We have had similar pinhole leaks in piping in the Marylland suburban area iin particular. Generally they have occured within the houses, not underground.
It has pretty much been decided that the problem is caused by changes in the water treatment although the water company won't redily admit it. The changes were mandated by the federal govt., I believe, and the pinhole leaks in copper pipe were an unexpected consequence.
I'm not sure where the situation stands now, but you might want to contact the WSSC (Washington Sanitary Sewer Commission). I'm sure they have a web site. If not, I can fiind the info. for you.
I don't think it is a stray electrical current problem. Ken
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