The challenge with most oil containment systems that do not use oil-water separating systems (with tanks and pumps) is how to deal with water filling the containment basin. Obviously, if the basin is full of water when an oil leak occurs, there is no longer a contained, controlled system in the event of an oil spill.
Additionally, typical oil-water separator systems are expensive and involve long-term maintenance. Other systems that have little to no maintenance may not meet newer spill requirements as they become more stringent over time. Finding a system that meets requirements, while not producing additional maintenance costs and resource demand, is a problem faced by most utilities.
For years, Avista used a below-grade, impermeable-lined basin around its transformer foundations to contain oil leaks and spills. This lining for a typical distribution station power transformer was 36-by-24 feet in size, and 2.5-feet deep, around a 9-by-12-foot transformer pad, which is offset inside the liner area. Most of the liner area was on one side of the transformer.
The system had a reglet cast into the concrete foundation of the transformer pad, which sealed the liner tight around the foundation. The lining was then filled with 1.5 – inches of rounded, wished gravel. A monitoring well pipe made of 12-inch PVC was installed off one of the foundation corners, which provided a means of pumping out any excess water that is caught in the basin. To protect the lining from damage, the entire containment area was enclosed within a plastic barrier chain and warning signs to keep equipment out.
Unfortunately, this system was hard to inspect to ensure the integrity of the lining. Over the years, the monitoring wells have become full of water and fine sandy debris, which does not filter through the fabric.