Understanding Variables That Define Secondary Containment Systems Design




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Throughout the years of providing secondary containment systems and solutions for utility companies, we’ve realized that the only constant in the design of C.I.Agent Oil Filtration Panel and Geomembrane Liner Systems is that there is no constant. Each site is unique, and requires a customized solution.

Each substation site has unique needs and variable. We use these to create customized containment solutions.
Each substation site has unique needs and variable. We use these to create customized containment solutions.

The variables that make each site unique differ case by case, but often include:
– The amount of oil
– The number of vessels
– The physical placement of the vessels
– The depth of gravel
– The area available for containment
– The type of sub-soil
– The topography

For years, C.I.Agent Solutions has provided secondary containment systems for utility companies. Each site is unique, and requires a customized solution.

 

The Role of Sub-Surface Soil

When we install containment on sites with clay sub-soil surfaces, no liner is required.
When we install containment on sites with clay sub-soil surfaces, no liner is required.

If any of the variables listed above differ or change from site to site, the design of the containment will change. SPCC 40 CFR 112 requires both the walls and floor of a containment system to be impervious. Sometimes this can be accomplished with the sub-surface soil, as in the case of a clay sub-surface. The EPA considers sites that have a sub-surface soil of clay to be impervious. Therefore, if we were installing the containment on a site with clay soil, we would not need to utilize a liner. C.I.Agent® Oil Filtration Panel would be placed in the clay sub-soil sealed with granule Bentonite® at the bottom edge and back filled with clean washed stone.

However, sites where the sub-soil is permeable would require a liner to prevent the possibility of an oil leak from contaminating the ground and nearby water sources. In containment systems requiring liners, the C.I.Agent® Oil Filtration Panel is constructed with a 4” flap that is placed under the liner’s outside edges and sealed with granular Bentonite®. Then it is covered and back filled with clean washed stone. Granular Bentonite® is also used to seal the overlap along the seams of the liner and around any conduit or obstructions on the site. The liner can be attached and sealed to the concrete transformer pads or piers with silicone mastic or a Bentonite® clay paste. The liner is held firmly in place by the pressure of the back filled stone. Other mechanical attachment methods may be incorporated.

Liners should be installed at sites with permeable sub-soil to prevent an oil spill from contaminating navigable waters.
Liners should be installed at sites with permeable sub-soil to prevent an oil spill from contaminating navigable waters.

 

Importance of Gravel Depth

The type and depth of the gravel on the site is one of the determining variables that impact the height and length of the C.I.Agent® Oil Filtration Panel. The Oil Filtration Panel has to be equal to or greater than the depth of the gravel to prevent the hydrocarbons from overflowing the containment system.

It’s important to cover the Oil Filtration Panel with gravel. After a heavy rain event or snow melt, visually inspect the site for exposed C.I.Agent® Oil Filtration Panel. If exposed, cover with stone. Berms may need to be reshaped using a hand rake.
It’s important to cover the Oil Filtration Panel with gravel. After a heavy rain event or snow melt, visually inspect the site for exposed C.I.Agent® Oil Filtration Panel. If exposed, cover with stone. Berms may need to be reshaped using a hand rake.

If the gravel is 6 inches in depth, the Oil Filtration Panel must be at least 6 inches high; 12 inch or 18 inch of gravel would require Oil Filtration Panel of 12 inch or 18 inch respectfully.

The height of the Oil Filtration Panel can also be affected by the size of the available foot print for the containment system. If the area is limited, the Oil Filtration Panel may have to be higher than the depth of the gravel, creating an above grade berm.

The amount of oil also can affect the height of the Oil Filtration Panel when volume exceeds the containment capacity of the gravel available.

Regardless of the height of the Oil Filtration Panel, the maximum length of an individual piece is 50 ft. As the Oil Filtration Panel is installed, it is sealed along the bottom edge with granular Bentonite® and each length is joined with a 4” overlap before it is back filled with clean washed stone.

Here’s a convenient formula we put together for calculating containment capacity.

 

 

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