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The pollutant removal efficiencies of stormwater runoff by settling were analyzed using field samples collected in 4 different raining events in a test bed installed in the Gwanpyung-Cheon stream in Daejeon. A 1.8 m high with 30 cm diameter cylindrical settling device was used for the settling test by measuring concentration of TSS, TP and TN for time and height. The pollutants removal rate was relatively high in the first 4 hours while 24 hours seem to be necessary to reach steady state in pollutant concentrations. However, there were no considerable differences in concentrations for height at a given time. This indicates most of particulate pollutant in the test seems to show independent settling with no interference to each other. Much part of particle sizes were distributed in the range of 10~100 µm. Average particulate fractions of TP and TN were estimated as 52.4% and 23.5%, respectively. This results explain why TN is difficult to remove by simple settling. This study indicates that a simple settling can provide effective method to remove significant amount of TSS and TP effectively and this can be used to protect urban river water quality.

The effectiveness of the first flush treatment system using settling process was evaluated to reduce urban nonpoint source pollutant loads to surface water during storm events. A pilot scale system was constructed and tested in the field and surface runoff samples were collected automatically according to pre-defined conditions. Nine rainfall events were tested and average removal efficiencies of TSS (Total Suspended Solid), TP (Total Phosphorus) and TN (Total Nitrogen) were evaluated as 87.4%, 75.3%, and 43.6%, respectively. Concentration and removal efficiency of pollutants were found to be affected by an amount of rainfall and rainfall intensities of the respective events. This seemed to be caused by the greater particulate fractions of first flushed samples than the samples collected in later time periods during the same rainfall events. The study showed that it is possible to remove a significant portion of the nonpoint source pollutant loads in initial rainfall runoff by using a simple settling process for TSS and TP without requiring additional power or chemicals.

An integrated management system was developed for the efficient operation of a storm water treatment unit to assist in the management of urban river water quality and flow. The SWMM hydrological model was calibrated and then used to predict the hydrograph and concentration graphs of surface runoff from a storm events based on weather forecasts. These results are used to decide how to operate the first flush treatment unit in the field by comparing water quality in the unit with that in runoff. This water quality monitoring system will also be used to reflect real-time field conditions, which will be used to improve the efficiency of the treatment system. The first flush treatment unit can be installed underground to use for storage of storm water. The system was tested against field data collected in a sub-basin of the Gwanpyung-cheon stream in Daejeon, Republic of Korea. Continuous monitoring results indicated that the first 4 hours of surface runoff exhibit higher concentrations than normal levels in the study site, and these levels can be used to determine the necessary volume for efficient treatment. When settling in the treatment system over 24 hours, the average removal efficiencies for TSS, TP and TN were 87.4%, 57.3%, and 43.6%, respectively.