9 land contamination

9.2 Environmental Legislation, Policies, Plans and Standards

9.2.1 Land Contamination impact assessment was conducted with reference to the “Guidance Note for Contaminated Land Assessment and Remediation” and “Guidance Notes for Investigation and Remediation of Contaminated Sites of Petrol Filling Stations, Boatyards and Car Repair /Dismantling Workshop” issued by Environmental Protection Department (EPD). In addition, the Risk-based Remediation Goals (RBRGs) stipulated in the ”Guidance Manual for Use of Risk-based Remediation Goals for Contaminated Land Management” issued by EPD (Guidance Manual) should be adopted as the criteria for assessing soil and groundwater contamination.

9.2.2 Further consideration of contamination issues is provided in Section 3 (Potential Contaminated Land Issues) of Annex 19 “Guidelines for Assessment of Impact on Sites of Cultural Heritage and Other Impacts” of the Technical memorandum on Environmental Impact Assessment Process (EIAO-TM).

9.3 Assessment Methodology

9.3.1 In order to identify and evaluate the potential contamination impacts associated with the Project, the following tasks have been undertaken:

Ÿ Desktop study to review the current and historical land uses; and

Ÿ Site inspection to confirm the existing land uses.

9.3.2 In addition, the following sources of information have been collated and reviewed:

Ÿ Aerial photographs from Lands Department;

Ÿ Ground investigation (GI) reports from Civil Engineering Development and Department (CEDD) Geotechnical Information Library;

Ÿ Hong Kong Geological Survey Map - Sheet 6 “Solid and Superficial Geology for Hong Kong & Kowloon”; and

Ÿ Records and photographs from site visit.

9.4 Description of the Environment

Site Geology and Superficial Geological Deposits

9.4.1 The nature of subsurface geology is one of the important factors of concern as contaminants, especially those associated with petroleum hydrocarbon products such as gasoline, fuels and oils, may enter the soil and groundwater through spills or leaks and migrate through the underground medium for some distances. According to the Hong Kong Geological Survey Map (Series: HGM20) – Sheet No. 6 (1:20,000 Scale) on the solid and superficial geology, the superficial geology of the assessment area was mainly fill materials and beach deposits under Holocene of Quaternary group. In general, fill materials containing natural earth and waste and beach deposits containing sands may have higher permeability and the ability of potential contaminant migration through this horizon is relatively high.

Geology and Hydrogeology

9.4.2 A review of previous GI reports undertaken at or in the vicinity of the Project boundary was conducted to obtain available information about the geological and hydrogeological conditions of the Project site. The following GI reports are reviewed:

Ÿ LRT Bridge D and Associates Works Site Investigation Report by Lam Geotechnics Limited (CEDD’s Geotechnical Information Unit Report No.10455)

Ÿ Footbridge F16 Extension Tuen Mun by Vibro (H.K.) Ltd. (CEDD’s Geotechnical Information Unit Report No.11745)

Ÿ Tuen Mun New Town, Area 1 by Scott Wilson Kirkpatrick & Partners (CEDD’s Geotechnical Information Unit Report No.7183)

Ÿ Provision of Access Facilities for the Elderly and Disabled at Existing Footbridges in New Territories- Phase I Investigation, Design and Construction Assignment, Ground Investigation Report by Geotechnics & Concrete Engineering (H.K.) Ltd. (CEDD’s Geotechnical Information Unit Report No.39222)

Ÿ N.T.D.D –Tuen Mun Road D9/Area 39 Ground Investigation Report by Vibro (H.K.) Ltd. (CEDD’s Geotechnical Information Unit Report No.4969)

Ÿ Tuen Mun New Town Castle Peak Bay by Hong Kong Malayan Drillers & Engineerings Ltd. (CEDD’s Geotechnical Information Unit Report No.724)

9.4.3 With reference to the GI reports, the general geological sequence around the Project site was mainly fill, marine deposit, alluvium and completely to highly decomposed granite. The immediate top layer of the fill was mainly yellowish brown silty fine to coarse sand with gravel. The top layer of soil was determined to be around 2-6m.

9.4.4 According to the groundwater levels recorded in some of the reviewed GI reports, the groundwater level varied from +6.3mPD near Castle Peak Road to +2.2mPD near the Kam Wah Garden. The general groundwater gradient likely flows from east to west. It was anticipated that the groundwater level was around 1m to 10m below ground surface around the assessment area.

Site History

9.4.5 Historical aerial photographs (Table 9.1) covering the study area was reviewed to evaluate any land use changes associated with potential contamination implication within the assessment area.

^{Table 9.1
Reviewed Historical Aerial Photographs}

Year	Ref. No.	Height (ft)
1949	5045	5800
1976	12410	4000
1978	23568	4000
1980	32350	4000
1982	41261	4000
1986	A06498	4000
1989	A18597	4000
1993	A36886	4000
1995	CN11048	3500
1999	CW24806	4000
2002	CW43972	4000
2006	CW1367	4000

Source of historical aerial photographs: Survey and Mapping Office, Lands Department.

9.4.6 The findings of the review of historical aerial photographs are summarized as follows:

Year 1949-1978

Ÿ The earliest aerial photo that is relevant to assessment area was taken in 1949. As shown from the aerial photo, the assessment area was an open sea. Cottages and farms were found near the Castle Peak Road in 1949. From the aerial photo of 1978, the assessment area was found to be reclaimed. TMR was also noted in the 1978 aerial photo.

Year 1980-2006

Ÿ The surrounding environment of the assessment area was found to be under development from 1980 to 1988. As shown in the aerial photos, the surrounding environment was mainly used for commercial and residential purposes.

Ÿ According to the aerial photos, Wong Chu Road Interchange and Tuen Hing Road Junction were not constructed until 1986. No apparent changes of the assessment area were found since then.

Existing Land Uses

9.4.7 A site inspection was conducted on 25 October 2007 to identify any contamination hotspots within the assessment boundary. All accessible areas were inspected as far as practicable to collect information about the current activities undertaken within the assessment area. Photo-documentation was also undertaken if possible and provided in Appendix 9.1. Findings of the site inspection are summarised as follows:

9.4.8 TMR was found to the west of the Castle Peak Road. As observed, the assessment area was mainly surrounded by residential buildings and shopping malls. Secondary schools were also found at the south western part of the assessment area. The areas within the vicinity of the assessment area have been mainly used for institution and community purposes since the known past until the current.

9.4.9 During the site inspection, a petrol filling station occupied by ESSO was found approximately 2m east from the boundary of the assessment area, located near the junction of Tuen Yan Street and Tuen Mun Road. The location of the petrol filling station is shown in Figure 9.1. According to the relevant topographic map and aerial photo reviewed, the petrol filling station has been present for more than 10 years. As observed from the site inspection, 3 dispensers were found within the filling station. Based on the information from the site personnel, a total of 4 underground fuel tanks were used for storage of diesel and petrol within the filling station. The ground was found to be paved with concrete and no apparent crack was observed during site inspection and only small areas of stains over the petrol fuelling area were observed.

9.5 Identification of Potential Sources of Environmental Impact

9.5.1 Based on the review of aerial photo, the assessment area had begun to develop since 1978. Wong Chu Road Interchange and Tuen Hing Road Junction were then found in 1986. During the site visit, surrounding environment of the assessment area was found to be mainly occupied by commercial and residential buildings for institution and community purposes. As observed, no workshop or vehicle cleaning area was found within the assessment area. Based on the information obtained, it is considered that land contamination within the assessment area is unlikely.

9.5.2 However, a petrol filling station as mentioned in Section 9.4.9 was identified at the up-gradient position of the alignment, approximately 2m beyond the assessment area boundary, during the site reconnaissance. Based on the review of aerial photo, the petrol filling station has been present for more than 10 years, which may give rise to indirect contamination concern to the nearby TMR alignment. As revealed from the staff of the petrol filling station, there are 4 underground fuel tanks for storage of diesel and petrol. Thus, the main contaminants of concern at the petrol filling station are total petroleum hydrocarbons (TPH), benzene, toluene, ethylbenzene and xylenes (BTEX) and heavy metals.

9.6 Identification of Sensitive Receivers

9.6.1 During the construction stage, construction workers might be exposed to potential contaminated materials when doing excavation and the preparation of foundation works. The principal exposure routes for workers include:

Ÿ Direct ingestion of contaminated soils through eating or drinking/ smoking on site;

Ÿ Dermal contact with contaminated soils; and

Ÿ Inhalation of contamination if the contaminants are volatile.

9.6.2 However, considering the environment of the Project area, no sensitive receivers are identified during the operation stage.

9.7 Prediction and Evaluation of Environmental Impacts

9.7.1 As the planned alignment of TMR would not be encroached upon the area of the petrol filling station and no potential contaminative sites have been identified within the assessment area during site inspection, there is no direct land contamination concern to the project.

9.7.2 Furthermore, since petrol filling station usually would execute their product lose prevention checking for the underground tanks and associated pipelines and filling facilities, possibility of unattended product lost is unlikely. Migration of contaminants from the petrol filling station to the assessment area in a down gradient direction, if any, may not be anticipated.

9.8 Mitigation Measures for Land Contamination

9.8.1 There is no direct land contamination identified in the site inspection. An indirect concern would be the petrol filling station located near the junction of Tuen Yan Street and Tuen Mun Road about 2 meters from the assessment area boundary, a preliminary land contamination survey is recommended to be conducted at the immediate down gradient from the petrol filling station, within the boundary of the assessment area, prior to the commencement of this portion of construction works. This is to serve as a baseline study of the soil and groundwater quality to ensure no adverse impacts arisen in the construction stage. Figure 9.2 showed the proposed sampling location. As a conservative approach, 3 boreholes have been proposed for the preliminary land contamination survey and a sampling and analysis programme for soil / groundwater samples should be prepared and implemented to assess the baseline condition of the underground media and the potential migration direction of the contamination.

9.8.2 The sampling and analysis of soil and groundwater should be conducted in accordance with the relevant EPD’s Guidance Note and Guidance Manual. If contamination is identified during the preliminary land contamination survey, a detailed site investigation should be conducted to confirm the presence and level of contamination (if any) in the area and possible remediation would be recommended after the SI results are obtained.

9.8.3 As a general measures, the following environmental and safety precautionary measures should be implemented and reviewed during the construction works, in order to minimize the potential health impact on the site workers:

Ÿ The use of bulk earth-moving excavator equipment would minimise construction workers’ potential contact with the contaminated materials; the requirements as stipulated in ETWB TCW No. 34/2002 for the management of excavated materials shall be followed

Ÿ Exposure to any contaminated materials can be minimised by the wearing of appropriate clothing and personal protective equipment such as gloves (when interacting directly with suspected contaminated material), providing adequate hygiene and washing facilities and preventing smoking and eating during such activities;

Ÿ Stockpiling of contaminated soil should be avoided as far as possible. If this cannot be avoided, the stockpile of contaminated materials should be segregated from the uncontaminated ones. Moreover, the contaminated materials should be properly covered with waterproof material (e.g. tarpaulin sheet) to avoid leaching of contaminants, especially during rainy season.

Ÿ Vehicles containing any excavated materials should be suitably covered to limit potential dust emissions or contaminated wastewater run-off, and truck bodies and tailgates should be sealed to prevent any leakage during transport or during wet conditions;

Ÿ Only licensed waste haulers should be used to collect and transport any contaminated material to an appropriate disposal site and procedures should be developed to ensure that illegal disposal of waste does not occur;

Ÿ Necessary waste disposal permits should be obtained, as required, from the appropriate authorities, in accordance with the Waste Disposal Ordinance (Cap 354), Waste Disposal (Chemical Waste) (General) Regulation (Cap 35), as required;

Ÿ Records of the quantities of wastes generated and disposed of should be maintained; Adequate washing facilities should be provided on site; and

Ÿ In accordance with good construction practice, silt traps should be used to reduce the impact to drainage caused by suspended solids arising from disturbed ground, or any construction materials such as cement and gravel. Groundwater should be disposed of in accordance with the Water Pollution Control Ordinance (Cap 358).

9.9 Evaluation of Residual Impacts

9.9.1 With the implementation of the recommended mitigation measures for the handling of any contaminated materials, no residual impact is expected to arise during the construction of the proposed Project.

9.10 Environmental Audit

9.10.1 A preliminary land contamination survey has been proposed at the immediate down gradient to the petrol filling station, within the boundary of the assessment area, to assess for the baseline condition of the soil and groundwater and the potential migration of contaminants towards the assessment area, if any. Details of the requirements for environmental monitoring and audit (EM&A) with respect to land contamination are provided in a stand-alone EM&A Manual.

9.11 Conclusion

9.11.1 An investigation of the historical / current land uses in respect of land contamination, including a desktop study and site inspection has been conducted around the TMR Town Centre Section.

9.11.2 Based on the site reconnaissance, there has been no potential land contamination concern within the project boundary. However, the existing petrol filling station located outside the assessment area, near the junction of Tuen Hing Street and TMR was identified as an indirect concern. This petrol filling station has been operated for over a decade and has potential of land contamination concern resulting from localised fuel leakage/ seepage. A preliminary land contamination survey is therefore proposed within boundary of the assessment area at the immediate down gradient of the petrol filling station to determine the baseline soil and groundwater conditions.

9.11.3 Mitigation measures have also been proposed for handling of the potential contaminated materials as general measures. No adverse residual impact in respect of land contamination is anticipated if necessary remediation actions are carried out at the contaminated areas confirmed by site investigation.

9.2.2 Further consideration of contamination issues is provided in Section 3 (Potential Contaminated Land Issues) of Annex 19 “Guidelines for Assessment of Impact on Sites of Cultural Heritage and Other Impacts” of the Technical memorandum on Environmental Impact Assessment Process (EIAO-TM).

9.3.2 In addition, the following sources of information have been collated and reviewed:

9.4.2 A review of previous GI reports undertaken at or in the vicinity of the Project boundary was conducted to obtain available information about the geological and hydrogeological conditions of the Project site. The following GI reports are reviewed:

9.4.5 Historical aerial photographs (Table 9.1) covering the study area was reviewed to evaluate any land use changes associated with potential contamination implication within the assessment area.

Year

Ref. No.

Height (ft)

1949

5045

5800

1976

12410

4000

1978

23568

4000

1980

32350

4000

1982

41261

4000

1986

A06498

4000

1989

A18597

4000

1993

A36886

4000

1995

CN11048

3500

1999

CW24806

4000

2002

CW43972

4000

2006

CW1367

4000

Source of historical aerial photographs: Survey and Mapping Office, Lands Department.

9.4.6 The findings of the review of historical aerial photographs are summarized as follows:

Year 1949-1978

Year 1980-2006

9.6 Identification of Sensitive Receivers

9.6.1 During the construction stage, construction workers might be exposed to potential contaminated materials when doing excavation and the preparation of foundation works. The principal exposure routes for workers include:

9.6.2 However, considering the environment of the Project area, no sensitive receivers are identified during the operation stage.

9.7.1 As the planned alignment of TMR would not be encroached upon the area of the petrol filling station and no potential contaminative sites have been identified within the assessment area during site inspection, there is no direct land contamination concern to the project.

9.8 Mitigation Measures for Land Contamination

9.8.3 As a general measures, the following environmental and safety precautionary measures should be implemented and reviewed during the construction works, in order to minimize the potential health impact on the site workers:

9.9.1 With the implementation of the recommended mitigation measures for the handling of any contaminated materials, no residual impact is expected to arise during the construction of the proposed Project.

9.11.1 An investigation of the historical / current land uses in respect of land contamination, including a desktop study and site inspection has been conducted around the TMR Town Centre Section.