Strong earth currents which complicated surface potential measurements and which after a time reversed the direction of flow were encountered on a section of pipe maintained by the East Bay Municipal Utility District in the vicinity of Oakland, California.
The phenomenon was noticed in making tests on a pipe line. High potential readings were obtained at a test location on the pipe line five miles from the nearest cathodic station. Surface earth currents flowing by the pipe line indicated current discharging on one side of the pipe. The same indications were obtained when test holes were drilled to pipe depth. But when the near electrode was placed within an inch or two of the pipe, the potential readings indicated current pick up and evidenced satisfactory protection for the pipe.
Further checking was done on surface potentials near the anode beds of several cathodic stations where some of the current was...
