There is a water break-out zone to the left of Sudbury Rd on the far side of the river as you head south and start to go uphill. I went in there to have a look and found a well that was actively emptying from recent rain. The structure was a rectangle of dry stone without mortar several feet above ground level.
Let's get a bit of color into the photo [click it to enlarge]:I read somewhere in an Ernest Seton Thompson book about "Indian wells" where Indians would get water at the edge of a swamp by digging a hole into the moist soil. The hole would rapidly fill in with sludge which would get emptied out. It would again fill with sludge and again get emptied. Each time the sludge would come in a little clearer until it was clear drinkable water. When we were kids we found a rectangular stone lined hole in a swamp next to Rt 2 in Lexington (now the first office building east of the 128 exit North) and later I wondered if that was an Indian well. So now I wonder about this structure from Concord. It would be nice to know something about it.