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Geology LibreTexts

14: Groundwater (Exercises)

Q14.1 How Long Will It Take?

i = (37-21)/80 = 0.2, V= 0.0002 x 0.2 = 0.00004 m/s.

At that rate it will take 2,000,000 s for the groundwater to flow from the gas station to the stream. That is 555 hours, or 23 days.

Q14.2 Cone of depression

The cone of depression increases the gradient of the water table in the area around the well. That should increase the rate at which water flows towards the well.

Q14.3 What is your water table doing?

[BC Ministry of the Environment at http://www.env.gov.bc.ca/wsd/data_se.../obswell/map/]

The water-level for a random observation well in BC is shown above. The water table is slowly rising at this location. Since 2004 the lowest water level has risen from just above 4 m below surface to around 3.6 m above surface and the highest level has risen from around 0.3 m below surface to nearly at surface (0 m). Prior to 2004, where the points are not joined with lines, the trend appears to be similar.

Q14.4 What goes on at your landfill?

Responses will vary

Q14.5 Finding a leaking UST in your community

Responses will vary

Q14.6 Manipulating a Contaminant Plume

What could you do at wells A and C to prevent this? Explain and use the diagram below to illustrate the expected changes to the water table and the movement of the plume.

Implications of pumping water from wells B and C and injecting water into well A [SE]

Possible Answer: Injection into well A will cause water table to rise there (like the reverse of a cone of depression), thus reversing flow direction to the right of well A and moving the plume towards Well B. Extraction from Wells B and C will cause cones of depression and help to reverse the flow and pull the plume back from the stream. Both wells B and C may receive contaminants and so the water from both may need treatment.