“Can we use your secondary oil containment systems even if we need to drive our maintenance trucks, equipment and vehicles into the containment area?”
We hear this question often, generally regarding older substations that need to be retrofitted for secondary oil containment systems. Routine maintenance procedures allow workers to drive vehicles very close to the oil-filled electrical equipment on site. Ideally, the utilities prefer to incorporate oil containment systems that don’t require them to adjust standard maintenance processes. We understand, so on that note, the short answer is yes, our secondary containment solutions would accommodate frequent drive over use.
But, based on our years of experience in this industry, the short answer just isn’t good enough. Protecting the environment while complying with strict regulations demands an upmost attention to detail, and it’s important to understand the different drivability options available with our oil containment systems. Let’s explore through two different scenarios.
Drivability Scenario 1: Below-Grade Oil Containment Systems
(Geomembrane Liner with Barrier Boom System, or Barrier Boom Secondary Containment System)
The key word is “below-grade.” For below-grade oil containment systems, drivability can usually be accommodated without the addition of a vehicle berm or ramp, as long as the design planned for such activity and was correctly installed. In most cases, the only requirements to drive over our below-grade systems is a simple matter of using the correct stone.
Six inches of pea stone must be laid below the liner, and geotextile fabric must be placed over the liner floor before the system is backfilled with clean, washed stone. Even without using compacted aggregate, a natural compaction will occur with substantial traffic. We recommend backfilling with 12-18 inches of stone (sized ¾ to 1.5 inches) to ensure the integrity of the liner is not compromised under additional weight, and to provide at least 30 to 40 percent void space. The formula for the size of material compaction and the acceptable displacement of 14 lbs. per square inch will ensure minimal compaction takes place.
Basically, the deeper the oil containment system is, the fewer concerns exist about vehicles driving over it. The only way the oil containment system can be compromised is if that weight displacement is exceeded. For example, if a crane outrigger is required, a 2-foot square pad will allow you 8000 or more pounds of lifting before compression would become a concern.
A word of caution: While drivability is easily accomplished with this system, take care in how you maneuver the vehicles, at least initially. Abrupt turns can cause displacement of the gravel. Always inspect the area after it is driven on, and rake gravel back into place if necessary. In cases in which larger equipment is required to drive over the containment, consider using a temporary weight displacement or ground protection mat.
Drivability Scenario 2: Oil Containment System with Berm
If it isn’t possible to install an oil containment system to grade or below grade, we recommend constructing a secondary containment berm as an alternative. The two types of permanent containment berms used most often are earthen berms and DGA (dense grade aggregate) berms. An earthen berm is constructed of soil, debris and stone to form an impervious surface. The DGA berm utilizes a finely crushed densely-graded mix to construct a relatively impermeable subsurface.
In diked applications of our Geomembrane Liner and/or Barrier Boom oil containment systems, we suggest combining these two berms to allow vehicles to drive over it. First, a permanent secondary containment earthen berm should be constructed over the Barrier Boom (or Geomembrane Liner with Barrier Boom) to allow for water flow. Designate an area for a vehicle ramp that will allow drive over use without high maintenance. The vehicle ramp should be packed using finely crushed limestone or similar to form a DGA berm. The best part about the DGA berm is that it turns into an almost asphalt state that is compliant with secondary containment regulations.
Contact BCI for All Secondary Oil Containment Solutions
BCI helps electric utilities meet SPCC requirements for oil containment. We design site-specific solutions and can work with engineers to prepare for drivability options if required. Contact us today for a quote or more information.