I assume that you have determined that you have an unacceptable coliform level. Once you have removed the source of contamination, you can pour Clorox into the well and then flush it through your domestic water system. It will take a week or longer to disipate the bleach. My experience is with a very productive 36″ diameter shallow well (13 feet deep) that has a larger-than-average resevoir of crushed stone around it. The well probably has several hundred gallons of water in it, normally. For this well, I used two gallons of bleach. You probably should limit the amount of clhorine going into your septic system. Probably best to do most of the flushing of your pipes out through the garden hose to someplace where the chlorine will not do damage to plants.