Contaminant plumes are finite – even in 2D laboratory experiment?

Sandip Chaudhary1, Prabhas K. Yadav2, Falk Händel3, Thomas Krause3, Rudolf Liedl3
1 University of Potsdam, Institute of Earth and Environmental Science
2 Sharda University, School of Engineering and Technology, Greater Noida, Indien
3 Technische Universität Dresden, Institute for Groundwater Management

O 15.7 in Forum Junge Hydrogeologen (H 36, NW III)

28.05.2014, 15:20-15:40, H36, NWIII

In the last ten years (approximately) a lot of natural attenuation scenarios have been modeled under the assumption that the degradation of pollutants occurs mainly at the reaction front. This was particularly facilitated by using numerical methods which readily covers a wide range of different hydrogeological scenarios to predict associated plume length. In contrast, due to experimental difficulties, only part of the scenarios has so far been simulated in laboratory experiments in order to assess the suitability of the models under controlled conditions.
This paper deals with the design and evaluation of natural attenuation scenario at laboratory scale in a tank experiment which is based on a vertical 2D experiment (tank dimension 200 cm * 2 cm * 15 cm). The study aims at the maximum spreading of electron donors (contaminant) reacting with the vertically entering electron acceptors (e.g. oxygen). In the experiment, this scenario was simulated by a base-acid pair with pH = 11.3 and pH = 2, respectively. An indicator mixing with both acid and base was used to visualize the reaction front. Glass beads (diameter 1.55 mm to 1.88 mm) was used as porous media. Experiments were evaluated after reaching steady conditions.
For the experimental setup, a special configuration was designed to uniformly supply acid vertically via the aid of suction cups, which are arranged linearly along the top of the glass beads, and supplying base horizontally using a multichannel peristaltic pump.
Besides this novelty, the experimental design also provided a way to optimize the time to achieve the steady state. This was achievable because the tank was first saturated with acid (electron acceptors) and then flooded with base (electron donors). So, as the electron donors entered the tank, reaction occurred simultaneously along the front, which accelerated the setup to achieve steady conditions.
The results of different experiments showed that plume height decreased along the flow direction almost reaching the bottom of the tank, however, exceeded the length of the test tank. Still with reference to the experimental results, it was possible to estimate the length of plume by extrapolation. Furthermore, values or ranges of transverse dispersivity were determined by inverting an analytical model and were found to correspond to data in the literature.
The developed experimental design is considered suitable to experimentally simulate vertical access of electron acceptors to contaminant plume. This can be a basis for comparison with corresponding numerical and analytical models which are intended to predict plume lengths.

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Letzte Änderung 30.04.2014