Table of Contents
4.1. Introduction
4.2. Environmental
Legislation, Policies, Plans, Standards, and Criteria
4.3. Description
of the Environment
4.4. Exposure
Scenarios
4.5. Chemicals
of Potential Concern (COPCs)
4.6. Radon
Emissions from Pulverized Fly Ash
4.7. Conservative
Assumptions, Uncertainties and Limitations
4.8. Definition
and Evaluation of Residual Environmental Impact
4.9. Identification
and Evaluation of Operational Phase Environmental Impact
4.10. Environmental
Monitoring and Audit
4.11. Conclusions
and Recommendations
4.12. Reference
4.1.1. This chapter presents the assessment of potential health impacts which may arise from the Project. Health impacts associated with decommissioning, site formation, and drainage works, and road works of the west portion and southern edge of the Middle Ash Lagoon are assessed.
4.1.2. With reference to Section 3.4.4 of the EIA Study Brief (No. ESB-243/2012) a health risk assessment shall be conducted to assess the potential health impact associated with the Project. According to Appendix C of the Study Brief, the health risk assessment should pay particular attention to assess any radon emissions from pulverized fly ash.
4.2.1. There is currently no regulatory requirement, nor official guidance on how to conduct health risk assessment for decommissioning projects.
4.2.2. The reference and criteria used for evaluating health impacts and the guidelines for health impact assessment are laid down below:
· Section 3.4.4, Appendix C of EIA Study Brief (No. ESB-243/2012)
· Human Health Risk Assessment, US Environmental Protection Agency (website accessed on Nov 2014: http://www.epa.gov/risk_assessment/health-risk.htm)
4.2.3. The Human Health Risk Assessment adopted by the US Environmental Protection Agency (USEPA) provides an authoritative and established framework to estimate the nature and probability of adverse health effects in humans who may be exposed to chemicals in contaminated environmental media. Similar approach has been used by a number of national governments and international organizations such as the World Health Organization (WHO), Department of Health and Aging from the Australian Government, and Department of Health, Government of United Kingdom.
4.3.1. The Subject Site is located at the existing ash lagoons in Tsang Tsui, Tuen Mun, overlooking the Deep Bay in the north-western New Territories. The Project has a site area of about 30,000m2 (3 hectares) located at the west portion of the Middle Ash Lagoon, was leased to China Light & Power Company Ltd. (CLP) for the storage of pulverized fuel ash (PFA). The Subject Site is depicted in Figure 1.1.
4.3.2. The Subject Site is located in the western part of the Middle Ash Lagoon in Tsang Tsui, Tuen Mun. The site has been operated by Castle Peak Power Company Limited (CAPCO) for the placement of water and pulverised fuel ash (PFA), a by-product of burned coal from the Castle Peak Power Station. The ash lagoons at Tsang Tsui was formed by reclamation in the 1980s and used by CAPCO exclusively.
4.4.1. As defined in Section 3.4.4 of the EIA Study Brief (ESB-243/2012), the Project shall conduct a health risk assessment to assess the potential health impact associated with the Project.
4.4.2. PFA is a by-product from the combustion process of an electric utility plant. The detritus consists of clays, quartz, pyrite and mixed carbonates. The constituents of PFA mainly include metal oxides which are glassy in nature, trace elements and unburnt coal (i). In addition to the chemical constituents in PFA which may cause health hazard, radon gas may be liberated from PFA contained in the ash lagoon. Coal contains uranium-238, which is the parent element of the uranium series. After the combustion process, the concentration of the radioactive content in the PFA may increase and consequently, the radon concentration as well as its health risk potential may also increase.
4.4.3. The exposure scenarios assumed for the construction and decommissioning of the Project define the media of concern for the analysis. Possible human exposure scenarios from the excavation, filling, handling, storage, transport and disposal of PFA arising from the decommissioning and construction of the Project include:
·
Inhalations
of fugitive dust emissions caused by excavation, filling, handling, storage and
transport of PFA works
·
There
shall be no export or disposal of PFA outside of site boundary
·
Exposure
to radon emissions from pulverized fuel ash
4.4.4. Due to the remote location of the Subject Site, the supply of fresh water to the site is limited. The Contractor shall be responsible for fresh water supply to workers on-site. As such, the ingestion of chemical/contaminants through the consumption of leachate water from nearby water streams is unlikely. Thus, possible exposure through ingestion is eliminated from the assessment.
4.4.5. The construction and decommissioning works mainly involve excavation, filling, handling, storage and transport of PFA within Site boundary. All PFA shall remain on site, and disposal of PFA shall be prohibited. The works shall mainly be carried out by operation of machines and equipment. Thus, the exposure to chemicals/contaminants through dermal contact is limited. Nevertheless, the Contractor shall provide shower facilities to wash away any PFA attached to skin surfaces. Hence, possible exposure through dermal contact is eliminated from the assessment.
4.5.1. Since currently no regulatory requirement or official guidance on health risk assessment for decommissioning projects, the approach of Human Health Risk Assessment from the US Environmental Protection Agency is adopted in this assessment. The suggested approach also provides an authoritative and established framework to estimate the nature and probability of adverse health effects in humans who may be exposed to chemicals in contaminated environmental media.
4.5.2. The 4 steps health risk assessment is used to estimate the nature and probability of adverse health effects in humans who would be exposed to chemicals in contaminated environmental media under a particular set of conditions and for a certain timeframe (i). The 4 steps are listed as follows:
1.
Hazard Identification: determines whether exposure to a stressor can
cause an increase in the incidence of specific adverse health effects.
2.
Dose-response Evaluation: the process of determining quantitatively (i) the
dose of an agent received by the exposed population and (ii) the relationship
between the magnitude of exposure and the probability of occurrence of the
health effects.
3.
Exposure Assessment: A process of measuring and estimation of the
magnitude, frequency and the duration of human exposure to an agent in the
environment. The magnitude of exposure during a specified time period can be
determined through with measurements or modeling.
4.
Risk Characterization: The final step in health risk assessment which
involves the integration of health effects and public exposure information to
give human risk estimates. These estimates will be accompanied by a description
and discussion of uncertainties and analytical assumptions
4.5.3. The Subject Site has been operated by Castle Peak Power Company Limited (CAPCO) for the placement of water and pulverized fuel ash (PFA), a by-product of burned coal from the Castle Peak Power Station. The construction of the Project mainly involves decommissioning works within the Subject Site.
4.5.4. PFA produced by power stations generally takes the form of an inert fine grey sand-like glassy material. The chemical compositions of PFA contain constituents of silica, alumina, iron and calcium, together with other compounds and combustion products. In United Kingdom, around 60 – 90% of PFA is present as silicon and aluminium oxides (ii). Similar results were found for PFA samples collected in Malaysia, with approximately 59 % of silicon and aluminium oxides in PFA (iii). The findings were further compared to a study which was carried out by Geotechnical Engineering Office (GEO), Civil Engineering Department of Hong Kong. Results show that around 14% - 46% and 38% - 77% of the PFA from Castle Peak, Hong Kong is present as aluminium and silicon oxides respectively (iv). The studies produced comparable results which identified metal oxides as a major chemical constituent in PFA. As described in Health Facts on Fly Ash Constituents published by Anne Arundel County Maryland's Department of Health, most common contaminants (aluminium, sulphate, and manganese) do not pose a significant risk for most individuals (v). Study conducted by Electrical Power Research Institute suggests that workers are unlikely to suffer important crystalline silica-related health effects as a result of exposure to coal fly ash in absence of high exposures for extended periods of time (xxiv).As such, the health hazards of silica and aluminium oxides to human receptors are considered to be minimal.
4.5.5.
Small quantities of trace
elements are also found in PFA.
These elements originate from the coal and condense in the fuel ash
during the combustion process. The concentrations of trace elements in PFA are
often higher than those of natural filters such as gravels and sand.
4.5.6.
A study carried out by GEO,
Civil Engineering Department of Hong Kong, in year 1995, which compares trace
elements concentrations in dry PFA from Castle Peak Power Station along with
other sources which are presented in Table 4.1(iv). The table
shows that the trace elements in PFA include arsenic, cadmium, chromium,
copper, lead, selenium, zinc and boron.
Table 4.1 Trace Elements Concentration in PFA from Castle Peak and Other
Sources
|
Trace Element |
Castle Peak |
USA |
United Kingdom |
|||
|
East |
West |
Mid |
Source A |
Source B |
||
|
Arsenic (As) |
11 – 89 |
159 |
119 |
73 |
110 |
80 |
|
Cadmium (Cd) |
0.1 – 0.8 |
nr |
nr |
nr |
5 |
6 |
|
Chromium (Cr) |
19 – 113 |
230 |
224 |
66 |
120 |
120 |
|
Copper (Cu) |
56 |
128 |
89 |
47 |
210 |
160 |
|
Lead (Pb) |
4 – 47 |
55 |
131 |
29 |
110 |
90 |
|
Selenium (Se) |
2 – 7 |
nr |
nr |
nr |
5 |
90 |
|
Zinc (Zn) |
122 |
230 |
743 |
258 |
130 |
90 |
|
Boron (B) |
nr |
265 |
731 |
258 |
210 |
170 |
|
Notes: |
(1)
All Figures
in ppm of dry PFA |
|||||
|
|
(2)
nr denotes
not reported |
|||||
|
|
(3)
Concentration
of other metals were not reported |
|||||
4.5.7.
USEPA (xxvi) and
GEO, Civil Engineering Department of Hong Kong both conducted studies to
identify the chemicals present in PFA samples. However, as PFA composition may differ
depending on the nature of the product and its manufacture process, the data
from USEPA was not used in the screening. As such, the GEO report and PFA
samples collected by CLP at the coal-fired power stations located at Castle
Peak in 2011 were used for identification of chemicals of potential concern
since they could provide most recent and local results of PFA samples. PFA
samples collected by CLP are shown in Appendix 4.1.
4.5.8.
With reference to various
journals and database, such as the Integrated Risk Information System (IRIS)
developed by USEPA and Hazardous Substance Data Bank, developed by the United
National Library of Medicine, the exposure pathway of the chemicals of concern
identified in this study are analysed.
4.5.9.
IRIS was chosen as the primary
source for identification of exposure pathway. IRIS is a human health
assessment program developed by USEPA that evaluates information on health
effects that may result from exposure to environment contaminants. IRIS
database contains information on more than 550 chemical substances and provides
structural and established information to support the USEPA’s regulatory
activities. Other sources of information have been reviewed to determine the
toxicity factors used in evaluating exposure and risk through inhalation. The
sources used are listed as below:
·
Integrated
Risk Information System (IRIS), USEPA
·
Air
Quality Guidelines for Europe Second Edition, World Health Organization (WHO)
·
Office
of Environmental Health Hazard Assessment (OEHHA), the lead state agency for
California
4.5.10. As mention in section 4.4, both ingestion and dermal contact with COPCs would be eliminated. Hence, only the exposure pathway through inhalation is included in the following dose response assessment.
Selection of Chemicals of Potential Concern (COPCs)
4.5.11.
The trace elements were firstly
identified in accordance with local study on PFA by GEO (GEO Report No. 53),
and supplemented with CLP’s PFA sampling test. These identified trace elements
were then checked against international guideline, including IRIS, WHO, and
OEHHA regarding the inhalation risk references. As mention in previous
sections, both ingestion and dermal contact with COPCs would be eliminated,
only the exposure pathway through inhalation is considered in this study.
Therefore, only elements with inhalation risk references were selected to be
assessed. The selected 7 COPCs for health impact assessment are arsenic,
cadmium, chromium (VI), lead, manganese, mercury, and nickel, and the
respective inhalation risk factors from IRIS, WHO, and OEHHA are presented in Table 4.2 respectively.
Table 4.2 Toxicity Factor for
COPCs
|
Trace Elements |
Inhalation
Unit Risk Factor (per µg/m3) (Cancer risk) |
Air
Quality Guideline Value/Reference Level (µg/m3) (Non-Cancer Risk, Chronic) |
||||||
|
Arsenic |
4.3x10-3 |
1.5x10-3 |
3.3x10-3 OEHHA |
1.5x10-2 |
||||
|
IRIS |
WHO |
OEHHA |
||||||
|
Cadmium |
1.8x10-3 |
1.8x10-3 |
4.2x10-3 |
3
x10-1 |
2 x10-2 |
|||
|
IRIS |
WHO |
OEHHA |
WHO |
OEHHA |
||||
|
Chromium (VI) |
1.2x10-2 |
4.0x10-2 |
1.5x10-1 |
1.0x10-1 |
2.0x10-1 |
|||
|
IRIS |
WHO |
OEHHA |
IRIS |
OEHHA |
||||
|
Lead |
1.2x10-5 |
5.0x10-1 |
||||||
|
WHO |
||||||||
|
Manganese |
NA |
5.0x10-2 |
1.5x10-1 |
9x10-2 |
||||
|
IRIS |
WHO |
OEHHA |
||||||
|
Mercury |
NA |
3x10-1 |
1 |
3x10-2 |
||||
|
IRIS |
WHO |
OEHHA |
||||||
|
Nickel |
4.0x10-4 |
2.6x10-4 |
1.4x10-2 |
|||||
|
WHO |
OEHHA |
OEHHA |
||||||
Note:
[1] IRIS
- http://cfpub.epa.gov/ncea/iris/index.cfm?fuseaction=iris.showSubstanceList&list_type=alpha&view=A
[2] WHO
(2000) - http://www.euro.who.int/__data/assets/pdf_file/0005/74732/E71922.pdf
[3] Office
of Environmental Health Hazard Assessment (OEHHA), the lead state agency for
California - http://oehha.ca.gov/air/allrels.html &
http://www.oehha.ca.gov/air/hot_spots/2009/AppendixA.pdf
4.5.12. The second step in the health risk assessment is to develop the relationship between the exposure to an amount of an agent (dose) and the subsequent health effects (response). The dose-response assessment shall undertake two steps: first to present all data and references available about the dosage; secondly to identify types of adverse health effects from the COPCs, and to define the relationship between the dosage and the likelihood or magnitude of an adverse health effect.
4.5.13. As the health hazard from COPCs identified above occurs via inhalation pathway, the concentration of each COPC (dosage) in air must be determined. The approach determine COPC in air is as follows:
1. Obtain the best available information for the ash content in Tsang Tsui Ash Lagoon in order to calculate the concentrations of COPCs. CLP has provided the best available information by soil samples of the PFA obtained from CLP at the coal-fired plants before transfer to Tsing Tsui Ash Lagoon. Details of CLP’s samples can be referred to Appendix 4.1.
2. Develop a model to determine COPC concentration in air. A fixed-box model has been used to determine COPC concentration levels in soil to air emission, taken into consideration of the emission factors, wind speed, mixing height, and dimension of Subject Site. The emission factors were obtained for both wind erosion and construction activity scenarios, both factors based on USEPA’s Compilation of Air Pollutant Emission Factors 5th edition, 1995 (AP-42). Since only the incremental cancer risk is considered in this study, which the risk caused by the additional COPCs during decommissioning works, no background will be considered in the cancer risk estimation. Details of the fixed-box model calculations and emission factors can be referred to Appendix 4.2.
4.5.14. The following sections aim to provide identification of the types of adverse health effects a COPC may potentially cause, and to define the relationship between the dose and the likelihood or magnitude of an adverse health effect. Adverse health effects are generally characterized as carcinogenic and non-carcinogenic. The toxicity of each COPCs will be supported by relevant studies. Dose-response values from these studies can be evaluated as inhalation unit risk factors for cancer risk, and chronic and acute non-cancer risk reference concentration (expressed in unit µg /m3).
Arsenic (As)
4.5.15. Arsenic has been known to create increased lung cancer mortality through inhalation, and other increased mortality from multiple internal organ cancers (liver, kidney, bladder, skin) observed through ingestion of water containing arsenic(xxii).
Cadmium (Cd)
4.5.16. Studies have been conducted to show that excess risk of lung cancer was present in the exposure to cadmium (xxiii).
Chromium (Cr) (VI)
4.5.17. According to the Toxicological Review of Hexavalent Chromium published by USEPA Integrated Risk Information System (IRIS) in 1998, occupational epidemiologic studies of chromium-exposed workers have demonstrated that chromium is carcinogenic by the inhalation route of exposure(vii). The studies have also shown that the effects of inhalation of chromium (VI) in humans’ lead to upper respiratory irritation and atrophy, lower respiratory effects, and renal effects. Following inhalation exposure, chromium (VI) may be absorbed into the systemic circulation, transferred to the gastrointestinal tract by mucociliary action, or remain in the lung. On a molecular level, chromium readily passes through cell membranes and produces a number of potentially mutagenic DNA lesions upon intracellular reduction to chromium (III). Animal data have been conducted to support the human carcinogenicity data, showing the following tumour types in animal assays: intramuscular injection site tumours in rats and mice, intrapleural implant site tumors in rats, intrabronchial implantation site tumours in rats, and subcutaneous injection site sarcomas in rats.
Lead (Pb)
4.5.18. According to IRIS, lead and lead compounds are considered “reasonably anticipated to be human carcinogens” (xxv). While IRIS provides no available information on inhalation health effects, oral exposure to inorganic lead and its compounds may lead to the following health effects: neurotoxicity; developmental delays; hypertension; impaired hearing acuity; impaired haemoglobin synthesis; and male reproductive impairment.
Nickel (Ni)
4.5.19. OEHHA has identified inhalation of nickel and nickel compounds with health effects targeting the respiratory and hematologic system (xi).
Manganese (Mn)
4.5.20. Manganese is a common element found in the human body, ingested in diet and it is essential for physiologic functioning(x). The effects stemming from manganese toxicity targets the respiratory system as well as the nervous system- manganese neurotoxicity (manganism). The non-cancer air quality guideline value/reference level for inhalation of manganese according to IRIS has been determined to be 5x10-2µg/m3. At this level, impairment of neurobehavioral function is observed. In addition, WHO and OEHHA have identified the non-cancer chronic air quality reference inhalation concentration to be 0.15 and 0.09 µg/m3 respectively.
Mercury (Hg)
4.5.21. Studies have shown that the exposure of mercury vapour through inhalation has caused chronic neurological dysfunction (xii), a hazard targeting the nervous system (xi). There was no sufficient information to support mercury exposure being linked to cancer, thus it is not listed as carcinogenic according to IRIS (xiii). The non-cancer air quality guideline value/reference level for inhalation of mercury according to IRIS has been determined to be 3x10-1 µg/m3. Health effects at this level include hand tremor, increases in memory disturbance, and slight subjective and objective evidence of autonomic dysfunction. WHO and OEHHA have identified non-cancer chronic air quality reference inhalation concentration to be 1 and 0.03 µg/m3 respectively.
4.5.22. The exposure assessment estimates exposure pathway and the amount of time workers for the Project is expected to spend on site. As discussed in Section 4.4, the exposure pathway is expected to be through inhalation. The amount of time workers expected to be on site is 12 hours per day, approximately 26 days per month, for a total of 6 months over the course of the decommissioning and construction period.
4.5.23. The exposure assessment shall utilize a fixed-box model to determine COPC concentration levels in soil to air emission, taken into consideration of the emission factors, wind speed, mixing height, and dimension of Subject Site. The following fixed-box model has been used, with details of model assumptions listed in Appendix 4.2:
|
c |
= |
b |
+ |
qL |
|
uH |
Where
c = concentration of pollutant in
air, (mg/m3);
b =
background
concentration of pollutant, (mg/m3), assumed to zero in cancer risk
estimation as only incremental risk is considered;
q = emission rate per unit area,
(mg/s*m2);
L = dimension of project side
parallel to wind direction, (m);
u = wind speed,
(m/s); and
H = mixing height, (m)
4.5.24. The emission contribution was determined by heavy construction activities due to the proposed work and wind erosion. Emission rates are based on USEPA’s Compilation of Air Pollutant Emission Factors 5th edition, 1995 (AP-42), and are summarized in Appendix 4.2.
4.5.25. Hourly wind speed at a mixing height of 20m was obtained from EPD’s 2010 MM5 data, under grid (10,36).
4.5.26. The Subject Site is split into two segments, in which a fixed-box model is developed for each respective segment: Site and Access Road. The length of fixed-box is taken as the longest perpendicular side for the Site and Access Road, which are 250m and 500m respectively.
4.5.27. In a final step of the health risk assessment, this section integrates the information from preceding components of the risk assessment, and draws on an overall conclusion on human health risk.
4.5.28. The risk assessment has been conducted for workers on site, taken as the worst-case scenario.
4.5.29. Potential incremental (“excess”) lifetime cancer risks have been calculated for the receptor (on-site worker), focusing on arsenic, cadmium, chromium (VI), lead, and nickel as identified to be carcinogenic. The cancer risk equation takes into account the concentration of each COPC and the exposure pathway, and is based on USEPA Health Hazard Risk Assessment Protocol Chapter 7: Characterizing Risk and hazard. The equation for estimating cancer risk is presented below:
Cancer
Risk = EC x URF
Where:
EC = Exposure
concentration (µg/m3)
URF = Unit risk factor (µg/m3)-1
4.5.30. The exposure concentration of COPC is calculated using the fixed-box model for both the Site and Access Road segments. The cancer risk equation is then used by multiplying the COPC concentration in long-term average by the respective inhalation unit risk factor from Table 4.2. The calculated cancer risk from the COPC emissions from decommissioning works for the Site and Access Road segments have been summarized in Table 4.3 respectively, with detailed calculation provided in Appendix 4.2.
Table 4.3 Calculated Incremental Cancer Risk (Unmitigated)
|
COPC |
Site |
Access
Road |
|
As |
2.13x10-6 |
2.18x10-6 |
|
Cd |
2.55x10-8 |
2.61x10-8 |
|
Pb |
1.50x10-8 |
1.53x10-8 |
|
Ni |
2.11x10-6 |
2.16x10-6 |
|
Cr(VI) |
1.70x10-5 |
1.74x10-5 |
“Unmitigated”
means 100% of area activity operating, and no water spraying for suppression of
dust.
Exceedance to
limit of 1x10-5 is bolded.
4.5.31. While there are no explicit designation of acceptable or unacceptable level of health risk, USEPA has suggested an upper limit acceptable level of 1x10-4 lifetime cancer risk for highly exposed individuals, and a target of protecting the greatest number of persons possible to an individual lifetime risk level no higher than approximately 1x10-6. It is reasonable to adopt the limit of predicted highest cancer risk arising from decommissioning works to be 1x10-5, which is intermediate between the 1x10-4 and 1x10-6 limits, and considered “As Low As Reasonably Practicable” (ALARP) level. As the incremental cancer risks deduced for the COPCs are all below this value, potential adverse health effects caused by the decommissioning works are not anticipated. However, various mitigation measures shall be provided on site to further minimize adverse health effects as far as practicable, as shown in Section 4.5.40.
4.5.32. The non-carcinogenic health impact posed by long term exposure of COPCs is determined by comparing the predicted COPC concentrations with the occupational air quality guideline value/reference level value presented in Table 4.2. The background concentrations of the COPCs assumed in this assessment are considered under wind erosion scenario as shown in Appendix 4.2. If the concentration of a particular COPC is found to be lower than the corresponding reference level, the non-carcinogenic health impact would be considered to be insignificant.
4.5.33. Various authorities presented different reference concentration values for non-cancer risk. These reference concentrations may take into account factors including local conditions, and therefore a priority for choosing acceptable toxicity shall be based on the following hierarchy:
·
Global
level (ie WHO)
·
Country
level (countries with well-established environmental regulation, ie USEPA- IRIS)
·
Local
level (states / cities with well-established environmental regulations, ie OEHHA)
4.5.34. Table 4.4 presents the assessment result for cumulative non-carcinogenic health impact due to long term COPCs exposure (average during the decommissioning period) by the worst-impacted human receptor, which are the on-site workers. The cumulative non-carcinogenic health impact includes the impact arising from decommissioning works plus the background contribution.
Table 4.4 Calculated Long term Non-carcinogenic Hazard
(Unmitigated)
|
COPC |
Air quality guideline value/reference level (µg /m3) |
Subject Site |
Access Road |
|
As |
1.50x10-2 |
6.08x10-3 |
6.11x10-3 |
|
Cd |
3.00x10-1 |
1.25x10-3 |
1.25x10-3 |
|
Pb |
5.00x10-1 |
5.00x10-2 |
5.01x10-2 |
|
Ni |
1.40x10-2 |
1.06x10-2 |
1.07x10-2 |
|
Cr (VI) |
1.00x10-1 |
7.79x10-4 |
7.89x10-4 |
|
Mn |
1.50x10-1 |
5.46x10-2 |
5.54x10-2 |
|
Hg |
1.00 |
2.26x10-4 |
2.26x10-4 |
“Unmitigated” means 100% of area activity
operating, and no water spraying for suppression of dust.
4.5.35. Cumulative long term health impact of the decommissioning works imposed to the impact human receptors are assessed and compared with the guidelines adopted. It is concluded that the levels of non-carcinogenic chemicals were found to be insignificant comparing to the adopted/derived reference levels.
4.5.36. Similar to long term COPCs exposure, the non-carcinogenic effects posed by acute exposure of COPCs via inhalation pathway are determined by comparing the predicted COPC concentrations at the worst-impacted human receptor (1-hr average concentration to the workers on site) with appropriate air quality guideline value/reference levels.
4.5.37. For the 1-hour COPCs standards, the following hierarchy, which is recommended in HHRAP (2005), is adopted to select the air quality guideline value/reference levels as follows:
· Cal/EPA Acute RELs
· AEGL-1
· ERPG-1
· TEEL-1
· AEGL-2
4.5.38. The adopted air quality guideline value/reference levels for acute exposure of COCs are presented in Table 4.5.
Table 4.5 Air quality guideline value/reference level for COPCs Acute
Exposure
|
COPCs |
Air
quality guideline value/reference level (μg/m3,
1-hr averaging time) |
Source (a) |
|
As |
0.2 |
Cal/EPA Acute REL |
|
Cd |
100 |
AEGL-1 |
|
Pb |
150/10
= 15 |
TEEL-1 (b) |
|
Ni |
0.2 |
Cal/EPA Acute REL |
|
Cr (VI) |
89/10
= 8.9 |
TEEL-1 (b) |
|
Mn |
3,000/10
= 300 |
TEEL-1 (b) |
|
Hg |
0.6 |
Cal/EPA Acute REL |
Notes:
(a)
Sources of References:
Cal/EPA Acute REL (as of June 2014): http://www.oehha.ca.gov/air/allrels.html
AEGL-1 (2012): http://www.atlintl.com/DOE/teels/teel/teel_pdf.html
TEEL-1 (2012): http://www.atlintl.com/DOE/teels/teel/teel_pdf.html
(b) With
reference to the Haber Rule, calculation of the 1-hour acute air quality
guideline value/reference level from 15-minute acute air quality guideline
value/reference level should be derived by (TEEL-1)/4. As a conservative
approach, (TEEL-1)/10 has been adopted as the acute air quality guideline
value/reference level.
4.5.39. Non-carcinogenic health impact posed by acute exposure of COPCs is determined by comparing the predicted COPC concentrations (Maximum concentrations during the decommissioning period) with air quality guideline value/reference level adopted which are presented in Table 4.5. The background concentrations of the COPCs assumed in this assessment are considered under wind erosion scenario as shown in Appendix 4.2. If the concentration of a particular COPC is found to be lower than the corresponding standard, the non-carcinogenic health impact would be considered to be insignificant. Table 4.6 present the assessment results for non-carcinogenic health impact due to acute COPCs exposure by the worst-impacted human receptor, which are the on-site workers in this case.
Table 4.6 Cumulative Non-carcinogenic Health Impact Arising from Acute COPC Exposure (Unmitigated)
|
COPC |
Air
quality guideline value/reference level (µg/m3) |
Subject
Site (µg/m3) |
Access
Road (µg/m3) |
|
As |
2.00x10-1 |
3.19x10-2 |
3.62x10-2 |
|
Cd |
1.00x102 |
1.51x10-3 |
1.55x10-3 |
|
Pb |
1.50x101 |
7.27x10-2 |
7.65x10-2 |
|
Ni |
2.00x10-1 |
1.07x10-1 |
1.22x10-1 |
|
Cr (VI) |
8.90 |
8.51x10-3 |
9.80x10-3 |
|
Mn |
3.00x102 |
6.84x10-1 |
7.88x10-1 |
|
Hg |
6.00x10-1 |
3.29x10-4 |
3.46x10-4 |
· Dust Suppression by watering of construction area at least 10 times per day;
· Provide covering of 50% of open area with impervious materials or concrete paving;
· Limited working period to 180 days.
· Provision pavement to Construction access road with concrete paving and provide wheel washing facility at entrance and exit.
4.5.41. With the implementation of the above mitigation measures, it is estimated that the incremental cancer risks and non-cancer hazard may be reduced. Table 4.7 summarize the cancer health risk, and Table 4.8 and Table 4.9 summarize the non-cancer hazard calculations based on the mitigation measures respectively. As shown, the deduced cumulative COPCs concentrations fall below cancer limit level and non-cancer air quality guideline value/reference level. Thus, adverse health impact from inhalation of COPCs is not anticipated, with the proposed mitigation measures in place.
Table 4.7 Calculated Incremental Cancer Risk (mitigated)
|
COPC |
Subject Site |
Access Road |
|
As |
1.78x10-7 |
1.71x10-7 |
|
Cd |
2.14x10-9 |
2.05x10-9 |
|
Pb |
1.25x10-9 |
1.20x10-9 |
|
Ni |
1.77x10-7 |
1.70x10-7 |
|
Cr (VI) |
1.42x10-6 |
1.37x10-6 |
“Mitigated” means 50% of area
activity operating, and watering 10 times per day
All calculated values within 1x10-5
cancer risk limit level, therefore no adverse health impact
Table 4.8 Calculated Long-term Non-carcinogenic Hazard (mitigated)
|
COPC |
Air quality guideline value/reference
level (µg/m3) |
Subject Site (µg/m3) |
Access Road(µg/m3) |
|
As |
1.50x10-2 |
4.78x10-3 |
4.77x10-3 |
|
Cd |
3.00x10-1 |
1.24x10-3 |
1.24x10-3 |
|
Pb |
5.00x10-1 |
4.89x10-2 |
4.89x10-2 |
|
Ni |
1.40x10-2 |
5.78x10-3 |
5.76x10-3 |
|
Cr (VI) |
1.00x10-1 |
3.89x10-4 |
3.88x10-4 |
|
Mn |
1.50x10-1 |
2.29x10-2 |
2.28x10-2 |
|
Hg |
1.00 |
2.20x10-4 |
2.20x10-4 |
“Mitigated” means 50% of area
activity operating, and watering 10 times per day
All calculated values less than air quality guideline
value/reference level, therefore no adverse health impact
Table 4.9 Cumulative Acute
Non-carcinogenic Health Hazard (mitigated)
|
COPC |
Air quality guideline value/reference level (µg/m3) |
Subject Site
(µg/m3) |
Access Road
(µg/m3) |
|
As |
2.00 x10-1 |
6.94 x10-3 |
7.13 x10-3 |
|
Cd |
1.00 x102 |
1.26 x10-3 |
1.26 x10-3 |
|
Pb |
1.50 x101 |
5.08 x10-2 |
5.10 x10-2 |
|
Ni |
2.00 x10-1 |
1.38 x10-2 |
1.45 x10-2 |
|
Cr (VI) |
8.90 |
1.04 x10-3 |
1.10 x10-3 |
|
Mn |
3.00 x102 |
7.56 x10-2 |
8.03 x10-2 |
|
Hg |
6.00 x10-1 |
2.29 x10-4 |
2.30 x10-4 |
“Mitigated”
means 50% of area activity operating, and watering 10 times per day
All calculated
values less than air quality guideline value/reference level, therefore no
adverse health impact
4.5.42. In addition to the above proposed mitigation measures, additional precautionary measures relevant to the Project are listed as follows:
· Signage and training shall be provided to inform the Contractor and respective personnel on-site to avoid ingestion of chemical/contaminants through the consumption of PFA soil and leachate water from nearby water streams.
· The Contractor shall provide shower facilities to workers to wash away any PFA attached to skin surfaces.
4.5.43. Under the “As Low as Reasonably Achievable” Principle (ALARA Principle), identified measures in previous sections are recommended to be considered during the design, decommissioning and construction of the Project to reduce risks from COPCs.
4.6.1. The Subject Site, Sludge Treatment Facility (EIA-155/2008) and proposed Integrated Waste Management Facility (EIA-201/2011) are located in the Tsang Tsui Pulverized Fly Ash Lagoon. The ash lagoons were constructed in the 1980s by CLP for the purpose of storing pulverized fuel ash (PFA).
4.6.2. 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 UK). Health concerns due to radon emissions of PFA applications have been raised more than 15 years ago. Studies assessing the potential health impacts associated with PFA have been conducted, which showed that PFA is an environmentally harmless material that can be safely used in bound and unbound applications.
4.6.3. The potential of health impact induced by radon emission from PFA in the ash lagoons at Tsang Tsui had been evaluated in detail by previously approved EIA studies, including Sludge Treatment Facility (EIA-155/2008), West New Territories (WENT) Landfill Extensions (EIA-171/2009), and proposed Integrated Waste Management Facility (EIA-201/2011). All these approved EIA concluded that the potential adverse health impact to be insignificant level to both on-site workers and off-site receivers.
4.6.4. Take into consideration of similar activities and sensitive receivers of this project to the aforementioned EIA studies, the potential adverse health impact are anticipated to be insignificant level to both on-site workers and off-site receivers.
4.6.5. The risk from the radon emissions, of the excavation, filling, handling, storage, transport and disposal of PFA arising from the decommissioning and construction of the project will be identified. The likelihood and consequences of exposure to the radon emissions will be then evaluated.
4.6.6. A quantitative environmental health risk assessment will be adopted to predict the risk of exposure to and the potential impacts from the radon emission during the decommissioning of the project. An annual limit of 1 mSv for general public as suggested by the International Commission on Radiological Protection (ICRP) will be adopted in the following assessment. Mitigation measures will be proposed as necessary.
4.6.7. 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 the order of appearance are shown in Figure 4.1. 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.
4.6.8. 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 (Lu et al., (xv)), 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 Hong Kong.
4.6.9. In 1994, the risk estimate of International Commission on Radiological Protection (ICRP, (xvi)) projected a lung cancer risk of 283 x 10-6 per WLM (working level month) posed by radon. ICRP further recommended "a detriment-adjusted nominal risk coefficient for a population of all ages in 2009 (XXVII), which is 8 x 10-10 per Bq h m-3 for exposure to radon-222 gas in equilibrium with its progeny (i.e. 5 x 10-4 per WLM).
4.6.10. 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.
4.6.11. A study on the radiological significance of utilization and disposal of coal ash from power stations was conducted by Green in 1986 (xvii). 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.
4.6.12. 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 analysed. 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
4.6.13. 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 4.10 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 (xv) is extracted and shown in Table 4.11.
4.6.14. 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 5m makes little impact on the surface radon flux.
Table 4.10 Radium Equivalent Activities of PFA, FBA and Coal from the Castle
Peak Power Station
|
Coal Source |
Date of Sample Collection |
Radium equivalent activity
(Bq/kg) |
||
|
Coal |
PFA |
FBA |
||
|
Columbia |
22/02/89 |
- |
233 |
255 |
|
Australia |
22/02/89 |
- |
373 |
347 |
|
Australia |
02/03/89 |
- |
532 |
163 |
|
South Africa |
07/03/89 |
- |
407 |
343 |
|
South Africa |
08/03/89 |
- |
- |
- |
|
South Africa |
10/03/89 |
72 |
423 |
382 |
|
South Africa |
15/03/89 |
66 |
443 |
335 |
|
Australia |
19/03/89 |
27 |
211 |
197 |
|
Sampled by RO |
1987 |
- |
377a |
- |
|
Source not specified |
1987 |
- |
378a |
- |
Remark:
(a) - Data from RO
Table 4.11 Radium Equivalent Activities of PFA, FBA and Coal from Power Plant
in other Countries
|
Power Plant |
Radium equivalent activity (Bq/kg) |
||
|
Coal |
PFA |
FBA |
|
|
Baoji, China |
86 |
350 |
298 |
|
Lodz, Poland |
26-71 |
157-309 |
97-248 |
|
India |
- |
283 |
- |
|
Hong Kong, China |
47 |
375 |
260 |
|
Shanghai, China |
94 |
408 |
307 |
|
Beijing, China |
86 |
285 |
- |
Reference: Natural radioactivity of coal and its by-products in
the Baoji coal-fired power plant, China, Xinwei Lu, XiaodanJia and Fengling Wang, July 2006 (xv)
4.6.15. While the potential human receptors, including office of WENT Landfill and sludge treatment facility, located at relatively far distance from the decommissioning area, on-site workers area considered the most affected receptor. Quantitative health assessment for Radon for on-site worker will be carried out. Whereas, the potential risks via different exposure pathways for various decommissioning procedure, including soil import, excavation, filling, handling, storage, transport of PFA and disposal of PFA, are discussed in following sections.
4.6.16. Excavation would be required for construction of retaining structure along the man-made channel. Since the excavation is limited within the ash lagoon, risk to nearby ASR would be insignificant. To the on-site worker, exposure pathways via dermal contact and incidental ingestion of PFA are considered as low risk, since eating will be prohibited. Whereas, major risks from radon emission would be mainly from two pathways: (1) external irradiation by g-radiation and (2) internal irradiation from 222Rn daughters. The quantitative health assessment for Radon only considers inhalation pathway as the major exposure pathway for calculation of exposure.
4.6.17. Filling of PFA would be required in general decommissioning works during levelling of PFA platform. Since the levelling amount is very limited and shall be controlled within the ash lagoon, risk to nearby ASR would be insignificant. To the on-site worker, exposure pathways via dermal contact and incidental ingestion of PFA are considered as low risk, since eating will be prohibited. Whereas, major risks from radon emission would be mainly from two pathways: (1) external irradiation by g-radiation and (2) internal irradiation from 222Rn daughters. The quantitative health assessment for Radon only considers inhalation pathway as the major exposure pathway for calculation of exposure.
4.6.18. Handling of PFA would be required in general decommissioning works during levelling of PFA platform. Since the levelling amount is very limited and shall be controlled within the ash lagoon, risk to nearby ASR would be insignificant. To the on-site worker, exposure pathways via dermal contact and incidental ingestion of PFA are considered as low risk, since eating will be prohibited. Whereas, major risks from radon emission would be mainly from two pathways: (1) external irradiation by g-radiation and (2) internal irradiation from 222Rn daughters. The quantitative health assessment for Radon only considers inhalation pathway as the major exposure pathway for calculation of exposure.
4.6.19. As the decommissioning method is placing soil cover over PFA platform, no additional storage of PFA would be required. Hence, the risk associated with PFA storage is not applicable.
4.6.20. Transport of PFA would be required in general decommissioning works during levelling of PFA platform. Since the levelling amount is very limited and shall be controlled within the ash lagoon, risk to nearby ASR would be insignificant. To the on-site worker, exposure pathways via dermal contact and incidental ingestion of PFA are considered as low risk, since eating will be prohibited. Whereas, major risks from radon emission would be mainly from two pathways: (1) external irradiation by g-radiation and (2) internal irradiation from 222Rn daughters. The quantitative health assessment for Radon only considers inhalation pathway as the major exposure pathway for calculation of exposure.
4.6.21. As the decommissioning method is placing soil cover over PFA platform, no disposal of PFA would be required. Hence, the risk associated with disposal of PFA is not applicable.
4.6.22. In this connection, on-site workers of decommissioning are considered as the target sensitive receivers. Whereas, the risk to off-site receivers is unlikely, as no PFA will be exported from the site area and identified air sensitive receivers are located in relatively far from the site (refer to section 3).
4.6.23. In addition, there may also be a risk potential from radon for the truck drivers who are expected to visit the Subject Site occasionally.
4.6.24. Since it is likely radon emission would mainly affect the on-site worker, the consequences of exposure will be quantified and to be checked against with the annual limit of 1 mSv for general public as suggested by the International Commission on Radiological Protection (ICRP).
4.6.25. During construction phase of the Project, the ash will remain in the lagoon and minor excavation of ash would take place for certain activities, such as utility installation within the lagoon area. Extensive transportation or disposal of ash would not take place offsite.
4.6.26. The National Radiological Protection Board (NRPB) conducted a study on radiological significance of the utilization and disposal of coal ash from power stations (Green, (xvii)). 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 4.12.
Table 4.12 Summary of Estimates of Annual Effective Dose Equivalents
|
Situation |
Normal Ground |
PFA disposal site 50cm soil
cover |
PFA disposal site no soil
cover |
||||||
|
From γ |
From Rn |
Total |
From γ |
From Rn |
Total |
From γ |
From Rn |
Total |
|
|
Indoors |
|
|
|
|
|
|
|
|
|
|
All-brick dwelling |
0.74 |
0.26 |
1.00 |
0.75 |
0.36 |
1.11 |
0.76 |
0.78 |
1.54 |
|
Heavy block dwelling |
0.70 |
0.29 |
0.99 |
0.71 |
0.40 |
1.11 |
0.72 |
0.82 |
1.54 |
|
Light block dwelling |
0.53 |
0.34 |
0.87 |
0.54 |
0.44 |
0.98 |
0.56 |
0.86 |
1.42 |
|
Outdoors |
|
|
|
|
|
|
|
|
|
|
Workers such as farm or disposal site labour
(2000 hrs in a year) |
0.056 |
0.057 |
0.11 |
0.070 |
0.060 |
0.13 |
0.13 |
0.060 |
0.19 |
|
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 |
|
Inhalation of Re-suspended Dust |
|
|
|
|
|
|
|||
|
(8,760 hrs in a year) |
|
|
0.011 |
|
|
|
|
|
0.035 |
|
(2,000 hrs in a year)4 |
|
|
|
|
|
|
|
|
0.016 |
Note:
1. Estimated
Values (including values from gamma ray dose and radon) were rounded to two
significant figures
2. N/A: Not applicable
3. All units in mSv
4.by Man-yin W.
Tso& John K. C. Leung (xviii)
4.6.27. The radon concentration and gamma rate exhaled from the dry ash lagoon are estimated by equations as suggested by Tso & Leung, 1995. As suggested by WHO and ICRP, the estimations would be affected by various environmental factors, including depth of PFA, changes in the radionuclide contents in the PFA, changes in the routes available for the passage of radon, changes in the rate of air exchange, variation in the geology of the area, changes in the pressure differential, and changes in meteorological conditions. In this connection, the latest site specific parameters will be adopted in the estimation, whereas the more conservative assumptions would be adopted, if the site specific values are not available.
4.6.28.
The external
4.6.29. The annual effective dose is then estimated by using the formula from UNSCEAR (UNSCEAR, 2000), which is a summation of (1) external irradiation by g-radiation and (2) internal irradiation from 222Rn daughters. The adopted equation is illustrated as shown below,
Eγ (mSvy-1) = (Eγ+ERn) (µSv y-1) x 10-3 (mSv / µSv)
Where,
Eγ = Dose rate (μGyh-1 ) × Exposed Hours(hr yr-1) × Cγ (SvGy-1)
ERn = Rn (Bqm-3) × Exposed Hours (hr yr -1) × CRn (μSv / Bqhm-3)
which,
Exposed Hours = 12 hr/d × 26 d/mth × 6 mth/yr = 1872 hr/yr
Dose rate = 0.414 μGyh-1 Note (1)
Cγ = 0.7 SvGy-1 Note (2)
Rn = 2.3 Bqm-3 Note (1)
CRn = 0.0141 μSv/Bqhm-3 Note (3)
Therefore,
E = 0.414 μGyh-1 × 1872 hr yr -1 × 0.7 SvGy -1
+2.3Bqm-3 × 1872 hr yr-1 × 0.0141μSv/Bqhm-3
= 0.60 mSvy-1
4.6.30. Assuming a worker works 12hrs per day with average of 26 days per month for total of 6 working month, the predicted annual effective dose will be 0.32mSv, which is less than the annual limit of 1 mSv for general public as suggested by the International Commission on Radiological Protection (ICRP).
4.6.31. In fact, the annual dose received by the public in Hong Kong from natural background radiation is about 2 mSv, in accordance with information shown in HKO website. In addition, the annual per caput effective dose to the global population due to all sources of ionizing radiation is about 3.1 mSv, as summarized in table 5 of UNSCEAR 2008 Report Volume I. In this connection, the predicted annual dose received by the on-site workers is considered as insignificant.
4.6.32. The effective dose equivalent to the workers during the construction phase of the decommissioning works is higher than the estimation in Green (xvii). The differences between the situations in Hong Kong and the UK mainly concern higher background radon level and longer working hours in Hong Kong.
4.6.33. When comparing the differences of radiation dose between the UK situation and the current situation for the Project, the background radiation levels should not be considered since it is not related to the Project. Whereas, only the incremental risk due to the PFA on site shall be considered.
4.6.34. Since the risk imposed on workers with direct radon exposure is not significant and there will be no off-site disposal of PFA in this Project, the risk on off-site air sensitive receivers will also be insignificant.
4.6.35. Tso and Leung (xviii) conducted a study to evaluate the radiological impact of coal ash from power plants in Hong Kong. The study involved collection of PFA samples from the two local electric companies and measurement of radon produced from the samples.
4.6.36. The study indicated that for PFA not covered with soil, the radon concentration at locations above the uncovered PFA is only slightly higher than the ambient background radon concentration. 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 construction stage would be insignificant.
4.6.37. The decommissioning and construction of the Project is scheduled from September 2015 to March 2016. Chan’s study indicated that the highest atmospheric radon level in these months was about 10 Bqm-3. There is no international guideline value for ambient radon level. For indoor environment, WHO(xx) recommends that countries adopt reference levels of 100 Bqm-3 to minimize health hazards due to radon exposure, which is well above the atmospheric radon level in Hong Kong.
4.6.38. All building structures, such as the site office would be removed after decommissioning works are completed. It is anticipated there is no staff workers on the site after completion of construction phase.
4.6.39. As supported by evidences in the literature review, site measurement and quantitative assessment, health risks for radon emissions from PFA due to decommissioning works at the Subject Site would be considered insignificant.
4.6.40. Staff working indoor may have potential for increased radiation exposure (compared to background level) from the radon flux when the ground is filled by PFA. However, with the implementation of the proper control measures, such as provision of sufficient ventilation, the indoor and outdoor radon levels would be similar. Therefore, health risks for radon emission to staff working indoor are considered insignificant.
4.6.41. The maximum reduction in gamma dose rate due to covering of ash by 1m of soil is estimated to be 35% in accordance with equations suggested by Tso & Leung, 1995 with conversion factors given by Kocher & Sjoreen, 1985.
4.6.42. Flux of 222Rn exhaled from an ash lagoon covered with 1m of soil was estimated by equation given by Brown et al 1984. It estimates the resultant Rn flux would be reduced to insignificant level that remaining Rn flux relate to background flux level from soil alone.
4.6.43. Therefore, the radiological hazard due to the ashes underneath the soil is considered negligible and the land safe for use. Likewise, it is expected that the 1m soil is adequate to reduce health hazard from potential radon emission after the completion of decommissioning. In addition, periodic measurements of both indoor and outdoor radon concentrations are suggested as a site specific reassurance measure.
4.6.44. As discussed, there is no significant radiological hazard to the workers at the proposed site on west portion of the Middle Ash Lagoon during decommissioning periods. However, under the “As Low as Reasonably Achievable” Principle (ALARA Principle), recommended measures shall be considered during the design, decommissioning and construction of the Project.
4.6.45. Prevention of radon influx from the PFA to the site office during construction stage is preferred. A soil cover can be provided beneath the buildings on top of ash lagoon prior to construction works to reduce the level of radon influx.
4.6.46. Sufficient ventilation of the interior of the site office should be provided. Forced and natural ventilation should be introduced properly to enhance air exchange rate in the buildings.
4.6.47. Periodic measurement of both indoor and outdoor radon concentrations during the work period should be conducted. The methodology of radon measurement shall refer to EPD’s ProPECC Practice Note PN 1/99 “Control of Radon Concentration in New Buildings”.
4.6.48. Under the “As Low as Reasonably Achievable” Principle (ALARA Principle), identified measures in previous sections are recommended to be considered during the design, decommissioning and construction of the Project to reduce risks from Radon.
4.7.1. The health impact assessment for COPCs is a complex process, requiring the integration of the following:
· Release of COPCs into the environment;
· Potential adverse health effects in human;
4.7.2. 7 COPCs are identified based on most likely exposure pathway and best available data and references. It should be noted that the assessed COPCs are only in trace amounts within PFA; the major constituent of PFA, silicon and aluminium oxides as discussed in Section 4.5.4, are identified to not have significant human health risk (v),(xxiv).
4.7.3. The air quality benchmarks adopted from various agencies as indicated in Table 4.2 would introduce uncertainty to the health assessment. These air quality benchmarks are used as single-point estimates throughout the analysis with uncertainty and variability associated with them. However, it should be noted that much of the uncertainty and variability associated with the air quality benchmarks shall be accounted for in the process that the agencies setting verified benchmarks.
Exposure Assessment
4.7.4. The health assessment is based on a fixed-box model to determine COPC concentration levels in soil-to-air emission. The fixed-box model has following conservative assumptions, uncertainties and limitations-
· Concentration of COPC is uniform within the fixed-box, assuming not higher at the downwind side than the upwind side. This means that at any given point within the fixed-box, the receiver (on site worker) is inhaling the concentration of COPC over the entire fixed-box area.
· Predicts concentration for only one specific meteorological condition. The model does not take into account different wind directions, but assumes wind only blows in the direction of the length of the fixed-box. Realistic application would be to sum concentrations over several hundred meteorological conditions and corresponding emission rates.
4.7.5. The fixed-box model predicts the worst case scenario which would not occur all the time. This conservative approach overestimates the risk.
4.7.6. The health assessment only considers inhalation pathway as the major exposure pathway for calculation of exposure. Other exposure pathways such as dermal contact and incidental ingestion of soil are not considered, which may underestimate the risk. However, the risk underestimation is considered insignificant because the exposure pathways not under consideration are expected to be minor for the potential human receptors.
Risk Characterization
4.7.7. The long-term incremental exposure of individual COPCs is characterized by calculating carcinogenic risk and non-carcinogenic hazard, along with calculations for acute exposure of COPCs, and comparing with respective air quality guideline/reference level. This approach provides a simple comparison to characterize the risk but it does not consider the possible cumulative effects (additional, synergistic or antagonistic effect) of exposure to multiple COPCs and introduce uncertainty to the health risk assessment.
4.7.8. The quantitative health assessment for Radon only considers inhalation pathway as the major exposure pathway for calculation of exposure. Other exposure pathways such as dermal contact and incidental ingestion of soil are not considered, which may underestimate the risk. However, the risk underestimation is considered insignificant because the exposure pathways not under consideration are expected to be minor for the potential human receptors.
4.7.9. The quantitative health assessment for Radon had estimated the annual effective dose for workers during construction period only, whereas the cumulative effect was not included. However, the predicted annual effective dose of 0.60mSv, which is much less than the annual limit of 1 mSv, is considered insignificant.
Residual environmental impact is not expected with implementation of dust mitigation measures suggested in previous sections.
As defined in Section 2.5, operational phase shall be defined as the period when the decommissioning works as detailed in Section 2.6 are completed. The operational phase of the Project shall be an idle buildable land to cater any future developments by the government. Since, the 1m of general fill cover over PFA is considered as adequate to prevent PFA from emitting into the air, and minimize the radon flux to the surface, adverse health impacts is not expected.
Further details of the specific EM&A requirements are detailed in Section 12 of this report and in the EM&A Manual, together with event action plans and procedures for complaints.
4.11.1. Health risks from the construction works for the Project are identified for COPCs in association with PFA contaminated dust emission. Human health risk had been evaluated in accordance with approach suggested by USEPA. The predicted incremental cancer risk to on-site workers would be below 1x10-5, which is negligible, and the long-term and acute non-cancer hazards would be below respective air quality guideline value/reference level, with implementation of dust control measures.
4.11.2. Human health risk introduced from radon flux associated PFA has also been assessed. The radon emission is considered as insignificant during construction phase. Provision of 1m general fill is considered adequate to prevent adverse health impact during operation phase. The overall adverse health impact is not anticipated.
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