The standard procedure for fixing similar issues with well water is standard household bleach + time to sit + a lot of running water to move everything through,

The standard procedure for fixing similar issues with well water is standard household bleach + time to sit + a lot of running water to move everything through, FWIW. Look up instructions for "chlorine shocking well water". You need to calculate the volume/concentration correctly, but there are lots of guidelines to make reasonable estimates of pipe + well volumes. FWIW, the main sanitizer used for kegs is the same thing used in restaurants for the standard "three sink" cleaning system (last dip is in sanitizer). Star San is the main brand name. It's a mild acid and it's both cheap and readily available. It works basically by denaturing proteins, which any acid will do, but the specific one is chosen to be harmless and relatively tasteless as well as easily clinging to surfaces to give extra contact time. I'm not sure it would be a good idea to use it, though, as it might eat away at some plumbing fixtures (e.g. galvanized pipe). If you did, you'd want the non-foaming variety (which is not called star san... Saniclean, I think? Same brand, either way).