Environmental Engineering Reference
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10 years. When distributing the extraction wells in the center of the plume
(Scenario 6), remediation becomes significantly more efficient.
4.6.1 Effectiveness of Passive Remediation
The passive remediation by the REMAT™ filled annular space of the
extraction wells was evaluated in an additional model. The detailed model
describes the development of the TCE concentration at the tip of the plume,
once active remediation has ceased. To this, additional simulations were car-
ried out following 10 years of remediation with a line of extraction wells
at the tip of the plume. Here, the groundwater is cleaned while it passes
the annular space of the extraction wells by the adsorption of TCE on the
REMAT™. As the hydraulic conditions of the reactive material are better
than those in the sediments, the sphere of influence of the passive wells is
slightly bigger than their large diameter. Nevertheless, the groundwater is
not completely captured because the distance from one well to the next is too
great. The numerical simulations were carried out for a period of 30 years.
The results show that the contaminant plume is not entirely captured by the
line of passive wells.
4.7 Evaluation of the Simulations
The simulations have shown that a complete passive remediation of the site
in an acceptable period of time is not possible. Despite the high number of
large diameter extraction and injection wells and their great depth, each of
the scenarios leads only to partial remediation. However, they do show that
the TCE mass and its spread can be reduced significantly. Passive remedia-
tion approaches, on the other hand, do not lead to a significant remediation
at this site. Moreover, the reactive material has only a limited adsorption
capacity and the installation of large diameter wells is rather expensive.
On the basis of numerical modeling, CRC CARE demonstrated that a
passive remediation would take several decades. Therefore, a remediation
concept consisting of an active source remediation and passive PRB sys-
tem which consists of large diameter bore wells was developed. Modeling
results demonstrate that both the source area treatment and long-term moni-
toring of PRB shall continue in order to achieve desired remediation goals.
CRC CARE has predicted the contamination scenarios at the site after 1, 2,
and 10 years of treatment as shown in Figures 4.7 through 4.9. This could
be compared to the status of groundwater contamination shown along with
groundwater flow contours in Figure 4.2.
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