Heap leaching is one of several leaching methods (in-situ leaching, dump leaching, pressure leaching and tank leaching) whereby metal and other ores are leached with various chemical solutions to extract valuable minerals. Commonly HDPE is used in the pad under the ore to protect the environment and to preserve the leached solution containing the desired mineral. The most extensive application of heap leach pads is for copper ore processing. In this application, weak sulphuric acid is usually used to dissolve copper from the mineral ore. Typically copper pregnant leach solution has a pH less than 2.0 with a concentration of copper that varies from 1 to 5g/l and iron concentration up to 5g/l. A program for examining the effect on the aging of HDPE geomembranes of these and other solutions relevant to heap leach pads at both very low and high pH and to low level radioactive waste facilities where the leachate has a high pH is described. Tests are being conducted at temperatures of 40, 65, 75, 85, and 95oC. The geomembrane properties and solution chemistry being used are also presented. Preliminarily antioxidant depletion rates for geomembrane incubated in a solution with a pH=0.5 are presented and a preliminary extrapolation to field temperature is provided.