There was an incident with a cargo train that resulted in a major accidental spill of harmful chemicals. The liquid chemicals quickly seeped through the sandy soil into the underlying groundwater system. The contaminated groundwater is migrating toward a river used for drinking water supply for a large population center. Immediate control and remediation is needed to avoid a catastrophe.
Construction of a drainage gallery and
an infiltration channel for aquifer flushing is proposed for the cleanup of the
contaminant plume approaching the river as shown in the figure below.
Operating water level in the gallery is projected at 275.3 meters above mean
sea level (amsl).
A.Develop a preliminary MAGNET model of the unit groundwater inflow (inflow per unit width) into the
drainage gallery during the month of May, if the effective aquifer recharge in
May is estimated to be 2.5 inches (i.e., 35%
of the total May precipitation). The
average altitude of the water surface in the river in May is 281.7 meters amsl,
and the water level in the infiltration channel is projected at 283.0 meters
amsl. Hydraulic conductivity of the
aquifer material is 2.1x10-4 m/s.
Other elements necessary for the calculation, as determined by field
investigations, are shown in the hydrogeological cross-section in the figure below.
B. Also solve the problem analytically and compare the results.
Figure: Plan view (top) and cross-sectional view (bottom) of
the proposed alternative for the aquifer remediation. 1: Direction of
groundwater flow in natural conditions. 2: possible direction of groundwater
flow between the infiltration channel and the river when the drainage gallery
is not operating. 3: direction of groundwater flow between the infiltration
channel and the river when the drainage gallery is operating.
MAGNET/Modeling Hints:
- Use 'Synthetic Mode' to set up your flow model domain ( 'Other Tools' > 'Utilities' > 'Go to Synthetic Case Area').
- Use the ‘Distance Display’ capabilities when editing geometric features and/or the ‘Ruler’ tool to properly represent distances between model features.
- Add prescribed head line or zone features near the left and right edges to represent the infiltration channel and river, respectively.
- Analyze the results using the Display Charts tool ('Analysis Tools' > 'Analysis' > 'Display Charts')