9a.1.1.1 This section presents the assessment of the potential health risk impact associated with the construction and operation phases of the IWMF located in Tsang Tsui Ash Lagoon (TTAL) site.
9a.1.1.2
With reference to the Section
· Assess the potential health impacts of aerial emissions from the IWMF during operational phase;
· Assess the potential health impacts of biogas from sorting and recycling plant;
· Assess the potential health impacts of fugitive emissions during transportation, storage and handling of the waste and ash;
· Assess the potential health impacts of any radon emissions from pulverized fly ash (PFA) within the Tsang Tsui Ash Lagoon during construction and operation of the IWMF; and
· Assess any other potential accidental events.
9a.2 Potential Health Impacts of Aerial Emissions from the IWMF during Operational Phase
9a.2.1.1 The TTAL site are located in the northwest New Territories adjacent to the West New Territories (WENT) Landfill and the China Light and Power Company Ltd. (CLP) Black Point Power Station and the Castle Peak Power Station. The ash lagoons were constructed in the 1980s by CLP for the purpose of storing pulverized fuel ash (PFA). In addition to storing PFA, the lagoons are periodically mined of ash for commercial use.
9a.2.2.1
Based on our desktop literature
search, the conduct of full quantified health risk assessments has become
fairly standard for incinerators, but there is generally no regulatory
requirement, nor official guidance on how to conduct risk assessments for
incinerators. For example, the WHO has general guidelines, but there are no
specific quantitative recommendations on assumptions or equations that should
be used. The risk assessment procedures used in the
9a.2.2.2 The purpose of the hazard identification step is to identify compounds of potential concern (COPC) for quantitative evaluation and to generate emissions estimates for short-term (acute) and long-term (chronic) exposures to the selected COPCs.
Compounds of Potential Concern
9a.2.2.3 An early step of the health risk assessment involved reviewing data for compounds potentially present in facility emissions (due to presence in the waste stream, presence in stack gas emissions as products of incomplete combustion, or as a result of emissions from fugitive sources associated with waste handling and the combustion process), and then identifying the most toxic, prevalent, mobile and persistent compounds. Based on this analysis, COPCs are selected for evaluation in the health risk assessment.
9a.2.2.4 The IWMF thermal treatment facility is currently in the planning stages. As such, facility specific stack gas emissions data are not available. Therefore, to identify COPCs and their associated emission rates, it was necessary to evaluate information from a variety of different sources.
9a.2.2.5 Sources of information for selection of COPCs included regulatory air quality requirements or stack gas permit limits such as those provided in the Environmental Protection Department’s (EPD) Guidance Note on the Best Practicable Means (BPM) for Incinerators (EPD, 2008). Additional consideration was given to identifying COPCs that may be considered Persistent, Bioaccumulative and Toxic (PBT) chemicals, often of particular concern through indirect (ingestion) exposure pathways.
COPCs
9a.2.2.6 The list of identified COPCs is provided below.
Trace Metals
· Antimony
· Arsenic
· Beryllium
· Cadmium
· Chromium
· Cobalt
· Copper
· Lead
· Manganese
· Mercury
· Nickel
· Thallium
· Vanadium
· Zinc
Organic Compounds
· Polychlorinated biphenyls (PCBs)
· Polychlorinated dibenzodioxins and furans (dioxins/furans)
· Polynuclear aromatic hydrocarbons (PAHs)
Other Compounds
· Carbon monoxide
· Hydrochloric acid
· Hydrogen fluoride
· Nitrogen dioxide
· Particulate matter (respirable)
·
9a.2.2.7 These COPCs are representative of MSW thermal treatment facilities in general and are expected to represent those compounds or groups of compounds for which regulatory permit limits may be applicable and those that may be the most toxic, prevalent, mobile and persistent compounds in MSW emissions. Most of the compounds listed above are subject to the target concentration limits set by the EPD. For those COPCs (i.e. Beryllium, Zinc, PCBs & PAHs) not listed on the BPM, the emission rates are made reference to the “Quantitative risk assessment of stack emissions from municipal waste combustors”[1].
9a.2.2.8 Long-term maximum stack emission rates (in grams per second) have been developed for each COPC identified. Because stack gas measurement data are not available for the planned MSW thermal treatment unit, emission factors upon which emission rates are based may be higher than actual emission rates. This is customary in permitting MSW thermal treatment units since (1) certain values (such as Target Emission Levels established as part of the EIA) may become permit limits; (2) emissions from MSW thermal treatment units are known to fluctuate as a result of variations in waste composition; and (3) it is prudent to take an approach that assures the emissions will not be understated. It is important to emphasize that the final design of the planned MSW thermal treatment unit will incorporate good engineering practices and air pollution control (APC) systems which will minimize actual emissions.
9a.2.2.9 Concentration limits have been established by the Hong Kong EPD (Guidance Note on the BPM for Incinerators (Municipal Waste Incineration), BPM 12/1 (08)) for most of the metals listed above as well as hydrogen chloride (HCl), nitrogen oxides (NOx), particulate matter and dioxins and furans. These concentration limits are proposed as the basis for estimating emission rates of those COPCs except NOx. For NOx, the target emission levels for the IWMF would be set as half of respective concentration limits stipulated in BPM 12/1 (08). The emission rates have been estimated by multiplying the target concentration limits and the stack gas flow rate, which were determined from preliminary design parameters for the combustion unit at the IWMF. For Be, Zn, PCBs & PAHs, the maximum emission rates stated in the “Quantitative risk assessment of stack emissions from municipal waste combustors” is for the combustion of 1500 tonnes of waste per day. Since the design capacity of the IWMF is 3000 tpd, therefore two times the maximum emission rates stated in the above paper have been adopted for the assessment. In accordance with the above paper, the anticipated normal emission rates for Be, Zn, PCBs & PAHs would only be 2% to 11% of their corresponding maximum emission rates, taking into consideration the waste composition and the incinerator design of the IWMF, the assumed emission rates for Be, Zn, PCBs & PAHs adopted in this assessment are indeed conservative.
9a.2.3 Air Dispersion and Deposition Modelling
9a.2.3.1 Air dispersion and deposition of aerial emissions from the planned MSW thermal treatment units have been predicted from a combination of modelling efforts to support the health risk assessment.
9a.2.3.2 Potential cumulative impacts due to dispersion of aerial emissions from the IWMF have been predicted at existing and planned/committed Air Sensitive Receivers (ASRs) with the use of Industrial Source Complex (ISC) model (for the near field ASRs (i.e. TT1 to TT6)) and the Pollutants in the Atmosphere and their Transport over Hong Kong (PATH) Model. The proposed representative ASRs are listed in Table 9a.1. The detailed methodology for modelling air dispersion is presented in Section 3 of this EIA Report.
Table 9a.1 Identified Air Sensitive Receivers for the TTAL Site
|
Description |
Nature of ASR (1) |
Building
Height, m |
Ground level,
mPD |
Distance to
Project Boundary, m |
|
|
TT1 |
Ha Pak Nai |
R |
9 |
3.4 |
1989 |
|
TT2 |
Sludge Treatment Facilities Site Office |
I |
- |
5.0 |
205 |
|
TT3 |
EPD WENT Landfill Site Office |
I |
6 |
5.7 |
625 |
|
TT4 |
|
G/IC |
3 |
4.7 |
88 |
|
TT5 |
Black Point Power Station (Office) |
I |
9 |
5.6 |
1130 |
|
TT6 |
Lung Kwu Sheung Tan |
R |
6 |
3.4 |
1871 |
|
TM1 |
Block F, |
G/IC |
66 |
5.8 |
5627 |
|
TM2 |
|
R |
104 |
4.5 |
6149 |
|
TM3 |
|
R |
89 |
5.8 |
5961 |
|
TM4 |
|
R |
96 |
5.0 |
5770 |
|
TM5 |
Block 4, |
R |
102 |
16.0 |
5245 |
|
TM6 |
Leung King
Estate |
R |
102 |
10.0 |
4261 |
|
TC1 |
|
CDA |
141 |
7.5 |
14291 |
|
TC2 |
|
CDA |
153 |
6.8 |
14508 |
|
TC3 |
Ling Liang Church Sau Tak primary School |
G/IC |
21 |
6.4 |
14590 |
|
TC4 |
|
R |
108 |
9.3 |
14954 |
|
TC5 |
|
R |
129 |
11.1 |
14664 |
|
TC6 |
Yat Tung Estate - Hong Yat House |
R |
105 |
9.7 |
15523 |
|
AP1 |
Chek Lap Kok Fire Station |
C |
9 |
7.5 |
13317 |
|
AP2 |
Gate Gourmet Catering Building |
C |
30 |
6.7 |
12890 |
|
AP3 |
DHL |
C |
30 |
5.4 |
13636 |
|
AP4 |
Regal Airport Hotel |
C |
90 |
5.3 |
11253 |
|
AP5 |
SkyCity Nine Eagles Golf Course |
C |
- |
6.2 |
11496 |
|
AP6 |
SkyCity Nine Eagles Golf Course |
C |
- |
6.2 |
11700 |
|
AP7 |
Hong Kong SKyCity Marriott Hotel |
C |
45 |
6.2 |
11414 |
|
AP8 |
Terminal 2 |
G/IC |
25 |
6.4 |
11573 |
|
SLW1 |
Sha Lo Wan House No.1 |
R |
9 |
5.0 |
14195 |
|
SLW2 |
|
R |
9 |
4.9 |
14556 |
|
SLW3 |
Tin Sum |
R |
9 |
5.7 |
14362 |
|
KT1 |
Block 6, Lai King Estate |
R |
42 |
40.1 |
22380 |
|
KT2 |
Block 7, Lai King Estate |
R |
66 |
40.1 |
22507 |
|
KT3 |
Lai King Home |
R |
12 |
40 |
22631 |
|
KT4 |
|
|
6 |
38.5 |
22867 |
|
KT5 |
Lai Hong House, |
R |
135 |
25 |
23526 |
|
KT6 |
|
G/IC |
30 |
38.9 |
23523 |
|
KT7 |
|
G/IC |
- |
7.6 |
24502 |
|
KT8 |
Hoi Yin House,
Hoi Lai Estate |
R |
108 |
5.9 |
24842 |
Note:
(1) R – Residential; C – Commercial; I –
Industrial; G/IC –Government / Institution / Community; CDA - Comprehensive
Development Area
Deposition Modelling Analysis
9a.2.3.3 Deposition of facility-related COPCs were used to evaluate potential cumulative indirect exposure through the food chain as a result of COPCs that are deposited onto soil and then taken up into the food chain. ISC model was used to predict deposition rates for particles and vapours emitted from the IWMF stack. ISC deposition modelling analysis have been conducted in accordance with USEPA recommendations for conducting modelling in support of health risk assessment as outlined in the HHRAP guidance (USEPA, 2005). The modelling procedures and input requirements required for modelling are discussed below.
9a.2.3.4
The modelling has been
performed with a unit (
9a.2.3.5 In addition to the physical stack parameters and exhaust stack parameters, particle size data on stack emission are required to perform deposition modelling.
9a.2.3.6 Unit-specific particle size data were not available since the unit has not yet been built. Therefore, the aerodynamic size distribution of emitted particulate was based on published data for similar types of units, which can be found in the open literature. For example, USEPA’s Technology Transfer Network Clearing House for Emission Inventories and Emission Factors (http://www.epa.gov/ttn/chief/ap42/) contains information on particle size distribution data and sized emission factors for selected sources, including municipal solid waste incinerators.
9a.2.3.7 In accordance with the HHRAP (USEPA, 2005), two different particle size distributions have been modelled. The distribution of particle mass was used to represent all metals except mercury when present. Semi-volatile organic species and some mercury species that tend to vaporize during combustion and condense on the surface of emitted flyash are represented by a surface area-weighted size distribution (“particle-bound”). Elemental mercury and a fraction of divalent mercury are modelled as vapours. This approach tends to produce more realistic deposition rates of these materials in the immediate vicinity of the source. The proposed particle distributions are shown in Table 9a.2.
Table 9a.2 Particle Size Distributions
|
Mean Particle Diameter (µm)(1) |
Mass Fraction(1) |
Surface Area Fraction(2) |
|
0.11 |
0.237 |
0.878 |
|
0.61 |
0.0661 |
0.0442 |
|
1.00 |
0.0577 |
0.0235 |
|
1.70 |
0.0717 |
0.0172 |
|
2.93 |
0.0785 |
0.0109 |
|
4.53 |
0.114 |
0.0102 |
|
6.68 |
0.174 |
0.0106 |
|
10.23 |
0.0877 |
0.00349 |
|
25.16 |
0.114 |
0.00184 |
|
(1) Compliance test at the Covanta Hempstead EfW
Facility (Radian, 1989) (2) Calculated based on assumed spherical particle diameter and mass fraction |
||
9a.2.3.8 The deposition modelling has been conducted based on the meteorological data extracted from the PATH model (i.e. MM5 hourly meteorological data).
Application of ISC
9a.2.3.9
ISC was applied to determine
long-term averages (based on one year modelled) of wet, dry, and total
deposition for vapours, particles, and particle-bound compounds. The modelling domain included an area in the
vicinity of the facility (
1)
wet
and dry deposition of particles, based on mass-weighted particle distribution
including plume depletion;
2)
wet
and dry deposition of particles, based on area-weighted particle size
distribution including plume depletion; and
3)
wet
and dry deposition of vaporous gases with plume depletion.
9a.2.4.1 In this step of the risk assessment process, hypothetical human receptors and potential exposure pathways through which such receptors may be exposed to facility-related COPCs were identified. Selection of such potential exposure scenarios was based on the characteristics of the facility and surrounding area, and activities that could take place in the vicinity of the facility. Dispersion of COPCs into the ambient air allows direct human exposure to COPCs through inhalation. COPCs that are deposited onto soil, water or plants (such as vegetables), are available for indirect exposure through the ingestion of soil, water, or produce. Additionally, the COPCs are potentially available to other secondary indirect pathways of exposure, including ingestion of locally raised agricultural products (beef, dairy, pork, and poultry products), or consumption of locally caught fish. The goal of the exposure assessment is to predict the magnitude of potential human exposure to COPCs in emissions from the facility through a variety of assumed exposure pathways.
9a.2.4.2
In the combustion risk
assessment process, the air dispersion and deposition modelling, discussed in Section
9a.2.4.3
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 TTAL site was considered so that the receptor scenarios chosen
for the health risk assessment would be appropriate for the
9a.2.4.4 The TTAL site is not identified as having a large population of sensitive receptors in the vicinity. A more detailed discussion on land use, focused on a vicinity of the facility is presented below to ensure that the maximally impacted receptors were evaluated in the risk assessment.
Chronic Exposure Scenarios
9a.2.4.5 The locations of current exposure scenarios have been selected based on a combination of the air dispersion and deposition modelling results and actual land uses identified in the vicinity of each site. Inhalation exposure has been evaluated under each scenario. The locations of the ASRs as described in Section 9a.2.3 above were evaluated in the context of the air modelling results to ensure that the locations of the maximum ambient concentrations were included in the evaluation. The indirect pathways have only been evaluated under the relevant scenarios (i.e., ingestion of fish is only be evaluated under the fisher scenario) and in relevant locations (i.e., areas capable of supporting the activity).
Residential
9a.2.4.6 A reasonable resident scenario was evaluated at the off-site location with the highest estimated soil (corresponding to the location of maximum total deposition) concentration to ensure that potential exposures for a resident are not underestimated.
9a.2.4.7
The Tsang Tsui Ash Lagoon is in
an isolated location away from
Farming
9a.2.4.8
Most agricultural produce
consumed in Hong Kong is imported from neighbouring mainland
9a.2.4.9 Local land use in the vicinity of the TTAL site with regards to agricultural production is described below in more detail.
9a.2.4.10
The TTAL site is located at the
CLP ash lagoons and is adjacent to the existing WENT Landfill and its future
extension. In accordance with the
information available from the Agriculture, Fisheries, and Conservation
Department (http://www.afcd.gov.hk/english/publications/publications_agr/files/Map_AFS_HK_10_2009.pdf),
several locally accredited farms are located in approximately
9a.2.4.11
As the vast majority of
foodstuffs in
Fishing
9a.2.4.12
Hong Kong’s commercial fishing
activities are conducted mainly in the waters of the adjacent continental shelf
in the South and
9a.2.4.13
The
9a.2.4.14 A compliance check of the maximum permitted concentration of certain metals present in foods due to the Project as stipulated in “Food Adulteration (Metallic Contamination) Regulations” by the Centre for Food Safety, was conducted based on the risk modelling results. Two schedules of the maximum permitted concentration of certain metals present in specified foods are listed below.
Table
9a.3 First
Schedule – Maximum
permitted concentration of certain metals naturally present in specified foods
|
Metal |
Description of food |
Maximum permitted
concentration in parts per million |
|
Arsenic |
Solids being fish and fish products |
6 |
|
Solids being shellfish and shellfish products |
10 |
Table
9a.4 Second Schedule – Maximum permitted concentration of certain metals
present in specified foods
|
Metal |
Description of food |
Maximum permitted
concentration in parts per million |
|
Antimony |
Cereals and vegetables |
1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
1 |
|
|
Meat of animal and poultry |
1 |
|
|
Arsenic |
Solids other than- |
1.4 |
|
All food in liquid form |
0.14 |
|
|
Cadmium |
Cereals and vegetables |
0.1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
2 |
|
|
Meat of animal and poultry |
0.2 |
|
|
Chromium |
Cereals and vegetables |
1 |
|
Fish, crab-meat, oysters, prawns and
shrimps |
1 |
|
|
Meat of animal and poultry |
1 |
|
|
Lead |
All food in solid form |
6 |
|
Mercury |
All food in solid form |
0.5 |
|
Tin |
All food in solid form |
230 |
Acute Exposure Scenarios
9a.2.4.15 Acute exposure has been evaluated at the selected ASRs described in Section 9a.2.3.
Chronic Residential Pathways
9a.2.4.16 Chronic exposure has been evaluated for adult and child residents via the following pathways:
· Inhalation of vapours and particulates
· Incidental ingestion of soil
· Ingestion of home-grown produce
9a.2.4.17
Fresh water is limited in Hong
Kong, with approximately 70-80% of fresh water coming directly from Dongjiang
(the
Chronic Farmer Pathways
9a.2.4.18
According to the Agriculture,
Fisheries, and Conservation Department of Hong Kong, at the end of 2008, land
used in Hong Kong for vegetable, flower, field crop, and orchard were
· Inhalation of vapours and particles
· Incidental ingestion of soil
· Ingestion of home-grown produce
· Ingestion of home-reared chicken and eggs
· Ingestion of home-reared pork
Chronic Fisherman Pathways
9a.2.4.19 Exposure via the following pathways have been evaluated for adult and child fishers:
· Inhalation of vapours and particles
· Incidental ingestion of soil
· Ingestion of home-grown produce
· Ingestion of fish
Acute Pathways
9a.2.4.20 Acute exposure has been evaluated via the inhalation pathway at the selected ASRs described in Section 9a.2.3.
9a.2.4.21 Except where noted in this EIA Report, the equations and input parameters presented in the final HHRAP guidance (2005) were used to estimate chemical concentrations in media and food sources for the standard exposure scenarios (resident, farmer, fisher).
Body Weight
9a.2.4.22 The exposure dose is defined as the amount of COPC taken into the receptor and is expressed in units of milligrams of COPC per kilogram of body weight per day (mg/kg-day). Because exposure is normalized by body weight (is in the denominator of the intake equation), small differences in body weight can substantially increase or decrease estimated intakes. In general, Asians are smaller than Americans. Therefore, use of the body weight assumptions recommended in the HHRAP (USEPA, 2005) is not appropriate and a population-specific body weight is proposed for use in this assessment.
9a.2.4.23
The adult and child body
weights used by the Hong Kong EPD to develop Risk-Based Remediation Goals
(RBRGs) are
Food Consumption Rates
9a.2.4.24
The WHO has implemented the
Global Environment Monitoring System/Food Contamination Monitoring and
Assessment Programme (GEMS/Food Regional Diets) to assess the levels and trends
of potentially hazardous chemicals in food and their significance for human
health and trade (WHO, 2003). As part of
this dietary exposure assessment mandate, GEMS/Food Regional Diets has
developed five regional diets which are currently used for predicting dietary
intake of pesticide residues according to internationally accepted
methodologies. The GEMS/Food Regional
Diets are based on Food Balance Sheet (FBS) data compiled by the Food and
Agriculture Organization of the United Nations (FAO) from selected countries to
represent five regional dietary patterns.
The regions covered are Middle Eastern, Far Eastern, African, Latin American,
and European. Hong Kong is included in
the Far East region along with
9a.2.4.25
Table 9a.5 summarizes
consumption rates in grams per day (g/day) for relevant food items from the
GEMS/Food Regional Diets (WHO, 2003;
http://www.who.int/foodsafety/chem/en/gems_regional_diet.pdf). The GEMS/ Food Regional Diets only provide
adult consumption rates. Therefore,
child meat consumption rates are assumed to be 15% of the adult value and child
vegetable consumption rates are assumed to be 30% of the adult value. The percentages used to adjust adult
consumption rates for children are based on the ratio between adult and child
food consumption rates for the
Table 9a.5 Food Consumption Rates
|
Individual
Adult Consumption Rates from the GEMS/Food (2003) for the |
|||||||
|
Total
Vegetables |
Total
Fish |
Poultry
Products |
Pork |
||||
|
Adult |
Child (a) |
Adult |
Child (b) |
Adult |
Child (b) |
Adult |
Child (b) |
|
287 |
86.1 |
31.5 |
4.7 |
24.6 |
3.7 |
28.2 |
4.2 |
Notes:
(a) 30% of adult
consumption rate.
(b) 15% of adult
consumption rate.
9a.2.4.26 Based on detailed national surveys, average food consumption estimates based on FBS data are about 15% higher than actual average food consumption in the worst cases (e.g. certain fruits and other highly perishable products). This is partly because GEMS/Food Regional Diet values are given for the whole raw agricultural commodity. This approach is conservative because the production rate data are provided in tons/day, but include edible and non-edible parts of such as bone and shell. In addition, waste at the household or individual level is not taken into account, which also overestimates consumption.
9a.2.4.27
Two additional sources of fish
consumption rates for Asian populations were located in the open scientific
literature that quoted higher fish consumption rates. A paper entitled “Mercury and Organochlorine
Exposure from Fish Consumption in Hong Kong” quotes an average Hong Kong fish
consumption rate of
9a.2.4.28 Despite the higher fish consumption rates found in these two papers, the GEMS/Food Regional Diets (WHO, 2003) consumption rates were used in the health risk assessment for all food items for the following reasons:
· The consumption rates recommended in the GEMS/Food Regional Diet are already being used to predict dietary intake of pesticide residues by the WHO and are, therefore, internationally accepted for use in estimating chronic hazards and risks;
· The GEMS/Food Regional Diets provide data on all of the food commodities, making it possible to use one source for all consumption rates, thus avoiding the potential internal inconsistencies that could arise if multiple sources of food consumption rates were used; and
· Original sources for the literature values could not be located for verification.
Estimation of Chemical Concentrations in Environmental Media
9a.2.4.29
Table 9a.6 summarizes the mechanisms by which environmental
media can become contaminated as a result of incinerator emissions. The table also summarizes the inputs
necessary for estimating those media concentrations. Equations and input parameters presented in
the HHRAP guidance (USEPA, 2005) were used to estimate chemical concentrations
in media and food sources. The HHRAP
guidance provides standard conservative fate and transport and
chemical-specific assumptions for each of the media and food sources of
interest. The HHRAP guidance was
developed for use in the
9a.2.4.30 Where the results of the risk assessment indicate that a default assumption may be unrealistically influencing the results of the assessment, site-specific refinements to the health risk assessment have been made and documented accordingly.
9a.2.4.31 For those exposure scenarios for which default fate and transport modelling parameters are not available in the HHRAP guidance, site specific parameters have been derived, consistent with the recommendations of the HHRAP guidance. Examples of site-specific inputs would include the delineation of the extent of the watersheds and water body surface areas (in the vicinity of the facility). Estimated input parameters for the algorithms outlined in the HHRAP was based on knowledge of the site and its vicinity (e.g., soil types, watershed areas, land slopes, etc.) obtained from existing reports, topographic maps, and/or soil surveys. It should be noted that the HHRAP model for evaluating watershed and water body impacts is designed and intended for use in evaluating freshwater streams, rivers, ponds and lakes. Therefore, the local marine environment was treated as a lake in the HHRAP modelling.
Table 9a.6 Mechanisms for Environmental Media Contamination
|
Pathway |
Mechanisms of Media Contamination |
Input |
|
Direct Inhalation |
Air concentration of a
pollutant based on air quality modelling run as described in Section |
1. Vapour phase air concentration |
|
Soil Ingestion |
Soil may become
contaminated by emissions through direct deposition onto the soil. The soil equation includes a loss term
which accounts for the loss of contaminant from the soil after deposition by
several mechanisms, including leaching, erosion, runoff, degradation, and
volatilization. |
2. Emission rates 3. Modelled vapour phase air
concentration, wet deposition from vapour phase, dry deposition from particle
phase, and wet deposition from particle phase 4. Soil concentration due to
deposition |
|
Consumption of
aboveground produce |
Produce may become
contaminated by emissions through direct deposition onto the plant, direct
uptake of vapour phase contaminant, and root uptake of contaminants deposited
on the soil. |
1. Emission rates 2. Modelled vapour phase air
concentration, wet deposition from vapour phase, dry deposition from particle
phase, and wet deposition from particle phase 3. Soil concentration due to
deposition 4. Air-to-plant biotransfer factors |
|
Consumption of Animal
Products |
Animal tissue may be
contaminated through ingestion of contaminated forage, grain, silage, and
soil by livestock or wildlife. |
1. Emission rates 2. Modelled vapour phase air
concentration, wet deposition from vapour phase, dry deposition from particle
phase, and wet deposition from particle phase 3. Soil concentration due to
deposition 4. Forage and silage concentrations 5. Beef concentration due to plant
and soil ingestion by cattle 6. Milk concentration due to plant
and soil ingestion by cows |
|
Consumption of
Drinking Water and Fish |
Contaminant
concentrations in a water body are partitioned between dissolved phase,
suspended sediment, and benthic sediment.
Contaminant concentrations in fish are calculated from the contaminant
concentrations in the water body. |
1. Soil concentration averaged across
the watershed 2. Total contaminant load to the
water body due to runoff, soil erosion, and direct deposition 3. Dissolved water concentration 4. Total water column concentration 5. Sediment concentration 6. Bioconcentration and/or
bioaccumulation factors 7. Biota-to-sediment accumulation
factors |
9a.2.4.32 Table 9a.7 presents a summary of the water body and watershed parameters that have been identified for input to the risk assessment. Equations for evaluating exposure and risk are presented in Appendix 9.1.
Table 9a.7 Summary of General Water Body and Watershed Parameters
|
Parameter |
Unit |
Fate & Transport Variable |
|
Average Annual Runoff |
cm/year |
220 |
|
Average Wind Speed |
m/s |
3.4 |
|
Water Body Surface Area |
m2 |
6 x 107 |
|
Total Watershed Area Receiving
Pollutant |
m2 |
5 x 107 |
|
Average Volumetric Flow Rate |
m3/year |
6.3 x 1011 |
|
Depth of Water Column |
m |
7 |
|
USLE Rainfall Factor |
per year |
550 |
9a.2.5.1 The purpose of the toxicity assessment is to identify the types of adverse health effects a COPC may potentially cause, and to define the relationship between the dose of a compound and the likelihood or magnitude of an adverse health effect (response). Adverse health effects are typically characterized in the health risk assessment as carcinogenic or non-carcinogenic for long-term exposure and acute hazard for short-term exposure.
Toxicity Criteria / Guidelines for Long-Term Exposure
9a.2.5.2 COPCs are classified as to whether they exhibit cancer and non-cancer health effects and whether health effects can result from ingestion or inhalation of the chemical.
9a.2.5.3 The toxicity of each COPC is based on toxicity factors developed by relevant studies. The toxicity factors are referred to as dose-response values, and are derived for both inhalation and oral routes of exposure. The dose-response values derived by evaluation of potential carcinogenic health effects resulting from long-term exposure to COPCs are called cancer slope factors [CSFs; expressed in units of (mg/kg-day)-1] for oral exposure pathways, and unit risk factors [URFs; expressed in units of (ug/m3)-1] for direct inhalation exposure pathways. The dose-response values derived for evaluation of potential non-carcinogenic health effects resulting from long-term exposure to COPC are called reference doses (RfDs) or tolerable daily intakes (TDI) expressed in units of mg/kg-day for oral exposure pathways and reference concentrations (RfCs) or tolerable concentrations in air (TCA) expressed in mg/m3) for inhalation exposure pathways. For some COPCs, both cancer and non-cancer toxicity factors are available because the chemical has been associated with both cancer and non-cancer health effects. The health risk assessment includes an evaluation of both potentially carcinogenic and non-carcinogenic COPCs.
Other COPCs
9a.2.5.5 For the other COPCs, the following sources of information have been reviewed to determine the toxicity factors for use in evaluating exposure and risk through inhalation and other indirect pathways (i.e. ingestion of food, soil, water)
· Air Quality Guidelines (AQG) values by the World Health Organization (WHO)
· World Health Organization (WHO) documents
· USEPA’s Integrated Risk Information System (IRIS)
· Publications of the USEPA’s Superfund Technical Support Center (STSC) (only toxicological indices which have supporting documentation on their derivation)
· Other relevant international publications of toxicology studies
9a.2.5.7 Table 9a.8 contains all the toxicity criteria used in the risk assessment. For the sake of sensitivity test, the selected toxicity factors have been taken as the most conservative toxicity factors, if available, from the sources of information reviewed under Section 9a.2.5.4 above.
Table 9a.8 Toxicity Factors for the Risk Assessment
|
COPCs |
Inhalation Unit Risk Factor (μg/m3)-1 |
Inhalation RfC (μg/m3) |
Cancer Slope Factor (mg/kg-day)-1 |
Oral RfD/TDI (mg/kg-day) |
|
Sb |
NA |
1 HSE (2005) |
NA |
0.006 WHO(2008) |
|
As |
0.0015 WHO (2000) |
NA(a) |
1.5 IRIS (2009) |
0.002 WHO (2008) |
|
Be |
0.0024 IRIS (2009) |
0.02 IRIS (2009) |
NA |
0.002 IRIS (2009) |
|
Cd |
0.0018 IRIS (2009) |
NA(b) |
NA |
0.0005 (water) 0.001 (food) IRIS (2009) |
|
Cr (VI) |
0.04 WHO (2000) |
0.1 (particulate) IRIS (2009) |
NA |
0.003 IRIS (2009) |
|
Co |
NA |
0.2 HSE (2005) |
NA |
NA |
|
Cu |
NA |
2 HSE (2005) |
NA |
NA |
|
Dioxins |
NA |
NA(c) |
150000 HEAST (1997) |
2.3 x 10-9 WHO (2001) |
|
HCl |
NA |
20 IRIS (2009) |
NA |
NA |
|
HF |
-- |
3 HSE (2005) |
-- |
-- |
|
Pb |
NA |
0.5 WHO (2000) |
NA |
0.0035 WHO (2008) |
|
Mn |
NA |
0.15 WHO (2000) |
NA |
0.06 WHO (2008) |
|
Hg |
NA |
1 WHO (2000) |
NA |
0.002 WHO (2008) |
|
Ni |
0.0004 WHO (2000) |
NA(d) |
NA |
0.012 WHO (2008) |
|
PCBs |
NA |
NA(e) |
2 IRIS (2009) |
NA |
|
PAHs |
0.09 (B(a)P) WHO (2000) |
3 (Naphthalene) IRIS (2009) |
0.5 (B(a)P) WHO (2008) |
0.02 (Naphthalene) IRIS (2009) |
|
Tl |
NA |
0.2 HSE (2005) |
NA |
0.00008 (chloride /carbonate) IRIS (2009) |
|
V |
NA |
1 WHO (2000) |
NA |
NA |
|
Zn |
NA |
NA(f) |
NA |
0.3 IRIS (2009) |
Note
(a)
Arsenic is a human
carcinogen. Present risk estimates have been derived from studies in exposed
human populations in
(b)
International Agency for
Research on Cancer has classified cadmium and cadmium compounds as human
carcinogens, having concluded that there was sufficient evidence that cadmium
can produce lung cancers in humans and animals exposed by inhalation. Yet
because of the identified and controversial influence of concomitant exposure
to arsenic in the epidemiological study, however, no reliable unit risk can be
derived to estimate the excess lifetime risk for lung cancer. (Reference: WHO
Air Quality Guidelines – 2nd Edition)
(c)
An air quality guideline
for Dioxins is not proposed because direct inhalation exposures constitute only
a small proportion of the total exposure, generally less than 5% of the daily
intake from food. (Reference: WHO Air Quality Guidelines – 2nd
Edition)
(d)
Even if the dermatological
effects of nickel are the most common, such effects are not considered to be
critically linked to ambient air levels. Nickel compounds are human carcinogens
by inhalation exposure. The present data are derived from studies in
occupationally exposed human populations. Yet assuming a linear dose response,
no safe level for nickel compounds can be recommended. (Reference: WHO Air
Quality Guidelines – 2nd Edition)
(e)
An air quality guideline
for PCBs is not proposed because direct inhalation exposures constitute only a
small proportion of the total exposure, in the order of 1-2% of the daily
intake from food. (Reference: WHO Air
Quality Guidelines – 2nd Edition)
(f)
No information from
WHO. With reference to IRIS (2009),
available data are not suitable for the derivation of an RfC for zinc. (Reference: http://www.epa.gov/iris/subst/0426.htm#refinhal)
(g)
Sources of References:
WHO (1998): http://www.who.int/ipcs/publications/en/exe-sum-final.pdf
WHO (2000): http://www.euro.who.int/document/e71922.pdf
WHO (2001): http://www.who.int/ipcs/food/jecfa/summaries/en/summary_57.pdf
WHO (2008): http://www.who.int/water_sanitation_health/dwq/fulltext.pdf
USEPA (IRIS, 2009): http://www.epa.gov/iris/index.html
HSE (2005): Health and
Safety Executive. EH40/2005 Workplace exposure limits
HEAST (1997): Health
Effects Assessment Summary Tables (HEAST). Fiscal Year 1997 Update". Office of Solid Waste and Emergency Response.
EPA-540-R-97-036. July 1997
9a.2.5.8 Discussed below are a few special cases for which the specification of toxicity criteria / guidelines is somewhat more complex.
9a.2.5.9 For the purpose of health risk assessment, chromium and chromium compounds need to be speciated into trivalent and hexavalent chromium species with trivalent chromium or Cr(III) being non-toxic and hexavalent chromium or Cr(VI) is toxic. With reference to the 2005 National Emissions Inventory Data prepared by USEPA, the percentage of Cr (VI) in total Cr is 19% for emissions of large municipal waste combustors. Therefore, a 19% Cr(VI) speciation factor is applied to the total Cr emissions in this health risk assessment.
Lead
9a.2.5.10 USEPA has not derived RfDs for lead due to uncertainties about the health effects and dose-response associated with exposures to lead. Based on findings that neurobehavioral effects in young children occur at exposure levels below those that have caused cancer in laboratory animals, an Integrated Exposure Uptake Biokinetic (IEUBK) Model for Lead in Children has been developed by USEPA (USEPA, 2002b). USEPA guidance (USEPA, 2005) has recommended the use of this IEUBK model in combustor health risk assessments.
9a.2.5.11 Several recent combustor facility risk studies have yielded extremely low incremental concentrations of lead in the modelled environmental media. Those concentrations are often so low that they are difficult to evaluate in the IEUBK model (due to threshold format restrictions). Therefore, the WHO (WHO, 2003) Tolerable Daily Intake (TDI) of 0.0035 mg/kg-day has been used to evaluate potential health risks associated with exposure to lead from the IWMF.
Polycyclic Aromatic Hydrocarbons (PAHs)
9a.2.5.12 Consistent with USEPA guidance (USEPA, 2005), the health risk assessment has considered both potential carcinogenic effects and non-carcinogenic toxicity for the potential PAH constituents. Potentially carcinogenic polycyclic aromatic hydrocarbon (PAH) are ranked in order of potency in relation to benzo(a)pyrene. For those PAH compounds that are potentially carcinogenic, the risk analysis has used the USEPA-developed comparative potency factors to derive cancer slope factors representative of these compounds and their potential toxicity relative to benzo(a)pyrene (USEPA, 1993), which are mostly consistent with those endorsed by the WHO (WHO, 1998). The only differences are for benzo(k)fluoranthene (WHO value of 0.1 vs. U.S. EPA value of 0.01) and chrysene (no WHO potency factor vs. the U.S. EPA recommended 0.001). Potential non-carcinogenic effects of PAHs has been evaluated using the RfD for naphthalene recommended by USEPA if total PAHs are evaluated or individual PAH toxicity factors recommended by USEPA if emission rates for individual PAHs are located in the literature.
9a.2.5.13 Although there are hundreds of dioxin and furan compounds, those compounds for which potential human health impacts can be quantitatively evaluated are the dibenzodioxin, and dibenzofuran congeners which have four chlorine molecules attached in positions 2, 3, 7, and 8 on the central ring structure. A CSF has been developed only for 2,3,7,8-tetrachloro-dibenzo-p-dioxin (2,3,7,8-TCDD).
9a.2.5.14 The WHO has established (1998) and re-evaluated (2005) toxicity equivalency factors (TEFs) for dioxins and related compounds. Other congeners are assigned WHO TEFs that relate their toxicities to that of 2,3,7,8-TCDD (Van den Berg et al., 2005). This concept parallels that used for evaluating PAHs, as explained above.
9a.2.5.15 For this evaluation, since emission rates were based on the combined concentration limit for dioxins and furans, there was no need to apply the WHO TEFs (emissions were not estimated for individual congeners). Potential carcinogenic health risks associated with the dioxin and furans have been evaluated in accordance with the approach developed by USEPA, and recommended in the 2005 HHRAP as follows: Risks have been calculated for combined dioxin and furans using the cancer slope factor for 2,3,7,8-TCDD listed in HEAST (USEPA, 1997).
9a.2.5.16 Dioxin and furan congeners may also have some risk of non-carcinogenic toxicity associated with them; however, there are no established RfDs with which to evaluate this hazard.
Polychlorinated Biphenyls
9a.2.5.17 Moderately chlorinated PCB congeners can have dioxin-like effects. This sub-category includes PCB congeners with four or more chlorine atoms and few substitutions in the ortho positions (positions designated 2, 2', 6, or 6'). They are sometimes referred to as “coplanar” PCBs, because the rings can rotate into the same plane if not blocked from rotation by ortho-substituted chlorine atoms. In this configuration, the shape of the PCB molecule is very similar to that of a dioxin molecule. Studies have shown that these dioxin-like congeners can react with the aryl hydrocarbon receptor; the same reaction believed to initiate the adverse effects of dioxins and furans.
9a.2.5.18 A recent revision of the TEF scheme was undertaken by the WHO (Van den Berg et al, 2005) in connection with a review of the WHO recommended Tolerable Daily Intake. The proposed scheme included coplanar congeners of PCBs within the overall TEQ scheme, by defining TEFs for 12 coplanar PCBs on the basis that their mode of action and the responses elicited in biological systems parallel those of the 2,3,7,8-positional dioxins and furans. The WHO-TEQ of the sample would be represented by the summation of the products of the concentrations of 17 dioxin/furan congeners and 12 PCB congeners by their respective TEFs. Risks from coplanar PCBs have been estimated by computing a toxicity equivalency quotient (TEQ) for PCBs, and then applying the slope factor for 2,3,7,8-TCDD.
9a.2.5.19 In addition to the coplanar (dioxin-like) PCB congeners, the remaining PCBs have also been evaluated in the risk assessment. After considering the accumulated research on PCBs and a number of studies of the transport and bioaccumulation of various congeners, USEPA derived three new CSFs to replace the former single CSF for PCBs. The upper-bound CSF designated for use when evaluating food-chain exposures and ingestion of soil is used to evaluate cancer risk associated with the remaining PCBs (the non-dioxin-like PCBs) in the mixture as recommended by USEPA.
Toxicity Criteria / Guidelines for Short-Term Exposure
9a.2.5.20 As currently recommended in the HHRAP guidance, it is proposed that potential risks due to short-term inhalation exposure (such as irritant or respiratory health effects) be evaluated in addition to the more commonly evaluated chronic risks to human health discussed above. Therefore, a screening level evaluation of short-term health effects has been conducted by comparing predicted short-term (maximum 1-hour) air concentrations against the findings of relevant toxicology studies.
Classical COPCs of the HKAQO
9a.2.5.21 For the classical COPCs of the HKAQO with potential acute health effects, the contribution of the IWMF project to the predicted cumulative short-term (hourly average) concentrations of these classical COPCs at the air sensitive receivers are analysed as part of this health risk assessment and compared against the findings of relevant toxicology studies.
Other COPCs
9a.2.5.22 For other COPCs with potential acute health effects, for the purpose of this risk assessment, the following sources of information have been reviewed to determine the inhalation reference level for use in evaluating exposure and risk through inhalation:
·
California EPA Acute Reference Exposure Levels (Cal/EPA,
2008);
·
Acute inhalation exposure guidelines (AEGL-1)
(USEPA, 2010);
·
Level 1 emergency planning guidelines (ERPG-1; DoE,
2010);
·
Temporary Emergency Exposure limits (TEEL-1; DoE,
2010); and
·
AEGL-2 values (USEPA, 2010).
9a.2.5.23 If no AEGL-1 value is available, but an AEGL-2 value is available, the AEGL-2 value was selected only if it is a more protective value (lower in concentration) than an ERPG-1, or a TEEL-1 value if either of these values is available.
9a.2.5.24 The adopted exposure limits/reference levels for short term exposure of COPCs are presented in Table 9a.9.
Table 9a.9 Exposure Limits/Reference Levels for COPCs Acute Exposure
|
COPC |
Exposure Limit/Reference Level (μg/m3,
1-hr averaging time) |
Source |
|
Sb |
1,500/10 = 150 |
TEEL-1 |
|
As |
30 /10 = 3 |
TEEL-1 |
|
Cd |
30/10 = 3 |
TEEL-1 |
|
Cr (VI) |
30/10 = 3 |
TEEL-1 |
|
Co |
3,000/10 = 300 |
TEEL-1 |
|
Cu |
100 |
Cal/EPA Acute
REL |
|
Dioxins |
No guideline |
- |
|
HCl |
2,100 |
Cal/EPA Acute
REL |
|
HF |
240 |
Cal/EPA Acute
REL |
|
Pb |
150/10 = 15 |
TEEL-1 |
|
Mn |
3,000/10 = 300 |
TEEL-1 |
|
Hg |
0.6 |
Cal/EPA Acute
REL |
|
Ni |
6.0 |
Cal/EPA Acute
REL |
|
Tl |
300/10 = 30 |
TEEL-1 |
|
V |
150/10 = 15 |
TEEL-1 |
9a.2.6.1 In the risk characterization step, the potential human health risks associated with COPC emissions from the MSW thermal treatment unit have been estimated. The risk characterization step combined the results of both the exposure assessment and the dose-response assessment to estimate the incremental potential risks to human health.
Classical COPCs of the HKAQO
9a.2.6.2
The highest cumulative annual
average SO2 concentrations predicted at the hot spot areas (see Section
9a.2.6.3 For the RSP, the highest cumulative annual average RSP concentrations predicted at the hot spot areas based on territory-wide scale model results (PATH model) would range from 39 to 48 μg/m3. The average contributions by the IWMF would be below 0.02%. As such, the associated additional risk for adverse health effects of RSP due to the IWMF are likely to be very small and are unlikely to be quantifiable[3].
9a.2.6.4 For NO2, the highest cumulative annual average NO2 concentrations predicted at the hot spot areas based on territory-wide scale model results (PATH model) would range from 13 to 40 μg/m3. The average contribution by the IWMF would range from 0.01 to 0.37%. The associated additional risk for adverse health effects of NO2 due to the IWMF are likely to be very small. As such, it is very unlikely that the NO2 emitted by the IWMF will cause significant long-term adverse health effects.
9a.2.6.5 The detailed percentage contributions of SO2, NO2 and RSP by the IWMF are presented in Appendix 9.3.
Other COPCs
9a.2.6.6 The cumulative non-carcinogenic health impact due to chronic inhalation, includes the impact arising from the IWMF plus the background contribution (including contribution from the nearby Sludge Treatment Facilities) are presented in Appendix 9.4. Cumulative chronic health impact of the IWMF at all receptors are assessed and compared with the exposure limits/reference levels. It is concluded that the effect are insignificant when compared to the proposed exposure limits/reference levels. No adverse chronic inhalation health effects are expected and no risks due to long-term exposure are expected.
9a.2.6.7 The potential for chemicals to cause adverse non-carcinogenic health effects has been assessed by dividing estimated exposure doses (determined for the exposure scenarios described above) by appropriate dose-response values, such as reference doses (RfDs). The resulting ratio is referred to as the "chemical-specific risk ratio" or hazard quotient. For individual chemicals, hazard quotients have been added across exposure pathways to determine the total non-carcinogenic hazard index (HI) for each receptor potentially exposed to facility-related COPC in the environment.
9a.2.6.8 The USEPA has determined that exposure to a chemical is not expected to cause significant adverse health effects if this total risk ratio, or HI, for all exposure pathways has a total value of 1 or less. The most recent USEPA risk management guidance (USEPA, 1998) describing management decisions for combustion facilities recommends, however, that it be assumed that 75% of this value is reserved for exposures that may come from other background sources. Thus, the guidance indicates that the remaining HI = 0.25 should serve as an initial screening benchmark for exposures that may be associated with the subject facility operations.
9a.2.6.9 Since a total HI of less than or equal to 1.0 generally indicates no significant risk of adverse non-carcinogenic human health effects, the more conservative approach of 0.25 would also support such a conclusion. The USEPA further recommends that if the resulting summation exceeds 0.25, the HI analysis should be re-examined and refined, such that only those chemicals exhibiting the same or similar toxicity endpoints (i.e., they affect the same target organ) are summed. Since chemicals may display a variety of effects depending on concentration, the toxic endpoint is defined in this context as the most sensitive non-carcinogenic health effect used to derive the RfD.
9a.2.6.10 With reference to risk assessment results on non-carcinogenic hazard presented in Appendix 9.5, it can be concluded that the Hazard Index at all receptors falls under 0.25. The highest hazard quotient occurs at receptor SLW2 with a value of 0.01. Therefore, the exposure of the receptors for the TTAL site to the non-carcinogenic COPCs is not expected to cause significant adverse health effects.
9a.2.6.11 Potential incremental ("excess") lifetime cancer risks have been calculated for each receptor by multiplying the appropriate CSF by the site-specific exposure dose level determined for each of the exposure scenarios described above. The cancer risks from each carcinogenic COPC and from each exposure pathway have been added together to estimate the total cancer risk for each receptor. The equation for estimating cancer risk is presented below:
Cancer Riski = I x ED x EF x CSF/AT x 365
Where:
I = Intake
(mg/kg-d)
ED = Exposure
duration (years)
EF = Exposure
frequency (days/year)
CSF = Cancer
slope factor (mg/kg-day)-1
AT = Averaging
time (days)
365 = Days/year
9a.2.6.12 Total cancer risk are calculated as follows:
Total
Cancer Risk = Σi Cancer
riski
9a.2.6.13 The USEPA risk management guidance[4] (USEPA, 1998) suggests a target risk level of 1x10-5 as an acceptable total for all contributions of carcinogenic risk at a designated individual receptor from the Project. In accordance with the USEPA risk management guidance, if a calculated risk falls within the target values, the authority may, without further investigation, conclude that the proposed project does not present an unacceptable risk.
9a.2.6.14 The predicted total carcinogenic risk at the representative receptors are summarized in Appendix 9.5. The results indicated that the predicted total carcinogenic risk from the Project at all receptors are less than 1x10-5. The highest total cancer risk occurs at receptor SLW2 with a value of 9.82x10-7. Therefore, it is expected that the Project would not present an unacceptable risk.
9a.2.6.15 Since the assessment results meet the both cancer risk and non-cancer hazard index criteria, no further analysis is presumed to be necessary.
Risks Due to Short-Term Exposure
9a.2.6.16
In addition to the potential
long-term risk to human health presented by COPCs emitted from the facility, short-term
or acute risk has been evaluated for direct inhalation COPCs. Acute exposure has been estimated, based on
maximum one-hour average air concentrations predicted from the atmospheric
dispersion modelling described in Section
Classical COPCs of the HKAQO
9a.2.6.17
The average contribution of
1-hr SO2 concentrations by the IWMF are predicted at the hot spot
areas (see Section
9a.2.6.18 For CO, the average contribution of 1-hr CO concentrations by the IWMF are predicted at the hot spot areas to be less than 0.04%. The predicted highest cumulative 1-hr average CO concentration is 1712µg/m3 based on territory-wide scale model results (PATH model) and is far below international safe levels[6]. Therefore, adverse health effect of CO contribution from the IWMF is negligible.
9a.2.6.19 For NO2, the predicted highest cumulative 1-hr average NO2 concentration is 275µg/m3 based on territory-wide scale model results (PATH model). The predicted 1-hr average concentration is below the level with clear observable acute health effects in many short term experimental toxicology studies[7]. Nevertheless, the average contribution of 1-hr average NO2 concentration at the hot spot areas by the IWMF is predicted to be in the range of 0.01% to 0.31%. Therefore, the acute adverse health effects of NO2 due to the IWMF would be very small and are unlikely to be quantifiable.
9a.2.6.20 In summary, the IWMF would make only small additional contributions to local concentration of CO, SO2 and NO2. While it is not possible to rule out adverse health effects from the IWMF with complete certainty, the impact on health from small additional air pollutants is likely to be very small and unlikely to be quantifiable.
Other COPCs
9a.2.6.21 The cumulative non-carcinogenic health impact due to direct inhalation, includes the impact arising from the IWMF plus the background contribution (including contribution from the nearby Sludge Treatment Facilities) are presented in Appendix 9.6. Cumulative acute health impact of the IWMF at all receptors are assessed and compared with the exposure limits/reference levels. It is concluded that the effect are insignificant when compared to the proposed exposure limits/reference levels. No adverse acute effects are expected.
9a.2.6.22 Maximum Permitted Concentration of Certain Metals present in Foods
9a.2.6.23 In order to determine the compliance of the maximum permitted concentration of certain metals present in foods due to the Project as stipulated in “Food Adulteration (Metallic Contamination) Regulations” by the Centre for Food Safety, a compliance check was conducted based on the risk modelling results. The concentrations of the metals listed in Table 9a.3 and Table 9a.4 at each receptor location were compared with the maximum permitted concentrations.
9a.2.6.24 Based on the assessment results presented in Appendix 9.7, it is concluded that food grown in the vicinity of all receptor locations would comply with the maximum permitted concentrations stipulated by the Centre for Food Safety. The concentrations of Antimony, Arsenic, Cadmium, Chromium, Lead and Mercury at all receptor locations fall under the maximum permitted concentrations listed in the first and second schedules in Table 9a.3 and Table 9a.4.
9a.2.6.25 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 models. In some cases, the values may vary widely between a conservative upper confidence limit and a mean 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.
9a.2.6.26 The health risk assessment is a complex process, requiring the integration of the followings:
·
Release of COPCs into the environment;
·
Transport of the COPCs 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.
9a.2.6.27 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.
Hazard Identification
9a.2.6.28 COPCs are identified based on the air pollutants listed in EPD’s BPM12/1. This list of chemicals may not cover all the chemicals emitted from the stack of the IWMF which could pose a threat to human health, which may underestimate the risk. However, it is considered that although the COPCs identified may not be exhaustive, it appeared sufficiently comprehensive for the purpose of the assessment because BPM12/1 serves the purpose to prevent the air pollutant emissions from incinerator stack from harming the environment and human health or creating nuisance.
9a.2.6.29 The adopted emission factors of COPCs from the IWMF stack for air quality modelling are based on the target exhaust gas concentration limits proposed for the IWMF. It is considered that this assumption would overestimate the risk because COPC emission rate from the IWMF would not reach the allowed maximum rate all the time. Moreover, the emission factors for individual heavy metals (except Hg) are based on the “exhaust gas concentration for combined metal species”[8], this would further overestimate the risk.
Exposure Assessment
9a.2.6.30 In this stage of the assessment, air dispersion model is used to predict the COPC dispersion in air and the COPC concentrations at potential human receptors. As computer models are simplifications of reality requiring exclusion of some variables that influence predictions, of which would introduce uncertainty in the prediction of COPC concentration at potential human receptors and may in turn overestimate or underestimate the risk.
9a.2.6.31 Moreover, the air quality modelling results adopted for exposure assessment are modelled based on the worst case scenario which would not occur all the time. This conservative approach in air quality modelling would overestimate the risk.
9a.2.6.32 The characteristic parameter values for human receptors used in the HHRA are adopted from the default values suggested in USEPA (2005). The values adopted may not precisely reflect the conditions of potential human receptors identified, which may overestimate or underestimate the risk.
Dose-response Assessment
9a.2.6.33 The toxicity criteria / guidelines[9] adopted from agencies would introduce uncertainty to the HHRA. These toxicity criteria / guidelines are used as single-point estimates throughout the analysis with uncertainty and variability associated with them. Moreover, the arbitrary application of safety factor to occupational exposure limit for derivation of toxicity criteria / guidelines for long term COPC exposure is another source of uncertainty. This uncertainty may overestimate or underestimate the risk. However, it should be noted that much of the uncertainty and variability associated with the toxicity criteria / guidelines shall be accounted for in the process that the agencies setting verified toxicity criteria / guidelines.
9a.3 Potential Health Impacts of Biogas from Sorting and Recycling Plant
9a.3.1.1 This section reviewed the potential health impact associated with biogas in sorting and recycling plant (i.e. Mechanical Treatment) operations. Mechanical Treatment Plant includes the following components:
· Municipal Solid Waste (MSW) receiving, storage and feeding system
· Mechanical treatment system including shredding and sorting facilities
· Products and by-products storage and handling system
· Odour control system
· Process control and monitoring system
9a.3.1.2 In a mechanical treatment process for mixed MSW treatment, mechanical part is used mainly to pre-treat the waste for the subsequent treatment process, and meanwhile recover the recyclable materials, such as metals, plastic and paper.
9a.3.2 Description of Potential Biogas Emissions
9a.3.2.1 The objectives of mechanical treatment process include preparation and sorting / separation of waste. Waste preparation is to split the refuse bags, remove bulky waste and shred and homogenise the waste into smaller particle sizes suitable for separation processes. The mechanical sorting processes then separate the prepared wastes into the following parts:
· Recyclable materials including metals, paper and plastics;
· Inappropriate constituents for subsequent biological treatment, including:
§
Over-size refuse such as textiles, wood and
residual paper and plastics;
§
Under-size refuse such as glass, sands and residual
metals.
9a.3.2.2
In the consideration of
9a.3.2.3 Since mechanical treatment will not generate the biogas, potential health impact to the staff due to biogas emission from mechanical treatment is not expected.
9a.3.3.1 In accordance with the description in Section 9a.3.2 above, biogas will not be generated in the mechanical treatment process. Potential health impact to the staff and nearby sensitive receivers due to biogas from sorting and recycling plant is therefore not expected.
9a.4
Potential
Health Impacts of Fugitive Emissions during Transportation, Storage and
Handling of Waste and Ash
9a.4.1.1 This section reviewed the potential health impact associated with fugitive emissions during transportation, storage and handling of waste and ash during operation of the IWMF.
9a.4.2
Description of Operation Process
9a.4.2.1
For the artificial land near
SKC, the mixed MSW would be delivered from various existing refuse transfer
stations in Hong Kong to the site by marine vessels (probably from Island East
(IETS), Island West (IWTS) and
9a.4.2.2 At the waste reception hall of the incineration plant, mixed MSW would be unloaded into the bunker. The waste is then transferred by overhead cranes into the combustion chamber for burning. Ash will be collected at the bottom of the combustion chamber and passes to the ash storage pit through an ash extractor and magnetic separator for ferrous metal recovery. These ashes, commonly known as bottom ash, would be delivered in containers to the landfill for final disposal or reuse.
9a.4.2.3 The hot flue gases from the combustion chambers would flow through the boiler, releasing thermal energy which turns the water in the boiler tubes into steam. The steam produced would be used to drive the turbine to generate electricity. The cooled flue gases would be treated by flue gas treatment system including scrubbers, activated carbon powder injection and fabric filter systems. The cleaned flue gases would then be released to the atmosphere via the stack. A relatively smaller amount of fly ash and residues would be collected from the boiler and flue gas equipments. The fly ash and residues would then be stabilized with cement or other suitable material before final disposal.
9a.4.2.4 As regards the MSW delivered to the mechanical treatment plant, they would be unloaded into a storage pit. The waste would then be shredded and separated by mechanical treatment systems for sorting of recyclable metals, recyclable plastics, oversize refuse, inert materials and organic matters. The recyclables would be collected, stored for delivery to other recycling sites. The organic matters would be further treated by biological processes. The inert materials would be delivered to the landfill for disposal. The oversize sorting residues would be combusted in the incineration plant or disposed of at landfills.
9a.4.2.5 The separated organic fraction of the waste would be treated by biological processes for stabilization and possible recovery of resources. Anaerobic digestion involves controlled biological degradation of organic wastes in the absence of oxygen. The process involves the anaerobic decomposition of organic wastes to produce a methane-rich biogas fuel and residual solids that can be used for making compost. The biogas produced in the digester is primarily composed of methane and carbon dioxide, with traces of hydrogen sulphide and ammonia. In the anaerobic digestion process, the organic materials would be degraded by microbial activity in the absence of oxygen to produce biogas. The biogas would be collected and used to generate electricity and/ or heat.
9a.4.3.1 As described above, the existing transportation mode of MSW to landfills will be adopted for the future transportation of waste and ash to and from the IWMF.
9a.4.3.2 Potential fugitive emission from waste would be expected during unloading to waste storage pit and transferring waste by overhead cranes grab into the combustion chamber. Ash will be generated after combustion and it will be collected at the bottom of combustion chamber. The ash will be conveyed to the ash storage pit automatically through enclosed extractor. Closed grab will be used to grab the ash to ash hopper and then transfer the ash to enclosed-type container.
9a.4.4.1 With reference to existing experience of MSW transportation to landfills, potential fugitive emission during transportation of waste and ash is not expected. The potential health impacts associated with the transportation of waste to the IWMF would be similar to those that associated with the current transportation of waste to the landfill and are considered insignificant.
9a.4.4.2 With regards to the storage and handling of waste and ash, given that all the reception halls and ash storage pits will be fully enclosed with slightly negative air pressure and closed grab will be use to grab waste and ash, leakage of any fugitive emissions to the outdoor environment is not expected.
9a.4.4.3 In order to minimize the potential health impacts to the worker who worked inside the plant, the following health risk control measures will be implemented. With the implementation of the following measures, the potential health impacts associated with the transportation, storage and handling of waste and ash are considered to be insignificant.
· Provide signage for clear indication of the travelling route of waste/ash trucks;
· Monitor and control the traffic flow inside the reception hall of the plant;
· Vehicle cleaning system should be provided to clean the waste/ash trucks before they leave the plant;
· Apply good practice during unloading of MSW to waste storage pit including: provide signage to assist waste/ash truck drivers to stop at appropriate unloading position; provide sufficient training to waste/ash truck drivers;
· Detection device / alarm should be installed to prevent overfilling of waste and ash storage pit;
· In case manual handling of waste/ash is needed, the workers involved should wear personal protective equipment;
· The on-site workers responsible for maintenance and cleaning of equipment or vehicles contaminated with waste/ash should wear personal protective equipment; and
· Emergency plan should be established and implemented to handle the situation of accidental incineration units shut down.
9a.5 Potential Health Impacts of Radon Emissions from Pulverized Fly Ash
9a.5.1.1
Pulverized Fly Ash (PFA) has
been used for a wide range of applications (e.g. fill for land formation and
reclamation as well as raw material in concrete) locally and in overseas
countries for a long period of time (more than 50 years in the
9a.5.1.2
Based on the findings from
various research projects and studies, which include local studies presented in
Section
9a.5.2.1 Radiation is a natural and ubiquitous phenomenon. The major natural radionuclides are potassium-40 and those in the decay series headed by thorium-232 and uranium-238.
9a.5.2.2 Radon-222 is an inert gas, which is the first radioactive decay product of Radium-226, which itself is a naturally-occurring radionuclide arising from the decay of uranium-238. The decay products of radon gas (radon-222) in their order of appearance are shown in Figure 9.1. They are called the "radon progeny". Each radioactive element on the list gives off either alpha or beta radiation and sometimes gamma radiation too, thereby transforming itself into the next element on the list. Lead-206, the last element on the list, is not radioactive. It does not decay, and therefore has no half-life.
9a.5.2.3
In living lung tissue, if the
DNA in one of the cells adjacent to an inhaled radioactive particle is damaged
by the emitted radiation, it may become a cancer cell later on, spreading
rapidly through the lung, causing lung cancer.
The relative risk model (Yu et al.), which takes into account various
factors, such as age and sex, has been used to estimate the lung cancer deaths
due to radon. It has been found that,
around the year of 1988, about 300 (about 13%) of the lung cancer deaths each
year are attributable to radon in
9a.5.2.4
The risk estimate of
International Commission on Radiological Protection (ICRP 1993) projected a
lung cancer risk of 283 x 10-6 per WLM (working level month) posed
by radon. Based on this risk factor,
together with the total annual indoor exposure of 0.22 WLM for Hong Kong with a
population of
9a.5.2.5 From the relative risk model, the number of Rn-induced lung cancer deaths is expected to grow with the population, unless the indoor radon concentration is reduced.
9a.5.3 Radon Associated with PFA
9a.5.3.1 As radioactive substances are found throughout the earth’s crust, substances extracted from it, including sand, clay, flint, marble, granite and coal, also contain radioactive material. Upon burning of coal for power generation, some of the radioactive materials are left behind in the ash, which consequently has a raised concentration of radioactivity per unit mass. With an average ash content of coal of about 16%, the activity per unit mass of ash would be expected to be about six times greater than the original coal.
9a.5.3.2 A study on the radiological significance of utilization and disposal of coal ash from power stations was conducted by Green in 1986. The main objectives of the study were to assess the radiological significance of the utilization of PFA as building materials and activities of workers and the general public on disposal sites, under both indoor and outdoor environment. This was calculated based on actual field studies, laboratory studies and mathematical models.
9a.5.3.3 Field measurements were taken at three coal ash disposal sites in the United Kingdom (UK). Radionuclide content, porosity, radon emanating fraction and exhalation rates of building blocks containing PFA were analyzed. Mathematical models were used to estimate the exposure to gamma-ray dose rates and radon concentrations under the tested conditions:
· Exposures from building materials; and
· Exposures from disposal sites under indoor and outdoor conditions
9a.5.3.4 From the field studies conducted, it was concluded that there is an increase of radionuclide content from coal to PFA. This agreed with the results of the assessment of the specific activity of samples of PFA, FBA (fuel bottom ash) and coal from the Castle Peak Power Stations conducted by the EPD and Royal Observatory (RO) in co-operation with CLP in 1989. The results are extracted and shown in Table 9a.10 below after conversion to radium equivalent activities. It indicates an increased activity from the un-burnt coal to PFA and FBA. A summary of the more recent measurements conducted by Lu et al (2006) is extracted and shown in Table 9a.11.
9a.5.3.5
Several observations were noted
when predicting flux for various thicknesses of PFA and of soil cover in the
field studies. It was noted that increasing the thickness of the PFA layer
beyond
Table 9a.10 Radium Equivalent Activities of PFA,
FBA and Coal from the
|
Coal Source |
Date of Sample
Collection |
Radium equivalent
activity (Bq/kg) |
||
|
Coal |
PFA |
FBA |
||
|
|
|
|
233 |
255 |
|
|
|
|
373 |
347 |
|
|
|
|
532 |
163 |
|
|
|
|
407 |
343 |
|
|
|
|
|
|
|
|
|
72 |
423 |
382 |
|
|
|
66 |
443 |
335 |
|
|
|
27 |
211 |
197 |
|
Sampled
by RO |
1987 |
|
377 (a) |
|
|
Source
not specified |
1987 |
|
378 (a) |
|
Remark: (a) Data from RO
Table 9a.11 Radium Equivalent Activities of PFA, FBA and Coal from Power Plant in other Countries
|
Power Plant |
Radium equivalent
activity (Bq/kg) |
||
|
Coal |
PFA |
FBA |
|
|
|
86 |
350 |
298 |
|
|
26-71 |
157-309 |
97-248 |
|
|
- |
283 |
- |
|
|
47 |
375 |
260 |
|
|
94 |
408 |
307 |
|
|
86 |
285 |
- |
Reference: Natural
radioactivity of coal and its by-products in the
9a.5.4 Health Impact Associated with PFA due to Radon Emissions
9a.5.4.1 During construction phase of the Project, the ash will mostly remain in the lagoon and excavation of ash would take place for certain activities, such as piling or utility installation within the lagoon area. Extensive transport or disposal of ash would unlikely take place offsite.
9a.5.4.2 As the construction activities would be mainly conducted on top of the existing ash lagoon, which can be considered as working outdoors, the health risk associated with radon emission is considered to be insignificant, which is explained by the paragraphs below.
9a.5.4.3 The National Radiological Protection Board (NRPB) conducted a study on radiological significance of the utilization and disposal of coal ash from power stations (Green (1986)). The study assessed exposure from building materials and exposure above ash disposal sites when used for either leisure or for construction. The estimated annual effective dose for both the reference situation and those involving power station ashes are shown in Table 9a.12.
9a.5.4.4 In Green (1986), the dose assessments of radon were conducted on the basis of a radon concentration above active or restored sites of 4 Bqm-3. It was estimated that the annual effective dose equivalent to a worker spending 2000 hours each year on an ash disposal site would be 60 mSv, a conversion factor of 10 mSv WLM-1 being used because of the breathing rate of workers.
Table 9a.12 Summary of Estimates of Annual Effective Dose
|
Situation |
Normal Ground |
PFA disposal site |
PFA disposal site no soil cover |
||||||
|
From gamma |
From radon |
Total |
From gamma |
From radon |
Total |
From gamma |
From radon |
Total |
|
|
Indoors |
|||||||||
|
All-brick dwelling |
0.740 |
0.260 |
1.000 |
0.750 |
0.360 |
1.110 |
0.760 |
0.780 |
1.540 |
|
Heavy block dwelling |
0.700 |
0.290 |
0.990 |
0.710 |
0.400 |
1.110 |
0.720 |
0.820 |
1.540 |
|
Light block dwelling |
0.530 |
0.340 |
0.870 |
0.540 |
0.440 |
0.980 |
0.560 |
0.860 |
1.420 |
|
Workers such as farm or disposal site labour (2000 hrs in a year) |
0.056 |
0.057 |
0.113 |
0.070 |
0.060 |
0.130 |
0.130 |
0.060 |
0.190 |
|
Members of the public (500 hrs in a year) |
0.014 |
0.007 |
0.021 |
0.018 |
0.008 |
0.026 |
N/A |
N/A |
N/A |
|
(8,760 hrs in a year) |
|
|
0.011 |
|
|
- |
|
|
0.035 |
Notes: Values are rounded to
three decimal places
N/A:
Not applicable
All
units in mSv
9a.5.4.5
The effective dose equivalent
to the workers during the construction phase of the IWMF should be more or less
similar to the estimation in Green (1986).
The differences between the situations in Hong Kong and the
9a.5.4.6
When comparing the differences
of radiation dose between the
9a.5.4.7
Tso and Leung (1996) conducted
a study to evaluate the radiological impact of coal ash from power plants in
9a.5.4.8 The study indicated for situation that the PFA is not covered with soil (e.g. construction phase for the IWMF project), the radon concentration at locations above the uncovered PFA is only slightly higher than the ambient background radon concentration. Also, precaution could be undertaken to suppress re-suspension of ash particles for protection to people on-site. Hence, the health impact associated with PFA due to emissions in the IWMF construction stage would be insignificant.
9a.5.4.9 The health risk due to radon emission from PFA in the operation phase would primarily involve the staff in the IWMF. As building structures would be constructed on the ash lagoon, it is expected that the ingress of radon into and subsequent accumulation inside the building structures may increase the radiation exposure when people stay within the buildings.
9a.5.4.10 Referring to Table 9a.10 & Table 9a.11, a higher radium equivalent activity is shown for PFA over coal. However, Stranden (1988) indicated that a higher specific activity is not necessarily indicative of higher radiation release. This is particularly true for radon as it is gaseous at room temperature and pressure and tends to emanate from materials containing radium. Since the radon emanation takes place into interstitial pores of a material and the subsequent releases or exhalation of radon through the pores is a complex issue.
9a.5.4.11 Stranden (1983) cited an example regarding the use of PFA in cement. It was expected that there would be an increase in the radon exhalation, however, the results of studies showed this perception is not true. Several authors found that the added PFA caused a decrease in radon exhalation, others found no significant difference between ordinary and PFA concrete and, in only a few cases, PFA concrete was found to exhale more radon than ordinary concrete. It is believed that the discrepancies in these studies are probably caused by differences in Ra-226 concentration, porosity, surface structure and PFA content in concrete in different countries.
9a.5.4.12
Sutton (2001) studied radon
emissions from a high volume coal fly ash structural fill site in
9a.5.4.13 The results of this long-term study indicated that a large-scale fly ash structural fill did not increase the presence of Radon-222 or other alpha emitters in structures located above the fill. The study provided evidence that radon should not be a major concern when locating a structure on a properly designed and constructed pulverized fly ash fill site.
9a.5.4.14
In Sutton’s (2001) study, it
was found that fly ash may contain more radium but emitted less radon than
local soils in the vicinity of Bull Run in
9a.5.4.15
The indoor radon concentration
within the structure on ash disposal site was studied in Green’s study
(1986). As shown in Table 9a.12, three scenarios, including normal ground, PFA
disposal site with
9a.5.4.16 As concluded by Green (1986), there may be a potential increase in the radiation exposure of occupants in the building structure over ash disposal sites due to the increased radon flux out of the ground. However, he commented that the increases were not of great radiological significance. Green suggested incorporating simple preventive measures at the planning stage of Projects involving PFA for the interest of keeping doses to levels as low as reasonably achievable.
9a.5.4.17 Also, in Tso and Leung (1996), radon exposure estimation based on the sample measurement results indicated that when the PFA in the ash lagoon is covered by soil, the radiological hazard due to the PFA underneath the soil will become negligible and the land covered with soil will be safe for use.
9a.5.4.18 In order to further reduce radiation impact, the limit on the radium-226, thorium-232 and potassium-40 contents (Table 9a.13) in building materials would be adopted. These limitations are aimed at reducing the external gamma radiation background in indoor and outdoor environment and the limit on radium-226 concentration is also aimed at reducing the source term of radon emanation.
Table 9a.13 Maximum Activity Concentration Limit
|
Standard |
Maximum activity
concentration (Bq/kg) |
||
|
Radium-226 |
Thorium-232 |
Potassium-40 |
|
|
EU (Radiation Protection 112) |
300 |
200 |
3000 |
|
|
370 |
260 |
4200 |
9a.5.4.19 WHO (2003) recommends that countries implement national programmes to reduce the population’s risk from exposure to the national average radon concentration, as well as reducing the risk for individuals exposed to high radon levels. WHO recommends that building codes should be implemented to reduce radon 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. In Hong Kong, in accordance with Appendix 2 of “Protocol of Radon Measurement for Non-residential Building” of EPD ProPECC Note PN 1/99 “Control of Radon Concentration in New Buildings”, the average radon concentration for all confined areas inside a building, but excluding areas where full-time occupancy is not anticipated, should preferably be lower than the territory-wide mean concentration of 100 Bq/m3 and in any case, any individual measurement must not exceed 200 Bq/m3.
9a.5.5.1 As supported by the studies reviewed in this literature review, health risks for radon emissions from PFA due to construction and operation activities of the IWMF at the TTAL site would be considered insignificant.
9a.5.5.2 There is a potential for increased radiation exposure (compared to background level) to the staff in the IWMF from the radon flux out of the ground filled by PFA. However, the increase would likely not be of great radiological significance and can be readily minimized by proper preventive measures.
9a.5.6 Recommended Measures to Control Radon Health Risk
9a.5.6.1 As discussed in the above, there is no significant radiological hazard to the workers at the IWMF on an ash lagoon during construction and operation periods. However, recommended measures shall be considered during the design, construction and operation of the IWMF.
9a.5.6.2 Prevention of radon influx from the PFA to the IWMF buildings is preferred. A soil cover can be provided beneath the buildings on top of ash lagoon prior to construction works because it reduces the level of radon influx significantly. Slab-on-grade can be an option on foundation design. In addition, soil suction can also prevent radon from entering the building by drawing the radon from below the building and venting it through a pipe, or pipes, to the air above the building.
9a.5.6.3 Sufficient ventilation of the interior of the IWMF buildings should be provided. Forced and natural ventilation should be introduced properly to enhance air exchange rate in the IWMF buildings. Regarding basement areas, pressurization by using a fan to blow air into the basement areas from outdoors is suggested. This would create enough pressure at the lowest level indoors to prevent radon from entering into the IWMF buildings.
9a.5.6.4 Regular maintenance should be provided for the floor slabs and walls. Cracks and other openings in the foundation should be properly sealed to reduce radon ingress. Sealing the cracks limits the flow of radon into the building thereby making other radon reduction techniques more effective and cost-efficient. It also reduces the loss of conditioned air.
9a.5.6.5 Prior to the occupation of the IWMF buildings and quarterly during the first year of operation of the IWMF, radon concentration shall be measured by professional persons in accordance with EPD’s ProPECC Note PN 1/99 Control of Radon Concentration in New Buildings Appendix 2, ”Protocol of Radon Measurement for Non-residential Building” to ensure the radon concentration is in compliance with the guidance value.
9a.6 Health Impacts Associated with other Potential Accidental Events
9a.6.1.1 The IWMF will be designed and operated as a modern facility. 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 9a.14
Table 9a.14 Potential Accidental Events and Preventive Measures
|
Risks |
Preventive Measures |
|
Aerial emissions (emission discharge exceed the discharge limit) |
Ø
Use of best
available techniques in emission stack design, implement continuous and
regular emission monitoring |
|
Transportation, storage and handling |
Ø
Implement good
waste/ash transportation, storage and handling practices (see Section 9.4) Ø
Plan transport
routes to avoid highly populated / sensitive areas Ø
Develop
procedures for and deploy as necessary emergency response including spill
response for accidents involving transport vehicles Ø
Enforce strict
driver skill standards and implement driver / navigator and road / marine
safety behaviour training |
|
Chemical spillage and leakage |
Ø
Implement proper
chemicals and chemical wastes handling and storage procedures Ø
Develop and
implement spill prevention and response plan including provision of spill
response equipment and trained personnel |
|
Employee health and safety |
Ø
Implement
industry best practice with reference to international standards and
guidelines |
9a.6.1.2 To further avoid or minimize the potential health impacts associated with other potential accidental events, an emergency response plan should be developed and properly implemented for the IWMF. It should be noted that the emergency response plan should be specific to the final design and operation of the IWMF. With the implementation of the preventive measures outlined in Table 9a.14 above and an effective emergency response plan for the IWMF, the health impacts associated with any potential accidental events could be minimized if not avoided.
9a.7.1.1 The cancer risk arising from exposure to compounds of potential concern (COPCs) associated with the emissions of the IWMF is evaluated in this section. The highest cancer risk arising from the IWMF is predicted to be 9.82x10-7 and it is considered that the Project would not present an unacceptable risk and no further analysis is necessary. The highest predicted total Hazard Index (HI) at all receptors are well below 0.25, which is derived from a conservative approach. Cumulative acute non-carcinogenic health impact of the IWMF imposed to the worst impacted human receptors were assessed and compared with local and overseas guideline levels. It was concluded that the levels of non-carcinogenic chemicals were found to be insignificant when compared to the adopted/derived reference levels. For the classical COPCs of the HKAQO, while it is not possible to rule out adverse health effects from the IWMF with complete certainty, the impact on health from small additional air pollutants is likely to be very small and unlikely to be quantifiable.
9a.7.1.2 The compliance check of the maximum permitted concentration of certain metals present in foods due to the Project as stipulated in “Food Adulteration (Metallic Contamination) Regulations” by the Centre for Food Safety, a compliance check was conducted. The concentrations of Antimony, Arsenic, Cadmium, Chromium, Lead and Mercury at all receptors fall under the maximum permitted concentrations listed in the first and second schedules of the Regulations.
9a.7.1.3 Biogas will not be generated in the mechanical treatment process of the mechanical treatment plant. Potential health impact to the staff and nearby sensitive receivers due to biogas from sorting and recycling plant is therefore not expected.
9a.7.1.4 The existing practices of waste transportation will be followed. With regards to the storage and handling of waste and ash, given that all the reception halls and ash storage pits will be fully enclosed with slightly negative air pressure and closed grab will be use to grab waste and ash, leakage of any fugitive emissions to the outdoor environment is not expected. With the implementation of the recommended health risk control measures, the potential health impacts associated with the transportation, storage and handling of waste and ash are considered to be insignificant.
9a.7.1.5 The potential health risk induced by radon emissions associated with PFA arising from the construction and operation was also evaluated. The estimation indicated that there would be no significant radiological hazard to workers working in the IWMF or in the restored/operating ash lagoon area adjacent to the IWMF.
9a.7.1.6 The IWMF will be designed and operated as a modern facility. 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 identified. To further avoid or minimize the potential health impacts associated with other potential accidental events, an emergency response plan should be developed and properly implemented for the IWMF. It should be noted that the emergency response plan should be specific to the final design and operation of the IWMF. With the implementation of the recommended preventive measures and an effective emergency response plan for the IWMF, the health impacts associated with any potential accidental events could be minimized if not avoided.
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[2] WHO Air quality guidelines for particulate
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of risk assessment, World Health Organization
[3] Fourth External Review Draft of Air Quality
Criteria for Particulate Matter (June, 2003), Appendix
[4] Region 6 Risk Management Addendum - Draft
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[5] Toxicological
Profile for Sulfur Dioxide, US Department of Health and Human Services
[6] Toxicological
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[7] WHO
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sulfur dioxide, Global update 2005, Summary of risk assessment, World
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[8] 0.05mg/m3 as
the limit for total concentration of Cd and Tl; 0.5mg/m3 as the
limit for total concentration of Sb, As, Pb, Co, Cr, Mn, V and Ni.
[9] Unit risk
factors, air quality standards/occupational exposure limit value for long term
COC exposure as well as exposure limits and reference level for acute COC
exposure.