Environmental Engineering Reference
In-Depth Information
not actually broaden the plume, this provides confirmation of plume cap-
ture. The particle tracking method is therefore an important control for the
correct positioning of the extraction and injection wells. The results show
that in none of the scenarios the TCE plume spread during remediation. In
fact, the extraction and reinjection of groundwater leads to a diminution of
the plume (>500 μg/L area, see appendices).
Owing to the low hydraulic conductivity of the sediments, the hydrau-
lic changes through extraction/injection of groundwater do not show up
quickly, but need quite a long time. In order to check this, the simulations of
Scenario 4.1 consider transient hydraulic conditions. The results show that
stable hydraulic conditions are only reached after a duration of about 1 year.
This has to be considered in the remediation design.
In the scenarios, the distribution of TCE (dissolved in the groundwater) is
demonstrated after 1, 3, and 10 years. Scenario 1 describes the natural situa-
tion without any remediation (even without trial remediation).
In conclusion, the remediation of the source zone with the current wells
(Scenario 2) is leading to a satisfactory clean up of TCE within the planned
timeframe of 10 years. The contaminant concentration has fallen to less than
100 μg/L of TCE leading to a separation of the remaining plume from the
original contaminant source. The same is true for the hot spot. Here, a small
number of remediation wells are leading to a relatively rapid remediation of
this spatially limited gravity center of the pollution (Scenario 3).
The remediation of the source zone and hot spot alone leads to a reduc-
tion of the TCE mass by 64%, leaving a remaining total mass of less than
20 kg (dissolved + adsorbed). The remediation at the tip of the plume has
little influence on the decreasing TCE mass. However, even in Scenarios 2
and 3, the two existing extraction and injection wells at the tip of the plume
contribute to TCE reduction. The effect of the additional wells at the tip of
the plume in Scenario 4 has only a minor influence on the removal of total
TCE mass.
The influence of the infiltration of cleaned groundwater can be seen from
Scenario 4.3. Compared to Scenario 4, where water is reinjected into the aqui-
fer at the tip of the plume, the northwestern part of the TCE plume remains
much broader in Scenario 4.3 In Scenario 4.3, the extraction rate for the line
of wells at the tip of the plume had to be reduced in order to avoid the wells
r u n n i n g d r y.
When building a second line of wells across the center of the plume
(Scenario 5), the contaminant mass in the center is reduced even more. The
reduction, however, is most significant at the tip of the plume. Moreover, by
reducing the total number of wells at the tip of the plume, the north-west-
ward spread of the TCE continues. In this scenario, the TCE mass is reduced
by 70% after 10 years and therefore, the remaining contaminant mass is
slightly lower than that in Scenario 4. It should be noted that with this well
positioning, a large area displays a mean remaining TCE concentration after
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