7. LAND CONTAMINATION IMPACT

7.1 Introduction

7.1.1.1 Past and present activities or land uses may cause land contamination problems which may affect the potential of future development. The overall objectives of this assessment is to provide a clear and detailed account of the present use of the land and the relevant past land history in relation to possible land contamination.

7.1.1.2 A Contamination Assessment Plan (CAP) is also prepared as part of this study for conducting detailed land contamination site investigation to determine the nature and the extent of the land contamination after the project sites have been resumed for the proposed project at a later stage.

7.2 Environmental Legislation, Policies, Plans, Standards and Criteria

7.2.1.1 Assessments of land contamination and the potential impacts are guided by the EPD's Professional Persons Environmental Consultative Committee Practice (ProPECC) Note 3/94 - Contaminated Land Assessment and Remediation, the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM), and the EPD's 1999 Guidance Notes for Investigation and Remediation of Contaminated Sites of Petrol Filling Stations, Boatyards, and Car Repair/Dismantling Workshops (Guidance Notes). In accordance with these documents, the assessment evaluation should:
· provide a clear and detailed account of the present use of the land in question and the relevant past land use history, in relation to possible land contamination;
· identify those areas of potential contamination and associated impacts, risks or hazards; and
· as required, submit a plan to evaluate the actual contamination conditions for soil and/or groundwater.

7.2.1.2 Under EIAO-TM Section 3 Potential Contaminated Land Issues of Annex 19 Guidelines for Assessment of Impacts on Sites of Cultural Heritage and Other Impacts and the Guidance Notes, consideration should be given to a number of potentially contaminating historical land uses, including petrol filling stations, oil installations, shipyards/boatyards, car repairing and dismantling, power plants and gas works.

7.2.1.3 The historical land uses of the site should be considered and reviewed for the potential to cause or to have caused land contamination. Once suspected land uses are identified, a Contamination Assessment Plan (CAP) is required for endorsement by EPD before conducting the land contamination assessment. Results will be compiled in a Contamination Assessment Report (CAR). If land contamination is confirmed, a Remediation Action Plan (RAP) has to be prepared to formulate necessary remedial measures. Any contaminated site should be cleaned up according to the approved RAP prior to any development or redevelopment.

7.2.1.4 The ProPECC PN 3/94 provides the technical guidance on the preparation of CAP, CAR and RAP. It sets out the requirements for proper site assessment and management of contaminated sites, the guidelines on site assessments and outlines of the practical remedial measures. This ProPECC Note also makes reference to criteria used for soil and groundwater in the "Dutch Ministry of Housing, Planning and Environmental Soil and Groundwater Standards" (the Dutch Guidelines) (1994) by the Netherlands for contaminated land.

7.2.1.5 The following legislation, documents and guidelines may also cover or have some bearing upon land contamination and the handling, treatment and disposal of contaminated waste in Hong Kong:
· Water Pollution Control Ordinance (WPCO);
· Waste Disposal Ordinance (Cap 354);
· Waste Disposal (Chemical Waste) (General) Regulation (Cap 354); and
· Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes, Environmental Protection Department (1992).

7.3 Assessment Methodology

7.3.1.1 The assessment methodology is based on the Practice Note ProPECC PN3/94 Contaminated Land Assessment and Remediation issued by EPD. The approach of the assessment involves a site history review including an account of the past and present land uses. If any potential contamination is identified, further surveys and detailed investigations to characterise the contaminated area will be formulated.

7.4 Baseline Conditions

7.4.1.1 The key items of this project include the expanded and upgraded San Wai Sewage Treatment Works, the expanded Ha Tsuen Pumping Station, and the emergency bypass culvert connecting the San Wai Sewage Treatment Works and the existing drainage channels. Four alternative alignments of the emergency bypass culvert are considered in this EIA. The locations of these key project items are shown in Figure 1.3.

7.4.1.2 Figure 7.1 shows the aerial photo of the existing conditions in the vicinity of the proposed site of the expanded San Wai STW. As shown in the aerial photo, the existing land uses within the expansion site include the existing San Wai STW to the south, two fishponds to the north and a container yard to the east. Existing land uses adjacent to the expansion site include some open storage areas, container yards, farm, and some vegetated areas. Photos of the existing land uses within and around the expansion site of the San Wai STW are shown in Figure 7.3.

7.4.1.3 Figure 7.2 shows the aerial photo of the existing conditions in the vicinity of the proposed site of the expanded Ha Tsuen Pumping Station. In the current design, the expanded pumping station will be entirely located within the currently site boundary of the Ha Tsuen Pumping Station and no additional land will be required outside the existing pumping station site boundary. As shown in the aerial photo, the expansion site only include the existing pumping station building to the south and the tree planting area to the north. Potential land contamination activities carried out within the existing pumping station include day-to-day maintenance and repair works. Given that these activities were and will be carried out with good practices and management, the potential of land contamination impacts is considered minimal. In view of the above, the potential land contamination impacts associated with the expansion site of the Ha Tsuen Pumping Station is considered insignificant.

7.4.1.4 With reference to Section 1.2 of this report, four alternative alignments of the emergency bypass culvert have been proposed and are shown in Figure 1.3. Some sections of the proposed emergency bypass culvert will cross over the proposed HSKNDA and will laid under the local roads of the proposed HSKNDA. The exact alignment of the proposed emergency bypass culvert will thus be subject to modifications as per the road alignment of the proposed HSKNDA. In order to minimise the impact associated with the construction of the emergency bypass culvert, the proposed emergency bypass culvert will be constructed at the same time as the infrastructure works of the proposed HSKNDA. The proposed emergency bypass culvert will only be used for conveying treated effluent from San Wai STW to existing drainage channel under the emergency event when the NWNT effluent tunnel or the Urmston Road outfall is out of operation. Land contamination impact related to the construction and operation of the proposed emergency bypass culvert is not expected.

7.4.1.5 With reference to the findings of the land contamination site appraisal presented in Technical Paper No. 13 Environmental Impact Assessment (Draft), November 2000, Agreement CE 66/96 Planning and Development Study on North West New Territories, a number of industrial hotspots are identified within the proposed HSKNDA and some are located close to Alternatives 1, 2, and 3 alignment of the proposed emergency bypass culvert. It was recommended in the above report to carry out a detailed land contamination assessment upon land resumption for the proposed HSKNDA development. The land contamination assessment will also serve to assess the potential land contamination impact associated with the infrastructure work, including the proposed emergency bypass culvert, to be built for the proposed HSKNDA.

7.5 Site History

7.5.1.1 Site history review is undertaken based on the observation and analysis of available historical aerial photographs. A list of the aerial photographs listed in Table 7.1 below were reviewed for general changes in land use, as well as specific development around the proposed expansion site of San Wai STW.

Table 7.1  Aerial Photographs Reviewed  

7.5.1.2 Figures 7.4 to 7.7 show the selected historical aerial photographs taken in 1964, 1981, 1988, and 1994 respectively over the proposed expansion site of San Wai STW. The following summaries the observations and findings:

Year      Observations

1964                      The entire area of the proposed expansion site was agricultural land.  Areas further away from the site were either hill slopes or agricultural land.  (see Figure 7.4)

1981                      A few large fishponds were formed and operated within the proposed expansion site.  The existing farm adjacent to the north of the proposed expansion site is noted.  Other areas adjacent to the proposed expansion site remained agricultural lands.  (see Figure 7.5)

1988                      Not much change of land uses is observed between 1981 to 1988.  Major land uses within and adjacent to the proposed expansion site remained agricultural land and fishponds.  (see Figure 7.6)

1994                      The fishpond to the south of the proposed expansion site was filled and the existing San Wai STW was constructed.  The fishpond adjacent to the east of the proposed expansion site was filled and converted to a container yard.  The fishpond adjacent to the west of the proposed expansion site was filled and no activity was observed on top.  The farm located to the north of the proposed expansion site remained in the same location.  Many of the agricultural lands further to the east of the proposed expansion site were converted to container yards.  (see Figure 7.7)

Existing Since 1994, more agricultural lands further to the east of the proposed expansion site have been converted to container yards.  Besides, more hill slopes and agricultural lands further to the west and northwest of the proposed expansion site have been converted to open storage areas.  (see Figure 7.1)

7.5.1.3 Historically, the proposed expansion site of San Wai STW was mostly composed of agricultural land and fishponds. Until recent years, the fishpond at the southern part of the expansion site was filled to construct the existing San Wai STW and the agricultural land at the eastern part of the expansion site was converted to container yard. For land uses outside and adjacent to the proposed site, they are the farm located to the north since 1980s, the container yards located to the east since early 1990s, and the open storage areas located to the west and northwest since late 1990s.

7.6 Site Inspection

7.6.1.1 Site visit was undertaken in September and November 2001 to collect more detailed information on existing site conditions of the proposed expansion site of San Wai STW. The visit has been carried out in a systematic way and specific features are marked with location numbers as shown in Figure 7.1. The findings are summarised in the following paragraphs.

7.6.1.2 Locations 1, 2 and 3 are the existing land uses within the proposed expansion site of San Wai STW. Location 1 is the existing San Wai STW (see Figure 7.3) with normal sewage treatment activities. No activity with potential land contamination impact was observed.

7.6.1.3 Location 2 is a container yard located at the eastern part of the proposed expansion site. As shown in Figure 7.1 and observed during the site visit, the container yard was mainly used for the storage of containers. Potential land contaminating activity was observed during the site visit.

7.6.1.4 Location 3 is two fishponds located at the northern part of the proposed expansion site. The absence of aerators and fish food combined with presence of dense vegetation on the pond bunds suggested that management is limited, and the ponds may only be harvested for domestic use.

7.6.1.5 Location 4 is an open storage area located outside the western boundary of the proposed expansion site. The open storage area is mainly used for the storage of construction materials together with some small workshops with vehicle and plant maintenance and repairing activities.

7.6.1.6 Location 5 is a pig farm located outside the northern boundary of the proposed expansion site. Access to within the pig farm was not possible during the site visit. Based on the observation from outside the pig farm, no potential land contaminating activity was identified.

7.7 Prediction and Evaluation of Environmental Impacts

7.7.1.1 Based on the review of the past and present land uses presented in Sections 7.5 and 7.6 above, it is noted that most part of the proposed expansion site, other than the existing San Wai STW, is occupied by the two fishponds to the north and the container yard to the east.

7.7.1.2 The areas of the two fishponds were used as agricultural land in the early 1940s and was then converted to fishponds. Land contamination issue related to the area of these two fishponds is not anticipated.

7.7.1.3 The area of the container yard located to the east of the site was previously agricultural land and fishpond and was then converted to container yard since early 1990s. The land use as a container yard remains unchanged up to the present moment. The site visit identified no potential land contaminating activity within the area. Nevertheless, in view of the nature of the site, minor vehicle maintenance and repairing activities, as well as fuel refilling activities may be possible. As a result, maintenance wastes such as air filters, empty lubricant oil cans, vehicle parts, as well as small amount of contaminated soil due to accidental spillage or leakage during refilling of fuel oil or lubrication oil might exist which require handling with proper waste handling procedures upon resuming the area for the proposed expansion.

7.7.1.4 One of the major adjacent land uses is the pig farm located to the north of the site. The pig farm commenced operation since early 1980s and is not considered as a land contamination source. Before the operation of the pig farm, the area was an agricultural land. Land contamination issue related to this area is not anticipated.

7.7.1.5 The other major adjacent land use is the open storage area located to the west of the site. The open storage area commenced operation in late 1990s. The open storage area is used for the storage of construction material as well as some workshops with some mechanical plant and vehicle maintenance and repairing activities. It may also be possible there are some fuel oil or lubrication oil refilling activities. In view of these, there could be some localised land contamination issues within this area related to maintenance wastes and small amount of contaminated soil due to accidental spillage or leakage during refilling of fuel oil or lubrication oil. Nevertheless, these land contamination issues are considered localised and should not affect the proposed expansion site.

7.8 Contamination Assessment Plan

7.8.1 Introduction

7.8.1.1 With reference to the evaluation presented in Section 7.7 above, land contamination issue related to the proposed expansion site of San Wai STW would be minor. The only potential land contamination issue within the expansion site would be the localised land contamination related to current operation of the container yard at the eastern part of the expansion site. There would also be some concern of land contamination associated with the activities of the adjacent open storage area to the west of the expansion site.

7.8.1.2 In order to verify the low potential of land contamination impact prior to the commencement of the construction of the San Wai STW expansion, the following Contamination Assessment Plan (CAP) outlines the background and the scope of the soil investigation work for endorsement by EPD. Based on the endorsed CAP, a contamination assessment, which includes intrusive sampling and testing, will be carried out prior to the construction phase of the project. The findings will be compiled in a Contamination Assessment Report (CAR) for approval by EPD. If the findings confirm that the site is contaminated, a Remedial Action Plan (RAP) will be drawn up.

7.8.1.3 This CAP is developed based on the Guidance Notes for Investigation Remediation of Contaminated Sites of Petrol Filling Stations, Boatyards, and Car Repair/Dismantling Workshops (Guidance Notes) and Practice Note for Professional Persons ProPECC PN 3/94 Contaminated Land Assessment and Remediation (PN3/94) published by EPD.

7.8.1.4 In the detailed design stage of the Project when access to the concerned areas is gained, this CAP should be reviewed and updated with the latest information including layout plans. Moreover, the number and location of sampling points and the testing parameters of the samples (determined with rationale behind) should be submitted to EPD for approval before the commencement of the actual drilling and sampling. Moreover, any CAR/RAP to be approved by EPD should be submitted in the detailed design stage of the project and preferably before the issue of the Environmental Permit. No work on the identified potential contaminated sites should be carried out unless and until the CAR and RAP submitted are approved by EPD.

7.8.2 Nature of Contaminants

7.8.2.1 Potential land contamination related to the container yard and the open storage area would likely be caused by vehicle and plant maintenance and repairing activities. Prior to the construction of the proposed San Wai STW expansion, the activities of the container yard and the open storage area might have changed. The area potentially would have a mixture of concerned contaminants.

7.8.2.2 Most of the ground surface of the container yard and open storage area was covered by concrete. The level of contamination should likely be very much localised. Contaminants may enter soil through cracks, broken surface, damaged drains (if contaminants were illegally disposed at drains).

7.8.2.3 To a certain extent, the chance of contaminating the land would be related to the operational practices of occupants of the container yard and the open storage area, which in turn depends on the management of those areas. Some well-managed maintenance and repairing activities would handle wastes or oils properly but some would not.

7.8.3 Sampling Strategy

Container Yard to the East

7.8.3.1 The site area of the container yard within the expansion site of San Wai STW is approximately 17,000m2, 20 sampling points are proposed for a full-scale investigation. The 20 sampling points would be selected strategically with reference to the identified hot-spot areas during site reconnaissance to be carried out after the entire area become accessible in the future and prior to the construction of the proposed expansion. The distribution of the sampling points should provide a good representation of the extent and nature of contamination.

Open Storage Area to the West

7.8.3.2 The open storage area is located outside but adjacent to the proposed expansion site of San Wai STW. In order to verify that there is no land contamination issue related to migration of contaminants from the open storage area to the proposed expansion site, 3 sampling points strategically located at the western boundary of the proposed expansion site are proposed. The distribution of the sampling points should provide a good representation of the extent and nature of contamination.

7.8.4 Sampling Procedures

7.8.4.1 All field personnel should wear adequate personal protective equipment when working in contaminated areas.

Soil Sampling

Boreholes Construction

7.8.4.2 Boreholes will be constructed on site for soil and groundwater sampling. Exact location of soil sampling would be adjusted on site due to site conditions or unforeseeable underground conditions. The boreholes shall be constructed to allow soil samples to be collected at:

1) 0.5m below surface;
2) 1.5m below surface; and
3) 3m below surface.

7.8.4.3 Inspection of soil should also be made at 0.5m intervals. The depth of the borehole shall be determined by the groundwater level and shall be at least 0.5 meter below groundwater level.

Equipment Cleaning

7.8.4.4 The excavator or other mechanical equipment must be in sound mechanical order and free of oil leaks. It must have a current registration and warrant of fitness. All equipment must be steam cleaned upon arrival at the site, before commencing each new hole and before leaving the site. If contamination is evident during borehole construction, the equipment will need to be cleaned between holes.
Soil Sampling

7.8.4.5 Sampling of soil will be by ceramic spoons. The sampling spoons must be cleaned between samples.

7.8.4.6 Field personnel will wear clean PVC/latex gloves whilst handling sampling equipment and carry out sampling. All sampling equipment will be cleaned prior to obtaining each sample. A clean area immediately adjacent to the sample location will be established, using a clean plastic sheet, on which all cleaned, and foil wrapped equipment may be placed. Samples of sub-surface material will be recovered from the depths specified above.

7.8.4.7 Sufficient sample (i.e. 400 grams or about 30 mL) should be placed in a pre-cleaned glass sample jar. The jar lid will be covered with laboratory solvent washed aluminium foil and lids. The jar must be filled with no void space (or otherwise if specified by the lab) for samples to be tested for VOCs.

7.8.4.8 Each sample jar will be labelled. Records will be made of the details of the sampling location and other pertinent data. A chain-of-custody form will be completed for the samples. All samples shall be stored on ice in portable ice chests between 0 - 4 oC whilst in the field or in transit.

Groundwater Sampling

7.8.4.9 The boreholes will be purged by removal of enough volumes of water to remove any stagnant water or water which is not representative of the aquifer. A hand-operated bailer may be used for this purpose. The presence of floating product and its thickness should also be recorded at each sampling point before and after groundwater purging. Care should be taken to avoid pumping too much groundwater as this may draw contaminants from outside areas into the borehole and cause the groundwater sample to be unrepresentative of the sampling location.

7.8.4.10 Groundwater samples shall be collected only after all required soil samples have been collected at each of the proposed sampling location. A groundwater monitoring well should then be installed at each of the drill holes. Upon completion of installation of monitoring wells, well developments (approximately five well volumes) should be carried out to remove silt and drilling fluid residue from the wells. The wells should then allow to stand for a day to permit groundwater conditions to equilibrate. Groundwater level and thickness of free product layer, if present, should be measured before groundwater samples are taken. Moreover, prior to groundwater sampling, the sampling wells should be purged (at least three well volumes) to remove fine-grained materials and to collect freshly refilled groundwater samples. After purging, one groundwater sample should then be collected at each sampling well with a Teflon bailer. The free products should also be sampled to allow identification by the laboratory.

7.8.4.11 Prior to commencement of sampling a clean piece of plastic shall be placed on the ground beside the well. All equipment shall be placed on this sheet when not in use and all cleaning will be carried out on the plastic sheet. As sampling equipment is removed from the well, care will be taken to place it on the plastic sheet.

7.8.4.12 Samples will be collected in a teflon/stainless steel downhole bailer, which will be decontaminated between sampling sites by cleaning in accordance with the procedures specified before. Care will be taken when sampling to avoid any opportunity for excess aeration of the sample.

7.8.4.13 Observations will be recorded in the form of strata log.

7.8.4.14 Water samples will be placed in appropriate containers as supplied by the analytical laboratory. Containers will be filled to over-flowing except those which have preservatives already added.

7.8.4.15 Samples for VOCs (i.e. hydrocarbons or BTEX) will be filled to overflowing and the foiled cap gently placed over and screwed down. The bottle should be inverted and gently tapped - if any air bubbles are present, the sample must be recollected.

7.8.4.16 All samples collected will be stored at <4°C. Transfer to the analytical laboratory will be completed within 24 hours of sample collection.
Testing Parameters

7.8.4.17 Soil and groundwater samples collected at each sampling point should be analysed for the parameters listed in Table 7.2 by a HOKLAS accredited laboratory.

Table 7.2  Testing Requirements for Soil and Groundwater Samples

Note : * equivalent international recognised standard methods could also be used.

Storage of Surplus Soil Samples

7.8.4.18 It is recommended that surplus soil samples be obtained and stored for further analysis. The contamination of the site may be localised and, in that case, the quantities of contaminated soil to be remediated and disposed of would be small. Landfill disposal may be a more favourable and practical option in this case and additional tests in terms of Toxicity Characteristic Leaching Procedure (TCLP) would be required to meet the criteria for disposal to landfills. For the landfill disposal of the contaminated soil, one should refer to the EPD's Guidance Notes for Investigation and Remediation of Contaminated Sites of Petrol Filling Stations, Car Repair/Dismantling Workshops and Boatyards.

7.8.4.19 Hence, surplus soil samples obtained during the site investigation would be stored for subsequent TCLP tests if identified necessary. TCLP tests for parameters cadmium, chromium, copper, nickel, lead, zinc, mercury, tin, silver, antimony, arsenic, beryllium, thallium, vanadium selenium and barium, using ASTM-E1391-90 method may need to be carried out. If the project proponent intends to propose landfill disposal as the remedial measure after reviewing the test results from the site investigation, he/she should submit the heavy metal test results and propose a TCLP test regime (the number and identity of stored samples for full screen and specific metal TCLP test) for EPD's agreement. The TCLP tests have to be completed before the submission of CAR/RAP and the results included in the CAR.

7.8.5 Contamination Assessment Report

7.8.5.1 A Contamination Assessment Report (CAR) should be compiled based on the results of contamination assessment and submitted to EPD for review and approval. If contamination is found, a Remediation Action Plan (RAP) should be prepared to formulate practical remedial measures that can be adopted for the clean-up of a contaminated site. The RAP and CAR should be submitted as a combined report to EPD for approval, referencing the corresponding CAP.

7.9 Conclusions

7.9.1.1 In the current design, the expanded pumping station will be entirely located within the currently site boundary of the Ha Tsuen Pumping Station and no additional land will be required outside the existing pumping station site boundary. The potential of land contamination impacts is considered minimal.

7.9.1.2 Some sections of the proposed emergency bypass culvert will cross over the proposed HSKNDA and will laid under the local roads of the proposed HSKNDA. In order to minimise the impact associated with the construction of the emergency bypass culvert, the proposed emergency bypass culvert will be constructed at the same time as the infrastructure works of the proposed HSKNDA. It is recommended to carry out a detailed land contamination assessment upon land resumption for the proposed HSKNDA development. The land contamination assessment will also serve to assess the potential land contamination impact associated with the infrastructure work, including the proposed emergency bypass culvert, to be built for the proposed HSKNDA.

7.9.1.3 Most part of the proposed expansion site of San Wai STW, other than the existing San Wai STW, is occupied by the two fishponds to the north and the container yard to the east. Based on the review of the past and present land uses, land contamination issue related to the area of the two fishponds is not anticipated.

7.9.1.4 The area of the container yard was previously agricultural land and fishpond and was then converted to container yard since early 1990s. Localised land contamination issues within this area would be related to vehicle and plant maintenance and repairing activities. Similar land contamination concern also applies to the open storage area to the west outside but adjacent to the proposed expansion site.

7.9.1.5 In order to verify the low potential of land contamination impact prior to the commencement of the construction of the San Wai STW expansion, a CAP outlines the background and the scope of the soil investigation work is formulated in this EIA. A contamination assessment which includes intrusive sampling and testing will be carried out prior to the construction phase of the project. If the findings confirm that the site is contaminated, a Remedial Action Plan (RAP) will be drawn up to formulate necessary remedial measures.