Solutions for a complex world:
Geophysics Can Offer Long-term Solutions Preventing Industrial and Ecological Disasters
Article by: Shawn Calendine | hydroGEOPHYSICS
HGI‘s chief technical officer Dr. Dale Rucker has been receiving interview requests to hear his assessment of the leak at the wastewater pond near Tampa, Florida. The New York Times, Associated Press, CBS News, and others’ request is due to HGI’s 20 plus years providing leak detection and location solutions at ponds similar to this. Operators at the Piney Point reservoir are currently trying to pump down the 77 acres lined facility to relieve pressures and mitigate risks of a catastrophic breach that could release 100s of millions of gallons of water to surrounding communities.
All lined ponds eventually leak, but taking the proper preventive measures can usually prevent catastrophic breach situations if engineering tools such as geophysics are used to understand structural conditions before it’s too late. In the Florida ponds case, two different geophysical investigations may have yielded information helping operators understand that their system was in duress. These include an electrical leak location survey to find tears in the liner below the water surface and a seismic investigation of the impoundment to understand the materials’ strength holding back the water. For the ponds, a tear in the liner could mean significant seepage that erodes impoundment material. Conversely, movement in the impoundment due to weak soils could cause a tear in the liner. Understanding both is essential to protect life and the environment.
For electrical leak location on geosynthetic lined ponds, electric current is passed through the same holes or tears where water flows. Most retained fluids can transmit electrical current, and the rate of current flow is related to the electrical properties of the fluid and the physical properties of the hole. Because the geosynthetics lining the pond are resistive to electrical current, the current will only pass through the liner where there are holes. Special sensors are then placed in the pond to detect the holes because the electrical potential (i.e., voltage) will increase around a hole and be lower across the resistive liner where there are no holes.
The schematic below shows a situation demonstrating a leak during an electric leak location survey. Notice the current path between where the current enters into the pond and the hole in the liner. This relationship allows the operator to detect the increased electrical potential around a liner hole and thus locate the leak. To learn more watch this short video.
Seismic surveys can help us understand the stability of soils beneath and around these massive impoundment structures. If a leak or many leaks develop in a liner and goes unnoticed, it can erode away the soil meant to support the structure. This type of erosion is often called piping, where soil is carried away along a path of least resistance away from the impoundment. As the erosion continues, the pathway gets bigger and bigger. When enough dirt is removed, the water’s tremendous pressure stresses the liner to the point where it will rip apart, causing the process to increase further until the entire area fails and all of the water in the reservoir is released. Seismic surveys can examine soil stability using sound waves. The sound waves are created by hitting a metal plate with a sledgehammer. As the sound travels through the earth, it will travel through different layers of rock, soil, and voids, causing a seismic echo. The echoes (sound waves) are received and recorded on the earth’s surface through geophones. Once interpreted, technicians can identify structures in the earth’s subsurface. In this case, a seismic survey may have been able to locate degraded soils and voids created by liner leaks and piping.
The massive Florida pond breach is a wake-up call to provide further attention to aging infrastructure. Geophysics is one of the many engineering tools we have at our disposal to examine these structures. It will take a different mindset, however, where we act proactively rather than reactively. Let’s hope the pond near Piney Point is the turning point in how we think about these large containment systems.
About the Author: Shawn Calendine | hydroGEOPHYSICS
Shawn Calendine is the Marketing & Development Manager at hydroGEOPHYSICS (HGI). Since joining HGI in 2005, Shawn has worked in many positions for HGI, most notably, as a team member managing the leak detection and monitoring (LDM) program for nuclear waste tanks at the Hanford Site in eastern Washington State. Following the LDM program, Shawn moved into field geophysics, gaining high-level experience with HGI’s geophysical technology toolbox.
In addition to work as a marketing consultant, Shawn participates, as a board member for several industry-related nonprofit organizations and authored several papers on geophysical methods relating to liner leak location and resistivity characterization. Over the past 15 years, Shawn has presented on geophysical topics at professional meetings and conferences. Shawn holds Bachelor of Science degrees in both Environmental Science and General Science with a minor in Biology from Portland State University.
Other Articles By Shawn Calendine
- How Geophysics Could Help Prevent Reservoir Breaches Like The Florida Industrial Pond
- Bare Liner Leak Location – The Water Puddle Method
- Pinpointing industrial pond liner leaks – HGI Leak Detection
- Electric Liner leak Location for Industrial Ponds
- Subsurface Characterization for Brownfields – Is There A Better Way?