Monday, June 12, 2017

Check List for Chlorine Shocking a Well

You disinfect a well and plumbing system by circulating a concentrated chlorine solution throughout the system. The level of chlorine to use is between 50 ppm and 200 ppm (parts per million) depending on which University extension office is asked. I typically use about 200 ppm as recommended by The Virginia Cooperative Extension where I volunteer unless I am addressing a significant iron bacteria problem in which case a much higher concentration of chlorine is necessary. Be aware that too concentrated a solution or too weak a solution will not be effective. Do it once the right way.

Why disinfect a well, there are several reasons, the most common reason is because coliform bacteria was found in the well water. In that case, standard protocol is:
  1. Carefully check the well and water system for points of contamination. Make sure you have a sound and secured sanitary well cap and that the soil around the well is packed to drain water away from the well. 
  2. Then treat the well and plumbing system with chlorine for 12-24 hours to disinfect system (thet 12-24 hours is essential). Then flush the chlorine from the system.
  3. Retest the water after the chlorine has left the system in about 10 days to two weeks. If coliform bacteria is “absent” you’re done. If not, then it is time to install a long term disinfection system.
Chlorine shocking a well is also used to knock back iron bacteria which can foul a well, damage pumps, stain plumbing fixtures, clog pipes, faucets, showerheads, and produce unpleasant tastes and odors in drinking water. There are no drinking water standards for iron bacteria so water is very rarely tested for it. Confirmation is usually based on visual symptoms in the water, including the slimy brown/red appearance (often most noticeable in the toilet tank) and an unpleasant musty odor. Over time as iron bacteria takes over the system the perceived quality of the well water declines as iron bacteria produce unpleasant tastes and odors commonly reported as: "swampy," "oily or petroleum," "cucumber," "sewage," "rotten vegetation," or "musty." There is often a discoloration of the water with the iron bacteria causing a slight yellow, orange, red or brown tint to the water. The standard protocol for treating iron bacteria is to chlorine shock the well at a recommended chlorine concentration of 500-1,000 parts per million unless the well is already fouled then the pumping equipment in the well must be removed and cleaned, which is usually a job for a well contractor or pump installer.

I have had iron bacteria problems and coliform bacteria in the past. I chlorine shock my well every couple of years simply to maintain water quality and knock back the iron bacteria. This practice was until recently fairly radical in the private well sector, but is common in small public supply wells.

This past weekend I helped someone who attended our Prince William County Drinking Water Clinic chlorine shock his well. He is someone who sought help from VAMWON where I volunteer and then came to the water clinic. He is a professional, bright and capable, but not an engineer and wanted help with the project. I know there is nowhere to turn to get your well done right, so when he pressed I agreed to show up and provide guidance on how to do it. Given my arthritic hands I am fairly useless with a wrench, but I can walk you through it and lend a hand and it is really an easier job with to people. Here is how you do it:

First you need to know how deep your well is to calculate how much chlorine to use. Also, the flow rate on the well will give you an idea on how long it will take to clear the well of chlorine. Get a copy of the Well Completion Report from the county. They will make a copy for you, but if you ask nicely they will just email it to you saving you a trip to the department of health.

Depth of well tells you how much water is stored in the well boring. The typical 6 inch diameter well stores 1.47 gallons per foot, so you multiply your well depth by 1.47 and then add about 110 gallons for the hot water heater and household plumbing . You will need about 3 pints of chlorine per 100 gallons. If you have a very large hot water heater and lots of treatment equipment you will need to add another half a gallon of chlorine. Buy extra- you might need it.


A few days before disinfecting your well you need to purchase all your supplies. You will need:
  • a plastic tarp, 
  • 3 -5 gallons of plain unscented Clorox bleach (you need 3 pints for every 100 gallons of water with standard bleach), 
  • an 8” diameter funnel, 
  • rubber gloves
  • a relatively new scrub brush 
  • a white 3 gallon bucket (I can’t easily lift a 5 gallon filled with water and chlorine), 
  • lots of chlorine test strips 
  • a clean and relatively new hose or hoses at least long enough to reach the well from the spigot
  • a pair of safety glasses or goggles
In addition, you will want to purchase 6 gallons (or more) of bottled water (to carry you while we have no water to use and make sure that our coffee and tea do not have any chlorine residue to spoil the taste), new refrigerator filters, and coliform home test kits for use in a couple of weeks.

When you are ready to disinfect your well, you need to have about 24-30 hours when you will not be able to use the water. Shock chlorinating a water supply system can potentially damage  pressure tanks, water softeners, filters and filter media, and other treatment devices, but the only way to kill the bacteria is to run the chlorinated water into the components and let it sit in the system. Virginia Cooperative Extension always recommends that you check with component manufacturers before shock chlorinating your water supply system to determine how to bypass or protect this equipment if necessary. With my components I consider this wear and tear. 


I began by filling my bucket with some water and chlorine then go into the basement and turn off the power to the well. Then turn off the power or gas to the hot water heater and drain it, and close the water intake valve. Once the well is fully chlorinated you will refill the hot water heater, but keep it cold (and turned off) during the hold time.

Now it is time to unbolt and remove the well cap. Examine the well cap to make sure it is in good condition and the screen on the base is sound. Next take your brush and clean off the well cap using the chlorinated water from your bucket. Once the well cap is good and clean place it on the plastic tarp or wrap it in a clean plastic bag. Next scrub the edger of the well casing to remove any dirt and take a rag dipped in chlorine water and wipe down the wires in the well examining them for any damage. Get the wiring nice and clean and push them aside.

  • Put on old clothes and safety glasses
  • Run your nice new hoses from the house to the well and place on the tarp
  • 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

What you are doing is recirculating the water. It is running from the well to the pressure tank to the hose and back again. This effectively is mixing the chlorine into the well water. The deeper your well the longer this takes. Also, if you have any treatment tanks installed ahead of the pressure tank they are also being included in this cycle. After about 45 minutes the water should look orange and test strongly for chlorine. 

  • Use the hose to wash down the inside of the well casing
  • Turn off the hose
  • Carefully bolt the well cap back in place
  • Fill your hot water heater with 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 it was no 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 takes longer. If you cannot run your well dry-it recharges faster than I can pump you need to keep diluting the chlorine.
  • After about 6 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.
  • Now it is time to drain the hot water heater again, refill it and turn it back on
  • Open each faucet in the house (one at a time) and let run it until the water tested 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. 
  • You are done. 
There are a few twists and turns that can come up. If you have iron bacteria in your well, your will see gunk in the water when you are re-circulating the water in the well. In that case I typically run off some water for an hour or so to get some of the gunk out. Then add an additional gallon of chlorine to the system and recirculate for another half an hour before I close up the well. Also if you have treatment tanks in your basement, you also want to drain after the chlorine has been flushed out of the system. Do not drain them into your septic system. Good luck.

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