A project is mixed when it requires both a planning permit and a class 1A or 1B environmental permit, for example the creation of an open-air car park with over 50 spaces.
This means that you must submit your two permit applications (planning and environmental) simultaneously, that there will only be one public enquiry and one review by the consultation committee and the implementation of both permits will be subject to the issuance of both permits.
You can find more information on the regional planning portal (in french or dutch only)
Below are some organisations that can help you with this issue.
Below you will find some news related to the subject.