Near-field dilution of wastewater effluents discharged from submerged ocean outfalls in Masan Bay

Abstract

The near-field initial dilution of the wastewater discharged into Masan Bay from a submerged ocean outfalls has been studied by field measurements and prediction model simulations. Ambient parameters of temperature, salinity, and currents were measured at the Masan outfalls site. Dilution rates of the wastewater effluents were obtained by a salinity deficit method using the field data observed in summer and winter. They were compared with Miami outfalls study (Proniet al., 1994) and the predictions of CORMIX model, i.e., a USEPA's mixing zone model. The model predictions showed a good agreement with the field measurements under the ambient conditions of summer stratification as well as winter isopycnal mixing with weak ambient currents. Seasonal variations in the dilution rates were simulated for four typical seasonal conditions with the observed currents at the outfall site. The highest dilution rate of 168 was found in winter with the strong ambient current. The lowest dilution rate of 26 was found in summer with the weak ambient current due to the trapping of the jet-plume at the thermocline depth. The similar results were also obtained through the hydraulic model tests for Boston outfalls (Robertset al., 1993).