It seems odd that two or more wells within say 20 feet of each other can have very different characteristics.  Homeowner well water typically exists as aquifers (a water bearing layer of water permeable sand or rock) and pockets of ground water (water that seeps in from surface sources.  Fractures in the earths crust can isolate portions of the aquifers and the pockets of ground water. Artesian wells are totally isolated aquifers.

Water is considered the “Universal Solvent.”  This solvent then leaches (drains away) the minerals and elements from the rocks around it into the water.  Because the nature of the ground surrounding the water can change, heavy rains and draught conditions affect ground water seeping into the well,  and because water can be found at different depths, the water in each well can have different chemicals in varying amounts within it.