Detail specification and detail design of a permanent oil containment and separation system for the rainwater collected from around major outdoor transformer bunded areas.  Rainfall records and NIWA intensity charts examined to optimise storage and oil separator capacities.  In-ground concrete tanks designed to collect surface rainwater and to store spilled oil.  The water is pumped through a flat plate oil separator, so that clean, oil-free water is discharged, and the oily waste collected for appropriate disposal.