Quality of Stormwater From Residential Areas.
Stormwater from urban residential areas has been found in several studies to contain a variety of pollutants. These include solids, nutrients, chlorides, bacteria, trace organics and heavy metals. The impact of these substances on a receiving environment is controlled by such factors as concentration, duration of discharge, time of discharge and the sensitivity of the receiving environment to a particular pollutant. As point sources of wastewater, residential stormwater can be, for brief durations, substantially in excess of existing water quality standards. Research using biological indicators of environmental impact has also shown that intermittent stormwater discharge can have a measurable impact on the receiving water downstream of storm sewer outfalls (Garrie 1986, Payne 1990, Willemsen 1990, Gast 1990).
Control of pollutants carried in stormwater from residential areas has not, however, usually been of sufficient concern to warrant specific control measures, although some American municipalities and states have in the last decade implemented substantive stormwater quality programs (Bissonette 1986, Zeno 1986, Livingston 1986, Shaver 1986).
Strategies for improving the quality of residential stormwater can range from elimination of polluting substances to end-of-pipe control. One strategy involves adding quality requirements for structures which are already required for the control of stormwater quantity. These structures include wet and dry detention ponds, wetlands, grassed swales, and groundwater recharge devices. The improvement in stormwater quality produced by these control structures is usually associated with a reduction in the suspended solids concentration in the stormwater. Pollutants such as BOD5, heavy metals and nutrients are removed to a varying extent by the removal of suspended solids. Nutrients and metals may also be removed from sediment and from water by plant growth in these structures.
Careful design and management of structures used for stormwater quality improvement is needed. Pollutants initially removed may eventually be discharged through re-suspension or re-solubization unless this is prevented through specific features of the design and operation of the facility. The research reported here was undertaken to help establish whether low density residential areas and/or commercial development in residential areas warrant stormwater treatment beyond that which currently exists. Specifically, the objectives of this research were to:
1. Characterize the quality of stormwater from two residential catchments and from a commercial catchment typical of those located in residential areas. The focus was on obtaining data on the maximum, and the steady state or clean concentration of several stormwater quality parameters.
2. Assess the impact of existing water quantity control structures on the quality of stormwater from two residential catchments.
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