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<br />CONCEPT 21: Confininq layers that seoarate aquifers usually leak. <br /> <br />Action: None; the confining layer in this model was designed not to <br />leak. <br /> <br />Discussion: Unlike the model, the presence of a confining layer is not <br />always sufficient to protect the aquifer below from contamination. Most <br />naturally occurring confining layers vary in thickness and may be <br />fractured or discontinuous. Also, when water is withdrawn from the <br />confined aquifer, a zone of lower pressure is created which induces <br />water movement downward through the confining layer. Water moves very <br />slowly through the confining layer, and may carry contamination with it. <br />Some contaminants may be adsorbed on the particles in the confining <br />layer and would not be carried through it. <br /> <br />CONCEPT 22: Water Quality can vary within an aquifer. <br /> <br />Action: Observe that the dye spots, when they first enter the aquifer, <br />occur only in a narrow zone. ~s the dye plumes move downgradient, they <br />become wider. <br /> <br />Discussion: Contaminants entering an aquifer often do so only at a <br />point or in a narrow zone. The concentration of the contaminant may be <br />quite high in that small volume of water. However, as groundwater <br />continues to move, the zone of contamination widens out. <br /> <br />CONCEPT 23: Contaminated surface water mavDollute Qroundwater. <br /> <br />Action: Add either the dye or the diluted dye to the lake. Mix the dye <br />with any water already in the lake. . <br /> <br />Discussion: The colored water will move into the sand around the lake; <br />especially if the sand is unsaturated. Eventually the color will move <br />into the groundwater. Pumping from one of the pumping wells will cause <br />the color to move toward the well. The pollution not only contaminates <br />the groundwater but, again, can end up in our drinking water supply. <br /> <br />CONCEPT 24: <br /> <br />Contaminated Qroundwater may Dollute surface water. <br /> <br />Action: <br />side). <br /> <br />Inject diluted dye into a piezometer near the lake (upgradient <br />The dye will eventually reach the lake. <br /> <br />Action: Use the injection well to add dye to the confined aquifer. <br />Allow the water pressure to spread the dye throughout the aquifer. The <br />dye will leave the aquifer through the artesian well and add color to <br />the lake. <br /> <br />Discussion: Groundwater can be a major source of water for a river or <br />lake. Contaminants in the groundwater would be discharged into the <br />river or lake. Natural processes such as sunlight, aeration, and <br />turbulence break down some pollutants. Other pollutants from <br /> <br />8 <br />