Germany has strict regulations regarding mineral waste, requiring contaminated soil and building materials to be reused wherever possible. Could organic topsoil containing elevated concentrations of geologically generated arsenic be used for an infill project without the arsenic leaching into the groundwater?
“Water Balance of an Earth Fill Built of Compacted Clay: Field Data and Numerical Modeling,” a new paper in the Journal of Geotechnical and Geoenvironmental Engineering, explores an alternative sealing system for noise protection embankments for a runway at Munich Airport. Authors Emanuel Birle, Elena von der Straten, and Manuel Melsbach examined contaminated topsoil to determine its mechanical and compaction properties as well as the hydraulic behavior under compacted conditions. The team performed field measurements and factored in precipitation records from 2008 to 2018 and analyzed the interaction between the soil and the atmosphere as well as the water movement within the layered test fill.
Based on their findings, published in the ASCE Library, the researchers suggest that mineral materials with low permeability can be used in fills without an extra sealing layer. Even with moderate amounts of environmentally hazardous substances, groundwater can still be protected in these settings. Their paper is available in the ASCE Library at https://doi.org/10.1061/(ASCE)GT.1943-5606.0002767. Here is its abstract:
With the aim of testing an alternative sealing system for noise protection embankments containing environmentally hazardous substances, a fill of compacted clay with organic and elevated arsenic content was tipped. The fill was extensively monitored to measure the water balance and seepage. Due to the low permeability of the soil, a simple capping, consisting of a geosynthetic drainage mat and a clayey top layer, was used. Measurements over a 10-year period demonstrate that the chosen capping system is very efficient in minimizing seepage from the core. The success is based on a high water retention capacity of the topsoil in combination with the capillary-breaking effect of the drainage mat. Numerical simulations of the water balance of the test fill indicated that the calculation results are very sensitive to the fineness of the finite-element mesh, the choice of the time steps, and the hydraulic properties of the drainage mat. After calibrating the hydraulic properties of the drainage mat using the measured data of the first 3 years, the measured water balance of the 10-year period could be reasonably predicted by the model. Differences between the measured and the calculated discharges from the drainage mat and the core material are attributed to heterogeneities of the materials in the field and to the hysteresis of the soil water retention curve not being considered in the model.
Read the full paper in the ASCE Library: https://doi.org/10.1061/(ASCE)GT.1943-5606.0002767