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Our transcription: One way in which we pollute groundwater is through badly designed or improperly maintained landfills. When rain leaches the pollutants from a landfill into the saturated zone, a plume of polluted waste spreads out in the direction of groundwater flow. Fortunately, engineers are now developing more effective techniques to minimize the impact of landfills on groundwater quality. One of the techniques that has been developed recently is a landfill liner system. Its multiple layers act as a barrier between the garbage and the surrounding environment. The base of the liner system is simply a layer of impermeable clay, which is spread around the landfill and compacted by heavy equipment. While the clay itself might be adequate to prevent the seepage of polluted water, or "leachate," out of the landfill, extra precautions are taken. A synthetic high-density plastic liner is placed on top of the clay. Next, a half meter or so of permeable sand along with drainage pipes is laid across the plastic. Here the leachate accumulates and flows out from beneath the landfill for safe disposal elsewhere.
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