PPS 21 Sustainable Development in the Countryside·Page 47·5.94
Acceptability of on-site sewage treatment plants
The number and type of acceptable on-site sewage treatment plants is determined by soil conditions, watercourse sensitivity and capacity, and water catchment vulnerability. Such installations must be located at least 15 metres from any dwelling and soakaways must not drain across neighbouring property.
The number and type of on-site sewage treatment plants which will be acceptable in a particular area will be determined by the sub-soil conditions, the sensitivity and capacity of the receiving watercourse and the vulnerability / sensitivity of water catchment areas. In addition such installations should be located at least 15 metres away from any dwelling and soakaways should not drain across the curtilage of any neighbouring property.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 21 - Sustainable Development in the Countryside.pdf