• impermeable:  not permitting passage (as of a fluid) through its substance
• permeable: having pores or openings that permit liquids or gases to pass through having pores or openings that permit liquids or gases to pass through

Anticipatory Set

Ask students to look out the window and describe what kind of groundcover they see. They may describe sidewalks, grass, garden, dirt, sand, woodchips, tar, pavement, cement, paving stones, etc. If you don’t have a variety of groundcover outside your window, have them imagine a familiar place that does. As they name what they see, write two lists on the board under the headings “Pavement” and “Dirt.” Groundcover like cement, patio blocks, and tar would go under “Pavement,” while sand, grass, and woodchips would go under “Dirt.”

• Tell the students that they are going to play a game in which they will role play as salespeople for either a dirt groundcover or a pavement groundcover company. They will be hired by either the dirt company or the pavement company, and they have to think of creative ways to promote their product or criticize the competition.
• Allow students to self-select into one of the two groups (dirt or pavement salespeople). Allow the groups to spend a few minutes talking about the useful and good things about their product before you come together as one group again. Stand in a circle with the two groups mixed together. Have them toss a ball around the circle randomly. When a player catches the ball, before tossing it to another player, he or she must either say one use or good thing about his or her assigned groundcover or one negative thing about the other groundcover. Encourage creativity and details. Keep a tally of points for each company. Set a time limit of 5 to 10 seconds per student. If a salesperson cannot think of something to say, he or she may pass.  Continue playing until salespeople start running out of ideas. The group with the most tallies at the end wins. After playing the game, review some of the useful traits of both types of groundcover.
• Tell the students that there are positive and negative things about pavement, but that there are serious problems that occur in cities when too much ground gets covered with pavement. Ask the students to brainstorm potential problems of too much pavement (some sample answers are “higher temperatures” and “less oxygen because there are fewer plants”). Tell them that when there is a lot of pavement, water has no place to go because it cannot soak through to the ground below.
• Share the definitions of permeable and impermeable with the students. Ask them to determine which word applies to dirt and pavement.
  Ask:
  What would happen if storm water met ground that (because of urban development) was not permeable? (Sample answers: runoff may create flooding, pollution, and degradation of wildlife habitats)
  Tell the students that pavement (whether it is considered a plus or a minus) renders the ground impermeable.

Poetry: Write a poem about the Earth.
Physical Education: Run a half mile on pavement and on grass. Compare personal times and determine the better surface for speed and comfort.
Science and Math: Pour a pint of water on two different surfaces. Time how long it takes for the water to soak into the ground. Compare.