You can fix the well.  Shock it, pump it, and then clean it.

Tj

A wood wall well, earthen well,even stone, you can't just shock it.  You have to pump it dry or in the case of old school bucket it dry.  You have to remove the biologic contamination, the nitrides, or its just a big petri dish waiting on the next bug to grow there.  

Back during the French Indian Wars and out west, the Indians use to throw dead animals down settlers wells.  That would put out of action till the well was shocked, pumped, and cleaned.  Without a secondary source for water till that job was done, it was a big deal.

Pretty much, you shock the well initially to keep you from getting sick while doing all the next steps.  You then pump it out dry then clean the walls, pretty much just brush them.  Depending on the well people use to climb in there with brushes but now days its more like cleaning a big gun with a bore brush.  Often while cleaning, you have or should keep pumping.  Once you got it clean and all the biologic material out of there, you let it fill one last time then shock it one last time.

You see a well sits too long and gets enough crap in there, its just like someone chucked an animal down there and until you can get all that biologic out of there, BOD (biological oxygen demand) down, even if you shock it, its going to recontaminate.  

It's like you really can't stop the bug, you take away the stuff it lives on.

I spent a lot of time on very old farms when I was boy.  Every now and then, we'd have to bring an old abandoned well back to life.  

Tj