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<br />room with basketballs. Why? Because 1) the void spaces are <br />bigger and the connections between the voids are bigger, and <br />2) a water molecule will have a shorter distance to go around <br />the large basketballs than it would around the smaller <br />baseballs or the stacked books. <br /> <br />in the model, the sand in the unconfined aquifer can be <br />thought of as being the baseballs, the gravel in the confined <br />aquifer can be thought of as being the basketballs, and the <br />bentonite/clay confining layer can be thought of as being the <br />books that are neatly and tightly stacked. <br /> <br />Some illustrations of the concept of 'parts per million;, <br />'parts per million' and 'parts per trillion' if you get into <br />the concentrations of contaminates in the ground water: <br />1 part per million: <br />1 inch in 16 miles <br />1 minute in 2 years <br />1 cent in $10,000 <br />1 ounce of salt in 31 tons of potato chips <br />1 bad apple in 2,000 barrels <br />1 part per billion: <br />1 inch in 16,000 miles <br />1 second in 32 years. <br />1 cent in $10 million <br />1 pinch of salt in 10 tons of potato chips <br />1 lob in 1,200,000 tennis matches <br />1 bad apple in 2 million barrels <br />1 part per trillion: <br />1 postage stamp in an area the size of Dallas <br />1 inch in 16 million miles (more than 600 times around <br />the earth) <br />1 second in 320 centuries <br />1 flea on 360 million elephants <br />1 grain of sugar in an Olympic-sized pool <br />i bad apple in 2 billion barrels <br />in terms of the ground water model, put ten drops of food <br />coloring in the 1000 milliliter flask and you will have 1 part <br />per thousand of food coloring in the water; put ten drops of <br />that solution into another 1000 milliliter flask and your new <br />concentration will be 1 part per million; put ten drops of <br />that solution into another 1000 milliliter flask and you will <br />have 1 part per billion; another way to look at this is if you <br />add one drop of food coloring to 100 flasks of water you will <br />end up with about 1 part per million of food coloring in the <br />water (these are rough, rounded off concentrations, but they <br />will serve to illustrate just how little contaminant is <br />required to degrade a water resource) . <br />