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When water passes through the soil and rocks in the ground, many pollutants are naturally filtered out of the water. Some pollutants attach themselves to the surrounding soil. Others are eaten away by microbes found in the soil. Either way, soil and rock serve as NATURAL filtration device for the groundwater. Parks, grassy lawns, paved roads, or playgrounds with wood chips. Which would least help this natural filtration process?
What is paved roads?