Problemsolving Lab

Make a Topographic Profile

How does water level vary in an artesian well?

Artesian aquifers contain water under pressure. The table provides data about an artesian aquifer for three sites that are spaced 100 m apart along a survey line. It shows the following: elevations of the land surface, the water table, the upper surface of the aquiclude on top of the artesian aquifer, and artesian pressure surface.

Analysis

1. Plot the elevation data on a graph with the sites on the x-axis and the elevations on the y-axis.

2. Make a topographic profile of the survey line from Site 1 to Site 3. Use a heavy line to indicate land surface.

artesian well?

Recharge area

Recharge area

Figure 10.13 An artesian aquifer contains water under pressure. Identify the features that cause the primary difference between an ordinary well and an artesian well.

Topographic Profile

Aquifer Data

Site

Surface Elevation (m)

Water Table Elevation (m)

Aquiclude Elevation (m)

Pressure Surface (m)

1

396

392

388

394

2

394

390

386

393

3

390

388

381

2. Analyze What are the depths of the water levels in the three wells before they are pumped?

3. Evaluate what would happen if a well were drilled into the confined aquifer at Site 3.

4. Consider At what sites could there be an

An important artesian aquifer in the United States is the Ogallala Aquifer, which underlies the Great Plains. This aquifer delivers water to a huge area stretching from South Dakota to Texas. The recharge areas of the Ogallala Aquifer are located in the Black Hills and the Rocky Mountains.

Threats to Our Water Supply

Freshwater is Earth's most precious natural resource. Human demands for freshwater are enormous, because it is essential for life. Water is also used extensively in agriculture and industry. Figure 10.14 shows freshwater usage in the United States. Groundwater supplies much of this water.

^p Reading Check Summarize why freshwater is Earth's most precious natural resource.

Estimates of water supplies are the result of a dynamic equilibrium between various factors. These factors include the amounts of precipitation and infiltration, the surface drainage, the porosity and permeability of subsurface rock or sediment, and the volume of groundwater naturally discharged back to the surface. Several of these factors vary naturally over time, and several can be affected by human activities. Changes to groundwater supplies can lead to environmental issues such as a lowered water table, subsidence, and pollution.

U.S. Water Use

Power generation 48%

Figure 10.14 Municipal water and private wells supply your daily water needs. Identify how you are involved with water use in each of the other areas.

Irrigation

Municipal \ " l

Indu:

Private wells less than 1%

Industrial 5%

Model an Artesian Well

How does an artesian well form? What causes the water to rise above the ground surface?

Procedure S E^

1. Read and complete the lab safety form.

2. Half fill a plastic shoe box or other container with sand. Add enough water to saturate the sand. Cover the sand completely with a 1- or 2-cm layer of clay or a similar impermeable material.

3. Tilt the box at an angle of about 10°. Use a book for a prop.

4. Using a straw, punch three holes through the clay, one near the low end, one near the middle, and one near the high end of the box. Insert a clear straw through each hole into the sand below. Seal the holes around the straws.

Analysis

1. Observe the water levels in the straws. Where is the water level the highest? The lowest?

2. Identify t he water table in the box.

3. Analyze Where is the water under greatest pressure? Explain.

4. Predict what will happen to the water table and the surface if the water flows from one of the straws.

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