Experiment V: CIVIL AND ENVIRONMENTAL ENGINEERING


Laboratory on Groundwater Flow and Pollutant Transport in an Aquifer

Objective
To demonstrate the principles of the hydrologic cycle and to illustrate how groundwater flows and can become polluted and how it can be cleaned up.This laboratory is more of a demonstration rather than a participatory event.

Materials

  1. Sand-Tank Groundwater Flow Model manufactured by University of Wisconsin Stevens Point, College of Natural Resources, Stevens Point, WI 54481. Phone: (715) 346-4613; Fax (715) 346-3624. Price: $250.00 plus $10.00 shipping. Waiting time: 2 - 4 months. The model comes with plastic syringes for injecting dye and a manual discussing how to set it up and suggestions for discussion points.

  2. 6 ft. of 1/2-inch plastic tubing to connect aquifer outlets toplastic bucket
  3. 1 plastic bucket (2-5 gal)
  4. red, blue, and green food coloring
  5. small (~ 1 pint) bottles (used Snapple bottles work just fine) in which to dilute food coloring in water
  6. 2 1-gallon plastic jugs (used milk jugs will do) for water supply
  7. 2 1-quart mason jars to provide constant-head reservoirs
  8. magic marker to mark position of water table on aquifer
  9. paper towels

Procedure
Place tank on a table and have the students sit in a semicircle around the table on the floor. Set up flow system per the directions in the manual that accompanies the tank. The students can get involved in discussions that are question-answer format. Some hands-on participation by the students can include: injecting dye into the tank at certain points when asked to do so by the instructor; tracing the water table location with a marker on the exterior of the tank; pumping the wells by withdrawing water with syringes; counting how many syringe-volumes of withdrawn water it takes to remove any injected dye.

Discussion

The concepts that can be discussed and illustrated include the following:

  1. General information about groundwater
    a. Groundwater flow is part of the hydrologic cycle.
    b. Groundwater is recharged by precipitation.
    c. Groundwater flow generally follows the surface topography -- it flows from upland to low areas.
    d. Groundwater is flows in pores and cracks in soil and rocks.
    e. Groundwater naturally flows very much more slowly than water in streams.
    f. Groundwater can be withdrawn from wells and is often the water supply for homes in non-urban areas.
    g. Groundwater supplies water to rivers in many areas (the reverse can also be true).
    h. Human activities such as disposing of wastes in landfills can contaminate groundwater.

  2. Water quality
    a.Pollutants can enter groundwater from a number of sources including leaking landfills and waste ponds, illegal disposal of wastes into abandoned wells, over-application of pesticides and fertilizers to land.
    b. Pollutants entering the subsurface can travel with groundwater and spread out due dilution and due to the flow of the dissolved pollutant around grains of soil or through crevices in rocks.
    c. Groundwater contamination occurs as a thin plume.
    d. Contaminated groundwater can pollute surface water.
    e. Contaminated surface water can pollute groundwater.

  3. Properties of aquifers
    a. Definition of an aquifer (confined vs. unconfined)
    b. Definition of a water table
    c. Where springs come from
    d. How the type of sand/rock affects the water flow rate

  4. Characteristics of water wells
    a. Groundwater can be withdrawn from wells.
    b. Pumping a well creates a cone of depression around the well.
    c. Pumped wells may interfere with each other
    d. Wells can be contaminated by pollution from distant sources.
    e. Wells can cause groundwater pollution.


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