Legislation requires domestic heating oil tanks to be bunded if:

. they are within 10 metres of a controlled water course i.e. drains, streams, rivers, etc.

. they are within 50 metres of a bore hole or spring.

. a spillage could run into a drain or loose fitting manhole cover.

. the vent pipe is not visible from the fill point, as in an offset fill.

. there is any other potential hazard to the individual site.

BS 5410: Part 1 Building control requires that for single family dwellings where the heating system does not exceed 45kw and storage does not exceed 3500 L, the tank:

. must have a non-combustable base of either concrete, with a minimum depth of 100mm or concrete slabs of 50mm on a suitable sub-structure, extending 300mm outside the tank on all sides.

. must be a minimum of 760mm from a boundary line, unless that boundary line is of non-combustable construction i.e, brick or blockwork, etc. 

. must be sited a minimum of 1.8m from windows / doors / combustable eves / sheds etc.

. if sited within 1.8m of an opening in a building wall, must be protected by a minimum of a 30 minute fire wall.