tide, a neap tide and the maximum over the 46-day computational period are shown in Figures 5 – 7.
Figure 5 shows concentrations of CODMn and Nitrogen at the high water levels during a spring tide (left panel - at 661 hours), a neap tide (middle panel - at 864 hours) and the maximum concentration (right panel). It can be seen that in this case (Scenario 1) the spreading of the pollutants is restricted in a small area around the outfall. The concentrations are very low during spring tides as expected. During neap tides, the concentrations are noticeably higher due to the weaker diluting power from the tides. The concentrations of both pollutants are found lower than 0.05 mg/L. The maximum concentrations of both pollutants over the computational duration are in a similar range. Taking into consideration of the background concentration of 0.255 mg/L for neap tides as listed in Table 2, and assuming a linear accumulation, the maximum concentration for CODMn is approximately 0.3 mg/L, which is below the regulatory limit of 4.0 mg/L, see Table 2. For Nitrogen, the maximum concentration is found to be approximately 0.123 mg/L. Combining this concentration with the background concentration of 0.230 mg/L for neap tides gives a resulting concentration of 0.353 mg/L, which is also below the regulatory limit of 0.4 mg/L. Therefore, for the normal operational conditions of both wastewater treatment and reclaimed water plants, the water quality in the study area is satisfactory.