England – Environment Agency Building Regulations (Part H-H2 Package Sewage Treatment Works) state that all sewage treatment plants should be sited 7m-10m from any inhabited part of the property. The building control officer for the site will make the final decision on exactly how far the plant should be sited. If the discharge is to a drainage field a sampling chamber must be provided before the drainage field. Drainage field drains must be constructed in the aerobic soil layer, i.e. within 700mm of ground level. Please visit your local Planning Portal website for further information.
Please check your local environment agency (England, Scotland, Wales and Northern Ireland) for regulations.