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Fiberglass tank on cart at the facotory with the lid off showing the filter packs inside.

Fiberglass Underground Oil Water Separator Tank

Oil/Water Separators are specialty tanks designed to separate free oil, grease and settleable solids from water.

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Since suspended solids settle out more readily than oil in water, the separator design is based on the difference in specific gravity between the oil and wastewater. They operate using coalescer packs of oleophilic plates. As contaminated water flows through the tank, it passes through a number of filter like packs made of plates that attract oil. The accumulation of oil on these plates causes the droplets to combine into larger masses, which naturally allows the oil to more easily rise to the top of the tank. The discharge outlet is situated so the clean water can exit the tank, leaving the oil to be collected for proper disposal.

We have 3 types of Underground Oil/Water Separators, CSI-10, CSI-15, and UL 2215, a premium UL Listed variation that offers continuous flow. Depending on the model, our Underground Oil/Water Separators feature 10 to 15 ppm effluent discharge, controlled by direct or pumped flow, with allowable flow rate determined by the concentrations and types of contaminants present.

Containment Solutions provides a full range of dependable products for the oil/water separator industry. Our underground separators utilize the same fiberglass manufacturing technology the petroleum industry relies on for environmental protection. The inherently non-corrosive properties of fiberglass provide the most compatible option for your separator application.

Our oil/water separators are constructed to remove hydrocarbons with a specific gravity up to 0.95 through the use of an enhanced oleophilic coalescer pack system. Oil/water separator designs vary based on required effluent quality and flow rates. An effluent quality of 10-15 parts per million (10 PPM-15 PPM) is typical but the difference between continuous flow and intermittent flow will drastically alter the coalescer pack sequence. We offer several options in both single and double-wall construction to meet your unique needs.

The UL 2215 model is a premium oil/water separator with next level performance. It is designed for continuous flow which is a significant distinction when comparing oil/water separators. These separators meet construction requirements for the holding vessel and undergo performance testing under simulated operating conditions to ensure their capabilities.


All CSI Oil/Water Separator Tanks are designed and tested in accordance with the following criteria

  • Stokes law
  • The APO manual on disposal of refinery wastes
  • API bulletin no. 1630 first edition
  • API bulletin no. 421
  • UL-1316
  • ASTM D-4021
  • EPA Test Methods 413.1 & 413.2
  • US Coast Guard 46CFR 162.050

Performance Features

Removes free floating oils and settable solids for oil/water mixtures to achieve an effluent quality not to exceed ppm listed below.


Effluent quality

CSI-10 10 ppm (mg/L)
CSI-15 15 ppm (mg/L)
UL 2215
10 ppm (mg/L)

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  • Containment Solutions Tank Sumps Brochure (Spanish)
Rendering of an oil water separator tank cut in half.

State-of-the-art enhanced oleophilic coalescers are positioned in a cross-flow configuration, a technically advanced design. Coalescer plates are removable for ease of maintenance.

Fiberglass oil water separator tank in the ground with backfill rocks around it.
Fiberglass oil water seperator tank on the ground at a job site with a crane in the background.

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