Disinfect Your Well After the Flood

I read in the New Your Times this week that as the flood water in North Carolina has receded the U.S. EPA and the North Carolina Department of Health have been offering free water testing for the homes with private wells which are a third of North Carolina residents. Every well owner should test their well after flooding. The New York Times reports that so far the state and federal testing are finding that 40% of the wells are contaminated. This is not surprising, but there are actions that can be taken to restore the wells. If the mechanical components of the well were damaged by flowing debris the homeowner might be eligible for FEMA assistance. You can apply for FEMA assistance online or by calling 800-621-3362. The first thing is to repair any damaged equipment.

Severe flooding can cause septic waste and even chemicals from cars, stores and factories can enter groundwater making it unsafe to drink for days or even months depending on the extent of contamination and flow rate of groundwater. Essentially, anything that seeped into the groundwater will have to clear itself through natural attenuation (filtering by the soil and the contamination moving with the flow of the groundwater). A well may not be a safe source of water after the flood, but in all likelihood it will recover. Often all you need to do is flush the well then disinfect it.

Be aware that wastewater from malfunctioning septic tanks or chemicals seeping into the ground can contaminate the groundwater for several weeks if there was significant flooding.  The first thing you need to do is respond to any immediate problems and then test the water periodically to verify the continued safety of drinking water. Repeated disinfection and filtration can keep the water safe to drink until the problem is solved. If the well does not return to normal, a permanent water treatment system might be necessary if the grouting to the well casing has been damaged. A well professional can help you determine if a well needs to be replaced or repaired with treatment equipment installed. Years ago several neighbor’s wells were impacted by a flooded and failed septic system. It took several months for the contamination to clear, but it ultimately did.

Unless your well was submerged near a trucking depot, gas station, animal feed lot or other industrial or commercial source of chemicals it is likely that torrential rains or flood waters have infiltrated your well and you have “dirty or brownish” water from surface infiltration. This is especially true if you do not have a sanitary cap on your well or have a well pit. Historically, it was common practice to construct a large diameter pit around a small diameter well. The pit was intended to provide convenient access to underground water line connections below the frost line. Unfortunately, wells pits tend to be unsanitary because they literally invite drainage into the well creating a contamination hazard to the water well system. 

It is most likely if your yard was flooded or your well submerged that you have some surface infiltration of water including flood water from your septic system. In that case, chlorine shocking your well should disinfect your well and last at least 7-14 days you may have to do it more than once until everything is back to operating normally and any contamination in the groundwater has passed. Sadly, if you have a private well you are pretty much on your own. FEMA assistance might pay for well repairs or equipment, but you are going to have to take charge of the situation, and flush and clean your own well. After a flood, you are going to have to dry out your septic system and get it functioning again. If the flood waters were high enough to top the septic tank, have it pumped and go light on water use until the leach field dries out.

If your water is brown, the first thing you should do is run your hoses (away from your septic system and down slope from your well) to clear the well. Run it for an hour or so and see if it runs clear. If not let it rest for 8-12 hours and run the hoses again. Several cycles should clear the well. What we are doing is pumping out any infiltration in the well area and letting the groundwater carry any contamination away from your well. In all likelihood the well will clear of obvious discoloration. Then it is time to disinfect your well. This is an emergency procedure that will kill any bacteria for 7 to 14 days. It needs to be repeated until the source of the contamination is removed.

After 10 days you need to test your well for bacteria (and chlorine) to make sure that it is still safe. Testing the well for bacteria would determine if the water were safe to drink. A bacteria test checks for the presence of total coliform bacteria and fecal coliform bacteria. These bacteria are not normally present in deeper groundwater sources. They are associated with warm-blooded animals, so they are normally found in surface water and in shallow groundwater (less than 20-40 feet deep). Most bacteria (with the exception of fecal and e-coli) are not harmful to humans, but are used as indicators of the safety of the water. The chlorine test tells you if the lack of bacteria is due to the continued presence of chlorine. You need for both bacteria and chlorine to test negative to have successfully “fixed” your well.

To disinfect a well you will need common unscented household bleach.  For a typical 6 inch diameter well you need 2 cups of regular laundry bleach for each 100 foot of well depth to achieve about 200 parts per million chlorine concentration. You will also need rubber gloves, old clothes and protective glasses to protect you from the inevitable splashes, and don't forget a bucket to mix  bleach with water to wash the well cap.

• Put on the old clothes and safety glasses
• Run your hoses from the house to the well
• Fill bucket with half water and half chlorine. 
• Turn off power to the well
• Drain the hot water tank
• Remove well cap
• Clean well cap with chlorine and water solution and place in clean plastic bag
• Clean well casing top and well cap base using brush dipped in chlorine water
• Pull wires in the well aside if they are blocking the top of the well and clean them with a rag dipped in chlorine water mixture. Make sure there are no nicks or cuts in the wires. 
• Put the funnel in the well top and pour in the chlorine and water mixture
• Now pour in the rest of the chlorine SLOWLY to minimize splashing
• Go back to the basement and turn the power to the well back on
• Turn on the hose and put it in the well 
• Sit down and wait for about 45 minutes or an hour
• After 45 minutes test the well to make sure that the chlorine is well mixed
• Use the hose to wash down the inside of the well casing
• Turn off the hose
• Carefully bolt the well cap back in place
• Now go back into the house
• Fill your hot water heater with water, but do not turn it on to heat the water
• Draw water to every faucet in the house until it tests positive for chlorine then flush all your toilets. Turn off your ice maker. 
• Then do not use the water for 12-24 hours 
• Set up your hoses to run to a gravel area or non-sensitive drainage area. The chlorine will damage plants 

 

After 16 hours turn on the hoses leave them to run for the next 6-12 hours. The time is dependent on the depth of the well and the recharge rate. Deeper wells with a faster recharge rate take longer. If you cannot run your well dry and it recharges faster than the hoses use water you will need to keep diluting the chlorine. If you can run your well dry, you might have to let it recharge and run the water off again to clear the chlorine.

After about 8 hours of running the hoses begin testing the water coming out of the hose for chlorine. Keep running the hose and testing the chlorine until the chlorine tests below about 1 ppm.

• Drain the hot water heater again, open the valve to refill it and turn it back on
• Open each faucet in the house (one at a time) and let run it until the water tests free of chlorine. Be aware the hot water will sputter- big time- until all the air is out of the system. Flush all the toilets
• Change the refrigerator filter cartridge and dump all your ice and turn your ice maker back on. 

It is important not to drink, cook, bath or wash with this water during the time period it contains high amounts of chlorine whose by products are a carcinogen. Run the water until there is no longer a chlorine odor. Turn the water off. The system should now be disinfected, and you can now use the water for 7 to 14 days when the effects of the disinfection wear off. Hopefully, a single disinfection will be enough. 

Unlike public water systems, private systems are entirely unregulated; consequently, the well testing, and treatment are the voluntary responsibility of the homeowner. The local extension office (here in Virginia) or the local Department of Health can provide information and resource links for private well owners.   I am happy to answer emails or questions to the blog. Remember after you chlorinate a well the water typically runs brown until all the iron, iron bacteria and other minerals in the groundwater that you just oxidized are flushed out. Do not panic, it will clear.

I regularly chlorinate my well to knock back the iron bacteria and generally clean it out and refresh the water. For years I did this when my husband was out of town to avoid inconveniencing him for what I considered spring cleaning. During the pandemic when he was home during the chlorination, he was totally convinced that the continued sporadic reappearance of brown in the water was an indication that I had ruined the well. I had to tell him multiple times wait- it will clear. Finally, I just let the hose run for another 24 hours straight, and the brown was completely gone, and the test strips did not detect any chlorine. Usually, to be less water wasteful, I just get close enough and let time take care of it. (During this period I use bottled water or filtered water to make coffee and cook and then change the filter on the refrigerator when it clears completely.)  After a flood there are probably not water concerns so flush the well with abandon.