11a.1.1.1 The landfill gas hazard assessment undertaken in the EIA Study identified the hazards that are likely to be generated from the proposed WENT Landfill Extensions, during the construction and operation phases of this Project and evaluated the associated risk. The EIA Report recommended that significant engineering protection measures would be required to protect the IWMF from the landfill gas risk associated with WENT Landfill Extensions. Use of “active control of gas, including barriers and detection systems”, and other appropriate gas control protection systems referenced from the EPD’s Landfill Gas Hazard Assessment Guidance Note were recommended. Regular monitoring during operation phase was also recommended.
11a.2 Monitoring and Measurement of Landfill Gas
11a.2.1.1
The measurements mentioned in s
11a.2.1.2
During construction of the
IWMF, if the WENT Extension project is in operation, a Safety Officer should be
appointed to carry out the monitoring works.
The monitoring frequency and areas to be monitored should be set down
prior to commencement of ground-works either by the Safety Officer or an
approved and appropriated qualified person.
The routine monitoring should be carried out in all excavations, manholes,
chambers, relocation of monitoring wells and any other confined spaces that may
have been created. All measurements in
excavations should be made with the extended monitoring tube located not more
than
11a.2.1.3
For excavations deeper
than
· at the ground surface before excavation commences;
· immediately before any worker enters the excavation;
· at the beginning of each working day for the entire period the excavation remains open; and
· periodically through the working day whilst workers are in the excavation.
11a.2.1.4
For excavations between
· directly after the excavation has been completed; and
· periodically whilst the excavation remains open
11a.2.1.5
For excavations less than
11a.2.1.6 Depending on the results of the measurements, actions required will vary and should be set down by the Safety Officer or other appropriately qualified person. As a minimum these should encompass those actions specified as follows:
Parameter |
Measurement |
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% |
LEL: Lower Explosion Limit
11a.2.1.7
Referencing WENT Landfill Extensions EIA Report, it was proposed that
landfill gas cut-off trench barrier will be built along the boundary between
the IWMF and the WENT Landfill Extensions under the WENT Landfill Extensions
project. This will cut off any gas
migration to the IWMF from the WENT Landfill Extensions. The indicative location of the proposed
cut-off trench barrier is shown in Figure 12a.6 of the
EIA Report.
11a.2.1.8
It was recommended that several landfill gas monitoring wells be
installed into the ground on the development side of the gas barrier. These would be used to measure the concentrations of CH4 and
CO2 within the ground and hence determine the effectiveness of the
measures in preventing LFG migration.
11a.2.1.9
During operation, regular
monitoring of landfill gas should be done at the monitoring wells mentioned above
in Section