Well Disinfection

STEP 1 - Isolate critical areas

Turn or push the bypass valves to the “bypass” or “out of service” position for all water treatment devices (water softeners, reverse osmosis systems, etc.) and appliances that cannot tolerate bleach. These may harbor organisms and need to be disinfected separately. Follow manufacturer’s instructions for disinfection procedures.

Remove all filters from devices and appliances. Bait tanks and livestock watering troughs may require special attention.

STEP 2 - Electrical safety

Turn OFF the electrical power to the pump. If the circuit breaker box has a lockout hasp, use it to prevent the breaker from being accidentally turned ON. Always use a voltmeter to verify that power has been cut to the well before proceeding with the disinfection process.

STEP 3 - Open the well

• Standard Well Cap: Remove the well cap and move the wires to the outside of the casing to avoid getting the wire connectors wet when doing Steps 6 and 7 (see Figure 1); or
• Sanitary Seal: Remove the vent (see Figure 2-top arrow). Do not remove the compression bolts from the compression fit well seal (see Figure 2-bottom arrow).

STEP 4 - Inspect these components

• Wire insulation for cracking, peeling, or missing wire connectors.
• Well casings for cracks or other damage..
• Well cap for missing bolts, damaged vent screens, or loose gaskets.

It is important that any plumbing or well defects are fixed so that surface water, insects, vermin, or other contaminants cannot enter the well.

STEP 5 - Mix a bleach solution

Water chemistry and water system sizes vary. These differences will determine the amount of bleach solution needed to properly disinfect your water system. You want between 50-200 parts per million (ppm) of chlorine in the recirculating water (Step 7) for disinfecting your water system. Do not use a bleach solution greater than 200 ppm as it will reduce the disinfection effectiveness.

1. Add water from the water system into a clean 5-gallon pail until it is about three-fourths full, then
2. Add the amount of bleach as indicated in the table below. The first column lists the number of feet of water in the well. The second, third, and fourth columns show the diameter of the well casing (in inches).

STEP 6 - Add bleach solution to the well

1. Use a funnel when pouring the bleach solution into the well.
2. Avoid getting any bleach solution on metal well cap components and wires. It will cause corrosion.

STEP 7 - Recirculate chlorinated water

1. Turn the circuit breaker to the pump ON. CAUTION: The wires in the well casing are now energized.
2. Connect a garden hose to the most convenient faucet.
3. Run water from the hose in an area away from the well, septic system, landscaping, and bodies of water until you smell bleach or detect chlorine with test strips. This may take 5-10 minutes and the water may be discolored. Continue monitoring and running the water until it runs clear. If flow significantly decreases, shut off power to the pump and contact a licensed well contractor.
4. Turn the water OFF.
5. Place the garden hose into the well.
6. Turn the water ON.
   
7. Recirculate water. Continue to recirculate for about 30 minutes after you first smell bleach from the garden hose. Use two chlorine test strips as visual indicators to determine if water from the hose is at least 50 ppm chlorine (high dose) or less than 1 ppm (trace amount). If below 50 ppm, go to STEP 5 and add more bleach solution and repeat STEPS 6 and 7.
8. Turn the circuit breaker to the pump OFF.
9. Rinse well components with fresh, unchlorinated water. Rinsing washes off bleach solution to prevent corrosion.
10. Replace wires and well cap.
11. Turn the circuit breaker to the pump ON.

STEP 8 - Bring bleach solution to all faucets and fixtures

1. Select your first faucet or fixture.
2. Remove faucet aerator, if present. This will prevent them from getting clogged from loosened scale.
3. Run hot water until a chlorine test strip indicates a minimum of 50 ppm. This will take time as the chlorinated water in the system must replace the entire volume of your water heater. If below 50 ppm, go to STEP 5 and add more bleach solution and repeat STEPS 6, 7, and 8.
   
4. Repeat the process with the cold faucet. It will take much less time for chlorinated cold water to appear.
5. Turn OFF the faucet and repeat for all remaining faucets and fixtures, including showers, tubs, toilets, water using appliances, exterior faucets, yard hydrants, and outbuildings.

STEP 9 - Disinfection time

1. Turn the circuit breaker to the pump OFF.
2. Place signs or disable faucets and fixtures to prevent anyone from using the water.
3. Let the bleach solution sit in the water system for a minimum of two hours, preferably six hours, or overnight.

STEP 10 – Remove the chlorinated water

1. Turn the circuit breaker to the pump ON.
2. Attach a garden hose from an outside faucet or yard hydrant. Do not discharge chlorinated water into or near your septic system, landscaping, or any water bodies, because bleach solution will harm them.
3. Run the water to flush the bleach solution out of the well. Monitor the process, it can take 30 minutes to 24 hours or more to flush all of the bleach solution from the well.
4. Use a chlorine test strip to verify that water coming from the outside faucet or yard hydrant is free from any bleach solution.
5. Flush the chlorinated water from water heaters.
6. Run the water from all interior and exterior water faucets and fixtures to flush the bleach solution from the rest of the water system. Use a chlorine test strips that reads down to 0 ppm of chlorine to verify that no bleach solution is present.

STEP 11 - Disinfect water treatment systems and appliances

To disinfect water treatment systems and appliances, follow the manufacturer’s instructions for each water treatment device or appliance. If disinfection information is unavailable, contact your water treatment or appliance service provider. Bleach solutions may damage or improperly disinfect filters that are a part of a water treatment system or appliance.

STEP 12 - Reconnect appliances, water softeners, and other treatment devices

Return bypass valves to the ON position after following the manufacturer’s directions for disinfecting appliances and water treatment devices.

STEP 13 – Test the water

After the bleach solution is removed from the water system, sampling is recommended to make sure the well water tests negative for total coliform before you use it for drinking or cooking. MDH recommends using an accredited laboratory to test your water. Contact an accredited laboratory to get sample containers and instructions or ask your county environmental or public health services if they provide well water testing services.

Replace filters on all devices and appliances when MDH or an MDH certified laboratory confirms your water system is total coliform free.