OCS

ScopeThis bulletin discusses how to install containment systems around oil-filled equipment.

Applicable Substation EquipmentSubstation items likely to require oil containment systems include:

• Transformers

• Voltage regulators

• Oil circuit breakers

• Reclosers

• Capacitors

EPA RequirementThe Environmental Protection Agency (EPA) requires a Spill Prevention Control and Countermeasure (SPCC) plan if the sum of the capacities of oil-filled containers with a volume of 55 gallons or greater exceeds 1,320 gallons, and there is a reasonable possibility that a spill from any oil-filled container could reach a waterway, stream (including a dry stream only seasonally wet), wetland, or underground aquifer.

Typical SolutionsThe typical solution is to install a pit around the equipment to capture and contain any spilled oil, until it can be removed safely. Pits are built using reinforced concrete, bentonite clay, or earth lined with plastic (typically, polyethylene), rubber, a spray-on liner or spray-on fiberglass.

Poured-in-place concrete collection pits are one solution. These are economical when the pit can be poured at the same time as the original foundation for the equipment.

A more common solution is to build a moat and pit around the equipment, and line it with a protective liner. The walls can be concrete, packed earth, or interlocking panels assembled on-site.

A drainpipe can be installed at the bottom of the pit to carry off rainwater and other liquids, to a nearby underground oil separator tank. See Figure 2. Oil is lighter than water, so it rises to the top in the tank. A pump, such as Oil-Minder, pumps out the water that has collected at the bottom of the tank, and leaves the oil in the tank for removal separately.

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Figure 1. An oil containment system around a power transformer. The pipe shown on the front wall connects to a sump in the containment.

Procedure

Sub-Grade Preparation

Excavate the oil containment pit to the depth and configuration shown on the drawings. The bottom of the pit must be free of loose earth, rocks, and debris. When excavating, be careful to not disturb soil underlying any footing or foundation already installed.

If required, place sand on the excavation to establish a smooth surface.

The excavation must be free of water, and approved by the liner installer.

Liner - Panels

Place the liner over the prepared surface, in accordance with the manufacturer’s requirements. Arrange the panels to minimize handling and field seaming. Sandbags may be used to hold the liners in position during installation.

Treat lining material with care. Wear soft-soled shoes when walking on lining material. Do not drag items across the surface, or allow equipment or materials to slide down slopes on the liner.

Fit liner sheets close together. Make seams and patches using the manufacturer’s approved methods and equipment.

Seal all outlets and projections through the lining using an approved sealing method. Seal linings to dikes using a mechanical anchor or other method approved by the lining manufac-turer. For batten strips, use stainless steel or aluminum; wood batten strips are not allowed.

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Strongwell

OCS

Spray-On Liner

Prepare the surface in accordance with the manufacture’s specifications. Lay down geotextile as a substrate. Spray-on the liner to a thickness of at least 40 mils. Create the liner with enough slack so it will not separate from the substrate during backfilling. The liner topcoat must show no streaks or uneven coloring.

Testing the Liner

Before backfilling, fill the containment basin with water to a depth of one-half the maximum depth. Mark the water level. Monitor it for 24 hours.

The liner is acceptable if the water recedes less than 1/4-inch, and there is no bubbling or other signs of leaks.

Top View

Side View

Transformerfoundation

Base of pitslopes to drain

Regulatorfoundation

Sloped PVCdrain pipe

Vault with pump Outlet

Transformerfoundation

Base of pitslopes to drain

Finish grade

RegulatorfoundationGeotextile fabric

Liner

Drain rock

Drain to pump

Figure 2. An oil containment system design.

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SUBSTATION CONSTRUCTION GUIDELINES

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