An electric utility installed a 60 mil HDPE liner and sump pump for secondary containment at a transformer pit. A few months later, a site inspector checked the pit’s sump can. Surprisingly, it contained no water. With an impervious liner system, water should only be released via a drainage mechanism. The empty sump can indicated the water must be escaping through the liner itself.
While the routine inspection revealed the problem before an oil leak event occurred, the risk of the transformer discharging its entire 3,605-gallon contents into the leaking pit and, subsequently, into the local harbor created an urgency to resolve the problem. Environmental incidents of that magnitude attract large scale media attention. Cleanup costs and regulatory fines can run into the millions.
The utility asked BCI to develop a solution, but with a catch. They required a hydrostatic pressure test to make sure the containment met their engineering standards – and to avoid another liner failure. With thousands of dollars already spent, management was heavily eyeing the project. There was no room for error.
Developing a New Secondary Containment Solution
The initial suggestion was to switch from the existing HDPE liner to a BCI 40 oz. PVC liner. After meetings with client engineers and contractors, as well as a site visit, an alternative solution emerged. Due to the number of cable and ground grid penetrations, as well as the slope of the pit, BCI realized it was a perfect opportunity for its new line of industrial coating applications.
Experts from both BCI’s Secondary Containment and Industrial Coatings solutions collaborated to develop an innovative design using an Ethylene Polymer PVC with Elvaloy® Technology Geomembrane liner and the BCI PolySeam® System. The patented spray-on liner system eliminates the need for excessive cuts and joins around liner penetrations. PolySeam also serves as an alternative to traditional batten bar attachment and creates a flexible, yet durable, seal along HDPE and Ethylene Polymer PVC with Elvaloy® Technology Geomembrane liner seams.
PolySeam® Secondary Containment System Installation Process
Rain initially hampered progress on site, since a dry surface is preferred to install a new liner. Once the weather cooperated, contractors removed the sump can from the pit and used a hydrovac truck to remove the existing stone. They left the existing HDPE liner in place to become the base for the new Ethylene Polymer PVC with Elvaloy® Technology Geomembrane liner. This saved contractor time and costs, while avoiding the problem of working on damp ground.
The installation began by power washing the transformer pad and existing HDPE to create a clean surface. Once completed, installers vacuumed out the remaining liquid. BCI applied the PolySeam liner to seal the transformer pad first. They supplemented the area around the base of the pad with geotextile fabric and sprayed accordingly.
Next, the team laid the Ethylene Polymer PVC with Elvaloy® Technology Geomembrane panels according to the pre-approved site drawing, hand welding the seams to provide a preliminary seal. BCI used their proprietary primer to ready the seams, followed by PolySeam to create a leak-proof join.
After a 24-hour curing period, the pit was ready to receive the stone filler and the much-awaited hydrostatic pressure test.
Performing the Hydrostatic Pressure Test
Hydrostatic pressure tests are commonly performed to check components such as pipelines, boilers and other pressure vessels for strength and leaks. To pass the test, the pit could lose no more than 1-in. of water in a 24-hour period, after factoring in evaporation.
Once the pit was half filled with stone, the team added water up to an agreed height. They established a control box outside the pit to evaluate evaporation. They added water and measured the starting height. After 24 hours, they measured the height again. They found only ¼- in. of water loss taking evaporation into account. The success of the project even surpassed the utility operator’s high standards.
Conclusion and Future Recommendations
BCI recommends the use of its VIPOR 100 SOWF system for drainage purposes for all transformer pits utilizing impervious liners. While many clients have automated sump pumps, there is a danger of pumping oil out of the sump and into a sewer system. The VIPOR 100 filters out clean water, but will shut off automatically upon detection of hydrocarbons thus keeping releases contained.
*Elvaloy® is a registered trademark of DuPont.