Seasonality assessment of the first flush phenomenon in a rainwater system

ABSTRACT

Surface runoff in urban areas is able to carry pollutants to water storage systems. The purpose of this study was to assess the concentration of pollutants in the initial diverter systems called First Flush (FF), and Reservoir (RR) rainwater samples by means of Average Event Means Concentrations (EMCs) and Concentration Curves (CC) in accordance with the seasons of the year. The methodology consisted of an analysis of 68 samples collected from the rainfall system of Rio de Janeiro (RJ), from 2013 to 2019, and statistical data handling. The parameters of Turbidity (TU), Total Dissolved Solids (TDS), Alkalinity (ALK), and Chloride (CHLO) in the FF and RR systems were analyzed. The results showed that there was a low correlation of data between the parameters and seasons of the year. In Summer, precipitation led to a greater dilution of the pollutants since the TU and TDS parameters had lower values than was the case in other seasons of the year, largely as a result of atmospheric instability. The CHLO and ALK showed that the first wash load (FWL) occurred more often in the Spring. The FF had a turbidity EMC of 73 UNT, while in the case of RR, the value was 4.3 UNT. The pattern of behavior was similar in the other parameters that were analyzed and provided evidence that the concentrations of pollutants in the FF system, are a means of separating the initial volume of runoff on the surface. It was concluded that the installation of FF is essential in rainfall systems due to the significant reduction of the EMC by the initial disposal of pollutants in the volume stored in the reservoir, regardless of the season of the year.

Keywords:
curves M(V); quality of rainwater; first flush; widespread pollution