chapter 4: temperature inside the landfill

eflections gives the temperature readings at different points along the cable. Spatial resolution,
the temperature resolution, the measurement time and the sensing length are the main parameters
defining the performance of the fiber optic distributed temperature measurement system.
There are two methods for detecting changes in the volumetric water content or liquid
flow in a landfill body. In the first method landfill temperatures and/or temperature changes are
directly employed to detect leakage through sealing materials, side seeps, and abnormal liquid
flow. For example, rapid temperature changes in a small localized area could be an indication of
a region with significant water flow. These temperature changes might also be an indication of
an unusually high gas flow rate.
In the second method, fiber optic cable and the surrounding waste is heated with a
heating cable. Increase in temperature for the waste is dependent on its conductivity and the
velocity of percolating fluid. The thermal conductivity of water increases with the amount of
water in the waste which reduces the rate of increase in temperature measured by the fiber optic
cable. Since thermal properties of waste and landfill construction materials are site-dependent,
this method is only useful to measure areal differences and/or temporal differences in volumetric
water content in the waste.
Fiber optic technology has been used in two landfills in Finland (Imhoff et al, 2007).
Anomalously low temperatures at one of the landfills aided locating frost resulting from cracks
in the geosynthetic liner. At another landfill, Mustankorkea landfill site, fiber optic sensors were
used in conjunction with electrical resistance sensors. High moisture content, observed by fiber
optic sensors was supported by independent observations using electrical resistance sensors.
Both sites indicated fiber optic technology can be used to monitor temperature as well as regions
of low and high volumetric water content.
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