The most significant construction damage in an installed geomembrane occurs while the geomembrane is being covered by materials such as soil, gravel or concrete. These leaks can be located using the dipole electrical leak location (ELL) method, whose procedures are standardized by the ASTM D7007. The effectiveness of the dipole survey is a function of site conditions, which are widely variable and ASTM D7007 includes little information on how to properly prepare a site for a dipole survey. ASTM procedures on calculating the leak detection distance (LDD), which forms the basis for measurement density, do not adequately portray the effectiveness of locating a real hole. ASTM procedures are also inadequate in controlling the precision of measurement locations and survey extent. Additionally, the ASTM D7007 requires general survey parameters to be presented in the ELL survey report. However, providing survey data in the report is optional and it may be only raw. Consequently, site owners have to put complete trust in an ELL contractor to conform to the minimum requirements of the ASTM D7007. The voltage mapping presented in this paper can show a site owner in one glance that the dipole survey was performed thoroughly and accurately, while providing an invaluable quality control document. This paper outlines the most significant factors in leak detection sensitivity using the dipole method and details how to prepare a site for a dipole ELL survey while maximizing the effectiveness of the method. Four field case studies are presented with dipole survey data in soil-covered geomembranes that show the shortcomings of the ASTM D7007. Voltage mapping and key elements of performing a survey thoroughly and accurately are detailed, including GPS-based data acquisition. The information presented in this paper will benefit site owners by providing the solutions to the ASTM procedure shortcomings.
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