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 |
087-04
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Agreement No. CE61/2007(CE) North East New Territories New Development Areas Planning and Engineering Study - Investigation |
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Contamination
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Chan |
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Draft
2 |
19/06/12 |
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Updated
with latest status of Health Risk Assessment requirement in Section 7. |
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Draft
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28/02/13 |
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Revised
in accordance with updated RODP |
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Draft
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Revised
in accordance with EPD’s comment on 19 March 2013 |
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Draft
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15/06/13 |
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Description |
Update
in accordance with comments of various departments from 10 May 2013 to 5 June
2013 |
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Prepared by |
Checked by |
Approved by |
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Name |
Various
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1.3 Statutory Legislation and Evaluation Criteria
2 Summary
of Sampling and Testing Strategy
2.1 Summary of Potentially Contaminated Sites
2.3 Proposed Sampling Locations and Depths
3.1 Soil and Groundwater Sampling
3.2 HOKLAS Accredited Laboratory
5 Interpretation
of Laboratory Testing Results
6 Investigation
of High Arsenic in KTN
6.1 Background of Investigation
6.2 Supplementary SI and Soil Sampling Schedule
7 Way
Forward for Dealing High Background Arsenic in KTN
9 Conclusion
and Recommendation
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
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
Strata Log Records of 3
Boreholes
Analytical Results of Soil
Samples
Analytical Results of
Groundwater Samples
Laboratory Testing Reports
of Soil Samples and Groundwater Samples
Historical Aerial Photos of
"Off-site" Location in KTN
Strata Log Record of
Borehole KTN-Off-site in Supplementary SI
Arsenic Cycle in Natural
Environment
Accreditation Certificate of
Brook Rank Laboratory, USA
Arsenic Specimen Testing
Reports
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.
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.
2.1 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 |
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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.
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 |
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VOCs |
SVOCs (1) |
Metals (2) |
TPH |
Cyanide (3) |
PCBs |
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Kwu Tung North (KTN) |
KTN-23b |
Chung Hing Hong, petrol station |
√ |
√ |
√ |
√ |
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KTN-35a |
Vehicle repairing workshops |
√ |
√ |
√ |
√ |
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KTN-77,78 |
Container trailer park |
√ |
√ |
√ |
√ |
√ |
√ |
|
Fanling North (FLN) |
FLN-9a |
Luen Fat, vehicle repairing workshop |
√ |
√ |
√ |
√ |
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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.
Locations |
Coordinates |
Sampling Strategy |
Estimated No. of
Samples (1) |
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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 |
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KTN-35a |
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 |
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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 |
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KTN 77,78-3 |
827989 |
840916 |
4 soil + 1 water
samples |
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KTN 77,78-4 |
828003 |
840921 |
4 soil + 1 water
samples |
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KTN 77,78-5 |
828021 |
840941 |
4 soil + 1 water
samples |
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KTN 77,78-6 |
828023 |
840925 |
4 soil + 1 water
samples |
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KTN 77,78-7 |
828014 |
840917 |
4 soil + 1 water
samples |
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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.
3.1 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 |
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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 4oC 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.
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 “
The future landuses and corresponding RBRGs of the 4 government sites
are summarized in Table
2.1.
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.
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 |
6.1 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.
6.3.1 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 |
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 1st 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.
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”.
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”.