Environmental Engineering Reference
In-Depth Information
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Water Table
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Flushing Zone
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Hydraulic Conductivity (m/d)
Figure 5.7
Estimated hydraulic conductivity profile for materials screened by well
MW-516.
ranged from 4.3 to 14.3 m/day using the drawdown data from five monitoring
wells with an average of 9.1 m/day for the aquifer. This average value of 9.1
m/day was then used to estimate the hydraulic conductivity profile using the
estimates of relative hydraulic conductivity for each interval measured during
the flowmeter study (Figure 5.7).
The estimates of hydraulic conductivity for the individual intervals with
the flowmeter test show variability with depth as would be expected based
on the site geology (Figure 5.7). The average hydraulic conductivity for the
materials in the overlying sands from 3 to 7.6 m bgs is approximately 14.9
m/day, which is much higher than the value of 6 m/day estimated by LFR.
The value for the lower sands from 7.6 to 10.7 m bgs of 3 m/day is signifi-
cantly lower than the upper sands and is similar to the value of 3.2 m/day
estimated by LFR.
The site characterization showed that the highest concentrations of PCE
contaminant in the aquifer sediment (6000 to 90,000 mg/kg) were from 8 to
9.2 m bgs (Jawitz et al., 2000). This corresponds approximately to the zone
with the lowest measured hydraulic conductivities. Based on the properties
of PCE, it has been shown that PCE will migrate downward through the
aquifer to a zone of lower permeable materials, where it will be trapped in
the pore space. Depending upon the volume of DNAPL moving through the
aquifer and the thickness of the zones with lower hydraulic conductivities,
it is possible for the DNAPL to break through these zones and move deeper
into the aquifer.
