5. LANDFILL GAS MONITORING

5.1 Landfill Gas Parameters (Methane, Carbon Dioxide, and Oxygen)

5.1.1 Although a comprehensive landfill gas management system has been constructed under the Restoration Contract for Tseung Kwan O Stage I Landfill, the efficiency of the system has not been demonstrated at this time. Landfill gas monitoring for methane, carbon dioxide and oxygen shall be carried out to identify any migration between the landfill and the site and to ensure the safety of the Contractor’s personnel.

5.1.2 Certain information, such as the proposed routing of utilities in relation to the sensitive elements of the development will be determined at the detailed design stage. It is mentioned in the EIA report that in the event that there are substantial changes in the alignments of Roads D1, D8 and D10, a review of the qualitative source-pathway-target analysis as presented in Table 7.15 of the EIA report is considered necessary.

5.1.3 Monitoring shall be carried out and reported in a similar manner to that for the Restoration Contract to provide comparable data. An example of landfill gas monitoring field measurement recording sheet as used in the Restoration Contract is presented in Appendix B3. The presentation format for landfill gas monitoring shall be based on this format and agreed with EPD.

5.2 Monitoring Equipment

~~Monitoring~~ of ~~Construction Works~~

5.2.1 Intrinsically safe, portable gas detectors shall 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 landfill gas monitoring instrument shall :

Ÿ Where possible, comply with BS6020 and be approved by BASEEFA as intrinsically safe, suitable for use in a Zone 2 area to BS5345;

Ÿ Be capable of continuous monitoring of methane, oxygen and carbon dioxide;

Ÿ Be capable of continuous barometric pressure and gas pressure measurement;

Ÿ Normally operate in diffusion mode unless required for spot sampling, when it should be capable of operating by means of an aspirator or pump;

Ÿ Have low battery, fault and over range indication incorporated;

Ÿ Store monitoring date, and shall be capable of being down-loaded directly to a PC;

Ÿ Measure in the following ranges:

Ÿ Methane 0-100% LEL & 0-100% v/v

Ÿ Oxygen 0-25% v/v

Ÿ Carbon dioxide 0-100% v/v

Ÿ Barometric pressure mBar (absolute)

Ÿ Gas pressure (relative to atmosphere) Pascals

Ÿ Temperature 0-100^oC

5.2.2 The monitoring equipment shall alarm (both audibly and visually) in the event that the concentrations of the following are exceeded :

Ÿ Methane – higher than 10 % LEL

Ÿ Carbon dioxide – higher than 0.5 %

Ÿ Oxygen – lower than 18 % by volume

5.2.3 The equipment used to monitor LFG concentrations in excavations may shall be the same as that described for routine for landfill gas monitoring LFG monitoring of for utility manholes and chambers. described in Section 5.2.1 above, as long as safety parameters described above can be achieved.

5.3 Monitoring Locations

Monitoring of Construction Works

5.3.1 During construction, excavations of 1m depth or more, LFG concentration shall be monitored before entry and periodically during the works. It is recommended that pre-entry monitoring shall be undertaken, where applicable, in accordance with the requirements of the Factories and Industrial Undertaking (Confined Spaces) Regulation. The periodic monitoring shall be undertaken at the beginning of each half working day (i.e. morning and afternoon) throughout the entire period the excavation remains open. 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.

Monitoring of Utilities

5.3.2 Following construction, pre-entry and routine monitoring may be required at service voids and utility boxes. It is recommended that pre-entry monitoring shall be undertaken, where applicable, in accordance with the requirements of the Factories and Industrial Undertaking (Confined Spaces) Regulation. The frequency of the routine monitoring is recommended to be biweekly during the initial stage. The “initial stage” is considered as the “initial stage” of the operational phase of the project. However, there is no government’s regulation/guideline on the duration of such “initial stage” for monitoring. As such, it is recommended that the “initial stage” refer to the first 3 months of the operational phase. The frequency shall be subsequently reviewed on a quarterly basis through discussion with EPD based on all the available monitoring data for methane, carbon dioxide and oxygen (including that of pre-entry monitoring). In the event that there are substantial changes in the alignments of Roads D1, D8 and D10, the monitoring requirement and specific locations of monitoring points should be established based on the findings of the review of the qualitative source-pathway-target analysis as presented in Table 7.15 of the EIA report. The need for continued monitoring should be reviewed on a quarterly basis through discussion with EPD, based on all the available monitoring data for methane, carbon dioxide and oxygen (including that of pre-entry monitoring).

Operational Landfill Gas Monitoring

5.3.3 In the event that there are substantial changes in the alignments of Roads D1, D8 and D10, the monitoring requirement during the operational phase should be established based on the findings of the review of the qualitative source-pathway-target analysis as presented in Table 7.15 of the EIA report, in consultation with EPD.

5.4 Limit Levels and Action Plan for Landfill Gas

5.4.1 As a general measure to minimise the risk of explosion due to the presence of methane, “no smoking” signs shall be placed at entry or access points of the work site.

5.4.2 The Limit Levels and relevant Action Plan for landfill gas detected in utilities and any on-site areas following construction are shown in Table 5.1 below.

Table 5.1 Limit Levels and Action Plan for Landfill Gas

Parameter	Level	Action
Oxygen	<19%	Ventilate trench/void to restore O₂ to >19%
Oxygen	<18%	Stop works Evacuate personnel / prohibit entry Increase ventilation to restore O₂ to >19%
Methane	>10% LEL	Post “No Smoking” signs at concerned areas in addition to to site entry/access points Prohibit hot works Increase ventilation to restore CH₄ to <10% LEL
Methane	>20% LEL	Stop works Evacuate personnel / prohibit entry Increase ventilation to restore CH₄ to <10% LEL
Carbon Dioxide	>0.5%	Ventilate to restore CO₂ to < 0.5%
Carbon Dioxide	>1.5%	Stop works Evacuate personnel / prohibit entry Increase ventilation to restore CO₂ to < 0.5%

5.5 Landfill Gas Mitigation Measures

5.5.1 The EIA report has recommended specific mitigation measures to be incorporated into the detailed design. The Contractor shall follow the safe working practices to detect landfill gas accumulations in any utility trenches. Safe working practices to detect landfill gas accumulations in the utilities trenches in the vicinity of the faults are outlined in EPD’s Landfill Gas Hazard Assessment - Guidance Note and shall be adopted by the relevant Utilities Companies.

5.5.2 Notwithstanding, the requirement for a critical review of the detailed design, mitigation measures to be incorporated in the detailed design include :

Ÿ Portable gas detectors shall be used to regularly check the levels of methane, carbon dioxide and oxygen in depressions, trenches, and other excavations;

Ÿ Void around any service ducts, pipes or cables etc. within conduits shall be filled with gas resistant mastic;

Ÿ All ducts, manholes and chambers shall be sealed off from the ground to prevent gas entry and provided with vented covers;

Ÿ Atmosphere within manholes or chambers shall be checked for methane, carbon dioxide and oxygen prior to entry; and

Ÿ Atmosphere within manholes or chambers shall be checked for methane, carbon dioxide and oxygen on a regular basis. The frequency of the monitoring will be subject to the results of the initial monitoring exercise.