Your OWS is the last line of defense between your facility and an environmental violation. When it works, nobody thinks about it. When it fails, the city shows up with questions you don't want to answer.
An oil/water separator is an underground or above-ground device that uses gravity and baffles to separate petroleum products from water before it enters the storm drain or sanitary sewer. They're typically found near vehicle maintenance areas, fueling stations, loading docks, and wash bays.
The device is passive. Oil floats, water sinks, baffles keep them separated. Clean water flows out. Oil stays trapped. Simple in theory, neglected in practice.
Over time, oil accumulates in your OWS. Sediment builds up on the bottom. If the oil layer gets too thick, it starts passing over the baffles and into the discharge. If sediment fills the chambers, the water doesn't have time to slow down and separate. Either way, you end up discharging contaminated water.
Regular maintenance means pumping out the accumulated oil and sediment, inspecting the baffles and outlet structure, and verifying the unit is functioning as designed. Most units need this quarterly at minimum.
A vacuum truck arrives at your facility. The technician opens the access hatches, measures the oil layer and sediment depth, then pumps out the contents. The baffles are inspected for damage. The chambers are visually inspected. Everything goes back together, and you get documentation showing the service was performed, the waste was properly manifested, and your unit is functioning.
The whole process usually takes 1-2 hours. Costs range from $300-800 per visit depending on the size of your unit and your location.
Visible sheen on water near your storm drains or outfall. Odors coming from the separator access hatches. The city or your stormwater permit inspector has flagged your discharge. You can't remember the last time it was serviced. Any of these mean it's time to call someone.
Read our detailed guide: Your Crew Is Dumping Degreaser Down the OWS: What Happens Next. It covers a real-world scenario where a facility's maintenance crew unknowingly destroyed their OWS function by pouring degreaser into it.