria having 4-day averaging time, for calculation in ERA – Aquatic Life)
8.48 As discussed in Sections 8.39 and 8.40, the TUa and TUc value adopted for the C/D CEPT effluent is 2.49 and 24.9 respectively. No TUa and TUc could be determined for C/D secondary treated effluent from the WETT result because it generally does not exert acute and chronic toxicity effect to the species tested. To evaluate the compliance of acute and chronic toxicity criteria, the estimated minimum dilution factor at edge of ZID and minimum 4-day average dilution factor at edge of mixing zone are used to determine the resultant acute and chronic toxicities at these two locations. Table 8.5 presents the acute and chronic toxicity results in the 3 project scenarios.
Table 8.5 Acute and Chronic Toxicities at Edge of ZID and Edge of Mixing Zone
|
Project
Scenario |
Acute Toxicity at Edge of ZID |
Chronic Toxicity at Edge of Mixing Zone |
|
Scenario 1 |
2.49 / 38 = 0.066 |
24.9 / 172 = 0.145 |
|
Scenario 2 |
2.49 / 35 = 0.071 |
24.9 / 128 = 0.195 |
|
Scenario 3 |
- |
- |
8.49 As observed in Table 8.5, the estimated acute toxicity at edge of ZID and chronic toxicity at edge of mixing zone are below the established criteria (TUa < 0.3 at edge of ZID, TUc < 1.0 at edge of mixing zone) in Project Scenarios 1 and 2. As discussed above, since C/D secondary treated effluent did not exert acute and chronic toxicity effect to marine species tested, non-compliance of acute and chronic toxicity criteria in Project Scenario 3 would not be expected.
8.50
In the ERA – Aquatic Life, HQ
due to exposure of individual selected COCs and HI due to exposure of all
selected COCs by aquatic life at the edge of mixing zone are determined for all
the 3 project scenarios. The
detailed assessment results are presented in Appendix 8.2.
Tables
Table
|
COC |
HQ at Edge of
Mixing Zonea – due to the Project |
HQ due to
Backgroundb |
Total HQ (due to Project
+ background) |
|
Potential CBPs |
|||
|
Total
Residual Chlorine |
0.142 |
0 |
0.142 |
|
Chloroform
|
0.00394 |
0 |
0.00394 |
|
Chloroacetic
acid |
0.000001 |
0 |
0.000001 |
|
Dibromoacetic
acid |
0.000046 |
0 |
0.000046 |
|
Dichloroacetic
acid |
0.00156 |
0 |
0.00156 |
|
Trichloroacetic
acid |
0.000002 |
0 |
0.000002 |
|
Tetrachloroethylene |
0.000993 |
0 |
0.000993 |
|
Trichloroethlyene |
0.00135 |
0 |
0.00135 |
|
2,4,6-trichlorophenol |
0.00132 |
0 |
0.00132 |
|
Hexachlorobenzene |
0.0563 |
0 |
0.0563 |
|
Beta-benzene
hexachloride |
0.0734 |
0 |
0.0734 |
|
Gamma-benzene
hexachloride |
0.0536 |
0 |
0.0536 |
|
Contaminants present in CEPT Effluent |
|||
|
Aluminium |
0.000001 |
0.0104 |
0.010401 |
|
Antimony |
0.000001 |
0.0000600 |
0.000061 |
|
Barium |
0.000026 |
0.00133 |
0.00136 |
|
Chromium
III |
0.00229 |
0.0102 |
0.0125 |
|
Copper |
0.0209 |
0.00400 |
0.0249 |
|
Lead |
0.000052 |
0.00679 |
0.00684 |
|
Nickel |
0.0620 |
0.154 |
0.216 |
|
Selenium |
0.000020 |
0.000986 |
0.00101 |
|
Silver |
0.000849 |
0.00429 |
0.00514 |
|
Tin |
0.000069 |
0.00172 |
0.00179 |
|
Vanadium |
0.00188 |
0.0173 |
0.0192 |
|
Zinc |
0.00715 |
0.119 |
0.126 |
|
Ammonia |
0.1616 |
0.253 |
0.414 |
|
Sulphide |
0.388 |
0.480 |
0.868 |
|
Dioxins
and Furans |
0.000013 |
0.00103 |
0.00104 |
|
Toluene |
0.00203 |
0 |
0.00203 |
|
Diazinon |
0.0324 |
0 |
0.0324 |
|
Malathion |
0.0105 |
0 |
0.0105 |
|
Total HI |
1.03 |
1.06 |
2.09 |
Table 8.6b Estimated
HQ and HI to Aquatic Life (Project Scenario 2)
|
COC |
HQ at Edge of
Mixing Zonea – due to the Project |
HQ due to
Backgroundb |
Total HQ (due to
Project + background) |
|
Potential CBPs |
|||
|
Total
Residual Chlorine |
0.179 |
0 |
0.179 |
|
Chloroform
|
0.00516 |
0 |
0.00516 |
|
Chloroacetic
acid |
0.000001 |
0 |
0.000001 |
|
Dibromoacetic
acid |
0.000051 |
0 |
0.000051 |
|
Dichloroacetic
acid |
0.00177 |
0 |
0.00177 |
|
Trichloroacetic
acid |
0.000002 |
0 |
0.000002 |
|
Tetrachloroethylene |
0.00130 |
0 |
0.00130 |
|
Trichloroethlyene |
0.00177 |
0 |
0.00177 |
|
2,4,6-trichlorophenol |
0.00146 |
0 |
0.00146 |
|
Hexachlorobenzene |
0.0737 |
0 |
0.0737 |
|
Beta-benzene
hexachloride |
0.0962 |
0 |
0.0962 |
|
Gamma-benzene
hexachloride |
0.0702 |
0 |
0.0702 |
|
Contaminants present in CEPT Effluent |
|||
|
Aluminium |
0.000002 |
0.0104 |
0.010402 |
|
Antimony |
0.000001 |
0.0000600 |
0.000061 |
|
Barium |
0.000029 |
0.00133 |
0.00136 |
|
Chromium
III |
0.00300 |
0.0102 |
0.0132 |
|
Copper |
0.0223 |
0.00400 |
0.0263 |
|
Lead |
0.000070 |
0.00679 |
0.00686 |
|
Nickel |
0.0661 |
0.154 |
0.220 |
|
Selenium |
0.000026 |
0.000986 |
0.00101 |
|
Silver |
0.00111 |
0.00429 |
0.00540 |
|
Tin |
0.000076 |
0.00172 |
0.00179 |
|
Vanadium |
0.00246 |
0.0173 |
0.0198 |
|
Zinc |
0.00762 |
0.119 |
0.126 |
|
Ammonia |
0.212 |
0.253 |
0.464 |
|
Sulphide |
0.429 |
0.480 |
0.909 |
|
Dioxins
and Furans |
0.000014 |
0.00103 |
0.00104 |
|
Toluene |
0.00266 |
0 |
0.00266 |
|
Diazinon |
0.0425 |
0 |
0.0425 |
|
Malathion |
0.0137 |
0 |
0.0137 |
|
Total HI |
1.23 |
1.06 |
2.30 |
Table
|
COC |
HQ at Edge of
Mixing Zonea – due to the Project |
HQ due to
Backgroundb |
Total HQ (due to
Project + background) |
|
Potential CBPs |
|||
|
Total
Residual Chlorine |
0.0179 |
0 |
0.0179 |
|
Bromoform |
0.00121 |
0 |
0.00121 |
|
Dibromochloromethane |
0.00208 |
0 |
0.00208 |
|
Dibromoacetic
acid |
0.000128 |
0 |
0.000128 |
|
Dichloroacetic
acid |
0.000115 |
0 |
0.000115 |
|
Trichloroacetic
acid |
0.000001 |
0 |
0.000001 |
|
Hexachlorobenzene |
0.0737 |
0 |
0.0737 |
|
Beta-benzene
hexachloride |
0.0962 |
0 |
0.0962 |
|
Gamma-benzene
hexachloride |
0.0702 |
0 |
0.0702 |
|
Contaminants present in Secondary Treated
Effluent |
|||
|
Antimony |
0.000001 |
0.000060 |
0.000061 |
|
Barium |
0.000030 |
0.00133 |
0.00136 |
|
Chromium
III |
0.00264 |
0.0102 |
0.0129 |
|
Copper |
0.0172 |
0.00400 |
0.0212 |
|
Nickel |
0.0559 |
0.154 |
0.210 |
|
Selenium |
0.000007 |
0.000986 |
0.000993 |
|
Silver |
0.000588 |
0.00429 |
0.00487 |
|
Tin |
0.000034 |
0.00172 |
0.00175 |
|
Vanadium |
0.00262 |
0.0173 |
0.0199 |
|
Zinc |
0.00482 |
0.119 |
0.123 |
|
Ammonia |
0.0386 |
0.253 |
0.291 |
|
Sulphide |
0.000442 |
0.480 |
0.480 |
|
Dioxins
and Furans |
0.000005 |
0.00103 |
0.00103 |
|
Diazinon |
0.0513 |
0 |
0.0513 |
|
Malathion |
0.00664 |
0 |
0.00664 |
|
Total HI |
0.425 |
1.06 |
1.49 |
Note: a The mixing zone of dichloroacetic acid and bromoform (the largest one among those of other COCs) was adopted for risk calculations for Scenarios 1/2 and Scenario 3 respectively
8.51
As seen in Tables
8.52 Taking the hazard index due to the pollutants at background level (1.06) and those present in HATS C/D CEPT/secondary treated effluent (0.43 to 1.23 at edge of mixing zone) into consideration, the hazard indices to aquatic life at the edge of mixing zone due to the Project in the 3 Project Scenarios are found to be slightly higher than the screening value of 1(1.49 to 2.30). Note that the hazard index due to pollutants at background level (1.06) already exceeds the screening value. According to USEPA (2005), the calculated HI exceeding the screening value (in this Study: 1) would not indicate that the proposed action is not safe or that it presents an unacceptable risk. Rather, it triggers further investigation. Further investigation on the risk to aquatic life is carried out based on the results of WETT, which is able to assess the impacts caused by aggregate toxic effect of the mixture of pollutants in effluent.
8.53 As mentioned above, the WETT conducted under this Study followed the protocol agreed and adopted in previous study (including the use of artificial seawater as dilution water), which is consistent with the WETT practice accepted by USEPA. WETT is a common tool adopted in USA NPDES to regulate and monitor effluent discharges, in order to protect receiving waters against adverse impacts upon water quality and aquatic life, and also to ensure “no toxics in toxic amounts” in ambient waters.
8.54 Results of WETT on C/D effluent are useful to supplement the ecological risk assessment, which provide information to determine whether the C/D effluent would induce adverse effects to aquatic life. The WETT is capable of considering all the chemical species present in the C/D effluent (including those not identified as COC in the ERA – Aquatic Life) and the possible additive/synergistic/antagonistic interactive effects among them. As presented in Table 8.5 above, the established toxicity criteria in all Project Scenarios are found to be well complied at both edge of ZID (0.07 TUa against acute toxicity criterion of 0.3 TUa) and edge of mixing zone (0.15 to 0.20 TUc against chronic criterion of 1.0 TUc). The results suggested that the potential risks due to C/D effluent imposed to aquatic life would be acceptable; with the comfortable margin (about 4/5 of the criteria value) to the established toxicity criteria, it is expected that the aquatic life present in the receiving water would not experience unacceptable toxicity even taking into account the background seawater conditions. This is further supported by the assessment results that concentration of all COCs would be complied with available local/overseas water quality standards at the edge of mixing zone. Moreover, as mentioned above, statistical analysis of WETT data revealed that C/D process did not induce additional toxicity to the sewage effluent.
8.55 In view of the findings of the ERA – aquatic life with supplement of WETT results, the potential ecological risk imposed to aquatic life due to C/D effluent would be considered acceptable.
8.56
In the ERA – Marine Mammals, HQ
due to exposure of individual selected COCs and HI due to exposure of all
selected COCs by marine mammals are determined for all the 3 project
scenarios. The detailed assessment results
are presented in Appendix 8.3. Tables
Table
|
COC |
HQ |
||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
|
|
Potential CBPs |
|||
|
Total Residual
Chlorine |
0.00000314 |
0.00000340 |
0.00000034 |
|
Bromoform |
- |
- |
0.0000167 |
|
Chloroform
|
0.00000384 |
0.00000415 |
- |
|
Dibromochloromethane |
- |
- |
0.00000266 |
|
Chloroacetic
acid |
0.00000286 |
0.00000309 |
- |
|
Dibromoacetic
acid |
0.0000472 |
0.0000510 |
0.000128 |
|
Dichloroacetic
acid |
0.000185 |
0.000200 |
0.0000131 |
|
Trichloroacetic
acid |
0.0000818 |
0.0000885 |
0.0000281 |
|
Tetrachloroethylene |
0.00000473 |
0.00000512 |
- |
|
Trichloroethlyene |
0.00000061 |
0.00000066 |
- |
|
2,4,6-trichlorophenol |
0.00000021 |
0.00000023 |
- |
|
Hexachlorobenzene |
0.000619 |
0.000669 |
0.000669 |
|
Beta-benzene
hexachloride |
0.000221 |
0.000239 |
0.000239 |
|
Gamma-benzene
hexachloride |
0.0000247 |
0.0000267 |
0.0000267 |
|
Contaminants present in CEPT / Secondary
Treated Effluent |
|||
|
Aluminium |
0.000109 |
0.000109 |
- |
|
Antimony |
0.0102 |
0.0103 |
0.0103 |
|
Barium |
0.0356 |
0.0357 |
0.0358 |
|
Chromium
III |
0.00000037 |
0.00000039 |
0.00000037 |
|
Copper |
0.00199 |
0.00213 |
0.00170 |
|
Lead |
0.000463 |
0.000465 |
- |
|
Nickel |
0.000297 |
0.000307 |
0.000288 |
|
Selenium |
0.0112 |
0.0112 |
0.0107 |
|
Silver |
0.00000594 |
0.00000611 |
0.00000503 |
|
Tin |
0.000118 |
0.000119 |
0.000112 |
|
Vanadium |
0.000268 |
0.000273 |
0.000278 |
|
Zinc |
0.00491 |
0.00494 |
0.00477 |
|
Ammonia |
0.000389 |
0.000409 |
0.000189 |
|
Dioxins
and Furans |
0.0616 |
0.0618 |
0.0606 |
|
Toluene |
0.000176 |
0.000190 |
- |
|
Diazinon |
0.00000162 |
0.00000176 |
0.00000212 |
|
Malathion |
0.00000003 |
0.00000003 |
0.00000001 |
|
Total HI |
0.129 |
0.129 |
0.126 |
Table 8.7b Estimated HQ and HI for Marine Mammals (Porpoises)
|
COC |
HQ |
||
|
Scenario 1 |
Scenario 2 |
Scenario 3 |
|
|
Potential CBPs |
|||
|
Total
Residual Chlorine |
0.00000189 |
0.00000204 |
0.00000020 |
|
Bromoform |
- |
- |
0.00000911 |
|
Chloroform
|
0.00000200 |
0.00000216 |
- |
|
Dibromochloromethane |
- |
- |
0.00000143 |
|
Chloroacetic
acid |
0.00000159 |
0.00000172 |
- |
|
Dibromoacetic
acid |
0.0000249 |
0.0000269 |
0.0000672 |
|
Dichloroacetic
acid |
0.0000961 |
0.000104 |
0.0000679 |
|
Trichloroacetic
acid |
0.0000361 |
0.0000391 |
0.0000124 |
|
Tetrachloroethylene |
0.0000027 |
0.00000292 |
- |
|
Trichloroethlyene |
0.00000033 |
0.00000036 |
- |
|
2,4,6-trichlorophenol |
0.00000018 |
0.00000019 |
- |
|
Hexachlorobenzene |
0.000442 |
0.000478 |
0.000478 |
|
Beta-benzene
hexachloride |
0.000130 |
0.000140 |
0.000140 |
|
Gamma-benzene
hexachloride |
0.0000140 |
0.0000151 |
0.0000151 |
|
Contaminants present in CEPT / Secondary
Treated Effluent |
|||
|
Aluminium |
0.0000453 |
0.0000453 |
- |
|
Antimony |
0.00455 |
0.00456 |
0.00458 |
|
Barium |
0.0174 |
0.0175 |
0.0175 |
|
Chromium
III |
0.00000015 |
0.00000015 |
0.00000014 |
|
Copper |
0.00302 |
0.00324 |
0.00257 |
|
Lead |
0.00160 |
0.00161 |
- |
|
Nickel |
0.000150 |
0.000154 |
0.000145 |
|
Selenium |
0.0222 |
0.0223 |
0.0212 |
|
Silver |
0.00000729 |
0.00000750 |
0.00000617 |
|
Tin |
0.0000815 |
0.0000820 |
0.0000778 |
|
Vanadium |
0.000161 |
0.000164 |
0.000167 |
|
Zinc |
0.00497 |
0.00500 |
0.00484 |
|
Ammonia |
0.000233 |
0.000245 |
0.000113 |
|
Dioxins
and Furans |
0.0242 |
0.0242 |
0.0238 |
|
Toluene |
0.0000717 |
0.0000775 |
- |
|
Diazinon |
0.00000097 |
0.00000105 |
0.00000126 |
|
Malathion |
0.00000001 |
0.00000002 |
0.00000001 |
|
Total HI |
0.0795 |
0.0800 |
0.0757 |
8.57
As seen in Tables
8.58 While the assessment focuses on assessing the potential risks/impacts to ecological resources due to chronic exposure to the contaminants produced in the disinfection process in the HATS effluent discharge, cumulative impact of the possible C/D effluent discharge from Tai Po/Shatin Sewage Treatment Works (TP/ST STW) and Pillar Point Sewage Treatment Works (PPSTW) has been considered and evaluated.
8.59 Results of water quality modelling showed that the effluent plume from SCISTW, TP/ST STW and PPSTW would not overlap each other. The results indicated that contaminants discharged from TP/ST STW and PPSTW would not significantly contribute to the concentration of CBPs at the edge of ZID, edge of mixing zone (of the effluent plume from SCISTW) and the Tsuen Wan beaches. Therefore, effluent discharged from the TP/ST STW would not induce cumulative impact with the C/D effluent from SCISTW.
8.60 The evaluation above is further supported by the findings of approved EIA Study for Tai Po Sewage Treatment Works - Stage V. The EIA Study for TPSTW Stage V indicated that the impact from the TPSTW and STSTW effluent would be very localized and confined within the Kai Tak Approach Channel and the existing Kwun Tong Typhoon Shelter. The effluent plume from SCISTW and TPSTW/STSTW would not overlap with each other.
8.61 A description of the assumptions associated with the ERA – Aquatic Life is presented below.
· For each COC, the maximum effluent concentration and the maximum background concentration are used to calculate the COC concentration at exposure point. This conservative approach yielded higher estimated risk than using mean concentrations.
· It is assumed that after the effluent is discharged, COCs in the effluent would only have their concentrations decrease as a result of dilution and dispersion. It is a conservative approach because COCs concentrations in the water column would also decrease because of different mechanisms such as degradation and / or volatilization.
· While calculating the risk to aquatic life at edge of mixing zone, the aquatic organisms are assumed to live their entire lives at the mixing zone. For planktonic and pelagic organisms that are mobile or migratory (e.g. zooplankton, fish), this assumption would overestimate the risk. In addition, some organisms may exhibit avoidance behaviour toward some chemicals, and their home range may extend beyond the mixing zone.
· Since a list of “regulated CBPs in sewage effluent” is not available locally or overseas, the COPC identification is based on literature search of documented potential CBPs[5] and regulatory practice of chlorinated organic substances in drinking water/sewage effluent[6]. This approach is conservative, as it may include chemicals that actually are not produced as COPC by chlorination of HATS effluent, as reflected by the fact that most of the identified COPC are not detected in C/D effluent. Nevertheless, for the purposes of the risk assessment, a concentration equivalent to half of the analytical detection limit of each undetected COC is adopted in the risk calculation. This conservative approach serves to counter the possibility that some chemicals from chlorination of HATS effluent may be present but are not included as a COPC in the risk calculation. Overall, in line with common practice, this approach to COPC identification is considered sufficiently comprehensive to assess the potential risk to ecological resources.
· The COC concentrations of chlorinated/dechlorinated effluent are obtained from a number of bench scale process simulating the C/D treatment using a higher hypochlorite dosage (higher than the dosage in actual full-scale process implementation) to provide conservatism.
· Dilution factor estimated by water quality modelling is used to predict the COC dispersion in water and the COC concentrations at exposure points. Computer models are sophisticated tools used to simulate mother-nature, and uncertainties inherent in these models have been minimized by vigorous model calibration and verification.
· The total hazard index to aquatic life is determined by summing COC-specific hazard quotients that are calculated utilizing TRVs based on different effects, toxicity endpoints and/or exposure durations. This approach to calculate hazard index is a well-established practice for risk characterization, which has been adopted in similar ecological risk assessments internationally. In addition, the compliance of acute and chronic toxicity water quality criteria suggests that the potential risk due to C/D HATS effluent imposed to aquatic life would be acceptable.
8.62 A description of the assumptions associated with the ERA – Marine Mammals is presented below.
· For each COC, the maximum effluent concentration and the maximum background concentration are used to calculate the COC concentration at exposure point. This conservative approach yields higher estimated risk than using mean concentrations.
· It is assumed that after the effluent is discharged, COCs in the effluent would only have their concentrations decrease as a result of dilution and dispersion. It is a conservative approach because COCs concentrations in the water column would also decrease because of different mechanisms such as degradation and / or volatilization.
· Calculated COC concentration in preys of marine mammals are based on the bioconcentration factors derived primarily from laboratory experiments in which test animals are continuously exposed to relatively high concentration of COCs. In the marine environment, exposures to relatively high concentration of COCs are probably limited to areas immediately adjacent to the outfall. These laboratory tests are therefore conservative in deriving the bioconcentration factors for preys living in the open sea.
·
The area use factors for dolphin (0.25) and
porpoise (0.15) adopted from Montgomery Watson (1998) are considered to be
conservative in view of their wide home range[7],
relative small area size of the ZID (less than
· Since a list of “regulated CBPs in sewage effluent” is not available locally or overseas, the COPC identification is based on literature search of documented potential CBPs and regulatory practice of chlorinated organic substances in drinking water/sewage effluent. This approach is conservative, as it may include chemicals that actually are not produced as COPC by chlorination of HATS effluent, as reflected by the fact that most of the identified COPC are not detected in C/D effluent. Nevertheless, for the purposes of the risk assessment, a concentration equivalent to half of the analytical detection limit of each undetected COC is adopted in the risk calculation. This conservative approach serves to counter the possibility that some chemicals from chlorination of HATS effluent may be present but are not included as a COPC in the risk calculation. Overall, in line with common practice, this approach to COPC identification is considered sufficiently comprehensive to assess the potential risk to ecological resources.
· The COC concentrations of chlorinated/dechlorinated effluent are obtained from a number of bench scale process simulating the C/D treatment using a higher hypochlorite dosage (higher than the dosage in actual full-scale process implementation) to provide conservatism.
· Dilution factor estimated by water quality modelling is used to predict the COC dispersion in water and the COC concentrations at exposure points. Computer models are sophisticated tools used to simulate mother-nature, and uncertainties inherent in these models have been minimized by vigorous model calibration and verification. Also, the approach of using 10%tile dilution factor[9] for risk calculation is a conservative approach that provides conservative risk estimates.
· Toxicity data specific to the dolphin or porpoise are not available. Therefore, toxicity data for surrogate species are used to derive toxicity reference dose (TRD) for hazard quotient calculation in the risk assessment. The use of toxicity data for surrogate species[10] may induce uncertainties. However, it should be noted that safety factors (from 0.0125 to 0.125[11]) are applied in the course of derivation of TRD to provide conservatism.
· Much of the information on the estimated fraction of fish and shellfish consumed by the dolphin and porpoise is based on data from stranded animals. Since stranded dolphins and/or porpoises are usually sick and stressed, they may not consume food in the same quantity or proportions as unstressed animals. Therefore, the type of food found in their stomachs may not be representative of the typical diet taken by active healthy animals. In addition, stomach contents are usually at least partially decomposed, making it very difficult to identify accurately the organisms that are consumed. Nevertheless, the fish / shellfish consumption fraction is estimated based on the best available data, which is an established practice for assessment of this kind.
·
Ingestion rates (
8.63 In summary the ecological risk assessment for aquatic life and marine mammals by design is very protective of ecological resources by overstating potential exposures and risks. Conservative assumptions made in the risk assessment include (i) adopting maximum effluent concentration and background seawater concentration for risk calculation; (ii) assuming COCs in effluent would only have their concentrations decrease as a result of dilution and dispersion; (iii) applying conservative exposure parameters (i.e. assumes aquatic life live their entire lives at the mixing zone and assumes conservative area use factor for marine mammals). Despite uncertainties involved in some aspects of the risk assessment, conservative treatments (e.g. applied safety factors in derivation of toxicity reference dose) are applied where appropriate. The ecological risk assessment represents the most useful tool that can be used to determine and protectively manage the risk to ecological resources. It is considered that the ecological risk assessment overall provided a conservative estimate of risk level and would not underestimate the risk.
8.64 The above ecological risk assessment (with supplementation of WETT results) indicated that calculated risks of all scenarios are found to be acceptable under the established criteria. In view that the inherent conservative ecological risk assessment indicated acceptable ecological risk levels, no residual impact from the Project on ecological resources would be anticipated.
8.65 Dechlorination process was incorporated into the effluent disinfection process to remove TRC and reduce formation of CBPs. As discussed above, there would be no unacceptable ecological risk induced by the Project and therefore no mitigation measures would be required.
8.66 It is recommended to establish a monitoring programme to determine whether the Project would induce increase of concentration of potential CBPs and other contaminants in seawater and to verify the predictions of the risk assessment. Details of the programme are provided in a stand-alone EM&A Manual.
8.67 A detailed risk assessment has been conducted to assess the potential adverse ecological effects that may result from exposure of toxic substances due to HATS effluent discharge. The findings are summarized below:
8.68 According to the findings of Ecological Risk Assessment – Aquatic Life, potential risk to aquatic life due to CBPs present in C/D HATS effluent would be lower than the screening value and considered acceptable. Cumulative risk assessment revealed that CBPs and other pollutants present in the C/D HATS effluent, together with the pollutants present in the ambient water, may induce a total hazard index level above the screening value of 1.0. It is noted that hazard index to aquatic life due to pollutants present in the background already exceeds the screening value. Effluent discharge from SCISTW would only induce low incremental risk (i.e. hazard quotient < 1) at edge of mixing zone for all pollutants considered, indicating that concentration of CBPs and pollutants would be complied with available local/overseas water quality standards at the edge of mixing zone.
8.69 According to USEPA (2005), the calculated HI exceeding the screening value would not indicate that the proposed action is not safe or that it presents an unacceptable risk. Rather, it triggers further investigation. Further investigation is carried out based on the results of WETT, which is able to assess the impacts caused by aggregate toxic effects of the mixture of pollutants in effluent.
8.70 Results of WETT on C/D effluent are used to supplement the findings of ERA – Aquatic Life and determine whether the C/D effluent would induce adverse effects to aquatic life. Statistical analysis of WETT data revealed that C/D process does not induce additional toxicity to the sewage effluent. Also, it is found that the established toxicity criteria are well complied with at both edge of ZID and edge of mixing zone in all Project Scenarios. With the comfortable margin (about 4/5 of the toxicity criteria value) to the established toxicity criteria, it is expected that the aquatic life present in the receiving water would not experience unacceptable toxicity even taking into account the background seawater conditions. This is supported by the assessment results that concentration of all COCs would be complied with available local/overseas water quality standards at the edge of mixing zone. Therefore, the potential risks due to C/D effluent imposed to aquatic life are expected to be acceptable.
8.71 Results of Ecological Risk Assessment – Marine Mammals indicated that potential risk to marine mammals due to CBPs present in C/D HATS effluent would be lower than the screening value and considered acceptable. Cumulative risk assessment revealed that CBPs and other pollutants present in the C/D HATS effluent in all the 3 Project Scenarios (Hazard Index from 0.126 to 0.129 for dolphins; Hazard Index from 0.0757 to 0.0800 for porpoises) would also be lower than the screening level and considered acceptable.
8.72 According to the risk assessment results, the Project would not cause unacceptable risk to ecological resources. Therefore, the Project is considered to be environmentally acceptable in terms of risks/impacts to marine ecological resources.
1.
ALS Technichem (HK) Pty Ltd
(2005). Testing of
Chlorinated/Dechlorinated CEPT Effluent from
2. CDM (2004). Environmental and Engineering Feasibility Assessment Studies in Relation to the Way Forward of the Harbour Area Treatment Scheme – Working Paper No. 8 Ecological and Human Health Risk Assessment (Final).
3. Centre for Coastal Pollution and Conservation (2001). Consultancy Study on Fisheries and Marine Ecological Criteria for Impact Assessment (Agreement No. CE 62/98).
4.
CityU Professional Services
Limited (2005). Testing of
Chlorinated/Dechlorinated Sewage Effluent from Tai
5. ERM (2005). Detailed Site Selection Study for a Proposed Contaminated Mud Disposal Facility within the Airport East/East of Sha Chau Area. Environmental Impact Assessment (EIA) and Final Site Selection Report.
6.
MCAL (2004). Tai
7.
8. USEPA (1986). Guidelines for the Health Risk Assessment of Chemical Mixtures.
9. USEPA (1991). Technical Support Document for Water Quality-based Toxics Control.
10. USEPA (2005). Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities.
[1] The 25 pollutants are regulated in NPDES due to their
presence in industrial effluent but not their possible generation in
chlorination process. However, a
conservative approach is adopted to study all these regulated chlorinated
organic substances, which are documented as potential CBPs, in
[2] The NPDES permit program controls water pollution by
regulating point sources that discharge pollutants into water of the
[3] HQ is the measure of health hazard due to exposure of a COC whereas HI
is the measure of health hazard due to exposure of all identified COCs, which
is calculated by summing the HQs of all identified COCs.
[4] “Acute-to-Chronic Ratio” (ACR) is
the ratio of the acute toxicity of an effluent to its chronic toxicity. ACR expresses the relationship between
the concentration of whole effluent toxicity causing acute toxicity to a
species and the concentration of whole effluent toxicity causing chronic
toxicity to the same species. An
ACR is commonly used to extrapolate to a “chronic toxicity” concentration using
exposure considerations and available acute toxicity when chronic toxicity data
for the species of concern are unavailable.
[5] Some of the documented potential
CBPs were generated by applying very high chlorine dose (in the order of
hundreds or thousands mg/L) to sewage effluent, which would not occur in the
HATS scenario.
[6] Regulation of chlorinated organic
substances was due to their presence in industrial effluent but not their
possible generation in chlorination process.
[7] The dolphins were observed from northern, western and southwestern
[8] Less than 3 dolphin individuals per
100km2 were recorded in Western Buffer Water Control Zone within 3
years surveying effort (refers to Section 9 for details).
[9] The 10%tile dilution factor is
exceeded 90% of the time
[10] Details of the TRD derivation (including the surrogate
species used) are presented in Appendix 8.5.
[11] The use of safety factors (from
0.0125 to 0.125) reduced the derived TRD by 8 to 80 times.