Civil Engineering and Development Department and Planning Department |
Agreement No.
CE61/2007(CE) North East New Territories New Development Areas Planning and
Engineering Study - Investigation |
Health Risk Assessment Report for High Arsenic Soil in Kwu Tung North New Development Area |
140-03 | June 2013 |
|
2 Arsenic Testing
during Phase 2 Ground Investigation
2.1 Phase
2 GI in Kwu Tung North
2.2 Phase
2 GI in Fanling North
3.1 Review
of Aerial Photographs
3.2 Review
of Historical Short-Term Tenancy Record
4.1 Objective
of Arsenic GI Programme
4.2 Details
of Arsenic GI Programme
4.3 Investigation
of Extremely High Arsenic Results
4.4 Profiling
of Arsenic Extent in KTN
5 Health Risk
Assessment of Ingestion Pathway
5.1 Arsenic,
Sources and Toxicity to Humans (1)
5.2 Route
of Absorption of Arsenic (1,2)
5.3 Arsenic
Concentration in Soil
5.4 Estimated
Dose of Arsenic Absorbed from Ingestion at Different Soil Concentrations
5.5 Discussion
on Ingestion Health Risk Assessment
5.6 Uncertainties
in Ingestion Health Risk Assessment
6 Health Risk
Assessment of Inhalation Pathway
6.1 Risk
of Inhalation of Arsenic-Containing Dust
6.2 Safe
Level for Inhalation Exposure of Arsenic-Containing Dust
6.3 Ambient
Arsenic Level in KTN
6.4 Construction
Dust Impact Assessment for Arsenic
6.5 Estimation
of Arsenic Intake by Inhalation
6.6 Uncertainties
in Inhalation Health Risk Assessment
7 Estimation of
Soil Quantity Require Treatment
7.2 Uncertainties
in Ground Investigation
7.4 Cement
Solidification/Stabilisation for Shallow Region
7.5 Planning
/ Land Lease Control for Basement Depth
7.6 Residual
Issue for Deep Foundation Region
8 Treatment Methods
of Arsenic-Containing Soil
8.2 Potential
Treatment Methods
8.4 Outline
Process and Operation of Treatment
8.5 Mitigation
Measures and Safety Measures
Figure
2.1 GI Location Plan of KTN
Figure
2.2 GI Location Plan of FLN
Figure
7.1 Hot Spot Area A for High Arsenic
in KTN NDA
Figure
7.2 Hot Spot Area B for High Arsenic
in KTN NDA
Figure
7.3 Hot Spot Area C for High Arsenic
in KTN NDA
Figure
7.4 Deep Foundation Region for High
Arsenic in KTN NDA
Figure
7.5 Treatment Measures Summary for
High Arsenic in KTN NDA
Figure
7.6 Residual Issues for High Arsenic
in KTN NDA
Strata Log Records of Phase
2 GI Boreholes in KTN
Laboratory Testing Reports
of Phase 2 GI in KTN
Strata Log Records of Phase
2 GI Boreholes in FLN
Laboratory Testing Reports
of Phase 2 GI in FLN
Locations of Site Landuse
may cause Arsenic Contamination
Strata Log Records of
Arsenic GI Boreholes
Laboratory Testing Reports
of Arsenic GI
Laboratory Testing Reports
of Further Tetsing of Soil Sample KTN-ASBH Offsite (20.5-20.95)
Photographic Records of
Mazier Samples
Detail Geological Log Record
of Mazier Samples
Laboratory Testing Report of
2 Sub-soil Samples of Mazier Sample
Co-relation Between Arsenic
Concentration and the Geology
Recommended Outline
Development Plan
Air Pollution Sources in KTN
NDA
Existing and Planned ASRs in
KTN
Locations of Development
Packages
Locations of Emission
Sources in KTN NDA for Year 2025
Locations Plan of Soil
Sampling Points
Derivation of Arsenic
Emission Factor
USEPA “Estimating
Particulate Matter Emission from Construction Operation - Final Report, 1999”
USEPA “Gap Filling PM10
Emission Factors for Selected Open Area Dust Source, EPA-450/4-88-003, 1988”
Justification of 6% Active
Operating Area
USEPA “Control of Open
Fugitive Dust Sources”
Calculation of TSP Removal
Efficiency (from Watering)
Hot Spot Areas with Arsenic
Concentration Above 571 mg/kg
KTN NDA together with Fanling North (FLN) NDA forms the North East New Territories (NENT) NDAs. The Planning and Engineering Study on NENT NDAs (the Study) was commissioned in June 2008 to formulate a land use framework and an implementation programme for the development of the NENT NDAs.
As part of the Environmental Impact Assessment (EIA) under the Study, a land contamination assessment to identify potential contaminated sites and to recommend remedial actions is required. It is relevant to note that under the previous Planning and Development Study on NENT, undertaken between January 1998 and October 2003, only desktop review of aerial photographs/survey maps and limited site inspections were conducted and the Arsenic issue was not revealed at that time.
Ground investigation (GI) needs to be conducted to determine the nature and extent of contamination. Normally, contamination is caused by human activities, e.g. fuel filling station and vehicle repairing workshop etc. As most of the potential contaminated sites fall within private land in KTN NDA and access requires land owners’ permission, GI is carried out within sites on government land. Subsequent to EPD’s agreement on the Contamination Assessment Plan (CAP) on 22 September 2009, GI, comprising 2 boreholes and 10 inspection pits for 3 sites on government land in KTN NDA was carried out between September 2009 and January 2010. The collected soil samples were tested in accordance with EPD’s “Guidance Manual for Use of Risk-Based Remediation Goals (RBRGs) for Contaminated Land Management” promulgated in 2007. The laboratory test results, received between March and May 2010, indicate that high concentration of the Arsenic was detected in 35 soil samples out of a total of 38 collected. The highest concentration detected is over 400 mg/kg which is about 20 times of the acceptable limit (21.8 mg/kg) specified in the RBRGs for Rural Residential use. On the other hand, all the soil samples complied with RBRGs for other contaminants, including those related to the current industrial activities at these sites, e.g. Total Petroleum Hydrocarbon, Lead and Copper. Therefore, the high levels of Arsenic at these 3 sites are considered anomalistic. The locations of boreholes and inspection pits at 3 government sites in KTN are shown in Figure 2.1.
A detailed review of the laboratory test results, historical land use of the areas concerned and the geochemistry in the northern New Territories was conducted by the Consultants. Based on the results of desktop review and laboratory testing, and as supported by the “Geochemical Atlas of Hong Kong” issued by GEO in 1999, It is considered that the high Arsenic levels are not anthropogenic activities resulting from industrial/commercial contamination.
In order to re-confirm the high level of Arsenic, to investigate the toxicity of the Arsenic detected, a supplementary GI comprising 1 boreholes and 3 inspection pits were carried out at the 3 government sites again and at an “Off-site” location without significant human and industrial activities (based on historical review of land use) in KTN NDA together with a comprehensive “Arsenic Specimen” testing by an overseas laboratory. The location of the “Offsite” borehole is shown in Figure 2.1. The supplementary GI as conducted between September and October 2010 and the laboratory test results, including those from an overseas laboratory, were received from October to December 2010. The test results re-confirm the very high Arsenic level in the 3 government sites. Also, Arsenic level, ranging from 114 mg/kg to 947 mg/kg, was recorded at the “Off-site” location. These results also reveal that the Arsenic level in the soil samples collected is dominated by the least toxic inorganic form of Arsenic, which usually dominates the soil solid phase in the natural environment. The details of the contamination assessment findings at 3 government site, and subsequent desktop review and arsenic specimen test could be referred to the “Contamination Assessment Report for Government Site”.
Soil samples have also been collected from 17 more boreholes in KTN NDA in conjunction with the Phase 2 GI for the NENT NDAs works between February and August 2011. The locations of these 17 boreholes were mainly for engineering purpose and not strategically selected for land contamination. The LT results from the Phase 2 GI show that the Arsenic levels vary from 1 mg/kg to over 800 mg/kg. The LT results re-confirmed high concentration of the contaminant exists at KTN NDA.
In order to further investigate the land contamination at KTN NDA, a further GI (i.e. Arsenic GI), comprising 18 boreholes, and associated LT were carried out between December 2011 and March 2012.
In view of the high level of As is not due to anthropogenic activities, therefore the guidelines and requirements under EPD’s Guidance Manual for Use of Risk-Based Remediation Goals for Contaminated Land Management are not applicable. Instead, a health risk assessment (HRA) was carried out focusing on two major exposure paths, namely inhalation and ingestion of As, during the construction and operation stages respectively. This report aims to provide the summary of Phase 2 GI and Arsenic GI programmes and the assessment findings on the health risk analysis on the ingestion of soil containing arsenic, and inhalation of arsenic-containing dust.
2.1 Phase 2 GI in Kwu Tung North
In order to further investigate the Arsenic distribution in KTN NDA, soil samples were collected during the Phase 2 geotechnical ground investigation (GI) between February 2011 and August 2011, which include 17 additional boreholes at different regions of KTN NDA. Although the main purpose of the GI is planned for geotechnical investigation, the locations of boreholes have been strategically selected in order to have broad coverage of KTN NDA. However, as most of the Phase 2 GI boreholes are located outside the Disturbed Area of KTN (i.e. area to be disturbed during construction stage) which limited the selection of representative borehole locations for profiling the Arsenic distribution. The Phase 2 GI programme of KTN is summarized in Table 2.1.
Table 2.1: Summary of Soil Sampling for Arsenic Testing during Phase 2 GI Programme in KTN
Borehole No. |
Range of Sampling Depths (meter below ground level, mbgl) |
Total No. of Soil Sample Collected |
KTN-BH11 |
0.5
– 3.5 |
4 |
KTN-BH12 |
0.5
– 17.4 |
5 |
KTN-BH13 |
0.5
– 50.6 |
15 |
KTN-BH14 |
0.5
– 15.7 |
7 |
KTN-BH15 |
0.5
– 7.7 |
5 |
KTN-BH16 |
0.5
– 4.6 |
4 |
KTN-BH17 |
0.5
– 11.6 |
6 |
KTN-BH18 |
0.5
– 1.50 |
3 |
KTN-BH19 |
0.5
– 14.8 |
7 |
KTN-BH20 |
0.5
– 18.5 |
7 |
KTN-BH21 |
0.6
– 11.5 |
7 |
KTN-BH22 |
0.5
– 19.7 |
8 |
KTN-BH23 |
0.5
– 18.7 |
8 |
KTN-BH24 |
0.5
– 17.0 |
8 |
KTN-BH25 |
0.5
– 13.6 |
6 |
KTN-BH26 |
0.5
– 7.2 |
5 |
KTN-BH28 |
0.5
– 16.7 |
7 |
Total No. of Sample: |
112 |
The Phase 2 GI works were carried out by Vibro (HK) Limited between February 2011 and August 2011. The as-built drawing showing locations of the Phase 2 GI boreholes in KTN are given in Figure 2.1. The strata logs of Phase 2 GI boreholes in KTN are given in Appendix A.
A total of 112 soil samples were collected from 17 boreholes. The collected soil samples were delivered to a local HOKLAS accredited environmental testing laboratory “ALS Technichem (HK) Ltd” for the testing of “Total Arsenic”.
The Arsenic test results of Phase 2 GI are summarized in Table 2.2. The laboratory testing reports are given in Appendix B. The testing results revealed that the arsenic was broadly distributed throughout the non-Disturbed Area of KTN at different locations and depths with different concentrations. However, the arsenic distribution within the Disturbed Area was still unclear.
Table 2.2: Summary of Arsenic Test Results in
Phase 2 GI Programme of KTN
Sampling Boreholes |
Sampling Depth (mbgl) |
Arsenic
Concentration
(mg/kg dry soil) |
KTN-BH11 |
0.5 |
78 |
1.0 |
66 |
|
1.5 |
38 |
|
3.05 - 3.50 |
818 |
|
KTN-BH12 |
0.5 |
20 |
1.0 |
22 |
|
1.5 |
42 |
|
4.15 - 4.60 |
8 |
|
17.05 - 17.39 |
20 |
|
KTN-BH13 |
0.5 |
75 |
1.0 |
128 |
|
1.5 |
50 |
|
3.0 |
29 |
|
6.2 |
10 |
|
10.8 |
23 |
|
14.1 |
10 |
|
18.1 |
16 |
|
21.1 |
11 |
|
24.45 |
17 |
|
29.0 |
29 |
|
34.8 |
60 |
|
38.4 |
2 |
|
44.15 - 44.45 |
19 |
|
50.15 - 50.60 |
106 |
|
KTN-BH14 |
0.5 |
24 |
1.0 |
33 |
|
1.5 |
19 |
|
3.05 - 3.50 |
11 |
|
7.10 - 7.55 |
13 |
|
11.15 - 11.60 |
7 |
|
15.20 - 15.65 |
21 |
|
KTN-BH15 |
0.6 |
676 |
1.18 |
308 |
|
1.6 |
308 |
|
3.15 - 3.60 |
188 |
|
7.20 - 7.65 |
74 |
|
KTN-BH16 |
0.5 |
14 |
1.0 |
3 |
|
1.5 |
4 |
|
4.15 - 4.60 |
15 |
|
KTN-BH17 |
0.5 |
56 |
1.0 |
17 |
|
1.5 |
24 |
|
3.05 - 3.50 |
46 |
|
7.10 - 7.55 |
6 |
|
11.15 - 11.60 |
6 |
|
KTN-BH18 |
0.5 |
33 |
1.0 |
66 |
|
1.5 |
36 |
|
KTN-BH19 |
0.5 |
5 |
1.0 |
8 |
|
1.5 |
2 |
|
3.05 - 3.50 |
4 |
|
6.20 - 6.65 |
19 |
|
10.25 - 10.70 |
10 |
|
14.30 - 14.75 |
34 |
|
KTN-BH20 |
0.6 |
17 |
1.0 |
20 |
|
1.6 |
13 |
|
3.15 - 3.60 |
22 |
|
7.20 - 7.65 |
95 |
|
13.75 - 14.20 |
94 |
|
18.05 - 18.50 |
86 |
|
KTN-BH21 |
0.6 |
46 |
1.1 |
75 |
|
1.6 |
81 |
|
2.0 |
46 |
|
3.55 - 4.00 |
18 |
|
6.55 - 7.00 |
3 |
|
11.05 - 11.50 |
39 |
|
KTN-BH22 |
0.5 |
9 |
1.0 |
14 |
|
1.5 |
30 |
|
3.05 - 3.50 |
276 |
|
7.05 -7.50 |
331 |
|
11.15 - 11.60 |
89 |
|
15.20 - 15.65 |
57 |
|
19.25 - 19.70 |
33 |
|
KTN-BH23 |
0.5 |
11 |
1.0 |
20 |
|
1.5 |
15 |
|
3.05 - 3.50 |
18 |
|
7.10 - 7.55 |
13 |
|
11.15 - 11.60 |
71 |
|
14.15 - 14.60 |
60 |
|
18.20 - 18.65 |
56 |
|
KTN-BH24 |
0.5 |
8 |
1.0 |
9 |
|
1.5 |
17 |
|
2.0 |
14 |
|
3.55 - 3.95 |
8 |
|
7.60 - 8.05 |
4 |
|
12.75 - 13.20 |
<1 |
|
16.75 - 17.00 |
<1 |
|
KTN-BH25 |
0.5 |
38 |
1.0 |
38 |
|
1.5 |
40 |
|
3.05 - 3.50 |
38 |
|
7.55 - 8.00 |
7 |
|
13.15 - 13.60 |
2 |
|
KTN-BH26 |
0.5 |
76 |
1.0 |
83 |
|
1.5 |
68 |
|
3.05 - 3.50 |
1 |
|
6.70 - 7.15 |
106 |
|
KTN-BH28 |
0.5 |
38 |
1.0 |
64 |
|
1.5 |
39 |
|
3.05 - 3.50 |
85 |
|
7.60 - 8.05 |
66 |
|
12.20 - 12.65 |
28 |
|
16.25 - 16.70 |
23 |
As RBRGs |
||
Rural Residential |
21.8 |
> 21.8,
< 22.1 |
Urban
Residential |
22.1 |
>22.1, <73.5 |
Public Parks |
73.5 |
> 73.5, <196 |
Industrial |
196 |
>196 |
2.2 Phase 2 GI in Fanling North
Apart from KTN, the Phase 2 GI was also conducted in Fanling North (FLN) NDA. In order to investigate whether the high arsenic are presented in FLN NDA, soil samples were also collected during the Phase 2 GI in this NDA and tested for arsenic. Soil samples were collected at 8 locations in FLN. The Phase 2 GI programme of FLN is summarized in Table 2.3.
Table 2.3: Summary of Soil Sampling for Arsenic Testing during Phase 2 GI Programme of FLN
Borehole No. |
Range of Sampling Depths (meter below ground level, mbgl) |
Total No. of Soil Sample Collected |
Fanling North (FLN) |
||
FLN-BH07 |
0.5
– 25.1 |
9 |
FLN-BH08 |
0.5
– 3.5 |
4 |
FLN-BH10 |
0.5
– 12.1 |
6 |
FLN-BH12 |
0.6
– 8.05 |
6 |
FLN-BH14 |
0.5
– 4.0 |
5 |
FLN-BH19 |
0.5
– 14.55 |
7 |
FLN-BH20 |
0.5
– 15.15 |
6 |
FLN-BH22 |
0.5
– 3.5 |
4 |
Total No. of Sample: |
47 |
The Phase 2 GI works were carried out by Vibro (HK) Limited between February 2011 and August 2011. The as-built drawing showing the locations of the Phase 2 GI boreholes in FLN is given in Figures 2.2. The strata logs of Phase 2 GI boreholes in FLN are given in Appendix C.
A total of 47 soil samples were collected from 8 boreholes in FLN. The collected soil samples were delivered to a local HOKLAS accredited environmental testing laboratory “ALS Technichem (HK) Ltd” for the testing of “Total Arsenic”.
The
Arsenic test results of Phase 2 GI of FLN are summarized in Table 2.4. The laboratory testing reports are given
in Appendix
D. The testing results revealed that only
slightly elevated arsenic level (i.e. up to 60 mg/kg) was detected along the
alignment of Fanling Bypass (i.e. Boreholes FLN-BH10 to FLN-BH22), and this
arsenic level has complied with the RBRGs of “Public Park” (73.5 mg/kg) and
“Industrial” (196 mg/kg), which are commonly adopted for the land use of road
works. The arsenic levels detected in FLN NDA (i.e. Boreholes FLN-BH07 and
FLN-BH08) has complied with the most stringent RBRG of “Rural Residential” (21.8mg/kg), and therefore
the high arsenic issue in FLN NDA is considered unlikely.
Table 2.4: Summary of Arsenic Test Results in
Phase 2 GI Programme of FLN
Sampling Boreholes |
Sampling Depth (mbgl) |
Arsenic
Concentration
(mg/kg dry soil) |
Fanling North
(FLN) |
||
FLN-BH07 |
0.5 |
6 |
1.0 |
4 |
|
1.5 |
6 |
|
3.10-3.55 |
8 |
|
6.50-6.95 |
3 |
|
10.50-10.95 |
1 |
|
16.55-17.00 |
3 |
|
20.60-21.05 |
3 |
|
24.65-25.10 |
2 |
|
FLN-BH08 |
0.5 |
14 |
1.0 |
12 |
|
1.5 |
14 |
|
3.05-3.50 |
6 |
|
FLN-BH10 |
1.0 |
60 |
1.5 |
50 |
|
2.0 |
50 |
|
3.55-4.00 |
43 |
|
7.60-8.05 |
7 |
|
11.65-12.10 |
15 |
|
FLN-BH12 |
0.6 |
37 |
1.10 |
42 |
|
1.60 |
41 |
|
2.00 |
38 |
|
3.55-4.00 |
23 |
|
7.60-8.05 |
34 |
|
FLN-BH14 |
0.5 |
50 |
1.0 |
22 |
|
1.5 |
28 |
|
2.0 |
30 |
|
3.55-4.00 |
16 |
|
FLN-BH19 |
0.5 |
18 |
1.0 |
21 |
|
1.5 |
19 |
|
2.0 |
25 |
|
3.55-4.00 |
3 |
|
8.95-9.40 |
4 |
|
14.10-14.55 |
3 |
|
FLN-BH20 |
0.5 |
16 |
1.0 |
18 |
|
1.5 |
13 |
|
3.05-3.50 |
9 |
|
10.65-11.10 |
46 |
|
14.70-15.15 |
18 |
|
FLN-BH22 |
0.5 |
35 |
1.0 |
41 |
|
1.5 |
4 |
|
3.05-3.50 |
14 |
As RBRGs |
||
Rural
Residential |
21.8 |
> 21.8,
< 22.1 |
Urban
Residential |
22.1 |
>22.1, <73.5 |
Public Parks |
73.5 |
> 73.5, <196 |
Industrial |
196 |
>196 |
3.1 Review of Aerial Photographs
The development history of the KTN was reviewed with the aid of the historical aerial photographs in Appendix E. The current and historical contamination concerns within KTN have been identified and are discussed below:
3.1.1 Aerial Photo of Year 1963
The aerial photograph for the
northern extent of the KTN is missing in 1963.
The southern extent of the development area is dominated by agricultural
fields with village housing concentrated along the main access roads in Fung
Kong and Tung Fong, Shek Tsa Long and Pak Shek Au. The
3.1.2 Aerial Photo of Year 1972
The aerial photograph in 1972 shows that there is a hill range in the north of the development area which is undeveloped, in contrast, the flat land between the hill slopes is used as agricultural land. As was the case in 1963, the dominant land use in 1972 is agricultural. Since 1963 there has been further development of the existing villages and these are more apparent in 1972 with the majority of development occurring in the south of the development area.
3.1.3 Aerial Photo of Year 1982
The aerial photograph for the
northern extent of the development area is missing in 1982. However, the southern section, particularly
by
3.1.4 Aerial Photo of Year 1993
By 1993 more residential development has occurred throughout the development area with agricultural land remaining in the eastern extent. Large plots of land have also been developed as storage and parking facilities.
3.1.5 Aerial Photo of Year 2001
By 2001 the
3.1.6 Aerial Photo of Year 2008
There has been little change between 2001 and 2008 in the KTN; residential and light industrial development remains scattered throughout the area.
3.2 Review of Historical Short-Term Tenancy Record
Apart from the historical aerial photos, investigation of land uses of KTN was also instigated so as to ascertain whether there is relationship between the levels of arsenic and land use(s).
It is well known that some economic activities, in particular industrial process will affect the level of arsenic in soil. The major human/industrial activities that would cause arsenic contamination are as follows:
·
Manufacturing
of leather products;
·
Wood
preservative / timber processing;
·
Production
of lead-acid batteries;
·
Production
of semiconductor used in various electronic appliance;
·
Chemical
processing industries; and
·
Manufacturing
of metals and alloys.
Other possible activities that would contribute arsenic into soil include:
·
Combustion
of municipal solid waste;
·
Land
filling of industrial wastes;
·
Application
of arsenical pesticides (herbicides, fungicides and insecticides);
·
Mining
and smelting of As-containing ores;
·
Combustion
of fossil fuels (especially coal); and
·
Petroleum
refining.
3.2.1 Review of Existing Land Uses
A total of 380 files of current land uses in KTN and FLN were reviewed. The file types include the following:-
·
Burial
grounds;
·
Government
land allocation/Temporary Government land allocation;
·
Crown
land licence/Government land licence;
·
Short
term tenancy;
·
Letter
of Approval; and
·
Modification
of Tenancy.
3.2.2 Review of Closed Files
Some of the past land uses might lead to the soil contamination by arsenic as well. Therefore, vetting of closed files for land uses already terminated and files for current short term waiver were carried out. A total of 280 files were checked.
3.2.3 Relationship between Arsenic Levels and Land uses
Based on the list of the human/industrial activities that may cause arsenic contamination or contribute to arsenic into soil, the users reported in the vetted files were checked to find out whether any of them fall within the aforesaid list. The major land uses both past and current relate to permission to erect residential accommodation etc. However, some past and current land uses may cause arsenic contamination as summarised in the Table 3.1.
Table 3.1: Summary of Past and Current Land Uses may cause Arsenic
Contamination
Site No. |
STT No.
etc. |
User |
Area
(approx. m2) |
Commencement
date |
Status |
Remarks |
1. |
STT No. 1275 |
Wooden product
workshop, warehouse and ancillary accommodation |
171 |
1/1/2003 |
Still in operation |
The former STT No. was 562,
a glove-sewing factory and this STT commenced on 1/10/1984. |
2 |
STT No. 573 |
Wood yard |
750 |
10/1/1983 |
Still in operation |
-- |
Based on the above land uses, the affected sites are superimposed on the plan in Appendix F to check whether there is any relationship between these uses and the levels of arsenic. It appears that there is no conclusion can be drawn that the high arsenic levels detected in KTN are due to these past or existing uses on site. Again, as the high arsenic level was detected at different depths up to 20 meter below ground level, it is unlikely that the past and current land uses could cause this high arsenic level at these depths.
4.1 Objective of Arsenic GI Programme
A comprehensive GI was carried out in order to profiling the extent of
arsenic in KTN, especially in the Disturbed Area (hereafter called the “Arsenic
GI programme”).
4.2
Details of Arsenic GI Programme
The Arsenic GI programme consists of 18 boreholes at different regions of KTN NDA. The locations of these 18 boreholes have been strategically selected in order to have broad coverage of the Disturbed Area of KTN and collect sufficient information for profiling the extent of arsenic level in the Disturbed Area. The Arsenic GI programme is summarized in Table 4.1.
Table 4.1: Summary of Soil Sampling for Arsenic Testing during Arsenic GI Programme
Borehole No. |
Range of Sampling Depths (meter below ground level, mbgl) |
Total No. of Soil Sample Collected |
KTN-ASBH01a |
0.5 – 38.0 |
17 |
KTN-ASBH04 |
0.5 – 20.5 |
11 |
KTN-ASBH06 |
0.5 – 45.5 |
21 |
KTN-ASBH07 |
0.5 – 40.5 |
19 |
KTN-ASBH08 |
0.5 – 40.5 |
19 |
KTN-ASBH09 |
0.5 – 28.0 |
14 |
KTN-ASBH12 |
0.5 – 35.5 |
17 |
KTN-ASBH13 |
0.5 – 53.5 |
24 |
KTN-ASBH14a |
0.5 – 18.0 |
9 |
KTN-ASBH14b |
0.5 – 45.0 |
21 |
KTN-ASBH15 |
0.6 – 25.5 |
12 |
KTN-ASBH20 |
0.5 – 35.5 |
16 |
KTN-ASBH21 |
0.5 – 33.0 |
15 |
KTN-ASBH29 |
0.5 – 8.0 |
6 |
KTN-ASBH32 |
0.5 – 23.0 |
11 |
KTN-ASBH38 |
0.5 – 15.5 |
9 |
KTN-ASBH Offsite |
0.5 – 30.5 |
15 |
KTN-ASBH Offsite(a) |
0.5 – 30.5 |
21 |
Total No. of Sample: |
277 |
The Arsenic GI works were carried out by Fugro Geotechnical Services Limited between 5 December 2011 and 29 February 2012. The as-built drawing showing locations of the Arsenic GI boreholes are given in Figure 2.1. The strata logs of Arsenic GI boreholes are given in Appendix G.
A total of 277 soil samples were collected from 18 boreholes. The collected soil samples were delivered to a local HOKLAS accredited environmental testing laboratory “ALS Technichem (HK) Ltd” for the testing of “Total Arsenic”.
The Arsenic test results of Arsenic GI programme are summarized in Table 4.2. The laboratory testing reports are given in Appendix H.
Table 4.2: Summary of Arsenic Test Results in Arsenic GI Programme
Sampling
Boreholes |
Sampling
Depth (mbgl) |
Arsenic Concentration (mg/kg dry
soil) |
KTN-ASBH01a |
0.5 |
148 |
1.0 |
51 |
|
1.5 |
75 |
|
3.0 - 3.45 |
97 |
|
5.5 - 5.95 |
414 |
|
8.0 - 8.45 |
805 |
|
10.5 - 10.95 |
224 |
|
13.0 - 13.45 |
792 |
|
15.5 - 15.95 |
21 |
|
18.0 - 18.45 |
64 |
|
20.5 - 20.95 |
66 |
|
23.0 - 23.45 |
530 |
|
25.5 - 25.95 |
132 |
|
28.0 - 28.45 |
50 |
|
30.5 - 30.95 |
142 |
|
35.5 |
155 |
|
38.0 |
475 |
|
KTN-ASBH04 |
0.5 |
7 |
1.0 |
46 |
|
1.5 |
53 |
|
3.0 - 3.45 |
133 |
|
5.5 - 5.95 |
190 |
|
8.0 - 8.45 |
118 |
|
10.5 - 10.95 |
74 |
|
13.0 - 13.45 |
239 |
|
15.5 - 15.95 |
79 |
|
18.0 - 18.45 |
38 |
|
20.5 |
31 |
|
KTN-ASBH06 |
0.5 |
21 |
1.0 |
44 |
|
1.5 |
77 |
|
3.0 - 3.45 |
13 |
|
5.5 - 5.95 |
16 |
|
8.0 - 8.45 |
14 |
|
10.5 - 10.95 |
115 |
|
13.0 - 13.45 |
77 |
|
15.5 - 15.95 |
9 |
|
18.0 - 18.45 |
13 |
|
20.5 - 20.95 |
3 |
|
23.0 - 23.45 |
16 |
|
25.5 - 25.95 |
3 |
|
28.0 - 28.45 |
2 |
|
30.5 - 30.95 |
103 |
|
33.0 - 33.45 |
5 |
|
35.5 - 35.95 |
24 |
|
38.0 - 38.45 |
71 |
|
40.5 - 40.95 |
12 |
|
43.0 - 43.45 |
18 |
|
45.5 - 45.95 |
128 |
|
KTN-ASBH07 |
0.5 |
49 |
1.0 |
71 |
|
1.5 |
168 |
|
3.0 - 3.45 |
63 |
|
5.5 - 5.95 |
84 |
|
8.0 - 8.45 |
11 |
|
10.5 - 10.95 |
356 |
|
13.0 - 13.45 |
15 |
|
15.5 - 15.95 |
650 |
|
18.0 - 18.45 |
633 |
|
20.5 - 20.95 |
160 |
|
23.0 - 23.45 |
19 |
|
25.5 - 25.95 |
176 |
|
28.0 - 28.45 |
188 |
|
30.5 - 30.95 |
8 |
|
33.0 - 33.45 |
12 |
|
35.5 - 35.95 |
10 |
|
38.0 - 38.45 |
13 |
|
40.5 - 40.95 |
1 |
|
KTN-ASBH08 |
0.5 |
25 |
1.0 |
62 |
|
1.5 |
61 |
|
3.0 |
8 |
|
5.5 |
666 |
|
8.0 - 8.45 |
358 |
|
10.5 - 10.95 |
1,020 |
|
13.0 - 13.45 |
218 |
|
15.5 - 15.95 |
252 |
|
18.0 - 18.45 |
377 |
|
20.5 - 20.95 |
103 |
|
23.0 - 23.45 |
112 |
|
25.5 - 25.95 |
147 |
|
28.0 - 28.45 |
73 |
|
30.5 - 30.95 |
149 |
|
33.0 - 33.45 |
234 |
|
35.5 - 35.95 |
127 |
|
38.0 - 38.45 |
39 |
|
40.5 - 40.95 |
68 |
|
KTN-ASBH09 |
0.5 |
442 |
1.0 |
338 |
|
1.5 |
186 |
|
3.0 - 3.45 |
258 |
|
5.5 - 5.95 |
412 |
|
8.0 - 8.45 |
134 |
|
10.5 - 10.95 |
60 |
|
13.0 - 13.45 |
67 |
|
15.5 - 15.95 |
16 |
|
18.0 - 18.45 |
25 |
|
20.5 - 20.95 |
59 |
|
23.0 - 23.45 |
129 |
|
25.5 - 25.95 |
95 |
|
28.0 |
19 |
|
KTN-ASBH12 |
0.5 |
41 |
1.0 |
274 |
|
1.5 |
257 |
|
3.0 - 3.45 |
432 |
|
5.5 - 5.95 |
52 |
|
8.0 - 8.45 |
21 |
|
10.5 - 10.95 |
9 |
|
13.0 - 13.45 |
130 |
|
15.5 - 15.95 |
214 |
|
18.0 - 18.45 |
13 |
|
20.5 - 20.95 |
33 |
|
23.0 - 23.45 |
76 |
|
25.5 |
100 |
|
28.0 - 28.45 |
61 |
|
30.5 - 30.95 |
108 |
|
33.0 - 33.45 |
255 |
|
35.5 |
401 |
|
KTN-ASBH13 |
0.5 |
65 |
1.0 |
101 |
|
1.5 |
96 |
|
3.0 - 3.45 |
177 |
|
5.5 - 5.95 |
162 |
|
8.0 - 8.45 |
58 |
|
10.5 - 10.95 |
52 |
|
13.0 - 13.45 |
811 |
|
15.5 - 15.95 |
1,220 |
|
18.0 |
137 |
|
20.5 |
179 |
|
23.0 |
119 |
|
25.5 - 25.95 |
324 |
|
28.0 - 28.45 |
16 |
|
30.5 - 30.95 |
592 |
|
33.0 - 33.45 |
80 |
|
35.5 - 35.95 |
7 |
|
38.0 - 38.45 |
13 |
|
40.5 - 40.95 |
4 |
|
43.0 - 43.45 |
18 |
|
45.5 - 45.95 |
6 |
|
48.0 - 48.45 |
17 |
|
50.5 - 50.95 |
8 |
|
53.5 |
16 |
|
KTN-ASBH14a |
0.5 |
52 |
1.0 |
101 |
|
1.5 |
191 |
|
3.0 - 3.45 |
5 |
|
5.5 - 5.95 |
52 |
|
10.5 - 10.95 |
15 |
|
13.0 - 13.45 |
10 |
|
15.5 - 15.95 |
7 |
|
18.0 |
11 |
|
KTN-ASBH14b |
0.5 |
417 |
1.0 |
400 |
|
1.5 |
55 |
|
3.0 - 3.45 |
93 |
|
5.5 - 5.95 |
56 |
|
8.0 - 8.45 |
28 |
|
10.5 - 10.95 |
79 |
|
13.0 - 13.45 |
322 |
|
15.5 - 15.95 |
174 |
|
18.0 - 18.45 |
97 |
|
20.5 - 20.95 |
102 |
|
23.0 - 23.45 |
79 |
|
25.5 - 25.95 |
68 |
|
28.0 - 28.45 |
82 |
|
30.5 - 30.95 |
158 |
|
33.0 |
315 |
|
35.50 |
240 |
|
38.0 - 38.45 |
78 |
|
40.5 - 40.95 |
127 |
|
43.0 - 43.45 |
114 |
|
45.5 - 45.95 |
58 |
|
KTN-ASBH15 |
0.5 |
31 |
1.0 |
68 |
|
1.5 |
51 |
|
3.0 - 3.45 |
7 |
|
5.5 |
71 |
|
8.0 |
73 |
|
10.5 - 10.81 |
28 |
|
13.0 |
46 |
|
18.0 - 18.45 |
227 |
|
20.5 - 20.95 |
25 |
|
23.0 |
945 |
|
25.5 |
78 |
|
KTN-ASBH20 |
0.5 |
219 |
1.0 |
40 |
|
1.5 |
43 |
|
3.0 - 3.45 |
27 |
|
6.0 |
12 |
|
8.0 - 8.45 |
86 |
|
10.5 - 10.95 |
263 |
|
13.0 - 13.45 |
74 |
|
15.5 - 15.95 |
100 |
|
18.0 - 18.45 |
98 |
|
20.5 - 20.95 |
194 |
|
23.0 - 23.45 |
6 |
|
25.5 - 25.95 |
161 |
|
28.0 - 28.45 |
134 |
|
30.5 - 30.95 |
710 |
|
35.0 - 35.95 |
21 |
|
KTN-ASBH21 |
0.5 |
73 |
1.0 |
56 |
|
1.5 |
62 |
|
5.5 |
2 |
|
8.0 - 8.45 |
131 |
|
10.5 - 10.95 |
25 |
|
13.0 - 13.45 |
90 |
|
15.5 - 15.95 |
75 |
|
18.0 - 18.45 |
198 |
|
20.5 - 20.95 |
98 |
|
23.0 - 23.45 |
71 |
|
25.5 - 25.95 |
94 |
|
28.0 - 28.45 |
38 |
|
30.5 |
134 |
|
33.0 - 33.45 |
86 |
|
KTN-ASBH29 |
0.5 |
72 |
1.0 |
124 |
|
1.5 |
155 |
|
3.0 - 3.45 |
124 |
|
5.5 - 5.95 |
214 |
|
8.0 - 8.45 |
95 |
|
KTN-ASBH32 |
0.5 |
21 |
1.0 |
30 |
|
1.5 |
65 |
|
3.0 - 3.45 |
36 |
|
5.5 - 5.95 |
16 |
|
8.0 - 8.45 |
45 |
|
10.5 - 10.95 |
30 |
|
13.0 - 13.45 |
2 |
|
15.5 - 15.95 |
8 |
|
18.0 - 18.45 |
85 |
|
23.0 |
10 |
|
KTN-ASBH38 |
0.5 |
12 |
1.0 |
22 |
|
1.5 |
5 |
|
3.0 - 3.45 |
2 |
|
5.5 |
1 |
|
8.0 - 8.45 |
13 |
|
10.5 - 10.95 |
20 |
|
13.0 - 13.45 |
39 |
|
15.5 |
20 |
|
KTN-ASBH
Offsite |
0.5 |
88 |
1.0 |
122 |
|
1.5 |
214 |
|
3.0 - 3.45 |
105 |
|
5.5 - 5.95 |
122 |
|
8.0 - 8.45 |
45 |
|
10.5 - 10.95 |
167 |
|
13.0 - 13.45 |
147 |
|
15.5 - 15.95 |
343 |
|
18.0 - 18.45 |
542 |
|
20.5 - 20.95 |
23,400 |
|
23.0 - 23.45 |
708 |
|
25.5 - 25.95 |
494 |
|
28.0 - 28.45 |
82 |
|
30.5 - 30.85 |
234 |
|
KTN-ASBH
Offsite (a) * |
0.5 |
195 |
1.0 |
128 |
|
1.5 |
262 |
|
3.6 |
128 |
|
5.9 |
163 |
|
8.2 |
80 |
|
10.0 |
151 |
|
12.8 |
176 |
|
15.0 |
504 |
|
17.2 |
105 |
|
18.4 |
74 |
|
19.5 |
64 |
|
20.6 |
86 |
|
21.8 |
70 |
|
23.0 |
73 |
|
24.1 |
111 |
|
25.2 |
457 |
|
26.3 |
203 |
|
27.5 |
806 |
|
29.5 |
238 |
|
30.5 |
320 |
Note *: Mazier sampling was
used at the borehole KTN-ASBH Offsite(a). Refer to Section 4.3.2 for
details.
As RBRGs |
||
Rural Residential |
21.8 |
>
21.8, < 22.1 |
Urban Residential |
22.1 |
>22.1, <73.5 |
Public Parks |
73.5 |
> 73.5,
<196 |
Industrial |
196 |
>196 |
4.3 Investigation of Extremely High Arsenic Results
An extremely high arsenic level of 23,400 mg/kg was detected in the soil sample collected at the depth of 20.5 – 20.95 mbgl of borehole “KTN-ASBH Offsite” (i.e. refer to Table 4.2, the cell highlighted with purple). This is the first time of recording the soil arsenic level which exceeds 10,000 mg/kg. It should be noted that the second highest detected arsenic level is only 1,220 mg/kg (i.e. at the depth of 15.5 – 15.95 mbgl of borehole KTN-ASBH13), and therefore the extremely high arsenic level of 23,400 mg/kg is considered anomalistic.
4.3.1 Further Testing of High Arsenic Soil Sample
As reported by the laboratory, some hard black colour material was found in this soil sample. In order to investigate the case, the soil sample was further inspected and tested. The testing strategy was summarized below:
1.
The GI
Contractor’s core box disturbed soil sample recovered from the cutting shoes at
the depth of 20.95 – 21.00 mbgl was sub-sampled for arsenic testing;
2. The black colour material, as recommended by
the laboratory, was carefully extracted out from the soil sample in laboratory
and then tested for arsenic; and
3.
The
remaining soil sample in the U76 sampler was extracted out, split into 7
portions and tested for arsenic.
The testing results and the arsenic distribution pattern in this U76
soil sample (i.e. 0.45m long from 20.50 – 20.95 mbgl) is illustrated below:
Arsenic
Profile in U76 sample collected at the depth of 20.50–20.95 mbgl of borehole KTN-ASBH
Offsite
Depth
(mbgl) |
U76
Sampler |
Sample
ID |
Arsenic Results (mg.kg dry weight) |
||
20.50 |
|
KTN-ASBH Offsite (20.5m - 6) |
738 |
||
|
|
KTN-ASBH Offsite (20.5m - 5) |
826 |
||
|
KTN-ASBH Offsite (20.5m - 4) |
2,290 |
|||
|
KTN-ASBH Offsite (20.5m - 3) |
1,520 |
|||
|
KTN-ASBH Offsite (20.5m - 2) |
469 |
|||
|
KTN-ASBH Offsite (20.5m - 1) |
5,470 |
|||
|
KTN-ASBH Offsite (20.5m - 0) |
13,400 |
|||
|
KTN-ASBH Offsite (20.5 - 20.95) |
23,400 |
|||
20.95 |
|
KTN-ASBH Offsite (20.5m - Black
Material) |
75,300 |
||
20.95 – 21.00 |
Core Box Disturbed Sample |
KTN-ASBH Offsite (Core Box 20.5) |
811 |
||
|
= |
Original sample collected during Arsenic
GI |
Extremely high arsenic level of up to 75,300 mg/kg arsenic (i.e. 7.53% of arsenic) was detected at the hard-black material. The testing results also clearly illustrated the gradually reduction of arsenic level from 23,400 mg/kg to 738 mg/kg along the U76 soil sample. The laboratory testing reports of this further soil testing are given in Appendix I.
These extremely high soil arsenic levels of 23,400 mg/kg and 75,300
mg/kg have never been recorded in Hong Kong, and are considered anomalistic.
Besides, the distribution pattern of arsenic
concentration from 738 mg/kg at the depth of 20.50 mbgl (i.e. upper level) to
the concentration of 23,400 mg/kg at the depth of 20.95 mbgl (i.e. lower level)
along the U76 soil sample also suggested that it is unlikely the extremely high
arsenic concentration caused by contamination, and is more likely that due to
high natural background.
4.3.2 Mazier Sampling at Borehole KTN-ASBH Offiste (a)
In view of this anomalistic high arsenic level, another borehole
“KTN-ASBH Offsite (a)” was drilled, which located approximately 5 m from the
borehole “KTN-ASBH Offsite”. Instead of U100 and U76 undisturbed soil samples,
“Mazier” undisturbed soil samples (i.e. 1-meter long, 76mm diameter plastic
tube) were collected continuously from the depths between 1.5 mbgl and 30.5mbgl
at borehole KTN-ASBH Offsite (a). Disturbed soil samples recovered from the
cutting shoes at different depths were also collected for arsenic testing. The
testing results are given in Table 4.2.
4.3.3 Geological Inspection of Spilt Mazier Sample
The collected Mazier soil samples were delivered to the geotechnical
laboratory of Gammon Construction Ltd. in TKO, and subsequently split into 2
halves. The split Mazier samples were visual inspected by GEO’s and
Consultant’s qualified geologists on 1 March 2012 for any sign of
“Mineralization”, which is considered as one of the evidences of occurring of
high nature elements, such as Arsenic.
The photographic records for longitudinal splitting of the Mazier
samples prepared by Gammon are given in Appendix J. The
detail geological logging record of Mazier samples prepared by Consultant’s
qualified geologist is given in Appendix K.
4.3.4
Sub-Sampling of Disturbed Soil Sample from Split
Mazier Sample
During the inspection of split Mazier samples, obvious black colour materials were identified at the depths of approximately 25.2 mbgl and 27.5 mbgl, which consists of high arsenic levels of 457 mg/kg and 806 mg/kg respectively (i.e. refer to Table 4.2). The disturbed soil samples with black colour materials were therefore sub-sampled from the split Mazier sample at the depths of 25.1 mbgl and 27.4 mbgl for arsenic testing. The testing results are summarized in Table 4.3. The laboratory testing reports of these 2 sub-soil samples are given in Appendix L.
Table 4.3: Summary of Arsenic Test Results Mazier Sub-sample
Borehole No. |
Sampling Depths (mbgl) |
Sample Source |
Arsenic Concentration (mg/kg dry soil) |
KTN-ASBH Offsite (a) |
25.1 |
Sub-sampled from spilt
Mazier sample |
17,700 |
25.2 |
Recovered from cutting
shoes |
457 |
|
27.4 |
Sub-sampled from spilt
Mazier sample |
12,200 |
|
27.5 |
Recovered from cutting
shoes |
806 |
The testing results revealed that the black colour materials consists
of high arsenic levels (i.e. exceeded 10,000 mg/kg) which similar to the case
of borehole KTN-ASBH Offsite.
4.3.5 Co-relation of Arsenic and Geology
Co-relation between the arsenic concentration and the geology has been
reviewed. It seems that the inferred mineralization zones are well co-related
with levels of high arsenic concentration (i.e. refer to Appendix M
for details). This observation provides a solid evidence of the extremely high arsenic
level found in boreholes KTN-ASBH Offsite and KTN-ASBH Offsite(a) is due to in situ
rock composition instead of surface contamination.
4.4 Profiling of Arsenic Extent in KTN
The soil arsenic results collected from the environmental site
investigation in 3 government site of KTN (i.e. refer to Section 1), the Phase 2 GI programme
(i.e. refer to Section
2.1) and the Arsenic GI Programme (i.e. refer to Section 4.2) are used for profiling
the arsenic extent in KTN by using the Geographical Information System (GIS).
Nevertheless, there is no correlation between the arsenic concentration and the
sampling locations and depths, and therefore not possible to develop the true
3-dimensional model (i.e. plume type feature) to illustrate the 3D arsenic
profiling.
Alternatively, a series of stacked contour plans showing the arsenic
concentration at different elevations were developed, and given in Appendix N. The
arsenic contour plans were developed at elevations levels of:
·
Current
ground level;
·
Proposed
site formation level;
·
+25mPD
level;
·
+20mPD
level;
·
+15mPD
level;
·
+10mPD
level;
·
+5mPD
level;
·
0mPD
level;
·
-5mPD
level;
·
-15mPD
level; and
·
-25mPD
level.
7 colour scales are used to illustrate various arsenic concentration
extents from 0 - 100 mg/kg (i.e. green colour) to over 600 mg/kg (i.e. red
colour). The general descriptions of arsenic distribution profile at each
elevation level are given in Table 4.4.
The GIS As profiling plans is used for estimating the quantity of
arsenic containing soil which require treatment (i.e. refer to Section 7
for details).
Table 4.4: General description of arsenic profile
Elevation Level |
General Description of Arsenic Distribution
Profile |
Current Ground Level |
The
arsenic concentration is ranged from 8 mg/kg to 676 mg/kg, with its peak
value of 676 mg/kg in the western part of KTN, and decreasing gradually to
all directions. Arsenic with concentration above 100 mg/kg lies mainly in the
western and southern part of KTN while Arsenic with concentration below 100
mg/kg is dominant in the northern and south-eastern parts of KTN. |
Proposed Site Formation
Level |
The
arsenic concentration is ranged from 5 mg/kg to 676 mg/kg, with its peak
value of 676 mg/kg in the western part of KTN, decreasing gradually to all
directions. Arsenic with concentration above 100 mg/kg lies mainly in the western
part of KTN while Arsenic with concentration below 100 mg/kg is dominant in the
central, northern and southern parts of KTN. |
+25mPD |
The
arsenic concentration is ranged from 13 mg/kg to 818 mg/kg, with its peak
value of 818 mg/kg in the western part of KTN, decreasing gradually to north
and south. Arsenic with concentration above 100 mg/kg lies mainly in the western
part of KTN while Arsenic with concentration below 100 mg/kg is dominant in the
northern parts of KTN. |
+20mPD |
The
arsenic concentration is ranged from 14 mg/kg to 432 mg/kg, with its peak
value of 432 mg/kg in the western part of KTN, decreasing gradually to the
west. Arsenic with concentration above 100 mg/kg lies mainly in the western
part of KTN while Arsenic with concentration below 100 mg/kg is dominant in
the northern and north-western parts of KTN. |
+15mPD |
The
arsenic concentration is ranged from 8 mg/kg to 805 mg/kg, with its peak
value of 805 mg/kg in the south-western part of KTN, decreasing gradually to
north. Arsenic with concentration above 100 mg/kg lies mainly in the south-western
part of KTN while Arsenic with concentration below 100 mg/kg is dominant in
the north-western part of KTN. |
+10mPD |
The
arsenic concentration is ranged from 6 mg/kg to 792 mg/kg, with its peak
value of 792 mg/kg in the south-western part of KTN, decreasing gradually to
all directions. Arsenic with concentration above 100 mg/kg lies mainly in the
south-western part of KTN while Arsenic with concentration below 100 mg/kg is
dominant in the northern and north-western parts of KTN. |
+5mPD |
The
arsenic concentration is ranged from 6 mg/kg to 75300 mg/kg. Two regional
peaks with arsenic concentration above 600 mg/kg are found. Arsenic
concentration reaches its first regional peak, 1,220 mg/kg, in the central
part of KTN, decreasing gradually to all directions. Arsenic concentration reaches
its second regional peak, 75,300 mg/kg, in western part of KTN, decreasing
gradually to the north and substantially to the south. Arsenic with
concentration above 100 mg/kg lies mainly in the central and western part of
KTN while Arsenic with concentration below 100 mg/kg is dominant in the north-western,
south-western and south-eastern parts of KTN. |
0mPD |
The
arsenic concentration is ranged from 2 mg/kg to 1,020 mg/kg. Two regional
peaks with arsenic concentration above 600 mg/kg are found. Arsenic
concentration reaches its first regional peak, 806 mg/kg, in the western part
of KTN, decreasing gradually to all directions. Arsenic concentration reaches
its second regional peak, 1,020 mg/kg, in central part of KTN, decreasing
gradually to all directions. Arsenic with concentration above 100 mg/kg lies
mainly in the central and western part of KTN while Arsenic with
concentration below 100 mg/kg is dominant in the northern part of KTN. |
-5mPD |
The
arsenic concentration is ranged from 1 mg/kg to 633 mg/kg, with its peak
value of 633 mg/kg in the central part of KTN, decreasing gradually to all
directions. Arsenic with concentration above 100 mg/kg lies mainly in the
central and western part of KTN while Arsenic with concentration below 100
mg/kg is dominant in the north-western and southern parts of KTN. |
-15mPD |
The
arsenic concentration is ranged from 60 mg/kg to 475 mg/kg with its peak
value of 475 mg/kg in the south-western part of KTN, decreasing gradually to
south-eastern direction. Arsenic with concentration above 100 mg/kg lies
mainly in the south-western part of KTN while Arsenic with concentration
below 100 mg/kg is dominant in the northern part of KTN. |
-25mPD |
The arsenic concentration is ranged from 19 mg/kg to
710 mg/kg with its peak value of 710 mg/kg, in the southern part of KTN,
decreasing gradually to north-western direction. Arsenic with concentration
above 100 mg/kg lies mainly in the southern part of KTN while Arsenic with
concentration below 100 mg/kg is dominant in the central part of KTN. |
In view of the high level of As is not due to anthropogenic activities, therefore the guidelines and requirements under EPD’s Guidance Manual for Use of Risk-Based Remediation Goals for Contaminated Land Management are not applicable. Instead, a “Health Risk Assessment” was carried out to assess the environmental health risk level during both construction and operational stages of the development. With consideration of the nature of the project and arsenic, the health risk assessment was carried out in focusing on the health risk of nearby sensitive receivers through inhalation of arsenic-containing dust during construction stage, and the health risk of future residents through ingestion of arsenic-containing soil.
Uptake of soil arsenic by vegetable and subsequently consumed by human is an indirect ingestion pathway of arsenic to human. The health risk level due to indirect ingestion through consumption of vegetables is considered negligible, and therefore the health risk assessment of this indirect ingestion pathway is considered not require.
The details of the health risk assessment are given in Section 5 and Section 6.
5.1 Arsenic, Sources and Toxicity to Humans (1)
Arsenic is widely distributed on Earth. In nature, it exists as inorganic compounds – sulphides, arsenides and arsenates in soil and water. Arsenic has been used in industry, and could contaminate soil and water. It could be released into air as trioxides mainly by high temperature thermal processes. Arsenic could be found in high concentrations in drinking water, either derived from soil or from man-made products such as wood preservatives and pesticides. Organic arsenic compounds are usually of lower toxicity than inorganic arsenic, and are found in seafood such as fish and shellfish. Rice contaminated by water containing high arsenic concentrations has been reported in Taiwan. The soluble form of inorganic arsenic is acutely toxic. Intake of inorganic arsenic over a long period can lead to chronic arsenic poisoning (arsenicosis).
Acute toxic effects include nausea, headache, stomach ache, vomiting and severe diarrhoea. Irregular heart heat (cardiac arrhythmias) has also been reported. Chronic effects, which can take years to develop depending on the level of exposure, include thickening of the skin (hyperkeratosis) and colour changes (pigmentation and depigmentation), anaemia, cough and sputum, peripheral neuropathy, gastrointestinal symptoms, diabetes, blood vessel, liver and kidney damages, cardiovascular disease and cancers of the lung, urinary bladder and skin. Arsenic is classified as a Group 1 Carcinogen by the International Agency for Research on Cancer (IARC).(2) Organic arsenic compounds, which are abundant in seafood, are less harmful to health and are rapidly eliminated by the body.
5.1.1 Minimal Risk Levels (MRL) of Arsenic
For the assessment of non-carcinogenic health risk, the oral Minimal Risk Levels (MRLs) recommended by the US Agency for Toxic Substances and Disease Registry (ATSDR) for acute exposures (exposures less than 2 weeks) and for chronic exposures (exposures greater than one year) are used.(34) The minimal risk level is a dose below which non-cancerous harmful effects are not expected.
5.1.1.1 Short-Term (Acute) Health Risk
ATSDR’s minimal risk level for short-term (acute) exposures is 0.005 mg/kg body weight per day. This acute oral MRL is derived by applying an uncertainty factor of 10 to the lowest-observed-adverse-effect level (LOAEL) and a factor of one for human variation. The LOAEL is the lowest level observed to cause harmful effects in humans.* When the MRL is exceeded, a concern might exist for harmful effects and further evaluation is needed.
5.1.1.2 Long-Term (Chronic) Health Risk
ATSDR uses the No Observed Adverse Effect Level (NOAEL) approach to derive MRLs for hazardous substances. They are set below levels that, based on current information, might cause adverse health effects in eh people most sensitive to such substance induced effects. A clear dose-response relationship was observed for characteristic skin lesions. The NOAEL for skin effects were determined as 0.0008 mg/kg body weight per day. The chronic oral MRL of 0.0003 mg/kg body weight per day was therefore by ATSDR by applying an uncertainty factor / safety margin of 3 to NOAEL for human variability.
5.1.1.3 Carcinogenic Risk
Much epidemiological evidence exists for an increased risk of lung cancer with inhalation of arsenic among workers in smelters and other chemical plants.(34) Convincing evidence also exists for an increased risk of skin cancer and arsenic ingestion (through drinking water).(35) No reference values are recommended for carcinogenic effects of arsenic.
The US EPA calculated a unit risk of 5 x 10-5, using the upper bound excess cancer risk from lifetime exposure to 0.001 mg As/ litre of water.(34) The guideline value recommended by the World Health Organization (WHO) for drinking water quality in 2011 is 0.01 mg As/ litre.(36) The standard of drinking water in the U.K. also follows the WHO guideline. This is equivalent to an oral index dose of arsenic intake of about 0.0003 mg/kg/day, and corresponds to an increased lifetime cancer risk of 4 x 10-3 to 4 x 10-4.(37) For the total dietary intake of inorganic arsenic (i.e. including arsenic from drinking water), the Joint FAO/WHO Expert Committee on Food Additives (JECFA) determined the lower limit of the benchmark dose for a 0.5% increase (or 5 x 10-3) in incidence of lung cancer (BMDL0.5) from epidemiological data to be 3 µg/kg body weight per day (range: 2-7 µg/kg body weight per day).(38) This was based on a range of assumptions to estimate the total dietary exposure to inorganic arsenic from food and drinking water.
All the above unit risks of cancer are only applicable to arsenic in food and water, and assume 100% bioavailability. Data on unit risk of cancer from soil ingestion are not available, but should be lower.
5.2 Route of Absorption of Arsenic (1,2)
The major route of intake of arsenic is through ingestion. Drinking water is a major source of arsenic intake in many countries where underground water is contaminated by naturally occurring arsenic. Intake of food grown in arsenic-containing soil or contaminated by pesticides containing arsenic is another important source. Ingestion of small amounts of soil, especially by children, is another route by which arsenic is absorbed into the body. Children commonly put their hands or objects such as toys into the mouth, or ingest food that has been dropped on to the ground and becomes contaminated by soil. Inhalation is a less important route. However, arsenic-containing dust particles that are large (‘non-respirable’) can be inhaled into the upper respiratory tract and trapped in the mucus of the respiratory epithelium. These particulates are then transported upwards by the ‘muco-ciliary escalator’, a protective mechanism of the respiratory system. The particulates will be swallowed into the gastrointestinal tract and contribute to the amount of arsenic ingested into the body. Dermal absorption is negligible.
Estimation of Arsenic Intake by Ingestion and Absorption
5.2.1 Assessment Equation
The following equation(3) is used to estimate the amount of arsenic a person absorbs from ingesting arsenic-containing soil exposure.
Daily Arsenic Dose =
(Soil As concentration)(milligrams soil ingested)(%
absorption)(0.000001 kg/mg)
Body weight in
kg
No local data on the rate of soil ingestion by children and adults are available. Reference on exposure was made from the Exposure Factors Handbook published by the United States Environmental Protection Agency (USEPA).(4) The amount of daily involuntary ingestion of soil (that refers to outdoor soil, outdoors settled dust and soil for indoor plant growth) plus the ingestion of indoor dust (which refers to dust that has settled indoors, and included dust tracked or blown into the indoor environment from outdoors) were adopted in the exposure assessment. Both values also take into account the ingestion of inhaled particles that are trapped in the respiratory epithelium. The rate of soil ingestion varies among children of different age groups, and in the Exposure Factors Handbook, several values are available. The rates of Central Tendency (Median) for children and adults are used in the exposure assessment. To be conservative, The Upper Percentile of exposure for children in the general population was also adopted as conservative approach. The values of different soil ingestion rate are shown in Table 5.1.
Table 5.1 Soil ingestion rates of different age groups
Age Group |
Distribution of Estimate |
Total Soil
and Dust Ingested # (mg/day) |
1 to 6 years |
General
Population Central Tendency |
100 |
Adult |
50 |
|
3 to 6 years |
General
Population Upper Percentile |
200 |
# Including
inhaled particles trapped in the mucus of the respiratory epithelium) per day
(rounded off to one significant figure)
The reference levels/values of arsenic
toxicity for ingestion, such as MRL and cancer risk, were developed from
studies of arsenic in water or aquatic form. The risk resulting from arsenic
ingestion depends on the dose of arsenic absorbed. Arsenic in water is in a
water-soluble form, and its absorption from the human gastrointestinal tract is
assumed to be 100%. Arsenic in soil is incompletely absorbed because some
arsenic compounds are present in water-insoluble forms; some are bound tightly
with soil or interact with other soil constituents. Logically, the diminished
absorption of arsenic from soil relative to water should be taken into
consideration when evaluating the cancer risk posed by arsenic exposure
(Roberts et al, 2002).(7)
Only part of the
ingested arsenic from soil is absorbed into the human body, and the percentage
of ingested arsenic that could be absorbed by human body is known as the Bioavailability. For consumption of
arsenic-containing water, the bioavailability is assumed to be 100%. Studies
have shown that assuming 100% bioavailability of arsenic from soils and mine
waste materials overestimates the risk associated with human exposure (Bruce et
al, 2007).(8) In the health risk assessment of arsenic from soil
ingestion, a lower bioavailability should be used. The Relative Bioavailability
(RBA) of arsenic in soil – the ratio of the fraction of arsenic absorbed from
the site medium (e.g., soil) to the fraction absorbed in toxicity studies, has
been determined in animal studies. The RBA of a test material may be estimated
by measuring the Urinary Excretion Fraction (UEF) of arsenic administered in
test material and in reference material (sodium arsenate), and calculating the
ratio of the two UEF values:
RBA(test material) = UEF(test material) /
UEF(sodium arsenate)
This value varies widely, depending on the
particle size and pH of the soil, the chemical state of arsenic, and the animal
used in experimental model. Most were based on mining or smelting area soils.
Of in-vivo studies, rabbits and rats are not ideal as experimental animals for
assessing RBA. Their habit of coprophagy (eating faeces) makes the estimation
of RBA unreliable. Moreover, there are large differences in their digestive
physiology compared to humans. By contrast, juvenile swine are considered to be
a useful anatomical proxy for the human neonatal digestive tract, and have been
used more often as animal models in bioavailability tests (Miller and Ullrey,
1987; Moughan et al, 1994).(9, 10) Primates are phylogenetically
close to humans and are considered to be the best animal model for determining
RBA. However, few studies are available.
From a review of studies on the
bioavailability of arsenic reporting maximum values (i.e. for soil, dust or
slag), the bioavailability ranges from 0% to 78%, (Battelle, 1996; Lorenzana
1996).(11, 12) The
bioavailability values of different studies are summarized in Table
5.2.
Table 5.2: Relative Bioavailability (RBA) values of different studies
Study |
Animal |
Soil
type |
RBA |
1.
Groen
et al, 1993 (13) |
Dog |
Bog ore-containing soil |
8.3+2% |
2.
Davis
A, et al, 1992 (14) |
Rabbit |
Blended mine waste site soil and roadside
soil |
11% |
3.
Freeman
et al, 1993 (15) |
Rabbit |
Smelter area soils |
48% |
4.
Lorenzana et
al., 1996 (12) |
Swine |
Mining
area soil / Mining area slag |
78%
/ 42% |
5.
Battelle, 1996 (11) |
Swine |
Mining
area slag |
Not detectable |
6.
Casteel et al., 1997 (16) |
Swine |
Soils and mining area wastes |
0%
– 50% |
7.
Rodriguez et al, 1999 (17) |
Swine |
Contaminated soils from mining/smelter sites |
2.7%
– 42.8% |
8.
Casteel et al., 2001 (18) |
Swine |
Residential soil |
18%
– 45% |
9.
Juhasz et al, 2007a (19) |
Swine |
1.
Gossan
soils (with high naturally occurring As |
16.4+9.1%,
12.1+8.5% |
2.
Mine
site soils |
6.9+5.0%,
40.8+7.4% |
||
10. Freeman
et al., 1995 (20) |
Monkey |
Mining area soils / Mining area dusts |
20%
/ 28% |
11. Roberts
et al., 2002 (7) |
Monkey |
Soil from contaminated sites |
10.7%
– 24.7% |
12. Roberts
et al., 2007 (21) |
Monkey |
Soil from contaminated sites |
5%
– 31% (most RBA in the 10% – 20% range) |
13. Bradham
et al. ,2011 (22) |
Mouse |
Residential
soil contaminated by mining or smelting |
11%
– 53%; mean=33% |
14. Ng
et al, 1998 (23) |
Rat |
Soil
contaminated with pesticides |
*Absolute
bioavailability:
As 3+: 1.02 – 9.87%; As5+: 0.26 –
2.98% |
15. Ellickson
et al, 2001 (24) |
Rat |
Standard
reference soil Montana Highly Elevated trace Element Concentration (SRM 2070,
sampled from Butte, Montana) |
37.8% |
16. Stanek
et al., 2010 (25) |
Human |
Sterilized
soil from cattle-dip site |
48.7%
(95% CI: 36.2% – 61.3%) |
In view of the limitations (for rat, mouse
and rabbit models) and the lack of similarity with human digestive physiology
(dogs), we shall disregard results from Studies No. 1 – 3 and 13 – 15
in Table 5.2, and only make reference to the swine,
monkey and human models.
Studies on Cebus monkeys exposed to
arsenic-contaminated soil from 5 waste sites in Florida reported lower
bioavailability values, ranged from 10.7% to 24.7% (Roberts et al, 2002).(7)
In this study, the authors also showed data confirming that the pharmacokinetic
and excretion behaviour of sodium arsenate in monkeys were similar to that of
humans. In a subsequent study by the same author (Roberts et al, 2007)(21)
on bioavailability of 14 soil samples from 12 different sites, using Cynomolgus
monkeys, a broad range of RBA (5% – 31%) was reported.
An RBA of 25%, based on the study of
contaminated soils in Florida by Roberts et al, 2002 (7) was adopted
as an upper-bound value for risk assessment by the Florida Department of
Environmental Protection (FDEP) and agreed by the USEPA (USEPA 2001).(26)
FDEP made a protective science-based policy decision to adopt the default
relative oral bioavailability factor of 33% (the maximum RBA value in the
University of Florida / FDEP study by Roberts et al, 2002 (7) as a
worst-case risk assessment; this was implemented in 2005 (Methodology Focus
Group, 2003; University of Florida, 2005).(27)
A pilot study on the relative bioavailability (RBA) of soil ingestion by human volunteers (Stanek et al, 2010)(25) was reported. The estimated relative bioavailability (RBA) was 48.7% (95% CI: 36.2% – 61.3%). One can argue that study results using human volunteers are most representative of RBA in humans and therefore most relevant in risk assessment. However, there are several important limitations. First, this is a pilot study, and the only human experimental study available. Secondly, the experiment is, for ethical reasons, less stringently controlled than animal studies. For example, it is not possible to place human subjects on an arsenic-free diet, and casual soil ingestion might have occurred. Incidental ingestion of other arsenic containing substances has been reported in one subject, who took a herbal pill that probably contained As. Thirdly, for ethical reasons, it is not possible to administer high doses of arsenic to human volunteers. Based on these reasons, we decide not to use the RBA results from the human study in our assessment. By contrast, the methodologies for in-vivo animal studies using the young swine model have been well-developed, and many such studies have been published (USEPA 2010).(28) Findings of these in-vivo studies in general produce comparable RBA values for similar species, the within-species differences being mainly explained by differences in type of testing materials, such as different types of soils (whether natural or contaminated by pesticides or mines) slag or dusts. Hence, in-vivo animal studies are still regarded as the standard for assessing RBA and values from these studies have been accepted by regulatory agencies such as the USEPA (Stanek III, personal communication).
Different types of in-vitro
bioaccessability (IVBA) tests, an alternative approach for estimating the
solubility of arsenic in soils and other solid material have been developed (US
EPA 1999).(29) The fraction of arsenic which solubilizes in an in
vitro system is referred to as in vitro bioaccessibility, while the fraction
that is absorbed in vivo is referred to as bioavailability. The IVBA of soil
samples from Casteel’s study (2001)(18) [Study No. 8 in Table 5.2], which ranged from 18.2 to 41.8%, showed a
moderately good correlation with the bioavailability data from the in-vivo
results (R2=0.645). In general, in-vitro study results (which
measure bioaccessibility instead of bioavailability) are higher than the
corresponding RBA values for the same soil specimens tested. Regression
equations have been developed to predict RBA from in-vitro data on
bioaccessibility. These tests have been recommended to provide data when
in-vivo studies are not available. However, in-vivo studies are still being
used as references for obtaining RBA values for risk assessment purposes. In an
in vitro assessment of arsenic containing soils (contaminated and natural), the
highest bioaccessibility was: 22% for natural gossan soil and 36% for mine site
soil (Juhasz et al 2007b).(30) In a study using meta analysis and
relative bioavailability-bioaccessibility regression models, the 95th
percentiles for standardized predicted arsenic RBA for naturally occurring
gossan soils was predicted to be 23.7%. For contaminated soil, the predicted
RBA (95th percentiles) were higher: 78.0% for copper-chrome-arsenate
posts, 78.4% for herbicides/ pesticide, 67.0% for mining / smelting sources
(Juhasz et al, 2011).(31) In a Guangzhou study of urban soils from
different sites (urban parks, residential areas, roadside, industrial areas)
using an in vitro gastrointestinal test, the bioaccessibility of arsenic was
11.3% in the stomach phase and 1.9% in the intestinal phase (Lu et al, 2011).(32)
While most in-vivo studies were done on contaminated soils
by various sources, one study of swine was based on uncontaminated
residential soil (Casteel et al, 2001)(18) [Study No. 8 in Table 5.2]. In this study,
a combination of
over 130 sub-samples of soil from 5 different locations in Denver, Colorado
were fed to 70 pigs. The soils in the sites are characterized by a mixture of
arsenic trioxide and lead arsenic oxide particles, with most of the particles
less than 10 µm in diameter. Essentially all arsenic-containing grains are
“liberated” (not contained within any other matrix). A mean bioavailability
value of 31%, with a range of 18% to 45%, was found. The upper 95% confidence
limit of 42% was recommended as an appropriate statistic for use in assessing
human health risk from arsenic in soil in Colorado. A range of relative
bioavailability from 40 – 60% has been used by the ATSDR in health risk
assessment of arsenic in soil in sites in East Omaha, Nebraska (ATSDR 2007).(33)
In three other studies [Study No. 4, 6
and 7 in Table 5.2] using the swine model that gave RBA
greater than the Casteel’s study (2001)(18) [Study No. 8 in Table 5.2], the media are contaminated soils from mines or
smelters, which have higher bioavailability than natural soil. Based on the
above studies, we can assume that compared to the bioavailability values (upper bound: 25%; maximum:
31%) derived from the studies on monkeys, using an RBA of 42% in our health
risk assessment is likely to be a conservative and an overestimate of human
absorption of arsenic from soil in Kwu Tung.
The justifications for using 42% as the RBA value for Kwu
Tung site are:
(i)
The Denver study is the one of few studies involving residential soil; most other studies
involve mining soils, slags, or soil contaminated by industrial or agricultural
use;
(ii)
The in-vivo results of this study are comparable to IVBA results with the same soil samples, the latter
giving a maximum value of 41.8%; and
(iii)
42% RBA, which represents the upper
95% confidence limit of bioavailability results, is already a conservative
estimate compared to RBA values obtained from primate studies, which range from
5 – 31%, with most values below 30%. To date, no swine studies on RBA of
natural soils give a value above 45%. Bioaccessibility results of naturally
occurring soils also yield values below 42%. In the absence of local
bioavailability / bioaccessibility data and data on soil chemistry, the use of
42% RBA, which represents the upper 95% confidence limit in health risk assessment
is, in professional point of view, appropriate.
5.3 Arsenic Concentration in Soil
The distribution of arsenic concentrations (mg/kg dry weight) in 437 soil samples collected during Environmental Site Investigation in late 2009/early 2010 (48 soil samples), Phase 2 Stage 2 GI in mid 2011 (112 soil samples) and Arsenic GI in late 2011/early 2012 (277 soil samples) is summarized in Table 5.3. The location plan showing all relevant GI works in Figure 2.1.
Table
5.3 Percentile distribution of arsenic concentrations in sampled soil
Percentile@ |
Arsenic Concentration in Soil
(mg/kg) |
Percentile |
Arsenic Concentration in Soil
(mg/kg) |
Percentile |
Arsenic Concentration in Soil
(mg/kg) |
Maximum |
1,220 |
95 |
461 |
70 |
122 |
99 |
816 |
90 |
323 |
65 |
103 |
98 |
735 |
85 |
226 |
60 |
88 |
97 |
649 |
80 |
179 |
Average |
125 |
96 |
520 |
75 |
147 |
Median |
71 |
5.4 Estimated Dose of Arsenic Absorbed from Ingestion at Different Soil Concentrations
The daily absorbed doses of arsenic from ingestion
of different soil concentrations was estimated using various assumptions of
daily soil ingestion rates and body weight, and summarized in Table
5.4. Table 5.5 shows the maximum
concentrations of arsenic in soil that do not exceed the MRL of 5 µg/kg/day for
short-term exposure for both children and adults, and 0.3 µg/kg/day chronic
exposure for adults from ingestion (including large particulates inhaled).
The equation presented in Section
5.2.1 is used for the calculation of Daily Arsenic Dose of Short Term (Acute) and Long Term (Chronic) health risks as
summarized in Table 5.4
and Table 5.5 respectively.
The following equation is used for calculating the maximum concentrations of arsenic in soil that do not
exceed the MRLs, as summarized in Table 5.6.
For Children and Adults:
Arsenic Concentration in Soil (mg/kg) = 0.005 mg * body weight (kg) *
1,000,000
Amount of soil ingested per day
* % absorption
For Adults:
Arsenic Concentration in Soil (mg/kg) = 0.0003 mg * body weight (kg) * 1,000,000
Amount of soil ingested per day
* % absorption
Short-term (Acute) MRL = 0.005 mg/kg/day = 5
µg/kg/day
Long-term (Chronic) MRL = 0.0003 mg/kg/day =
0.3 µg/kg/day
Table 5.4 Daily
dose of arsenic absorbed in µg/kg body weight (BW) from soil ingestion
(including trapped particles inhaled) for Short-Term (Acute) health risk
As Concentration in Soil
Samples |
Amount of
Soil Ingested Per Day (mg) |
% Absorption* |
Daily Dose
of Arsenic Absorbed (µg) |
Body Weight # (kg) |
Daily Arsenic Dose (µg/kg BW) |
||
Percentiles |
(mg/kg dry weight) |
||||||
Maximum |
1,220@ |
3 to 6 years (Upper percentile) |
200 |
42% |
102.5 |
13 (median) 11 (10%) 10.5 (3%) |
7.9 9.3 9.8 |
1 to 6 years (Central
Tendency) |
100 |
51.2 |
9 (median) 8 (10%) 7 (3%) |
5.7 6.4 7.3 |
|||
99% |
816 |
3 to 6 years (Upper percentile) |
200 |
42% |
68.5 |
13 (median) 11 (10%) 10.5 (3%) |
5.3 6.2 6.5 |
1 to 6 years (Central
Tendency) |
100 |
34.3 |
9 (median) 8 (10%) 7 (3%) |
3.8 4.3 4.9 |
|||
98% |
735 |
3 to 6 years (Upper percentile) |
200 |
42% |
61.7 |
13 (median) 11 (10%) 10.5 (3%) |
4.7 5.6 5.9 |
1 to 6 years (Central
Tendency) |
100 |
30.9 |
9 (median) 8 (10%) 7 (3%) |
3.4 3.9 4.8 |
|||
97% |
649 |
3 to 6 years (Upper percentile) |
200 |
42% |
54.5 |
13 (median) 11 (10%) 10.5 (3%) |
4.2 5.0 5.2 |
1 to 6 years (Central
Tendency) |
100 |
27.3 |
9 (median) 8 (10%) 7 (3%) |
3.0 3.4 3.9 |
|||
96% |
520 |
3 to 6 years (Upper percentile) |
200 |
42% |
43.6 |
13 (median) 11 (10%) 10.5 (3%) |
3.4 4.0 4.2 |
1 to 6 years (Central
Tendency) |
100 |
21.8 |
9 (median) 8 (10%) 7 (3%) |
2.4 2.7 3.1 |
|||
95% |
461 |
3 to 6 years (Upper percentile) |
200 |
42% |
38.7 |
13 (median) 11 (10%) 10.5 (3%) |
3.0 3.5 3.7 |
1 to 6 years (Central
Tendency) |
100 |
19.4 |
9 (median) 8 (10%) 7 (3%) |
2.2 2.4 2.8 |
|||
90% |
323 |
3 to 6 years (Upper percentile) |
200 |
42% |
27.1 |
13 (median) 11 (10%) 10.5 (3%) |
2.1 2.5 2.6 |
1 to 6 years (Central
Tendency) |
100 |
13.6 |
9 (median) 8 (10%) 7 (3%) |
1.5 1.7 1.9 |
|||
85% |
226 |
3 to 6 years (Upper percentile) |
200 |
42% |
19.0 |
13 (median) 11 (10%) 10.5 (3%) |
1.5 1.7 1.8 |
1 to 6 years (Central
Tendency) |
100 |
9.5 |
9 (median) 8 (10%) 7 (3%) |
1.1 1.2 1.4 |
|||
80% |
179 |
3 to 6 years (Upper percentile) |
200 |
42% |
15.0 |
13 (median) 11 (10%) 10.5 (3%) |
1.2 1.4 1.4 |
1 to 6 years (Central
Tendency) |
100 |
7.5 |
9 (median) 8 (10%) 7 (3%) |
0.8 0.9 1.1 |
|||
75% |
147 |
3 to 6 years (Upper percentile) |
200 |
42% |
12.3 |
13 (median) 11 (10%) 10.5 (3%) |
0.9 1.1 1.2 |
1 to 6 years (Central
Tendency) |
100 |
6.2 |
9 (median) 8 (10%) 7 (3%) |
0.7 0.8 0.9 |
|||
Average |
125 |
3 to 6 years (Upper percentile) |
200 |
42% |
10.5 |
13 (median) 11 (10%) 10.5 (3%) |
0.8 1.0 1.0 |
1 to 6 years (Central
Tendency) |
100 |
5.3 |
9 (median) 8 (10%) 7 (3%) |
0.6 0.7 0.8 |
|||
Median |
71 |
3 to 6 years (Upper percentile) |
200 |
42% |
6.0 |
13 (median) 11 (10%) 10.5 (3%) |
0.5 0.5 0.6 |
1 to 6 years (Central
Tendency) |
100 |
3.0 |
9 (median) 8 (10%) 7 (3%) |
0.3 0.4 0.4 |
Note: Percentile
distribution based on results of 437 soil samples.
* Assuming 95th percentile of bioavailability, based on a
USEPA study in Denver. (See Ref. 16)
# Body weight of female children aged 1 and 3 years and female adults (aged
18 years) from Leung et al. Growth standard from Southern Chinese. Hong Kong Growth
Survey 1993, were used in the calculation.
@ The maximum soil arsenic concentration of 23,400 mg/kg is
considered as “Outliner” as the second highest soil arsenic concentration is
only 1,220 mg/kg and the 99 percentile of soil arsenic concentration is 816
mg/kg.
Daily doses exceeding the
MRL for short-term (acute) health effects are shown in RED.
Table 5.5 Daily dose of arsenic absorbed in µg/kg
body weight (BW) from soil ingestion (including trapped particles inhaled) for
Long-Term (Chronic) health risk
As Concentration in Soil
Samples |
Amount of
Soil Ingested Per Day (mg) |
% Absorption* |
Daily Dose
of Arsenic Absorbed (µg) |
Body Weight # (kg) |
Daily Arsenic Dose (µg/kg BW) |
||
Percentiles |
(mg/kg dry weight) |
||||||
Maximum |
1,220@ |
Adult (Central
Tendency) |
50 |
42% |
25.6 |
51 (median) 43 (10%) 40 (3%) |
0.50 0.60 0.64 |
99% |
816 |
Adult (Central
Tendency) |
50 |
42% |
17.1 |
51 (median) 43 (10%) 40 (3%) |
0.34 0.40 0.43 |
98% |
735 |
Adult (Central
Tendency) |
50 |
42% |
15.4 |
51 (median) 43 (10%) 40 (3%) |
0.30 0.36 0.39 |
97% |
649 |
Adult (Central
Tendency) |
50 |
42% |
13.6 |
51 (median) 43 (10%) 40 (3%) |
0.27 0.32 0.34 |
96% |
520 |
Adult (Central Tendency) |
50 |
42% |
10.9 |
51 (median) 43 (10%) 40 (3%) |
0.21 0.25 0.27 |
95% |
461 |
Adult (Central
Tendency) |
50 |
42% |
9.7 |
51 (median) 43 (10%) 40 (3%) |
0.19 0.23 0.24 |
90% |
323 |
Adult (Central
Tendency) |
50 |
42% |
6.8 |
51 (median) 43 (10%) 40 (3%) |
0.13 0.16 0.17 |
85% |
226 |
Adult (Central
Tendency) |
50 |
42% |
4.8 |
51 (median) 43 (10%) 40 (3%) |
0.09 0.11 0.12 |
80% |
179 |
Adult (Central
Tendency) |
50 |
42% |
3.8 |
51 (median) 43 (10%) 40 (3%) |
0.07 0.09 0.09 |
75% |
147 |
Adult (Central
Tendency) |
50 |
42% |
3.1 |
51 (median) 43 (10%) 40 (3%) |
0.06 0.07 0.08 |
Average |
125 |
Adult (Central
Tendency) |
50 |
42% |
2.6 |
51 (median) 43 (10%) 40 (3%) |
0.05 0.06 0.07 |
Median |
71 |
Adult (Central
Tendency) |
50 |
42% |
1.5 |
51 (median) 43 (10%) 40 (3%) |
0.03 0.03 0.04 |
Note: Percentile
distribution based on results of 437 soil samples.
* Assuming 95th percentile of bioavailability, based on a
USEPA study in Denver. (See Ref. 16)
# Body weight of female children aged 1 and 3 years and female adults (aged
18 years) from Leung et al. Growth standard from Southern Chinese. Hong Kong Growth
Survey 1993, were used in the calculation.
@ The maximum soil arsenic concentration of 23,400 mg/kg is
considered as “Outliner” as the second highest soil arsenic concentration is
only 1,220 mg/kg and the 99 percentile of soil arsenic concentration is 816
mg/kg.
Daily doses exceeding the MRL for long-term (chronic) health effects are
shown in BLUE. those
exceeding the chronic MRL (which is equivalent
Table 5.6 Estimated arsenic concentration in soil
(mg/kg) below the MRLs for short-term exposure (0.005mg/kg/day) for children,
and long-term exposure (0.0003mg/kg/day) for adult by ingestion, including
trapped particles inhaled.
Age (year) |
Body Weight (kg) |
Estimated Daily Soil Ingestion (mg/day) |
Bioavailability |
Estimated
Soil Arsenic Concentration (mg/kg) |
1 |
9 (median) |
100 |
42% |
1,071 |
8 (10%) |
952 |
|||
7 (3%) |
833 |
|||
3 |
13 (median) |
200 |
42% |
774 |
11 (10%) |
655 |
|||
10.5 (3%) |
625 |
|||
18 |
51 (median) |
50 |
42% |
729 |
43 (10%) |
614 |
|||
40 (3%) |
571 |
5.5 Discussion on Ingestion Health Risk Assessment
Based on the rate of soil ingestion at the upper percentile of US children aged 3 to 6 years, and a more conservative assumption of local data on body weight (i.e. females children aged 3 years, at 3rd percentile of body weight), the short-term MRL of 5.0 µg/kg/day will be exceeded through ingestion of soil if exposed to the arsenic concentration of the soil sample at the 97th percentile (at 649 mg/kg). For one-year-old children (i.e. females at 3rd percentile of body weight), with a median soil ingestion rate, the short-term MRL will be exceeded if exposed to the soil sample at maximum level, at 1,220 mg/kg.
The long-term MRL for non-carcinogenic effects is about the same as the U.K. index dose for intake of food and water for an increased lifetime cancer risk of 4 x 10-3 to 4 x 10-4. Since the rate of soil ingestion rapidly declines when the child grows older, the long-term MRL and carcinogenic risk are only applicable to adults. Exposure to soil concentration of arsenic at the 97th percentile of the soil samples (at 649 mg/kg) will exceed the long-term MRL of 0.3 µg/kg/day.
The maximum arsenic concentration in the soil above which the short-term MRL would not be exceeded for 3-year-old female children at 3rd percentile of body weight children through ingestion is estimated to be 625 mg/kg. The maximum arsenic concentration in the soil above which chronic (long-term) MRL would not be exceeded for female adults at 3rd percentile of body weight who are exposed through ingestion is slightly lower, at 571 mg/kg.
It should be noted that the health risk assessment of arsenic
absorption through soil ingestion also includes the ingestion of inhaled
arsenic-containing soil dust particles that are removed by the upper
respiratory tract and swallowed into the gut.
5.6 Uncertainties in Ingestion Health Risk Assessment
There are wide variations in the assumption of the rate of soil ingestion. The rate at the upper percentile (only available for children aged 3 to 6 years), used in this assessment, is twice of that at the median. It is reasonable to assume that the use of US data on exposure represents an over-estimation of risk as children living in a typical US home, a suburban house with a garden, have a much higher chance to be exposed to soil compared to Hong Kong children, whose typical home is a high-rise flat. Besides the obvious difference in the home-living environments between Hong Kong and US households, there probably exists a cultural difference as well – Chinese children in Hong Kong are commonly discouraged to play with soil. Hence, it is believed that the aforementioned risk estimates are relatively conservative. The use of female children at a lower percentile of body weight is another conservative approach in this risk assessment.
Another uncertainty that affects the magnitude of the risk
estimates is the assumption of bioavailability. While it is accepted that only
a proportion of arsenic ingested can be absorbed, this percentage has a wide
range. A value of 42%, the 95th percentile of a US study (18)
was used in the risk assessment. This value is based on residential soil fed to
swine, and is considerably higher than studies of mining / contaminated soils
on monkeys, thought to be a more appropriate animal model for humans because of
the similarities of their digestive system. Using bioavailability values
obtained from studies on monkeys would result in risk estimates ranging from
half to two thirds of the estimates presented in this Report.
Uncertainties in MRL and BMD for arsenic toxicity as recommended by
the ATSDR are dealt with by the use of safety factors that widen the “safety
margin” of these values.
6.1 Risk of Inhalation of Arsenic-Containing Dust
Compared to oral ingestion, inhalation is a much less
important route of exposure to arsenic. In a WHO document, it was stated that
“Non-occupational human exposure to arsenic in the environment is primarily
through the ingestion of food and water. Of these, food is generally the
principal contributor to the daily intake of total arsenic. In some areas
arsenic in drinking-water is a significant source of exposure to inorganic
arsenic. In these cases, arsenic in drinking-water often constitutes the
principal contributor to the daily arsenic intake. Contaminated soils such as
mine tailings are also a potential source of arsenic exposure”.(42)
Evidence on health outcomes (systemic toxicity and carcinogenic effects) from inhalation of arsenic has been derived from studies of workers occupationally exposed dust or fumes containing arsenic – copper smelters, tin miners and workers exposed to pesticides containing arsenic, where exposure levels are high.(43) Reports of toxicity from inhalation of arsenic in non-occupational settings are linked to handling or burning arsenic treated wood. Small (but inconsistent) increases in risk of lung cancer have been reported in residents living near smelters or arsenic chemical plants.(43) By contrast, epidemiological studies on health outcomes of ingestion of arsenic are mostly from consumption of contaminated food or drinking water, and from accidental, suicidal or medicinal ingestion of arsenic. No incidents of arsenic toxicity from inhalation of arsenic dust originating from soil have ever been reported.
There is a potential risk of exposure through inhalation of Respirable Suspended Particulate (RSP) containing arsenic by workers on site during the construction phase of the development, as the site workers should be protected by enforcing relevant labour safety regulations and provision of suitable personal protective equipment. It is considered that risks of arsenic inhalation to residents living near construction sites are much smaller than that from accidental/unintentional ingestion of soil. The health risk assessment due to inhalation of RSP (or PM10) was focused for the sensitive receivers in the vicinity of the area.
6.2 Safe Level for Inhalation Exposure of Arsenic-Containing Dust
Comprehensive
searching of safe level for inhalation exposure of arsenic-containing dust has
been conducted. Relevant
standards and guidelines
published by various environmental and health authorities of advanced countries
have been reviewed, but no safe level was established.
The most relevant value was found in World Health Organization (WHO) Air Quality Guideline for Europe 2nd Edition (WHO Regional Publications, European Series, No. 91). In this guideline, a pooled risk estimate was derived from studies in exposed smelter workers in Sweden and United States, when assuming a linear dose-response relationship. A safe level for inhalation exposure of arsenic-containing dust is not recommended. At an air concentration of 1µg/m3, the estimated lifetime cancer risk (i.e. for 70 years) is 1.5 x 10-3. This implies that the excess lifetime cancer risk level is 1 in 100,000 , or 1 x 10-5 at an air concentration of about 6.6ng/m3. For an excess cancer risk of 1 x 10-4 and 1 x 10-6, the corresponding airborne concentrations of arsenic are 66 ng/m3 and 0.66 ng/m3. There is no international consensus as to which risk level is an acceptable standard. It is generally considered that a risk level of higher than 1 x 10-4 would be too high, and remedial / measures are required to reduce the risk. A risk level of 1 x 10-6 is generally regarded as “safe”, as it is approximately equivalent to the background risk level of cancer. A cancer risk limit of 1 x 10-5 is a subjective decision that is intermediate between what is generally regarded as the “high end” of risk level and that which represents the background risk level. In evaluating this carcinogenic risk from inhalation of airborne arsenic, one should consider that the 2011 WHO guideline for drinking water quality of 10 µg of arsenic /litre corresponds to an increased lifetime cancer risk of 4 x 10-3 to 4 x 10-4.(37) The Joint FAO/WHO Expert Committee on Food Additives (JECFA) determined the lower limit of the benchmark dose for a 0.5% increase (or 5 x 10-3) in incidence of lung cancer (BMDL0.5) from epidemiological data to be 3 µg/kg body weight per day (range: 2-7 µg/kg body weight per day).(38) This was based on a range of assumptions to estimate the total dietary exposure to inorganic arsenic from food and drinking water. These cancer risk levels from arsenic in food and drinking water from the WHO and FAO are much higher than that attributable to inhalation of arsenic containing respirable particulates. For comparison, the cancer risk attributable to inhalation of arsenic at 6.6 ng/m3 is much lower (0.25% to 2.5%) that the risk from food and water. The magnitude of risk from arsenic inhalation must be interpreted in its proper perspective.
6.3 Ambient Arsenic Level in KTN
Ambient arsenic concentrations at different regions of HKSAR are monitored by EPD’s Air Quality Monitoring Stations. However, there is no air quality monitoring station set at Kwn Tung area, and the station nearest to KTN is Yuen Long Air Quality Monitoring Station. Therefore the ambient arsenic levels recorded by Yuen Long Air Quality Monitoring Station from year 2008 – 2012 (i.e. 5 year-average) is adopted to represent the background ambient arsenic level in KTN. In fact, adoption of 5-year average of EPD’s air quality data to represent the background level for subsequent air quality modelling and assessment is an acceptable and commonly adopted approach.
The ambient arsenic levels recorded by EPD’s Yuen Long Air Quality Monitoring Station from year 2008 to 2012 are summarized in Table 6.1.
Table 6.1 Summary of annual ambient arsenic levels recorded by EPD’s Yuen Long Air Quality Monitoring Station
Arsenic
Level (ng/m3) |
Year |
||||
2008 |
2009 |
2010 |
2011 |
2012 |
|
Annual As Average |
5.5 |
4.0 |
4.1 |
5.5 |
4.3 |
5-year As Average |
4.7 |
The 5-year average Yuen Long ambient arsenic level of 4.7 ng/m3 is adopted as the background level in KTN for the subsequent arsenic impact assessment in Section 6.4.
6.4 Construction Dust Impact Assessment for Arsenic
This section presents the assessment of potential air quality impacts due to the ambient arsenic on air sensitive uses in development areas under the revised Recommended Outline Development Plan (RODP). The revised RODP is given Appendix O. It evaluates the potential air quality implications and the environmental acceptability of the proposed landuses, including the identification and assessment of pollution emission sources associated with the proposed developments, and the impacts on the existing and planned sensitive receivers.
KTN area (KTN) is predominantly rural with low population density. The local air quality is dominated by vehicular emissions from Fanling Highway and Castle Peak Road, as well as rural industries scattered in the area.
Location of KTN NDA and the air pollution sources within Study Area are shown in Appendix P.
The Yuen Long 5-year average ambient arsenic level recorded by EPD’s Yuen Long air monitoring station is adopted as the baseline condition of KTN (refer to Section 6.3 for details).
A review of the tentative construction programme has been conducted to
identify the construction period which is deemed to have significant impact on
nearby Air Sensitive Receivers (ASRs). Based on the latest Construction
Programme as shown in Appendix Q, it is
identified that most of the dusty construction activities such as site
clearance, ground excavation, construction of the associated facilities, etc.
would be taken place during Year 2025. Hence, Year 2025 is considered
appropriate to represent the worst-case scenario and therefore taken as the
assessment year.
The representative ASRs within 500m of the KTN NDA boundary have been identified. These include any domestic premises, hotel, hospital, clinic, nursery, temporary housing accommodation, school, educational institution, office, factory, shop and shopping centre, place of public worship, library, court of law, sports stadium or performing arts centre. Existing ASRs outside the site boundary mainly comprise village houses and residential developments. Locations of representative existing and planned ASRs in the vicinity of KTN NDA are shown in Appendix R. The existing ASRs are tabulated in Table 6.2.
Table 6.2 Existing
ASRs in the vicinity of KTN NDA in 2025
ASR ID |
Locations |
Existing Landuse (1) |
KTN-E24 |
Temporary Structure near Sheung
Yue River |
OU |
KTN-E85 |
Yin Kong Tsuen |
R |
KTN-E86 |
R |
|
KTN-E87 |
R |
|
KTN-E88 |
Sports Ground near Enchi Lodge |
RC |
KTN-E89 |
Temporary Structure near Castle Peak
Road |
OU |
KTN-E90 |
OU |
|
KTN-E91 |
OU |
|
KTN-E94 |
Ho Sheung Heung Temple |
W |
KTN-E97 |
Ho Sheung Heung Village |
R |
KTN-E99 |
R |
|
KTN-E100 |
R |
|
KTN-E101 |
R |
|
KTN-E102 |
Temporary Structure Northern to
Ho Sheung Heung Village |
OU |
KTN-E104 |
Village Houses near Tsung Yuen |
R |
KTN-E106 |
R |
|
KTN-E108 |
R |
|
KTN-E109 |
Temporary Structure at Tsung
Yuen |
R |
KTN-E110 |
Temporary Structure near Lo Wu
Correctional Institution |
OU |
KTN-E111 |
Lo Wu Correctional Institution
Basketball Court |
RC |
KTN-E112 |
Lo Wu Correctional Institution |
IC |
KTN-E123 |
Lo Wu Firing Range (Eastern) |
IC |
KTN-E128 |
Lo Wu Firing Range (Western) |
IC |
KTN-E154 |
Ho Sheung Heung Village |
R |
KTN-E155 |
R |
|
KTN-E156 |
R |
|
KTN-E162 |
Temporary Structure near Fanling
Highway (near Pak Shek Au) |
OU |
KTN-E163 |
OU |
|
KTN-E164 |
OU |
|
KTN-E170 |
Temporary Structure at Pak Shek
Au |
OU |
KTN-E171 |
OU |
|
KTN-E172 |
OU |
|
KTN-E173 |
OU |
|
KTN-E174 |
OU |
|
KTN-E175 |
OU |
|
KTN-E209 |
Ma Tso Lung San Tsuen |
R |
KTN-E1001 |
Open Storage along Castle Peak
Road - San Tin |
OS |
KTN-E1002 |
Container Trailer Park along Kwu
Tung Road |
OS |
KTN-E1003 |
Europa Garden Phase I |
R |
KTN-E1004 |
Lady Ho Tung Welfare Centre |
IC |
KTN-E1005 |
Valais Phase 1 |
R |
KTN-E1006 |
R |
|
KTN-E1007 |
R |
|
KTN-E1008 |
Village House north to Casas
Domingo |
R |
KTN-E1009 |
St Paul's House of Prayer |
W |
KTN-E1010 |
Kam Tsin Village Ho Tung School |
E |
KTN-E1011 |
Golf Parkview |
R |
KTN-E1012 |
Tsung Pak Long |
R |
KTN-E1013 |
Tsung Pak Long (Hakka Wai) |
R |
KTN-E1014 |
Tai Tau Leng |
R |
KTN-E1015 |
R |
|
KTN-E1016 |
Choi Ngan House |
R |
KTN-E1017 |
Scattered Village Houses at
Northern Boundary of KTN |
R |
KTN-E1018 |
R |
|
KTN-E1019 |
Village Houses at Ma Tso Lung |
R |
KTN-E1020 |
Village Houses at Tit Hang |
R |
KTN-E1021 |
Workshop northwest to Pak Shek
Au |
I |
KTN-E1022 |
Chau Tau Tsuen |
R |
KTN-E1023 |
Village House southeast to Chau
Tau Tsuen |
R |
KTN-E1024 |
Open Storage north to Pai Tau Lo |
OS |
Note:
(1) R– Residential; E –
Educational; H – Hospital/Clinic/ home for the aged; G – Government; IC –
Institution and Community; O – Open space; OS – Open storage; RC – Recreational; OU – Other specific uses
Locations of representative future and committed ASRs located within KTN NDA by year 2025 have been identified based on revised RODP and the construction programme. The planned ASRs are shown in Appendix R and tabulated in Table 6.3.
Table 6.3 Future
and Committed ASRs in KTN NDA (1)
ASR ID |
Lot No |
Landuse (2) |
Remarks |
KTN-1 to KTN-11 |
A1-2 |
PRH |
Residential home for the elderly
(RCHEs); Nursery Classes and Kindergartens; Local Rehousing (3) |
KTN-12 to KTN-18 |
A1-4 |
R1c |
Nursery Classes and
Kindergartens |
KTN-19 to KTN-28 |
A1-5 |
CDA |
Nursery Classes and
Kindergartens; Post Offices |
KTN-82 to KTN-99 |
A2-2 |
PRH |
Nursery Classes and
Kindergartens (2 nos); District Elderly Community Centre(3) |
KTN-220 to KTN-224 |
B2-5 |
E |
Primary School |
KTN-225 to KTN-230 |
B2-6 |
E |
Secondary School |
KTN-231 to KTN-232 |
B2-7 |
E |
Primary School |
KTN-233 to KTN-237 |
B2-8 |
GIC |
Sports Centre , District
Library, Integrated Children and Youth Services Centre and Family Service
Centre; Integrated Community Centre for Mental Wellness, Child Care
Centre and Social Security Field Unit |
KTN-248 to KTN-249 |
B3-16 |
GIC |
Visitor Centre |
KTN-272 to KTN287 |
C1-9 |
GIC |
Long Valley Core Area, Area for
Wetland Enhancement Works and |
|
Area for Facilities Supporting
the Nature Park |
||
KTN-302 to KTN308 |
D1-12 |
GIC |
Potential Activity Centre |
KTN-309 to KTN314 |
D1-13 |
GIC |
Potential Activity Centre |
KTN-321 to KTN-326 |
D1-5 |
VR |
Village Resite |
KTN-354 to KTN-358 |
E1-3 |
GIC |
Reprovisioning of Fan Garden
Junior Police Officers' Police Married Quarters |
KTN-377 to KTN-382 |
E1-6 |
GIC |
Fire Station and Ambulance Depot |
KTN-408 to KTN-411 |
F1-4 |
GIC |
Disused School (Potential for
Eco-tourism Education Centre, Holiday Camping or Other Recreational Uses) |
KTN-C1 |
PFS |
R |
Proposed houses at Zone A/NE
-Temporary Structure/267 |
Note:
(1) Based on revised RODP shown
in Appendix O
(2) R1c –
Residential Zone 1 (with Commercial); R2 – Residential Zone 2; R3 – Residential
Zone 3; E – Educational; CDA –
Comprehensive Development Areas; PRH – Public Rental Housing; GIC – Government,
Institution & Community, VR – Village Resite; OU (C, R &D) – Other
Specified Uses (Commercial, Research & Development); OU (NP) – Other
Specified Uses (Nature Park); OU (R &D) – Other Specified Uses (Research
& Development); O – Open Space
(3) Free
standing non-domestic purpose-built buildings in PRH sites are for retail and
carparking facilities (all carparks assumed to be underground) are assumed
6.4.4 Identification of Pollution Sources
6.4.4.1 Project Emission
According to the construction programme of KTN NDA, the major construction works associated with the development of the KTN NDA are:
· Site formation;
· Construction of road networks, highway structures, and other essential infrastructures; and
· Construction of superstructures.
The construction works are targeted to commence in Year 2017, under six development packages. The locations of the development packages are shown in Appendix S. For each development package, it comprises a number of works contracts from which construction works will be carried out and are considered as Arsenic emission sources.
Most of the dusty construction works, including site formation and infrastructure works, at different development packages will be carried out in Year 2025, so it is taken as the assessment year in the arsenic impact assessment to represent the worst case scenario. Arsenic emission sources are identified and summarized in Table 6.4 below. All developable areas of NDAs have been identified as arsenic sources during construction phase. Locations of emission sources in KTN NDA for Year 2025 are shown in Appendix T.
Table 6.4 Arsenic
emission sources for impact assessment (1)
Commencement Year of Major Construction Works |
Development Packages |
Works Contracts (Arsenic Emission Sources) |
Year 2025 |
Package 2 – Infrastructure and Development at KTN (South) |
WC10, WC11, WC26 |
Package 3 – Infrastructure and Development at KTN (North) |
WC12, WC21 |
Note: (1)
Based on the general layout of Development Packages of revised RODP
shown in Appendix S.
As the construction sequences of each Works Contract have yet been confirmed, it is assumed that works area of each Work Contract are divided into three sub-areas, and construction works at each sub-area will be carried out separately.
6.4.4.2
Concurrent Construction Activities
According to the best
available information at the time of this study, the only concurrent project
activity for cumulative air quality assessment is the site formation from the
construction work of Lok Ma Chau Loop during Year 2025. Hence, this concurrent construction activity is
included in the construction impact assessment.
6.4.5.1 Soil Arsenic Levels for Determination of Arsenic Emission Factor
Total 437 soil samples were collected during the Environmental Site Investigation in KTN in late 2009/early 2010 (48 soil samples from 13 locations), Phase 2 Stage 2 Ground Investigation (Phase 2 Stage 2 GI) in mid 2011 (112 soil samples from 17 locations) and Arsenic Ground Investigation (Arsenic GI) in late 2011/early 2012 (277 soil samples from 18 locations). The location plan of the soil sampling points is given in Appendix U. The number of soil samples, sampling depths and arsenic concentration (i.e. range and average) collected at each sampling locations are summarized in Table 6.5.
Table 6.5 Summary of
soil sampling location and sampling depths
Borehole
No. |
No. of Soil Samples Collected |
Sampling Depth (meter below ground level, mbgl) |
Arsenic Results (mg/kg dry weight) |
|
Range |
Average |
|||
Environmental
Site Investigation (late 2009/early 2010, 48 soil samples from 13 locations) |
||||
KTN-23b1 |
3 |
0 – 1.5 |
42 – 160 |
90.3 |
KTN-23b2 |
3 |
0 – 1.5 |
43 – 120 |
94.3 |
KTN-35a-1 |
3 |
0 – 1.5 |
25 – 110 |
63.7 |
KTN-35a-2 |
3 |
0 – 1.5 |
24 – 110 |
63.7 |
KTN-77,78-1 |
5 |
0 -6.0 |
78 – 210 |
127.6 |
KTN-77,78-2 |
2 |
0 – 0.9 |
170 – 220 |
195.0 |
KTN-77,78-3 |
2 |
0 – 1.0 |
12 – 120 |
66.0 |
KTN-77,78-4 |
5 |
0 – 6.0 |
4.9 – 110 |
61.0 |
KTN-77,78-5 |
3 |
0 – 1.5 |
67 – 160 |
119.0 |
KTN-77,78-6 |
3 |
0 – 1.5 |
100 – 330 |
220.0 |
KTN-77,78-7 |
3 |
0 – 1.5 |
330 – 380 |
350.0 |
KTN-77,78-8 |
3 |
0 – 1.5 |
400 – 430 |
413.3 |
KTN-Offsite |
10 |
0 – 21.0 |
114 – 947 |
296.3 |
Phase 2
Stage 2 GI (mid 2011, 112 soil samples from 17 locations) |
||||
KTN-BH11 |
4 |
0 – 3.0 |
38 – 818 |
250.0 |
KTN-BH12 |
5 |
0 – 17.0 |
8 – 42 |
22.4 |
KTN-BH13 |
15 |
0 -50.15 |
2 – 128 |
39.0 |
KTN-BH14 |
7 |
0 – 15.2 |
7 – 33 |
18.3 |
KTN-BH15 |
5 |
0 - 7.2 |
74 – 676 |
310.8 |
KTN-BH16 |
4 |
0 – 4.15 |
3 – 15 |
9.0 |
KTN-BH17 |
6 |
0 – 11.15 |
6 – 56 |
25.8 |
KTN-BH18 |
3 |
0 – 1.5 |
33 – 66 |
45.0 |
KTN-BH19 |
7 |
0 – 14.3 |
2 – 34 |
11.7 |
KTN-BH20 |
7 |
0 – 18.05 |
22 – 95 |
49.6 |
KTN-BH21 |
7 |
0 – 11.05 |
3 – 81 |
44.0 |
KTN-BH22 |
8 |
0 – 19.25 |
9 – 331 |
104.9 |
KTN-BH23 |
8 |
0 – 18.2 |
11 – 71 |
33.0 |
KTN-BH24 |
8 |
0 – 16.75 |
1 – 17 |
7.8 |
KTN-BH25 |
6 |
0 – 13.15 |
2 – 40 |
27.2 |
KTN-BH26 |
5 |
0 – 6.7 |
1 – 106 |
66.8 |
KTN-BH28 |
7 |
0 – 16.25 |
23 – 85 |
49.0 |
Arsenic GI
(late 2011/early 2012, 277 soil samples from 18 locations) |
||||
KTN-ASBH01a |
17 |
0 – 38.0 |
21 – 805 |
249.5 |
KTN-ASBH04 |
11 |
0 -20.5 |
7 – 239 |
91.6 |
KTN-ASBH06 |
21 |
0 – 45.5 |
2 – 128 |
37.3 |
KTN-ASBH07 |
19 |
0 - 40.5 |
1 – 650 |
141.4 |
KTN-ASBH08 |
19 |
0 – 40.5 |
8 – 1,020 |
215.7 |
KTN-ASBH09 |
14 |
0 – 28.0 |
16 – 442 |
160.0 |
KTN-ASBH12 |
17 |
0 – 35.5 |
9 – 432 |
145.7 |
KTN-ASBH13 |
24 |
0 – 53.5 |
4 – 1,220 |
178.3 |
KTN-ASBH14a |
9 |
0 – 18.0 |
5 – 191 |
49.3 |
KTN-ASBH14b |
21 |
0 -45.0 |
28 – 417 |
149.6 |
KTN-ASBH15 |
12 |
0 – 25.5 |
7 – 945 |
137.5 |
KTN-ASBH20 |
16 |
0 – 35.5 |
6 – 710 |
136.8 |
KTN-ASBH21 |
15 |
0 – 33.0 |
2 – 198 |
82.2 |
KTN-ASBH29 |
6 |
0 – 8.0 |
72 – 214 |
130.7 |
KTN-ASBH32 |
11 |
0 – 23.0 |
2 – 85 |
31.6 |
KTN-ASBH38 |
9 |
0 – 15.5 |
1 – 39 |
14.9 |
KTN-ASBH Offsite (1) |
15 |
0 – 30.5 |
45 – 708 |
243.8 |
KTN-ASBH Offsite(a) |
21 |
0 -30.5 |
64 - 457 |
209.2 |
Note: (1) A soil
arsenic concentration of 23,400 mg/kg was detected at borehole KTN-ASBH
Offsite. However, this data is considered as “Outliner” and has not been
included in this risk assessment as the second highest soil arsenic
concentration is only 1,220 mg/kg and the 99 percentile of soil arsenic concentration
is 816 mg/kg.
Before drilling/excavation, the sampler and all equipment in contact with the ground were thoroughly decontaminated prior to use at each boreholes / IP by phosphate-free detergent between each sampling event to minimize potential cross contamination. All drilling machines were decontaminated by phosphate free detergent and high pressure hot water jet before mobilization to site. During sampling and decontamination activities, disposable latex gloves were worn to prevent the transfer of contaminants from other source.
The collected soil samples were properly labelled and stored in cool boxes at around 4oC until delivered to the analytical laboratory. All the collected soil and groundwater samples were analyzed by the laboratories accredited under Hong Kong Laboratory Accreditation Scheme (HOKLAS). USEPA Method 6020 (i.e. Inductively Coupled Plasma Mass Spectrometry method (ICP-MS)) was adopted for soil arsenic testing.
Different percentile so the soil arsenic results are used for determination of the Arsenic Emission Factor, as detailed in Section 6.4.5.2.
6.4.5.2 Emission Inventory
Arsenic impact assessment was carried out based on typical
values and emission factors from United States Environmental Protection Agency
(USEPA) Compilation of Air Pollution
Emission Factors (AP-42), 5th Edition. Detailed calculation of arsenic emission factors is given in Appendix V.
As the risk of
inhalation is directly related to the amount of inhalable arsenic particulate
in the atmosphere, arsenic rich particulate with aerodynamic diameter of less
than 10 mm is the primary concern in this risk
analysis. In order to quantify
the fine fraction of arsenic within the construction dust emission, RSP
emission factor was first derived by applying the RSP/TSP relationship on AP-42’s TSP emission factor, and the
portion of fine mode arsenic emission was subsequently estimated by an
arsenic/RSP ratio. The calculation is presented as follow:
As the site specific source’s
arsenic/RSP ratio is not available in any literature, soil arsenic content was
adopted as conservative estimate of source’s arsenic/RSP ratio. Hence, the
calculation will become:
RSP emission factor are derived with reference to the emission factor of TSP from AP-42 and the typical RSP/TSP ratio (i.e. 30%) from USEPA “Estimating Particulate Matter Emission from Construction Operations – Final Report, 1999” (USEPA Final Report, 1999) (Appendix W). By applying different percentiles of arsenic content of all collected soil samples (i.e. total 437 soil samples) on the estimated RSP emission factor, emission factors of arsenic for different dust generating activities are estimated and summarized in Table 6.6.
Table 6.6 References
of Arsenic emission factors for different activities.
Activities |
Arsenic Content (mg/kg) |
Operating Sites |
Arsenic Emission Factor (for Annual Emission) (g/sq.m/s) |
Heavy Construction Activities[1] |
1,220
(Maximum) |
All construction and excavation sites |
5.26×10-9
|
461
(95 percentile) |
1.99×10-9 |
||
125
(Average) |
5.39×10-10 |
||
71
(Median) |
3.06×10-10 |
||
Wind Erosion |
1,220
(Maximum) |
All construction sites, any stockpile areas,
barging area (all open sites) |
5.92×10-11 |
461
(95 percentile) |
2.24×10-11 |
||
125
(Average) |
6.06×10-12 |
||
71
(Median) |
3.44×10-12 |
Note: (1) According to AP-42, heavy construction activities can be associated with land
clearing, drilling and blasting, ground excavation, cut and fill operations
(i.e. earth moving), and construction of a particular facility.
In view of the latest construction programme of KTN development, the construction activities with major concerns of dust generation mainly involve the cutting/filling/earth removal activities. In a separate study of USEPA “Gap Filling PM10 Emission Factors for Selected Open Area Dust Source, EPA-450/4-88-003,1988” (USEPA Study Report) (Appendix X), average RSP/TSP ratio for the activities of “Cut & Fill, “Earth Removal”, and “Top Soil Removal” are ranged from 0.22 to 0.27. Hence, the proposed RSP/TSP ratio of 0.3 is considered to be a conservative estimate for dust emission during construction stage of KTN development.
6.4.5.3 Operating Areas and Hours
For the calculation of annual arsenic concentration, an active operating area over a whole year period would be less than for a typical hour and typical day, and 6% active operating area would be a practicable assumption. Justification of 6% active operating area is given in Appendix Y.
Subject to the construction work at night-time and during weekend or holiday, construction working periods of 26 days a month and 12 hours a day are assumed.
6.4.5.4 Arsenic Dispersion Modelling
Arsenic assessment was undertaken using the Fugitive Dust Model (FDM) approved by USEPA and EPD. It is a well-known Gaussian Plume model designed for computing air dispersion model for dust sources. Modelling parameters include the Emission Factors, Particles Size Distributions, Surface Roughness, etc will be determined based on EPD’s “Guideline on Choice of Models and Model Parameters” and USEPA’s AP-42. According to Section 13.2.4.3 of AP-42, construction dust particles may be grouped into five particle size classes, including:
· 0 – 2.5μm;
· 2.5 – 5μm;
· 5 – 10μm;
· 10 – 15μm; and
· 15 – 30μm.
Due to the lack of specific information regarding the detailed particle size distribution below 10μm (i.e. no distinguish of particle sizes during field measurement of RSP in KTN), it is assumed that all particles are within the size range of “0 – 2.5μm” (i.e. 100 %) as worse case assumption. Particle density of 2.5g/m3 will be adopted and Surface Roughness of 100 cm is assumed in the model in order to represent the roughness effect the terrain.
During daytime working hours (7am to 7pm), it is assumed that arsenic emissions would be generated from all dust generating activities and site erosion. During night-time non-working hours (7pm to 7am of the next day), weekend and statutory holidays, arsenic emission source would only be site erosion as construction activities during these hours are ceased.
The annual average arsenic levels in KTN based on different soil arsenic concentration were calculated based on real meteorological data including wind direction, wind speed, temperature and stability collected from Tak Kwu Ling meteorological station in Year 2011. The Ta Kwu Ling meteorological station is considered to be the nearest meteorological station to the construction sites in KTN NDA and the corresponding anemometer height at Ta Kwu Ling is 13m above ground.
The assessment was conducted at 1.5m above local ground level. Since all the dust generating sources are at ground level, this assessment height would represent the worst-case scenario.
A summary of modelling parameters adopted in the assessment are given in the Table 6.7.
Table 6.7 Modelling
parameters
Parameters |
Input |
Remark |
Particle Size Distribution |
1.25um = 100% |
Assume all the particles are within the size
range of 0 – 2.5μm as worse case assumption for dispersion modelling
only. |
Background Concentration |
Annual arsenic level = 4.7 ng/m3 |
The detailed estimation of annual arsenic
level in KTN is given Section 6.2. |
Modelling Mode |
Flatted terrain |
- |
Meteorological Data |
Data recorded in 2011 at Ta Kwu Ling (TKL)
Meteorological Station |
|
Anemometer Height |
13m for TKL |
- |
Surface Roughness |
100cm |
- |
Emission Period |
General construction activities during
daytime working hours (7 am to 7 pm) |
|
ASR Calculating Level |
1.5m |
- |
6.4.6 Prediction and Evaluation of Impacts
For Arsenic impacts, both Mitigated Scenario and Unmitigated Scenario for the assessment are presented. Since dust suppression measure such as watering would be adopted as good site practise during the construction stage, the Mitigated Scenario would reflect the realistic site situation while Unmitigated Scenario represent a worse-case overestimation for the purpose of assessment only. Hence, both scenarios should be presented in place for a clear presentation on the overall risk level. Results of ambient arsenic levels under mitigated and unmitigated scenarios are discussed in Section 6.4.8.
During construction stage, dust suppression by regular watering under a good site practice will be adopted. In accordance with the “Control of Open Fugitive Dust Sources” (USEPA AP-42) as given in Appendix Z, 92.1% of TSP removal efficiency could be achieved by watering the exposed work site at the frequency once per hour. In another word, there should be only 7.9% of TSP emission left in each open work site with regular watering. The assumptions and details of the calculation of this TSP removal efficiency (from watering) is given in Appendix AA.
Provided that 30% of TSP is assumed to be RSP (refer to Section 6.4.5.2), and under a worst case assumption that all the TSP emission left (7.9%) are within the size range of 0 – 10μm (i.e. RSP) and all the soil arsenic are evenly distributed over this size range, the percentage of arsenic-containing RSP suppressed by regular watering should be 73.6%. The rationale of the suppression of arsenic-containing RSP is illustrated in the following diagram, and the calculation of the percentage of arsenic-containing RSP suppressed by regular watering is summarized in the following equation:
|
|
|
|
|
|
|||||
|
Assume
all 7.9% TSP emission left are within 0 - 10 μm (i.e. RSP) and all the
soil arsenic are evenly distributed over this size range |
|||||||||
RSP |
7.9% Left |
|||||||||
(30% |
|
|||||||||
of TSP) |
Water |
|
||||||||
|
TSP |
Spraying |
|
|||||||
|
(100% |
|
92.1% |
|
|
|
|
|
||
|
Emission) |
Emission |
|
|
|
|
|
|||
|
|
Removal |
|
|
|
|
|
|||
|
|
|
|
|
|
|
||||
|
|
|
|
|
|
|
||||
|
|
|
|
|
|
|
||||
|
|
|
|
|
% of arsenic-containing RSP suppressed by regular
watering |
= |
100 % - |
Remaining TSP(%) in
the emission after water suppression |
||
% of RSP in TSP |
|||||
= |
100 % - |
7.9% |
|
||
30% |
|
||||
= |
73.6% |
|
|||
|
The annual ambient arsenic concentrations were assessed base on different percentiles of soil arsenic levels, including Maximum, 95 Percentile, Mean, and Median values. The cumulative annual arsenic levels at identified ASRs in the vicinity of KTN NDA under Unmitigated and Mitigated scenario are summarized in Table 6.8 and Table 6.9 respectively. The contour of annual arsenic concentration at 1.5m above ground under Unmitigated and Mitigated scenario are given in Appendix BB.
Table 6.8 Predicted
UNMITIGATED cumulative annual arsenic concentrations at 1.5m above ground in
the vicinity of KTN NDA (including background concentration of 4.7ng/m3)
ASR ID |
Site No. |
Remarks |
Annual
Average Arsenic for Year 2025 under Unmitigated Scenario (ng/m3) (1) |
|||
Maximum Arsenic Content |
95th percentile Arsenic Content |
Mean Arsenic Content |
Median Arsenic Content |
|||
Existing ASRs |
||||||
KTN-E24 |
- |
Temporary Structure near Sheung
Yue River |
17.7 |
9.7 |
5.7 |
5.7 |
KTN-E85 |
- |
Yin Kong Tsuen |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-E86 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E87 |
- |
5.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E88 |
- |
Sports Ground near Enchi Lodge |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E89 |
- |
Temporary Structure near Castle
Peak Road |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E90 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E91 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E94 |
- |
Ho Sheung Heung Temple |
9.7 |
6.7 |
5.7 |
4.7 |
KTN-E97 |
- |
Ho Sheung Heung Village |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E99 |
- |
7.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E100 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E101 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E102 |
- |
Temporary Structure Northern to
Ho Sheung Heung Village |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E104 |
- |
Village Houses near Tsung Yuen |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-E106 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E108 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E109 |
- |
Temporary Structure at Tsung
Yuen |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E110 |
- |
Temporary Structure near Lo Wu
Correctional Institution |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E111 |
- |
Lo Wu Correctional Institution
Basketball Court |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E112 |
- |
Lo Wu Correctional Institution |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E123 |
- |
Lo Wu Firing Range (Eastern) |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E128 |
- |
Lo Wu Firing Range (Western) |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E154 |
- |
Ho Sheung Heung Village |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E155 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E156 |
- |
5.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E162 |
- |
Temporary Structure near Fanling
Highway (near Pak Shek Au) |
14.7 |
8.7 |
5.7 |
5.7 |
KTN-E163 |
- |
12.7 |
7.7 |
5.7 |
4.7 |
|
KTN-E164 |
- |
10.7 |
6.7 |
5.7 |
4.7 |
|
KTN-E170 |
- |
Temporary Structure at Pak Shek
Au |
11.7 |
7.7 |
5.7 |
4.7 |
KTN-E171 |
- |
10.7 |
6.7 |
5.7 |
4.7 |
|
KTN-E172 |
- |
9.7 |
6.7 |
4.7 |
4.7 |
|
KTN-E173 |
- |
13.7 |
7.7 |
5.7 |
5.7 |
|
KTN-E174 |
- |
13.7 |
7.7 |
5.7 |
5.7 |
|
KTN-E175 |
- |
15.7 |
8.7 |
5.7 |
5.7 |
|
KTN-E209 |
- |
Ma Tso Lung San Tsuen |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-E1001 |
- |
Open Storage along Castle Peak
Road - San Tin |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1002 |
- |
Container Trailer Park along Kwu
Tung Road |
8.7 |
6.7 |
4.7 |
4.7 |
KTN-E1003 |
- |
Europa Garden Phase I |
8.7 |
5.7 |
4.7 |
4.7 |
KTN-E1004 |
- |
Lady Ho Tung Welfare Centre |
8.7 |
5.7 |
4.7 |
4.7 |
KTN-E1005 |
- |
Valais Phase 1 |
10.7 |
6.7 |
5.7 |
4.7 |
KTN-E1006 |
- |
12.7 |
7.7 |
5.7 |
4.7 |
|
KTN-E1007 |
- |
10.7 |
6.7 |
5.7 |
4.7 |
|
KTN-E1008 |
- |
Village House north to Casas
Domingo |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E1009 |
- |
St Paul's House of Prayer |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E1010 |
- |
Kam Tsin Village Ho Tung School |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1011 |
- |
Golf Parkview |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1012 |
- |
Tsung Pak Long |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1013 |
- |
Tsung Pak Long (Hakka Wai) |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1014 |
- |
Tai Tau Leng |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1015 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E1016 |
- |
Choi Ngan House |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1017 |
- |
Scattered Village Houses at
Northern Boundary of KTN |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-E1018 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E1019 |
- |
Village Houses at Ma Tso Lung |
10.7 |
6.7 |
5.7 |
4.7 |
KTN-E1020 |
- |
Village Houses at Tit Hang |
9.7 |
6.7 |
5.7 |
4.7 |
KTN-E1021 |
- |
Workshop northwest to Pak Shek
Au |
11.7 |
7.7 |
5.7 |
4.7 |
KTN-E1022 |
- |
Chau Tau Tsuen |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1023 |
- |
Village House southeast to Chau
Tau Tsuen |
9.7 |
6.7 |
4.7 |
4.7 |
KTN-E1024 |
- |
Open Storage north to Pai Tau Lo |
4.7 |
4.7 |
4.7 |
4.7 |
Planned ASRs |
||||||
KTN-1 |
A1-2 |
Residential home for the
elderly; Nursery Classes and Kindergartens |
9.7 |
6.7 |
4.7 |
4.7 |
KTN-2 |
9.7 |
6.7 |
4.7 |
4.7 |
||
KTN-3 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-4 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-5 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-6 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-7 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-8 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-9 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-10 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-11 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-12 |
A1-4 |
Nursery Classes and
Kindergartens |
12.7 |
7.7 |
5.7 |
4.7 |
KTN-13 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-14 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-15 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-16 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-17 |
13.7 |
7.7 |
5.7 |
5.7 |
||
KTN-18 |
13.7 |
7.7 |
5.7 |
5.7 |
||
KTN-19 |
A1-5 |
Nursery Classes and
Kindergartens; Post Offices |
16.7 |
8.7 |
5.7 |
5.7 |
KTN-20 |
14.7 |
8.7 |
5.7 |
5.7 |
||
KTN-21 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-22 |
13.7 |
7.7 |
5.7 |
5.7 |
||
KTN-23 |
16.7 |
9.7 |
5.7 |
5.7 |
||
KTN-24 |
17.7 |
9.7 |
5.7 |
5.7 |
||
KTN-25 |
19.7 |
10.7 |
6.7 |
5.7 |
||
KTN-26 |
20.7 |
10.7 |
6.7 |
5.7 |
||
KTN-27 |
19.7 |
10.7 |
6.7 |
5.7 |
||
KTN-28 |
17.7 |
9.7 |
5.7 |
5.7 |
||
KTN-82 |
A2-2 |
Nursery Classes and
Kindergartens (2 nos); District Elderly Community Centre |
11.7 |
7.7 |
5.7 |
4.7 |
KTN-83 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-84 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-85 |
13.7 |
8.7 |
5.7 |
5.7 |
||
KTN-86 |
16.7 |
9.7 |
5.7 |
5.7 |
||
KTN-87 |
17.7 |
9.7 |
5.7 |
5.7 |
||
KTN-88 |
20.7 |
10.7 |
6.7 |
5.7 |
||
KTN-89 |
22.7 |
11.7 |
6.7 |
5.7 |
||
KTN-90 |
26.7 |
12.7 |
6.7 |
5.7 |
||
KTN-91 |
21.7 |
10.7 |
6.7 |
5.7 |
||
KTN-92 |
15.7 |
8.7 |
5.7 |
5.7 |
||
KTN-93 |
15.7 |
8.7 |
5.7 |
5.7 |
||
KTN-94 |
14.7 |
8.7 |
5.7 |
5.7 |
||
KTN-95 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-96 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-97 |
24.7 |
12.7 |
6.7 |
5.7 |
||
KTN-98 |
25.7 |
12.7 |
6.7 |
5.7 |
||
KTN-99 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-220 |
B2-5 |
Primary School |
9.7 |
6.7 |
5.7 |
4.7 |
KTN-221 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-222 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-223 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-224 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-225 |
B2-6 |
Secondary School |
10.7 |
6.7 |
5.7 |
4.7 |
KTN-226 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-227 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-228 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-229 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-230 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-231 |
B2-7 |
Primary School |
12.7 |
7.7 |
5.7 |
4.7 |
KTN-232 |
12.7 |
7.7 |
5.7 |
4.7 |
||
KTN-233 |
B2-8 |
Sports Centre (Site Area:
0.6ha), District Library, Integrated Children and Youth Services |
14.7 |
8.7 |
5.7 |
5.7 |
KTN-234 |
15.7 |
8.7 |
5.7 |
5.7 |
||
KTN-235 |
13.7 |
7.7 |
5.7 |
5.7 |
||
KTN-236 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-237 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-248 |
B3-16 |
Visitor Centre |
14.7 |
8.7 |
5.7 |
5.7 |
KTN-249 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-272 |
C1-9 |
Long Valley Core Area, Area for
Wetland Enhancement Works and |
13.7 |
7.7 |
5.7 |
5.7 |
KTN-273 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-274 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-275 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-276 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-277 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-278 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-279 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-280 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-281 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-282 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-283 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-284 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-285 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-286 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-287 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-302 |
D1-12 |
Potential Activity Centre |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-303 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-304 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-305 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-306 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-307 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-308 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-309 |
D1-13 |
Potential Activity Centre |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-310 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-311 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-312 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-313 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-314 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-321 |
D1-5 |
Village Resite |
8.7 |
6.7 |
4.7 |
4.7 |
KTN-322 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-323 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-324 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-325 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-326 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-354 |
E1-3 |
District Headquarters, District
Headquarters Associated Married Staff Quarters, Divisional Police Station and
Reprovisioning of Fan Garden Junior Police Officers’ Police Married Quarters |
23.7 |
11.7 |
6.7 |
5.7 |
KTN-355 |
28.7 |
13.7 |
6.7 |
5.7 |
||
KTN-356 |
23.7 |
11.7 |
6.7 |
5.7 |
||
KTN-357 |
20.7 |
10.7 |
6.7 |
5.7 |
||
KTN-358 |
21.7 |
11.7 |
6.7 |
5.7 |
||
KTN-377 |
E1-6 |
Fire Station and Ambulance Depot
|
11.7 |
7.7 |
5.7 |
4.7 |
KTN-378 |
13.7 |
7.7 |
5.7 |
4.7 |
||
KTN-379 |
14.7 |
8.7 |
5.7 |
5.7 |
||
KTN-380 |
18.7 |
9.7 |
5.7 |
5.7 |
||
KTN-381 |
17.7 |
9.7 |
5.7 |
5.7 |
||
KTN-382 |
14.7 |
8.7 |
5.7 |
5.7 |
||
KTN-408 |
F1-4 |
Disused School (Potential for
Eco-tourism Education Centre, Holiday Camping or Other Recreational Uses); |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-409 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-410 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-411 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-C1 |
PFS |
Proposed houses at Zone A/NE
-TS/267 |
9.7 |
6.7 |
5.7 |
4.7 |
Note: (1) The highest annual average arsenic levels
under each soil arsenic percentile are bold and highlighted by RED
Table 6.9 Predicted
MITIGATED cumulative annual arsenic concentrations at 1.5m above ground in the
vicinity of KTN NDA (including background concentration of 4.7ng/m3)
ASR ID |
Site No. |
Remarks |
Annual
Average Arsenic for Year 2025 under Unmitigated Scenario (ng/m3) (1) |
|||
Maximum Arsenic Content |
95th percentile Arsenic Content |
Mean Arsenic Content |
Median Arsenic Content |
|||
Existing ASRs |
||||||
KTN-E24 |
- |
Temporary Structure near Sheung
Yue River |
8.7 |
5.7 |
4.7 |
4.7 |
KTN-E85 |
- |
Yin Kong Tsuen |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E86 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E87 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E88 |
- |
Sports Ground near Enchi Lodge |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E89 |
- |
Temporary Structure near Castle
Peak Road |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E90 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E91 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E94 |
- |
Ho Sheung Heung Temple |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E97 |
- |
Ho Sheung Heung Village |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E99 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E100 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E101 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E102 |
- |
Temporary Structure Northern to
Ho Sheung Heung Village |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E104 |
- |
Village Houses near Tsung Yuen |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E106 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E108 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E109 |
- |
Temporary Structure at Tsung
Yuen |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E110 |
- |
Temporary Structure near Lo Wu
Correctional Institution |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E111 |
- |
Lo Wu Correctional Institution
Basketball Court |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E112 |
- |
Lo Wu Correctional Institution |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E123 |
- |
Lo Wu Firing Range (Eastern) |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E128 |
- |
Lo Wu Firing Range (Western) |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E154 |
- |
Ho Sheung Heung Village |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E155 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E156 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E162 |
- |
Temporary Structure near Fanling
Highway (near Pak Shek Au) |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-E163 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E164 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E170 |
- |
Temporary Structure at Pak Shek
Au |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E171 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E172 |
- |
5.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E173 |
- |
7.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E174 |
- |
7.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E175 |
- |
7.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E209 |
- |
Ma Tso Lung San Tsuen |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1001 |
- |
Open Storage along Castle Peak
Road - San Tin |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1002 |
- |
Container Trailer Park along Kwu
Tung Road |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1003 |
- |
Europa Garden Phase I |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1004 |
- |
Lady Ho Tung Welfare Centre |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1005 |
- |
Valais Phase 1 |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1006 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E1007 |
- |
6.7 |
5.7 |
4.7 |
4.7 |
|
KTN-E1008 |
- |
Village House north to Casas
Domingo |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1009 |
- |
St Paul's House of Prayer |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1010 |
- |
Kam Tsin Village Ho Tung School |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1011 |
- |
Golf Parkview |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1012 |
- |
Tsung Pak Long |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1013 |
- |
Tsung Pak Long (Hakka Wai) |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1014 |
- |
Tai Tau Leng |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1015 |
- |
4.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E1016 |
- |
Choi Ngan House |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1017 |
- |
Scattered Village Houses at
Northern Boundary of KTN |
4.7 |
4.7 |
4.7 |
4.7 |
KTN-E1018 |
- |
5.7 |
4.7 |
4.7 |
4.7 |
|
KTN-E1019 |
- |
Village Houses at Ma Tso Lung |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1020 |
- |
Village Houses at Tit Hang |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1021 |
- |
Workshop northwest to Pak Shek
Au |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-E1022 |
- |
Chau Tau Tsuen |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-E1023 |
- |
Village House southeast to Chau
Tau Tsuen |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-E1024 |
- |
Open Storage north to Pai Tau Lo |
4.7 |
4.7 |
4.7 |
4.7 |
Planned
ASRs |
||||||
KTN-1 |
A1-2 |
Residential home for the
elderly; Nursery Classes and Kindergartens |
5.7 |
5.7 |
4.7 |
4.7 |
KTN-2 |
5.7 |
5.7 |
4.7 |
4.7 |
||
KTN-3 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-4 |
5.7 |
5.7 |
4.7 |
4.7 |
||
KTN-5 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-6 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-7 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-8 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-9 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-10 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-11 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-12 |
A1-4 |
Nursery Classes and
Kindergartens |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-13 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-14 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-15 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-16 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-17 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-18 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-19 |
A1-5 |
Nursery Classes and
Kindergartens; Post Offices |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-20 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-21 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-22 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-23 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-24 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-25 |
8.7 |
6.7 |
4.7 |
4.7 |
||
KTN-26 |
9.7 |
6.7 |
4.7 |
4.7 |
||
KTN-27 |
8.7 |
6.7 |
4.7 |
4.7 |
||
KTN-28 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-82 |
A2-2 |
Nursery Classes and
Kindergartens (2 nos); District Elderly Community Centre |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-83 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-84 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-85 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-86 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-87 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-88 |
9.7 |
6.7 |
4.7 |
4.7 |
||
KTN-89 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-90 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-91 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-92 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-93 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-94 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-95 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-96 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-97 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-98 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-99 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-220 |
B2-5 |
Primary School |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-221 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-222 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-223 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-224 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-225 |
B2-6 |
Secondary School |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-226 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-227 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-228 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-229 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-230 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-231 |
B2-7 |
Primary School |
6.7 |
5.7 |
4.7 |
4.7 |
KTN-232 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-233 |
B2-8 |
Sports Centre (Site Area:
0.6ha), District Library, Integrated Children and Youth Services |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-234 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-235 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-236 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-237 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-248 |
B3-16 |
Visitor Centre |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-249 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-272 |
C1-9 |
Long Valley Core Area, Area for
Wetland Enhancement Works and |
7.7 |
5.7 |
4.7 |
4.7 |
KTN-273 |
6.7 |
5.7 |
4.7 |
4.7 |
||
KTN-274 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-275 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-276 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-277 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-278 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-279 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-280 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-281 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-282 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-283 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-284 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-285 |
4.7 |
4.7 |
4.7 |
4.7 |
||
KTN-286 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-287 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-302 |
D1-12 |
Potential Activity Centre |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-303 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-304 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-305 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-306 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-307 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-308 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-309 |
D1-13 |
Potential Activity Centre |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-310 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-311 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-312 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-313 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-314 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-321 |
D1-5 |
Village Resite |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-322 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-323 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-324 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-325 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-326 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-354 |
E1-3 |
District Headquarters, District
Headquarters Associated Married Staff Quarters, Divisional Police Station and
Reprovisioning of Fan Garden Junior Police Officers’ Police Married Quarters |
10.7 |
6.7 |
5.7 |
4.7 |
KTN-355 |
11.7 |
7.7 |
5.7 |
4.7 |
||
KTN-356 |
10.7 |
6.7 |
5.7 |
4.7 |
||
KTN-357 |
9.7 |
6.7 |
4.7 |
4.7 |
||
KTN-358 |
9.7 |
6.7 |
5.7 |
4.7 |
||
KTN-377 |
E1-6 |
Fire Station and Ambulance Depot
|
6.7 |
5.7 |
4.7 |
4.7 |
KTN-378 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-379 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-380 |
8.7 |
6.7 |
4.7 |
4.7 |
||
KTN-381 |
8.7 |
5.7 |
4.7 |
4.7 |
||
KTN-382 |
7.7 |
5.7 |
4.7 |
4.7 |
||
KTN-408 |
F1-4 |
Disused School (Potential for
Eco-tourism Education Centre, Holiday Camping or Other Recreational Uses); |
5.7 |
4.7 |
4.7 |
4.7 |
KTN-409 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-410 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-411 |
5.7 |
4.7 |
4.7 |
4.7 |
||
KTN-C1 |
PFS |
Proposed houses at Zone A/NE
-TS/267 |
6.7 |
5.7 |
4.7 |
4.7 |
Note: (1)
The highest annual average arsenic levels under each soil arsenic
percentile are bold and highlighted by BLUE
The
highest arsenic levels among all identified ASRs in the vicinity of KTN NDA under Unmitigated
Scenario and Mitigated Scenario are summarized in Table 6.10.
Table 6.10 Highest ambient arsenic levels during construction under Unmitigated and Mitigated Scenario
Percentile (1) |
As in Soil
(mg/kg) |
Arsenic in
Air during 10-year Construction (ng/m3) |
|
Unmitigated
Scenario |
Mitigated Scenario |
||
Maximum |
1,220 |
28.7 |
11.7 |
95 percentile |
461 |
13.7 |
7.7 |
Average |
125 |
6.7 |
5.7 |
Median |
71 |
5.7 |
4.7 |
Note:
(1) Total 437 soil arsenic
results. An “Outliner” arsenic result (23,400 mg/kg) is not included in the
risk assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
The highest arsenic levels summarized in Table 6.10 will be adopted for the risk assessment of inhalation as detailed in Section 6.5.
6.5 Estimation of Arsenic Intake by Inhalation
6.5.1 Inhalation Risk Assessment
The
maximum annual arsenic level for year 2025 has been assessed (refer to Section 6.4
for details). The highest arsenic levels among all identified ASRs in the
vicinity of KTN NDA under Unmitigated Scenario (i.e. no
mitigation measures in place) and Mitigated Scenario (i.e. water
spraying for dust suppression, refer to Section 6.4.7 for details)
) are summarized in Table
6.11. The risk assessment is detailed in the below sections.
Table 6.11 Highest
ambient arsenic levels during construction under Unmitigated and Mitigated
Scenario
Percentile (1) |
As in Soil
(mg/kg) |
Arsenic in
Air during 10-year Construction (ng/m3) |
|
Unmitigated
Scenario |
Mitigated
Scenario |
||
Maximum |
1,220 |
28.7 |
11.7 |
95 percentile |
461 |
13.7 |
7.7 |
Average |
125 |
6.7 |
5.7 |
Median |
71 |
5.7 |
4.7 |
Note:
(1) Total 437 soil arsenic
results. An “Outliner” arsenic result (23,400 mg/kg) is not included in the
risk assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
6.5.1.1 Cancer Risk
Unmitigated Scenario
Adopting
the carcinogenic risk level according to the risk estimate by the WHO Air Quality Guideline for Europe 2nd
Edition, an average annual level of arsenic at 6.6 ng/m3 for
continuous exposure for 70 years corresponds to an increased risk of 1 x 10-5
(Refer to Section
6.3 for details). At background ambient arsenic concentration of 4.7
ng/m3, the increased cancer risk is 7.12 x 10-6. Assuming
the worst-case scenario of exposure to an annual arsenic concentration of 28.7
ng/m3 for 10 years construction period, the cancer risk would be 1.23
x 10-5, which exceed the lifetime risk level of 1 x 10-5
by 23% (i.e. refer to Section 6.2).
The equation for calculating the cancer risk level is given below:
Cancer Risk Level = [(AsC x 10 years) + (AsB x 60 years)]
x (1 x 10-5)
6.6 x 70 years
Where:
AsC = Annual arsenic exposure concentration during construction
period (in ng/m3)
10 years = Construction
period
AsB = Background ambient arsenic concentration after construction
period (i.e. 4.7 ng/m3, refer to Section 6.3 for details)
60 years = 60
years after 10 year construction period
6.6 = Average annual arsenic level (in ng/m3) for
continuous exposure for 70 years corresponds to lifetime time risk level of 1 x
10-5
70 years = Continuous
exposure period adopted by WHO
1 x 10-5 = WHO’s lifetime risk level for exposure to ambient
arsenic
However,
the above “Worst-case Scenario” based on the Maximal soil arsenic concentration of 1,220 mg/kg last for
10 years construction period is unlikely to occur as there is only 3 soil
samples (i.e. total 437 soil samples) were detected with arsenic concentration
above 1,000mg/kg. In addition, all these 3 soil samples were collected at the
depth below 10m from ground surface; therefore continuously disturbance of this
high-arsenic soil (i.e. over 1,000mg/kg) for 10 years is unlikely.
On the
other hand, using the 95th
Percentile soil arsenic concentration of 461 mg/kg, the airborne
arsenic concentration in PM10 (RSP) would be 13.7 ng/m3,
and the associated cancer risk for 10 years construction period would be 9.07 x
10-6. If the Mean
and Median soil arsenic
concentrations of 125 mg/kg and 71 mg/kg (i.e. more realistic scenario) are
adopted, the airborne arsenic concentrations in PM10 would be 6.7
ng/m3 and 5.7 ng/m3 respectively, and the associated
cancer risk for 10 years construction period would be 7.55 x 10-6
and 7.34 x 10-6 respectively. These levels of risk are lower than
that attributed to ingestion of arsenic from soil, and also below the adopted
lifetime time risk level (1 x 10-5).
The estimated risk levels under unmitigated
scenario are summarized in Table 6.12.
Table 6.12 Estimated risk
levels under Unmitigated Scenario
|
Arsenic Concentration |
Overall Risk
Level (2) (3) |
||
|
Percentile (1) |
As in Soil
(mg/kg) |
As in Air during 10-year Construction (ng/m3) |
|
KTN Development |
Maximum |
1,220 |
28.7 |
1.23 x 10-5 |
95 percentile |
461 |
13.7 |
9.07 x 10-6 |
|
Average |
125 |
6.7 |
7.55 x 10-6 |
|
Median |
71 |
5.7 |
7.34 x 10-6 |
|
WHO Information |
Average annual level at 6.6 ng/m3 |
1 x 10-5 |
Note:
(1) Total 437 soil arsenic
results. An “Outliner” arsenic result (23,400 mg/kg) is not included in the
risk assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
(2) The Overall Risk Levels are estimated for 70 years
lifetime exposure. In this assessment, 10 years exposure of the estimated
ambient arsenic level during construction, plus 60 years exposure of KTN
background arsenic level (i.e. 4.7 ng/m3, refer to Section 6.3
for details) is applied.
(3) As part of the high arsenic soils will be treated
during the construction stage, and the soil-exposed area in KTN will be reduced
after completion of KTN, the wind-blown arsenic-containing dust in KTN after
development should be further reduced. Therefore, the application of KTN
background arsenic level 4.7 ng/m3 for 60 years exposure in this
risk assessment is considered appropriate.
It should
be noted that the estimations presented in the aforementioned paragraphs are
under “Unmitigated Scenario” which is not likely to happen as the
implementation of mitigation measures (i.e. water spraying for dust
suppression) has been confirmed as one of the mitigation measures recommended
in Air Quality Assessment for construction dust impact.
The
assessment under the realistic scenario with implementation of mitigation
measure is presented below:
Mitigated Scenario
When
mitigation measure is taken (i.e. water spraying for dust suppression, refer to
Section 6.4.7 for details), the ambient
arsenic concentrations in PM10 are estimated to be: 11.7 ng/m3
(Maximal soil arsenic
concentration of 1,220 mg/kg), 7.7 ng/m3 (95th Percentile soil arsenic concentration of 461
mg/kg), 5.7 ng/m3 (Mean
soil arsenic concentration of 125 mg/kg), and 4.7 ng/m3 (Median soil arsenic
concentration 71 mg/kg) respectively. The corresponding cancer risks are: 8.64
x 10-6, 7.77 x 10-6, 7.34 x 10-6 and 7.12 x 10-6
respectively. All these three estimated cancer risk levels are below the adopted
lifetime risk level (1 x 10-5).
The estimated risk levels under mitigated
scenario are summarized in Table 6.13.
Table 6.13 Estimated
risk levels under Mitigated Scenario
|
Arsenic Concentration |
Overall Risk
Level (2) (3) |
||
|
Percentile (1) |
As in Soil
(mg/kg) |
As in Air during 10-year Construction (ng/m3) |
|
KTN Development |
Maximum |
1,220 |
11.7 |
8.64 x 10-6 |
95 percentile |
461 |
7.7 |
7.77 x 10-6 |
|
Average |
125 |
5.7 |
7.34 x 10-6 |
|
Median |
71 |
4.7 |
7.12 x 10-6 |
|
WHO Information |
Average annual level at 6.6 ng/m3 |
1 x 10-5 |
Note:
(1) Total 437 soil arsenic
results. An “Outliner” arsenic result (23,400 mg/kg) is not included in the
risk assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
(2) The Overall Risk Levels are estimated for 70 years
lifetime exposure. In this assessment, 10 years exposure of the estimated
ambient arsenic level during construction, plus 60 years exposure of KTN
background arsenic level (i.e. 4.7 ng/m3, refer to Section 6.3
for details) is applied.
(3) As part of the high arsenic soils will be treated
during the construction stage, and the soil-exposed area in KTN will be reduced
after completion of KTN, the wind-blown arsenic-containing dust in KTN after
development should be further reduced. Therefore, the application of KTN
background arsenic level 4.7 ng/m3 for 60 years exposure in this
risk assessment is considered appropriate.
6.5.1.2 Non-Cancer Risk (Long-Term)
No local exposure factor for inhalation risk is available. The U.S. EPA Exposure Factor Handbook (4) recommends that the 95th percentile daily volume of air inhaled by an adult (both sexes combined) aged 16-20 years is 24.6 m3 (mean = 16.3 m3). The mean volume for Hong Kong adults, assuming a tidal volume of 500 ml, a respiratory rate of 19.5/min, and a mean body weight of 55.3 kg (averaged for men and women), is lower, at 14.0 m3. Using a conservative risk estimate with 24.6 m3 of air inhaled per day, but using a lower body weight of 55.3 kg for Hong Kong people, and an airborne concentration of arsenic at 28.7 ng/m3, the daily intake is 0.0128 µg/kg/day, or 4.3% of the minimal risk level (MRL) (at 0.3µg/kg/day) as recommended by ATSDR (34). In interpreting this MRL, which is derived from epidemiological data on oral intake of arsenic from drinking water, one should note that the assumption is that arsenic in drinking water is completely absorbed into the blood to produce systemic effects (skin changes). Our comparison of the systemic effects attributed to arsenic inhalation is also based on the assumption that respirable arsenic particulates, once inhaled into the smaller airways beyond the muco-ciliary escalator, cannot be expelled from the respiratory tract and is absorbed completely into the systemic circulation (similar to the assumption that arsenic in drinking water is absorbed completely). Hence, the effects on health from arsenic inhalation should be similar to that from oral ingestion of arsenic-contaminated water.
The daily arsenic intake via inhalation of arsenic-containing dust under Unmitigated and Mitigated Scenario are summarized in Table 6.14 and Table 6.15 respectively.
Table 6.14 Daily
intake of ambient arsenic under Unmitigated Scenario
|
Arsenic Concentration |
Daily Intake
(µg/kg/day) (2) |
% of MRL |
||
|
Percentile (1) |
As in Soil
(mg/kg) |
As in Air during 10-year Construction (ng/m3) |
||
KTN Development |
Maximum |
1,220 |
28.7 |
0.0128 |
4.3% |
95 percentile |
461 |
13.7 |
0.0061 |
2.0% |
|
Average |
125 |
6.7 |
0.0030 |
1.0% |
|
Median |
71 |
5.7 |
0.0025 |
0.83% |
|
MRL |
|
|
|
0.3 |
- - |
Note:
(1) Total 437 soil arsenic
results. An “Outliner” arsenic result (23,400 mg/kg) is not included in the
risk assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
(2) Body
Weight of 55.3 kg and Daily Inhalation Rate of 24.6m3 are adopted
for the estimation of Daily Intake of arsenic through inhalation.
Table 6.15 Daily
intake of ambient arsenic under Mitigated Scenario
|
Arsenic Concentration |
Daily Intake
(µg/kg/day) (2) |
% of MRL |
||
|
Percentile (1) |
As in Soil
(mg/kg) |
As in Air during 10-year Construction (ng/m3) |
||
KTN Development |
Maximum |
1,220 |
11.7 |
0.0052 |
1.7% |
95 percentile |
461 |
7.7 |
0.0034 |
1.1% |
|
Average |
125 |
5.7 |
0.0025 |
0.83% |
|
Median |
71 |
4.7 |
0.0021 |
0.70% |
|
MRL |
|
|
|
0.3 |
- - |
Note:
(1) Total 437 soil arsenic results.
An “Outliner” arsenic result (23,400 mg/kg) is not included in the risk
assessment as the 99 percentile of 437 soil arsenic results is only 816
mg/kg.
(2) Body
Weight of 55.3 kg and Daily Inhalation Rate of 24.6m3 are adopted
for the estimation of Daily Intake of arsenic through inhalation.
6.6 Uncertainties in Inhalation Health Risk Assessment
The risk estimates
for cancer risk from inhalation of arsenic are derived from extrapolation of
findings from workers exposed to high concentrations of arsenic in different
occupational settings, assuming a linear exposure-response relationship. Exposure data in occupational studies are
difficult to obtain and often unreliable. Extrapolation from a high dose
environment to a low dose environment creates uncertainties in risk estimate.
The estimation of arsenic in the air during construction is subject to
uncertainties in the model choice and assumptions of arsenic emissions and
meteorological data. Hence, for long-term, non-cancer risk to health,
conservative estimate based on a high ambient concentrations of arsenic of 28.7
ng/m3 and 13.7 ng/m3 (i.e. derived from the Maximal soil
arsenic result of 1,220 mg/kg and 95 percentile of soil arsenic results of 461
mg/kg respectively) were used in order to demonstrate that the adopted lifetime
risk level is only exceeded at this worst condition under unmitigated scenario.
A more realistic assumption of Mean and Median soil and ambient arsenic
concentrations, and consideration of mitigation measures result in much reduced
risk estimates.
Based on the result of the ingestion health risk analysis, the acceptance soil arsenic level is calculated as 571 mg/kg (refer to Section 5 for details). Treatment will be required for the disturbed soil with arsenic concentration above 571 mg/kg.
Hot spot areas with arsenic concentration above 571 mg/kg at different datum levels are given in Appendix CC. It is noted that the areas with arsenic concentration above 571 mg/kg are widely scattered in different areas of KTN and at different datum levels.
7.2 Uncertainties in Ground Investigation
The borehole is an important mean to investigation the distribution of the arsenic underground. However, KTN is mainly private land and there is major difficulty in carrying out ground investigation in some of the areas due to land ownership issue. During the investigation stage, boreholes have been arranged on government land and best effort is paid to analyse the available information, but it is acknowledged that there are uncertainties on the arsenic distribution in-between boreholes derived by interpolation. There are risks due to the unavailable ground investigation in private land at this investigation stage.
It is therefore strongly suggested that further ground investigation should be arranged at closer intervals after the land resumption process, in particular on the identified hot spot area and on the existing private land. The treatment proposal could then be refined based on the latest findings.
The hot spot areas with arsenic level above 571 mg/kg is widely scattered in different areas of KTN and at different datum levels. The observed arsenic profile is analysed to be highly likely due to natural geological formation.
Owing to the large volume and some of the hot spot locating deep below ground, it is impractical to treat all natural arsenic-containing soil in KTN by Cement Solidification/ Stabilisation (S/S). A combination of cement stabilisation and planning / land lease control is therefore proposed for managing the specific situation in KTN. The details of proposed treatment method “Cement Solidification/Stabilization” is given in Section 8.
Several assumptions are proposed for managing the teh arsenic-containing soil in KTN.
(i)
Arsenic beneath green belt area remains in-situ.
Some of the hot spot areas are located beneath the hillside, slope and burial ground area in KTN. There areas are zoned Green Belt and is not proposed to be disturbed by the NENT NDA development. Any excavation to treat the underground soil will disturb the natural setting and graves in these areas. Since these hot spots are capped below the existing ground level and not likely be disturbed by future development, it is considered that no treatment is arranged for these areas.
(ii)
Government treats the arsenic-containing
soil (with concentration > 571 mg/kg) in shallow region which is likely to be disturbed by
basement, shallow foundation and utility work in future.
It is assumed that the government will treat the arsenic-containing soil in the shallow region by S/S before the land allocation / land lease. The depth of the treatment depends on the future land use of the land parcels in the revised Recommended Outline Development Plan (RODP).
In residential and commercial zones, it is considered that two levels of underground basement are sufficient and is reasonable assumption for the underground car parking requirement. Hence it is assumed that 0 to 8m below site formation level will be treated by the government.
In most government facilities, schools and road, it is considered that two levels of underground basements are unlikely. One level of basement is assumed. Hence it is assumed that 0 to 4m below site formation level will be treated by the government. This depth also cleans the soil for most future utility excavation by utility undertakers.
The locations of the future underground parking, pile cap and utility are undetermined before the detailed design of the buildings by the developer. It is impractical to restrict the structural location during the planning stage. It is therefore assumed that the whole land parcels are treated to provide the flexibility for future structural locations.
It is suggested that the above assumptions on the treatment depth by the government has to be correspondingly reflected in the land lease control. For instance, should the developer intends that basement level is beneath 8m below site formation level, then application has to be made and any further treatment needed will have to be bound by the developer.
The arsenic content is chemically bond by the cement after S/S. It is proposed that the treated soil will be backfilled to its original location before future excavation.
(iii)
Arsenic-containing soil (with concentration
> 571 mg/kg) in deep region remains in-situ by foundation design, or any
excavated mucking out is treated by the developer.
Regarding the deeper arsenic-containing soil, large-scale treatment before land lease is impractical due to the deep excavation required and the wide coverage of the hot spots.
The arsenic-containing soil in this region is usually not disturbed unless during deep excavation or foundation mucking out. The quantity of arsenic-containing soil distributed is relatively less than the site formation and shallow basement construction.
It is assumed that land lease condition will be arranged for the developer to bear the treatment to any excavation of arsenic-containing soil due to deep foundation mucking out.
The developer can either avoid the mucking out by using displacement piles instead of replacement piles, or arrange the treatment to the mucking out in accordance to the land lease condition.
7.4 Cement Solidification/Stabilisation for Shallow Region
It is assumed that cement S/S will be carried out to the identified hot spot area in the shallow region for underground basement, pile cap and utility.
Based on the ground investigation and the arsenic profile on soil with arsenic concentration > 571 mg/kg (refer to Section 4.4 for details), it is identified that there are three major hot spot areas in the shallow region in KTN NDA which is more likely to be disturbed in future NENT NDA development. The three hot spot areas are analysed as below.
The summary of the extent of treatment is shown on Figure 7.5.
7.4.1 Hot Spot A
The hot spot area A is shown on Figure 7.1. It is located at northwest part of KTN NDA. Vast area of the hot spot is located within the green belt area and not anticipated to be disturbed by future development in KTN NDA.
A small area covers the proposed police headquarters, fire station and school site. The proposed site formation level at this area is about +28.5mPD. In consideration of the land use, basement parking is not anticipated.
Arsenic-containing soil with concentration >571 mg/kg is observed at +25mPD (about 2.5m to 4.5m below site formation level). However the arsenic level becomes lower than the acceptance level at +20mPD.
In order to ensure that the future pile cap and utility
excavation will be in treated soil, it is proposed to treat the soil 0 to 4m below site formation level
in this area. The extent of treatment
for Hot Spot Area A is around 18,000 m².
7.4.2 Hot Spot B
The hot spot area B is shown on Figure 7.2. It is located at southwest part of Kwu Tung North NDA and is part of the advance work land parcels. Based on the land use, it is subdivided into hot spot areas B1, B2 & B3.
Hot spot area B1 is currently zoned Public Rental Housing (Rehousing) and Residential Zone 1 (with commercial). The proposed site formation level falls gradually from about +22mPD at the west to +20mPD at the east. The basement parking for the residential and commercial use is assumed to be 2-storey up to 8m below site formation level.
Arsenic-containing soil with concentration > 571 mg/kg is observed at +15mPD and +10mPD (about 4 to 13m below site formation level). Arsenic level is low at the surface level at +20mPD.
It is proposed to treat the soil 2 to 8m below site formation level in this area B1 for
future basement excavation. Extra
cut-fill is required for excavating the soil out for cemment S/S. The extent for treatment for area B1 is around
46,000 m².
Alternatively the administration can consider to restrict the excavation to 1-storey depth in this land parcel by allowing some degree of above-ground parking, in order to minimise the disturbance to the arsenic-containing soil.
Hot spot area B2 at the south is currently planned for hospital, school site, power supply substation and internal roads. The proposed site formation level falls from +17mPD at the north to +12mPD at the south on Castle Peak Road. The basement parking, if any, is anticipated to be 1-storey, up to 4m below site formation level.
At this hot spot are B2, higher arsenic concentration is observed at +15mPD (about ground level to 3m below site formation level). The arsenic concentration becomes low at +10mPD.
It is proposed to treat the soil 0 to 4m below site formation level in this area B2 for
future pile cap and utility excavation.
The extent for treatment for area B2 is around 90,000 m².
Hot spot area B3 is at the location of the district cooling system in
KTN. There is underground excavation to house the plant of the district cooling
system. It is assumed that the
underground structure is 10m depth.
There is limited number of boreholes in the area and hence there is
uncertainty in the arsenic distribution.
As it is likely that the district cooling system will be arranged in a
separated works contract, it is proposed that the arsenic-containing soil could
be treated during the excavation for the underground structure. The extent for treatment for area B3 is
around 12,000 m².
7.4.3 Hot Spot C
The hot spot area C is shown on Figure 7.3. Hot Spot C is located at southern side of Fung Kong Shan.
About half of the hot spot area falls deep below the green belt area of Fung Kong Shan. It is not anticipated to be disturbed by the future development in KTN NDA.
Hot spot area C is currently zoned as Public Rental Housing and Residential Zone 2. The proposed site formation falls gradually from +18mPD at the northern edge to +12.5mPD at the southern edge. The basement parking for the residential and commercial use is assumed to be 2-storey up to 8m below site formation level.
Arsenic-containing soil with concentration > 571 mg/kg is observed at +5mPD (about 6.5 to 8.5m below site formation level). Arsenic level is low at the higher datum levels.
As such if a 2-storey basement is intended on the southern side of the land parcels, the lower level of the basement can marginally encroach the arsenic-containing soil. However if a 2-storey basement is located further north where the site formation level is higher, the basement will not encroach into the arsenic-containing soil with concentration > 571 mg/kg.
Hence the extent of treatment is suggested to be limited to southern side of the land parcels. It is proposed to treat the soil 6m to 8m below site formation level. The extent of treatment for ho spot area C is around 41,000 m². It should be highlighted that this arrangement requires the soil 0 to 6m below site formation level to be excavated out first before the concerned soil at 6m to 8m below site formation level can be treated. There is a cost involved in the extra cut-fill, but however provides the highest flexibility for the building arrangement.
Alternatively planning / land lease control can be arranged to either restrict the excavation up to 6m at southern side only, or to limit 2-storey basement at the northern part of the land parcels only. This will avoid the basement from disturbing the arsenic-containing soil and can avoid the treatment cost for Hot Spot C, except the residual deep foundation issue.
7.4.4 Preliminary Volume Estimates
Based on the aforementioned assumptions, a preliminary estimation of arsenic-containing soil quantity to be treated by the government is carried out, and summarized in Table 7.1.
Table 7.1 Preliminary volume estimates for treatment
in Kwu Tung North NDA
Hot Spot Area |
Treatment Area (m²) (A) |
Treatment Thickness (m) (B) |
Treatment Volume (m³) (C) = (A) x (B) |
Extra Cut-fill Thickness
(m) (E) |
Extra Cut-fill Volume (m³) (F) = (A) x (E) |
A |
18,000 |
4 |
72,000 |
4 |
72,000 |
B1 |
46,000 |
6 |
276,000 |
8 |
368,000 |
B2 |
90,000 |
4 |
360,000 |
4 |
360,000 |
B3 |
12,000 |
10 |
120,000 |
0 |
0 |
C |
41,000 |
2 |
82,000 |
8 |
328,000 |
Total |
207,000 |
|
910,000 |
|
1,128,000 |
It is highlighted that as more ground investigation would be conducted after the land resumption process, the above volumes might be adjusted accordingly. There are also potential refinements in the site formation level to minimise the excavation of the arsenic-containing soil.
7.5 Planning / Land Lease Control for Basement Depth
The extent of treatment carried out by the government, as described in previous sections, is based on an assumption of the shallow basement depth. It is proposed that 0 to 8m below site formation level is treated for the residential and commercial zones, and 0 to 4m below site formation level for most government facilities, schools and road. The planning / land lease condition should correspondingly reflect this assumption, in order to avoid the developer from excavating deeper basement (i.e. to area not treated by the government) without carrying out appropriate treatment.
The extent of treatment and the corresponding planning / land lease control is summarised in Figure 7.5.
7.6 Residual Issue for Deep Foundation Region
The treatment work by the government in shallow region would treat the soil in future basement, shallow foundation and utility excavation, which is the major excavation. However, practically any excavated material from deep foundation construction could only be treated at the time when the building foundation is constructed.
The distribution of the deeper arsenic-containing soil which might be disturbed during deep foundation construction is presented on Figure 7.4. The distribution is scattered at different datum levels in different areas of KTN.
It is anticipated that practically this residual issue for deep foundation region has to be addressed by the developer during building construction. The residual issue can be addressed in several possible ways:
1. Arrange building layout to avoid the arsenic-containing area within the site;
2. Use displacement pile type instead of replacement pile to avoid mucking out of arsenic-containing soil, if the geotechnical design allows;
3. Carry out treatment to the mucking out.
The land lease condition will therefore have to incorporate the residual issues to be addressed by the developer. Details may include the ground investigation, environmental monitoring, approval procedure and treatment responsibility regarding the arsenic-containing soil.
The land parcels which required specific land lease condition for the arsenic issue is summarised in Figure 7.6. The land parcels also covers those involving shallow area treatment. The extent is based on the available ground investigation information at this stage. It should be noted that most land parcels in KTN is included.
This section presents possible treatment technologies and recommends
appropriate treatment method for treating high arsenic-containing soil found in KTN.
The objectives of this section are as follows:
·
To
propose treatment method(s) for the high arsenic-containing soil;
·
To propose
a mean to confirm completed excavation of high arsenic-containing soil; and
·
To
provide guidelines regarding the handling and/or disposal of high arsenic-containing
soil.
8.2 Potential Treatment Methods
8.2.1 Selection Criteria
Soil treatment options applicable to the high arsenic-containing soil
in KTN were addressed based on the followings:
·
Technical
and cost effectiveness;
·
Technology
development status;
·
Environmental
benefits and disbenefits;
·
Commercial
availability;
·
Experience;
and
·
Expertise
requirement.
8.2.2 Available Soil Treatment Methods
A number of soil treatment technologies considered suitable for the
metal Arsenic are selected for detailed examination. The applicability and
limitations of the candidate treatment technologies are detail in Table 8.1.
In assisting the formulation of appropriate remedial measures, the
following factors suggested in the Practice
Guide for Investigation and Remediation of Contaminated Land issued by EPD would
also be taken into consideration when evaluating different available treatment
methods:
·
Degree
and extent of the high arsenic-containing soil;
·
Anticipated
future use of the site;
·
Nature
of the contaminants (i.e. arsenic);
·
Soil
characteristics; and
·
Time
available for remediation.
Table 8.1 List
of possible soil treatment methods for metal-containing Soil
Remediation Option |
Descriptions |
Applicability / Environmental Benefits |
Limitations / Environmental Disbenefits |
Solidification
/ Stabilization |
Ex-situ
immobilization technique treating contaminated soil by mixing soil with
binding agents, e.g. cement so as to physically bind contaminants into stable
mass. |
·
Applicable to clean-up inorganic contaminants such
as heavy metals. ·
Solidification/stabilization are used on certain
contaminated sites in Hong Kong and successfully demonstrated treatment
method for inorganic contaminated soil, e.g. decontamination works at the
Cheoy Lee Shipyard at Penny’s Bay, reclamation works at North Tsing Yi
Shipyard site and few isolated sites identified in the Deep Bay Link project. |
·
The effectiveness reduces with the presence of
organic contaminants. ·
Large boulders may hinder the mixing process. Soil
sorting is necessary before the treatment taken place. ·
Organics are generally not immobilised. ·
Long-term effectiveness has not been demonstrated
for many contaminant/ process combinations. ·
If VOCs/ SVOCs is present underneath, it should be
removed before stabilisation/ soil solidification. |
Soil
Washing |
An
Ex-situ soil separation method primarily based on mineral processing
techniques. A water-based process for scrubbing soils ex-situ to remove
contaminants. |
·
Applicable to clean inorganic contaminants such as
heavy metals from coarse-grained soils. |
·
Effectiveness of treatment dependent on soil
coarseness. Fine soil particles may require addition of polymer for removal
of contaminant by the washing fluid. ·
Complex waste mixtures make formulating washing
fluid difficult. ·
Further treatment and disposal for residuals
required. ·
Lack of local experience. |
Electrokinetic Separation |
This
In-situ method uses electrochemical and electrokinetic processes to desorb
and remove metals and polar organics from soil. Low intensity direct current
is applied to the soil to mobilize the charged species. |
·
Applicable to treat soil with low permeability and
heavily contaminated with metals. |
·
Effectiveness dependent on moisture content of soil
and decreases with moisture content less than 10%. ·
Require further treatment for removal of desorbed
contaminants and thus increase cost of remediation. ·
Variability of electrical conductivity in soil may
be induced by presence of anomalies such as large gravels and insulating
material. This may reduce treatment effectiveness. ·
Lack of local experience. |
Excavation
and Landfill Disposal |
Ex-situ
method whereby contaminants are removed by excavation of the contaminated
soil and direct disposal of the contaminated soil to landfill |
·
Simplest and quickest way to dispose of large volume
of contaminated soil ·
Contamination is removed definitely ·
Higher certainty of success ·
Wide experience in Hong Kong ·
Applicable to all waste or mixture that meet land
disposal restriction treatment standards. ·
Common practice for shallow, highly-contaminated
soils. |
·
Pre-treatment may be required for contaminated soil
to meet landfill disposal criteria. ·
Landfill space limited and valuable. ·
Indirect costs to the landfill management on
monitoring and maintenance. ·
Potential long-term liabilities to landfill. ·
Need large volume of clean backfill materials. ·
No access to the working site until completion of
backfilling. ·
Least desirable management option. |
Considering the cost effectiveness and applicability of different
remediation methods listed in Table 8.1, “Excavation”
followed by “Solidification/Stabilization” are regarded as the most
practical and cost-effective method to remediate the arsenic contaminated soil.
8.3.1 Solidification/Stabilization
Solidification/Stabilization (S/S) is an immobilisation technique
applicable to the treatment of soil containing metals such as arsenic. By mixing metal-containing soil with binders
such as Portland cement or lime, the arsenic in soil become physically bound
within a stable mass. The solid monolithic block is extremely resistant to the
leaching of metals. Additives such as phosphate or sulfur reagents could also
be added not only to reduce the setting or curing time and leachability of
metals, but also to assist in chemically binding the metals in a matrix that
typically shows unconfined compressive strengths similar to a soil-cement mix.
Beside several local successful case studies as listed in Table 8.1, other
overseas case studies, as stipulated in “Solidification/Stabilization
Use at Superfund Sites” published by U.S. Environmental Protection Agency’s
Technology Innovation Office under EPA Contract Number 68-W-99-003 (http://www.clu-in.org/s.focus/c/pub/i/611/), also reveals that inorganic contaminants in
USEPA superfund remedial sites could be successfully treated by S/S method.
Another technical document “Arsenic
Treatment Technologies for Soil, Waste, and Water” published by U.S.
Environmental Protection Agency’s Technology Innovation Office under EPA
Contract Numbers 68-W-99-003 and 68-W-02-034”
(http://www.clu-in.org/download/remed/542r02004/arsenic_report.pdf) also indicates that S/S method has been
widely applied for treating the arsenic-containing soil and was the most common
treatment method for arsenic–containing soil.
The recommended treatment method as discussed above is summarized in Table 8.2. The
design and operation of the recommended remediation method is presented in the
outline process in the following sections.
Table 8.2 Recommended
remediation method for arsenic-contaminated soil
Material need to be treated
|
Treatment Method |
Justification |
Arsenic |
Excavation followed by Solidification/Stabilization. |
·
Well developed technology with operation experience
in Hong Kong ·
Higher certainty of success ·
Simple operation without necessity of further
treatment ·
Cost effective ·
Treated soil is acceptable to be reused as backfill |
8.4 Outline Process and Operation of Treatment
8.4.1 Excavation
Further GI should be conducted to further ascertain the extent and
quantity of soil requiring treatment prior to excavation. Detailed design
drawings for planned excavation areas should be prepared by the Contractor
responsible for treatment. Factors such as excavation areas and depths,
engineering properties and stability of the soils should be considered for safe
working conditions. The excavations should be designed in accordance with the geotechnical
properties of the soils and appropriate safety factors by a qualified and
professional engineer of the appropriate discipline and proper set-out on site.
The excavated areas should be set out by an appropriate qualified and licensed
land surveyor.
The excavation sequence would be
as follows:
· At each location as set out by the surveyor, the clean top soil above and in-between the identified treatment depths would be excavated and transferred to a designated area for stockpiling.
· After the clean soil is removed, the soil at the identified treatment depth would be excavated and transferred to a designated area for treatment. The soil should be placed on heavy-duty impermeable sheeting within the soil treatment area.
· Both the stockpiles of clean soil and soil requiring treatment should be fully covered by impermeable sheeting to prevent dust emission and runoff.
· Any free product (if encountered) during excavation should be recovered and drummed properly and collected by licensed chemical waste collector for proper handling and treatment.
· Closure Assessment (i.e. refer to Section 8.4.2) should be undertaken to confirm the closure/completion for the excavation work.
· Backfill the excavation with suitable imported or reworked site materials such as treated materials.
8.4.2 Closure Assessment
The objective of closure assessment is to determine if all soil
requiring treatment has been excavated before backfilling takes place.
Following excavation and prior to the backfilling, confirmatory
sampling and analysis should be carried out at the limits/sidewalls and base of
the excavations to confirm that all the contaminated soil has been excavated.
As the areas requiring soil treatment are relatively large (i.e. over 10,000m2
in size), confirmation samples should be collected from sidewalls of the
excavation with a lateral spacing of not more than 15m. The depth of sidewall
samples should be at the depth where the high arsenic was identified.
Confirmation samples from the bottom of excavation areas should be collected on
grid spacing not larger than 15m x 15m (i.e. one sample per approximately every
225m2).
The collected confirmation soil samples should be analysed for the arsenic.
If the analytical results exceed the acceptable level of 571 mg/kg (i.e, refer to Section 5.5 for details), additional soil samples
should be excavated in 0.5m increments vertically and 7.5m in horizontal
increments depending on whether the exceeding confirmation sample is collected
along the boundary or from excavation base. Additional samples should be
collected and analysed until all confirmation samples are below the acceptable
level of 571 mg/kg. If the analytical results are below the acceptable level of
571 mg/kg, removal of soil for treatment should be considered complete and the
open excavations were then backfilled with suitable imported or reworked site
materials.
All construction activities should be carried out by persons
appropriately trained in health and safety and appropriated personal protective
equipment should be used by the person engaged in treatment activities. The
following guidelines of health and safety should be strictly followed by all
site personal working on the treatment areas at all times:
· Temporary fencing or warning ribbons should be provided to the boundary of excavation, slope crest and temporarily stockpiled areas. Where necessary, the exposed areas should be temporarily covered with impermeable sheeting during heavy rainstorm.
· Workers are required to wear appropriate protective clothing and safety equipment.
· Smoking, eating and drinking are strictly prohibited.
· Relevant occupational health and safety regulations and guidelines during excavation should be observed.
The excavation and confirmatory sampling works should be supervised by
a qualified Soil Treatment Specialist. Subsequent construction activities could
only be carried out after closure assessment or remediation at the subject site
is completed as agreed by the Soil Treatment Specialist.
8.4.3 Solidification/Stabilization (S/S)
A treatment area should be confined for carrying out the S/S mixing and
temporary soil stockpile. Prior to solidification, the contaminated soils
should be screened to segregate soil from debris, rock fragments and other materials
and to break soil clumps into sizes allow effective mixing solidifying agents.
During the S/S process, Ordinary Portland Cement (OPC) (or other
equivalent), water and/or other additive(s) (such as fly ash, lime and soluble
silicates etc) should be added to the arsenic containing soils to form a solid
matrix. Uniform mixing of contaminated soils, cement, water and other
additives(s) should be undertaken within a pugmill, lorry mixer or equivalent
at the designated treatment area to minimise the potential leaching during
solidification process. Detail S/S method statements, include but not limit to the
proposed solidify agents and additives, mixing ratio, mixing equipment, and
mixing trial test proposal etc should be prepared by the Contractor responsible
for treatment and verified and approved by the Soil Treatment Specialist prior
to the commencement of S/S treatment.
The total volume of the cement blocks could be increased by up to 10%
from the original soil volume. The solidified blocks should be of suitable size
to allow easy handling and transporting, and large blocks should be broken up
into smaller size for transportation.
The soil mixture in the cement blocks would be solidified within about
1 week. After setting, the samples of the blocks should be collected for
testing to confirm if the contaminated materials meet the:
(i)
Toxicity
Characteristic Leaching Procedure (TCLP) Test; and
(ii)
Unconfined
Compressive Strength (UCS) Test.
which indicate the achievement of the stabilization targets.
8.4.4 Toxicity Characteristic Leaching Procedure (TCLP) Test
The sampling frequency for the TCLP test should be 1 TCLP sample per 200m3
of broken up hardened mixture after S/S treatment. Each TCLP sample should be a
composite sample collected at 5 locations throughout the 200m3
broken up hardened mixture. Same volume of sample should be collected at each
of the 5 locations in order to facilitate unbiased sample compositing.
Any hardened samples to be submitted to laboratory for TCLP analysis
should be broken up to small pieces with maximum diameter of 10cm. The sample
preparation method of USEPA Method 1311 will be followed for the TCLP analysis.
It is specified in USEPA Method 1311 that the maximum grain size of samples to
be analysed is 1cm. As such, the samples should be further broken up in the
laboratory prior to TCLP analysis.
TCLP tests should be conducted in accordance with USEPA Method 1311 and
USEPA Method 6020 for arsenic. “Universal Treatment Standards” (UTS) as
specified in EPD’s Practice Guide for Investigation
and Remediation of Contaminated Land should be used for interpretation of
the TCLP testing results. The UTS for the arsenic is given in Table 7.3.
Table 7.3 Universal Treatment
Standards (UTS) for On-site Reuse of Cement Stabilization / Solidification
Treated Soil
Parameter (1) |
TCLP Limit (mg/L) |
Arsenic |
5 |
Note:
(1) Universal Treatment Standard - US 40
CFR 268.48.
Any pile of broken up solidified mixture that does not meet the UTS of arsenic
should be crushed and re-treated by S/S. The re-treated pile should be tested
again for TCLP to confirm if it could be reused on site.
8.4.5 Unconfined Compressive Strength (UCS)
The treated material should be allowed to set to achieve the Unconfined
Compressive Strength (UCS) of not less than 1MPa with reference to the USEPA
guideline (1986) – Handbook of Stabilization / Solidification of Hazardous
Wastes, EPA/540/2-86-00. The test procedure of UCS test should be based on BS
1377 - Methods of test for soils for civil engineering purposes.
8.4.6 Handling of Treated Material
Upon completion of the leachability testing and meeting the UTS and the
UCS requirements, the solidified materials should be reused on-site or off-site
as backfilling. As the maximum grain size of filling material is 250mm (i.e.
according to the general practice), the solidified soil should be broken down
to below this size before being used as filling materials.
8.5 Mitigation Measures and Safety Measures
8.5.1 Environmental Mitigation Measure
In order to minimise the potentially environmental impacts arising from
the handling of arsenic-containing soil, the following environmental mitigation
measures are recommended during the course of the treatment:
8.5.1.1 Excavation and Transportation
· Excavation profiles must be properly designed and executed with attention to the relevant requirements for environment, health and safety;
· In case the soil to be excavated is situated beneath the groundwater table, it may be necessary to lower the groundwater table by installing well points or similar means;
· Excavation should be carried out during dry season as far as possible to minimise runoff from excavated soils;
· Stockpiling site(s) should be lined with impermeable sheeting and bunded. Stockpiles should be properly covered by impermeable sheeting to reduce dust emission during dry season or contaminated run-off during rainy season. Watering should be avoided on stockpiles of soil to minimise runoff;
· Supply of suitable clean backfill material after excavation, if require;
· Vehicles containing any excavated materials should be suitably covered to limit potential dust emissions or run-off, and truck bodies and tailgates should be sealed to prevent any discharge during transport or during wet season;
· Speed control for the trucks carrying excavated materials should be enforced; and
· Vehicle wheel washing facilities at the site’s exit points should be established and used.
8.5.1.2 Solidification / Stabilization
·
The
loading, unloading, handling, transfer or storage of cement should be carried
out in an enclosed system;
·
Mixing
process and other associated material handling activities should be properly
scheduled to minimise potential noise impact and dust emission;
·
The
mixing facilities should be sited as far apart as practicable from the nearby
noise sensitive receivers;
·
Mixing
of soil and cement / water / other additive(s) should be undertaken at a
solidification plant to minimise the potential for leaching;
·
Runoff
from the solidification / stabilization area should be prevented by
constructing a concrete bund along the perimeter of the solidification /
stabilization area;
·
If
stockpile of treated soil is required, the stockpiling site(s) should be lined
with impermeable sheeting and bunded. Stockpiles should be properly covered by
impermeable sheeting to reduce dust emission during dry season or site run-off
during rainy season; and
·
If
necessary, there should be clear and separated areas for stockpiling of
untreated and treated materials.
8.5.2 Safety Measures
In order to minimize the potential adverse effects on health and safety
of construction workers during the course of site remediation, the Occupation
Safety and Health Ordinance (OSHO) (Chapter 509) and its subsidiary Regulations
should be followed by all site personnel working on the site at all times. In
addition, basic health and safety measures should be implemented, including but
not limited to the followings:
·
Set up a
list of safety measures for site workers;
·
Provide
written information and training on safety for site workers;
·
Keep a
log-book and plan showing the zones requiring treatment and clean zones;
·
Maintain
a hygienic working environment;
·
Avoid
dust generation;
·
Provide
face and respiratory protection gear to site workers if necessary;
·
Provide
personal protective clothing (e.g. chemical resistant jackboot, liquid tight
gloves) to site workers if necessary;
·
Provide
first aid training and materials to site worker;
·
Bulk
earth moving equipment should be utilized as much as possible to minimize
workers’ handling and contact of the excavated materials; and
·
Eating,
drinking and smoking should not be allowed in the excavation areas and
treatment areas to avoid inadvertent ingestion of arsenic containing soil.
Arsenic Treatment Report (ATR) for identified zones with high arenic
containing soil upon completion of treatment should be prepared by the Soil
Treatment Specialist to report the treatment process and demonstrate that all
targeted arsenic containing soil are removed, properly handled, treated and
reinstated. All relevant information, including details of closure assessment
and photographical records, should be included in the ATR. The ATR should be
submitted to EPD for record and agreement prior to the commencement of any
construction works.
The soil arsenic results collected at different GI programs have been presented and reviewed. Extremely high soil arsenic level of 23,400 mg/kg was investigated by collecting additional Mazier sample for geological inspection, and concluded that the extremely high arsenic level is due to in situ rock composition instead of surface contamination
The health risk of arsenic through soil ingestion reaches the ‘threshold’ of long-term MRL at a soil concentration of arsenic at 571 mg/kg, while the short-term MRL for children will be exceeded at a soil concentration of 625 mg/kg. Both are above the 97th percentile of soil concentration of arsenic in the collected soil samples. It is recommended that, to minimize the long-term health risk, remedial action should be taken to maintain the soil concentration of arsenic at or below 571 mg/kg.
For the health risk of arsenic through
inhalation, under the mitigated scenario, the estimated cancer risk levels
based on different
percentile (i.e. maximum, 95 percentile, mean value and median value) of 437
soil arsenic results collected in KTN are below the adopted lifetime risk level
(1 x 10-5). Cancer risk caused by the inhalation of
arsenic-containing dust during construction stage with dust suppression is
unlikely to be anticipated.
The estimated non-cancer risk levels (long-term) based on different percentile (i.e. maximum, 95 percentile, mean value and median value) of 437 soil arsenic results collected in KTN are also low. The estimated daily intake level of arsenic through inhalation of arsenic-containing dust under worst scenario is only 4.3% of the minimal risk level (MRL) as recommended by ASTDR(34).
The health risk of arsenic through inhalation
of arsenic-containing dust during construction stage of KTN development is insignificant for both Cancer Risk Level and
Non-cancer Risk Level.
The hot spots of soil containing high arsenic
level (i.e. exceed 571 mg/kg) in KTN have been identified based all the GI data
collected at different stages. After
review of various treatment methods, “Solidification/Stabilization” (S/S)
treatment method was proposed for the treating the arsenic-containing soil.
(1) IPCS (2001). Arsenic and arsenic compounds, 2nd ed. Geneva, World Health Organization, International Programme on Chemical Safety (Environmental Health Criteria 224; http://whqlibdoc.who.int/ehc/WHO_EHC_224.pdf) .Accessed on 12 March 2012.
(2) IARC Monographs 100C (2012). International Agency for Research on Cancer. http://monographs.iarc.fr/ENG/Monographs/vol100C/mono100C-6.pdf . Accessed on 18 March 2012).
(3) US Agency for Toxic Substances and Disease Registry (2007). Health Consultation: Arsenic in soil in Eastern Omaha, Nebraska: US Department of Health and Human Services, March.
(4) Environmental Protection Agency (2001). Exposure Factors Handbook: US Environmental Protection Agency; October.
(5) Tseng WP (1977). Effects and dose-response relationships of skin cancer and blackfoot disease with arsenic. Environmental Health Perspectives; 19:109-119.
(6) Tseng WP, Chu HM, How SW, Fong JM, Lin CS, Yeh S (1968). Prevalence of skin cancer in an endemic area of chronic arsenicism in Taiwan. J Natl Cancer Inst; 40, 453-463.
(7) Roberts SM, Weimer WR, Vinson JRT, Munson JW. 2002. Measurement of arsenic biavailability in soil using a primate model. Toxicol Sci;67:303–10.
(8) Bruce S., Noller B., Matanitobua V., Ng J.(2007). In vitro physiologically based extraction test (PBET) and bioaccessibility of arsenic and lead from various mine waste materials. J Toxicol Environ Health; 70(19):1700-1711.
(9) Miller E.R., Ullrey D.E. (1987). The pig as a model for human nutrition. Annu Rev Nutr; 7:361-382.
(10) Moughan P.J., Cranwell P.., Darragy A.J., Rowan A.M. (1994). The piglet as a model animal for studying aspects of digestion and absorption in milk-fed human infants. World Rev Nutr Dietetics; 67:40-113.
(11) Battelle (1996). Determination of the Bioavailability of Arsenic in Slag Following Oral Administration in Microswine. Battelle Laboratories, Columbus, OH.
(12) Lorenzana, R.M., Duncan, B., Ketterer, M., Lowry, J., Simon, J., Dawson, M. and Poppenga, R. (1996). Bioavailability of arsenic and lead in environmental substrates. 1. Results of an oral dosing study of immature swine. United States Environmental Protection Agency, Region 10, Seattle, WA, EPA 910/R-96-002.
(13) Groen K., Vaessen H.A.M.G., Kliest J.J.G., de Boer J.L.M., van Ooik T., Timmerman A., Vlug R.F. (1993). Bioavailability of inorganic arsenic from bog ore-containing soil in the dog. Environ Health Perspect ; 102:182-184.
(14) Davis A., Ruby M.V., Bergstrom P.D. (1992). Bioavailability of arsenic and lead in soils from the Butte, Montana, Mining District. Environ. Sci. Technol.; 26(3):461-468.
(15)
Freeman,
G.B., Johnson, J.D., Killinger, J.M., Liao, S.C., Davis, A.O., Ruby, M.V.,
Chaney, R.L., Lovre, S.C., and Bergstrom, P.D. (1993). Bioavailability of
arsenic in soil impacted by smelter activities following oral administration in
rabbits. Fundam. Appl. Toxicol. 21,
83-88.
(16) Casteel, S.W., Brown, L.D., Dunsmore, M.E., Weis, C.P., Henningsen, G.M., Hoffman, E, Brattin, W.J., and Hammon, T.L. (1997). Relative bioavailability of arsenic in mining wastes. United States Environmental Protection Agency, Region 8, Denver, CO.
(17) Rodriguez R.R., Basta N.T., Casteel S.W., Pace L.W. (1999). An in-vitro gastrointestinal method to estimate bioavailable arsenic in contaminated soils and solid media. Environ Sci Technol.; 33:642-649.
(18) Casteel SW, Evans T, Dunsmore ME, et al. (2001). Relative bioavailability of arsenic in soils from the VBI70 Site. Final report. Denver, CO: US Environmental Protection Agency, Region 8.
(19) Juhasz A.L., Smith E., Weber J., Rees M., Rofe A., Kuchel T., Sansom L., Naidu R. (2007). Comparison of in-vivo and in-vitro methodologies for the assessment of arsenic bioavailability in contaminated soils. Chemosphere; 69:961-966.
(20) Freeman, G.B., Schoof, R.A., Ruby, M.V., Davis, A.O., Dill, J.A., Liao, S.C., Lapin, C.A., and Bergstrom, P.D. (1995). Bioavailability of arsenic in soil and house dust impacted by smelter activities following oral administration in cynomolgus monkeys. Fundam. Appl. Toxicol. 28, 215-222.
(21) Roberts S.M., Munson J.W., Lowney Y.W., Ruby M.V. (2007) Relative oral bioavailability from contaminated soils measured in the cynomolgus monkey. Toxicological Sciences; 95, 281-288.
(22) Bradham K.D., Scheckel K.G., Nelson C.M., Seales P.E., Lee G.E., Hughes M.F., Miller B.W., Yeow A. Gilmore T., Serda S.M., Harper S., Thomas D.J.(2011) Relative bioavailability and bioaccessibility and speciation of arsenic in contaminated soils. Environ Health Perspect; 119,1629-1634.
(23) Ng J.C., Kratzmann S.M., Qi L., Crawley H., Chiswell B., Moore M.R. (1998). Speciation and absolute bioavailability: risk assessment of arsenic-contaminated sites in a residential suburb in Canberra. Analyst; 123:889-892.
(24) Ellickson K.M., Meeker R.J., Gallo M.A., Buckley B.T., Lioy P.J. (2001), Oral bioavailability of lead and arsenic from a NIST standard reference soil material. Arch. Environ. Contam. Toxicol ; 40, 128–135.
(25) Stanek III E.J., Calabrese E.J., Barnes R.M., Danku J.M.C., Zhou Y., Kostecki P.T., Zillioux E. (2010). Relative bioavailability of arsenic in soil: pilot study results and design considerations. Human and Experimental Toxicology; 29,945-960.
(26) USEPA (2001). Inorganic arsenic – Report of the Hazard Identification Assessment Review Committee. U.S. Environmental Protection Agency, Health Effects Division, Aug 21. (Available at: http://www.epa.gov/scipoly/sap/meetings/2001/october/inorganicarsenic.pdf
(27) Methodology Focus Group, Contaminated Soil Forum (2003). Arsenic Bioavailability from Florida Soils: Uncertainty Evaluation of the University of Florida / Florida Department of Environmental Protection Study, Jan 8, 2003.
(28) USEPA (2010). Relative bioavailability of arsenic in soils at 11 hazardous waste sites using an in vivo juvenile swine method. Bioavailability Subcommittee of the Technical Review Workgroup, Office of Solid Waste and Emergency Response, US Environmental Protection Agency, June 2010.
(29) USEPA (1999). Quality Assurance Project Plan for Vasquez Blvd-I70. Bioavailability of Arsenic in Site Soils Using Juvenile Swine as an Animal Model. Report prepared by ISSI Consulting Group for USEPA Region VIII, US Environmental Protection Agency.
(30) Juhasz A.L., Smith E., Weber J., Rees M., Rofe A., Kuchel T., Sansom L., Naidu R. (2007). In vitro assessment of arsenic bioaccessibility in contaminated (anthropogenic and geogenic) soils. Chemosphere; 69:69-78.
(31) Juhasz A.L., Weber J., Smith E. (2011). Predicting arsenic relative bioavailability in contaminated soils using meta analysis and relative bioavailability-bioaccessibility regression models. Environ Sci Technol; 45:10676-10683.
(32) Lu Y., Yin W., Huang L., Zhang G., Zhao Y. (2011). Assessment of bioaccessibility and exposure risk of arsenic and lead in urban soils of Guangzhou City, China. Environ Geochem Health; 33:93–102.
(33) ATSDR (2007). Health Consultation: Arsenic in soil in east Omaha, Nebraska. Agency for Toxic Substances and Disease Registry, Division of Health Assessment and Consultation, US Department of Health and Human Services, Atlanta, Georgia, March 2007.
(34) Agency for Toxic Substances and Disease Registry (2007). Toxicological profile for arsenic: US Department of Health and Human Services; August.
(35) Tseng W.P. (1977). Effects and dose-response relationship of skin cancer and blackfoot disease with arsenic. Environ Health Perspect; 19, 109-119.
(36) WHO (2008). Guidelines for drinking-water quality, 3rd edition incorporating 1st and 2nd addenda. Vol. 1. Recommendations. Geneva, World Health Organization, pp. 306–308b. (http://www.who.int/water_sanitation_health/dwq/GDW12rev1and2.pdf)
(37) Soil Guideline Values for inorganic arsenic in soil (2009). Science Report SC050021/arsenic SGV, Environment Agency, U.K.
(38)
Safety evaluation of certain
additives in food. WHO Food Additives Series 63, FAO JECFA Monograph 8, World
Health Organization, Food and Agriculture Organization of the United Nation,
Geneva, 2011. (http://whqlibdoc.who.int/publications/2011/9789241660631_eng.pdf)
(39) Environmental Protection Agency (2001). Baseline human health risk assessment, Vasquez Boulevard and I-70 Superfund Site, Denver, CO. Denver: US Environmental Protection Agency; August.
(40) USEPA (1999). Quality Assurance Project Plan for Vasquez Blvd-I70. Bioavailability of Arsenic in Site Soils Using Juvenile Swine as an Animal Model. Report prepared by ISSI Consulting Group for USEPA Region VIII, US Environmental Protection Agency.
(41) Leung SSF, et al. Growth standard from Southern Chinese. Hong Kong growth survey 1993. http://www.cuhk.edu.hk/proj/growthstd/english/gs_surve.htm (Accessed on 12 March 2012)
(42) Arsenic and arsenic compounds. Environmental Health Criteria 224, World Health Organization, Geneva, 2001.
(43) Agency for Toxic Substances and Disease Registry, Public Health Service, U.S. Department of Health and Human Services, 2007; Chapter 1: Public Health Statement, p4-6, 44, 73.
* The provisional acute oral MRL was derived from a human
poisoning episode that showed several transient (i.e., temporary) effects at an
estimated dose of 0.05 mg/kg/day. The transient effects observed included
nausea, vomiting, abdominal pain, and diarrhea (Mizuta 1956). The acute effect
level of 0.05 mg/kg/day identified in the Mizuta investigation is supported by
another study (Franzblau 1989). The acute oral MRL applies to non-cancerous
effects only; it is not used to determine whether people could develop cancer
(ATSDR 2000).