Everyone should have an initial baseline test for total coliform bacteria and nitrate nitrogen. After that based on the results, nitrate nitrogen should be checked semi-annually or annually until a normal track record has been established usually 2-3 tests under the MCL. Bacteria should be checked anytime the well is opened or you notice a change in taste, odor or color.
Any accredited laboratory can evaluate the test report for you. If you want a second opinion contact a groundwater professional from you local area to interpret the results.
Most well owners cannot safely open the well seal to apply the proper amount of disinfectant to the well. In addition, if the well has been flooded and contains organic matter, the disinfection chemical could create a cancer-causing disinfection by-product called trihalomethanes. Well disinfection can be a simple or a complex process depending on how the contamination got there. It’s best to pay a licensed insured ground water professional to disinfect your well.
Check with your local regulatory authority for a copy of the applicable regulations. Contact a licensed water well contractor for an estimate on how to bring the well back into compliance.