PROJECT DESCRIPTION
BACKGROUND
As demonstrated by a number of scientific investigations, capillary barriers are an efficient type of sealing system that can be used as a final cover on landfills and remediation sites. This pilot project, covering two hectares of a sloping section of the landfill at Breinermoor in the German state of Lower Saxony (Niedersachsen), was set up to demonstrate that large-scale capillary barriers will be technologically feasible in a number of landfills in various locations. A capillary barrier consists of two sloping layers. Fine-grained sand is used in the capillary layer, which overlies a coarse-grained layer (the capillary block). The capillary barrier is an innovative sealing system, which exploits the fact that a layer of fine sand has become highly saturated with water from above. Capillary forces counteract the power of gravity and prevent the water in the capillary layer from seeping down into the capillary block. Instead, the water is held just above the interface between the two layers and runs off laterally into a ditch containing a drain at the foot of the slope. In suitable applications, and given the correct choice of materials, a capillary block will provide an efficient surface seal. The capillary barrier effect depends on the relation between the water content, the suction tension of the sand and the hydraulic conduction ability.
OBJECTIVES
The project was carried out with two main objectives: · Gather experience on large-scale applications, using a capillary barrier of 2 ha, on the solid waste landfill at Breinermoor. · Prove that the capillary barrier provides sufficient protection with measurements of the seepage carried out at the test field over several years. In the landfill Breinermoor, a pilot demonstration field covering an area was built as the first part of the surface seal. Particular attention was paid to the adoption of suitable construction methods, as well as to quality assurance and quality control. A synthetic liner was laid directly above the capillary barrier, since combined seals are the legal requirement in Germany. In one part of the 2 ha demonstration field there was a smaller test field with a slope width of 15m. This field contained a capillary barrier without an overlying synthetic liner, so that the functional efficiency of this sealing system could be verified.
RESULTS
Capillary barriers are a new type of sealing system with potential for use in solid waste landfill and remediation sites that have sufficiently steep slopes. A key benefit of capillary barriers are that they are more reliable in the long term, since they do not dry out, and they are insensitive to settlement. The key objectives, to test an alternative capillary barrier system for closed landfills and to gain technical and economic results for a large-scale application have been achieved. The technical results of the EU testfield were below expectations: Only in the flat section of the test field were passable results obtained, with 23 mm breakthroughs in the year 2000 with an average rainfall of 800 mm. Yet the breakthroughs were most probably caused by leaks at the edges of the sealing and will not appear in the large-scale application as there this fault was ruled out. From the technical and financial point of view, the use of the capillary barriers could prove to be an advantage to many of the federal states, regional authorities and commercial landfill operators in Germany. In fact, capillary barriers could be used in any country where the climatic conditions resemble to those of Germany. Capillary barriers are a new type of sealing system with potential for use in solid waste landfill and remediation sites that have sufficiently steep slopes. A key benefit of capillary barriers are that they are more reliable in the long term, since they do not dry out, and they are insensitive to settlement. The key objectives, to test an alternative capillary barrier system for closed landfills and to gain technical and economic results for a large-scale application have been achieved. The technical results of the EU testfield were below expectations: Only in the flat section of the test field were passable results obtained, with 23 mm breakthroughs in the year 2000 with an average rainfall of 800 mm. Yet the breakthroughs were most probably caused by leaks at the edges of the sealing and will not appear in the large-scale application as there this fault was ruled out. From the technical and financial point of view, the use of the capillary barriers could prove to be an advantage to many of the federal states, regional authorities and commercial landfill operators in Germany. In fact, capillary barriers could be used in any country where the climatic conditions resemble to those of Germany.