Evaluation and imptovement of quality characteristics of urban stormwater. October 1976.

Stormwater from three Sydney urban catchments show that in separately sewered areas has a greater concentration and carries a greater total load of pollutants than effluent from secondary sewage treatment plants. Pollution and nutrient indicators are highly concentrated in the first flush of a storm, but fall rapidly to low levels. An important exception is that phosphate concentration remains approximately constant. When the discharge increases sharply, the suspended solids and phosphates increase slightly. Faecal coliform concentration is usually between one and two orders of magnitude less than raw sewage. Some stormwater samples were subject to simple settling for up to an hour: typically, these showed that on an annual basis , short duration settling of storm water could remove amounts of pollutants comparable to the amount which could be removed by tertiary treatment of secondary sewage effluent from the same catchment. The cost of settling would be fav less than tertiary treatment of effluent