For Scenario 2, the computed results exhibit the similar patterns to those in Scenario 1. The maximum concentrations of CODMn and Nitrogen over the computational duration are shown in Figure 6. It can be noticed that the spreading of the pollutants is wider. The maximum concentrations for both pollutants are higher than those in Scenario 1. The maximum concentration of CODMn is found to be around 0.336 mg/L. Combining this with the background concentration gives the resulting concentration of CODMn 0.591 mg/L. This again is within the regulatory limit. However, the maximum concentration for Nitrogen is found to be 0.204mg/L, almost twice as high as that in Scenario 1. Together with the background concentration for neap tides, the resulting concentration is 0.434 mg/L, and exceeds the regulatory limit of 0.4 mg/L. But it should be pointed out that high concentration of Nitrogen is only limited in a small area. As the receiving area of the treated wastewater is larger than 600 km2, it is within the regulatory requirements if the area with high concentration is no larger than 3.0 km2 at any time.
For Scenario 3, the computed concentrations of both pollutants are shown in Figure 7, similar to those in Figure 5. In comparison, it can be found that there is a large area where the concentrations of both pollutants are higher than 0.15 mg/L, the upper scale of the figure set for inter-comparison reasons. It is also important to notice that the high concentration area is mainly close to the shoreline, which can impose a greater threat to the public health. The maximum concentration of CODMn is 3.36 mg/L which is just below the regulatory limit. However, the maximum concentration for Nitrogen is 1.429 mg/L, which is far exceeding the regulatory limit. The affected area is also much more extended during the neap tides.