What happens with stormwater?
Stormwater either infiltrates the soil, is conveyed over the soil surface, or it is detained by an impermeable material at the surface. Natural chemical and bacteriological processes that occur in the top few inches of soil break down oils and chemicals to help prevent the surface runoff from contaminating the groundwater. In places like cities where limited permeable surfaces exist, special infiltration basin structures may be built alone or as the base courses to pavement. Ponds and wetlands function like natural treatment plants because they allow particles to settle out, and chemicals to be absorbed and decomposed in the bottom sediment. Because extended infiltration is a treatment process that relies on the physical properties of nature like sunlight, air, soil and microorganisms, it can also be much less expensive than mechanical treatment. Sometimes, when ponding occurs over long periods, heavy peat begins to form which makes the soil even less permeable.
