- Asset
- Oil-water separator / interceptor
- Retained material
- Free oil and settled material, depending on design
- Key records
- Model, capacity, alarm and maintenance instructions
- Do not assume
- A separator treats every dissolved or emulsified contaminant
Separator type and the area it serves
A separator’s duty depends on its design and the area draining to it. The make, model and drainage plan show how the chambers, filters, alarms and other components are arranged. It should not be treated as simply an underground tank.
The Environment Agency says oil separators may be needed where drainage from hard surfaces is at risk of oil contamination. Its guidance for England also says sites storing or using hydrotreated vegetable oil (HVO) in the separator catchment should speak to the supplier about any additional filters required. If fuels or site activities change, the original separator specification should be checked rather than assumed to remain suitable.
Oil and silt levels
Maintenance needs to consider both retained oil and settled silt. The manufacturer’s checks should cover the components fitted to that separator, including alarms where present. A normal-looking liquid level is not evidence that the unit is operating correctly.
The Environment Agency lists significant oil or silt build-up, an oil spill and alarm activation as reasons to empty and service a separator. What entered the unit also matters when the removed material is classified and handled.
Emptying and return to service
For England, Environment Agency guidance states that trapped oil or sediment removed from a separator is hazardous waste. It must move under a hazardous waste consignment note and go to a permitted facility that can accept that waste type.
The same guidance says the separator must be refilled with clean water before it is put back into use, and that settled water removed from the separator should not be used for the refill. Manufacturer servicing instructions still apply because emptying alone does not cover every component or functional check.
Service records and recurring faults
Record which chambers were serviced, what was removed, which components were checked and any defects found. Repeated alarms, unusually rapid build-up or poor downstream performance may point to a connected drainage issue, changed operating conditions or a separator fault that needs separate investigation.