Appendix 8.4 - Health Risk Assessment Report for High Arsenic Soil in Kwu Tung North New Development Area

1 Overview

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 Arsenic Testing during Phase 2 Ground Investigation

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 Historical Land Use of KTN

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 Shek Sheung River runs parallel to the north eastern border of the development area and a tributary cuts through the middle of the development area from the north.

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 Fanling Highway and other main roads, has greatly developed since 1982 with the expansion of villages into towns and the first signs of large housing estates in the west. There are also large expanses of cleared ground.

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 Sheung Yue River and Shek Sheung River have been narrowed and channelized and there are an increased number of river crossings, improving accessibility to the growing residential areas. The area east of the Sheung Yue River and some land to the northwest remains the sole agricultural land use. Light industry and storage and car parking facilities are located west of the Sheung Yue River.

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 Arsenic GI Programme

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.

4.5 Health Risk Assessment

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 Health Risk Assessment of Ingestion Pathway

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 (BMDL_0.5) 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	General Population *Central Tendency*	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)

5.2.2 Bioavailability

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%
9. Juhasz et al, 2007a ⁽¹⁹⁾	Swine	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 95^th percentiles for standardized predicted arsenic RBA for naturally occurring gossan soils was predicted to be 23.7%. For contaminated soil, the predicted RBA (95^th 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

@ 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.

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

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)
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

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)
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

6 Health Risk Assessment of Inhalation Pathway

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 2^nd 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^-4would 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 (BMDL_0.5) 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
Arsenic Level (ng/m³)	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.

6.4.1 Baseline Condition

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).

6.4.2 Assessment Year

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.

6.4.3 Air Sensitive Receivers

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	Tai Tau Leng	R
KTN-E1016	Choi Ngan House	R
KTN-E1017	Scattered Village Houses at Northern Boundary of KTN	R
KTN-E1018	Scattered Village Houses at Northern Boundary of KTN	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
Year 2025	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 Assessment Methodology

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)
Borehole No.	No. of Soil Samples Collected	Sampling Depth (meter below ground level, mbgl)	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.

Disturbed soil samples were generally collected at about 0.5, 1.0 and 1.5 meter below ground level (mbgl) by excavation of Inspection Pit (IP). Undisturbed soil samples at the depth below 3.0mbgl were collected by U100 sampling or Mazier sampling methods by boreholes drilling.

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 4^oC 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), 5^th 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.

6.4.7 Mitigation Measures

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%*

6.4.8 Assessment Results

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⁾
ASR ID	Site No.	Remarks	Maximum Arsenic Content	95^th 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	-	Tai Tau Leng	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	-	Scattered Village Houses at Northern Boundary of KTN	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	B2-7	Primary School	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	B3-16	Visitor Centre	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⁾
ASR ID	Site No.	Remarks	Maximum Arsenic Content	95^th 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	-	Tai Tau Leng	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	-	Scattered Village Houses at Northern Boundary of KTN	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	B2-7	Primary School	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	B3-16	Visitor Centre	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)
Percentile ⁽¹⁾	As in Soil (mg/kg)	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)
Percentile ⁽¹⁾	As in Soil (mg/kg)	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 2^nd 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 95^th 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)	Overall Risk Level ^{(2) (3)}
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 (95^th 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)	Overall Risk Level ^{(2) (3)}
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.

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 95^th 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)	Daily Intake (µg/kg/day) ⁽²⁾	% of MRL
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)	Daily Intake (µg/kg/day) ⁽²⁾	% of MRL
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/m³and 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.

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.

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

Parameter ⁽¹⁾	TCLP Limit (mg/L)
Arsenic	5

* 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).

	Document Verification


Job title			Agreement No. CE61/2007(CE) North East New Territories New Development Areas Planning and Engineering Study - Investigation					Job number
Job title								25278

Document title			Health Risk Assessment Report for High Arsenic Soil in Kwu Tung North New Development Area					File reference
Document title								14.10

Document ref			140-02

Revision		Date	Filename	Report.docx

Draft 1		30/11/12	Description	First draft
				Prepared by		Checked by	Approved by
			Name	Various		Thomas Chan	Davis Lee
			Signature

Draft 2		28/02/13	Filename
			Description	Revised in accordance with the comments of DH and EPD, & the revised RODP and implementation programme.
				Prepared by		Checked by	Approved by
			Name	Various		Thomas Chan	Davis Lee
			Signature

Draft 3		15/04/13	Filename
			Description	Revised in accordance with the comments of various departments.
				Prepared by		Checked by	Approved by
			Name
			Signature

Draft 4		15/06/13	Filename
			Description	Update in accordance with comments of various departments from 10 May 2013 to 5 June 2013
				Prepared by		Checked by	Approved by
			Name
			Signature

					Issue Document Verification with Document				ü

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

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