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Evapotranspiration-optimized capping systems
Published on 08 December 2019
Germany
This is the good practice's implementation level. It can be national, regional or local.
About this good practice
According to the German Landfill Ordinance, on top of a landfill of non-hazardous waste a sealing system has to be installed after the operation phase. For a mineral-waste landfills alternatively to a geomembrane a soil layer can be installed which reduces the groundwater recharge rate (GRR) to <20mm/a. An organic-rich or more contaminated mineral-waste landfill needs two sealing components. Alternatively to one of the two sealing components (usually the mineral layer is substituted) a soil layer can be installed which reduces the GRR to <60 mm/a. For information: The average precipitation is 550 - 1300 mm/a in Germany (Brandenburg <650 mm/a).
In order to meet the requirements of maximum GRR a certain quality of soil is necessary to retain plenty of water, to sustain plant growth, and hence to maximize evapotranspiration rate. The available water capacity considering the whole soil depth has to be >220 mm. Soil depth has to be >1.5 m. The vegetation layer is crucial for evapotranspiration, with higher rates for trees than for meadow. However, it has to be considered, that on a landfill with a geomembrane or a mineral layer beneath, no trees can be planted as their roots may harm the sealing system when soil layer depth is less than 3 m. In case the soil layer is the only element of the capping system trees can be planted.
Before the installation of the soil layer, water household has to be modelled. After installation, GRR has to be monitored and practically quantified.
In order to meet the requirements of maximum GRR a certain quality of soil is necessary to retain plenty of water, to sustain plant growth, and hence to maximize evapotranspiration rate. The available water capacity considering the whole soil depth has to be >220 mm. Soil depth has to be >1.5 m. The vegetation layer is crucial for evapotranspiration, with higher rates for trees than for meadow. However, it has to be considered, that on a landfill with a geomembrane or a mineral layer beneath, no trees can be planted as their roots may harm the sealing system when soil layer depth is less than 3 m. In case the soil layer is the only element of the capping system trees can be planted.
Before the installation of the soil layer, water household has to be modelled. After installation, GRR has to be monitored and practically quantified.
Resources needed
The costs for the soil and the installation as part of the capping system are about 150,000 Euro per hectare.
Evidence of success
A testfield on the landfill Deetz; Germany, Brandenburg, showed that a low groundwater recharge rate with less than 60 mm could be achieved by the installation of a soil layer. This requirement has to be met five years after installation of the system acc. to the German Landfill Ordinance. The measured groundwater recharge rate in Deetz was in the range of 36-61 mm (dry and extremely wet year, respectively).
Potential for learning or transfer
This practice could be replicable as a single-capping system for non-hazardous waste landfills where mineral waste was deposited or as one of two capping elements for higher contaminated non-hazardous waste landfills. The practice is in particular suitable for southern Europe, where precipitation is low. However, high peaks in seasonal precipitation have to be considered in evaluating the functionality of the system. For regions with humid, moderate climate with precipitation rates >700 mm the practice may be inadequate. In order to evaluate potential success of the measure, the WRR has to be modelled in advance.
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Germany
Brandenburg
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