What can I do if I have shock chlorinated my well several times, but my sample results still come back positive for bacteria?

Local geology – Groundwater can be vulnerable to contamination in certain types of geology including sandy/gravelly soil, karst geology, and shallow bedrock. Sands and gravels have high permeability, which means water (and contaminants) can easily move through the soil. Karst geology is where you can find caves, caverns, and sinkholes which act as conduits for surface contamination. Last, when a shallow well is drilled in bedrock that is at or near the surface, as seen in many areas of New York state, surface contamination can easily enter the fractures in the water which lead to the well.

A breach or poor construction – If you have a dug or bored well, they are made to allow water to seep into the well along most of the depth of the well and are typically more susceptible to surface contamination. Older dug or bored wells that do not meet current water well codes are at high risk.

If you have a deeper well, with casing to a considerable depth, it could also be that the well wasn’t properly constructed. If there are holes in the casing or if it was not grouted properly, water from near the surface can enter the well.

Ensure you are carefully following the instructions. When you bleach your well, you need to make sure all of the lines are flushed and that you let the bleach water sit in the plumbing allowing it time to kill any bacteria. Having your bleach mixture too weak could also prevent the treatment from being effective.

Determine the source of contamination. Examine the well or have a professional assess your well to find out where the contamination is coming from. A simple repair such as replacing a cracked well cap, or a more extensive upgrade to meet current well codes, may resolve the issue.

Clean the well. If the bacteria have been present for a long time, the colonies may be too thick for shock chlorination to work. The well may need to be thoroughly cleaned to remove the biofilm buildup. Contact a local well professional that offers well cleaning services.

Seal the well and drill a new one. If a deeper aquifer exists, a well owner may choose to abandon the old well and have a new well properly constructed in a deeper aquifer. If you abandoned a well, have it properly sealed to prevent contamination of the groundwater.

Add continuous disinfection. If you cannot do any of the above or if you use a spring for your source of drinking water, you will need to add continuous treatment for bacteria. The most common types are continuous chlorination and ultraviolet (UV) disinfection. Contact your local health authority or a water treatment specialist for advice on the best water treatment option(s) for your system.