Moisture monitoring in waste disposal surface barriers.

Surface barriers for waste disposal sites should prevent waste water and gas emission into the environment. It is necessary to assess their proper operation by monitoring the water regime of the containment. A set of three new water content measuring devices has been developed that provide an economical solution for monitoring the moisture distribution and water dynamic. They will give an early warning service if the barrier system is at risk of being damaged. The cryo soil moisture sensor 'LUMBRICUS' is an in situ self-calibrating absolute water content measuring device. It measures moisture profiles at spot locations down to 2.5 m depth with an accuracy of better than 1.5% and a depth resolution of 0.03 m. The sensor inherently measures density changes and initial cracks of shrinking materials like clay minerals. The large area soil moisture sensor 'TAUPE' is a moisture sensitive electric cable network to be buried in the mineral barrier material of the cover. A report will be given with results and experiences on an exemplary installation at the Waste Disposal Facility Karlsruhe-West. 800 m2 of the barrier construction have been continuously monitored since December 1997. Volumetric water content differences of 1.5% have been detected and localised within 4 m. This device is already installed in two other waste disposal sites. A modified 'TAUPE' was constructed for the control of tunnels and river dams as well. Thin sheet moisture sensor 'FORMI' is specifically designed for moisture measurements in liners like bentonite, textile and plastic. Due to its flexibility it follows the curvature of the liner. The sensor measures independently from neighbouring materials and can be matched to a wide range of different thickness of the material. The sensors are patented in several countries.