In the ground-water study illustrated in Figures 17.25 and 17.26, ...

[sc00by25]

In the ground-water study illustrated in Figures 17.25 and 17.26, a chemical tracer was injected at 640 parts per million. After 461 days, the highest concentration measured was only 39 parts per million. How did the chemical tracer get so diluted?
 
  What will be an ideal response?

Question 2

Why does ground water flow more slowly than water in streams?
 
  What will be an ideal response?

[shailee]

Answer to Question 1

The chemical tracer was diluted by spreading out over a large area. Each time the water containing the tracer encountered a sand grain, it had to flow around the grain. The flow of water over many curving paths caused the chemical tracer to spread out over a larger and larger area, diluting its concentration.

Answer to Question 2

In ground water, most of the water is in tiny pores and is in contact with nearby solid surfaces. Friction along these surfaces slows the water down. In a stream, only the thin layer of water along the perimeter of the channel is slowed down by friction.