Source: Geoscientists Without Borders®, Society of Exploration Geophysicists Foundation.
Adapted with permission.
The United Nations includes clean water and sanitation in its sustainable development goals. Many places face severe water shortages. The Geoscientists Without Borders® (GWB) program supports teams to collaborate with communities to solve problems, including water shortages.
GWB scientists use geophysical techniques to find underground layers of sediments or rock that contain enough water to be drilled for water wells. These kinds of rock layers are called aquifers. In this activity you will build a model aquifer.
• Clear container about 5–8cm deep
• Wide drinking straw, cut to the depth of the container
• Narrow clear tube that easily fits into the wide drinking straw (such as a narrow drinking straw or aquarium airline tubing), cut to 2–3cm longer than the wide straw
• Medium-sized gravel (such as aquarium gravel with grains 3–5mm wide), enough to fill the container to 1–2cm below the top
• Gauze, about 5cm square
• Rubber band
• Water with blue food coloring
• Sharpened pencil
- Add gravel to the container to 1–2cm below the top.
- Add colored water to the container. Stop when the water is about halfway up the gravel.
- The gravel models the unconsolidated sediments of an aquifer. The water models the groundwater in the pore spaces between sediments. The water level represents the top of the saturated zone in the ground called the water table.
- Cover one end of the wide straw with gauze. Secure it with the rubber band.
- The wide straw models the well casing. The screen at the bottom keeps sediments out but allows in the water.
- Use the pencil to push aside the gravel while carefully inserting the wide straw, gauze-covered end down, vertically into the gravel until the bottom is 2–3cm below the water level.
- Slide the narrow tubing into the wide straw until its end rests against the gauze.
- Put a finger over the top of the narrow tube and lift it out of the wide tube — but before doing this, predict what you will see as you lift the tube out.
Once a suitable aquifer is located, a well system is installed that keeps the water safe from contamination while allowing it to be pumped to the surface for use.
The water from some wells can be contaminated by salty groundwater. This is called saltwater intrusion. Suppose you added salty water to the gravel in your aquifer model. Do you think the salt would get into the well? How could you safely test the well water for salt?