others stated it better, pretty much it is contacting the various government bodies first.
being in Arizonia, i would imagine well's in general is even bigger deal vs here in illinois. and keeping records and like at a government location. and with that.. when well was put in, it most likely had info, (depth, diameter, pump info, gpm, along with who did it and when), all sent into some local government agency. and you should be able to look this stuff up.
you may be able to get all the info online, or you may have to actual visit / request info from a government agency, (depends on how up to date with internet they are, rules/regs that have been put in place since then in retrieving information).
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beyond that, it is taking top off well,
--and pulling the pump out if there is one, and finding spec's on it,
--along with "inside diameter" of the pipe connected to the pump.
--and how deep the well is,
--how deep the water is in it
--diameter of the well to figure how much water it holds
--finding how fast the water comes back into the well (gpm)
--getting well water tested ((a local water company might charge you / free)), you may have a county office that gives away free test kits, and a small service fee to have water tested))
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you might be able to contact company that put in well. and get some info from them on the specs of the well. ((again government agency first))