Event Mean Concentrations (EMCs) and First Flush Characteristics of Runoff from a Public Park in Korea

Characteristics of non-point source (NPS) pollution runoff from a public park in Gwangju, Korea were investigated. Results exhibited the highest pollutant concentrations at the start of the rainfall events due to their build-up and wash off processes. The average event mean concentrations (EMCs) were 27.8, 7.2, 56.3, 7.5, and 0.84 mg/L (range: 4.2-54.8 mg/L) for COD, (0.5-20.8 mg/L) for TOC, (22.3-138.4) for SS, (1.4-18.5 mg/L) for T-N, and (0.17-2.02 mg/L) for T-P, respectively. The study site presented a strong first flush effect for most rainfall events. However, no first flush effect was observed in rainfall events with small rainfall factors (e.g. intensity, amount, and runoff depth). On the other hand, the ratios of total pollution loads discharged by the first 20% of runoff volume were 32% for COD, 34% for TOC, 36% for SS, 42% for T-N, and 50% for T-P. Especially, MFF20 (mass first flush) values of T-N and T-P were larger than those of other pollutants (COD, TOC, SS), indicating that T-N and T-P are easily transported by stormwater runoff from the public park. First flush management of T-N and T-P, therefore, is required for efficient water quality management of the public park.