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Fig. 19.13 Groundwater flow pattern for a small basin including a river
another example of flow focusing is illustrated. Here a small basin was simulated
with the inflow of uniform recharge (365 mm year 1 ) and the discharge point corre-
sponding to a river located at the groundwater divide. Particle tracking simulations
using the code MODPATH (Pollock 1994 ) clearly show the focusing of path lines
close to the river, resulting, also in this case, in a stronger mixing and, therefore, a
potentially more efficient reactive zone.
19.5 Case Study: Transport of Ammonium from a Landfill
Examples of scenario specific modeling for the identification of governing pro-
cesses and importance of parameters have been shown in the previous section.
In this section an application of reactive transport modeling for a real case study
is presented.The domestic waste landfill site close to the village of “Osterhofen”
in south-western Germany has been investigated systematically as monitored
Natural Attenuation (MNA) reference site by order of the state EPA (LfU Baden-
Württemberg). Like many others, this landfill emits an extended plume of ammo-
nium (NH 4 + ) as major contaminant. A detailed characterization of the site and the
assessment of monitored Natural Attenuation as land management option can be
found in Rügner et al. ( 2004 ). The investigation of the site by integral pumping tests
is described in Bayer-Raich et al. ( 2004 ) and the modeling approach in Maier and
Grathwohl ( 2006 ).
The former gravel pit was filled with municipal waste between 1969 and 1977.
The area is built up by moraine sediments and periglacial deposits from the latest
alpine glaciation period. The contaminated gravel aquifer has a thickness between
two and five meters. Groundwater flow velocities between two and three meters per
day were observed. Annual water table fluctuations between 1.5 and 3.5 m have been
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