19. Prior to the commencement of the authorised development (with the exception of the highway works which are governed by requirements 4 and 5 and Schedules 19 and 20 (protection of interests)), excluding earthworks, archaeology works or ecological mitigation works, a foul water drainage strategy must be submitted to and approved in writing by the local planning authority. Except where it is constructed in accordance with the approved foul water drainage strategy, no phase of the authorised development is to commence until written details of the foul water drainage system for that phase have been submitted to and approved in writing by the local planning authority. Such details must be implemented as approved by the local planning authority.