A solution will be developed as a combination of an innovative group small-scale sewage treatment plant adapted to the specific needs, as well as group sewage treatment plants and a specified leaching system. A group small-scale sewage treatment plant (GKKA) is a sewage treatment plant to which between 5 and 500 population equivalents (EEC) can be connected. Within the framework of the project, the term GKKA is deliberately placed across the current administrative boundary of conventional KKAs (50 EEC), since the problems and challenges of such installations are the same up to 500 EEC. In the case of existing KKAs, currently only the discharge of the pre-cleaned waste water into a pre-drainer or the collection and removal by slurry vehicles is planned. This is not economically and environmentally acceptable in the proposed use cases, but it is often not possible at all. The aim of the project is therefore the research and development of a holistic system for the construction and operation of group small-scale sewage treatment plant with combined leaching of the treated waste water and accruing rainwater. The leaching is to be measured taking into account the site-specific hydrogeological and ecological framework conditions.