Numerical modeling of water balance for temporary landfill cover in North Germany

Abstract

At the end of waste disposal in 2005, a temporary mineral system was constructed to cover the waste body of the municipal landfill in Rastorf (N Germany). The aim of this study was to evaluate the effectiveness of this temporary cover system in limiting the infiltration of surface water into the waste body. The numerical modeling for the hydrological year 2012 was performed in FEFLOW 6.0. The required input data for modeling were achieved by laboratory measurements of the saturated hydraulic conductivity and the water retention characteristics of the mineral layers. The assumed initial and boundary conditions were based on in-situ measurements of matrix potential and volumetric water content at three different measuring points by tensiometers, FDR sensors and observed meteorological conditions. The model was applied according to Darcy's and Richards' equations for variably saturated flow. Our results allowed assessing the components of water balance for a temporary cover system, especially water seepage into the waste body. The correlation between the measured and modeled volumetric soil water content in the layered temporary cover system was observed (R 2 = 0.56 to 0.90). Deviations between the measured and modeled values are superficially related to the soil|'s heterogeneity. In conclusion, the measured and modeled water balance parameters indicate that the temporary coverage system remains effective in limiting the infiltration rate. However, our studies revealed that the calculated and measured water seepage exceeded the values allowable by the German regulations. Additional studies have to assess variations in the soil water characteristics caused by weatherrelated wetting and drying cycles and influence of waste settlement changing the profile of slope.

Compost quality and its function as a soil conditioner of recultivation layers – a critical review

“…Additionally, a weather station located close to the landfill recorded the actual meteorological data (including precipitation, air temperature, wind speed, wind direction, air pressure, relative humidity and solar radiation). The actual evapotranspiration calculations are based on the potential evapotranspiration for grassland vegetation according to the Penman-Monteith formula (Allen et al, 1998) and a relation of actual to reference evapotranspiration typical for Schleswig-Holstein (Widomski et al, 2015).…”

“…The design and the determination of the layer thickness of the temporary landfill capping system in Rastorf (Northwest Germany) are adapted to maintain both the water balance and physical properties of the utilized natural origin boulder marl (Widomski et al, 2015). It is the subtarget of the temporary landfill capping system to minimize the drainage of precipitation water towards the compacted surface sealing layer and into the underlying waste body by maximizing the evapotranspiration rate from the soil surface and the locally appropriate vegetation by improved plant growth due to compost addition (Laner et al, 2012;Stępniewski et al, 2011).…”

Shrink-swell potential, hydraulic conductivity and geotechnical properties of clay materials for landfill liner construction

“…Isolation of landfills should be long-term and self-sustainable (Laner et al, 2012;Horn and Stępniewski, 2004), especially the permanent one, but temporary solutions may also be included (Widomski et al, 2015).…”

Effectiveness of Grassland Vegetation on a Temporary Capped Landfill Site

“…Longer phases during the vegetative period (July-September) nearly reached the wilting point of 65 mm, so, the evaporative zone (0.5 m) dried out more strongly and the transpiration capacity and thereby the ETa values of the grassland were restricted by (a) the inadequate water availability in the evaporative zone and (b) the limited water storage capacity, and (c) the limited capillary rise from deeper soil layers due to the compacted construction of the temporary capping system [5,6]. Thus, phases with water contents below the critical field capacity of 95 mm should be as short as possible to prevent desiccation in the deeper layer, thus, the modelled water content is a first indicator to describe the hydraulic stability of the capping system.…”

“…In case of this study, semipermeable, temporary capping systems intend a specific shutdown of the bioreactor, containing heterogeneous wastes and different amounts of biodegradable material, through controlled infiltration of precipitation into the waste body [4] and also allow biogas extraction [5].…”