Quite likely the crew working here was servicing paired lead-sheathed telephone cable. I believe canvas tents erected upon sites like this one assisted splicers. I fondly remember "pole tents" as a kid here in MA during the 1960s and noting the small fallen "dots" or "splatterings" of lead from such aerial work. They were difficult to detach from the sidewalk but I had some fun collecting the end-snips of the colored plastic wires. I also recall one NET&T splicer telling me (around 1963) that girls liked to save these colorful snips for making artistic braiding thingies that they wore. Hopefully they didn't do much if anything with the lead splatterings....