The Model UL is designed for long-term permanent use to obtain accurate potential measurements on buried structures. It is the best choice for those applications where easy installation is possible, such as an open hole or trench. For those situations where there is limited access, the EDI Model US is recommended. A Cu / CuSO4 element should be used in low chloride soils (<500 ppm), while a Ag / AgCl element is recommended for high chloride soil (>500 ppm) in order to obtain the longest possible life. Further information is available from Farwest.