Thermal gradient tests were undertaken in the laboratory of the Department of Water Affairs and Forestry in which a lagoon system was built with an overlying 300mm thick layer of stone on top of the primary composite liner beneath which we had a synthetic drainage or leak detection layer over an underlying geomembrane. The lagoon was filled with water and elevated to a temperature of 50^oC.

This collage shows the lagoon of 20m² under construction and the 3000W heater element with overlying thermal insulation layer.

The initial results confirmed a large diurnal vacillation of temperature prior to the introduction of a liquid which confirms the specific heat difference between a gas and a fluid. Thereafter the heating element was turned on and off. We followed conventional heating and cooling curves of liquids. Note the very similar rise and fall of temperature of the secondary liner system and geosynthetic drainage layer.

When the liquid contained the the lagoon had reached a static level of close to 50^oC, the fan was turned on to draw ambient air through the leak detection system. After an initial phase of excessive temperature reduction of heat removal a state of equilibrium is reached. By integrating the area between the inlet and outlet thermocouples, records were able to calculate the amount of heat that is removed from the barrier system which could be translated to a temperature reduction. Literature show that for the stoichiometry of a NSW Landfill we need to remove about 4.8 joules per m² per second and, in this test, using ambient air we were able to remove 10 joules per m² per second.

If required, the efficiency of heat removal can be further increased by changing the velocity of the fluid in the lead detection system or the fuel itself. Note that water has a density a thousand times higher than specific heat and 4.2 times greater than air and thus, by changing the fluid under negative pressure from air to water, it will increase the rate of heat removal by a factor of 4,200.

The diffusion testing results were undertaken using an operational lagoon which was drained to allow us to insert four test panels of 7m width each and formed the left to the right hand side across the lagoon walls and floor. The same know configuration as in the previous tests was used and after consideration a lagoon filled with leachate and liquid hazardous waste.

Initial tests undertaken using a vacuum extractor which drew air samples from the leak detection system show that significant volatile organic compounds are present in the leak detection system although there is a high degree of variability on concentration which is explained in the variation in densities of VOCs.

An extraction system has been installed and started operating. However, at the time of presentation, results of this are not available although, theoretically, it is obvious that the system should work for drawing air through the leak detection system.

In conclusion then, we can see that the coupled solution of drawing a fluid over negative pressure through the adjacent pervious layer such as the leak detection system allows for the removal of heat to reverse the negative effects of elevated tempertures, allows for the introduction of moisture and allows for air removal which would remove diffused VOCs with the commensurate total improvement of barrier system performance.