TABLE OF CONTENTS

Page

13........ HEALTH IMPACT. 13-2

13.1..... Introduction. 13-2

13.2..... Literature Review for Environmental Legislation, Standards and Guidelines. 13-2

13.3..... Development of Conceptual Model 13-5

13.4..... Hazard Identification. 13-5

13.5..... Exposure Assessment 13-18

13.6..... Exposure Response Relationship. 13-24

13.7..... Risk Characterization. 13-25

13.8..... Reuse of Effluent Water 13-31

13.9..... Radon. 13-32

13.10... Uncertainty Analysis. 13-33

13.11... Risk Control and Management 13-34

13.12... Conclusion. 13-35

13.13... References. 13-36

LIST OF TABLES

Table 13.1 TAPs from Criteria Air Pollutants of HKAQOs. 13-7

Table 13.2 TAP Considered in Various STW-related Literature and Guidelines. 13-7

Table 13.3 Basis of the Toxicity Values from Various Standards / Guidelines. 13-10

Table 13.4 Toxicity Criteria of the Non-carcinogenic Risk Assessment of the Identified TAPs. 13-10

Table 13.5 Toxicity Criteria of Carcinogenic Risks of the Identified TAPs. 13-12

Table 13.6 List of Detectable TAPs. 13-14

Table 13.7 List of Non-detectable TAPs. 13-15

Table 13.8 Summary of short-listed TAPs for Non-Carcinogenic Risk Assessment 13-16

Table 13.9 Summary of short-listed TAPs for Carcinogenic Risk Assessment 13-18

Table 13.10 Representative HRs in the vicinity of Relocated STSTW for Operational Health Impact Assessment 13-19

Table 13.11 Summary of Concentration Levels of Detectable TAPs at Emission Sources. 13-21

Table 13.12 Removal Efficiency of Deodourizer for Different TAPs. 13-22

Table 13.13 Summary of Maximum Incremental Concentration of TAPs with Non-carcinogenic Risk Level 13-24

Table 13.14 Background Concentration of Criteria Pollutants from PATH Model 13-26

Table 13.15 Background TAPs Concentrations. 13-28

Table 13.16 Maximum Predicted Cumulative Annual Average Concentrations of TAPs. 13-28

Table 13.17 Maximum Predicted Cumulative Hourly Average Concentrations of TAPs. 13-29

Table 13.18 Cancer Risk Guidance. 13-30

Table 13.19 Total Incremental Cancer Risk due to the Identified TAPs. 13-30

Table 13.20 Indoor Air Quality Objectives for Office and Public Places. 13-32

Table 13.21 Potential Accidental Events and Preventive Measures. 13-34

List of DIAGRAMS

Diagram 13.01 Detailed UK Format for Health Risk Assessment Conceptual Process. 13-4

Diagram 13.02 Schematic Flow of Treatment Process for Relocated STSTW.. 13-6

LIST OF FIGURES

60334056/EIA/13.01 Potential Hukman Receptors for Health Impact From kRelocated STSTW

LIST OF APPENDICES

Appendix 13.01 Review of TAP Toxicity Values

Appendix 13.02 TAP Carcinogenic Effect and Classification

Appendix 13.03 Summary of TAP Analysis and Emission Inventory

Appendix 13.04 Report of TAPs Sampling and Analysis for Concentration

Appendix 13.05 Report of TAPs Sampling and Analysis for Emission Rate

Appendix 13.06 (a to dd) Calculation of Emission Rate of CSTW

Appendix 13.07 (a to c) Predicted Incremental Annual/Hourly Average Concentration Levels of TAPs at Human Receptors due to CSTW

Appendix 13.08 (a to v)Predicted Cancer Risk of TAPs at Human Receptors

13 HEALTH IMPACT

13.1 Introduction

13.1.1.1 This section presents the framework for assessing potential health impact on the adjacent population in relation to Toxic Air Pollutants (TAPs) emissions associated with activities during the operation of the CSTW and the assessment findings.

13.1.1.2 With reference to Section 3.4.10.2 of the EIA Study Brief No. ESB-273/2014 for this Project, the Health Impact Assessment (HIA) shall cover the following aspects:

· TAPs emissions associated with activities during the operation of the CSTW; and

· Effluent reuse activities.

13.1.1.3 It should be noted that some TAPs may have malodorous properties at concentrations below those for toxic effects. However, the objective of this section is to assess the TAPs potential health impact against the toxicity criteria. Details of potential odour impact are addressed separately in Section 3 of this EIA Report.

13.2 Literature Review for Environmental Legislation, Standards and Guidelines

13.2.1 United Kingdom (UK) and European Union (EU) Guidance

13.2.1.1 The UK Department of Environment, Food, and Rural Affairs (DEFRA) under its previous name Department of Environment Transport and Regions (DETR) published definitive Guidelines for Environmental Risk Assessment and Management (refers to Diagram 13.01) in 2000.

Diagram 13.01 Detailed UK Format for Health Risk Assessment Conceptual Process

13.2.1.2 In Europe, this guidance also formed the foundation for the later guidance recommended by European Groundwater and Contaminated Land Remediation Information System (EUGRIS). The EUGRIS group represents 6 countries: Denmark, France, Germany, Hungary, Italy and United Kingdom, and it is coordinated by the Federal Environmental Agency of Germany. They have developed "Integrated Soil and Water Protection: Risks from Large Scale Diffuse Pollution" (EURIG-SOWA, 2005), which recommends utilizing the UK DEFRA guidance for health risk assessment.

13.2.1.3 More recently Scotland and Ireland have developed an updated version of the DEFRA/DETR 2000 document, which they have published as “Scotland & Northern Ireland Forum for Environmental Research” (SNIFFER, 2007) guide. Although it references locally specific regulations, it contains the same fundamental principles and structure.

13.2.1.4 In addition, World Health Organization (WHO) has also sponsored an effort to harmonize the various guidance documents for Human Health Risk Assessment (HHRA). In 2010 they have developed a Human Health Risk Assessment Toolkit: Chemical Hazards. It offers a simplified approach, when appropriate, for the local project situation.

13.2.2 USEPA Guidance

13.2.2.1 The USEPA has published many specific guidance documents for various aspects of HHRA following the landmark “Risk Assessment in the Federal Government: Managing the Process” (NRC, 1983) publication of the most fundamental guide to principles for practice in the US. Several US states such as California, Minnesota and Texas have also developed separate regulatory programs specific to various industrial systems and new facilities in their states, for which chemical emissions to the air, water or soil are of concern. The principal USEPA versions identified below are those that most closely resemble the UK DEFRA Guidelines (2000) detailed above.

13.2.2.2 The particular USEPA publications most relevant to HHRA for HIA use include:

a) “Risk Characterization Policy; Guidance for Cumulative Assessment, Part 1: Planning and Scoping” (USEPA, 1997a);

b) Risk Assessment Guidance for Superfund, or RAGS http://www.epa.gov/oswer/riskassessment/risk_superfund.htm) (USEPA, 1989a- current); and

c) The current chemical toxicity database system: IRIS, the Integrated Risk Information System (http://www.epa.gov/iris/ , 2015).

13.2.3 Approach Determination

13.2.3.1 All of these versions call for the following general steps for HHRA and require a staged approach as follows:

Stage 1: Development of Conceptual Model of the Site

Stage 2: Hazard Identification

Stage 3: Exposure Assessment

Stage 4: Exposure Response Relationship

Stage 5: Hazard / Risk Characterization and Assessment

Stage 6: Risk Control and Management

13.3 Development of Conceptual Model

13.3.1.1 In several previous EIA projects around the globe, including the UK, Israel, and Hong Kong (Integrated Waste Management Facilities EIA Report, EIA Study Brief No. ESB- 184/2008), a Conceptual Site Model (CSM) has been developed as an initial step. This step precedes the use of a predictive air quality model, such as the ISCST3 model, for detailed quantitative calculations of potential environmental air concentrations to support the advanced risk assessment. This quantitative analysis is performed after completion of the CSM, and upon agreement with the responsible agency on the results of the subsequent qualitative strategic review that determines which calculations are necessary and most appropriate.

13.4 Hazard Identification

13.4.1 General

13.4.1.1 The purpose of the hazard identification is to identify TAPs of potential concern for quantitative evaluation and to generate emissions estimates for non-carcinogenic (short- term (acute) and long-term (chronic)) and carcinogenic risks of exposure to the selected TAPs.

13.4.2 Sewage Treatment Process and Potential TAPs

13.4.2.1 As explained in Section 2 of this EIA Report, in order to meet the required effluent quality, the treatment process of biological treatment is proposed. The process of biological treatment for relocated STSTW is schematically illustrated in Diagram 13.02 below:

Diagram 13.02 Schematic Flow of Treatment Process for Relocated STSTW

13.4.2.2 As noted above, the preliminary plan for the disinfection stage for the relocated STSTW will utilize UV irradiation instead of sodium hypochlorite (NaOCl) or other forms of chlorine. Because this avoids additional, but manageable, hazards of fugitive chlorine gas exposures to the public, chlorine gas related hazards were not included in this study. Only certain chlorinated chemical compounds, such as chloroform, were considered in the assessment due to reported presence and potential discharge of such compounds (of unknown origin) from the incoming raw sewage.

13.4.2.3 As explained in Section 2 of this Report, no anaerobic digestion with digesters are proposed inside caverns owing to fire safety and health concerns. With anaerobic digestion for the sludge treatment eliminated, the essential condition for the production of methane, i.e. a consistent anaerobic environment, would no longer exist, and therefore methane was excluded from this study.

13.4.2.4 Under normally controlled conditions, remaining organic matter entering any of the tanks (and forming sludge) can be decomposed by micro-organisms aerobically. The resultant products are primarily carbon dioxide and water:

Organic matter + oxygen → energy + carbon dioxide + water

13.4.2.5 When the organic load exceeds the carrying capacity of oxygen within the water, oxygen is not available for aerobic digestion. If seawater is used as the alternative source of oxygen for anaerobic digestion by micro-organisms, sulphate in the seawater can react with the organic matters to produce hydrogen sulphide. Organic-rich sediments act as a substrate for the action of sulphate-reducing bacteria (SRBs), which reduce sulphate in the absence of oxygen. Organic sulphur compounds, such as mercaptans, can also intensify any odours from hydrogen sulphide in a similar process:

Organic matter + sulphate → energy + hydrogen sulphide (H2S) + water

Organic matter with sulphide → energy + mercaptans + water (minor pathway)

13.4.2.6 Both hydrogen sulphide and mercaptans contribute to odour. In upset conditions, indoor exposures to trapped H₂S can potentially give rise to health effect to humans.

13.4.2.7 Incoming raw sewage are products of various daily activities like flushing and cleaning and therefore have complicated composition and may carry many different chemicals, which is also a source of TAPs. However, the concentration is believed to be very low as they were diluted by the flushing water or tap water.

13.4.3 Literature Review for Chemicals of Potential Concern (COPC)

13.4.3.1 A literature search for the published list of TAPs was carried out from various sources including:

· EPD of HKSAR government published criteria air pollutants specified under the AQOs;

· EPD published technical memorandum under the APCO (Cap.311); and

· USEPA published list of Hazardous Air Pollutants (HAPs) under the Clean Air Act, 1990.

13.4.3.2 The criteria air pollutants for which standards are specified under the AQOs in Hong Kong include sulphur dioxide, respirable suspended and fine suspended particulates, nitrogen dioxide, ozone, carbon monoxide and lead. These criteria air pollutants are regarded as indicators of air quality in Hong Kong and continuously monitored by EPD.

13.4.3.3 Of these criteria air pollutants, respirable suspended and fine particulates are normally generated from human activities such as the burning of fossil fuels in vehicles and other combustion activities. To minimize fire risks in caverns, no combustion activities would be allowed within the caverns. The operation of vehicles would be minimal and limited to that required for sludge delivery and staff transport only. For the above reasons, respirable suspended and fine particulates were not considered further in this study.

13.4.3.4 Ozone is mainly formed by photochemical reactions in the atmosphere in daylight. As the UV disinfection for the relocated STSTW would be conducted in water using UV lamps designed to minimize ozone generation (e.g. with doped quartz sleeves to restrict UV wavelengths favourable for ozone formation), the production of ozone (O₃) would be negligible, and therefore ozone was not covered in this assessment.

13.4.3.5 The major source of heavy metals in the ambient air is from the traffic vehicles with combustion of fossil fuels. The heavy metals detected in air samples are bound to particulate matters. As discussed in the paragraph above, there is no combustion activities allowed inside the caverns and the use of vehicles in the relocated cavern STW is limited and should not be a concern. Hence, the heavy metals were not considered further in this assessment.

13.4.3.6 Therefore, three criteria air pollutants of Hong Kong’s AQOs, namely sulphur dioxide, nitrogen dioxide and carbon monoxide, were selected for further assessment as shown in Table 13.1.

Table 13.1 TAPs from Criteria Air Pollutants of HKAQOs

Item	Chemical	Source
1	Sulphur dioxide	Criteria air pollutants
2	Nitrogen dioxide	Criteria air pollutants
3	Carbon monoxide	Criteria air pollutants

13.4.3.7 Apart from the criteria pollutants, a number of TAPs would be emitted from the operation of relocated STSTW. Relevant literatures as published since 1980 on STW were also selected for review. These literatures cover various countries including United States, New Zealand, United Kingdom, Japan, France, and Canada. Table 13.2 presents a summary of the review results with the TAPs as studied in these STW-related literatures and relevant guidelines as described in Section 13.4.3.1.

Table 13.2 TAP Considered in Various STW-related Literature and Guidelines

Item	Chemical	USEPA ^[NOTE1]	HKEPD ^[NOTE2]	Group of Species	Reference Study/ Literature in Section 13.13.1
4	Hydrogen sulphide			Inorganic compound	[1]-[4], [7]-[10], [12], [15]-[19], [22]-[24], [25]
5	Ammonia			Inorganic compound	[1]-[3], [7], [9], [12], [15]-[16], [18], [21], [23]-[24], [25]
6	Dimethyl sulphide			Organosulfur compound	[10], [12], [15], [17], [18], [24]
7	Diethyl sulphide			Organosulfur compound	[16]
8	Acetone			Ketone	[5], [6], [8]
9	Butanone (Methyl ethyl ketone)			Ketone	[8], [11], [13]
10	Acetaldehyde	√		VOCs	[2], [7], [24]
11	Benzene	√	√	VOCs	[5], [13], [22], [26]
12	Carbon disulphide	√		VOCs	[16], [17]
13	Carbon tetrachloride	√	√	VOCs	[26]
14	Chlorobenzene	√		VOCs	[5], [26]
15	Chloroform	√	√	VOCs	[5], [6], [22], [26]
16	Formaldehyde	√	√	VOCs	[12]
17	Hexane (or n-hexane)	√		VOCs	[11]
18	Methanol	√		VOCs	[2]
19	Methyl chloride (Chloromethane)	√		VOCs	[22]
20	Methyl chloroform (1,1,1-Trichloroethane)	√		VOCs	[26]
21	Methylene chloride (Dichloromethane)	√	√	VOCs	[6], [22]
22	Styrene	√		VOCs	[6], [24]
23	1,1,2,2-Tetrachloroethane	√	√	VOCs	[22]
24	Tetrachloroethylene (Perchloroethylene)	√		VOCs	[5], [22]
25	Toluene	√		VOCs	[5], [6], [11], [13], [22], [26]
26	1,2,4-Trichlorobenzene	√		VOCs	[26]
27	1,1,2-Trichloroethane	√		VOCs	[5]
28	Trichloroethylene	√	√	VOCs	[26]
29	Xylenes (isomers and mixture)	√		VOCs	[13], [22], [26]
30	Methyl mercaptan (Methanethiol)			VOCs	[2], [8], [10], [15], [17], [18]
31	Ethyl mercaptan (Ethanethiol)			VOCs	[2], [8], [10], [16], [18], [25]
32	1,2-Dichloroethane			VOCs	[26]
33	Ethylbenzene			VOCs	[26]
34	a-Pinene			VOCs	[13]
35	n-Decane			VOCs	[13]
36	d-Limonene			VOCs	[13]
37	Terpenes			VOCs	[18]
38	o-Dichlorobenzene (1,2-Dichlorobenzene)			VOCs	[22], [26]
39	m-Dichlorobenzene (1,3-Dichlorobenzene)			VOCs	[22], [26]
40	p-Dichlorobenzene (1,4-Dichlorobenzene)			VOCs	[22], [26]
41	Naphthalene	√		PAHs	[27]
42	Benzo(a)Pyrene		√	PAHs	[27]
43	Acenaphthylene			PAHs	[27]
44	Acenaphthene			PAHs	[27]
45	Fluorene			PAHs	[27]
46	Phenanthrene			PAHs	[27]
47	Anthracene			PAHs	[27]
48	Fluoranthene			PAHs	[27]
49	Pyrene			PAHs	[27]
50	Benz(a)anthracene			PAHs	[27]
51	Chrysene			PAHs	[27]
52	Benzo(b)fluoranthene			PAHs	[27]
53	Benzo(k)fluoranthene			PAHs	[27]
54	Indeno (1,2,3-cd)pyrene			PAHs	[27]
55	Dibenz(a,h)anthracene			PAHs	[27]
56	Benzo(g,h,i)perylene			PAHs	[27]

Notes:

[NOTE1] USEPA published list of Hazardous Air Pollutants under the Clean Air Act, 1990

[NOTE2] HKEPD published technical memorandum under the Air Pollution Control Ordinance (Cap.311)

13.4.3.8 The review of STW-related literature and guidelines as described above have identified total 56 nos. TAPs. These 56 nos. TAPs, as summarized in Table 13.1 and Table 13.2 above, has established the initial long TAP list for further quantitative evaluation.

13.4.4 Literature Review for Toxicity Values

13.4.4.1 The purpose of this review is to identify the types of adverse health effects a TAP may potentially cause, and to define the relationship between the concentration of a TAP and the likelihood or magnitude of an adverse health effect (response). Adverse health effects are typically characterized in the health risk assessment as non-carcinogenic health risk, which includes the chronic hazard related to long-term average exposure and acute hazard related to short-term exposure, as well as the carcinogenic health risk.

13.4.4.2 In reference to the chemical summary of USEPA, the chronic health hazard assessment for non-carcinogenic effects could be divided into both chronic inhalation exposure and chronic oral exposure. Since the general public (including visitors) would be restricted from direct contact with the sewage within the sewage treatment works or pumping stations, direct oral exposure by Human Receptors (HRs) is almost impossible to happen. Given the physicochemical characteristics of the TAPs and relatively low concentration, the deposited TAPs onto soil, water or plants (such as vegetables) are so minor that the indirect exposure through the ingestion of soil, water, or locally raised products (beef, dairy, pork and poultry products) are negligible. Therefore, further evaluation of carcinogenic and non-carcinogenic health risks posed by the inhalation exposure to these TAPs shall be undertaken.

13.4.4.3 For carcinogenic health risk, it is measured as the increase in the number of cases of cancer per million populations that is attributable to a TAP. The inhalation risk is expressed as an “inhalation unit risk (IUR)”, defined as the risk of developing cancer if a person is continuously exposed to a unit concentration (usually presented as 1 µg/m³) for a life time of 70 years.

13.4.4.4 For non-carcinogenic health risk, it is measured using an “inhalation reference concentration” (RfC), which is defined as an estimate of a continuous inhalation exposure to a chemical that is likely to be without risk of deleterious noncancer effect. In terms of the exposure duration, the RfC values are divided into chronic RfC for long-term exposure duration (i.e. over one year) and acute RfC for short-term exposure duration (i.e. over 1 hour).

13.4.4.5 To determine the toxicity values (IUR and RfC) for these identified TAPs in Section 13.4.3, various guidelines from international to local were reviewed. With reference to the Health Impact Assessment of the Expansion of Hong Kong International Airport to a Three-Runway System (3RS) (AEIAR-185/2014) in selection of toxicity values, the following hierarchy is established to determine the acceptable values for this assessment:

Worldwide Level:

· WHO

Country Level:

· USEPA’s Integrated Risk Information System (IRIS) (https://cfpub.epa.gov/ncea/iris2/atoz.cfm)

· Agency for Toxic Substances and Disease Registry (ATSDR) under United States Department of Health and Human Services

Local Level:

· Reference exposure levels (RELs) established by Office of Environmental Health Hazard Assessment (OEHHA) under California Environmental Protection Agency (Cal/EPA)

13.4.4.6 The toxicity values for non-carcinogenic pollutants can only be applied if the exposure duration are specified. The basis of the toxicity values amongst different guidelines are different, as illustrated in Section 13.4.4.5. Table 13.3 summarizes the basis for various standards / guidelines:

Table 13.3 Basis of the Toxicity Values from Various Standards / Guidelines

Standards / Guidelines	Description
WHO	Typical averaging times are 24 hours for acute exposure and one year for chronic health effects. Some guideline values are for health effects with averaging time of 30 min for acute risk.
USEPA - IRIS	Based on the concentration of a chemical that one can breathe every day for a lifetime that is anticipated to cause harmful health effects. The chronic RfC is for concentration protective over 7 years.
USHHS - ATSDR	Minimal Risk Levels (MRLs) were developed by ATSDR as an estimate of the daily human exposure to a hazardous substance that is likely to be over a specified duration of exposure. MRLs are derived for acute (1-14 days) and chronic (365 days and longer) exposure durations for inhalation routes of exposure.
Cal/EPA - OEHHA	Reference Exposure Levels (RELs) were established by OEHHA as an estimate for health risk to humans. Exposure averaging time for acute RELs is 1 hour and chronic RELs are designed to address continuous exposure for up to a lifetime.

13.4.4.7 Appendix 13.01 shows the toxicity values of the identified 56 nos. TAPs and the determination of toxicity values in terms of the hierarchy system as described above. Table 13.4 and Table 13.5 summarize the toxicity values for non-carcinogenic and carcinogenic and risk assessment separately.

Table 13.4 Toxicity Criteria of the Non-carcinogenic Risk Assessment of the Identified TAPs

Item	Chemical	Group of Species	RfC for Chronic Risk Assessment (μg/m^3)	Standard / Guideline ^[1]	RfC for Acute Risk Assessment (μg/m^3) ^[2]	Standard / Guideline ^[3]
1	Sulphur dioxide	Criteria air pollutants	- ^[4]	-	20 (24 hr)	WHO
2	Nitrogen dioxide	Criteria air pollutants	40 (annual)	WHO	200 (1 hr)	WHO
3	Carbon monoxide	Criteria air pollutants	- ^[5]	-	30000 (1 hr)	WHO
4	Hydrogen sulphide	Inorganic compound	2	USEPA-IRIS	150 (24 hrs)	WHO
5	Ammonia	Inorganic compound	70	USHHA-ATSDR	1190	USHHS-ATSDR
6	Dimethyl sulphide	Organosulfur compound	-	-	-	-
7	Diethyl sulphide	Organosulfur compound	-	-	-	-
8	Acetone	Ketone	30863	USHHS-ATSDR	61725	USHHS-ATSDR
9	Butanone (Methyl ethyl ketone)	Ketone	5000	USEPA-IRIS	13000	Cal/EPD-OEHHA
10	Acetaldehyde	VOCs	9	USEPA-IRIS	470	Cal/EPD-OEHHA
11	Benzene	VOCs	10	USHHS-ATSDR	29	USHHS-ATSDR
12	Carbon disulphide	VOCs	700	USEPA-IRIS	100 (24 hrs)	WHO
13	Carbon tetrachloride	VOCs	100	USEPA-IRIS	1900	Cal/EPA-OEHHA
14	Chlorobenzene	VOCs	1000	Cal/EPA-OEHHA	-	-
15	Chloroform	VOCs	98	USHHS-ATSDR	488	USHHS-ATSDR
16	Formaldehyde	VOCs	100 ^[6]	WHO	49	USHHS-ATSDR
17	Hexane (or n-hexane)	VOCs	700	USEPA-IRIS	-	-
18	Methanol	VOCs	20000	USEPA-IRIS	28000^[7]	Cal/EPA-OEHHA
19	Methyl chloride (Chloromethane)	VOCs	90	USEPA-IRIS	1032	USHHS-ATSDR
20	Methyl chloroform (1,1,1-Trichloroethane)	VOCs	5000	USEPA-IRIS	10906	USHHS-ATSDR
21	Methylene chloride (Dichloromethane)	VOCs	600	USEPA-IRIS	3000 (24 hrs)	WHO
22	Styrene	VOCs	851	USHHS-ATSDR	21286 ^[8]	USHHS-ATSDR
23	1,1,2,2-Tetrachloroethane	VOCs	-	-	-	-
24	Tetrachloroethylene (Perchloroethylene)	VOCs	250	WHO	41	USHHS-ATSDR
25	Toluene	VOCs	3766 ^[9]	USHHS-ATSDR	7533	USHHS-ATSDR
26	1,2,4-Trichlorobenzene	VOCs	-	-	-	-
27	1,1,2-Trichloroethane	VOCs	-	-	-	-
28	Trichloroethylene	VOCs	2	USEPA-IRIS	-^[10]	-
29	Xylenes (isomers and mixture)	VOCs	870	WHO	8679	USEPA-IRIS
30	Methyl mercaptan (Methanethiol)	VOCs	-	-	-	-
31	Ethyl mercaptan (Ethanethiol)	VOCs	-	-	-	-
32	1,2-Dichloroethane	VOCs	2427	USHHS-ATSDR	700 (24 hrs)	WHO
33	Ethylbenzene	VOCs	22000	WHO	21699	USHHS-ATSDR
34	a-Pinene	VOCs	-	-	-	-
35	n-Decane	VOCs	-	-	-	-
36	d-Limonene	VOCs	-	-	-	-
37	Terpenes	VOCs	-	-	-	-
38	o-Dichlorobenzene (1,2-Dichlorobenzene)	VOCs	-	-	-	-
39	m-Dichlorobenzene(1,3-Dichlorobenzene)	VOCs	-	-	-	-
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	VOCs	60	USHHS-ATSDR	12017	USHHS-ATSDR
41	Naphthalene	PAHs	10	WHO	-	-
42	Benzo(a)Pyrene	PAHs	-	-	-	-
43	Acenaphthylene	PAHs	-	-	-	-
44	Acenaphthene	PAHs	-	-	-	-
45	Fluorene	PAHs	-	-	-	-
46	Phenanthrene	PAHs	-	-	-	-
47	Anthracene	PAHs	-	-	-	-
48	Fluoranthene	PAHs	-	-	-	-
49	Pyrene	PAHs	-	-	-	-
50	Benz(a)anthracene	PAHs	-	-	-	-
51	Chrysene	PAHs	-	-	-	-
52	Benzo(b)fluoranthene	PAHs	-	-	-	-
53	Benzo(k)fluoranthene	PAHs	-	-	-	-
54	Indeno (1,2,3-cd)pyrene	PAHs	-	-	-	-
55	Dibenz(a,h)anthracene	PAHs	-	-	-	-
56	Benzo(g,h,i)perylene	PAHs	-	-	-	-

Notes:

[1] The hierarchy in selecting reference standard for chronic risk is WHO > More Stringent Value from USEPA – IRIS and USHHS – ATSDR > CAL/EPA-OEHAA.

[2] The hierarchy in selecting the WHO averaging time for acute risk is WHO (1 hr) > WHO (24 hr) > WHO (8 hr). The guidance values for averaging time less than 1 hr (such as 15 min or 30 min) and 1 week are not adopted unless particularly specialised in the WHO guidance, e.g. formaldehyde have the 30 min guideline value but it is also applicable for long-term effects according to the guideline by WHO [note 6 below]).

[3] The hierarchy in selecting reference standard for acute risk is WHO > USHHS – ATSDR > CAL/EPA-OEHHA (no acute risk level from USEPA-IRIS).

[4] According to WHO Air Quality Guidelines, the air quality guideline values for sulphur dioxide are for averaging time of 1 hour and 10 min. Thus, the chronic risk level for averaging time of 1 year is not available.

[5] According to WHO Air Quality Guidelines for Europe, the air quality guideline values for carbon monoxide are for averaging time of 24 hour and 8 hours. Thus, the chronic risk level for averaging time of 1 year is not available.

[6] According to WHO Guideline for Indoor Air Quality (IAQ), the short-term (30-min) guideline of 0.1mg/m³ of formaldehyde will also prevent long-term health effects, including cancer.

[7] According to WHO (Environmental Health Criteria), the occupational exposure limit for methanol is 260 mg/m³ for an 8 hr working day. But the data is for comparison and reference only, data on human dermal exposure methanol is limited for establishment of guidance values.

[8] According to WHO Air Quality Guidelines for Europe, only odour detection threshold level of 70 µg/m³ was set as the air quality guideline for styrene. Hence it is not selected as acute RfC. The combined impact of all odorous chemicals was addressed in Section 3 of this EIA Report.

[9] According to WHO Air Quality Guidelines for Europe, the air quality guideline values for toluene are for averaging time of 1 week. Thus, the chronic risk level for averaging time of 1 year is not available.

[10] According to WHO, the air quality guideline value for trichloroethylene is a time-weighted average recommended by study group for reference. These values are varied from different nations without final conclusion. Thus the value is not adopted.

Table 13.5 Toxicity Criteria of Carcinogenic Risks of the Identified TAPs

Item	Chemical	Group of Species	IUR (μg/m^3)^-1	Standard / Guideline ^[1]
1	Sulphur dioxide	Criteria air pollutants	-	-
2	Nitrogen dioxide	Criteria air pollutants	-	-
3	Carbon monoxide	Criteria air pollutants	-	-
4	Hydrogen sulphide	Inorganic compound	-	-
5	Ammonia	Inorganic compound	-	-
6	Dimethyl sulphide	Organosulfur compound	-	-
7	Diethyl sulphide	Organosulfur compound	-	-
8	Acetone	Ketone	-	-
9	Butanone (Methyl ethyl ketone)	Ketone	-	-
10	Acetaldehyde	VOCs	2.2E-06	USEPA-IRIS
11	Benzene	VOCs	6.0E-06	WHO
12	Carbon disulphide	VOCs	-	-
13	Carbon tetrachloride	VOCs	6.0E-06	USEPA-IRIS
14	Chlorobenzene	VOCs	-	-
15	Chloroform	VOCs	2.3E-05	USEPA-IRIS
16	Formaldehyde	VOCs	1.3E-05	USEPA-IRIS
17	Hexane (or n-hexane)	VOCs	-	-
18	Methanol	VOCs	-	-
19	Methyl chloride (Chloromethane)	VOCs	-	-
20	Methyl chloroform (1,1,1-Trichloroethane)	VOCs	-	-
21	Methylene chloride (Dichloromethane)	VOCs	1.0E-08	USEPA-IRIS
22	Styrene	VOCs	-	-
23	1,1,2,2-Tetrachloroethane	VOCs	5.8E-05	OEHHA
24	Tetrachloroethylene (Perchloroethylene)	VOCs	2.6E-07	USEPA-IRIS
25	Toluene	VOCs	-	-
26	1,2,4-Trichlorobenzene	VOCs	-	-
27	1,1,2-Trichloroethane	VOCs	1.6E-05	USEPA-IRIS
28	Trichloroethylene	VOCs	4.3E-07	WHO
29	Xylenes (isomers and mixture)	VOCs	-	-
30	Methyl mercaptan (Methanethiol)	VOCs	-	-
31	Ethyl mercaptan (Ethanethiol)	VOCs	-	-
32	1,2-Dichloroethane	VOCs	2.6E-05	USEPA-IRIS
33	Ethylbenzene	VOCs	2.5E-06	OEHHA
34	a-Pinene	VOCs	-	-
35	n-Decane	VOCs	-	-
36	d-Limonene	VOCs	-	-
37	Terpenes	VOCs	-	-
38	o-Dichlorobenzene (1,2-Dichlorobenzene)	VOCs	-	-
39	m-Dichlorobenzene(1,3-Dichlorobenzene)	VOCs	-	-
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	VOCs	1.1E-05	OEHHA
41	Naphthalene	PAHs	3.4E-05	OEHHA
42	Benzo(a)Pyrene	PAHs	8.7E-02	WHO
43	Acenaphthylene	PAHs	-	-
44	Acenaphthene	PAHs	-	-
45	Fluorene	PAHs	-	-
46	Phenanthrene	PAHs	-	-
47	Anthracene	PAHs	-	-
48	Fluoranthene	PAHs	-	-
49	Pyrene	PAHs	-	-
50	Benz(a)anthracene	PAHs	1.1E-04	OEHHA
51	Chrysene	PAHs	1.1E-05	OEHHA
52	Benzo(b)fluoranthene	PAHs	1.1E-04	OEHHA
53	Benzo(k)fluoranthene	PAHs	1.1E-04	OEHHA
54	Indeno (1,2,3-cd)pyrene	PAHs	1.1E-04	OEHHA
55	Dibenz(a,h)anthracene	PAHs	1.2E-03	OEHHA
56	Benzo(g,h,i)perylene	PAHs	-	-

Note:

[1] The hierarchy in selecting standard / guideline is WHO > USEPA – IRIS > CAL/EPA-OEHAA (no IUR value from USHHS-ATSDR).

13.4.5 TAP Sampling and Laboratory Analysis

13.4.5.1 The characteristics of the sewage to be treated in the relocated STSTW should be similar to the existing scenario as the catchment remains the same and both facilities will adopt / adopted biological treatment process. The predicted source concentration levels of identified TAPs of sewage treatment facilities for the relocated STSTW therefore make reference to the TAPs concentration levels of treatment facilities in the existing STSTW. The treatment facilities include: open areas of inlet works, screening skips, primary sedimentation tanks, SBR tanks, aeration tanks, final sedimentation tanks, dewatered sludge skips at sludge dewatering house, influent and effluent channels of primary sedimentation tanks, mixed liquor channels for final sedimentation tanks, sludge holding tanks and overflow chambers of the digestion tanks, sludge transfer pumping station, covered surface of primary sedimentation tanks and the sludge dewatering house.

13.4.5.2 Sampling and testing were conducted at the facilities of existing STSTW to build the emission inventory of the TAPs. The findings of TAP analysis for ambient air concentrations are reported in Appendix 13.04, with emission rates results presented in Appendix 13.05.

13.4.5.3 Of those TAPs identified from literature review performed under Section 13.4.3, only 17 nos. TAPs can be detected, as shown in Appendix 13.03 and summarized in Table 13.6. The remaining non-detectable TAPs are believed to be either not exist or with concentration below the detection limit of the apparatus. Some of those detected TAPs have historically been associated with sewage treatment plants in general. These are thus expected to represent those compounds or groups of compounds for which regulatory permit limits may be applicable, whenever they appear to be the most toxic, prevalent, and persistent compounds in sewage treatment plants emissions.

Table 13.6 List of Detectable TAPs

Item	Chemical	Group of Species
1	Sulphur dioxide	Criteria air pollutants
2	Nitrogen dioxide	Criteria air pollutants
4	Hydrogen sulphide	Inorganic compound
5	Ammonia	Inorganic compound
6	Dimethyl sulphide	Organosulfur compounds
12	Carbon disulphide	VOCs
15	Chloroform	VOCs
18	Methanol	VOCs
21	Methylene chloride (Dichloromethane)	VOCs
24	Tetrachloroethylene (Perchloroethylene)	VOCs
25	Toluene	VOCs
28	Trichloroethylene	VOCs
29	Xylenes	VOCs
33	Ethylbenzene	VOCs
35	n-Decane	VOCs
36	d-Limonene	VOCs
41	Naphthalene ^[1]	PAHs

Note:

[1] Naphthalene is also a chemical compound of VOCs Group.

13.4.5.4 Of these detected TAPs, there are two air-quality related compounds (nitrogen dioxide and sulphur dioxide). Nitrogen dioxide and sulphur dioxide, which are criteria air pollutants of HKAQOs, have generally been found to be common in urban areas around the globe, are primarily the results of transportation, power generation and space heating combustion sources, rather than any direct association with wastewater treatment facilities. However, their inclusion in this assessment study may be useful for establishing their contribution to the “background” health risk situation in the vicinity of both the current and future facility operations.

13.4.5.5 The ammonia and hydrogen sulphide are the main sources of odour issues which may indirectly affect health, even if concentrations are below levels that could cause physical harm. If they or associated mercaptan odours are present at elevated “nuisance” levels, i.e. odour, they may promote public anxiety, which can be an emotional health issue. The combined impact due to various odorous chemicals are discussed in Section 3 of this EIA Report.

13.4.6 Screening of TAPs for Non-carcinogenic Effect

13.4.6.1 Appendix 13.03 presented a summary of TAP analysis for ambient concentrations and emission inventory. By reviewing the TAP analysis results for the detectable and undetectable TAPs, it is found that some VOCs, such as formaldehyde, acetaldehyde and benzene, were not detected at all sampling location. For most non-detectable TAPs, their measurement detection limits are far below the toxicity level for both chronic risk and acute risk, as shown in Table 13.7. It is thus concluded that the non-carcinogenic health effect from these TAPs are small as the detection limit is far below the standards.

Table 13.7 List of Non-detectable TAPs

Item	Chemical	Group of Species	Detection Limit (μg/m^3)	Chronic RfC (μg/m^3)	Acute RfC (μg/m^3)
3	Carbon monoxide	Criteria air pollutants	1	-	30000 (1 hr)
7	Diethyl sulphide	Organosulfur compounds	369	-	-
8	Acetone	Ketone	237	30863	61725
9	Butanone (Methyl ethyl ketone)	Ketone	295	5000	13000
10	Acetaldehyde	VOCs	36	9	470
11	Benzene	VOCs	3	10	29
13	Carbon tetrachloride	VOCs	6	100	1900
14	Chlorobenzene	VOCs	5	1000	-
16	Formaldehyde	VOCs	25	100	49
17	Hexane (or n-hexane)	VOCs	4	700	-
19	Methyl chloride (Chloromethane)	VOCs	2	90	1032
20	Methyl chloroform (1,1,1-Trichloroethane)	VOCs	6	5000	10906
22	Styrene	VOCs	4	851	21286
23	1,1,2,2-Tetrachloroethane	VOCs	7	-	-
26	1,2,4-Trichlorobenzene	VOCs	7	-	-
27	1,1,2-Trichloroethane	VOCs	1	-	-
30	Methyl mercaptan (Methanethiol)	VOCs	2	-	-
31	Ethyl mercaptan (Ethanethiol)	VOCs	3	-	-
32	1,2-Dichloroethane	VOCs	4	2427	700 (24 hrs)
34	a-Pinene	VOCs	6	-	-
37	Terpenes	VOCs	11	-	-
38	o-Dichlorobenzene (1,2-Dichlorobenzene)	VOCs	6	-	-
39	m-Dichlorobenzene(1,3-Dichlorobenzene)	VOCs	6	-	-
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	VOCs	6	60	12017
42	Benzo(a)Pyrene	PAHs	0.75	-	-
43	Acenaphthylene	PAHs	0.75	-	-
44	Acenaphthene	PAHs	0.75	-	-
45	Fluorene	PAHs	0.75	-	-
46	Phenanthrene	PAHs	0.75	-	-
47	Anthracene	PAHs	0.75	-	-
48	Fluoranthene	PAHs	0.75	-	-
49	Pyrene	PAHs	0.75	-	-
50	Benz(a)anthracene	PAHs	0.75	-	-
51	Chrysene	PAHs	0.75	-	-
52	Benzo(b)fluoranthene	PAHs	0.75	-	-
53	Benzo(k)fluoranthene	PAHs	0.75	-	-
54	Indeno (1,2,3-cd)pyrene	PAHs	0.75	-	-
55	Dibenz(a,h)anthracene	PAHs	0.75	-	-
56	Benzo(g,h,i)perylene	PAHs	0.75	-	-

13.4.6.2 The measurement detection limits of acetaldehyde, benzene and formaldehyde are 36 µg/m³, 3 µg/m³ and 25 µg/m³ respectively. These levels are close to the chronic reference exposure levels of 9 µg/m³ (acetaldehyde), 10 µg/m³ (benzene) and the acute reference exposure level of 49 µg/m³ (formaldehyde). Although it is likely that the new facility may emit similar concentration of these compounds as the existing STSTW, the concentrations of acetaldehyde, benzene and formaldehyde on HRs would be extremely low after a dilution and dispersion factor of approximately 0.126 (i.e. the minimum dispersion factor as derived from dispersion model and tabulated in Appendix 13.07b) upon being released to the ambient air and disperse to HRs from the ventilation shaft. Thus, the potential adverse non-carcinogenic health effects are expected to be within an acceptable risk range, if not negligible.

13.4.6.3 Of all the PAHs, only naphthalene was detected at the existing inlet works. Naphthalene is of both PAHs group and VOC group due to its chemical structure consisting only of a fused pair of benzene rings. The measured detection limit of all the PAHs is 0.75 µg/m³. However, there is no non-carcinogenic inhalation criteria identified in the cited references for the PAHs except for naphthalene. For most PAHs, they have low solubility in water and low volatility, and are therefore predominantly in solid state or suspended in liquid rather than in ambient air. It is thus reasonable to conclude that these PAHs will have no non-carcinogenic adverse health impact even though the exact concentration level or reference level is not available.

13.4.6.4 Of all the identified criteria air pollutants from HKAQOs, carbon monoxide was not detected. The measurement detection limit of carbon monoxide is 2,000 ppb (~ 2289 µg/m³) and this is already far below the chronic reference exposure level limit (10,000 µg/m³) and acute chronic reference exposure level limit (30,000 µg/m³). It is reasonable to conclude, therefore, that carbon monoxide will have no non-carcinogenic adverse health impact even though the exact concentration level is not available.

13.4.6.5 No ketones (acetone or butanone) were detected during site measurement. The measurement detection limit of acetone and butanone is 100 ppb (~ 237 µg/m³ for acetone and ~ 295 µg/m³ for butanone) and this is already far below the chronic reference exposure level (30,836 µg/m³ for acetone and 5,000 µg/m³ for butanone) and the acute reference exposure level (61,725 µg/m³ for acetone and 13,000 µg/m³ for butanone). It is thus reasonable to conclude that these ketones will have no non-carcinogenic adverse health impact even though the exact concentration level is not available.

13.4.6.6 It is thus expected that there are no significant emissions of these undetected pollutants from the existing sewage treatment works. This is because their concentrations are too low to be detected using available methodology. Even if they present at their detection limits, their concentrations would be too low to have non-carcinogenic effect. In light of these results, no adverse non-carcinogenic health effects from these undetected compounds are anticipated under this project.

13.4.6.7 Besides the undetectable TAPs, the 17 nos. detectable TAPs were also reviewed before the quantitative assessment is proceeded. Based on the summary results in Table 13.4, it is observed that there is no published non-carcinogenic risk level (RfC) for dimethyl sulphide, d-limonene or n-decane available from WHO, USEPA-IRIS, USHHS-ATSDR or Cal/EPA-OEHHA. Therefore, further evaluation of non-carcinogenic effect posed by the inhalation exposure to these four compounds is not possible. As a result, only fourteen TAPs, as a short-listed TAPs summarized in Table 13.8, are covered for further non-carcinogenic risk assessment.

Table 13.8 Summary of short-listed TAPs for Non-Carcinogenic Risk Assessment

Item	Chemical	Group of Species
1	Sulphur dioxide	Criteria air pollutants
2	Nitrogen dioxide	Criteria air pollutants
4	Hydrogen sulphide	Inorganic compound
5	Ammonia	Inorganic compound
12	Carbon disulphide	VOCs
15	Chloroform	VOCs
18	Methanol	VOCs
21	Methylene chloride (Dichloromethane)	VOCs
24	Tetrachloroethylene (Perchloroethylene)	VOCs
25	Toluene	VOCs
28	Trichloroethylene	VOCs
29	Xylenes	VOCs
33	Ethylbenzene	VOCs
41	Naphthalene ^[1]	PAHs

Note:

[1] Naphthalene is also a chemical compound of VOCs Group.

13.4.7 Screening of TAPs for Carcinogenic Effect

13.4.7.1 Unlike the non-carcinogenic effect, the carcinogenic effect is evaluated in terms of the accumulative incremental cancer risk contributed by inhalation exposure to each TAPs. There are 39 nos. of TAPs found to be undetectable. (Details as listed in Appendix 13.03). They may either not exist or exist in concentration below the detection limit of the apparatus. These TAPs, if exist, may also contribute to carcinogenic effect, although small.

13.4.7.2 As a conservative approach for the calculation of the accumulative carcinogenic risk, it is necessary to consider the possible existence of all TAPs even though they are undetectable. It has assumed that these undetected TAPs will exist in concentration equivalent to 50% of the detection limit, which represents an averaged value of all the undetectable TAPs as some may have concentrations close to the detection limit or far below the detection limit. This assumption is built to develop the emission rates profile for the TAPs of carcinogenic impact to humans.

13.4.7.3 Prior to the quantitative evaluation of the carcinogenic effect, the carcinogenic effect of these 56 nos. TAPs should be considered. The recommendation from International Agency for Research on Cancer (IARC) under WHO on the carcinogenicity classifications of these TAPs are adopted. There are 5 classifications defined by IARC, including

Group 1	Carcinogenic to humans
Group 2A	Probably carcinogenic to humans
Group 2B	Possibly carcinogenic to humans
Group 3	Not classifiable as to its carcinogenicity to humans
Group 4	Probably not carcinogenic to humans

13.4.7.4 The carcinogenic effect and classification of TAPs were reviewed, as described in Appendix 13.02. According to the classification from IARC, there are 16 nos. TAPs, such as toluene, sulphur dioxide, identified as Group 3, i.e. not classifiable as to its carcinogenicity to humans. Furthermore, there are no carcinogenic toxicity values (IUR) for these TAPs (except for 1,1,2-Trichloroethane) according to the summary in Table 13.4. Therefore, further carcinogenic risk assessment on these groups of TAPs is not necessary.

13.4.7.5 Meanwhile, there is no published carcinogenic toxicity values (IUR) for other 20 nos. of TAPs available from WHO, USEPA-IRIS, Cal/EPA-OEHHA, and none of these TAPs is classified as Group 1 carcinogenic chemical by IARC. Therefore, no further evaluation of carcinogenic effect is possible for these 20 nos. of TAPs.

13.4.7.6 Based on the detailed screening process in Section 13.4.7.4 and 13.4.7.5, a short-listed TAPs are summarized in Table 13.9 for further carcinogenic risk assessment.

Table 13.9 Summary of short-listed TAPs for Carcinogenic Risk Assessment

Item	Chemical	Group of Species	IUR (μg/m^3)^-1	Standard / Guideline ^[1]	IARC Group ^[2]
10	Acetaldehyde	VOCs	2.2E-06	USEPA-IRIS	Group 2B
11	Benzene	VOCs	6.0E-06	WHO	Group 1
13	Carbon tetrachloride	VOCs	6.0E-06	USEPA-IRIS	Group 2B
15	Chloroform	VOCs	2.3E-05	USEPA-IRIS	Group 2B
16	Formaldehyde	VOCs	1.3E-05	USEPA-IRIS	Group 1
21	Methylene chloride (Dichloromethane)	VOCs	1.0E-08	USEPA-IRIS	Group 2A
23	1,1,2,2-Tetrachloroethane	VOCs	5.8E-05	Cal/EPA-OEHHA	Group 2B
24	Tetrachloroethylene (Perchloroethylene)	VOCs	2.6E-07	USEPA-IRIS	Group 2A
28	Trichloroethylene	VOCs	4.3E-07	WHO	Group 1
32	1,2-Dichloroethane	VOCs	2.6E-05	USEPA-IRIS	Group 2B
33	Ethylbenzene	VOCs	2.5E-06	Cal/EPA-OEHHA	Group 2B
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	VOCs	1.1E-05	Cal/EPA-OEHHA	Group 2B
41	Naphthalene	PAHs	3.4E-05	Cal/EPA-OEHHA	Group 2B
42	Benzo(a)Pyrene	PAHs	8.7E-02	WHO	Group 1
50	Benz(a)anthracene	PAHs	1.1E-04	Cal/EPA-OEHHA	Group 2B
51	Chrysene	PAHs	1.1E-05	Cal/EPA-OEHHA	Group 2B
52	Benzo(b)fluoranthene	PAHs	1.1E-04	Cal/EPA-OEHHA	Group 2B
53	Benzo(k)fluoranthene	PAHs	1.1E-04	Cal/EPA-OEHHA	Group 2B
54	Indeno (1,2,3-cd)pyrene	PAHs	1.1E-04	Cal/EPA-OEHHA	Group 2B
55	Dibenz(a,h)anthracene	PAHs	1.2E-03	Cal/EPA-OEHHA	Group 2A

Notes:

[1] The hierarchy in selecting standard / guideline is WHO > USEPA – IRIS > CAL/EPA-OEHAA

[2] The group of carcinogenic risk is based on the classification of WHO International Agency for Research on Cancer (IARC), http://www.iarc.fr/.

13.5 Exposure Assessment

13.5.1 Identification of HRs

13.5.1.1 In accordance with Technical Memorandum of Air Pollution Control Ordinance (Cap.311), domestic premises, hotel, hostel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop, shopping centre, place of public worship, library, court of law, sports stadium or performing arts centre are considered as sensitive receptors, also known as HRs.

13.5.1.2 Populations in the vicinity of the Project have been identified as potential HRs. Due to a few public’s concern on the potential health impact on the local community, potential HRs outside the 500m study area are also identified to investigate the potential impact in a longer range.

13.5.1.3 In this assessment, it is assumed that the relocated STSTW will operate on a 24-hour-per-day schedule with continuous air exhaust from the ventilation shaft. For evaluating chronic effects from long- term exposure to air pollutants, the exposure period is usually at least one year according to the definition of “chronic” in USEPA-IRIS, USHHS-ATSDR and Cal/EPA-OEHHA as summarised in Appendix 13.01. Since visitors to the charity and recreational parks will not be subject to long-term exposure from air pollutants, it is considered appropriate to exclude these HRs (HR9, HR10 and HR 15) from chronic risk assessment. Although the exposure time for the staff of government office (HR19), hospital (HR11, HR12 and HR26) and industry (HR28) as well as the students of schools (HR2, HR3, HR4, HR7 and HR29) is around 8 hours per day and 5 days per week, the exposure duration will be long in terms of a job and education. Being a conservative approach, these HRs are included in chronic risk assessment.

13.5.1.4 Similar to long-term exposure, the non-carcinogenic effects posed by acute exposure of TAPs via inhalation pathway are determined by assessing the predicted TAPs concentrations at HRs (1-hr average concentration). Given the duration of acute exposure, all HRs are included for acute risk assessment.

13.5.1.5 The representative HRs have been identified and are given in Table 13.10 below. Their locations are illustrated in Figure No. 60334056/EIA/13.01.

Table 13.10 Representative HRs in the vicinity of Relocated STSTW for Operational Health Impact Assessment

HRs	Description	Land Use	Assessment Height Above Ground (mAG)	Shortest Distance from the Ventilation Shaft / Portal / Caverns (m)	Acute Risk	Chronic Risk
HR1	Chevalier Garden	Residential	1.5, 5, 10, up to 80 with 10m interval	810	√	√
HR1a	Chevalier Garden (Block 17)	Residential	1.5, 5, 10, up to 80 with 10m interval	800	√	√
HR1b	Chevalier Garden (Block 6)	Residential	1.5, 5, 10, up to 70 with 10m interval	870	√	√
HR1c	Chevalier Garden (Block 1)	Residential	1.5, 5, 10, up to 70 with 10m interval	810	√	√
HR2	Wellborn Kindergarten	Education	1.5, 5, 10, 20	800	√	√
HR3	Hay Nien Primary School	Education	1.5, 5, 10, 20, 30	940	√	√
HR4	Ma On Shan Tsung Tsin Secondary School	Education	1.5, 5, 10, 20, 30	970	√	√
HR5	Tai Shui Hang Village	Residential	1.5, 5, 10	1000	√	√
HR6	Block H, Kam Tai Court	Residential	1.5, 5, 10, up to 120 with 10m interval	1100	√	√
HR7	S.K.H. Ma On Shan Holy Spirit Primary School	Education	1.5, 5, 10, 20, 30	1130	√	√
HR8	Ah Kung Kok Fishermen Village	Residential / Retail	1.5, 5, 10	800	√	√
HR9	China Hong Kong Mountaineering and Climbing Union	Societal / Storage	1.5, 5, 10	800	√	-
HR10	Breakthrough Youth Village	Religion / Charity	1.5, 5, 10, 20, 30	420	√	-
HR11	Cheshire Home Sha Tin	Hospital	1.5, 5, 10, 20	530	√	√
HR12	The Neighbourhood Advice-Action Council Harmony Manor	Mental Health Hospital	1.5, 5, 10, 20	320	√	√
HR13	Shing Mun Springs Rehabilitation Centre	Rehabilitation Centre	1.5, 5, 10, 20	420	√	√
HR14	Mui Tsz Lam Village	Residential	1.5, 5, 10	1360	√	√
HR15	Ma On Shan Park / Promenade	Recreational Use	1.5	1180	√	-
HR16	Block F, Kam Tai Court	Residential	1.5, 5, 10, up to 120 with 10m interval	1200	√	√
HR17	Sausalito	Residential	1.5, 5, 10, up to 90 with 10m interval	1650	√	√
HR18	Ocean View	Residential	1.5, 5, 10, up to 100 with 10m interval	1970	√	√
HR19	Marine Police Outer Waters District Headquarters and Marine Police North Police Station	Government Office	1.5, 5, 10, 20	1720	√	√
HR20	Ah Kung Kok Fishermen Village	Residential	1.5, 5, 10	800	√	√
HR21	Seaview Villa	Residential	1.5, 5, 10	1730	√	√
HR22	Racecourse Gardens	Residential	1.5, 5, 10, up to 50 with 10m interval	1610	√	√
HR23	Pictoria Garden	Residential	1.5, 5, 10, up to 70 with 10m interval	1230	√	√
HR24	Kam On Garden	Residential	1.5, 5, 10	1860	√	√
HR25	Royal Ascot	Residential	1.5, 5, 10, up to 120 with 10m interval	1950	√	√
HR26	Sha Tin Hospital	Hospital	1.5, 5, 10, up to 40 with 10m interval	900	√	√
HR27	Garden Vista	Residential	1.5, 5, 10, up to 80 with 10m interval	1240	√	√
HR28	Topsail Plaza	Industrial	1.5, 5, 10, up to 50 with 10m interval	1020	√	√
HR29	Hong Kong Baptist University Affiliated School Wong Kam Fai Secondary School	Education	1.5, 5, 10, up to 50 with 10m interval	1020	√	√
HR30	The Castello	Residential	1.5, 5, 10, up to 120 with 10m interval	1050	√	√
HR31	Planned HR at existing STSTW site	Residential & Recreational	1.5, 5, 10, up to 120 with 10m interval	1400	√	√

13.5.2 Emission Inventory

13.5.2.1 Based on the TAP analysis results in Appendix 13.04, the VOCs including naphthalene were mainly detected at the inlet works. As discussed in Section 13.4.2.2, no NaOCl or other forms of chlorine is adopted for disinfection purpose. The chlorine related VOCs observed at the inlet works are mainly come from incoming sewage instead of emission from sewage treatment process.

13.5.2.2 On the other hand, the concentration levels of sulphur dioxide (SO₂) have been detected to be relatively high at several emission sources (such as inlet fine screen and channel). The high concentration levels may possibly come from upstream pumping stations and pipelines where sulphate reducing bacteria may exist and produce H₂S and SO₂ in a combination from anaerobic and acid environments. This presumption is supported by the measured high concentrations levels at the inlet works (including inlet fine screen, inlet channel and aerated grit channel). Other sources, such as the gas burner of the existing STSTW located close to and upwind of the sampling point, may also contribute.

13.5.2.3 Nitrogen dioxide (NO₂) was either not detected or found with very small concentrations (as compared to the toxicity level of NO₂) except the sampling point near the digested sludge holding tank. The concentration levels of NO₂ at the digested sludge holding tank was detected to be above 1,000 ppb (~ 1,800 ug/m³). NO₂ could be an intermediate product of both denitrification and dissimilatory nitrate reduction to ammonia (DNRA) in the anaerobic digestion process. This subject is not well studied scientifically. It is suspected that the accumulation of NO₂ in the digested sludge holding tank is also due to the absence of ventilation in the tank head space. The surrounding environment of this sampling location has also been investigated, with strong indication that the NO₂ content in the air sample is contributed by the existence of NO₂ in the background ambient air as NO₂ will be generated from the heavy traffic on Tate’s Cairn Highway and may possibly generated from the nearby waste gas burner, power house and salt water pumping station.

13.5.2.4 The maximum concentration level for each compound with major emission sources are summarized in the Table 13.11 below.

Table 13.11 Summary of Concentration Levels of Detectable TAPs at Emission Sources

Item	Toxic Air Pollutants (TAPs)	Max. Concentration Detected (µg/m3)	Major Emission Sources
1	Sulphur dioxide	3,150	All treatment tanks
2	Nitrogen dioxide	2,614	Digested Sludge Holding Tank^[1]
4	Hydrogen sulphide	110,000	Inlet Works, Primary Sediment Tank, Aeration Tank
5	Ammonia	1,230	Inlet Works, Primary Sediment Tank, Sludge Skip ^[2]
12	Carbon disulphide	6.7	Inlet Works, Aeration Tank
15	Chloroform	171	Inlet Works, Aeration Tank
18	Methanol	231.5	Inlet Works ^[3]
21	Methylene chloride (Dichloromethane)	21.5	Inlet Works, Aeration Tank
24	Tetrachloroethylene (Perchloroethylene)	1,238	Inlet Works, Aeration Tank
25	Toluene	28.2	Inlet Works
28	Trichloroethylene	24	Inlet Works ^[3]
29	Xylenes	48	Inlet Works ^[3]
33	Ethylbenzene	13.4	Inlet Works ^[3]
41	Naphthalene	1.24	Inlet Works ^[3]

Notes:

[1] NO₂ was mainly detected at the digested sludge tank. The concentration of NO₂ measured at other potential sources were very small and is close to the detection limit 30 µg/m³.

[2] The concentration of ammonia in another sampling event is measured to be 179 µg/m³.

[3] TAP was detected at this location under one sampling event.

13.5.2.5 In determining the Receptor Concentration Level (RCL) at HR, further measurement of the emission rates of the identified TAPs have been conducted. The CSTW would be located inside the modified cavern. All treatment units with potential TAPs emission will be covered and the collected air will be conveyed to the deodourizer for treatment before being discharged to the atmosphere. The residual TAPs in the exhaust air after deodouriziation and being dispersed to the atmosphere via the ventilation shaft, if found to be in a high concentration, might possibly cause potential health impact during the operation phase.

13.5.2.6 Based on some previous studies on the performance of deodourizer, the removal efficiency of deodourizer on the selected TAPs is tabulated in the Table 13.12 below.

Table 13.12 Removal Efficiency of Deodourizer for Different TAPs

Item	Toxic Air Pollutants (TAPs)	Deodourizer Removal Efficiency (%)
1	Sulphur dioxide	0
2	Nitrogen dioxide	0
4	Hydrogen sulphide	99.5
5	Ammonia	0
10	Acetaldehyde	50 ^[41]
11	Benzene	50 ^[41]
12	Carbon disulfide	50 ^[30]
13	Carbon tetrachloride	50 ^[31]
15	Chloroform	50 ^[28]
16	Formaldehyde	50 ^[31]
18	Methanol	50 ^[32]
21	Methylene chloride (Dichloromethane)	50 ^[31]
23	1,1,2,2-Tetrachloroethane	50 ^[29]
24	Tetrachloroethylene (Perchloroethylene)	50 ^[28]
25	Toluene	50 ^[28]
28	Trichloroethylene	50 ^[28]
29	Xylenes	50 ^[28]
32	1,2-Dichloroethane	50 ^[30]
33	Ethylbenzene	50 ^[28]
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	0
41	Naphthalene	50 ^[29]
42	Benzo(a)Pyrene	50 ^[28]
50	Benz(a)anthracene	50 ^[32]
51	Chrysene	0
52	Benzo(b)fluoranthene	50 ^[28]
54	Indeno (1,2,3-cd)pyrene	50 ^[28]
55	Dibenz(a,h)anthracene	50 ^[28]

Note:

The reference details of [28] to [32] are listed in Section 13.13.2.

13.5.2.7 The removal efficiency of deodourization systems e.g. bio-trickling or activated carbon on H₂S can typically achieve 99.5%, which will also be specified in the future works contracts as an requirement. This removal efficiency, with appropriate design conditions, is achievable and guaranteed by deodourizer suppliers and verified by commissioning tests. As such, this removal efficiency is directly used for calculation of concentration of residual H₂S in the exhausted air from the ventilation shaft. The removal efficiencies of each species of VOCs and PAHs by deodourisation systems are different. Some previous studies have revealed that deodourization system using activated carbon type could remove at least 75% of most species of VOCs and PAHs, some may even have removal efficiency higher than 99%. As a conservative approach, the removal efficiency of 50% is used for all these VOCs and PAHs as tabulated in the Table 13.12 above. Although it is known that the deodourizer could also remove ammonia (NH₃), SO₂, NO₂, 1,4-Dichlorobenzene and Chrysene to certain levels, without sufficient literature support, it is assumed that the removal efficiency is zero for these five TAPs aiming to have a more conservative assessment results.

13.5.2.8 As discussed in Section 13.4.2.3 and Section 2 of this EIA Report, no anaerobic digestion with digesters are proposed inside caverns owing to fire safety and health concerns. Further study of the emission rates of the identified TAPs from non-digestion sludge shall be performed for the acceptable data in this assessment.

13.5.2.9 It is well known that the emission of H₂S in non-digested sludge would be higher than the digested sludge. Thus, the emission rate of H₂S measured from undigested sludge from SCISTW, which has no digestion process unlike the existing STSTW, was adopted to represent the future emission rate of H₂S from relocated STSTW in caverns. The calculation of H₂S emission rate is presented in Appendix 13.06a. However, it should be noted that the treatment process adopted in SCISTW is CEPT which would generate more H₂S than a biological treatment process which will be adopted in relocated STSTW. In other words, this approach is considered on the conservative side.

13.5.2.10 NH₃ is a natural by-product in the digestion process in bio-degradation of organic material. Therefore, ammonium/ammonia level in digested sludge is typically higher than raw sludge. As the relocated STSTW in caverns will not have sludge digestion process, ammonia emission sampling data from SCISTW was adopted to represent the relocated STSTW in caverns. The calculation of NH₃ emission rate is presented in Appendix 13.06b.

13.5.2.11 SO₂ may be produced in anaerobic conditions such as digestion process which is known as dissimilatory sulfate reduction. Generally, this process reduces sulfate, oxidizes hydrogen and organic compound and generates hydrogen sulfide. In some cases where sulfur-containing compounds are degraded with the use of sulfate, SO₂ may be produced although compounds such as mercaptans would be more prevalent. ^[33] Based on the above, with the absence of anaerobic digestion process, the SO₂ quantity associated with the sludge handling process at the relocated STSTW in caverns is expected to be similar or even lower than at the existing STSTW. Therefore, adopting the emission samples at the existing STSTW is considered on the conservative side. The calculation of SO₂ emission rate is presented in Appendix 13.06c.

13.5.2.12 The sampling of NO₂ at the existing STSTW using Ogawa Passive Sampler is a passive sampling approach by absorbing the NO₂ from the ambient air on the surface of the absorbent pad for further laboratory testing. This NO₂ Ogawa Passive Sampler (1.5 x 1.5 x 2 inches in dimensions) could not be used on emission rate measurement because it could not be placed into the outlet of the flux hood (1/4 inches in diameter). Therefore, the emission rates of NO₂ at the designated locations could not be measured directly due to the restriction of the apparatus. For a conservative assessment purpose, the measured maximum NO₂ concentration as indicated in Appendix 13.04 would be adopted as the concentration entering into the deodourizer. The calculation of NO₂ emission rate is presented in Appendix 13.06d.

13.5.2.13 In general, the VOCs emissions from digestion process are relatively low and insignificant in comparison with the emissions from aeration tank and inlet works. ^[34] For PAHs compounds having two aromatic rings, i.e. naphthalene, they are volatile and always considered as VOCs species. As a conservative approach, the VOCs and PAHs (naphthalene) measured from the inlet works at existing STSTW are adopted as the quantity associated with the sludge handling process at the relocated STSTW in caverns. For other PAHs compounds identified as listed in Table 13.9, they have four to five aromatic rings but are non-detectable at existing STSTW according to Appendix 13.05. The carcinogenic risk assessment of these VOCs and PAHs would be carried out assuming that they will exist in concentrations equivalent to 50% of the detection limit as described in Section 13.4.7.2. The emission rate calculations of these VOCs and PAHs are presented in Appendix 13.06e to 13.06dd.

13.5.2.14 A summary of emission rates of the identified TAPs after deodourizer from CSTW is presented in Appendix 13.06.

13.5.3 Dispersion Model

13.5.3.1 The CSTW will operate 24-hour-per-day with continuous air exhaust from the ventilation shaft. The assessment heights are at predetermined heights above ground level according to the height of each HRs. The predicted TAPs concentration levels at the worst affected heights of the HRs are produced.

13.5.3.2 As the TAPs would be dispersed in a mode similar to the dispersion of odour causing compounds, the odour dispersion model with details presented in Section 3 of the EIA Report would also be adopted in the assessment for TAPs. The dispersion factors of the selected TAPs at representative HRs are derived from the odour dispersion model as shown in Appendix 13.07 and would be used for subsequent assessment of TAPs.

13.5.4 Receptor Concentration Levels

13.5.4.1 For the chronic risk assessment, i.e. long-term exposure scenario, the incremental annual average concentration level of the selected TAPs on representative HRs due to the operation of CSTW is predicted and the assessment results are shown in Appendix 13.07b.

13.5.4.2 For the acute risk assessment, i.e. short-term exposure scenario, the incremental hourly concentration level of the selected TAPs on representative HRs due to the operation of CSTW is predicted and the assessment results are shown in Appendix 13.07c.

13.5.4.3 Based on the results summary as shown in Appendix 13.07a, the predicted maximum incremental annual and hourly average concentration levels of the identified TAPs due to the operation of CSTW are illustrated in the Table 13.13 below. The predicted incremental annual average TAPs concentrations on all HRs with sensitive uses at these levels are relatively small as compared to the chronic and acute reference exposure levels.

Table 13.13 Summary of Maximum Incremental Concentration of TAPs with Non-carcinogenic Risk Level

Item	TAPs	Max. Incremental Annual Average Concentration at HR due to Operation of CSTW (µg/m3)	Chronic RfC (µg/m3)	Max. Incremental Hourly Average Concentration at HR due to Operation of CSTW (µg/m^3)	Acute RfC (µg/m3)
1	Sulphur dioxide	1.7E-03 (-)	-	3.3E-01 (1.6628%)	20
2	Nitrogen dioxide	2.7E-02 (0.0684%)	40	5.3E+00 (2.6371%)	200
4	Hydrogen sulphide	4.6E-04 (0.0230%)	2	8.9E-02 (0.0591%)	150
5	Ammonia	1.9E-04 (0.0003%)	70	3.6E-02 (0.0030%)	1190
12	Carbon disulphide	1.0E-05 (0.0000%)	700	2.0E-03 (0.0020%)	100
15	Chloroform	1.2E-04 (0.0001%)	98	2.4E-02 (0.0048%)	488
18	Methanol	2.2E-04 (0.0000%)	20000	4.3E-02 (0.0002%)	28000
21	Methylene chloride	2.8E-05 (0.0000%)	600	5.4E-03 (0.0002%)	3000
24	Tetrachloroethylene (Perchloroethylene)	5.2E-04 (0.0002%)	250	9.9E-02 (0.2426%)	41
25	Toluene	1.6E-05 (0.0000%)	3766	3.1E-03 (0.0000%)	7533
28	Trichloroethylene	2.6E-05 (0.0013%)	2	5.0E-03 (-)	-
29	Xylenes	3.0E-05 (0.0000%)	870	5.8E-03 (0.0001%)	8679
33	Ethylbenzene	1.2E-05 (0.0000%)	22000	2.3E-03 (0.0000%)	21699
41	Naphthalene	1.6E-06 (0.0000%)	10	3.1E-04 (-)	-

Note:

[1] Incremental percentage changes against the reference exposure levels are listed in the ( ).

13.6 Exposure Response Relationship

13.6.1 General

13.6.1.1 In this step of the risk assessment process, hypothetical HRs and their potential exposure pathways were identified. Selection of such potential exposure scenario was based on the characteristics of the sewage treatment works and surrounding area, and activities that could take place in the vicinity of the sewage treatment works. Dispersion of TAPs into ambient air allows direct human exposure to TAPs through inhalation. Since the general public (including visitors) would be restricted from direct contact with the sewage within the sewage treatment works or pumping stations, direct oral exposure by HRs is almost impossible to happen. Other exposure possibility is described in the following paragraphs.

13.6.2 Exposure Scenarios

13.6.2.1 The HHRAP (USEPA, 2005) suggests the evaluation of three pairs of potential receptors: a non-farming resident (child and adult), a subsistence farmer (child and adult), and a subsistence fisher (child and adult). However, the exact receptors to be evaluated were made site-specific based on land use and human activity patterns. Information on land use in the vicinity of the relocated STSTW was considered so that the receptor scenarios chosen for the health risk assessment would be appropriate for local receptors in Sha Tin.

13.6.2.2 The locations for potential exposure to STSTW-related TAPs have been selected based on a combination of the concentration levels on HRs and actual land uses identified in the vicinity of the site. Inhalation exposure has been evaluated under each scenario. The locations of the HRs as described in Table 13.5 above were evaluated in the context of the dispersion results to ensure that the locations of the maximum ambient concentrations were included in the evaluation. Under this scenario, the predicted annual average TAPs concentrations at HRs are adopted as chronic exposure for further assessment.

Residential

13.6.2.3 A reasonable resident scenario was evaluated at the off-site location with the highest estimated concentration for each TAP to ensure that potential exposures for a resident are not underestimated. Chronic exposure due to inhalation of vapour phase TAPs has been evaluated by air concentration modeling for adult and child residents.

Farming and Fishing

13.6.2.4 Given the physicochemical characteristics of the TAPs and their relatively low concentration, the deposited TAPs onto soil, water or plants (such as vegetables) are so minor that the indirect exposure through the ingestion of soil, water, or locally raised products (fish, beef, dairy, pork and poultry products) are negligible.

13.6.2.5 In conclusion, this exposure assessment is to predict the magnitude of potential human exposure to TAPs emissions from the ventilation shaft through the inhalation exposure pathway.

13.7 Risk Characterization

13.7.1.1 In the risk characterization step, potential human health risks associated with TAPs emissions from the relocated STSTW have been estimated. The risk characterization step combined the results of the exposure assessment and exposure response relationship to estimate the potential risks to human health.

Criteria Air Pollutants

13.7.2 Background Concentration of Criteria Pollutants

13.7.2.1 As suggested by “Guidelines on Assessing the Total Air Quality Impacts”, an integrated modelling system “Pollutants in the Atmosphere and their Transport over Hong Kong” model (PATH) which is developed and maintained by HKEPD is applied to estimate the background pollutant concentrations. The study area covers seven grid cells of PATH, namely grid (31, 35), (32, 35), (31, 34), (32, 34), (31, 33), (32, 33) and (33, 34). PATH dataset (Year 2020) of these seven grid cells, which is the best available background data, are adopted as the background concentration of SO₂ and NO₂ for the assessment. The background concentration at all the HRs are tabulated in Table 13.14 below.

Table 13.14 Background Concentration of Criteria Pollutants from PATH Model

HRs	PATH Grid	Annual Average NO2 Concentration (µg/m^3)	Annual Average SO2 Concentration (µg/m^3)	Maximum Hourly Average NO2 Concentration (µg/m^3)	Maximum Daily Average SO2 Concentration (µg/m^3)
HR 1	(32, 35)	17	6	201	28
HR 1a	(32, 35)	17	6	201	28
HR 1b	(32, 35)	17	6	201	28
HR 1c	(32, 35)	17	6	201	28
HR 2	(32, 35)	17	6	201	28
HR 3	(32, 35)	17	6	201	28
HR 4	(32, 35)	17	6	201	28
HR 5	(32, 35)	17	6	201	28
HR 6	(32, 35)	17	6	201	28
HR 7	(32, 35)	17	6	201	28
HR 8	(32, 35)	17	6	201	28
HR 9	(32, 35)	17	6	201	28
HR 10	(32, 34)	14	6	178	25
HR 11	(32, 34)	14	6	178	25
HR 12	(32, 34)	14	6	178	25
HR 13	(32, 34)	14	6	178	25
HR 14	(33, 34)	13	6	156	25
HR 15	(32, 35)	17	6	201	28
HR 16	(32, 35)	17	6	201	28
HR 17	(32, 35)	17	6	201	28
HR 18	(32, 35)	17	6	201	28
HR 19	(31, 35)	20	6	211	30
HR 20	(32, 35)	17	6	201	28
HR 21	(31, 35)	20	6	211	30
HR 22	(31, 35)	20	6	211	30
HR 23	(31, 34)	19	6	214	29
HR 24	(31, 35)	20	6	211	30
HR 25	(31, 35)	20	6	211	30
HR 26	(31, 34)	19	6	214	29
HR 27	(31, 34)	19	6	214	29
HR 28	(31, 34)	19	6	214	29
HR 29	(31, 33)	17	6	188	29
HR 30	(32, 33)	14	6	167	25
HR 31	(31, 35)	20	6	211	30

13.7.3 Risk Due to Chronic Exposure to Criteria Pollutants

13.7.3.1 As shown in Table 13.14, the background annual average SO₂ concentration predicted at all HRs based on territory-wide scale model results (PATH model) are 6 μg/m³.  The maximum predicted incremental SO₂ concentration due to the operation of CSTW is 1.7E-03 μg/m³, as indicated in Appendix 13.07.  The maximum cumulative annual average SO₂ concentration is predicted to be 6.0017 μg/m³, and the contribution percentage by the operation of CSTW is only 0.03%. Nevertheless, there is no exact risk criteria of SO₂ due to chronic exposure.  While it is not possible to totally rule out its potential health effect, the additional health effect, if presents, are likely to be very small.

13.7.3.2 For NO₂, the background annual average concentrations predicted at all HRs based on territory-wide scale model results (PATH model) would range from 13 to 20 μg/m³ as shown in Table 13.14.  The maximum predicted incremental NO₂ concentration due to the operation of CSTW is 0.0270 μg/m³, as indicated in Appendix 13.07. The maximum cumulative annual average contribution of NO₂ is predicted to be 20.0270 μg/m³, and the contribution percentage by the operation of CSTW is only 0.13%. While it is not possible to totally rule out its potential health effect, the additional health effect, if presents, are likely to be very small.

13.7.4 Risk Due to Acute Exposure to Criteria Pollutants

13.7.4.1 As shown in Table 13.14, the background daily average concentration of SO₂ at all HRs would range from 25 to 30 µg/m³ based on territory-wide scale model results (PATH model), which already exceeds the acute toxicity criteria of 20 μg/m³. Nevertheless, the maximum contribution of incremental SO₂ concentrations at all HRs by the operation of CSTW would be around 1%. Therefore, the additional acute adverse health effects would be negligible.

13.7.4.2 For NO₂, the background hourly average concentrations would range from 156 to 214 µg/m³ based on territory-wide scale model results (PATH model).  The predicted cumulative hourly concentration of NO₂ due to the operation of CSTW plus the background concentration would range from 161.3 to 219.3 μg/m³. While it can be noted that the cumulative hourly average NO₂ at some HRs would be occasionally greater than the acute toxicity criteria of 200 μg/m³ due to the high background level. Nevertheless, the contribution of incremental NO₂ concentrations at all HRs by the operation of CSTW would range from 2% to 3%. Therefore, the acute adverse health effects of NO₂ due to the operation of CSTW would be very small.

13.7.4.3 In summary, the operation of CSTW would make only very small additional contributions to local concentration of SO₂ and NO₂.  While it is not possible to rule out any potential adverse health effects from the operation of CSTW with complete certainty, the impact on health from small additional air pollutants is likely to be very small.

Other TAPs

13.7.5 Background Contribution of other TAPs

13.7.5.1 HKEPD has conducted VOC and carbonyl compounds measurements at the air quality monitoring stations (AQMS) in Yuen Long, Tung Chung, Tsuen Wan and Central Western. The Yuen Long AQMS and Tsuen Wan AQMS were characterised by the industrial activities in the vicinity. The Tung Chung AQMS were possibly influenced by the aircraft emissions from the airport and are too remote from Sha Tin. Therefore, the Central Western AQMS, which is less influenced by industrial or aircraft emission sources than the other AQMSs, has been adopted as a reference on background TAP concentrations, except ammonia for which the relevant data were only available from the Tsuen Wan AQMS.

13.7.5.2 The latest available yearly complete measurement data at Central Western AQMS and Tsuen Wan AQMS (for ammonia) in Year 2014 have formed the basis in determining the best available information on ambient TAP concentrations. Table 13.15 lists the detailed TAP measurements in Central Western AQMS and Tsuen Wan AQMS in Year 2014.

Table 13.15 Background TAPs Concentrations

Item	Toxic Air Pollutants	Annual Average Concentration in Year 2014 for Chronic Risk Assessment (µg/m^3) ^[1]	Max. Daily/Hourly Concentration for Acute Risk Assessment (µg/m^3) ^[1]
4	Hydrogen sulphide^[3]	-	-
5	Ammonia ^[2]	8.0E+00	2.7E+01
12	Carbon disulphide	-	-
15	Chloroform	4.4E-01	8.6E-01
18	Methanol ^[3]	-	-
21	Methylene Chloride	5.4E+00	1.2E+01
24	Tetrachloroethylene (Perchloroethylene)	6.2E-01	2.0E+00
25	Toluene	6.0E+00	2.7E+01
28	Trichloroethylene	2.7E-01	1.4E+00
29	Xylenes	2.8E+00	8.4E+00
33	Ethylbenzene	1.2E+00	3.4E+00
41	Naphthalene	1.0E+00	4.6E+00

Notes:

[1] The average and maximum values of the latest available yearly TAPs monitoring results were adopted as the background ambient concentrations of TAPs for chronic and acute risk assessment separately.

[2] The ammonia monitoring results is only available in Tsuen Wan AQMS.

[3] “-“means no measurement at the AQMS.

13.7.6 Risk Due to Chronic Exposure to other TAPs

13.7.6.1 The chronic risk has been evaluated for residency exposure to TAPs via direct inhalation. To determine the likelihood of adverse health effects, the factors of primary interest are the predicted incremental cumulative concentrations of these identified TAPs arising from the operation of CSTW at different HRs, as identified in Appendix 13.07 plus the background contribution as listed in Table 13.15 above.

13.7.6.2 Based on the maximum predicted cumulative annual average concentrations of TAPs as summarised in Table 13.13, it can be noted that the cumulative annual average TAP concentrations at all HRs would comply with all the chronic toxicity criteria. Therefore, the exposure of HRs to the TAPs is not anticipated to cause an adverse chronic non-carcinogenic health effects.

Table 13.16 Maximum Predicted Cumulative Annual Average Concentrations of TAPs

Item	TAP	Max. Cumulative Annual Average Concentration (µg/m3) ^[2] [3]	Chronic RfC (µg/m3)
4	Hydrogen sulphide^[1]	-	2
5	Ammonia	8.0002 (YES)	70
12	Carbon disulphide^[2]	-	700
15	Chloroform	0.4401 (YES)	98
18	Methanol	-	20000
21	Methylene chloride	5.4000 (YES)	600
24	Tetrachloroethylene (Perchloroethylene)	0.6205 (YES)	250
25	Toluene	6.0000 (YES)	3766
28	Trichloroethylene	0.2700 (YES)	2
29	Xylenes	2.8000 (YES)	870
33	Ethylbenzene	1.2000 (YES)	22000
41	Naphthalene	1.0000 (YES)	10

Notes:

[1] Background concentrations in EPD’s Central Western AQMS and Tsuen Wan AQMS is not available.

[2] For predicted cumulative annual average TAP concentration, “YES” refers to its compliance with criteria.

[3] Compliance against the criteria is shown in the ( ).

13.7.7 Risk Due to Acute Exposure to other TAPs

13.7.7.1 In addition to the potential risk due to chronic exposure, the acute exposure risk has been evaluated based on the predicted incremental hourly average concentrations of these identified TAPs arising from the operation of CSTW, as identified in Appendix 13.07 plus the background contribution as listed in Table 13.15 above.

13.7.7.2 According to the maximum predicted cumulative hourly average concentrations of TAPs as summarised in Table 13.13, it can be noted that the cumulative hourly average TAP concentrations at all HRs would comply with all acute toxicity criteria. Therefore, the exposure of HRs to the TAPs is not anticipated to cause an adverse acute non-carcinogenic health effects.

Table 13.17 Maximum Predicted Cumulative Hourly Average Concentrations of TAPs

Item	TAP	Max. Cumulative Hourly Average Concentration (µg/m3)	Acute RfC (µg/m3)
4	Hydrogen sulphide ^[1]	-	150
5	Ammonia	27.0356 (YES)	1190
12	Carbon disulphide ^[1]	-	100
15	Chloroform	0.8836 (YES)	488
18	Methanol ^[1]	-	28000
21	Methylene chloride	12.0054 (YES)	3000
24	Tetrachloroethylene (Perchloroethylene)	2.0995 (YES)	41
25	Toluene	27.0031 (YES)	7533
28	Trichloroethylene ^[4]	1.4050 (YES)	-
29	Xylenes	8.4058 (YES)	8679
33	Ethylbenzene	3.4023 (YES)	21699
41	Naphthalene ^[4]	4.6003	-

Notes:

[1] Background concentrations in EPD’s Central Western AQMS and Tsuen Wan AQMS is not available.

[2] For predicted cumulative hourly average TAP concentration, “YES” refers to its compliance with criteria.

[3] Compliance against the criteria is shown in the ( ).

[4] Acute toxicity criteria is not available.

13.7.7.3 In summary, as discussed in Sections 13.7.6 and 13.7.7 above, the cumulative concentration of individual TAP at each HR due to the operation of CSTW is not anticipated to cause any adverse impact when compare to either the long-term or short-term exposure toxicity risk levels. In this connection, the non-carcinogenic health risk for long-term or short-terms exposure to the identified TAPs with emission from the relocated STSTW could virtually be ignored.

13.7.8 Calculation of Carcinogenic Health Risk

13.7.8.1 The USEPA has established the methodology for cancer risk estimates, as explained in Section 13.2.1 of its publication “Air Toxics Risk Assessment Reference Library – Volume 1 Technical Resource Manual”. The estimated individual cancer risk is expressed as the upper bound probability that a person may develop cancer over the course of their lifetime as a result of the exposure.

13.7.8.2 For inhalation exposures, the chronic cancer risks (i.e. carcinogenic health risk of individual TAP) is estimated using the Equation 13-1 below:

Risk inh(i) = ECL x IUR (Equation 13-1)

Where:

Risk inh(i) = Cancer risk to an individual (expressed as an upper-bound risk of contracting cancer over a lifetime);

ECL = Estimate of long-term inhalation exposure concentration for a specific TAP; and

IUR = the corresponding inhalation unit risk estimate for that TAP.

This calculation is performed to estimate the probability of developing cancer over a lifetime (usually assumed to be 70 years) due to the continuous exposure to a specific TAP of EC_L concentration. The EC_L is an estimated based on the modelling data for one-year’s worth of time.

Characterization of Cancer Risk from Exposure to Multiple Pollutants is summarized as follows:

Total Incremental Cancer Risk = Cancer Riskinh(1) + Cancer Riskinh(2) + … + Incremental Cancer Risk inh(N) (Equation 13-2)

13.7.8.3 The USEPA has established relevant criteria for human health impact assessment for the carcinogenic risk for an individual potentially exposed to one or more TAP. The guidance is in Table 13.18 below:

Table 13.18 Cancer Risk Guidance

Risk Value	Description
Cancer risks less than or equal to one in a million (1E- 06)	Acceptable and no further evaluation warranted.
Cancer risks between 1E- 04 to 1E- 06	Considered by the DAQ Risk Management Committee on a case-by-case bases. Sources with risk falling within this range must take steps to minimize the projected risk before a Pre-Construction Permit can be issued.
Cancer risks greater than or equal to one in ten thousand (1E- 04)	Unacceptable.

13.7.8.4 The incremental cancer risk of these identified TAPs at each HR due to the project are calculated and presented in Appendix 13.08. The highest incremental cancer risk for each individual TAP, as well as the total incremental cancer risk, at the HRs is 7.1E-08, as presented in Appendix 13.08v. The calculated highest incremental cancer risk is far below the acceptable target risk goal of one in a million (1E-06), according to the guidance established in Table 13.18 above, and as shown in Table 13.19 below.

Table 13.19 Total Incremental Cancer Risk due to the Identified TAPs

Item	Toxic Air Pollutants	IUR (ug/m^3)^-1	Max. Predicted Incremental Concentration ECL (ug/m^3)	Highest Cancer Risk
10	Acetaldehyde	2.2E-06	3.5E-05	7.7E-11
11	Benzene	6.0E-06	2.7E-06	1.6E-11
13	Carbon tetrachloride	6.0E-06	6.3E-06	3.8E-11
15	Chloroform	2.3E-05	1.2E-04	2.8E-09
16	Formaldehyde	1.3E-05	2.4E-05	3.1E-10
21	Methylene chloride (Dichloromethane)	1.0E-08	2.8E-05	2.8E-13
23	1,1,2,2-Tetrachloroethane	5.8E-05	2.6E-05	4.2E-10
24	Tetrachloroethylene (Perchloroethylene)	2.6E-07	5.2E-04	1.3E-10
28	Trichloroethylene	4.3E-07	7.3E-06	1.1E-11
32	1,2-Dichloroethane	2.6E-05	3.6E-06	9.5E-11
33	Ethylbenzene	2.5E-06	1.2E-05	3.0E-11
40	p-Dichlorobenzene (1,4-Dichlorobenzene)	1.1E-05	1.3E-05	1.4E-10
41	Naphthalene	3.4E-05	1.6E-06	5.6E-11
42	Benzo(a)Pyrene	8.7E-02	7.5E-07	6.6E-08
50	Benz(a)anthracene	1.1E-04	7.5E-07	8.3E-11
51	Chrysene	1.1E-05	1.5E-06	1.7E-11
52	Benzo(b)fluoranthene	1.1E-04	7.5E-07	8.3E-11
53	Benzo(k)fluoranthene	1.1E-04	7.5E-07	8.3E-11
54	Indeno (1,2,3-cd)pyrene	1.1E-04	7.5E-07	8.3E-11
55	Dibenz(a,h)anthracene	1.2E-03	7.5E-07	9.0E-10
	Total Incremental Cancer Risk (highest):			7.1E-08

13.7.8.5 In summary, for those non-human carcinogen or Group 3 IARC TAPs, such as hydrogen sulphide, ammonia, nitrogen dioxide, sulphur dioxide and xylenes, which are not covered in the calculation of total incremental cancer risk above, their potential contribution to the total incremental cancer risk can be ignored due to their non-carcinogenic properties. Therefore, considering the cancer risk results presented in Table 13.19, there is no significant carcinogenic health risk due to the exposure to be expected from emissions of any of the identified TAPs from the relocated STSTW.

13.8 Reuse of Effluent Water

13.8.1.1 The reuse of treated effluent from the STSTW by general public is not proposed in view of its high capital and recurrent costs as explained in Section 2.5.1.2. Treated effluent from the Project would be limited to non-potable use inside the plant i.e. polymer preparation. Polymer preparation will not involve direct human contact and the reused effluent will go back to the treatment unit for further treatment before being discharged. The health impact to humans is not expected during the operation phase of the effluent reuse system.

13.8.1.2 To avoid cross-connection of the effluent reuse system to the potable water supply, the pipes for the reused effluent water will be specially arranged to differentiate them from that of the potable water pipes, e.g. clearly labeled with warning signs and notices, colour-coded, and/or using different pipe size, so that physical connection of the reclaimed water pipes with the potable water fitting would not be possible.

13.9 Radon

13.9.1.1 Although the assessment of health risk of radon (Rn) emissions from the construction and operation of the Project is not required in the EIA Study Brief as it is more related to occupational health and safety, the issue is also discussed here for completeness.

13.9.1.2 Nui Po Shan cavern site is located within granite that is will contain uranium. As uranium in the granite decays radioactively, gaseous Rn (and its associated ionizing radiation “daughter products) will be continuously formed and released in the caverns.

13.9.1.3 The use of granite in concrete walls and floors and other construction materials in the relocated STSTW facilities may also contribute to elevated indoor Rn levels. The release of Rn from appropriately cured or sealed concrete is however expected to be minimal in view of its lower porosity, which inhibits the diffusion of Rn. Also, the uranium content in concrete or other construction material is generally lower when compared with granite. Based on the above, the release of Rn from concrete and other construction materials is not considered a concern compared with unlined granite walls or ceilings. In all cases adequately designed ventilation and filtration systems can be utilized to control Rn to acceptable levels.

Indoor Air Quality Objectives for Office and Public Places

13.9.1.4 As given in Table 13.20, the Indoor Air Quality Objectives for Office and Public Places also recommended the Rn level for IAQ. The Rn level for “Excellent Class” offices and public spaces shall be below 150 Bq/m³, while that for “Good Class” shall be under 200 Bq/m³.

Table 13.20 Indoor Air Quality Objectives for Office and Public Places

Parameter	Unit	8-hour average
		Excellent Class	Good Class
Radon (Rn)	Bq/m3	< 150	< 200

ProPECC PN 1/99 Control of Radon Concentration in New Buildings

13.9.1.5 A PN for Professional Persons was issued by the EPD to provide guidance for the control and mitigation of indoor Rn level in new buildings. A number of measures to minimize potential impacts from accumulation of Rn in new buildings are outlined in the PN. These measures should be followed as far as possible during operation.

WHO Recommendation

13.9.1.6 WHO recommends that countries implement national programmes to reduce the population’s risk from exposure to the national average Rn concentration, as well as reducing the risk for individuals exposed to high Rn levels. Building codes should be implemented to reduce Rn levels in homes under construction. A national reference level of 100 Bq/m³ is recommended. However, if this level cannot be reached under the prevailing country-specific conditions, the reference level should not exceed 300 Bq/m³.

13.9.1.7 Adequate ventilation would be maintained at the relocated STSTW to remove excessive heat from the treatment process and plants, as well as fugitive sewer gas or Rn from inside the caverns. Sufficient air change would help to ensure the removal of Rn and reduce the health risk (associated with Rn) to the exposed personnel (mainly worker in the relocated STSTW). With reference to the successful operation experience and monitoring data for Rn at Stanley STW (also a cavern STW), it is expected that the level of Rn exposure inside cavern would be sufficiently low with provision of suitable ventilation.

13.9.1.8 Monitoring of indoor Rn level at locations where human activities are expected can further minimize the potential exposure by allowing the removal of elevated Rn a (by increased ventilation rate) before the arrival of working personnel.

13.9.1.9 Since the risk posed to workers from direct Rn exposure is not significant when a proper ventilation system is available to adequately dilute the Rn concentration, the risk on off-site HRs will also be insignificant. The Occupational Safety and Health Ordinance provides the statutory authority for controlling the occupational health.

13.10 Uncertainty Analysis

13.10.1.1 Within any risk assessment process, a number of assumptions and simplifications are made in recognition of the lack of complete scientific knowledge and inherent variability in many of the parameters used in risk assessment. In some cases, the values may vary widely between a conservative upper confidence limit and an average value. In other cases, measurement data are too sparse to develop a statistically robust estimate of the mean. In those cases, judgments must be made in selecting an assumed value that is credible, but unlikely to be exceeded when future measurements become available.

13.10.1.2 The health risk assessment is a complex process, requiring the integration of the following:

· Identification of TAPs release into the environment;

· Transport of the TAPs by air dispersion in a variety of different and variable environments;

· Potential for adverse health effects in human, as extrapolated from animal studies; and

· Probability of adverse effects in a human population that is highly variable genetically, and in age, activity level and lifestyle.

13.10.1.3 Uncertainty can be introduced in the assessment at many steps of the process. The following paragraphs discuss the uncertainties associated with each stage of the assessment.

13.10.2 Hazard Identification

13.10.2.1 TAPs are identified based on the air pollutants listed in USEPA, HKEPD and other literature search related to sewage treatment works. This list of chemicals may not cover all the chemicals emitted from the relocated STSTW, which may underestimate the risk. However, it is considered that although the TAPs identified may not be exhaustive, it appeared sufficiently comprehensive for the purpose of the assessment.

13.10.3 Exposure Assessment

13.10.3.1 In this stage of the assessment, the dispersion factors derived from the odour dispersion model are used to predict the dispersed TAPs concentration levels at HRs. As the dispersion factors are simplifications of reality requiring exclusion of some variables that influence predications, which would introduce uncertainty in the prediction of TAPs concentrations at potential HRs, this model may in turn overestimate or underestimate the risk.

13.10.3.2 In the calculation of the accumulative carcinogenic risk, the concentration equivalent to 50% of the detection limit is adopted to present the concentration of undetected TAPs. As the percentage of 50% is an average value to represent all the undetectable TAPs, which would introduce uncertainty in the calculation of accumulative carcinogenic risk. However, the highest accumulative cancer risk is found far below the acceptable guidance level by approximately 2 order of magnitude, as presented in Section 13.7.4. Thus, this uncertainty introduced by this assumption is acceptable.

13.10.3.3 In the development of the emission inventory for NO₂, the emission rates of NO₂ at the designated locations could not be measured directly due to the restriction of the apparatus as discussed in Section 13.5.2.12. For a more conservative assessment, the maximum measured NO₂ concentration is assumed to be the concentration level at each designated location for further calculation. Thus, the predicted concentration of NO₂ at all the HRs and the corresponding non-carcinogenic risk would be overestimated as the existence of NO₂ in ambient air (e.g. emissions from vehicles) were also measured.

13.10.3.4 The quantity of incoming sewage to CSTW is expected to reach 280,000 m³/day at Year 2036 (hereafter as interim stage) while the design capacity of 340,000 m³/day (hereafter as Ultimate Stage) has allowed certain contingencies and buffer in population growth beyond Year 2041. The potential TAP emission after deodorization treatment is estimated based on the Ultimate Stage. Thus, the predicted risk due to the emission of TAPs would be overestimated before the population reach the Ultimate Stage.

13.11 Risk Control and Management

13.11.1.1 The possible sources of the TAPs to the ventilation shaft for the relocated STSTW could be:

· Emissions from preliminary treatment units, such as screenings and grits;

· Emissions from sludge treatment facilities, such as dewatering equipment and sludge loading/disposal mechanism; and

· Emissions (e.g., H2S) due to leakage from covered tankage or improper installation;

· Emissions from leakage during upset conditions;

· Unusual emissions, when storm water runoff containing automotive oils or rubbish from unintended connections enter the system in an uncontrolled manner.

13.11.1.2 The relocated STSTW will be designed and operated as a modern facility. All treatment units with potential odour emission will be covered and the exhausted air will be conveyed to the deodourizer for treatment before discharge to the environment via ventilation shaft. With thorough control and monitoring system, the leakage during normal operation are not anticipated.

13.11.1.3 The operator must also be well trained to avoid any accidental events. The possible accidental events associated with health impacts and their corresponding preventive measures are listed in Table 13.21.

Table 13.21 Potential Accidental Events and Preventive Measures

Risks	Preventive Measures
Emission during upset conditions	➢ Provision of sufficient standby units for all major treatment units and E&M equipment; ➢ Provision of dual power supply to the sewage treatment works.
Emission from leakage from covered tankage or improper installation	➢ Install real-time monitoring sensor to continuous monitor the concentration. When concentration exceed the action limit, the operator will carry out investigation and repairing works as soon as practicable.
Aerial emissions (emission discharge exceed the discharge limit)	➢ Use of best available techniques in emission stack design, implement continuous and regular emission monitoring.
Transportation, storage and handling	➢ Implement good waste/sludge transportation, storage and handling practices; ➢ Develop procedures for and deploy as necessary emergency response including spill response for accidents involving transport vehicles; ➢ Enforce strict driver skill standards and implement driver and road safety behavior training.
Chemical spillage and leakage	➢ Implement proper chemicals and chemical wastes handling and storage procedures; ➢ Develop and implement spill prevention and response plan including provision of spill response equipment and trained personnel.
Employee health and safety	➢ Implement industry best practice with reference to international standards and guidelines.

13.11.1.4 To further avoid or minimize the potential health impacts associated with other possible accidental events, an emergency response plan should be developed and properly implemented for the Project. It should be noted that the emergency response plan should be specific to the final design and operation of the Project. With the implementation of the preventive measures outlined in Table 13.21 above, and with an effective emergency response plan for the Project, the health impacts associated with any potential accidental events could be minimized, if not entirely avoided.

13.12 Conclusion

13.12.1.1 The CSTW is fully enclosed in the cavern and the potential TAP emission from the sewage treatment facilities would be treated by the deodourizing units before being discharged into atmosphere from the ventilation shaft which is located at a remote uphill area.

13.12.1.2 The risk arising from exposure to TAPs associated with the emissions of the relocated STSTW is evaluated in this section. The non-carcinogenic and carcinogenic health impact of the TAPs imposed to the impacted HRs were assessed and compared with international guideline levels. It is concluded that the levels of TAPs at HRs were found to be extremely small when compared to the derived reference levels. The highest incremental cancer risk arising from the operation of CSTW is predicted to be 7.1E-08 which is far below the guidance level of 1E-06 adopted by USEPA and it is considered that the Project would not present an unacceptable risk and no further analysis is necessary. For the criteria air pollutants, while it is not possible to rule out the additional potential health effects from the operation of CSTW with complete certainty, the impact on health from extremely small additional air pollutants is likely to be very small and unlikely to be quantifiable.

13.12.1.3 Reuse of treated effluent from the Project by general public is not proposed. The treated effluent from the Project would be limited to non-potable use inside the plant. No direct human contact is involved and the health impact to humans is not expected during the operation phase of the effluent reuse system.

13.12.1.4 The results are sound and reasonable as the influent to the STSTW is mainly domestic waste water generated from day-to-day human activities. No further mitigation measures are required.

13.13 References

13.13.1 Literature for STW-related TAPs

[1] New Zealand Institute of Chemistry, 1998. Chemical Processes in New Zealand, Water Section, Article on Sewage Treatment (http://nzic.org.nz/ChemProcesses/water/13C.pdf)

[2] Water Environment Federation and American Society of Civil Engineers, 1995.  Odor Control in Wastewater Treatment Plants.  Water Environment Federation Manual of Practice No. 22 and ASCE Manuals and Reports on Engineering Practice No. 82. Alexandria, Va.: Water Environment Federation and American Society of Civil Engineers.

[3] Meridian Engineering and Technology, Consulting Engineers and Scientists, 1993. Reference Data Sheet on Sewer Gas(ES). (http://www.meridianeng.com/sewergas.html)

[4] Reviews in Environmental Science and Bio/Technology, 2006. Treatment of Biogas Produced in Anaerobic Reactors for Domestic Wastewater: Odor Control and Energy/Resource Recovery, (2006), 93-114. DOI 10.1007/s11157-005-2754-6

[5 ]Journal of Hazardous Materials, 2003. Recent advances in VOCs removal from water by pervaporation, (2003), 69-90. (www.elsevier.com/locate/jhazmat)

[6] Water Environment Research Foundation. Municipal Wastewater Treatment, Washington Statement Air Toxic Sources and Emmision Methods.

[7] Environmental Protection Agency, 1997. Wastewater Treatment Manuals-Primary, Secondary and Tertiary Treatment, 79-80.

[8] Water Environment Research Foundation, 2007. Minimization of Odors and Corrosion in Collection System. (http://tools.werf.org/Files/Front%20Matter.pdf)

[9] Water Environment Research Foundation, 2007. Odor Control “ABC’s” How to Compare and Evaluate Odor Control Technologies. (http://www.gesodorcontrol.com/abcs.pdf)

[10] Aysen M., 2002. A Study of Volatile Organic Sulfur Emissons Causing Urban Odors. Chemosphere. 51 (2003) 245-252.

[11] Applied Microbiology and Biotechnology, 2012. Abatement of Odorant Compounds in One-and two-phase Biotrickling Filters under Steady and Transient Conditions, 97: 4627-4638. DOI 10.1007/s00253-01204247-1

[12] Water Environment Research Foundation, 2007. Odor Control, Operation of Muicipal Wastewaer Treatment Plants, WEF Manual of Practice No.11, Sixth Edition. (http://www. Wef.org)

[13] Chemical Engineering Transactions, 2012. Characterising Volatile Organic Compounds from Sewer Emissions by Thermal Desorption Coupled with Gas-Chromatography-Mass Spectrometry, 30(2012), 73-78. DOI: 10.3303/CET1230013. (www.aidic.it/cet)

[14] Water Pollution Control Fedration, 1985. Eliminatin of Odor at Six Major Wastewter Treatment Plants, 57(10), 1027-1032. (http://www.jstor.org/stable/25042774)

[15] Sensors, 2009. Emmison Characteristics and Factors of Selected Odorous Compounds at a Wastewater Treatment Plant, 9(2009), 311-326. DOI: 10.3390/s90100311. (www.mdpi.com/journal/sensors)

[16] Water Science and Technolody, 1998. Fate of Dissolved Odorous Compounds in Sewage Treatment Plants, 38(3), 337-344. PII: S0273-1223(98)00560-5

[17] Water Research, 1994. Identification and Quantidication of Sulfur and Nitrogen Containing Odorous Compounds in Wastewater, 29(2), 711-718.

[18] Water Environment Research Foundation, 2003. Identifying and Controlling Odor in the Municipal Wastewater Environment Phase I: Literature Search and Review.

[19] Water Environment Research Foundation, 2003. Identifying and Controlling Odor in the Municipal Wastewater Environment Phase II: Impacts of In-Plant Paremeters on Biosolids Odor Quality.

[20] United States Environmental Protection Agency (USEPA) published list of Hazardous Air Pollutants under the Clean Air Act, 1990; https://www.epa.gov/haps/initial-list-hazardous-air-pollutants-modifications)

[21] Research Gate, 2005. Odor Abatement in Wastewater Treatment Plants. (http://www.researchgate.net/publication/229522985)

[22] Water Environment Research, 2003. Odor and Volatile Organic Compound Removal from Wastewater Treatment Plant Headworks Ventilation Air Using a Biofilter, 75(5), 444-454. (http://www.jstor.org/stable/25045719)

[23] Water Environment Federation, 1980. Odor Control: An Operator's Guide, 52(10), 2523-2537. http://www.jstor.org/stable/25040916

[24] Water Pollution Control Federation, 1980. Odor Control of Wastewater Treatment Plants, 52(5), 906-913. (http://ww.jstor.org/stable/25040812)

[25] Water Air and Soil Pollution, 2012. Simultaneous Removal of H2S, NH3 and Ethyl Mercaptan in Biotrickling Filters Packed with Poplar Wood and Polyyurethane Foam: Impact of pH During Startup and Crossed Effects Evaluation, 223(2012), 3485-3497. DOI: 10.1007/s11270-012-1126-4

[26] Water Environment Federation, Water Pollution Control Federation, 1986. Volatile Organic in the Wastewater and Airspaces of Three Wastewter Treatment Plants, 58(9), 886-895. (http://www.jstor.org/stable/25043074)

[27] Environment Research, 2004. Polycyclic Aromatic Hydrocarbons and Polychlorobiphenyls in Wastewaters and Sewage Sludges from the Paris Area (France), 95(2):184-97. (http://www.ncbi.nlm.nih.gov/pubmed/15147924)

13.13.2 Reference for Emission Inventory

[28] Zeszyty Naukowe Wyższej Szkoły Zarządzania Ochroną Pracy W Katowicach, 2014. The Effectiveness Adsorption of Carcinogenic PAHs on Mineral and on Organic Sorbents, 10(2014), 5-16.

[29] Journal of Environmental Science and Health, Part A, Toxic/Hazardous Substance & Environmental Engineering, 2012. Effect of Carbon Sources on the Removal of 1,1,2-trichloroethane and 1,1,2,2-tetrachloroethane in UASB Reactor, 47(4), 638-644.

http://www.ncbi.nlm.nih.gov/pubmed/22375547

[30] Applied Microbiology and Biotechnology, 1994. Increased Removal Capacity for 1,2-Dichloroethane by Biological Modification of the Granular Activated Carbon Process, 42(1), 167-172. http://www.ncbi.nlm.nih.gov/pubmed/7765815

[31] Asian Journal of Atmospheric Environment, 2011. Efficiency Evaluation of Adsorbents for the Removal of VOC and NO₂ in an Underground Subway Station, 5(2), 113-120.

[32] Taylor & Francis Group, 2005. Activated Carbon Adsorption, 431-434.

[33] A Jone Willey & Sons, Inc.,Publications, 2006. Wastewater Bacteria, 119-122.

[34] Levis Publications, 2003. VOC Emissions from Wastewater Treatment Plants, 87-88.

13.13.3 Reference for Methodology

[35] EPD, Hong Kong. 2014. EIA Study Brief No. ESB-273/2014.

[36] Raymond K.S. Chan. 2011. Future Cavern Development in Hong Kong. Presentation to the HKIE-HKIP Joint Conference on Planning and Development of Underground Space.

[37] AECOM/Mansell. 2007. Kai Tak Development Engineering Study cum Design and Construction of Advance Works –Investigation, Design and Construction. KTAC Odour Assessment Methodology Paper. Agreement No. CE 35/2006 (CE).

[38] AECOM. 2008. Sludge Treatment Facilities EIA, EIA Study Brief No. ESB-169/2007, Potential Human Health Risk Assessment from the Construction and Operation of Sludge Treatment Facilities. Available at: (http://www.epd.gov.hk/eia/register/report/eiareport/eia_1552008/EIA%20Report/html/Tex t/S4_HRA.htm).

[39] AECOM. 2011. Tsang Tsui Ash Lagoon EIA, EIA Study Brief No. ESB-184/2008, Potential Health Impacts of Aerial Emissions from the IWMF during Operational Phase. Available at:

(http://www.epd.gov.hk/eia/register/report/eiareport/eia_2012011/EIA/EIA_HTML/S9a_He althImpact-TTAL.htm).

[40] Airport Authority Hong Kong. 2014. Expansion of Hong Kong International Airport into a Three-Runway System EIA, EIA Study Brief No. ESB-250/2012, Human Impact Assessment for Emissions of TAPs associated with the Operation of the Three-Runway System. Available at:

(http://www.epd.gov.hk/eia/register/report/eiareport/eia_2232014/html/Ch%2017%20-

%20Health.pdf).

[41] UK Department of Environment, Transport and region (DETR)/Department of Environment Food, Rural Areas. 2000. https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69450/pb1 3670-green-leaves-iii-1111071.pdf

[42] EUGRIS (European groundwater and contaminated land remediation information system). 2005. "Integrated Soil and Water Protection: Risks from Large Scale Diffuse Pollution" (SOWA). http://www.eugris.info/aboutEugris/EUGRIS%20Outline.pdf

[43] Scotland & Northern Ireland Forum for Environmental Research (SNIFFER). 2007. “Environmental Legislation and Human Health – Guidance for Assessing Risk. http://www.sniffer.org

[44] Brown, NJ. 1997. Health Hazard Manual: Wastewater Treatment Plant and Sewer Workers, Manuals and User Guides. Cornell University ILR School, http://digitalcommons.ilr.cornell.edu/manuals/.

[45] US EPA/USAID. 1992. Report EPA/625/R-92/004, US EPA (Office of Water) and USAID, Washington DC.

[46] US EPA. 1973. Water quality criteria. Ecological Research Series, EPA R-3-73-033. US Environmental Protection Agency, Washington, DC. US EPA (1986), EPA440/5-84-002. Office of Water Regulations and Standards Division, Washington DC.

[47] WHO. 2001. Water Quality: Guidelines, Standards and Health. Chap. 8, Risk Assessment. Edited by Lorna Fewtrell and Jamie Bartram. Published by IWA Publishing, London, UK. ISBN: 1 900222 28 0.

[48] WHO. 1993. Guidelines for Drinking Water Quality. Volume 1: Recommendations. Geneva.

[49] WHO. 1996. Guidelines for Drinking Water Quality. Volume 2: Health criteria and other supporting information. Geneva.

[50] WHO. 1997. Guidelines for Drinking Water Quality. Volume 3: Surveillance and control of community supplies. Geneva

[51] WHO. 1989. Health Guidelines for the Use of Wastewater in Agriculture and Aquaculture. Report of a WHO Scientific Group, Technical Report Series No. 778, WHO, Geneva.

[52] WHO. 1973. Reuse of Effluents: Methods of Wastewater Treatment and Public Health Safeguards. Report of a WHO Meeting of Experts, Technical Report Series No. 517, WHO, Geneva.

[53] WHO, 2006. WHO Air Quality Guidelines for Particulate Matter, Ozone, Nitrogen dioxide, and Sulphur Dioxide. Global update 2005. Summary of Risk Assessment.

WHO/SDE/PHE/OEH/06.02. Geneva.

[54] WHO. 2010. WHO Human Health Risk Assessment Toolkit: Chemical Hazards. http://www.who.int/ipcs/methods/risk_assessment/en/Environmental Health Guidance for Wastewater Applications. Geneva

13.13.4 Health Risk Assessment Guidance

[55] Lakes Environmental, 2005. IRAP-h (Integrated Risk Assessment Protocol – health), a Computer Model, which implements the analyses defined in the US EPA’s 2005 HHRAP (Human Health Risk Assessment Protocol. Toronto, CA. http://www.weblakes.com/products/iraph/

[56] National Research Council. 1983. Risk Assessment in the Federal Government: Managing the Process. http://www.nap.edu/openbook.php?isbn=0309033497

[57] Rebecca T. Parkin. 2008. Foundations and Frameworks for Human Microbial Risk Assessment. Center for Risk Science and Public Health School of Public Health and Health Services, the George Washington University Medical Center. Submitted to US EPA, Washington, DC.

[58] U.S. EPA. Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities, EPA530-R-05-006. Office Of Solid Waste. September 2005

[59] U.S. EPA. 2005. Guidelines for Carcinogen Risk Assessment. EPA/630/P-03/001F. Risk Assessment Forum, Washington DC. U.S. EPA. 1994a. Air Emissions Models for Waste and Wastewater. EPA-453/R-94-080-A Appendix C. OAQPS, RTP, NC.

[60] U.S. EPA. 2001-2014.. Integrated Risk Information System (IRIS). National Center for Environmental Assessment, Office of Research and Development, Washington, DC. Available online at http://www.epa.gov/iris/.

[61] U.S. EPA. 1998b. Methodology for Assessing Health Risks Associated with Multiple Exposure Pathways to Combustor Emissions. Update to EPA-600/6-90-003 Methodology for Assessing Health Risks Associated with Indirect Exposure to Combustor Emissions. EPA-600/R-98-137. National Center for Environmental Assessment, Cincinnati, OH.

[62] U.S. EPA. 1997. “Risk Characterization Policy; Guidance for Cumulative Assessment, Part 1: Planning and Scoping” (USEPA, 1997a);

[63] U.S. EPA. 1997a. Exposure Factors Handbook. Office of Research and Development, National Center for Environmental Assessment. Office of Solid Waste and Emergency Response, Washington, DC.

[64] U.S. EPA. 1997b. Health Effects Assessment Summary Tables (HEAST). EPA-540-R-97-

036. FY 1997 Update.

[65] U.S. EPA. 1989. Development of Risk Assessment Methodology for Municipal Sludge Landfilling. EPA 600/6-90-008. ORD, Washington, DC.

[66] U.S. EPA.. 1989. Risk Assessment Guidance for Superfund, or RAGS http://www.epa.gov/oswer/riskassessment/risk_superfund.htm

[67] U.S. EPA. 1987b. Processes, Coefficients, and Models for Simulation Toxic Organics and Heavy Metals in Surface Waters. EPA/600/3-87/015. Office of Research and Development, Athens, GA.

[68] Odor and Biological Hazard Exposure Measurement Studies for Sewage Treatment Plants:

[69] Abdou, Mamdouh HM. 2007. Health Impacts on Workers in Wastewater Treatment Plants in Jeddah City, Saudi Arabia. J Egypt Public Health Assoc., 82, No. 5 & 6.

[70] Fracchia, L; Pietronave, S; Rinaldi, M; Martinotti, MG. 2006. Site-related airborne biological hazard and seasonal variations in two wastewater treatment plants. Water Research, 40:1985-94.

[71] Johnson, DE; et, al. 1978. Health Implications of Sewage Treatment Facilities, Southwest Research Institute, San Antonio, TX, Contract No. 68-02-1746, USEPA Health Effects Research Laboratory, Cincinnati, OH.

[72] King County Dept. of Natural Resources and Parks. 2003. Bridgewater Project, Appendix 5-A. Odor and Air Quality: Treatment Plant. Seattle, Washington.

[73] Nielson, EM, et al.. Bioaerosol Exposure in Waste Collection: A Comparative Study on the Significance of Collection Equipment, Type of Waste and Seasonal Variation. Ann. Occup. Hyg. 41, No. 3, pp 325-344. 1997.

[74] Walters, M; Milton, D; Larsson, L; and Ford, T. Airborne Environmental Endotoxins: A Cross Validation of Sampling and Analysis Techniques. Appl. and Envir. Microbiology, 60, No. 3, p.996-1005, March 1994.

[75] WHO/UNEP. 1991. Environmental Impact Assessment: Sewage Treatment Plant for Port Said. UNEP Regional Seas Reports and Studies No. 133. Ministry of Development, New Communities, Housing and Public Utilities of Egypt.

[76] Trace Toxic Chemical Exposure to Sewage Treatment Plant Workers:

[77] Elia, VJ; Clark, CS; Majeti, VA; Gartside, PS; MacDonald, T; Richdale, N; Meyer, CR; Van Meer, GL; Hunninen, K. 1983. Hazardous chemical exposure at a municipal wastewater treatment plant. Environ Res.; 32 (2):360-71. Copyright 2010, 1105 Media

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[78] Environmental Protection Bureau. 2009. Investigation and Evaluation of VOCs Total Emissions from the Storm and Sewerage Systems in Kaohsiung City Area, Environmental Protection Bureau, Kaohsiung City Government Report (in Chinese), Taiwan.

[79] Occupational Health & Safety Newsletter. March 24, 2012.. Two Workers Die from Hydrogen Sulphide Inhalation, (10/12/11), Firm Fined $166,890 (USD).

13.13.5 Radon Assessment

[80] AECOM (2003). Sludge Treatment Facilities – Feasibility Study – EIA Report (Agreement No. CE 28/2003).

[81] Arup (2009). West New Territories (WENT) Landfill Extensions – Feasibility Study – EIA Report (Agreement No. CE 43/2006).

<End of Section 13>