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Electrical Methods for Evaluating & Monitoring Geomembrane Landfill Caps

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TTP#: SF2-1-SS21; Tech ID: 3050

Project Overview
Lawrence Livermore National Laboratory (LLNL) has pioneered the development of electrical imaging techniques, including electrical resistance tomography (ERT) and electrical impedance tomography (EIT). One of the technologies which has grown out of this work is excitation of the mass (EOM) for current imaging. Persons at LLNL have been working for a year, using internal LLNL funding, to develop EOM for detecting leaks in geomembrane lined waste storage ponds (Binley et al., 1997). It is believed that a modification of this technology can be used to detect and locate leaks in geomembrane lined landfill caps.
Technology Description
Many landfills are constructed with a cap as an upper barrier to shed water and keep the landfill contents dry. Many of these caps, especilally the newer ones, rely on high density polyethylene (HDPE) or similar impermeable membrane as a primary barrier to liquid water. This membrane is protected below and above by layers of soil or sand but even this protection is not sufficient to ensure that a liner installed intact will remain so throughout its lifetime. Sometimes the mechanical loading of the soil itself will cause settline and the membrane will be stretched and torn. There are many possible failure modes, however. Once compromised, water can enter the landfill. What is needed is a simple and robust method for detecting leaks in the cap - places where water may leak into the landfill proper. It would also be important to be able to locate the lead point to facilitate repair. Because of the very long lifetimes for landfills, the method should also be appropriate for long term monitoring of a cap. Excitation of Mass (EOM) has been used experimentally to detect and locate leaks in a geomembrane lined pond. The application of EOM to characterize a landfill cap uses the fact that a geomembrane liner (HDPE, PVC or similar material) is electrically insulating - electrical current does not flow through it unless it has a hole(s) in it. However, current will flow through soil or sand on either side of the membrane. A potential difference is established in soil on either side of the liner. If intact, the liner will inhibit any current from flowing from the high to low potential. However, a break in the liner provides a path for water to move across the barrier as well as electrical current to flow. If current does flow it establishes a potential field, which is measured from an array of electrodes that could be arranged around the periphery of the cap. The location of the current source(s) (leak) is then calculated from these voltages and the measurable conductivity distribution in the soil.

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