 Sand filters are very useful in treating runoff from confined hard surfaces such as car parks and from heavily urbanised and built-up areas.They usually do not support vegetation owing to the filtration media (sand) not retaining sufficient moisture and because they are usually installed underground.The filter usually consists of a sedimentation chamber as pre-treatment device to remove litter, debris, gross pollutants and medium-sized sediments; a weir; followed by a sand layer that filters sediments, finer particulates and dissolved pollutants.