The ASTM ballot closed last December, making official some significant revisions to the ASTM standards that govern Electrical Leak Location (ELL) practices. This newsletter summarizes the important revisions to three ASTM standard practices (D7002, D7703, D7007) and one ASTM standard guide (D6747). These revisions will be presented in the 2015 versions of the D35 standards.
All of the aforementioned standards were updated with consistent terminology and figures. The recently published standard practice for the newly adopted arc testing method, ASTM D7953, was included as a reference in all of the revised standards as an additional method for surveying exposed geomembranes.
It is important to note that all of the ELL standards have been modified to recognize new installation procedures for conductive-backed geomembranes. If these installation procedures are used, which isolate the top non-conductive geomembrane layer from the bottom conductive layer, all of the ELL methods can be applied to conductive-backed geomembrane, which previously could only be testing using the spark testing method (ASTM D7240). ASTM D7240 is also currently undergoing revision to address this point, with a revision date anticipated for either late 2015 or early 2016.
The guide for assisting the selection of electrical leak location techniques was reorganized into two sections: one for exposed geomembranes and the other for covered geomembranes. Descriptions of all of the methods are presented, along with tables, to provide a comparison of the various methods.
The exposed geomembrane standards ASTM D7002 and D7703 were made consistent with each other. The sensitivity testing protocol is now the same for each method, requiring a noticeable signal on either a drilled 1mm hole or an artificial leak consisting of a solid core 18 AWG insulated wire with the end cut off. An artificial leak “puck” is no longer allowed for the water lance method. A clause is now present in all of the exposed geomembrane standards to allow for an alternative ASTM Standard Practice when “warranted by adverse site conditions, clearly technical superiority, logistics, or schedule”.
The covered geomembrane standard has undergone significant revisions, particularly in the performance of the sensitivity testing for soil-covered surveys, which is now referred to as leak detection distance testing. If an artificial leak is used, it must be grounded at least three meters away from the return electrode of the power source. If an actual leak is used, the measurements of “noise” must be taken with the survey area activated by the power supply. Formerly, the survey grid measurement spacing was specified to be no more than twice the leak detection distance. Now, only 1.5 times the leak detection distance is allowed. For example, if the proposed measurement spacing is ten feet by ten feet, then the leak detection distance must be determined to be 6’8” or greater for the target leak size. In addition, the maximum allowable measurement spacing is specified to be 3.05 meters (10 feet).
An Appendix was added to detail soil-covered dipole survey data analysis methods. Both graphical and voltage contour mapping methods are now presented and detailed. The new ASTM figures providing examples of the different data analysis methods are presented here as Figures 1 and 2.
Previously, the ASTM stated that the data should be analyzed after performance of the survey, but it did not detail how the analysis was to be done. Now, examples are provided, as is a table comparing the data analysis methodologies.