RBF_Cover (for eps) - National Water Research Institute
RBF_Cover (for eps) - National Water Research Institute
RBF_Cover (for eps) - National Water Research Institute
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intuitive system behavior. In the case of <strong>RBF</strong>, such examples might be:<br />
• The reductive dissolution of iron oxides by DOC and the resulting release of sorbed<br />
heavy metals.<br />
• The assessment of pesticide mobility during flood events.<br />
Denitrification, degradation of pesticides, and dissolution of minerals are closely linked to DOC,<br />
a key component of river water whose concentration can vary depending on the season and flow<br />
events. Because of the reaeration process, river water is oxygenated compared to groundwater.<br />
During the induced infiltration process, oxygen-rich river water enters the aquifer, as does DOC.<br />
On its travel path, DOC from river water is oxidized and either mineralizes completely or is<br />
trans<strong>for</strong>med to intermediates through bacterial catalysis, together with the organic carbon that is<br />
perhaps naturally abundant in the aquifer as sediment-bound organic matter. Oxygen in<br />
the invading water is used as an electron acceptor in the process. Normally, there is sufficient<br />
carbon available <strong>for</strong> microbial use; however, oxygen can become in short supply along the flow<br />
path. Once microbes consume the oxygen, an anoxic zone develops where the nitrate of the<br />
infiltrating river water and groundwater is used as a substitute electron acceptor. This leads to the<br />
reduction of nitrate along the flow path. Once nitrate is also depleted, thermodynamically less<br />
favorable oxidized iron and manganese minerals and/or sulfate might act as alternative electron<br />
acceptors. Note that the simulation of the oxidation of one or multiple organic substrates using a<br />
sequence of electron acceptors is routinely applied in the field of bioremediation modeling, mainly<br />
where the transport and natural attenuation of oxidizable organic contaminants is simulated<br />
(Barry et al., 2002).<br />
The simultaneous simulation of <strong>RBF</strong>-typical denitrification and mineral dissolution reactions can<br />
be handled by a number of existing codes (<strong>for</strong> examples, see Table 1). One such code is EASY-<br />
LEACHER (Stuyfzand and Lüers, 2000), which was used to simulate reactions along a transect of<br />
the Torgau <strong>RBF</strong> site on the Elbe River in Germany. EASY-LEACHER is a two-dimensional<br />
reactive transport code in EXCEL spreadsheet, combining chemical principles with empirical<br />
rules in an expert system. The code was found useful to attain a first estimate of water quality in<br />
the production well <strong>for</strong> a <strong>RBF</strong> site where the operation of wells is started and <strong>for</strong> an easy<br />
calculation of different boundary conditions. In contrast to EASY LEACHER, which uses a<br />
collection of (one-dimensional) flow tubes to account <strong>for</strong> the transport of chemicals, the<br />
FEREACT model (see Tebes-Stevens et al., 1998; Tebes-Stevens and Valocchi, 2000) is a<br />
Table 1. Examples of Reactive Multi-Component Transport Models<br />
Model Reference<br />
CRUNCH Steefel (2001)<br />
EASY-LEACHER Stuyfzand and Lüers (2000)<br />
FEREACT Tebes-Stevens et al. (1998)<br />
PHT3D Prommer et al. (2003a)<br />
PHAST Parkhurst et al. (1995)<br />
MIN3P Mayer (1999)<br />
TBC Schäfer et al. (1998)<br />
HBGC123D Salvage and Yeh (1998)<br />
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