Soil Covered Liners & Leach Pads
hydroGEOPHYSICS Inc. (HGI) uses electrical geophysics to locate leaks on soil covered liners & leach pads. Examples include landfills in the solid waste management industry and ore-covered leach pads in the mining industry.
The most significant cause of leaks on soil covered liners & leach pads or waste covered geomembranes, is damage caused by machinery placing the materials on the liners…
The integrity of the geomembrane in soil covered liners & leach pads can be compromised by many factors including faulty construction, inadequate subgrade, or poor quality material placed on the geomembrane allowing tears to occur in the liner . In addition, accidents and carelessness after installation can play a large role in creating leaks in these systems. The most significant cause of leaks in earth, or waste covered geomembranes, is damage caused by the machinery placing the materials on the liners. Electrical leak location is one of only a few methods available to locate leaks in these types of lined systems, and it is also the most robust with over 30 years of effective use. Geomembranes are also used as fluid transport mechanisms; for example in the heap leaching process a solution will percolate through a leach dump dissolving precious metals. When the solution reaches the liner as (Pregnant Leachate Solution) PLS, it then flows along the top of the liner to containment ponds for processing. Therefore, ideally it is advantageous for geomembranes to have no leakage to ensure production, and the environment is protected.
The Electrical Leak Location method is based on the capacity of earth materials to transmit electric current. Changes in soil conditions affect the resulting electric potential data acquired at surface. Fluid leaking across a liner boundary can also form electric current flow pathways. This is due to soil moisture content being the most significant contribution to detectable changes in electrical potential values. If the underlying liner is undamaged, then the liner acts as an electrical insulator and the electric field response will be constant. If tears or holes exist in the liner, the electric field readily transmits through these areas by the leaked solution. A current is induced through the material by a transmitting electrode pair, and the resulting changes in the electric potential field are mapped along relatively closely spaced survey lines.
Using electrical methods, HGI develops unique and site specific surveys to geophysically detect and characterize subsurface leaks occurring along covered liner surfaces . Our objective is to acquire sufficient geophysical coverage capable of laterally defining leak areas so excavation and liner repair efforts can be performed with confidence and in a timely fashion.
Below is a color contoured plot of a soil covered liner & leach pad showing leak locations from an electrical resistivity liner survey. Note that the magnitude of the response is related to leak size, i.e. leak ‘B’ is likely larger than leak ‘A’ or leak ‘C’.