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WATER PUMPS, TANKS, TESTS, WELLS, REPAIRS
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WATER PUMP REPAIR GUIDE
WATER PRESSURE LOSS DIAGNOSIS & REPAIR
WATER PUMP SHORT CYCLING
WATER SOFTENERS & CONDITIONERS
WATER TANK REPAIR PROCEDURES
WATER TANK: USES, TROUBLESHOOTING
WATER TESTS, CONTAMINANTS, TREATMENT
WATER TREATMENT EQUIPMENT CHOICES
WELLS CISTERNS & SPRINGS
WELL CHLORINATION & DISINFECTION
WELL FLOW RATE
WELL WATER PRESSURE DIAGNOSIS
WELL YIELD IMPROVEMENT
WINTERIZE A BUILDING
How to shock or disinfect a well: this article explains how to shock a well, when, why, and exactly how to chlorinate a drinking water well. We provide a table explaining the quantity of bleach needed to disinfect a well, and a table comparing the 3 Common Well Water Disinfectants: Chloramine, Chlorine and Chlorine Dioxide.
We include a detailed description of the well shocking procedure using household bleach to sterilize well water and water equipment. The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time. Page top sketch illustrating both deep and shallow water well construction and depths is provided courtesy of Carson Dunlop Associates.
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When and How to Shock or Chlorinate a Well - Procedure for Shocking a Well to (temporarily or maybe longer) "Correct" Bacterial Contamination in Well Water
This information is from the Dutchess County Health Department's environmental laboratory, with annotations, expansion & annotation, but you'll find that it is consistent with the well shocking or well chlorination procedures recommended by most health authorities.
[Click to enlarge any image]
The purpose of shock disinfection of a well system is to destroy bacterial contamination present in the well system at the time of disinfection and is not intended to kill bacteria that might be introduced at a later time.
Our photo shows an owner who has lifted the loose, poorly-sealed well piping and cap right off of the steel well casing. This well needed repairs and it needed to be sterilized using the well chlorination procedure we discuss here.
Therefore it is vital that the well be constructed so that no new contamination may enter the well following completion of the shock disinfection. In order to achieve a satisfactory disinfection of the system, the bacteria must be brought in contact with a chlorine solution of sufficient strength and remain in contact with that solution for a sufficient time to achieve a complete kill of all bacteria and other microorganisms.
Article series contents
This article series on well water contamination, testing, & cures explains many common water contamination tests for bacteria and other contaminants in water samples. We describe what to do about contaminated water, listing common corrective measures when water test results are unsatisfactory. We include water testing and water correction measures warnings for home owners and especially for home buyers when certain conditions are encountered, with advice about what to do when these circumstances are encountered. Various treatment methods for contaminated water are reviewed and the pros and cons of each are discussed.
Details of the Well Chlorination Procedure - Exactly How to Shock a Well, Where to Put Chlorine, How Much Chlorine to Use to Shock the Well
If drinking water has been tested and has not passed standards for safe drinking, or any time the building water supply system has been opened for repairs (such as replacing a submersible well pump or a jet pump foot valve), the well should be disinfected following these procedures, and should be re-tested as described below.
Our photo shows a standard modern 6" steel well casing - it's easy to spot at a property.
If you don't know where the well is located you'll have to find it before this well chlorination procedure can be best performed.
See WELLS CISTERNS & SPRINGS for articles that describe different types of water wells, what they look like, where they're found, and their operating characteristics.
It's possible to get chlorine into the well by sending it through the building piping and pump but that step won't sterilize the interior and sides of the well casing - so the procedure below is a better one.
Watch out: when working with chlorine, people should be in a well-ventilated place. The powder or strong liquid should not come in contact with skin or clothing. Solutions are best handled in wood or crockery containers because metals are corroded by strong chlorine solutions.
Watch out: if using chlorine disinfectants in equipment that heats water such water heaters, be sure your heater has been turned OFF and has cooled down to at least room temperature before trying to run chlorine through it. Heating water that contains a high level of chlorine might produce potentially dangerous chlorine gas coming out of a hot water faucet.
Watch out: Leaving too much chlorine in any water system can be dangerous: drinking concentrated chlorinated water could be sickening or even fatal, and less seriously, doing laundry with chlorinated water may bleach clothing by accident.
Watch out: for difficult well or equipment sterilization cases such as after area flooding or where there is a persistent bacteria source, pH adjustment of the disinfection solution may be necessary for the disinfectant to be effective, (WELL DISINFECTANT pH ADJUSTMENT )
Watch out: if the well source water contains hydrogen sulfide (H2S), when preparing a well disinfection solution you must allow the water to aerate so the H2S dissipates, otherwise the acid formed will cause an immediate release of H2S gas from the water, which poses a serious health risk.
For details about exposure to various toxic and irritating gases see
This topic has moved to a separate article found at WELL DISINFECTANT CHOICES.
This topic has been moved to WATER TREATMENT EQUIPMENT DISINFECTION
This topic has been moved to a separate article found at WELL DISINFECTANT TABLE, POST FLOODING
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs)
Question: How Long Will It Take for Chlorinated Water in a Shocked Well to Reach the House?
In a well 700ft deep - how long until the chlorine smell will be get to the house? - B.S.
Reply: We Must Calculate How Much Water is in the Well and House Water Pipes, the Pump Rate, the Piping Distance:
A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a well water problem problem. That said, here is how we figure out how quickly the chlorinated well water should appear in the house:
The answer to your question includes the following factors and the simple calculations we present below.
Provided that you used the proper concentration of bleach or chlorine to get the well water level to contain the proper amount of chlorine (as per the text at WELL CHLORINATION SHOCKING PROCEDURE or per your local health department), the water will definitely smell like "bleach" or "chlorine" at a faucet as soon as well water has run through the well piping, to the building, through building plumbing, and out the mouth of the faucet.
The real answer to your question depends not on the depth of the well (700 feet in your case) so much as the diameter and length of well piping between the well bottom and the water faucet where you are sniffing. We can presume that the chlorine you poured into the well mixes quickly with the water already in the well (the static head), and that the mixing is further agitated if you washed down the well casing sides with chlorinated water as we advise.
A second factor is the water flow rate of your well pump in gallons per minute. For this calculation we will assume your well pump delivers a conservative 10 gallons per minute of water flow through the system piping when the pump is running. (The true answer is more difficult to calculate because when the pump is not running the water pressure in the piping depends on the water pressure tank and is not constant.)
But we can make make some assumptions based on common values to get in the right ballpark of the time needed for chlorine to show up at the tap of a shocked well.
If for simplicity we assume that all of the piping between the well bottom and the faucet has an average diameter of one inch, then the formula for how much water there is in a foot of pipe is the formula for the volume of a cylinder:
The formula for calculating the volume of a cylinder is:
pi * radius2 * height (pi is 3.1416) - [We discuss this calculation in more detail at WATER TANK SIZE & VOLUME.]
In the formula above, the radius (which is half of the pipe diameter) should be squared. That is, divide the diameter in half to obtain the radius, and multiply r x r to obtain r2.
So for a 12" length (one foot), of one-inch inside diameter water pipe the volume of water is (keeping all measurements in inches)
3.1416 x (1/2)2 x 12 = 18.8 cubic inches of water per foot.
We convert cubic inches to gallons by dividing the cubic inches by 231 (a constant) or we can multiply the cubic inches by 0.004329 (another constant).
18.8 / 231 = 0.81385, so 18.8 cubic inches of water is 0.081385 gallons.
So your theoretical one-inch water pipe contains about 0.08 gallons per linear foot.
You didn't say how far the well is from the house nor how many feet of piping are between the house point of water entry and the faucet, so we'll make some assumptions and you can plug in your own numbers.
Assuming 200 feet distance from well bottom to point of entry of water in the home, and another 50 feet of water piping through the home before water gets to the faucet where you've placed your nose [Watch out: don't get chlorinated water in your eye. ] then
250 feet of pipe contains (0.08 gallons per foot x 150) = 20 gallons.
So we have about 20 gallons of water in the 250 feet. Actually your volume will be less because probably piping in your house is smaller in diameter and probably there is less distance of piping between point of water entry in the house and the faucet.
If your well pump is pumping at 10 gallons per minute, it would take about 20 (gallons) / 10 (gallons per minute) = 2 minutes or less for chlorinated water to show up at the faucet [in a simple and perfect world, which it is not.]
It's a little more complicated.
Some of the incoming water from the well may be diverted into the water pressure tank where it is diluted and in that sense "delayed", and if you are running hot water, some of the incoming water is being diverted and run through your hot water tank where it is significantly diluted.
So if you only ran hot water (the worst case) it could take five minutes or even longer for some diluted but still chlorine-smelling water to appear at the hot water faucet. The cold water faucet output should smell like bleach sooner.
It's reasonable to expect to smell the chlorinated water at a faucet in a typical one family home within 4 to 10 minutes after shocking the well.
If you run the water for 15 or 20 minutes and you still don't smell the bleach, either you need a more careful look at the distance and size of water piping or a closer look at how accurately you calculated the amount of bleach you poured into the well.
Don't forget that when you are running the chlorinated well-shocked water through the building piping and fixtures, you want to run it at every fixture so that everything is being sterilized.
Don't forget to thoroughly flush out the chlorinated water 24 hours later.
CONTACT us with suggestions or comments.
you need to WARN people = re water discharge/well shocking. i ran my well out of water and made the situation WORSE. Tell people not to run the water outside only for a half hour or so at a time!!!! NOT until Chlorox smell is gone - can take forever o get rid of Chlorox smell.... well needs to recharge. Now, listening to you folks, I have an even BIGGER problem. - M.P.
Reply: Indeed the well flush-out procedure can disclose another problem with poor well flow rate or poor well recovery rate
Thank you for the note complaining about discovering that your well could run dry during an attempt to flush out the chlorine odor from a bleach-shock of the well. We were of course sorry to read that your well shock process disclosed a second fault - a well with a poor recovery rate.
We have reviewed our well water article on the topic (WELL CHLORINATION SHOCKING PROCEDURE) to be sure that there are warnings about running out of water during well testing or well shocking. In the main article explaining how to shock and flush out a well following a failed bacteria test you will see several WATCH OUT warnings that include discussion about problems that can arise during the bleach flush-out process. Here we'll add some more detailed suggestions that can help address the worry of running out of well water during well shocking and flushing.
Indeed while it has not come up during well shocking this problem has been discovered by building inspectors more than once during a septic loading and dye test to test for septic system failure - as that water test volume is run, typically 250 gallons or so, the inspectors discovered that the well itself was inadequate when the well flow diminished or stopped entirely. It sounds as if you have run into the same problem of a poor or inadequate well flow rate.
Low flow rate wells usually recover but watch out for pump damage
As long as no one makes the mistake of leaving a well pump running when it is dry of water, the system is not damaged, and the well will recover, usually in a few hours; but once discovering that your well has a poor flow rate, indeed you will want to take steps to address the problem, either by adding water storage capacity or by increasing the well yield, or in the worst case, drilling a better well.
Steps to protect from running out of well water during shocking and flushing out a well
But in all cases if the well runs "dry" during well flush-out after a well shocking procedure or during a septic loading and dye test, as long as you haven't done something unusual like just leaving water on for hours unattended, you've discovered a double fault if your water well runs dry during well-shock-bleach flushout: contaminated well water and a low yield or low flow-rate well.
Question/Comment: well contaminating bacteria may hide in a slime layer in the draw-down section of the well casing. Attending to water pH is very important when sanitizing a well.
In an earlier response to Mark DanJoeFriedman said (with details added here)::
Mark Comments Further:
[This article describes the formation of both biofilm and mineral deposits that accumulate inside a water well over time, and argues for using a pH-adjusted chlorine solution to the well to increase the biocidal effectiveness of the disinfectant. - Ed.]
In general, they adjust water in a tank to a pH of 4.5 and THEN add chlorine. I wasn't aware of this procedure until after I mixed up my solution. Now that I have an actual personal experience in this I think that I can comment on it... I mixed up a 200ppm sodium hypochlorite solution (8.25% Clorox) in 275 gallons of pH neutral water (my spring water is nearly dead-on, 6.8 - 7.0 pH). I had ASSUMED, based on all the casual experts comments (in addition to information from various water publications [people that actually should be responsible]), that I shouldn't be too far off pH-wise- WRONG! I'm over 8.4 pH!
Thanks Mark, important details to add both about the algae or bacterial slime that might be present in some well casings, depending on water chemistry, as well as the importance of well water pH.
Question: how do I get rid of chlorine in well water after shocking the well?
We shocked the well, it was 425 ft deep so we used 1 1/2 gal of bleach, it did not smell right away like it said. ran water in house for about 20 min and nothing, let set over night and then ran hose to recycle water. then we started smelling so we let it set again.
When flushing out we ran directly from where water enters home to outside plus rand faucets to clear out. Still strong chlorine, when I test it is orange when chlorine tester only has yellow. We do get a lot of sediment from our well, ( brown Water) if used a lot. Any Idea how much longer it will be to clear out. Getting tired of having chlorine showers and smelling it all day long. - P.D., property manager, Harrisburg PA 8/27/2013
IF (and this is not quite the case) your 425 ft. well were completely full of water and assuming it's a 6-inch casing, that's about 640 gallons of water in the well, plus additional water volume in the piping system.
According to CHLORINATION WELL SHOCKING PROCEDURE 1.5 gallons of household bleach was a stronger concentration than needed (1 gallon would treat about 500 ft. of water in a 6-inch well casing). Considering that if your well's total depth was just 425 ft. and that most likely the static head of water in that well was less than 425 feet total, the well was overdosed.
Overdosing with chlorine can indeed make for some extra trouble in flushing out the chlorine or bleach later.
Flushing out the well needs to run more than that volume, however, since you cannot by running water just draw out the static water that was treated with bleach; rather, water running into the well dilutes the bleached-water already therein;
You'll need to use water for several days to fully flush out the chlorine bleach; the exact volume and rate of flush-out also depends on the flow rate of the well.
Further, as you've run chlorinated water into a water pressure tank and water heater tank, those too need to be flushed, or simply drained and refilled - a step that can speed the flushout procedure. Try that and keep me posted.
I believe [the chlorine concentration in our well water] is at 10ppm
The maximum residual disinfectant level goal (MRDLG) and also the maximum residual disinfectant level (MRDL) set by the U.S. EPA for chlorine in drinking water is
I would - shut off water to the building, drain the water heater tank and pump pressure tank, run water outside - straight from the well via an outdoor faucet - and check the chlorine level there. That will help sort out chlorine remaining in the well water supply from chlorine that may have been left in water tanks and piping in the building.
If bleach was introduced into the well by pouring it directly into the well casing, it might help the flush-out procedure if you used a garden hose to recirculate some of the well water back to the well, using it to wash down the casing sides and center piping before continuing with the actual flush-out of the well itself.
Keep me posted; send along photos of your well equipment, tanks &c as that may permit further comment.
Citation on limits of chlorine in drinking water:
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