10.1.1 This section describes the landfill gas monitoring requirements at the Project sites within the Sai Tso Wan Landfill Consultation Zone during the construction and operational phases. The precautionary measures to minimise landfill gas risk are summarised in the Implementation Schedule.
10.2 Monitoring Parameters, Locations and Frequency
10.2.1 Monitoring of landfill gases shall be conducted during the construction and operational phases of the Project. It is recommended that pre-entry monitoring should be undertaken, where applicable, in accordance with the requirements of the Factories and Industrial Undertaking (Confined Spaces) Regulation. For excavations of 1m depth or more, landfill gas should be monitored before entry and periodically during the works. If drilling is required, the procedures for safety management and working procedures described in the EPD’s Landfill Gas Hazard Assessment Guidance Note should be adopted.
10.2.2 The monitoring programme and detailed actions should be submitted to EPD for approval in the detailed design stage. The proposed parameters, locations and frequency of landfill gas monitoring for various phases of Project are summarised in Table 10.1.
Table 10.1 Parameters, Locations and Frequency of Landfill Gas Monitoring
|
Phase |
Monitoring Location |
Monitoring Frequency* |
Monitoring Parameters |
|
Construction |
All excavations, manholes, chambers, relocation of monitoring wells and any other confined spaces |
At least daily before starting the work of the day |
· Methane · Carbon Dioxide · Oxygen |
|
Operational |
At tunnel, subway, and any other underground structures; At buildings and enclosures (e.g. administration building, ventilation building, workshop, tunnel etc) |
Prior to the operation and monthly for the first year of operation |
· Methane · Carbon Dioxide · Oxygen |
|
|
Any construction required for the maintenance work during operational stage |
At least daily before starting the work of the day |
· Methane · Carbon Dioxide · Oxygen |
Notes:
*Tentative schedule. The actual monitoring requirements shall be discussed and agreed with EPD before the commencement of works and operation.
10.3.1 Intrinsically safe, portable gas detectors should be used when working in any confined space, which has the potential for the presence of landfill gas, and the risk of explosion or asphyxiation. The detector should be appropriately calibrated and able to measure the following gases in the ranges indicated below:
|
Methane |
0-100% LEL and 0-100% v/v |
|
Carbon dioxide |
0-100% |
|
Oxygen |
0-21% |
10.3.2 All measurements in excavations should be made with the extended monitoring tube located not more than 10 mm from the exposed ground surface.
10.3.3 The Contractor may elect to carry out monitoring via an automated monitoring system. In this event, the gas levels specified in Table 10.2 shall be so programmed to automate the actions in the table and in the event of the trigger levels being breached, to activate suitable audible and visual warning devices.
10.4 Limit Levels and Event and Action Plan (EAP) for Landfill Gas
10.4.1 The Limit levels and relevant Action Plans for landfill gas detected in facilities and any on-site areas during construction are shown in Table 11.2 below.
Table 10.2 Limit Levels and Action Plan for Landfill Gas
|
Parameter |
Limit Level |
Action |
|
Oxygen |
<19% |
· Ventilate to restore oxygen to >19% |
|
<18% |
· Stop works · Evacuate personnel/prohibit entry · Increase ventilation to restore oxygen to >19% |
|
|
Methane |
>10% LEL (i.e. > 0.5% by volume) |
· Prohibit hot works · Ventilate to restore methane to <10% LEL |
|
>20% LEL (i.e. > 1% by volume) |
· Stop works · Evacuate personnel / prohibit entry · Increase ventilation to restore methane to <10% LEL |
|
|
Carbon Dioxide |
>0.5% |
· Ventilate to restore carbon dioxide to < 0.5% |
|
>1.5% |
· Stop works · Evacuate personnel / prohibit entry · Increase ventilation to restore carbon dioxide to < 0.5% |
10.4.2 During operation, regular monitoring of methane, carbon dioxide and oxygen should be done at the tunnel, subway, and any other underground structures within the landfill consultation zone a precautionary measure.
10.4.3 Inspection and LFG monitoring should be carried out at buildings and enclosures (e.g. administration building, ventilation building, workshop, tunnel etc) prior to the operation as preventive measures. The monitoring should be continued through the operation of the Project. In particular for the first year of operation, monthly monitoring is recommended. Should the monitoring reveal the presence of landfill gas within the tunnel, buildings or other confined area, the seal of the joints shall be inspected and consideration shall be given to seal the cracks.
10.4.4 In addition, if any construction is required for the maintenance work during operational stage, the responsible party should follow the monitoring works as recommend above.