6.2.2.1 Deep hot spots
Dousing of deep hot spots is typically undertaken from existing gas extraction wells, leachate collection systems or, in some cases, from specific points drilled into the waste mass. To undertake successful dousing, the following information should be obtained:
• location and depth of hot spot;
• depth of installation(s) where liquid is to be injected; and
• maximum volume of liquid that will be permitted, under the licence or permit to inject
into the waste mass.
It is essential that the relationship between the depth of the injection points and the hot spot is determined. If the hot spot is at a shallower depth than the installation, consideration should be given to installing a temporary packer into the injection point to ensure that the liquid enters the waste mass at the correct depth. Without knowing the actual depth of the hot spot, pouring a liquid down a gas or leachate well only has a slim chance of successfully extinguishing the hot spot. Since the hydraulic conductivity of waste is much lower along the vertical axis than the horizontal axis, dousing from above is less likely to reach the hot spot than introducing water close to the horizon containing the hot spot. The most suitable method for identifying the potential depth of a hot spot is through temperature surveys (see Section 4).Dousing is often undertaken as an initial control measure and the hot spot is assumed to have ceased when temperatures at distant wells are seen to fall. However, this apparent drop in temperature may be caused by the cooling of waste adjacent to the hot spot area rather than the extinguishing of the core. It may also be a result of other actions such as reducing the gas extraction system or sealing off air ingress. Long term monitoring is required to confirm whether dousing has been successful.
6.2.2.1 Deep hot spots
Dousing of deep hot spots is typically undertaken from existing gas extraction wells, leachate collection systems or, in some cases, from specific points drilled into the waste mass. To undertake successful dousing, the following information should be obtained:
• location and depth of hot spot;
• depth of installation(s) where liquid is to be injected; and
• maximum volume of liquid that will be permitted, under the licence or permit to inject
into the waste mass.
It is essential that the relationship between the depth of the injection points and the hot spot is determined. If the hot spot is at a shallower depth than the installation, consideration should be given to installing a temporary packer into the injection point to ensure that the liquid enters the waste mass at the correct depth. Without knowing the actual depth of the hot spot, pouring a liquid down a gas or leachate well only has a slim chance of successfully extinguishing the hot spot. Since the hydraulic conductivity of waste is much lower along the vertical axis than the horizontal axis, dousing from above is less likely to reach the hot spot than introducing water close to the horizon containing the hot spot. The most suitable method for identifying the potential depth of a hot spot is through temperature surveys (see Section 4).Dousing is often undertaken as an initial control measure and the hot spot is assumed to have ceased when temperatures at distant wells are seen to fall. However, this apparent drop in temperature may be caused by the cooling of waste adjacent to the hot spot area rather than the extinguishing of the core. It may also be a result of other actions such as reducing the gas extraction system or sealing off air ingress. Long term monitoring is required to confirm whether dousing has been successful.
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