The commissioner of this thesis was The Environment Centre of Keski-Uusimaa which operates in five municipalities (Järvenpää, Kerava, Mäntsälä, Nurmijärvi and Tuusula). The objective of this thesis was to create a prioritization model for wastewater (on site-sanitation) regulatory control. “Control areas” were defined for the model. The control areas were designated on geographical information system (GIS) program. The aim was to define the priority of the control areas based on the risk of environment pollution and health hazard. The prioritization was done in order to allocate resources on areas with the most need for regulatory control.

The methods of this thesis were multiple criteria decision analysis (multi-criteria assessment) and value-tree analysis. The prioritization model is based on those methods.

Literature, laws, interviews and workshops were used on planning and creating the prioritization model and the control areas.

The control areas were defined and prioritized in Municipalities of Järvenpää, Kerava and Tuusula.

Conclusion of this thesis was that the prioritization model is useable for the Environment Centre of Keski-Uusimaa. It can also be used on other municipalities in Finland. The control areas in municipalities of Mäntsälä and Nurmijärvi will be defined later on.