Coliforms after a disinfection on a 250 ft well would indicate a leak into the well, inadequate disinfection, or the sample getting contaminated as you draw the sample.
http://www.moravecwaterwells.com/index.php/maintainance/disinfection-and-testing is the disinfection method that I like. If you just pour a jug of bleach down the casing, that does not wash the casing above the water. The bleach can just run down one side of the casing. If you don't sufficiently s freeanitize the faucet with bleach or heat, you can get stuff from the faucet that you use.
Do you know how deep the casing on this well goes? What I say below may be more likely than usual to be wrong: I would think that Ohio wells would usually have casing all of the way down. In many wells, especially in the west, they run casing down only part of the way -- until they first hit rock. If the casing were only down a short distance, that would seem to make the cementing job to be more critical in keeping surface water out of the well.