Civil Engineering and Development Department and Planning Department

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

Contamination Assessment Report for Government Sites

Report Ref

087-04 | June 2013

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Job title			Agreement No. CE61/2007(CE) North East New Territories New Development Areas Planning and Engineering Study - Investigation					Job number
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Document title			Contamination Assessment Report for Government Site					File reference
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Draft 1		17/05/11	Description	First draft
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			Description	Updated with latest status of Health Risk Assessment requirement in Section 7.
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			Name	Various		Thomas Chan			Davis Lee
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Draft 5		15/06/13	Filename
			Description	Update in accordance with comments of various departments from 10 May 2013 to 5 June 2013
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Contents

Page

1 Introduction 1

1.1 Overview 1

1.2 Objectives 1

1.3 Statutory Legislation and Evaluation Criteria 1

2 Summary of Sampling and Testing Strategy 2

2.1 Summary of Potentially Contaminated Sites 2

2.2 Chemicals of Concern 3

2.3 Proposed Sampling Locations and Depths 4

3 Site Investigation Works 6

3.1 Soil and Groundwater Sampling 6

3.2 HOKLAS Accredited Laboratory 7

3.3 Strata Logging 7

4 Assessment Criteria 8

5 Interpretation of Laboratory Testing Results 9

5.1 Soil Contamination 9

5.2 Groundwater Contamination 9

6 Investigation of High Arsenic in KTN 11

6.1 Background of Investigation 11

6.2 Supplementary SI and Soil Sampling Schedule 11

6.3 Arsenic Specimen Testing 13

7 Way Forward for Dealing High Background Arsenic in KTN 17

9 Conclusion and Recommendation 18

Figures

Figure 1.1 NENT NDA Project Boundaries

Figure 2.1.1 Locations of Potentially Contaminated Sites at Government Lot in Kwu Tung North

Figure 2.1.2 Location of Potentially Contaminated Site at Government Lot in Fanling North

Figure 2.2.1 Locations of Proposed Boreholes at Government Lot in Kwu Tung North (KTN-23b)

Figure 2.2.2 Locations of Proposed Boreholes at Government Lot in Kwu Tung North (KTN-35a)

Figure 2.2.3 Locations of Proposed Boreholes at Government Lot in Kwu Tung North (KTN-77,78)

Figure 2.2.4 Locations of Proposed Boreholes at Government Lot in Fanling North (FLN-9a)

Figure 3.1.1 Actual Locations of Inspection Pits at Government Lot in Kwu Tung North (KTN-23b)

Figure 3.1.2 Actual Locations of Inspection Pits at Government Lot in Kwu Tung North (KTN-35a)

Figure 3.1.3 Actual Locations of Inspection Pits and Boreholes at Government Lot in Kwu Tung North (KTN-77,78)

Figure 3.1.4 Actual Locations of Inspection Pits and Borehole at Government Lot in Fanling North (FLN-9a)

Figurer 6.1 Locations of Potentially Contaminated Sites at Government Lot and the “Off-site Location” in Kwu Tung North

Figure 6.2.1 Actual Location of Inspection Pit KTN-23b-1 in Supplementary SI

Figure 6.2.2 Actual Location of Inspection Pit KTN-35a-1 in Supplementary SI

Figure 6.2.3 Actual Location of Inspection Pit KTN-77,78-8 in Supplementary SI

Figure 6.2.4 Actual Location of Borehole KTN-Off-site in Supplementary SI

Appendices

Appendix A

Strata Log Records of 3 Boreholes

Appendix B

RBRGs Criteria

Appendix C

Analytical Results of Soil Samples

Appendix D

Analytical Results of Groundwater Samples

Appendix E

Laboratory Testing Reports of Soil Samples and Groundwater Samples

Appendix F

Geochemical Map of Arsenic

Appendix G

Historical Aerial Photos of "Off-site" Location in KTN

Appendix H

Strata Log Record of Borehole KTN-Off-site in Supplementary SI

Appendix I

Arsenic Cycle in Natural Environment

Appendix J

Accreditation Certificate of Brook Rank Laboratory, USA

Appendix K

Arsenic Specimen Testing Reports

1 Introduction

1.1 Overview

Section 3.4.9.4 of the EIA Study Brief No.: ESB-176/2008 for the NENT NDAs project dated January 2008 issued by the EPD specified that a land contamination assessment shall be undertaken and that a Contamination Assessment Plan (CAP) shall be submitted to the EPD for endorsement prior to conducting the assessment.

The CAP prepared for 4 identified government sites (3 sites in Kwun Tung North (KTN) and 1 site in Fanling North (FLN)) with potential land contamination issue where access for site investigation is available was submitted to EPD on 2 September 2009. EPD agreed in principle of the CAP on 22 September 2009.

1.2 Objectives

This Contamination Assessment Report (CAR) and Remediation Action Plan (RAP) summarize the following issues:

· Contamination assessment program for 4 government sites;

· Investigation procedures and methodologies;

· Analytical results of soil and groundwater samples;

· Scope of any remedial work required; and

· The particular health and safety requirement that may be required during the works.

1.3 Statutory Legislation and Evaluation Criteria

This CAR and RAP is prepared in accordance with the following Technical Memorandum and Guidance Notes:

· Annex 19 of the Technical Memorandum on Environmental Impact Assessment Process (TM-EIA), Guidelines for Assessment of Impact On Sites of Cultural Heritage and Other Impacts (Section 3 : Potential Contaminated Land Issues);

· Guidance Notes for Investigation Remediation of Contaminated Sites of Petrol Filling Stations, Boatyards, and Car Repairing/Dismantling Workshops, EPD, 1999 (i.e. superseded in August 2011);

· Guidance Notes for Contaminated Land Assessment and Remediation;

· Guidance Manual for Use of Risk-Based Remediation Goals (RBRGs) for Contaminated Land Management, EPD, 2007; and

· Practice Guide for Investigation and Remediation of Contaminated Land, EPD, 2011.

2 Summary of Sampling and Testing Strategy

2.1 Summary of Potentially Contaminated Sites

Locations of these 4 potentially contaminated government sites are given in Figures 2.1.1 – 2.1.2 and summarised in Table 2.1.

Table 2.1: Potentially Contaminated Government Sites

Site No.	Location	Current Land Use	Lot No.	Potentially Sources of Contamination	Approximate Area (m²)	Recommended No. of Boreholes^(1)	Future Landuse (Corresponding RBRGs)
KTN-23b	Chung Hing Hong, petrol station (partially paved) Shell Gas (North of Castle Peak Road)	Fuelling Area/ Fuel Storage	DD95–T19636	Possible spillage/ leakage of fuel	203	2	Amenity (Public Park)
KTN-35a	Vehicle repair and maintenance (partially unpaved) (North of Ma Tso Lung Road)	Vehicle Repair	STT344	Potential spillage/ leakage of fuels and oils during maintenance activities	632	2	Public Rental Housing, Open Space (Urban Residential)
KTN-77	Container trailer park with vehicle repairing workshop (unpaved). Metal workshop (unpaved). (area behind saw mills) (Behind Saw Mills KTN-76)	Heavy Vehicle Parking and Repairing. Metal Painting on Unpaved Ground	No record	Possible spillage/ leakage of fuels, oils and other chemicals during previous storage and dumping activities (i.e. oil stain observed in some area)	5,421	8	Public Rental Housing, Open Space (Urban Residential)
KTN-78	Combined with 77		No record
FLN-9a	Luen Fat, vehicle repairing workshop (paved) (To the east of Woodland Crest)	Vehicle Repair	DD51–STT435	Possible spillage/ leakage of fuels and oils during maintenance activities	343	3	Road network (Lower of Industrial or Public Park)

Note 1: All 4 government sites have been accessed and hotspots have been identified.

2.2 Chemicals of Concern

The proposed sampling and testing schedule for the chemicals of concern (COCs) at each potentially contaminated government site are summarized in Table 2.2

Table 2.2: Sampling and Testing Schedule

Locations		Existing Landuse	Testing Parameters
			VOCs	SVOCs ^(1)	Metals ^(2)	TPH	Cyanide ^(3)	PCBs
Kwu Tung North (KTN)	KTN-23b	Chung Hing Hong, petrol station	√	√	√	√
	KTN-35a	Vehicle repairing workshops	√	√	√	√
	KTN-77,78	Container trailer park	√	√	√	√	√	√
Fanling North (FLN)	FLN-9a	Luen Fat, vehicle repairing workshop	√	√	√	√

Note 1: Only 11 out of 19 SVOCs parameters are required for groundwater sample.

Note 2: Only “Mercury” test is required for groundwater sample.

Note 3: “Cyanide” is not required for groundwater sample.

· Volatile Organic Compounds (VOCs): acetone, benzene, bromodichloromethane, 2-butanoe, chloroform, ethylbenzene, methyl tert-butyl ether, methylene chloride, styrene, tetrachloroethene, toluene, trichloroethene, xylenes (total)

· Semi Volatile Organic Compounds (SVOCs): acenaphthene, acenaphthylene, anthracene, benzo(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(g.h.i)perylene, benzo(k)fluoranthene, bis-(2-ethylhexyl)phthalate, chrysene, dibenzo(a,h)anthracene, fluoranthene, fluorene, hexachlorobenzene, indeno(1,2,3-cd)pyrene, naphthalene, phenanthrene, phenol, pyrene

· Metals: antimony, arsenic, barium, cadmium, chromium III, chromium VI, cobalt, copper, lead, manganese, mercury, molybdenum, nickel, tin, zinc

· Total Petroleum Hydrocarbon (TPH): Carbon Ranges C6-C8, C9-C16 and C17-C35

· Polychlorinated Biphenyls (PCBs)

· Cyanide: Cyanide, free (i.e. only for soil samples)

The selection of chemicals of concern (COCs) for the 4 potentially contaminated government sites was based on the historical land use and the information collected during the site survey with reference to RBRGs and EPD’s Guidance Notes for Investigation and Remediation of Contaminated Sites of Petrol Filling Stations, Boatyards, and Car Repairing/Dismantling Workshops. However, as only 4 government lot sites are accessible and allowed for intrusive site investigation throughout the NDAs at this stage, it was proposed to use a board testing approach, including VOCs, SVOCs, full-list Metals and TPH for these 4 accessible government lot sites in order to gather as much data as possible. PCBs and Cyanide are also proposed for site KTN-77,78 due to the worse site observation. The gathered data could provide the Project Proponent (PP) a preliminary picture and understanding of land contamination level/extent of other potentially contaminated sites with similar industrial activity.

2.3 Proposed Sampling Locations and Depths

The sampling locations and sampling depths proposed in the CAP for identified government sites are in Table 2.3. The proposed sampling locations are shown in Figures 2.2.1 to 2.2.4.

Table 2.3: Sampling strategy

Locations			Coordinates		Sampling Strategy		Estimated No. of Samples ^(1)
NDA	Site ID	Borehole No.	Easting	Northing	Termination Level for Environmental Sampling (bgl) (mbgl) ^(1)	Frequency of Sampling Analysis ^(2)
Kwu Tung North	KTN-23b (Figures 2.1.1 & 2.2.1)	KTN 23b-1	828497	840470	14.20 - (Drillhole Record at (E828509.67, N840339.42) in Jan 95 was referred. (i.e. ALLUVIUM ended at Saprolite layer of 14.10mbgl)	Drilling of a borehole and collection of soil samples at depths of 0.5, 1.5 & 3.0, and then at 3.0m intervals to the termination level for environmental sampling. One groundwater sample if encountered.	6 soil + 1 water samples
		KTN 23b-2	828504	840458			6 soil + 1 water samples
	KTN-35a (Figure 2.1.1, 2.2.2)	KTN 35a-1	828455	841025	6.45 - (Drillhole Record at (E828480.29, N841189.88) in April 97 was referred. (i.e. COLLUVIUM ended at Saprolite layer of 6.45mbgl)		4 soil + 1 water samples
		KTN 35a-2	828468	841029			4 soil + 1 water samples
	KTN-77,78 (Figures 2.1.1 & 2.2.3)	KTN 77,78-1	827968	840911	1.50 + 4.50 = 6.00 (Drillhole Record at (E827999.14, N840957.17) in Nov/Dec 97 was referred. Owing to the relative thin COLLUVIUM layer ended at Saprolite layer of 1.5m, it is recommended to extend the Termination Level into the first layer of Saprolite (Grade V slightly gravelly sandy SILT/CLAY) from 1.5 to 6.0m		4 soil + 1 water samples
		KTN 77,78-2	827983	840935			4 soil + 1 water samples
		KTN 77,78-3	827989	840916			4 soil + 1 water samples
		KTN 77,78-4	828003	840921			4 soil + 1 water samples
		KTN 77,78-5	828021	840941			4 soil + 1 water samples
		KTN 77,78-6	828023	840925			4 soil + 1 water samples
		KTN 77,78-7	828014	840917			4 soil + 1 water samples
		KTN 77,78-8	828025	840907			4 soil + 1 water samples
Fanling North	FLN-9a (Figure 2.1.2 & 2.2.4)	FLN 9a-1	832062	840917	10.3 - (Drillhole Record at (E832033, N840928) in Aug 88 was referred. (i.e. ALLUVIUM stopped at Saprolite layer of 10.3mbgl)		5 soil + 1 water samples
		FLN 9a-2	832073	840915			5 soil + 1 water samples
		FLN 9a-3	832075	840906			5 soil + 1 water samples

Note 1: The proposed Termination Levels for Environmental Sampling and Estimated No. of Samples are just for reference purpose. The exact termination levels and no. of soil/ groundwater samples of each borehole should be decided by the on-site Land Contamination Specialist.

Note 2: Historical drillhole records indicated that the water levels in the nearby areas of proposed boreholes are approximately ranged from 2 to 5 mbgl, hence, it is very likely to encounter the groundwater table of each proposed borehole.

3 Site Investigation Works

3.1 Soil and Groundwater Sampling

3.1.1 Borehole and Inspection Pit Locations

Site investigation works were carried out by Fugro Geotechnical Services Limited between 21 September 2009 and 22 January 2010. Due to the site constraints and limitations (i.e. all 4 government sites were still in operation during SI), borehole drilling is not feasible at most of the hotspot locations, and therefore inspection pits (IP) were excavated at those locations in order to investigate the contamination levels of first 1.5m top soil. The actual locations of the boreholes / IP are slightly shifted from the proposed locations due to the site constraint and limitation. Nevertheless, the entire SI programme was supervised by the on-site Land Contaminated Specialist to ensure the representative locations are chosen. The actual locations and depths of the boreholes and inspection pits at 4 government sites are summarized in Table 3.1.

Table 3.1: Sampling location and drilling depths

Site ID (SI Date)	Borehole / IP No.	As-Built Co-ordinates of Borehole / IP		Termination Level for Env Sampling (mbgl)	Ground Level (mPD)	Remarks
		Easting	Northing
KTN-23b (09/11/09 – 12/11/09)	KTN-23b-1	828497.85	840462.38	1.5	+10.49	Inspection Pit
	KTN-23b-2	828503.04	840458.03	1.5	+10.38	Inspection Pit
KTN-35a (22/01/10)	KTN-35a-1	828454.44	841022.66	1.5	+14.26	Inspection Pit
	KTN-35a-2	828446.18	841024.31	1.3	+13.90	Inspection Pit
KTN-77,78 ^(1) (09/11/09 – 13/11/09)	KTN-77,78-1	827965.56	840910.70	6.0	+18.36	Borehole
	KTN-77,78-2	827981.55	840941.59	0.9	+18.60	Inspection Pit
	KTN-77,78-3	827996.84	840919.21	1.0	+18.14	Inspection Pit
	KTN-77,78-4	828013.88	840942.95	6.0	+17.70	Borehole
	KTN-77,78-5	828026.23	840943.12	1.5	+17.30	Inspection Pit
	KTN-77,78-6	828020.79	840922.13	1.5	+16.86	Inspection Pit
	KTN-77,78-7	828019.08	840916.88	1.5	+16.88	Inspection Pit
	KTN-77,78-8	828021.90	840908.37	1.5	+16.72	Inspection Pit
FLN-9a ^(2) (21/09/09 – 23/09/09)	FLN-9a-1	832060.05	840921.19	1.5	+9.26	Inspection Pit
	FLN-9a-2	832072.57	840914.91	1.5	+9.40	Inspection Pit
	FLN-9a-3	832075.51	840906.51	6.0	+9.35	Boreholes

Note 1: IP KTN-77,78-2 and KTN-77,78-3 were terminated at 0.9 and 1.0mbgl respectively due to encounter of boulder.

Note 2: The borehole / IP no of FLN-9a-1 and FLN-9a-3 were swap with each other during the SI works.

The as-built drawing showing the actual boreholes / IP locations are given in Figure 3.1.1 to 3.1.4

3.1.2 Soil Sampling

Disturbed soil samples were generally collected at about 0.5, 1.0 and 1.5 meter below ground level (mbgl) at most of the IP except KTN-77,78-2 and KTN-77,78-3 (i.e. refer to Table 3.1 for details). Soil samples at the depths of 3.0 mbgl and 6.0 mbgl were also collected at the locations with boreholes drilling (i.e. KTN-77,78-1, KTN-77,78-4 and FLN-9a-3).

3.1.3 Groundwater Sampling

After completion of soil sampling, groundwater samples were collected at the 3 boreholes (i.e. KTN-77,78-1, KTN-77,78-4 and FLN-9a-3) by a Teflon bailer. No free product was encountered during the groundwater sampling.

3.1.4 Decontamination Procedures

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.

3.2 HOKLAS Accredited Laboratory

The collected soil and groundwater 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 “Wellab Ltd” (i.e. accredited under Hong Kong Laboratory Accreditation Scheme (HOKLAS)) and its sub-contracting laboratory “Maxxam Analytics” (i.e. accredited by HOKLAS’s Mutual Recognition Arrangement Partners) in Canada. All soil and groundwater samples were analyzed in accordance with the analysis schedules detailed in Table 2.2.

3.3 Strata Logging

Strata logging for 3 boreholes KTN-77,78-1, KTN-77,78-4 and FLN-9a-3 was undertaken during the course of drilling and sampling by qualified geologists. The logs included the general stratigraphic descriptions, depth of soil sampling, and sample notation etc.

The strata logs of 3 boreholes are given in Appendix A.

4 Assessment Criteria

The chemicals of concern (COCs) listed in EPD’s Guidance Manual for Use of Risk-Based Remediation Goals (RBRGs) for Contaminated Land Management were referred to when proposing the analytical parameters of VOCs, SVOCs, Metals, TPH, PCBs, and Cyanide. The RBRGs for soil and soil saturation limits and RBRGs for groundwater and groundwater solubility limits are given in Appendix B.

The RBRGs have developed four different post-restoration land uses, namely “Urban Residential”, “Rural Residential”, “Industrial” and “Public Parks”, to reflect the actual settings which people could be exposed to contaminated soil or groundwater. Definition of post-restoration land uses are given in EPD’s Guidance Note for Contaminated Land Assessment and Remediation and RBRGs Guidance Manual.

The future landuses and corresponding RBRGs of the 4 government sites are summarized in Table 2.1.

5 Interpretation of Laboratory Testing Results

5.1 Soil Contamination

A total of 49 soil samples were collected from 15 identified hotpots at 4 government sites (i.e. 3 in KTN and 1 in FLN) from 21 September 2009 to 22 January 2010. All available laboratory testing results of the soil samples have been reviewed.

The testing results indicated that all the soil samples were below the value of RBRG for Rural Residential (i.e. the stringent set of RBRGs for VOCs, SVOCs, Metals, TPH, PCBs, Cyanide) except the concentration of metal “Arsenic (As)” in 35 soil samples collected from 12 identified hotspots at 3 government sites in KTN that exceeded the RBRGs of Rural Residential to Industrial land uses. The laboratory testing results exceeding the RBRGs is summarized in Table 5.1. The testing results of the soil samples are detailed in Appendix C, and the laboratory testing reports are given in Appendix E.

5.2 Groundwater Contamination

Groundwater samples were taken from 3 boreholes (i.e. 1 at FLN-9a and 2 at KTN-77,78). The testing results indicated that none of the groundwater samples exceeded the RBRG levels for Rural Residential land use. Groundwater table was not encountered in the sites KTN-23b and KTN-35a. The testing results of the groundwater samples are detailed in Appendix D, and the laboratory testing reports are given in Appendix E.

Table 5.1: Summary of soil samples exceeding RBRGs

Site ID	Hotspot No.	Depth of Soil Sampling (mbgl)	Contaminant	Concentration (mg/kg dry soil)	RBRGs of Arsenic (mg/kg dry soil)
KTN-23b	KTN-23b-1	0.5	Arsenic	42	Rural Residential : 21.8 Urban Residential : 22.1 Public Parks : 73.5 Industrial : 196
		1.0	Arsenic	69
		1.5	Arsenic	160
	KTN-23b-2	0.5	Arsenic	43
		1.0	Arsenic	120
		1.5	Arsenic	120
KTN-35a	KTN-35a-1	0.5	Arsenic	25
		1.0	Arsenic	110
		1.5	Arsenic	56
	KTN-35a-2	0.5	Arsenic	24
		1.0	Arsenic	57
		1.3	Arsenic	110
KTN-77,78	KTN-77,78-1	0.5	Arsenic	110
		1.0	Arsenic	130
		1.5	Arsenic	78
		3.0	Arsenic	210
		6.0	Arsenic	110
	KTN-77,78-2	0.5	Arsenic	170
		0.9	Arsenic	220
	KTN-77,78-3	0.5	Arsenic	120
	KTN-77,78-4	0.5	Arsenic	75
		1.0	Arsenic	110
		1.5	Arsenic	100
	KTN-77,78-5	0.5	Arsenic	130
		1.0	Arsenic	160
		1.5	Arsenic	97
	KTN-77,78-6	0.5	Arsenic	270
		1.0	Arsenic	330
		1.5	Arsenic	100
	KTN-77,78-7	0.5	Arsenic	300
		1.0	Arsenic	380
		1.5	Arsenic	340
	KTN-77,78-8	0.5	Arsenic	410
		1.0	Arsenic	430
		1.5	Arsenic	400

6 Investigation of High Arsenic in KTN

6.1 Background of Investigation

As presented in Table 5.1, high arsenic levels (i.e. up to over 400mg/kg which is about 20 times of the acceptable limit (21.8 mg/kg) specified in the RBRGs for Rural Residential use) were recorded at 3 government sites in KTN. 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.

Desks-top review of geochemistry in northern New Territories has been conducted. In accordance with “Geochemical Atlas of Hong Kong, GEO 1999”, high levels of arsenic were recorded in the Lok Ma Chau (117-492ppm), Ngau Tam Mei (118-922ppm), Lin Tong Mei (149-1145ppm) and Pat Heung (124-494ppm). The Geochemical Map of Arsenic also shows a board distribution pattern of high Arsenic levels in northern New Territories which indicated the high natural background level of Arsenic in this region include KTN. The Geochemical Map of Arsenic is given in Appendix F.

Although the arsenic could be contributed by the application of pesticide during the agricultural age in KTN, both the board detection of high Arsenic levels at 3 government sites and its continuity at different soil depths suggested that it is very likely the high natural background instead of industrial/commercial contamination.

In order to investigate the toxicity of high Arsenic levels detected in KTN, a supplementary Env SI with comprehensive “Arsenic Specimen” testing was conducted for the 3 government sites in KTN. An “Off-site” Location in KTN (i.e. a location without significant human and industrial activities base on the review of historical aerial photos) is also selected to provide further “background” information of Arsenic level in KTN. The historical aerial photos showing the “Off-site” Location is given in Appendix G.

6.2 Supplementary SI and Soil Sampling Schedule

The supplementary SI works were carried out by Fugro Geotechnical Services Limited between on 30 September 2010 and 5 October 2010. The inspection pit with highest Arsenic level at each of the 3 government lot sites (i.e. KTN-23b-1, KT-35a-1 and KTN-77,78-8) were selected for supplementary SI and soil sampling and testing. The actual supplementary SI and soil sampling schedule of these 3 locations and “KTN-Off-site” location is summarized in Table 6.1. Locations of these 3 government sites and “KTN-Off-site” are given in Figures 6.1. The as-built drawing showing the actual boreholes / IP locations of supplementary SI are given in Figure 6.2.1 to 6.2.4. The strata log of borehole “KTN-Off-site” is given in Appendix H.

Table 6.1: Actual supplementary SI and soil sampling strategy

Locations			Coordinates		Sampling Schedule		No. of Soil Samples Collected	Ground Level (mPD)
NDA	Site ID	Borehole / IP No. ^(1)	Easting	Northing	Termination Level for Environmental Sampling (mbgl)	Frequency of Sampling Analysis
Kwu Tung North	KTN-23b (30/09/10)	KTN 23b-1	828497.92	840461.28	1.5 (i.e. by Inspection Pit)	Excavation of inspection pit to the depths of 1.5m. Collection of soil samples at depths of 0.5, 1.0 and 1.5m.	3	10.48
	KTN-35a (30/09/10)	KTN 35a-1	828453.68	841023.31	1.5 (i.e. by Inspection Pit)		3	14.26
	KTN-77,78 (30/09/10)	KTN 77,78-8	828021.86	840907.36	1.5 (i.e. by Inspection Pit)		3	16.90
	Off Site Location (30/09/10 – 05/10/10)	KTN-Off Site	827801.81	840974.84	21.45 (i.e. 0m – 1.5m by inspection pit. 1.5m – 21.0m by borehole drilling)	Excavation of inspection pit, and then drilling of borehole. Collection of soil samples at depths of 0.5, 1.5, 3.0, 6.0, 9.0, 12, 15, 18 and 21m.	9	26.62

Note 1: The IPs KTN-23b-1, KTN-35a-1 and KTN-77,78 were selected for supplementary SI as they were the IPs with highest Arsenic level recorded in previous SI. The actual locations of these 3 IPs were approximately 1m shifted from their original locations in previous SI as their original locations have been disturbed in previous SI.

Similar technical procedures such as decontamination requirements and soil sampling procedures in previous SI have been adopted during the supplementary SI.

6.3 Arsenic Specimen Testing

6.3.1 Arsenic Chemistry

Arsenic, with atomic number 33, and situated in Group 15 of the periodic table, may exist in four different oxidation states which include (-III), (0), (III) and (V). However, oxidized As(III) and As(V) are the most widespread forms in nature. Arsenate, As(V), is the prevalent form in soils under oxidizing conditions, and dominates the soil solid phase in natural environment. As(V) is the least toxic of inorganic form of arsenic. Arsenite, As(III), on the other hand, is expected to be primary form of As encountered in waste environments and under reducing conditions, such as water-saturated soils or soils with significant organic matter or waste. As(III), is known to be the most toxic of inorganic form of arsenic, and is more mobile than As(V). In general, inorganic As species are more mobile and toxic than organic forms to living organisms, including plants, animals and humans. In view of high toxicity of inorganic arsenic, especially the As(III), the arsenic specimen test will focus on the testing of its inorganic species.

6.3.2 Laboratory Testing of Soil Samples

Total 19 soil samples were collected during the supplementary SI. All collected soil samples were tested by local laboratory for “Total Arsenic”. Based on the testing results of Total Arsenic, 13 soil samples were then be delivered to oversea laboratory for analysis of “Arsenic Speciation”. The details of “Arsenic Speciation” analysis is given in Table 6.2. The Arsenic Cycle in natural environment is shown in Appendix I.

Table 6.2: Arsenic specimen test

Analyte	Method
Total Arsenic	EPA 6020
Arsenite, As(III)	EPA 1632, Modified
Arsenate, As(V)	By difference of “Inorganic Arsenic” and “Arsenite”
Inorganic Arsenic	EPA 1632, Modified
Monomethylarsonic acid (MMA) & Dimethylarsinic acid (DMA)	EPA 1632, Modified

Reporting Limits:

· Total Arsenic : 1mg/kg

· Arsenic Speciation: 0.01 mg/kg for each analyte (on wet weight basis)

6.3.3 Accreditation Status of Laboratory

The collected soil samples were delivered to a local HOKLAS accredited environmental testing laboratory “ALS Technichem (HK) Ltd” for the testing of “Total Arsenic”.

However, as there was no local laboratory could conduct the arsenic specimen test, the selected soil samples were shipped to ALS’s sub-contractor “Brook Rank Laboratory” in USA for the testing of “Arsenic Speciation”. Brook Rank Laboratory is accredited by several international laboratory accreditation bodies such as the National Environmental Laboratory Accreditation Program (NELAP) through the State of Florida Department of Health, Bureau of Laboratories (E87982), and the Department of Ecology of The State of Washington, USA. The accreditation by the Department of Ecology of The State of Washington, USA is accepted by EPD for the sediment testing, so it is considered acceptable in this high arsenic investigation while it is not the member of HOKLAS’s Mutual Recognition Partners Arrangement. The accreditation certificates of Brook Rank Laboratory are attached in Appendix J.

6.3.4 Laboratory Testing Results

The arsenic specimen testing results is summarized in Table 6.3. The laboratory testing reports are given in Appendix K.

The Total Arsenic levels of supplementary SI soil samples collected at 3 government lot sites are comparable with the testing results of previous SI. On the other hand, high Total Arsenic level was also detected at all sampling depths of the Off-site location ranged from 114 mg/kg to 947 mg/kg. It should be noted that the highest Total Arsenic level, 947 mg/kg, was detected at the depth of 18.0-18.45 mbgl, which indicated that the natural background level of Total Arsenic is extremely high in KTN.

The arsenic specimen testing results revealed that the concentration of Inorganic Arsenite As(III), the most toxic inorganic form of arsenic, are negligible in all soil samples, ranged from 0.122 mg/kg to 2.37 mg/kg, which only count for less than 0.5% of the Total Arsenic content.

The testing results also revealed that the arsenic level in soil samples was dominated by Inorganic Arsenate As(V), the least toxic inorganic form of arsenic, which contributed approximately 80 to 95% of Total Arsenic. As mentioned in Section 6.3.1, Inorganic Arsenate As(V) dominates the soil solid phase in natural environment, and the testing results shown the similar natural soil condition.

The remaining arsenic portion was mainly the organic arsenic Monomethylarsonic acid (MMA) and Dimethylarsinic acid (DMA).

Table 6.3: Summary of arsenic specimen testing results

Location ID	Sampling Depths (mbgl)	As (mg/kg) from 1^st SI (Tested by Wellab )	As (mg/kg) from Supplementary SI (Tested by ALS)	RBRGs of Arsenic (mg/kg dry soil)	Soil Type*	Selected for As Speciation Test	Arsenic Specimen Test
							As (III) (mg/kg)	As (V) (mg/kg)	Inorganic As** (mg/kg)	MMAs*** (mg/kg)	DMAs*** (mg/kg)
KTN-23b-1	0.5	42	72	Rural Residential : 21.8 Urban Residential : 22.1 Public Parks : 73.5 Industrial : 196	Fill materials plus clay soil	- -	- -	- -	- -	- -	- -
	1.0	69	312			√	0.912	214	215	9.18	11.5
	1.5	160	115			√	0.345	129	129	8.74	10.9
KTN-35a-1	0.5	25	58		Fill materials plus clay soil	√	0.122	18.5	18.6	7.66	9.57
	1.0	110	53			- -	- -	- -	- -	- -	- -
	1.5	56	88			√	0.288	79.2	79.5	8.68	10.8
KTN-77,78-8	0.5	410	429		Fill materials plus clay soil	- -	- -	- -	- -	- -	- -
	1.0	430	686			√	1.89	636	638	10.4	12.9
	1.5	400	471			√	2.05	473	475	9.31	11.6
KTN-Off-site	0.5	- -	159		FILL materials	- -	- -	- -	- -	- -	- -
	1.0	- -	185			√	1.54	177	179	8.33	10.4
	1.5	- -	114			- -	- -	- -	- -	- -	- -
	3.0 - 3.45	- -	184		Firm, slightly sandy, very clayey SILT	√	0.606	179	180	10.3	12.9
	6.0 - 6.45	- -	221			√	0.434	179	179	9.77	12.2
	9.0 - 9.45	- -	267			√	0.593	201	202	10.0	12.5
	12.0 - 12.45	- -	180			- -	- -	- -	- -	- -	- -
	15.0 - 15.45	- -	233			√	0.683	225	226	40.0	50.0
	18.0 - 18.45	- -	947			√	2.37	1200	1200	9.30	11.6
	21.0 - 21.45	- -	473			√	1.46	486	487	42.7	53.4

Note: All testing results are reported in dry-weight basis

* The soil type of Inspection Pits KTN-23b-1, KTN-35a-1 and KTN-77,78-8 is classified by observation on-site.

** Inorganic As = As (III) + As (V)

*** Monomethylarsonic acid (MMAs) and Dimethylarsinic acid (DMAs) are both organic arsenic

It should be noted that in some of the tested samples, the concentration of total arsenic is lower than the summing concentration of the arsenic speciation. The likely cause of the anomaly between the results is sample heterogeneity and the analytical precision. Detail explanation of the anomaly is given in Appendix K.

7 Way Forward for Dealing High Background Arsenic in KTN

Soil samples have been further collected for arsenic testing from 17 more boreholes in KTN NDA in conjunction with the Phase 2 GI for the NENT NDAs works between February and August 2011. In order to further investigate the land contamination at KTN NDA after Phase 2 GI, further GI (i.e. Arsenic GI), comprising 18 boreholes, and associated LT were also 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) should be carried out focusing on two major exposure paths, namely inhalation and ingestion of As, during the construction and operation stages respectively.

The summary of Phase 2 GI and Arsenic GI programmes, and the health risk assessment findings on the health risk analysis on the ingestion of soil containing arsenic and inhalation of arsenic-containing dust are given in the “Health Risk Assessment Report for High Arsenic Soil in Kwu Tung North New Development Area”.

9 Conclusion and Recommendation

Site investigation works involving sampling and testing of soil and groundwater were conducted from 21 September 2009 to 22 January 2010 with reference to the CAP for 4 identified government sites that EPD indicated no further comment in September 2009.

Groundwater samples were taken from 3 boreholes (i.e. 1 at FLN-9a and 2 at KTN-77,78). The testing results indicated that none of the groundwater samples exceeded the RBRG levels for Rural Residential land use. Remediation of groundwater is not required.

A total of 49 soil samples were collected from 15 identified hotpots at 4 government sites (i.e. 3 in KTN and 1 in FLN) from 21 September 2009 to 22 January 2010. The testing results indicated that all the soil samples were below the value of RBRG for Rural Residential (i.e. the stringent set of RBRGs for VOCs, SVOCs, Metals, TPH, PCBs, Cyanide) except the concentration of metal “Arsenic (As)” in 35 soil samples collected from 12 identified hotspots at 3 government sites in KTN that exceeded the RBRGs of Rural Residential to Industrial land uses. As 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.

Desks-top review of geochemistry in northern New Territories has been conducted. In accordance with “Geochemical Atlas of Hong Kong, GEO 1999”, high levels of arsenic were recorded in the Lok Ma Chau (117-492ppm), Ngau Tam Mei (118-922ppm), Lin Tong Mei (149-1145ppm) and Pat Heung (124-494ppm). The Geochemical Map of Arsenic also shows a board distribution pattern of high Arsenic levels in northern New Territories which indicated the high natural background level of Arsenic in this region include KTN.

A supplementary Env SI with comprehensive “Arsenic Specimen” testing was conducted for the 3 government sites in KTN for investigating the toxicity of high Arsenic levels detected in KTN. An “Off-site” Location in KTN (i.e. a location without significant human and industrial activities base on the review of historical aerial photos) is also selected to provide further “background” information of Arsenic level in KTN.

The Total Arsenic levels of supplementary SI soil samples collected at 3 government lot sites are comparable with the testing results of previous SI. On the other hand, high Total Arsenic level was also detected at all sampling depths of the Off-site location ranged from 114 mg/kg to 947 mg/kg. The highest Total Arsenic level, 947 mg/kg, was detected at the depth of 18.0-18.45 mbgl, which indicated that the natural background level of Total Arsenic is extremely high in KTN.

The arsenic specimen testing results revealed that the concentration of Inorganic Arsenite As(III), the most toxic inorganic form of arsenic, are negligible in all soil samples, ranged from 0.122 mg/kg to 2.37 mg/kg, which only count for less than 0.5% of the Total Arsenic content.

The testing results also revealed that the arsenic level in soil samples was dominated by Inorganic Arsenate As(V), the least toxic inorganic form of arsenic, which contributed approximately 80 to 95% of Total Arsenic. The inorganic Arsenate As(V) usually dominates the soil solid phase in natural environment, and the testing results shown the similar natural soil condition.

Soil samples have been further collected for arsenic testing from 17 more boreholes in KTN NDA in conjunction with the Phase 2 GI for the NENT NDAs works between February and August 2011. In order to further investigate the land contamination at KTN NDA after Phase 2 GI, further GI (i.e. Arsenic GI), comprising 18 boreholes, and associated LT were also 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) should be carried out focusing on two major exposure paths, namely inhalation and ingestion of As, during the construction and operation stages respectively.

The summary of Phase 2 GI and Arsenic GI programmes and the health risk assessment findings on the health risk analysis on the ingestion of soil containing arsenic, and inhalation of arsenic-containing dust are given in the “Health Risk Assessment Report for High Arsenic Soil in Kwu Tung North New Development Area”.