I woke up around 3 am last night. So after I get back in bed and after 30 minutes of lying there, drifting off, a thought on this mystery entered my head. I was thinking about how straight that line is, and how low the mound is (what, maybe 18" to 24"?). It was then that the thought came to me; why not an iron pipe? One they just laid on the ground, and as an afterthought, decided to cover it so the water inside would resist freezing. Pipelines, at least those without elbows or 45's or what-not, are bound to be super straight if they are connected correctly.
No? Yes? Maybe?
By the way, thinking of this, I looked at the 1930 aerial again. I don't see the mound after all, so maybe later it was put in. Then again, 1930 is an aerial, not lidar.
I see now Dash, you were on that track of a pipe earlier in this thread. Need to get out there with a shovel.