Dry wells are gravity-fed excavated pits lined with perforated casing that are backfilled with gravel or stone. They are typically 3 feet wide and 15 to 50 feet deep with a number of small openings in the casing on the side and at the bottom. Dry wells can be used as a Low Impact development (LID) tool to help infiltrate and retain, filter, or slowly release stormwater at a given site(s). Numerous designs have been used, some including pre-treatment features such as vegetated swales and sedimentation basins that help trap sediment and other pollutants. These features help minimize clogging in the dry well as well as reducing contaminants released into the subsurface.