In January 2020, the Guidelines for Countermeasures against Water Intrusion during rainstorms (Draft) were issued to study and implement effective and efficient countermeasures against the problem of water intrusion during rainstorms due to aging pipelines and cross connection in separate sewer system.

　The guidelines state that it is effective to conduct a screening survey to narrow down the area where infiltration occurs, followed by a detailed survey to determine the location and cause of the intrusion.

　Although the area is within the inflow area of a manhole pumping station, we propose a method to estimate the percentage of water infiltration during rainy weather using smart meter electricity consumption as a screening survey, and to narrow down the area where water infiltration occurs during rainy weather based on the percentage.

　In estimating the percentage of water infiltration during rainy weather, a new method is introduced to estimate the amount of electricity used without rainfall on rainy days by using the cumulative probability of electricity use on sunny and rainy days.

　Wastewater treatment plants sometimes discharge primary effluent without biological treatment during wet weather. Then, reducing the discharge load is a critical issue. On the other hand, if the volume of treated water is increased excessively, the quality of treated wastewater (nitrogen and SS) may deteriorate due to a decrease in the biological treatment performance and overflow of activated sludge from the final sedimentation tank. Therefore, in this study, the maximum amount of treated wastewater to keep the quality of treated water below the control standard was estimated for an advanced treatment system by using a model to estimate sludge overflow and a treatment simulator with an activated sludge model, considering the power consumption. As a result of trial calculations and a verification experiment in an actual plant, the verification targets (treated water quality below the control standard, treated water volume at least 1.6 times higher than that under dry weather, and operation time at least 6 hours) were achieved. The system was also able to operate stably even when the treated water volume was increased up to 1.7 times of dry weather. The results also showed that the system can reduce the primary effluent discharge by 70%, the hourly SS load by 59%, and the nitrogen load by 33% compared to the conventional wet-weather treatment conditions.