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unilogo Universität Stuttgart
Institute of Hydraulic Engineering

Research: VEGAS - Research Facility for Subsurface Remediation

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Investigations on the impact of contact time and strong rain falls on the eluate concentration in the leachate
Project manager:Dr.-Ing. Norbert Klaas, M.Sc., Jürgen Braun, Ph.D.
Research assistants:Dr.-Ing. Sylvia Mackenberg
Duration:1.9.2006 - 30.4.2007
Funding:BMBF
Comments:

This project is part of the research area:
Behaviour of Contaminants in the Subsurface


Abstract:

With leachate prognosis, the BBodSchV has established an estimation method of the resulting pollution into the ground water from both contaminated materials and polluted surfaces. The point of compliance is at the interface zone between the unsaturated and saturated zone. The research differentiates between the terms 'source strength' (concentration and mass flux on the bottom edge of the material) and 'transport prognosis' (potential changes of the mass concentration in the leachate while transgressing to the interface zone). The objective of the research was to conduct systematic column trials focusing on the source strength concentrations. These trials both continued and expanded on the research from the previously completed project 02WP0556 on the impact of column length and flow rates on the eluate concentration in saturated and unsaturated column tests. Additionally, strong rain falls and dry spells were approximated respectively by increasing the flow rate and interrupted water flow in the saturated column trials. The results indicate that the column length does not impact the selected criteria, with a few exceptions, neither in saturated nor in unsaturated conditions. An increase of the flow rate has negligible impact on the eluate concentration. Interruptions of the flow result in a temporary increased concentration for some of the parameters. Adjusting the flow rate to real rainfall quantities only resulted in differing eluate concentrations in a few of the parameters when compared to faster flow rates. Comparisons of lab results with field trials are congruent. In conclusion, column trials with saturated conditions can generally be recommended for determining the source strengths of most inorganic parameters. This can not be said for PAHs for which up-scaling from laboratory results to actual sites continues to be problematic. For some conditions (e.g. materials with neutral pH-values) biodegradation already occurs within the source strength material in field tests. Thus, saturated column trials can result in severe over-estimation of the leachate in actual unsaturated conditions.