I just spoke to my well guy and he said any new well has to be 20 feet from the old one. I guess that is our County requirement.
He basically said point blank "You don't want to use the existing well for your new home's potable use, You should drill a new one".
I know, I know...he wants to make $$ by drilling me a new well but his reasoning was that we could dump ~$15K in "attempting" to rehab the existing well with no guaranteed positive outcome or spend ~$20K to drill a new well, install a 3-5 hp submersible and have it be pristine. He also said we could use the existing three pahse electrical service to feed the additional well while still keeping the existing well in place and active for our orchard's irrigation system.
At this point I am leaning to the new well. I am still meeting him onsite Saturday to further discuss the situation.
IMO, you want a new well and it must be out of the well head protection area of the old one and, the old one out of the wellhead protection of the new one. IOWs, you do not want either well effecting the recovery rate of the other. That 20', even in a rock bore well is nowhere near enough to accomplish that.
Another way to say it is, neither well should be in the recovery area or especially in the cone of depression of the other. If that is not done, your water quality can suffer and both wells will be drawing the other well down; especially the old well because it will be pumping more water than the house will use.
When you get the new well, then you must find the peak demand gpm the house requires and size the pump to be able to provide them at the pressure you want to run the system at, and then you find the hp to get the job done from whatever depth the pump is expected to have to pump from. To be thinking of a 3-5 hp pump for a 300' deep well and just a house, you must be building an 8 bathroom mansion with 4-6 body spray 2 person showers and large 2 person whirlpool tubs...
I think his prices are way high.