Mixing zone delimitation for submarine outfall in tropical marine water using the uranine dilution measurement approach

Submarine outfalls are standard wastewater management systems implemented in coastal areas. This manuscript presents a methodology for mixing zone delimitation of wastewater plume discharged through a submarine outfall in tropical marine waters. Sodium fluorescein (Uranine) was used as a tracer to track wastewater mixing and dilution factor in the coastal water of Cartagena de Indias (Colombia). Historical marine water quality, marine currents, and meteorology data were obtained, and analyzed. Two field campaigns were carried out to monitor coliforms, enterococci, and uranine concentrations in the studied area. The results showed that the water column was well mixed, and stratification was negligible due to the low vertical variations in temperature (29.0–29.35 °C), salinity (35.8–36.2), and density (1022.6–1023.0 kg ⋅ m−3). The initial dilution during the dry to the rainy (April) and from the rainy to the dry (December) seasons reached similar dilution factors up to 1:43000 in less than 150 m. The regulatory mixing zone was delimited to an area of 6.6 km2. Uranine is suitable for delimiting the wastewater mixing zone in tropical marine waters.