Permeable surfaces have interconnected pore spaces within the material allowing water to drain into the soil to filter out pollutants. Impermeable surfaces are solid surfaces that don’t allow water to penetrate, forcing it to run off. Permeable pavers and artificial turf are often laid on a bed of sand or gravel to enhance drainage properties. According to the US Environment Protection Agency, permeable surfaces such as pavements can also reduce the need for road salt and reduce construction costs for residential and commercial developments by reducing the need for some conventional drainage features