You are right on the ball, I,ve just spoken to a client regarding a treatment plant system for a house near Bridgewater. The archiects were asking about distances from the property to site the new system. As you say the local building control dept are the best source to discuss the matter. I think the main concern is always the location of the soakaway fron any structure, in small sites the use of some from of effluent pump transfering treated effluent to a location away from the property is always a good idea. Drainman www.mtmdrains.co.uk