Throughout the years of providing secondary containment systems and solutions for utility companies, we’ve realized that the only constant in the design of Geomembrane Liner with Barrier Boom systems is that there is no constant. Each site is unique, and requires a customized solution.
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
The Role of Sub-Surface Soil
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. Barrier Boom walls 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 Barrier Boom Secondary Oil Containment is constructed with a 4-inch 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.
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 Barrier Boom Secondary Oil Containment. It must be equal to or greater than the depth of the gravel to prevent the hydrocarbons from overflowing the containment system.
If the gravel is 6 inches in depth, the Barrier Boom must be at least 6 inches high; 12 inches or 18 inches of gravel would require Barrier Boom of 12 inches or 18 inches respectfully.
The Barrier Boom height can also be affected by the size of the available foot print for the containment system. If the area is limited, the wall 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 Barrier Boom when volume exceeds the containment capacity of the gravel available.
Regardless of the height of the Barrier Boom, the maximum length of an individual piece is 50 feet. As the wall is installed, it is sealed along the bottom edge with granular Bentonite and each length is joined with a 4-inch overlap before it is backfilled with clean, washed stone.
Contact BCI to Design Site-Specific Oil Containment
BCI provides a number of custom below- and above-grade secondary containment solutions to meet SPCC requirements. Contact us today for a quote or more information.