Stormwater pollution in soakaways
The polluting potential of stormwater run-off from man-made surfaces has become increasingly recognised. Run-off can carry a variety of contaminants, including amongst others heavy metals and hydrocarbons. A number of techniques have emerged for the quantity and quality control of urban run-off. The main two have been widely and successfully applied. These have involved the use of ‘hard’ engineered structures, such as underground storage, treatment and flow control facilities and the ‘soft’ engineered structures such as swales, wetlands and ponds.
While there is currently a focus on ‘new’ development activity, it is likely that this will need to be broadened in the future, to look at older/existing development infrastructure, as water-quality requirements tighten . This will demand the adoption of increasingly innovative design approaches, in which clusters of techniques are integrated together and implemented around existing infrastructure in an overall complementary fashion.
Sediment particles can adsorb some chemical pollutants such as phosphates and pesticides, and also tend to be associated with other pollutants including heavy metals and hydrocarbons. As such, sediment entrained in urban run-off should ideally be prevented from entering watercourses.
The optimal design of systems to remove pollutants from stormwater relies somewhat on an understanding of pollutant characteristics. In particular, for sediment removal, it is useful to have an understanding of the physical and chemical characteristics of the sediments, such that those presenting most potential to pollute can be specifically targeted.
