below ground oil water separator

August 31, 2020

Our single wall or double wall below ground parallel, corrugated plate oil/water separators meet and exceed API 421 requirements, removing essentially 100% of dispersed non-emulsified oil droplets in the waste stream.

These separators are special purpose prefabricated parallel corrugated plate, cylindrical, gravity displacement oil water separators, containing an inlet compartment, sludge chamber, separation chamber, oil storage area and clean water compartment.

As shown below, the separation process if fairly simple. Wastewater flows into the inlet compartment. A baffle interrupts the flow and allows solids to drop out. Next the oil water moves into the separation chamber where our innovative media causes small oil droplets entrained in the water to coalesce into larger ones which then separate from the water and float to the surface. The clean water then travels into the clean water compartment through the outlet to the sewer.


  • Patented, revolutionary, non- plugging coalescing plates which remove free oil droplets as small as 20 microns
  • Single wall or double wall construction with interstitial space for leak detection
  • Rectangular access manhole with 3’ extension to service and maintain coalescing media
  • Fittings for vent, oil pump out, sludge pump out, gauging and lifting lugs
  • Exterior sandblasted and coated
  • Will achieve discharge of 5 ppm or less in accordance with CEN EN 858-1
  • Warranted for (5) years on material and workmanship and (30) years against external and internal corrosion
  • Construction in accordance with UL58 and corrosion protection in accordance with UL1746
Below Ground Oil Water Separator Design
Featuring one of our oil water separator designs to be placed under ground.


  • Internal coating for corrosion protection
  • Grit chamber for high solids applications
  • Hold down straps
  • Leak and Level detection systems


  • Parking Lots
  • Re-fueling Facilities
  • Marinas
  • Military Installations
  • Truck and Equipment Washes

How does it work?


With these separators, we can provide analysis, which indicates that the separator will be provided with the required square feet of projected plate separation area to achieve the specified performance under laminar flow (i.e. Reynolds Number of less than 500) conditions. This service can include calculations signed by a registered professional engineer.

Underground Oil Water Separator Specifications
Model # Average Flow Rate (GPM) Capacity (GALLONS) Dimensions, D x L (FT)
WB-QB-342 30-60 350 3.5 x 6
WB-QB-548 55-110 550 4 x 6
WB-QB-1048 100-200 1000 4 x 10.75
WB-QB-2064 200-400 2000 5.3 x 12
WB-QB-3064 300-600 3000 5.3 x 18
WB-QB-4064 400-800 4000 5.3 x 24
Larger sizes available.

Underground Oil Water Separator Specifications

Frequently Asked Questions


April 22, 2014

Oil Water Separator for Stormwater
Our stormwater oil water separators will remove solids and all free and dispersed non-emulsified oil droplets 20 micron or greater in size and produce an effluent discharge of less than 5 PPM.

The first phase of a rainstorm can be deceiving. The peaceful melody of the droplets can quickly disperse over parking lots, fueling depots, and washing areas that all contain pollutants, such as oil and grease. Because impervious surfaces do not allow rain to infiltrate into the ground, storm water runoff is generated. Surface runoff or storm water runoff then becomes a major threat to our nation and our clean water supply.

In order to protect our clean water supply these waters have to be treated before being discharged from storm sewers to surface waters. Our WB-QB oil water separators will remove solids and all free and dispersed non-emulsified oil droplets 20 micron or greater in size and produce an effluent discharge of less than 5 PPM.

Most municipalities have storm water departments that are made to protect water resources and reduce impacts from storm water runoff.  They also are responsible for the compliance of requirements for the National Pollutant Discharge Elimination System (NPDES) permits.

Our efficient, below ground separators meet pretreatment SPCC and NPDES permits for local communities.

Our proprietary design incorporates patented revolutionary non-plugging poly-propylene coalescing plates. Our coalescing media exceeds all known American performance standards including UL 2215, and has been tested in accordance with European Union Standard CEN EN858-1, which requires a discharge limit of less than 5 PPM. Our separator tanks are manufactured to UL 58 and UL 1746 Standards. Construction can be either single wall or double wall with a corrosion protection system.  Sizes are available up to 4000 GPM flow rate.

Operation Maintenance

  • All models can be serviced from grade level
  • No confined spaces
  • Plates easily removed, washed down and put back in place
  • Solids can be pumped out through large access opening from grade level

Options Available

  • Grit chamber for solids removal prior to coalescing compartment
  • Effluent pump out chamber after coalescing compartment
  • Oil stop valve to retain lighter liquids from leaving separator
  • Leak detection and level indicating systems
Model # Average Flowrate (GPM) Approximate Capacity (Gallons) Dimensions Diameter x Length (FT)
WB-QB-342 10-30 350 3.5 x 6
WB-QB-548 30-50 500 3.5 x 9
WB-QB-1048 50-100 1000 4 x 11
WB-QB-2064 100-200 1500 5 x 12
WB-QB-2564 200-300 2000 5 x 21
WB-QB-2572 300-400 2500 6 x 12
WB-QB-3272 400-500 3200 6 x 15
WB-QB-4072 500-800 4000 6 x 19

September 18, 2012

In many cases, a below ground oil water separator is the best option due to space restrictions and layout. You can use gravity to drain into a below ground system and then into the sanitary sewer system so there is no need for pumps and controls. In other cases, a below ground system has been previously specified and it is not possible to change the specifications.

North Carolina


At, we have been specializing in high tech, custom-engineered solutions to complex washing and wastewater issues since 1991.
+ 1 800-453-8639


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